Fraunhofer Institute for Machine Tools and Forming Technology IWU
Recent publications
Micro-milling is essential for manufacturing miniature precision components. The process involves free/restricted tool overhