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Geometrical metrology for metal additive manufacturing
Abstract
The needs, requirements, and ongoing and future research issues in geometrical metrology for metal additive manufacturing are addressed. The infrastructure under development for specification standards in AM is presented, and the research on geometrical dimensioning and tolerancing for AM is reviewed. Post-process metrology is covered, including the measurement of surface form, texture and internal features. In-process requirements and developments in AM are discussed along with the materials metrology that is pertinent to geometrical measurement. Issues of traceability, including benchmarking artefacts, are presented. The information in the review sections is summarized in a synthesis of current requirements and future research topics.
Supplementary resource (1)
Data
August 2019
... Although there are many benefits to metal PBF technologies, the processes are poorly understood when compared to traditional subtractive manufacturing methods, resulting in a relative lack of confidence in the quality of parts being built [12,13]. A significant cause for the lack of confidence in additive components stems from the complex phenomena present during the build process [13][14][15][16], such as the meltpool mechanics, as well as cost concerns associated with wasted time and discarded raw materials when a build process fails [13,[17][18][19]. ...
... Although there are many benefits to metal PBF technologies, the processes are poorly understood when compared to traditional subtractive manufacturing methods, resulting in a relative lack of confidence in the quality of parts being built [12,13]. A significant cause for the lack of confidence in additive components stems from the complex phenomena present during the build process [13][14][15][16], such as the meltpool mechanics, as well as cost concerns associated with wasted time and discarded raw materials when a build process fails [13,[17][18][19]. In an effort to improve understanding of the complex phenomena that occur during the PBF build process, many have turned to metrology solutions to analyse not only components that have been built through PBF methods, post manufacture, but also the process itself in real-time as the build is happening. ...
... Although there are many benefits to metal PBF technologies, the processes are poorly understood when compared to traditional subtractive manufacturing methods, resulting in a relative lack of confidence in the quality of parts being built [12,13]. A significant cause for the lack of confidence in additive components stems from the complex phenomena present during the build process [13][14][15][16], such as the meltpool mechanics, as well as cost concerns associated with wasted time and discarded raw materials when a build process fails [13,[17][18][19]. In an effort to improve understanding of the complex phenomena that occur during the PBF build process, many have turned to metrology solutions to analyse not only components that have been built through PBF methods, post manufacture, but also the process itself in real-time as the build is happening. ...
Metal powder bed fusion systems have been rapidly gaining interest from high-value manufacturing sectors, such as aerospace and biomedical, due to the unique benefits the technology can offer in terms of part design flexibility and bespoke manufacturing. In-process monitoring techniques for metal powder bed fusion have become increasingly popular as the technology continues to mature. However, adequate methods of handling data collected from the manufacturing process have yet to be explored in depth. Due to the large quantities of potential data and the temporal constraints when monitoring the PBF process, automated data interpretation is essential to allow for real time defect detection to be achieved. In this thesis, a novel measurement method for PBF systems is proposed that uses multi-view fringe projection to acquire high-resolution surface topography information of the powder bed. Measurements were made using a mock-up of a commercial powder bed fusion system to assess the system’s accuracy and precision in comparison to conventional single-view fringe projection techniques for the same application. Featured based characterisation methods were applied to the measured topography to extract salient information about spatter and particles with the data being compared against a higher resolution reference measurement (focus variation). Results show that the multi-view system is more accurate, but less precise, than single view fringe projection on a point-by-point basis. The multi-view system also achieves a high degree of surface coverage by using alternate views to access areas not measured by a single camera. Measurements from the multi-view fringe projection system achieved similar reconstruction fidelity to the reference focus variation, in particular at the scales required for the largest targeted features (200 µm size and up). Topography partitioning and feature identification results achieved by feature based characterisation were comparable between fringe projection and focus variation.
... Non-destructive measurements, comprehensively reviewed in [16], are usually performed to reconstruct the overall geometry of the manufactured part, for example by means of fringe projection 3D scanning [17] or X-ray Computed Tomography [18]. In particular, [17] identified the former as the ideal solution for metal AM, as the tradeoff between speed, field of view, resolution and adaptability to surface properties fits well typical AM parts. ...
... Convolutional layers [16,32,64,128], [16,16,32,32], [16,32,64], [32,32,32], [ 16], [32,16] network concatenates the resulting vector of the CNN with numerical and one-hot encoded data, and finally outputs the required targets. A full overview of the hyperparameters used during training can be found in Table 1. ...
... Convolutional layers [16,32,64,128], [16,16,32,32], [16,32,64], [32,32,32], [ 16], [32,16] network concatenates the resulting vector of the CNN with numerical and one-hot encoded data, and finally outputs the required targets. A full overview of the hyperparameters used during training can be found in Table 1. ...
Laser Metal Deposition (LMD) is an additive manufacturing technology that attracts great interest from the industry, thanks to its potential to realize parts with complex geometries in one piece, and to repair damaged ones, while maintaining good mechanical properties. Nevertheless, the complexity of this process has limited its widespread adoption, since different part geometries, strategies and boundary conditions can yield very different results in terms of external shapes and inner flaws. Moreover, monitoring part quality during the process execution is very challenging, as direct measurements of both structural and geometrical properties are mostly impracticable. This work proposes an on-line monitoring and prediction approach for LMD that exploits coaxial melt pool images, together with process input data, to estimate the size of a track deposited by LMD. In particular, a novel deep learning architecture combines the output of a convolutional neural network (that takes melt pool images as inputs) with scalar variables (process and trajectory data). Various network architectures are evaluated, suggesting to use at least three convolutional layers. Furthermore, results imply a certain degree of invariance to the number and size of dense layers. The effectiveness of the proposed method is demonstrated basing on experiments performed on single tracks deposited by LMD using powders of Inconel 718, a relevant material for the aerospace and automotive sectors.
... The recesses may result from incomplete seams between tracks, balling phenomena, or micro-pores [6,8,9]. Sphere-like protrusions are formed mainly from unmolten or partially melted powder particles and spatter particles (i.e., molten metal material ejected from the melt pool) [10,11]. A better understanding of the AM process and the formation of the surface topography requires a fundamental analysis of the surface textures. ...
... In previous studies, the acquisition of the surface topography in AM was usually conducted with the tactile method and optical method [10]. The tactile method belongs to the contact technique which uses a stylus tip to scan the whole surface area, and the surface topography can be reconstructed based on the vertical displacement of the tip. ...
... Moreover, a higher resolution can be achieved by the optical methods. In the field of the AM surface metrology, optical methods still face many challenges, such as high slopes of local areas, variable aspect-ratios, the alternation of dark and overly bright regions, and non-uniform optical properties caused by local oxidization or micro-roughness effects [6,10]. There are numerous studies on surface texture metrology using optical approaches, and the vast majority of reports are related to the PBF-fabricated surfaces [6,[12][13][14][15]. ...
In this paper, multiscale characterization methods for additive manufactured surfaces are proposed based on the acquired 3D topographic data at different resolutions measured from a confocal laser scanning microscope. The purpose is to provide a general solution to extract the critical information of typical surface textures manufactured by additive technology. In detail, point pattern analysis is conducted for the low-resolution data to study the global distribution of the unmolten particle features; roughness characterization is carried out for the data with medium resolution; feature-based characterization is applied to precisely assess the geometric parameters of the distinctive features such as weld tracks and particle features. The results show that the unmolten particle features tend to have a random spatial distribution at macro scale. In medium resolution, the weld track features make more contribution to the overall roughness, while the particle features are less significant. At micro scale, the watershed segmentation combined with the Wolf-pruning method leads to a satisfactory result to precisely extract the geometric parameters of the features on the surfaces.
... One of these challenges is the surface finish of as-built AM parts, which is still poor when compared to that achievable with well-established methods (e.g. subtractive manufacturing) [8,9]. In general, the understanding of the complex physical interactions occurring during AM processes is still limited [10][11][12]. ...
... Common issues of surface metrology for metal and polymer AM arise from the complex and highly irregular surface topographies that result from the AM processes. Metal AM surfaces typically present local high slopes, deep recesses, high aspect-ratio features and undercuts, as well as varying surface texture and regions with a large variation in reflectance [8,9]. In the case of polymer AM, surfaces are often translucent or have low reflectivity [15][16][17]. ...
... weld tracks, weld ripples and spatter formations. This realisation suggests that the correlation of surface topography with process parameters can be used to provide feedback for process control [8][9][10][48][49][50][51][52][53][54][55][56][57][58][59]]. ...
Additive manufacturing (AM) is increasingly being used to fabricate fully functional parts. In this scenario, tolerances for dimensions and surface finish become crucial, especially for applications with stringent requirements. Therefore, the measurement of AM parts is essential to ensure adequate performance and to inform the manufacturing process. Typical metal AM surfaces are highly irregular, exhibiting a large number of high aspect-ratio topographic features, deep recesses and loose particles, while polymer AM surfaces are often translucent or have low reflectivity. Because of these characteristics, it can be challenging for any surface measuring technique to accurately measure the topography of metal and polymer AM surfaces. Coherence scanning interferometry (CSI) is one of the most accurate methods for areal surface topography measurement. CSI uses an interferometric objective lens and spatially extended, spectrally broadband illumination. When scanning a surface along the optical axis through the focus of the interferometric objective lens, interference fringes will be visible only within a narrow surface height range, corresponding to the zero group-velocity optical path difference of the interferometer. This phenomenon is known as ‘low-coherence interference’ and provides a highly accurate non-contact sensing mechanism to determine the three-dimensional topography of a surface. CSI has the ability to measure a wide range of surface types, from optically smooth to rough, as well as discontinuous surfaces without the 2π ambiguity that can arise with single-wavelength, phase-shifting interferometry. However, due to the limited numerical aperture of the imaging system, CSI may suffer from poor signal-to-noise ratios when measuring high-slope angle topographic features and surfaces with significant texture, or more generally, surfaces with low reflectance, compromising the ability to reliably determine surface heights. Although previous CSI technologies have shown difficulties when measuring AM surfaces, recent progress in the development of CSI allows a significantly enhanced detection sensitivity through the use of advanced analysis techniques, such as filtering of the light source spectrum bandwidth, high dynamic range lighting levels, oversampling (i.e. adjusting the number of camera acquisitions over each interference fringe) and sophisticated topography reconstruction algorithms. In this thesis, the effects of the aforementioned advanced analysis techniques on the measurement of typical as-built metal AM surfaces covering various textures and slope distributions are empirically investigated and systematically analysed. Guidelines are provided for the optimisation of the measurement of metal AM surfaces by balancing the total data acquisition time, the size of the measurement area, and the percentage of measured data points (i.e. data coverage). The detailed surface topography information captured with CSI is essential for providing feedback to the manufacturing process and for quality control of AM products. To validate this, a challenging case study has been considered. The feasibility of ink-jet printing a transparent polymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride (known as THV) to produce films of a few nanometres to several micrometres in thickness has been assessed using CSI. Solutions to minimise the ‘coffee ring’ effect and the formation of undesired wrinkle-like features on the surface when ink-jet printing THV are demonstrated. This work contributes to the field of polymer AM by providing insight into how to control and optimise the quality of ink-jet printed parts with the aid of surface metrology. Reducing measurement noise in CSI is an important consideration when measuring AM surfaces, in particular when the ability to capture data is compromised by poor signal-to-noise ratios. This thesis contributes to the understanding of the workings of measurement noise reduction methods and compares their effects when measuring surface topography in the presence of environmental vibration. The results provide guidance for the reduction of error in surface measurement for AM surfaces, and could be applied in a wider range of applications. The knowledge developed in this research is relevant to the manufacturing and scientific communities as CSI technologies are increasingly applied to the measurement of complex surfaces and in environments that resemble production areas more than metrology laboratories.
... X-ray computed tomography (XCT) is an imaging technique that utilizes the penetrating properties of X-rays to create a digital reconstruction of a scanned workpiece in terms of a three-dimensional attenuation map comprising volumetric picture elements, or voxels [7]. The volumetric image can be converted to a surface model by applying an attenuation threshold, enabling the measurement of otherwise inaccessible internal features and making XCT a preferred method for inspecting AM components [8]. Internal geometries such as cooling channels, cavities for light-weighting, or embedded dissimilar materials can be analyzed without the need for traditional destructive testing. ...
... The accuracy of least-squares cylinder and plane fitting algorithms used was verified using reference datasets from the NIST algorithm testing service [45]. For each feature, the standard deviation of the thirty repeated XCT measurements was used as u p , the standard uncertainty associated with the measurement procedure, defined in Eq. (8). ...
... The Shapiro-Wilk test was chosen as the test for normality because of its statistical power compared to other methods [46]. VDI/VDE 2630 Part 2.1 defines u p as the standard deviation of more than 20 replicate measurements, as in Eq. (8). If the measurement data presented in this work has been shown not to follow a Gaussian distribution and has been shown to have significant outliers, it may be more appropriate to use a different measure of dispersion to define u p . ...
Lattice structures created via additive manufacturing are of interest in several demanding industries, however the qualification of these components via X-ray computed tomography (XCT) is limited due to traceability requirements. In this work, a novel measurement reference object is presented to study task specific uncertainty in the XCT measurement of a simplified lattice structure. The design of this reference object, the calibration routines, and XCT acquisition are described. The description of uncertainty calculation is presented. The methodology for data sampling, registration, and measurement is detailed. The measurement results are tested for normality and show variations in the underlying distribution for different measurands. A discussion on uncertainty variation and normality of measurements is then presented. Variations in measurement bias and uncertainty are analyzed across various features of the reference object. It is shown that the measurement uncertainty and bias are not consistent across pin diameter measurement, indicating the need for similarity between the reference object and subsequent component measurements.
... The production environment will, however, be dramatically altered by the use of metals or ceramics in additive manufacturing in the aerospace and medical sectors. By predominantly using metal and ceramic in the form of fused powders, AM varies from traditional manufacturing or subtractive manufacturing, because there aren't enough machine makers and quantifying surface texture in additive manufacturing is more difficult than it is in traditional machining, WAAM hasn't fully industrialized [3]. The demand for high quality production and complicated metal structures has fueled the growth of additive manufacturing over the past few decades. ...
... MRRV olume o f material removed mm3 T ime takem f or complete cutting o f one specimen (min) Volume removed Perimeter of specimen × Dia. of wire× thickness of work-piece.• Perimeter 4 × each side size (5 mm) • Diameter of wire 0.25 mm.• Thickness of specimen 5 mm.• ...
Incurrent times wire arc additive manufacturing is becoming popular and alternate to conventional machining because of its eco-friendly as wastages. Wire arc additive manufacturing (WAAM) develops the parts by depositing wire material one layer above other because it is based on old technology i.e., welding. It even has ability to generate complex parts. As WAAM requires post processing to obtain the better surface and accuracy of dimensions. To study about the post processing of WAAM specimen, in this work Wire cut EDM is used, which can machine complicated shapes with high accuracy for any conducting material without taking into account the hardness of the material. Selection of input parameters is the key for better material removal and surface finish in Wire EDM.In this study Pulse on time, Wire tension, Servo Voltage withthree levelswereconsidered as input parameter and Material removal, Surface roughness are considered as output responses. Response surface Methodology is used for designing the experiment. It is observed that wire tension plays vital role in material removal and surface finish, pulse on time is important in material removal but not in surface finish. Servo voltage predominant for surface roughness but less influenced on material removal rate.
... Однако технологические характеристики производства изделий данным методом, такие как точность формообразования, качество поверхностного слоя, трудо-емкость и себестоимость, а также влияние на них параметров режима изучены недостаточно [15][16][17]. Важным направлением в этой области исследований является анализ метрологических проблем измерения показателей точности и качества поверхностного слоя [18,19]. Такой анализ в области аддитивных процессов изготовления металлических компонентов проведен в [19]. ...
... Важным направлением в этой области исследований является анализ метрологических проблем измерения показателей точности и качества поверхностного слоя [18,19]. Такой анализ в области аддитивных процессов изготовления металлических компонентов проведен в [19]. Рассмотрены существующие технологии, стандарты, методы и средства оценки точности и шероховатости изделий. ...
The paper presents the results of a statistical study of the parameters of the microgeometry of the surface of the vertical walls of the construction objects during additive shaping via electron beam melting. An assessment was made of the influence of the construction condi-tions and the hatching mode parameters on the surface roughness. The influence of the hatching mode parameters on the roughness of the side surface, when constructing samples with vertical walls, was established. It is shown that the value of the average size of the height of the irregularities Rz increases with the intensification of the energy regime of hatching. A physical model is proposed that describes the influence of the hatching mode on the roughness of vertical walls, based on the hypothesis of a possibility of penetration of the melt micro-flow during hatching onto the outer surface of the contour. It is shown that the distribution of the surface roughness values of the vertical walls has a non-Gaussian character, the curves are, as a rule, right asymmetric (the mode is located to the left of the size grouping center), which indicates the influence of non-random factors, the number or values of which systematically change over time.
... Here, it is emphasized that AM processes for metals such as LPBF are rarely the sole manufacturing process required to produce a functional product. The LPBF process is well understood to produce geometry with poor dimensional control [32], gross deformation due to residual stress, high surface roughness [33], low microstructural heterogeneity [34], and high volumetric defect content [35]. As such, secondary manufacturing processes are often leveraged to address these shortcomings [16]. ...
... Even so, there are still AM-specific considerations to be addressed. Surface finishing may take on greater importance and require novel approaches due to the characteristically rough surfaces produced by AM [32,33]. Quality and NDE steps such as X-ray computed tomography (XCT) may be essential due to the defect prone nature of AM [34,35,37] and complex geometries difficult to inspect via traditional methods. ...
Additive manufacturing (AM) has matured beyond limited use-cases in rapid prototyping into a process capable of competing with conventional manufacturing methods in the production of end-use components. As such, many manufacturers are evaluating candidate products for redesign for AM, with interest in improving component performance, streamlining manufacturing, and reducing costs. In this study, the authors argue for systematic use of opportunistic design tools such as generative design and for the inclusion of restrictions imposed by the entire manufacturing process workflow to be included in the design process. Emphasis is placed on how secondary processing steps, that is, those other than the primary AM process, inform design. A bicycle stem is used as an exemplar case study of component redesign for AM. Generative design is used to optimize the component's weight given the design constraints. An end-to-end manufacturing process chain is consequently developed and analyzed for viability, covering design for additive manufacturing (DFAM) and post processing. Through this comprehensive case study, it is shown that significant weight savings, greater than 25% in the present case, can be achieved through the DFAM process. Guidelines from the DFAM process are generalized for application to further cases.
... XCT can be used to examine internal geometry, e.g., cavities, pores, hollow areas, or difficult to access features, e.g., undercut geometry or high aspect ratio bores and grooves. This has made XCT a popular dimensional metrology method for additively manufactured components [3][4][5][6] such as lattice structures [7,8], aerospace components such as turbine blades [9,10], and complex multi-component assemblies [2]. However, dimensional XCT suffers from multiple issues which limit accuracy and precision in dimensional metrology tasks [5,6,11,12], due to (1) errors in machine and sensor construction, (2) complex reconstruction and data processing steps, and (3) the fundamental process physics. ...
... This has made XCT a popular dimensional metrology method for additively manufactured components [3][4][5][6] such as lattice structures [7,8], aerospace components such as turbine blades [9,10], and complex multi-component assemblies [2]. However, dimensional XCT suffers from multiple issues which limit accuracy and precision in dimensional metrology tasks [5,6,11,12], due to (1) errors in machine and sensor construction, (2) complex reconstruction and data processing steps, and (3) the fundamental process physics. Machine construction errors are generally a concern for any metrology system but are often compensated and thus contribute relatively little to the total error in XCT measurement [12][13][14]. ...
X-ray computed tomography (XCT) provides a unique set of dimensional measurement capabilities suitable for assessing complex geometry. However, due to the origins of XCT as a medical imaging method and qualitative non-destructive examination technique, only recently has XCT been rigorously investigated as a dimensional metrology tool. Although the data produced via XCT may be leveraged with conventional coordinate metrology techniques, the instrument physics and volumetric reconstruction methods which govern the accuracy and precision of the data are complex, workpiece-specific, and non-negligible. In particular, there is minimal prior work which has studied complex multi-step metrology tasks such as datum reference frame (DRF) construction and feature position measurement. In this work, a qualified artifact was used to evaluate the fitness of XCT for such a task. Multiple XCT systems were used, and multiple instrument magnification levels compared. The form error of planar and cylindrical features was evaluated. Further, the influence of individual feature reconstruction on the development of datums and upstream position measurements was studied. It was found that negative, i.e., bore-like, and positive, i.e., pin-like configurations of certain features were subject to distinct XCT artifact effects which caused upstream measurement errors when these features were used to construct a DRF. High magnification and X-ray scatter produced high spatial frequency noise in surface reconstruction while beam hardening and beam penetration distance variation produced gross apparent form error. The latter was associated with greater measurement errors in feature position measurement within an DRF.
... This traceability is often a requirement for the establishment of quality management systems and therefore the qualification of components [9]. However, it has commonly been used for comparison measurements, and research continues on developing traceable measurement techniques for internal or geometrically complex features [10,11]. Because of this, the measurement of lattice structures using XCT is often paired with other measurement techniques for comparison [12]. ...
... The discussed issues constitute a major barrier for a wider adoption of the LPBF technology, especially in industrial sectors with demanding standard requirements such as aerospace and biomedical [4]. For this reason, reliable metrology solutions are currently needed to improve the understanding of LPBF process dynamics and to gain control over the process stability [5]. In this context, X-ray computed tomography (XCT) is an attractive solution for non-destructive and holistic post-process evaluations of AM specimens, including dimensional and geometrical measurements as well as internal porosity analysis [6]. ...
Despite the capability of fabricating complex and customized components, metal laser powder bed fusion (LPBF) is still affected by manufacturing issues, which can lead to significant geometrical and dimensional errors and internal defects. These aspects can represent a major barrier to a wider industrial application of LPBF, particularly if considering that relevant applications of additive manufacturing are in sectors such as biomedical and aerospace, which have stringent requirements in terms of defects and product quality. The requests for precision improvement are orienting research activities towards the development of inprocess monitoring systems able to perform accurate analyses during the fabrication itself, hence providing useful information for improving the quality of produced parts. To this aim, several in-process monitoring methods have been proposed in the literature to identify and correct out-of-control process conditions. In spite of the aforementioned research efforts, work is still needed to reliably correlate in-process measurements to actual defects. The focus of this experimental study is the definition of a robust methodology to compare in-process optical acquisitions to post-process X-ray computed tomography (XCT) measurements of actual defects. XCT unique capabilities are therefore exploited to support and improve the LPBF process through the implementation of an accurate comparison methodology.
... Although the characterization of L-PBF surfaces considering the differences in microstructure and property has been paid attention by researchers, the importance of incorporating morphology, roughness and microstructure diversity of L-PBF surfaces still needs to be emphasized. In addition, it is necessary to pay attention to the parameters of surface roughness measurement, such as cut-off values, for a more valuable evaluation of additively manufactured surfaces [15,16]. Since surface finish dominates multiple functional properties, such as biological response and fluid dynamics, it is necessary to apply proper polishing process to L-PBF inner surfaces and investigate material removal mechanism. ...
A R T I C L E I N F O Keywords: Electropolishing, laser-based powder bed fusion Internal surface Material removal Un-sintered powders, sintered area A B S T R A C T Investigating electropolishing (EP) effects on the material removal process of laser-based powder bed fused internal surfaces is crucial for the application of EP in the polishing of complex internal structures. This study aims to electropolish various internal surfaces of 316L stainless steel fabricated by laser-based powder bed fusion (L-PBF). Un-sintered powders and sintered area on top, face up, side and face down internal surfaces were characterized. Based on the material removal characteristics of different surface features, a two-step EP was proposed using different potentials and polishing time for L-PBF internal surfaces after parametric study in a developed EP system which is capable of circulating electrolytes in high-speed. Material removal process and anodic dissolution of L-PBF internal surfaces were then discussed based on experimental results and impedance analysis. The comprehensive characterizations of morphology, roughness and cross sections with microstructure differences in consideration are important for analyzing the evolution of L-PBF surfaces during polishing. The study demonstrates the high efficiency of the two-step EP in polishing various L-PBF internal surfaces.
... In connection with the specificity of additive techniques, this relationship translates into preparing the appropriate geometry of the basis models [17]. When models are made 3D printing process, there are differences between the nominal 3D-CAD model and the manufactured object [18,19]. These differences result mainly from the subsequent hardening layers and the type of material used during 3D printing [20,21]. ...
... In this section, we are focused to explain the applications of 3D digital measurement technology in different aspects including dimensions (section 3.1), displacements (section 3.2), and deformations (section 3.3) of the parts. Today, there are different fields where this technique is applied, especially in parts produced by additive manufacturing [16][17][18]. Moreover, it is a good way of moving forward in terms of integration using a digital chain between advanced manufacturing technologies and 3D optical devices. ...
The 3D digital measurement is commonly used nowadays when parts are with complex geometry, and fast development is required. This comes also from constant technological improvements of devices like 3D scanners. However, the use of them for particular applications needs research that shows the wide range of usability. The purpose of this study has to do with better understanding of the measurement of dimensions, displacements, and deformations of the parts using non-contact techniques, which are elaborated with the case studies for each investigation. Base on the presented research, we see the approach of using the 3D scanning technique for several applications. From a general point of view, we conclude that the use of 3D digital measurement is a useful and flexible methodology for different parts, shown by the presented work. Future research should deal with improvements that are required in terms of the integrated measurement approach.
... WA-DED has been shown to be a manufacturing process with excellent material efficiency when compared to other metal AM processes. However, it is well recognised that on balance other metal AM processes can achieve better surface finishes than the WA-DED process (Leach et al. 2019). In recent years, the mechanical properties of WA-DED printed material has improved drastically and in some cases matches or exceeds mechanical properties of components produced by traditional casting methods (Yili et al. 2018). ...
Wire Arc Directed Energy Deposition (WA-DED) also known as Wire Arc Additive Manufacture (WAAM) is a niche additive manufacturing technique for metals that is increasingly offering a competitive advantage to traditional forging and casting methods. Characteristics of WA-DED are high deposition rates and feedstock that is inexpensive compared to powder processes, making it highly efficient for manufacture of large components. This paper reviews WA-DED as a technique for large component manufacture by assessing aspects of the process scalability. Arc processes are compared in terms of their production characteristics showing the relative suitability of each power source. Additional in-situ processes have been identified that can alleviate defects and improve mechanical performance. Investigation of process planning for WA-DED has revealed the potential for material savings that can be achieved by preventing accumulation of errors throughout manufacture. The major finding is that additional in-situ processes and process planning combined with a closed loop feed forward control system can significantly improve the process in terms of mechanical performance, geometric repeatability and resolution. Additionally, it was found that although the degree of isotropy of mechanical performance is commonly investigated, research into the heterogeneity of mechanical performance is limited, and does not assess tensile properties at different locations within deposited material.
... In connection with the specificity of additive techniques, this relationship translates into preparing the appropriate geometry of the output models [22]. When models are made of polymeric materials, there are differences between the nominal 3D-CAD model and the manufactured product [23][24][25]. These differences result mainly from the subsequent hardening layers and the type of material used during 3D printing [26][27][28]. ...
The article presents the results of strength tests of screw-nut threaded connections made of polymeric materials such as: ABS, PLA, PET-G and RGD720. In order to make physical models, three 3D printing techniques were used: Fused Deposition Modeling (FDM), Fused Filament Fabrication (FFF), and PolyJet. The tests took into account the stresses caused by the axial force generated when the bolt is screwed into the nut or other structural element. Due to the complexity of the issue, the presented studies are only a starting point for further research.
... The analysis should ideally account deviations from form to roughness. The need for a geometric description of the geometry of AM parts was highlighted earlier [33]. The currently applied standards for surface topography analysis ISO 4287 and ISO 4288 probably need to be revised for description of AM surfaces [34]. ...
Recently, additive manufacturing (AM) of structural metallic components is analyzed regarding its potential use by industry and research. Next to the development of manufacturing processes, the mechanical properties are under investigation today. One of the quality measures of metallic components is the surface topography. DED-arc processes (direct energy deposition) result in relatively coarse surfaces, characterized by a distinct waviness with wave amplitudes in the mm-range. This is enhanced when applying horizontal building position in comparison to vertical position. Next to increased waviness, the load-bearing net cross sections are reduced as well. The surface topography determines the fatigue life properties of metallic components. While stress raising surface effects are generally well understood and fatigue (Structures 31: 576–589, 2021) of welded metals is established well, the fatigue behaviour of additively manufactured components is less investigated yet. In order to define surface quality levels for DED-arc components, the effects of surface topography on mechanical performance need to be understood. This article presents the manufacturing of high strength steel test coupons by the DED-arc process. The process parameters were varied with regard to the building position and different levels of surface quality were generated. The surfaces of different specimens were characterized and fatigue tests were conducted. The results were used to derive the surface influence on both, the effective load-bearing wall thickness and notch effects induced by the layer-by-layer building approach. A correlation between building position, surface waviness and fatigue strength was proven. In general, higher waviness resulted in reduced effective wall thickness and lowered fatigue strength. A difference in fatigue strength at 2 million load cycles of 20 to 30% was proven when printing in different building positions. The surface effect can be captured in the design concept when applying the effective notch stress approach with an averaging length of of ρ * = 0.4 mm. The fatigue strength is describable by a design S–N curve FAT160 and a k -value of 4.
... The complex geometries afforded through the AM process create significant challenge for component inspection. Thus, the geometrical qualification of AM components has required a new, developing, area of research [2]. ...
Dimensional qualification of additive manufacturing (AM) components is a continuing research problem. Different measurement techniques implemented on the same feature can yield different measurement results. While this can also be true for components made from more traditional manufacturing processes, the deviations between measurement techniques are often increased by an order of magnitude due to greater form and surface texture variations that occur on AM components. Understanding the origins of deviations and comparability of measurement processes is crucial to the measurement of AM components. In this work, identically designed components are produced using a laser powder-bed fusion process. The components are then measured using manual gaging and a coordinate measurement machine. The measurement of diameter is executed using various association criteria. A statistical analysis is performed to determine the comparability between the measurement techniques. Results indicate that the selection of different association criteria can provide statistically significant differences in the measurement result.
... Last, there exists great value in the exploration of the projection optics system and fundamental transport phenomena governing the high-resolution 3D CLIP print process. A combination of the digital twin with an in-line 3D scanner or micro-CT inspection system (79,80) would further allow the development of a machine learningbased model. Using the theoretical model as a baseline to adjust the predicted cured-height landscape and translate to actual dimensions, additional parameters can be captured that cannot be easily simulated by the theoretical model to achieve higher print accuracy. ...
To date, a compromise between resolution and print speed has rendered most high-resolution additive manufacturing technologies unscalable with limited applications. By combining a reduction lens optics system for single-digit-micrometer resolution, an in-line camera system for contrast-based sharpness optimization, and continuous liquid interface production (CLIP) technology for high scalability, we introduce a single-digit-micrometer-resolution CLIP-based 3D printer that can create millimeter-scale 3D prints with single-digit-micrometer-resolution features in just a few minutes. A simulation model is developed in parallel to probe the fundamental governing principles in optics, chemical kinetics, and mass transport in the 3D printing process. A print strategy with tunable parameters informed by the simulation model is adopted to achieve both the optimal resolution and the maximum print speed. Together, the high-resolution 3D CLIP printer has opened the door to various applications including, but not limited to, biomedical, MEMS, and microelectronics.
... Any manufacturing process is affected by limitations which in turn have repercussions on the entire lifecycle, therefore they must be well understood and solutions for these limitations must be incorporated into the design at an early stage. Therefore, when a manufacturing process is being industrialized, it must be fully characterized to determine limits, tolerances, repeatability, and reproducibility to allow designers to achieve optimal solutions [8]. Once a manufacturing process has been baselined, adjustments or improvements can be made to further optimize it, like, for example, the inclusion of secondary steps if gaps were identified. ...
Heat exchangers for use in propulsion applications are very critical components because they must be efficient, compact and light and often operate with working fluids at extreme temperatures or pressures or both. Various components and systems use heat exchangers such as combustion chambers of gas turbines and internal combustion engines, fuel cells (air supply and thermal management), electric batteries (thermal management), evaporators and recuperators of waste-heat-to-power systems, and rocket engines. Even if the results are more generally applicable, the heat exchangers applications to which this study is more closely related are regeneratively cooled rocket nozzles and chambers, and repressurization systems for the launch vehicles. These components are often thin-walled and contain pressurized fluids, like propellants at cryogenic or elevated temperatures. Given that the environments that these propulsion components must endure are challenging, the manufacturing to meet these specifications often require long lead times due to specialty processes and unique tooling associated with the combined thin-wall integral channel and large-scale structures. Additive manufacturing (AM) offers programmatic advantages for reduction in processing time and cost in addition to various technical advantages, including the possibility to achieve enhanced hardware complexity targeted to superior performance, part consolidation, and the capability of processing of novel alloys. While AM is already being utilized for heat exchanger components in propulsion applications, almost all these AM components are made by means of Laser Powder Bed Fusion (L-PBF). L-PBF allows for fine features but is rather limited with respect to the overall size of the components that can be manufactured. Recent developments are maturing the Laser Powder Directed Energy Deposition (LP-DED) process which may be used, for example, to make integral channel thin-wall regeneratively-cooled rocket nozzles with diameters greater than 1 m. This paper highlights some integral channel heat exchanger demonstrator hardware applications of LP-DED, as well as the characterization of this process in combination with the use of the NASA HR-1 alloy. To properly utilize LP-DED for heat exchanger manufacturing, various aspects are being characterized such as geometry limitations, measurement of surface texture and geometric angled surfaces, surface enhancements for internal channels, and material evaluation. NASA HR-1 (Fe-Ni-Cr) is a high strength hydrogen resistant superalloy developed for use in aerospace applications, such as heat exchangers. Some aspects and considerations about the design of heat exchangers are summarized together with data relevant to LP-DED manufacturing in combination with the NASA HR-1 alloy. Microchannels were successful deposited down to 2.54 mm and 1 mm wall thickness, wall angles of 30°, both with high reproducibility. It was also found that the areal surface roughness is highly dependent on the size of the powder feedstock used for deposition. The characterization of these LP-DED features is critical for fluid flow and heat transfer predictions as it can be exploited to enhance heat transfer at the cost of increased pressure drop.
... Furthermore, since capturing the porosity defect after printing means wasting resources on useless work after the defect's appearance, researchers are developing in-process monitoring systems to locate them early in the process. A term for one such technique that is getting increasingly popular is "optical tomography"; it combines the layers' images into a single 3D model to facilitate the search of internal defects (Leach et al., 2019). ...
The product creation process involves various quantitative and qualitative decisions related to designing the product and the system executing its development and manufacturing operations. This comprehensive procedure includes many engineering and manufacturing disciplines interwoven by numerous technical, functional, and economic requirements. Currently, there is a challenge of providing an integrated perspective across the disciplines with an accurate quantitative evaluation of the case. Perhaps, changes to product or manufacturing process and system design demonstrate this most vividly: the whole system needs to be re-evaluated even if only one element is modified. Moreover, the introduction of innovative technologies further escalates competitiveness in product development (PD) endeavors. Additive manufacturing (AM) – a key component of the next era production paradigm – impacts the whole creation process and brings the domains of engineering and manufacturing even closer due to its digital nature.
Therefore, in planning change management, or PD activities in general, it is vital to make a comprehensive multidomain analysis considering the influence of AM. In this regard, there is a lack of tools that can quantitatively assess the time- and cost- implications of the decision options and facilitate selecting the best alternative.
This dissertation brings three contributions that collectively pursue closing the stated research gap. First, it elaborates the conception of integrated change management (ICM) by proposing the reference processes and highlighting the critical interconnections. Second, it reports the insights on AM impact obtained through an interview-based case study with a large energy sector manufacturer applying a metal printing technique to produce and maintain the functional components. Third, this work presents a simulation-based analytical framework enabling an integrated quantitative assessment of the engineering and manufacturing planning decisions, considering the AM context. Its capabilities have been tested and validated on a realistic aerospace case study, quantifying the impact of various decisions on change lead time and cost.
This input is expected to empower the practitioners with a holistic view on the management of changes, thus improving the coordination and reducing resource expenditure within the PD projects. The AM context consideration further emphasizes this study’s value as it underlines the benefits and difficulties in technology uptake. With the proposed framework, the company can improve the ICM process architecture by selecting the constituent steps and iteration patterns among them, leading to better process reliability and robustness. Also, it aids in configuring the manufacturing system in the number of machines and workers, lot sizing, shift mode, or layout design for the most efficient performance in terms of the techno-economic indicators significant for a given case. Altogether, the proposed perspectives and modeling capabilities can support the planning of PD and manufacturing operations and catalyze the adoption of AM.
In conclusion, the thesis discusses the utility, limitations, and challenges associated with the ICM concept, framework application, and its physical validation on a real case study. Finally, it gives an outlook for future research related to modeling the product creation activities and development of AM and the manufacturing workforce.
... In a production-line scenario, the employment of multi-view configurations for the inspection of fabricated workpieces could be beneficial to shop floor productivity, ultimately speeding up quality checks by maximising measurement coverage and improving measurement results by minimising the effects of occlusions. Particularly, the inspection of large objects (for example, the complete assembled body of an automotive vehicle) or freeform geometries (such as those produced via additive manufacturing) may appear as challenging due to the limited field-of-view of conventional single-view instruments [113]. To overcome this limitation, the simultaneous measurement of an object from multiple viewpoints could significantly reduce the inspection time, meaning both the time required to either rotate the object placed on a rotary stage or move the robot-mounted sensor around it, and the time required to merge multiple acquisitions into a single scanning output. ...
Manufacturing has recently experienced increased adoption of optimised and fast solutions for checking product quality during fabrication, allowing for manufacturing times and costs to be significantly reduced. Due to the integration of machine learning algorithms, advanced sensors and faster processing systems, smart instruments can autonomously plan measurement pipelines, perform decisional tasks and trigger correctional actions as required. In this paper, we summarise the state of the art in smart optical metrology, covering the latest advances in integrated intelligent solutions in optical coordinate and surface metrology, respectively for the measurement of part geometry and surface texture. Within this field, we include the use of a priori knowledge and implementation of machine learning algorithms for measurement planning optimisation. We also cover the development of multi-sensor and multi-view instrument configurations to speed up the measurement process, as well as the design of novel feedback tools for measurement quality evaluation.
... Non-contact methods were found to be the most common for areal measurements, particularly optical techniques including focus variation microscopy (FVM), confocal microscopy (CM) [97] and coherence scanning interferometry (CSI) [98]. [81]. It is worth noting that for this investigation, surface features and textures on the micron scale were of most interest and so the discrepancies caused by each of these techniques on the sub-micron scale had a smaller bearing on the choice of measurement technique. ...
The Super High Temperature Additively manufactured Resistojet (STAR) is an ongoing project to develop a novel resistojet thruster which will act as the primary propulsion device on small satellites. To enable the complicated geometry of the resistojet, Selective Laser Melting (SLM) was chosen as the production method. Post processing on internal features was limited for this same reason. Multiphysics modelling was used to predict the temperatures reached in the hottest parts of the thruster. However initial simulations revealed large discrepancies between the actual and predicted temperatures. These differences were attributed to the materials properties used for emissivity and resistivity. Emissivity is largely dependent on surface texture while resistivity can be influenced by the density and microstructure. Both properties are also highly dependent on temperature. SLM as-built parts can have vastly different surface textures and microstructure compared to cast or machined parts, but there is little data on resistivity and emissivity available. Furthermore, material structure and properties from SLM can vary significantly depending on process parameters. This motivated the project aim to obtain accurate emissivity and resistivity data of SLM metals and to study the relationship between SLM process parameters and the total hemispherical emissivity and resistivity of representative test coupons for as built 316L stainless steel. This was achieved by varying process parameters and measuring how these affected the output factors (responses) of surface texture, microstructure and part density which were then related to emissivity and resistivity. The relationship between the inputs and surface texture parameters (Sa, Sq, Ssk, Sku and Sdq) was a particular focus as there are currently no standards on how to measure or quantify surface roughness of SLM parts, leading to a lack of consistency in the literature. The input parameters chosen were those that make up the volumetric energy density (laser power, scanning speed, hatch spacing and layer thickness) and build orientation. A definitive screening Design of Experiments method was used to gain as much understanding of the influence of these input parameters on responses with as few experimental runs as possible. Seventeen experimental runs were completed, each varying the input parameters over one of three levels (low, mid, and high). Emissivity and resistivity were measured over a range of elevated temperatures using the calorimetric and four probe methods respectively. Finally, multiple linear regression models were created to identify which factors more strongly affected the responses. Results showed that emissivity ranges of most of the as-built SLM parts were similar to cast parts, but the 0° samples were consistently higher. SLM resistivity was also consistently higher than cast parts over the entire measured temperature range. When emissivity was determined using surface area from nominal sample dimensions measured using callipers, some of the values obtained were higher than the maximum emissivity of a black body. Using X-ray microcomputed tomography (microCT) imaging to determine sample dimensions gave higher surface areas and yielded lower emissivity values that were within physically admissible limits. Emissivity was found to correlate strongly to surface area regardless of temperature or emissive power, decreasing as surface area increased. When considering roughness on the size scale similar to the wavelength of the radiation, emissivity is governed by internal reflections within surface features. The SLM surfaces produced may not have had the types of features that led to more internal reflections but only increased the overall surface area. Thus the emissive power per unit area decreased, as did the emissivity. No trend was found between emissivity and any of the surface texture parameters. Resistivity was found to strongly correlate with the density of the samples, increasing as the density decreased, likely due to the interruption of conductive pathways. Multiple linear regression models found that build angle and layer thickness were the most significant factors that affected surface area and emissivity. More accurate temperature predictions were successfully obtained with multiphysics simulations using the newly measured values for emissivity and resistivity, particularly at higher temperatures. Emissivity values based on nominal sample dimensions, despite being impossibly high, were found to produce accurate simulation results by incorporating the effect of the higher surface area revealed by microCT but not directly included in the simulated geometry. The emissivity and resistivity measurements done using the techniques described in this thesis enabled accurate temperature simulations of the resistojet thruster which allowed for better estimation of the performance of the thruster. Whilst only 316L stainless steel is described in this thesis, the same setup and techniques were used to also measure the emissivity and resistivity of other, higher temperature materials used to build the resistojet. These measurements and the better understanding of emissivity and resistivity of SLM materials are also useful in wider application areas, such as predicting temperatures in nuclear reactors or making in-situ temperature measurements during the SLM process
... AM also offers several other advantages, including a shorter manufacturing lead time, reduced inventory and lot size, lower transportation costs, and the flexibility to match client needs while decreasing production waste [8], energizing the manufacturing sector and opening new research prospects [9]. AM has gained popularity in industries such as aerospace [10], automotive [11], construction [12], defence [13], health care [14], and machine tool [15]. In addition, the AM technique can make parts with complex geometries [16] using metals and alloys, polymers and composites, ceramics, and concrete [16,17]. ...
Wire arc additive manufacturing (WAAM) created aluminium alloy components are in high demand across a wide range of industries. The WAAM deposits are weakened by the non-uniform thermal cycles that they encounter. In order to successfully use WAAM components in various industries, high-quality, defect-free components are required. Therefore, close control over the process and post-process variants favour defect-free deposits with promising properties. Hence, the current review article delineates the influence of different process and post-process variants on metallurgical characteristics and mechanical properties of WAAM processed aluminium alloys. This article has three sections. The first section briefly introduces Additive Manufacturing (AM) techniques, classification, and benefits. The second section focuses on the WAAM of aluminium alloys, process and post-process variants, and their influence on metallurgical and mechanical characteristics. The final section provides possible scientific solutions to address the challenges associated with WAAM processed aluminium alloys.
... Metal additive manufacturing (AM) has attracted more attention in industrial production due to its wide applicability and its ability to produce parts with complex geometry [1]. PBF-LB, in which parts are built layer by layer by fusing metal powders using a laser, is a promising metal AM method. ...
... Surfaces, from structured surfaces [1] to additive surfaces [2], are the critical parts of components. We have developed a new method for surface characterisation combining light scattering and machine learning (ML). ...
... Several AM processes have been established and elaborated as per the available literature, which possesses some quality-related aspects [120,121]. To critically inspect the various surface and geometrically related issues of these AM parts and components, inspection and quality control methods to finalise the produced details for their end-use with the utmost level of quality, and functional necessities of the user are required [122][123][124]. Further, the different surface quality and staircase effects developed over the three-dimensional printing parts hurdle its growth in the competitive market structure. ...
Today, additive manufacturing (AM) is employed in various sectors, including aerospace, automobiles, healthcare, architecture, toys, arts and design, construction, etc. The AM used a set of technologies like 3D printing, 3D scanning, and designing, scanning, and printing software. 3D printing technologies are used to build 3D objects from computer-aided design models by layering material on top of material until a genuine part is formed. It is anticipated that AM will significantly impact manufacturing and, ultimately, on all of our lives. However, a sustained research effort into AM metrology is required to make the manufacturing revolution a reality. Tolerance and quality control methods must be in place for AM processes, starting with offline metrology and progressing to closed-loop control utilising inline metrology. This paper discusses the various significant capabilities of AM with their metrological aspects. Furthermore, several crucial industrial prospects of AM for measurement systems are discussed briefly. Finally, the paper discusses the significant features of inspection and quality control. A reliable methodology for the metrological assessment of AM parts would be highly advantageous in expanding AM’s utility. As a result of the extensive literature evaluation, the current study will assist students, engineers, designers, manufacturers, and metrologists in identifying research gaps and potential for the field’s progress.
... Previous reviews showed that Rz values for metal surfaces lie between tens of nanometres to hundreds of micrometres (e.g., with an additively manufactured surface) and results show a high dependence of contact CMS measurement uncertainties on surface texture [227]. This surface texture issue is significant: it is not clear that contact CMSs can be used for traceable reference measurement without the use of a high-degree of filtering À this remains an open research question, especially with the rough surfaces encountered in additive manufacturing (AM) [173] (see Fig. 33). ...
X-ray computed tomography (XCT) is increasingly being used for evaluating quality and conformance of complex products, including assemblies and additively manufactured parts. The metrological performance and traceability of XCT nevertheless remains an important research area that is reviewed in this paper. The error sources influencing XCT measurement results are discussed, along with related qualification, calibration and optimization procedures. Moreover, progress on performance verification testing and on the determination of task-specific measurement uncertainty is covered. Results of interlaboratory comparisons are summarized and performance in various dimensional measurement fields is illustrated. Conclusions and an outlook for future research activities are also provided.
... al investigate empirical or black box models for the whole process of fused filament fabrication but not for single filament lines [5]. One of the fastest growing topics for metal-based AM is the inclusion of in-situ metrology [6]. For fused filament fabrication, no previous research on the application of on machine metrology could be found. ...
Although often seen as a hobbyist niche, polymer additive manufacturing has its advantages for small sized batch production and is
therefore more and more frequently considered as a potential investment for small- to medium-sized enterprises. One of the main
concerns regarding the process is often the reliability of the structural strength of the printed parts and the necessary experience to
circumvent corresponding production issues. In order to resolve these reservations, the influence of the large variety of adjustable
print process parameters on the quality of the final product needs to be investigated to its full extend. In this work, a method is
proposed to investigate the dependency of the part density on the shape of the individual filament lines. By integrating laser line
triangulation sensors into a common fused filament fabrication printer, the influence of the print process parameters on the filament
shape as well as the interaction between neighbouring and stacked lines of filament can be measured during the print process
... As one of the mainstream optical three-dimensional sensing techniques, structured light profilometry (SLP) has been researched for years [1,2]. With the increased demand for analyzing dynamic behavior including motion trajectory, speed and structural deformation, high-speed 3D shape recording using SLP attracts scholars' attention and many advances have been made in recent years [3,4]. Many of these advances occured in fringe projection profilmetry (FPP) due to its ability to provide 3D data with both high spatial and temporal resolution [5,6]. ...
High-speed three-dimensional (3D) shape measurement has been continuously researched due to the demand for analyzing dynamic behavior in transient scenes. In this work, a time-overlapping structured-light 3D shape measuring technique is proposed to realize high-speed and high-performance measurement on complex dynamic scenes. Time-overlapping structured-light projection is presented to maximumly reduce the information redundancy in temporal sequences and improve the measuring efficiency; generalized tripartite phase unwrapping (Tri-PU) is used to ensure the measuring robustness; fringe period extension is achieved by improving overlapping rate to further double the encoding fringe periods for higher measuring accuracy. Based on the proposed measuring technique, one new pixel-to-pixel and unambiguous 3D reconstruction result can be updated with three newly required patterns at a reconstruction rate of 3174 fps. Three transient scenes including collapsing wood blocks struck by a flying arrow, free-falling foam snowflakes and flying water balloon towards metal grids were measured to verify the high performance of the proposed method in various complex dynamic scenes.
The process of control of complex parts is characterized by labor intensity, increased complexity, and requires careful selection of measuring tools. This article proposes a method of decision-making on the quality of the control process of complex parts. This method takes into account the main shortcomings of the process, which are the difficulties that may arise in the choice of universal and standardized measuring instruments that are ineffective in the presence of advanced and automated controls; in the appointment of measuring instruments, which is conducted separately for each operation, which is inefficient for multi-item production; in the high complexity of control in the absence of automated tools for the formation of control results, as well as the lack of training of controllers, in connection with the use of simple control and measuring instruments. Proposed method is based on the application of the proposed universal integrated indicator, “the quality level of the process of complex parts control”, based on which decisions are made. The article also offers recommendations for evaluating individual process indicators and suggestions for decision-making on the quality of the process.KeywordsProcessControlComplex partMethod
Quality levelIndustrial growth
In the standardized processing of surface topography data, the form removal and filtering operations are clearly separated. This is reflected in the current ISO standards concerning profile surface texture and areal surface texture, the ISO 21920 and the ISO 25178 series respectively. When the scale-limited surface texture is significant compared to the form to be removed, for example with additive manufactured surfaces, the dependence of the surface Fourier spectrum on the removed form and orientation may become significant. This may lead to interaction between the form removal and filtering operations. To counter this interaction, in this paper, the lower-order discrete Legendre polynomials that describe the form are combined with cosine functions that describe the surface texture. This set of base functions is orthonormalized using a Gram-Schmidt procedure. This results in a set of orthonormal functions that allow an independent parameterization of both form and texture. The concept and the related theory are given and illustrated using examples of filtering profiles and areal topographies, description of cylinders and treatment of missing data. The examples show that the concept as presented in this paper is useful for filtering surfaces with a dominant form and can be used in the parametrization of surfaces and cylindrical geometries. Also, the methods presented here can be used for filtering and parametrization in the case of missing points in the data, actual holes in the profile or non-rectangular surfaces.
Today, additive manufacturing (AM) is used in many industries, including aircraft, transportation, medicine, architecture, toys, arts & design, and construction. The 3D model is created in a computer-aided design (CAD) software, and this model is converted into a standard translating language (STL) and then transferred to a 3D printing machine, creating a physical model via a material joining process into a layer-by-layer pattern. AM is expected to have a tremendous impact on the industry and, eventually, every aspect of our life. To make the manufacturing revolution a reality, though, there needs to be an ongoing research effort into AM metrology. AM processes require the implementation of tolerance and quality control techniques, starting with offline metrology and moving toward closed-loop control using inline metrology. The several significant capabilities of AM are covered in this paper, along with their metrological implications. Additionally, several significant challenges of AM for measurement systems are briefly explored.
The potential of additive manufacturing (AM) to build products in a layer over layer basis from a digital three-dimensional model with tremendous variability in accordance with the criticality of design has propelled it to the forefront in the manufacturing technology sector. Furthermore, AM requires no extra tooling equipment and can make parts with little to almost no material wastage. Even after having these technological benefits, AM has still yet to realize its full potentiality, owing to a dearth of proper knowledge of all AM procedures and coordinated efforts in the area of standardizing, metrology (measurement science), qualification, as well as certification. Consequently, AM manufactures products with greater complexity and characteristics but with lower dimensional accuracy, precision, requisite tolerances, and desired material characteristics. Method-specific standardized metrology and inspection procedures for AM parts, in particular, play a critical role in achieving the requisite quality and, as a result, simplifying the AM product certification process. This chapter offers a brief introduction to the metrology of AM, its need, and the challenges associated with it along with a detailed evaluation of general metrology methods as well as for AM-specific metrology methods.
Additive manufacturing has long enabled complex and less restrictive design capabilities in the world of modern manufacturing. However, industry applications require extensive analysis into reliability concerns over repeatability that currently prevent the technology from maturing to an adequate, widespread production method. With current research focus expanding on additive manufacturing technologies, a need has developed to ensure repeatability in already established methods. This paper reviews the current certification landscape surrounding additive components as well as similarly variable manufacturing processes as baselines for comparison. Next, concerns in the repeatability of additive manufacturing methods are outlined for both their occurrences and effects. Lastly, methods of verification and current developments in design and verification methodologies are presented with the aim of analyzing potential future developments to aid industry adoption of additive manufacturing.
As one of the key technologies of Industry 4.0, additive manufacturing (AM) has been gaining rapid momentum in R&D and industry applications. However, achieving high consistency of material properties and dimensional accuracy of the additively manufactured parts remains a challenge. Hence, it is necessary to make the AM process intelligent to address the issues. In this paper, development of advanced laser aided additive manufacturing (LAAM) technology through digitization, sensorization and machine learning was introduced. A sensor-based adaptive dimension correction strategy using 3D point clouds as the feedback data was explored. A laser displacement sensor was integrated into an LAAM system to perform on-machine laser scanning measurement and in-process surface deviation correction of the intermediate layers. Finally, image-based process monitoring and control was investigated. The melt pool width was measured and fed back to a closed-loop controller that adjusts the laser power. The controller was developed with a novel multi-tasking architecture that incorporated an auto-tuning unit that optimises controller parameters automatically to achieve adaptable control of the process to different part shapes, materials, toolpaths, and process parameters. With this monitoring and control system implemented, the process stability and geometric accuracy of the deposited material can be improved.KeywordsAdditive manufacturingIn-process sensingMonitoringAdaptive controlMachine learning
A method has been proposed to verify geometric tolerances by X-ray computed tomography (XCT) without the need for image segmentation The method is based on the direct comparison of a part XCT image to a volumetric representation of its geometric tolerance. In previous works the method was directly applied to raw images. However, filters are commonly applied to XCT images. Usually, they mitigate noise or enhance details. In this work, we study if the segmentation-free verification benefits from the application of filters to XCT images. Standard filters a considered, e.g. Gaussian and non-local means.
In the laser powder bed fusion additive manufacturing of metals, extreme thermal conditions create many highly dynamic physical phenomena, such as vaporization and recoil, Marangoni convection, and protrusion and keyhole instability. Collectively, however, the full set of phenomena is too complicated for practical applications and, in reality, the melting modes are used as a guideline for printing. With an increasing local material temperature beyond the boiling point, the mode can change from conduction to keyhole. These mode designations ignore laser-matter interaction details but in many cases are adequate to determine the approximate microstructures, and hence the properties of the build. To date no consistent, common, and coherent definitions have been agreed upon because of historic limitations in melt pool and vapor depression morphology measurements. In this review, process-based definitions of different melting modes are distinguished from those based on postmortem evidence. The latter are derived mainly from the transverse cross sections of the fusion zone, whereas the former come directly from time-resolved x-ray imaging of melt pool and vapor depression morphologies. These process-based definitions are more strict and physically sound, and they offer new guidelines for laser additive manufacturing practices and create new research directions. The significance of the keyhole, which substantially enhances the laser energy absorption by the melt pool, is highlighted. Recent studies strongly suggest that stable-keyhole laser melting enables efficient, sustainable, and robust additive manufacturing. The realization of this scenario demands the development of multiphysics models, signal translations from morphology to other feasible signals, and in-process metrology across platforms and scales.
This work for the first time presents the results of optimization of printing parameters in the Binder Jetting technology in terms of the possibility of using an irregular aluminum powder which is much cheaper and more common than spheroidal. The influence of binder saturation (15–100 %), roller traverse speed (10–110 mm/sec), layer thickness (30–90 µm), and sintering atmosphere (vacuum, argon, hydrogen) on the quality of aluminum printed parts has been investigated. The study included the density, shrinkage, porosity, surface topography, and roughness of printed, and sintered aluminum parts. An anisotropy of linear contraction in the X, Y, and Z directions was observed, with the largest linear shrinkage occurring in the Z direction. In terms of roughness, the top surfaces (XY direction) turned out to be the smoothest and the side surfaces (YZ direction) were the roughest. Samples that were sintered under vacuum resulted in higher density, lower shrinkage, and lower porosity compared to those sintered in argon or hydrogen. On the basis of results, it was found that generally, increasing the saturation level and layer thickness causes a decrease in density and increases the shrinkage and the porosity of additive manufactured parts.
Electron beam powder bed fusion (EB-PBF) has been given much attention in recent years for its potential in the aerospace and medical industries, particularly with Ti-6Al-4V. However, these processes produce parts with inherent rough surface finishes, impacting the performance and generating additional challenges and costs with surface post-processing. This review examines the primary mechanisms responsible for surface roughness generation in EB-PBF and the process variables that have been verified to influence the surface quality of Ti-6Al-4V parts. The challenges in surface metrology of metallic PBF parts are also discussed, as are new perspectives and guidelines for future research.
Additive manufacturing (AM) has transformed the manufacturing industries by providing numerous opportunities for rethinking and remodeling existing systems. Complex fabrication, rapid prototyping, reduced cost of pre-production tools, and customizations are the main features of this technique. Although, the proper and deep understanding of process parameters is required because it significantly influences the microstructure, mechanical properties, and dimensional accuracy of components. In this work, the design-for-metrology (DFM) approach is used to check the dimensional deviations of 316L stainless steel (SS) samples manufactured via selective laser melting (SLM) process. Laser power, scan speed, layer thickness, and hatch spacing are the chosen parameters to check their influence on fabricated parts. The geometric feature such as height, diameter, and cylindricity of samples was measured by a coordinate measuring machine (CMM). The uncertainty of measurement in geometric features is evaluated by the law of propagation of uncertainty (LPU) method. The result shows that dimensional deviation is more at high energy density. Also, the dimensional deviation is not that high for selected geometric features, which shows that the SLM process has good dimensional accuracy
Machine learning for additive manufacturing (ML4AM) has emerged as a viable strategy in recent years to enhance 3D printing performance. However, the amount of data required for model training and the lack of ability to infer AM process insights can be serious barriers for black-box learning methods. Due to the nature of low-volume fabrication of infinite product variety in AM, ML4AM also faces “small data, big tasks” challenges to learn heterogeneous point cloud data and control the quality of new designs. To address these challenges, this work establishes an impulse response formulation of layer-wise AM processes to relate design inputs with the deformed final products. To enable prescriptive learning from a small sample of printed parts with different 3D shapes, we develop a fabrication-aware input-output representation, where each product is constructed by a large amount of basic shape primitives. The impulse response model depicts how the 2D shape primitives (circular sectors, line segments, and corner segments) in each layer are stacked up to become final 3D shape primitives. A geometric quality of a new design can therefore be predicted through the construction of learned shape primitives. Essentially, the small-sample learning of printed products is transformed into a large-sample learning of printed shape primitives under the impulse response formulation of AM. This fabrication-aware formulation builds the foundation for applying well-established control theory to the intelligent quality control in AM. It not only provides theoretical underpinning and justification of our previous work, but also enable new opportunities in ML4AM. As an example, it leads to transfer function characterization of AM processes to uncover process insights. It also provides block-diagram representation of AM processes to design and optimize the control of AM quality.
One of the key measurement parameters of the surface topography is the measurement area. It influences the possibility of using filters separating components of surface texture and thus determines the reliability of the obtained measurement results. The currently applicable standard does not define the size of the measuring area. To determine its size, fractal analysis was carried out in the article. The paper presents research on two types of geometry: simple geometry in the form of cylindrical and spherical surfaces and more complex geometry represented by free surfaces such as crowns and molars of teeth. In the process of making the research models, four 3D printing techniques were used: Fused Deposition Modeling (FDM), Melted and Extruded Modeling (MEM) Fused Filament Fabrication (FFF) and Material Jetting (MJ). 3D measurements of surface texture were made using a contact profilometer and a focus variation microscope. The analysis of topography images and selected parameters of the surface topography showed that the optical method gave better measurement results than the contact method. In the case of models made with the FDM and MEM techniques, similar values of the Sa parameter were obtained. Slightly smaller values of Sa were recorded for FFF models, while the highest for MJ models. Models made using the FFF method were also characterized by the lowest variability of results. Models made using the MJ method were characterized by relatively deep valleys in comparison with the other models, which was reflected in the Ssk and Svk parameters. The valleys counting from the top surface of the specimen were the shallowest for models made with the FFF method. Surfaces with simpler geometry were characterized by smaller variability of parameters values.
The research aimed to verify algorithms for evaluating selected parameters of additively produced samples using Industrial Computed Tomography. A 3D model of the lattice structure was created by CAD (Computer-Aided-Design) software PTC Creo Parametric 8 and samples were made using FDM (Fused Deposition Modelling) technology from ABS (Acrylonitrile butadiene styrene) base material and P400SR support material. In this paper, two samples were observed in detail. One of them was subjected to a mechanical test under uniaxial load until the internal structure of the sample broke (tested one), the other was not mechanically loaded (untested one). Samples evaluation focused on their surface software reconstruction from CT (Computed Tomography) data, on the accuracy of production and finally on their porosity. Due to residual support material in the untested sample, the surface was correctly determined only if the CAD model was used as the starting surface. The dimensional analysis shows that the sample is approximately 0.5 mm higher than the CAD model thus production accuracy does not correspond with the accuracy specified by the manufacturer. The volume of material in both samples differs by 0.63 % and thus the repeatability of production is adequate. Porosity analysis shows that the samples have a comparable porosity of 10 % and their percentage difference is 1.2 %.
Additive manufacturing is now regularly used for customised fabrication of parts with complex shapes and geometries. However, the large range of relevant scales, high slopes, step-like transitions, undercuts, alternation between dark and overly bright regions and other complex features present on the surfaces, in particular of metal additive parts, represent a significant challenge for current optical measurement technologies. Measuring surfaces with such complex features requires high numerical aperture optics, and state-of-the-art systems commonly include optics that can only reliably acquire surface topographies over a small field of view, typically tens or hundreds of micrometers. Such measurements are often insufficient for practical applications. Here, we present an optical system that features a large numerical aperture (>0.3) and a wide field of view p2.9ˆ2.9q mm, capable of measuring additive manufacturing parts in a single measurement, without the need for lateral stitching to increase the field of view. The proposed system exhibits optical properties that provide facility for large-field, high-resolution measurement of industrially-produced additively manufactured parts.
Technology opportunity identification leads to technological advances with future-oriented ideas by predicting the direction of change in technological trends. Many researchers have proposed several processes for identifying technology opportunities using various types of data sources. Among them, patents have been widely used as a dominant source in that they can serve as a reliable source of knowledge. Previous studies have built patent maps and explored outliers or vacant spaces on the map to discover new technology opportunities. They also have developed a morphological matrix and modified the shapes of its dimensions to produce new ideas. However, they have dealt with measuring generic potential values without taking account of a firm’s internal capabilities. To secure meaningful opportunities, it is necessary to examine how well the opportunities identified are suitable for the internal capabilities. Moreover, they have focused on the technology opportunities at the present time. Technology opportunities, however, have value in the future, not the present. Motivated to address these limitations, this study proposes a novel approach that facilitates a firm to identify potential technology opportunities realizable from its internal capabilities. This study is expected to improve R&D planning capabilities and contribute to the establishment of a next-generation R&D planning system.
We present the design and characterisation of a high-speed sintering additive manufacturing benchmarking artefact following a design-for-metrology approach. In an important improvement over conventional approaches, the specifications and operating principles of the instruments that would be used to measure the manufactured artefact were taken into account during its design process. With the design-for-metrology methodology, we aim to improve and facilitate measurements on parts produced using additive manufacturing. The benchmarking artefact has a number of geometrical features, including sphericity, cylindricity, coaxiality and minimum feature size, all of which are measured using contact, optical and X-ray computed tomography coordinate measuring systems. The results highlight the differences between the measuring methods, and the need to establish a specification standards and guidance for the dimensional assessment of additive manufacturing parts.
Purpose
The purpose of this study is the introduction and validation of a new technique for process monitoring during electron beam melting (EBM).
Design/methodology/approach
In this study, a backscatter electron detector inside the building chamber is used for image acquisition during EBM process. By systematic variation of process parameters, the ability of displaying different topographies, especially pores, is investigated. The results are evaluated in terms of porosity and compared with optical microscopy and X-ray computed tomography.
Findings
The method is capable of detecting major flaws (e.g. pores) and gives information about the quality of the resulting component.
Originality/value
Image acquisition by evaluating backscatter electrons during EBM process is a new approach in process monitoring which avoids disadvantages restricting previously investigated techniques.
Additive manufactured (AM) components, specifically those created through laser powder bed fusion (LPBF) methods, exhibit an abundance of surface textures of varying forms and patterns. These topographies have historically been categorized solely using their Ra values, a metric which offers limited information to discern differences among the morphologies of AM surfaces. This diversity is illustrated not only among parts made using different machines or processing parameters, but also between different locations in the build chamber and even on the same part. Current instruments have the potential to acquire three dimensional (3D) maps of the AM surface, enabling a range of field and feature based descriptors that offer potential in characterizing AM surface morphology. This work explores feature-based metrology of AM surfaces in an effort to relate features to part quality, as well as aid the modeling community in better understanding of melt pool geometry. The feature of interest in this work, the chevron pattern seen on top of scan lines, is theorized to be connected to the laser parameters used in the printing of the part. This research explores the chevron pattern, observing changes in this feature over a range of laser power and velocity combinations. INTRODUCTION Metal AM is a growing technology which fabricates parts directly from 3D computer aided design (CAD) models. Parts are built up layer-by-layer starting at the substrate. A single layer of
Electron beam additive manufacturing (EBAM) is an additive manufacturing (AM) technique increasingly used by many industrial sectors, including medical and aerospace industries. The application of this technology is still, however, challenged by many technical barriers. One of the major issues is the lack of process monitoring and control system to monitor process repeatability and component quality reproducibility. Various techniques, mainly involving infrared (IR) and optical cameras, have been employed in previous attempts to study the quality of the EBAM process. However, all attempts lack the flexibility to zoom-in and focus on multiple regions of the processing area. In this paper, a digital electronic imaging system prototype and a piece of macroscopic process quality analysis software are presented. The prototype aims to provide flexibility in magnifications and the selection of fields of view (FOV). The software aims to monitor the EBAM process on a layer-by-layer basis. Digital electronic images were generated by detecting both secondary electrons (SE) and backscattered electrons (BSE) originating from interactions between the machine electron beam and the processing area using specially designed hardware. Prototype capability experiments, software verification and demonstration were conducted at room temperature on the top layer of an EBAM test build. Digital images of different magnifications and FOVs were generated. The upper range of the magnification achieved in the experiments was 95 and the demonstration verified the potential ability of the software to be applied in process monitoring. It is believed that the prototype and software have significant potential to be used for in-process EBAM monitoring in many manufacturing sectors. This study is thought to be the necessary precursor for future work which will establish whether the concept is suited to working under in-process EBAM operating conditions.
Selective laser melting is an increasingly attractive technology for the manufacture of complex and low volume/high value metal parts. However, the inevitable residual stresses that are generated can lead to defects or build failure. Due to the complexity of this process, efficient and accurate prediction of residual stress in large components remains challenging. For the development of predictive models of residual stress, knowledge on their generation is needed. This study investigates the geometrical effect of scan strategy on residual stress development. It was found that the arrangement of scan vectors due to geometry, heavily influenced the thermal history within a part, which in turn significantly affected the transverse residual stresses generated. However, irrespective of the choice of scanned geometry and the thermal history, the higher magnitude longitudinal stresses had consistent behaviour based on the scan vector length. It was shown that the laser scan strategy becomes less important for scan vector length beyond 3 mm. Together, these findings, provide a route towards optimising scan strategies at the meso-scale, and additionally, developing a model abstraction for predicting residual stress based on scan vectors alone.
Powder bed fusion (PBF) is a popular additive manufacturing (AM) process with wide applications in key industrial sectors, including aerospace, automotive, healthcare, defence. However, a deficiency of PBF is its low quality of surface finish. A number of PBF process variables and other factors (e.g. powders, recoater) can influence the surface quality. It is of significant importance to measure and characterise PBF surfaces for the benefits of process optimisation, product performance evaluation and also product design. A state-of-the-art review is given to summarise the current research work on the characterisation of AM surfaces, particularly PBF surfaces. It is recognised that AM processes are different from conventional manufacturing processes and their produced surface topographies are different as well. In this paper, the surface characterisation framework is updated to reflect the unique characteristics of PBF processes. The surface spatial wavelength components and other process signature features are described and their production mechanisms are elaborated. A bespoke surface characterisation procedure is developed based on the updated framework. The robust Gaussian regression filter and the morphological filters are proposed to be used for the separation of the waviness component due to their robustness. The watershed segmentation is enhanced to extract globules from the residual surface. Two AM components produced by electron beam melting (EBM) and selective laser melting (SLM), are measured and characterised by the proposed methodology. Both of the two filters are qualified for the extraction of melted tracks. The watershed segmentation can enable the extraction of globules. The standard surface texture parameters of different surface wavelength components are compared. A set of bespoke parameters are intentionally developed to offer a quantitative evaluation of the globules.
Additive manufacturing (AM) has enabled the production of complex geometries such as conformal lattices, topology optimized shapes, and organic structures. These complex geometric shapes must sometimes meet functional requirements, including (1) following specific curves or surfaces and (2) being bounded by specific surfaces. Mechanisms such as Theoretical Supplemental Surfaces (TSS) have been proposed for tolerancing of such geometric shapes, though challenges remain with inspection and validation requirements. A Theoretical Supplemental Geometry (TSG, including curves – TSC, surfaces – TSS and volumes – TSV) concept is introduced. To address these measurement and verification challenges, Derived Supplemental Surfaces (DSS) are introduced. The verification of a TSS specification using 3D scanning and DSS is demonstrated on a lattice surface using Chebyshev and Least Squares fitting.
From an industrial perspective this paper aims to explore the state of the art regarding GD&T for metal additive manufacturing, specifically regarding product definition and inspection. The available techniques for geometry assurance for parts with small scale features and rough surfaces are evaluated in terms of suitability for the task and readiness for industrial implementation. It is found that many of the remaining challenges seem to be related to processing of data rather than obtaining data. Current difficulties are related to issues such as calibration, surface determination and defining the most relevant parameters to tolerance and inspect.
Additive manufacturing (AM) technologies are rapidly expanding in industrial domains that were typically dominated by conventional manufacturing technologies. For example, AM technologies are starting to be used to produce metal threaded products, including dental implants. Threaded joints are extensively used in many industrial applications and account for approximately 50 % of all joints produced in mechanical systems. In particular, they allow obtaining assembly characterized by high strength and high rigidity as well as easy disassembly for maintenance or recycling purposes. X-ray computed tomography (CT) is an advanced measuring technique increasingly used for several industrial metrology applications. For the application of screw threads measurements, CT is capable of overcoming the limitations of conventional measuring techniques (i.e. tactile and optical measuring systems). In particular, CT allows holistic non-destructive evaluations of both internal and external threads, even when they are included in fragile or deformable parts (e.g. polymeric parts) or they are characterized by high form errors and highly complex texture (e.g. AM parts). This work proposes a CT-based methodology for measuring the geometry and local form errors of a threaded AM part. Moreover, the paper investigates and discusses the accuracy of CT dimensional measurement results.
Additive Manufacturing, Process Monitoring, Optical Tomography, X-ray Tomography, Lack of Fusion Defect, Plastification
The additive manufacturing (AM) of aluminum alloys promises to considerably enhance the performance of lightweight critical parts in various industrial applications. AlSi10Mg is one of the compatible Al alloys used in the selective laser melting of lightweight components. However, the surface defects obtained from the as-built parts affect their mechanical properties, and thus represent an obstacle to using them as final products. This study aims to improve the surface characteristics of the as-built AlSi10Mg parts using shot peening (SP). To achieve this goal, different SP intensities were applied to various surface textures of the as-built samples. The SP results showed a significant improvement in the as-built surface topography and a higher value of effective depth using 22.9 A intensity and Gp165 glass beads. The area near the shot-peened surface showed a significant microstructure refinement to a specific depth due to the dynamic precipitation of nanoscale Si particles. Surface hardening was also detected and high compressive residual stresses were generated due to severe plastic deformation. The surface characteristics obtained after SP could result in a significant improvement in the mechanical properties and fatigue strength, and thus promise performance enhancement for critical parts in various industrial applications.
This paper presents the design of a high speed, high resolution silicon based thermal imaging instrument and its
application to thermally image the temperature distributions of an electron beam melting additive manufacturing
system. Typically, thermal images are produced at mid or long wavelengths of infrared radiation. Using the shorter
wavelengths that silicon focal plane arrays are sensitive to allows the use of standard windows in the optical path.
It also affords fewer modifications to the machine and enables us to make use of mature silicon camera
technology. With this new instrument, in situ thermal imaging of the entire build area has been made possible at
high speed, allowing defect detection and melt pool tracking. Melt pool tracking was used to implement an
emissivity correction algorithm, which produced more accurate temperatures of the melted areas of the layer.
Additive manufacturing of lightweight or functional structures by selective laser beam (SLM) or electron beam melting (EBM) is widespread, especially in the field of medical applications. SLM and EBM processes were applied to prepare Ti6Al4V test specimens with different surface orientations (0°, 45° and 90°). Roughness measurements of the surfaces were conducted and cell behavior on these surfaces was analyzed. Hence, human osteoblasts were seeded on test specimens to determine cell viability (metabolic activity, live-dead staining) and gene expression of collagen type 1 (Col1A1), matrix metalloprotease (MMP) 1 and its natural inhibitor, TIMP1, after 3 and 7 days. The surface orientation of specimens during the manufacturing process significantly influenced the roughness. Surface roughness showed significant impact on cellular viability, whereas differences between the time points day 3 and 7 were not found. Collagen type 1 mRNA synthesis rates in human osteoblasts were enhanced with increasing roughness. Both manufacturing techniques further influenced the induction of bone formation process in the cell culture. Moreover, the relationship between osteoblastic collagen type 1 mRNA synthesis rates and specimen orientation during the building process could be characterized by functional formulas. These findings are useful in the designing of biomedical applications and medical devices.
Full geometrical alignment of CT instruments remains a complicated endeavor. This paper therefore presents a fast and comprehensive method for determination and compensation of geometrical misalignments. First, a reference object, consisting of spheres mounted on a carbon fiber tube, is X-ray imaged at different angular positions. Subsequently, the misalignment parameters of the CT instrument are determined by minimizing the residual errors between observed and modelled sphere center coordinates. Finally, the FDK-based tomographic reconstruction algorithm is adapted to account for the determined misalignment parameters. The paper discusses the fundamentals of the approach and provides an experimental validation of its performance.
The objective of this study is to investigate the relationship between the melt pool characteristics and the defect occurrence in an as-built additive manufacturing part. One of the major detrimental microstructure properties associated with additive manufacturing (AM) is porosity within final parts. State-of-the-art porosity detection methods focus primarily on post-manufacturing approaches that are susceptible to high cost of process, longer process time, and are incapable of characterizing pores during fabrication. A real-time porosity prediction method is developed using morphological characteristics of the melt pool boundary (i.e., features obtained via functional principal component analysis (FPCA)). A thermal monitoring system is used to capture the time-varying melt pool signal, which are labeled as either pores or normal melt pools by X-ray tomography. Supervised learning methods are utilized to identify the patterns of melt pool images and build a black-box model for the probability distribution of class labels (namely, porosity) based on data characteristics of predictors (e.g., melt pool characteristics). The resultant model does not depend on specific design of specimens with varying material properties; and can be effectively developed as long as thermal-porosity data can be obtained. In the current study, multiple supervised machine learning approaches are used to classify melt pools to predict porosity in a part. Two different accuracy measures are used and numerical experiments show that among the classification approaches used (i.e., Decision Tree (DT), K-Nearest Neighbor (KNN), Support Vector Machine (SVM), Linear Discriminant Analysis (LDA), and Quadratic Discriminant Analysis (QDA)), KNN results in the highest rate of accurately classifying melt pools (98.44%). However, DT results in the lowest rate for incorrectly identifying normal melt pools as pores (0.03%). A comparative study is conducted that compares the performance of supervised learning methods leveraging the proposed morphological model and simple metrics of the melt pool. Numerical experiments show that the morphological model combined with supervised learning techniques vastly outperform the simple melt pool metrics combined with supervised learning techniques (approximately 250% better performance for correctly predicting abnormal melt pools). Our approach may potentially be applied to other AM processes that share similar energy-material interactions (e.g., powder bed fusion, electron beam melting).
Many test artefact designs have been proposed for use with additive manufacturing (AM) systems. These test artefacts have primarily been designed for the evaluation of AM form and dimensional performance. A series of surface-specific measurement test artefacts designed for use in the verification of AM manufacturing processes are proposed here. Surface-specific test artefacts can be made more compact because they do not require the large dimensions needed for accurate dimensional and form measurements. The series of three test artefacts are designed to provide comprehensive information pertaining to the manufactured surface. Measurement possibilities include deviation analysis, surface texture parameter data generation, sub-surface analysis, layer step analysis and build resolution comparison. The test artefacts are designed to provide easy access for measurement using conventional surface measurement techniques, for example, focus variation microscopy, stylus profilometry, confocal microscopy and scanning electron microscopy. Additionally, the test artefacts may be simply visually inspected as a comparative tool, giving a fast indication of process variation between builds. The three test artefacts are small enough to be included in every build and include built-in manufacturing traceability information, making them a convenient physical record of the build.
Micro manufacturing using micro direct metal deposition was successfully implemented on NiTi powder alloy. Micro direct metal deposition was optimized through a set of process parameters and designed experiments to improve the geometrical accuracy and repeatability of micro fabrication. Scanning electron microscopy and micro X-ray computed tomography were used to analyze the surface quality, micro porosity, and deviations of products with respect to nominal geometrical models. Results showed that increasing scanning speed is an efficient way to improve the surface quality and decrease the micro porosity content. Below 15% deviation to nominal geometrical models was achieved in hollow NiTi samples through a set of micro direct metal deposition process parameters and designed experiments.
AlSi10Mg inclined struts with angle of 45° were fabricated by selective laser melting (SLM) using different scanning speed and hatch spacing to gain insight into the evolution of the molten pool morphology, surface roughness, and dimensional accuracy. The results show that the average width and depth of the molten pool, the lower surface roughness and dimensional deviation decrease with the increase of scanning speed and hatch spacing. The upper surface roughness is found to be almost constant under different processing parameters. The width and depth of the molten pool on powder-supported zone are larger than that of the molten pool on the solid-supported zone, while the width changes more significantly than that of depth. However, if the scanning speed is high enough, the width and depth of the molten pool and the lower surface roughness almost keep constant as the density is still high. Therefore, high dimensional accuracy and density as well as good surface quality can be achieved simultaneously by using high scanning speed during SLMed cellular lattice strut.
Recent studies have shown that X-ray computed tomography (XCT) can be used to measure the surface topography of additively manufactured parts. However, further research is necessary to fully understand XCT measurement performance. Here, we show how magnification of the X-ray projections and resolution of the volumetric reconstruction grid influence the determination of surface topography in the XCT data processing pipeline. We also compare XCT results to coherence scanning interferometry (CSI) measurements and find that by increasing the magnification of the X-ray projections, smaller topographic detail can be resolved, approaching the lateral resolution of CSI. Results show that there is an optimum setting for magnification, below and above which XCT measurement performance can degrade. The resolution of the volumetric reconstruction grid has a less pronounced effect, but in general, adopting higher or lower resolutions than the default leads to degraded repeatability in surface determination. The problem of determining sensitivity of XCT surface measurement as a function of setup parameters is complex, and it is not yet possible to provide optimal setup configurations that work regardless of object geometry. However, the methods presented here, as well as the results obtained, represent a useful contribution to good practice for XCT measurement of surfaces.
Recent advances in X-ray computed tomography (XCT) have allowed for measurement resolutions approaching the point where XCT can be used for measuring surface topography. These advances make XCT appealing for measuring hard-to-reach or internal surfaces, such as those often present in additively manufactured parts. To demonstrate the feasibility and potential of XCT for topography measurement, topography datasets obtained using two XCT systems are compared to those acquired using coherence scanning interferometry and focus variation microscopy. A hollow Ti6Al4V part produced by laser powder bed fusion is used as a measurement artefact. The artefact comprises two component halves that can be separated to expose the internal surfaces. Measured surface datasets are accurately aligned and similarly cropped, and compared by various qualitative and quantitative means, including the computation of ISO 25178-2 areal surface texture parameters, commonly used in part quality assessment. Results show that XCT can non-destructively provide surface information comparable with more conventional surface measurement technologies, thus representing a viable alternative to more conventional measurement, particularly appealing for hard-to-reach and internal surfaces.
In this study, an eddy current (EC) detector is integrated in an additive/subtractive hybrid manufacturing (ASHM) process. The detector facilitates in-process inspection and repair operations through material deposition, defect detection, and removal processes layer by layer. A feasibility test is carried out on eddy current detection of subsurface defects in additively manufactured parts by using an EC detector. The study compares the results obtained from the EC detection with those by the X-ray computed tomography and the destructive methods. Experiments and simulations are conducted to investigate the effect of excitation frequency on intensity of the eddy current signal. The effects of residual heat of an additively manufactured specimen and lift-off distance of an EC probe on impedance changes are also investigated. In addition, the effect of defect width on EC signal is analyzed. The study shows that the EC method is capable of detecting subsurface defects in the ASHM parts. It is promising to integrate the EC detection and subtractive manufacturing into additive manufacturing to produce parts with improved quality and better performances.
Surface topography is a key element between process parameters and manufactured part performances. Within the context of 3D printed parts, one difficulty is to consider the total 3D surface topography including internal porosity. In this paper, an original method is proposed for the characterization of the surface topography, both internal and external. Starting from volumetric data obtained by Computed Tomography measurements, a method of surface extraction is performed that identifies skin voxels corresponding to the internal and external part surface, and which are the support to the calculation of the Specific Surface Area (SSA). A multi-scale analysis is thus proposed to characterize the total surface, (SSA), obtained at different scales. The interest of the multi-scale analysis is illustrated through various examples that attempt to link process parameters to part properties.
Several cylindrical specimens and dental implants, presenting diagonal lattice structures with different cell sizes (600, 900 and 1200 μm) were additively manufactured by selective laser melting process. Then they were implanted for two months in a sheep. After removal, they were studied by Archimedes’ method as well as X-ray computed tomography in order to assess the penetration of bone into the lattice. We observed that the additive manufactured parts were geometrically conformed to the theoretical specifications. However, several particles were left adhering to the surface of the lattice, thereby partly or entirely obstructing the cells. Nevertheless, bone penetration was clearly visible. We conclude that the 900 μm lattice cell size is more favourable to bone penetration than the 1200 μm lattice cell size, as the bone penetration is 84% for 900 μm against 54% for 1200 μm cell structures. The lower bone penetration value for the 1200 μm lattice cell could possibly be attributed to the short residence time in the sheep. Our results lead to the conclusion that lattice implants additively manufactured by selective laser melting enable better bone integration.
Laser powder bed fusion offers many advantages over conventional manufacturing methods, such as the integration of multiple parts which can result in significant weight-savings. The increased design freedom that layer-wise manufacture allows has also been seen to enhance component performance at little or no added cost. However, for such benefits to be realised, the material quality must first be assured. Laser ultrasonic testing is a non-contact inspection technique which has been proposed as suitable for in-situ monitoring of metal additive manufacturing processes. This paper explores the current capability of this technique to detect manufactured, sub-surface defects in Ti-6Al-4V samples, ex-situ. The results are compared with x-ray computed tomography reconstructions and focus variation microscopy. Whilst laser ultrasound has been used to identify material discontinuities, further work is required before this technique could be implemented in-situ.
The powder bed fusion additive manufacturing process enables fabrication of metal parts with complex geometry and elaborate internal features, the simplification of the assembly process, and the reduction of development time; however, its tremendous potential for widespread application in industry is hampered by the lack of consistent quality. This limits its ability as a viable manufacturing process particularly in the aerospace and medical industries where high quality and repeatability are critical. A variety of defects, which may be initiated during powder bed fusion additive manufacturing, compromise the repeatability, precision, and resulting mechanical properties of the final part. One approach that has been more recently proposed to try to control the process by detecting, avoiding, and/or eliminating defects is online monitoring. In order to support the design and implementation of effective monitoring and control strategies, this paper identifies, analyzes, and classifies the common defects and their contributing parameters reported in the literature, and defines the relationship between the two. Next, both defects and contributing parameters are categorized under an umbrella of manufacturing features for monitoring and control purposes. The quintuple set of manufacturing features presented here is meant to be employed for online monitoring and control in order to ultimately achieve a defect-free part. This categorization is established based on three criteria: (1) covering all the defects generated during the process, (2) including the essential contributing parameters for the majority of defects, and (3) the defects need to be detectable by existing monitoring approaches as well as controllable through standard process parameters. Finally, the monitoring of signatures instead of actual defects is presented as an alternative approach to controlling the process “indirectly.”
In recent years, x-ray computed tomography has been successfully applied as an innovative coordinate measurement technology for dimensional metrology. An important characteristic to be evaluated when testing the metrological performances of computed tomography systems is the metrological structural resolution for dimensional measurements, which describes the size of the smallest structure that can still be measured within error limits to be specified. The 'two-spheres' concept allows for the investigation of the metrological structural resolution by using a simple reference standard consisting of two touching spheres with the same nominal diameter. This work is aimed at defining and validating an enhanced method based on the 'two-spheres' concept and on a new measurement strategy. Advantages in using this method are discussed and a selection of the factors influencing the results are evaluated through experimental and simulation analyses.
The high level of surface roughness of additively manufactured (AM) parts post challenges to the applicability of different dimensional measurement techniques, including tactile, optical and XCT. Tactile measurement is traditionally considered to have the best accuracy and traceability. However, tactile measurement can be significantly affected by the mechanical filtering effect. This work sets out to investigate the influence of the mechanical filtering effect of tactile measurement on AM parts. Both experiential and simulation work are unitised to reveal this effect. Particularly the numerical simulation based on the morphological method allows the single influence factor, i.e., the tip diameter to be investigated. The maximum measurement errors caused by the stylus tip mechanical effect are determined by the convex hull points of the measurement profile, which is equivalent to using an infinitely large stylus tip. The CMM and XCT results of measuring the AM cylinder diameters are compared, along with the application of morphological method to "compensate" the mechanical filtering effect of the stylus tip. Additive manufacturing, dimensional metrology, surface roughness, morphological method.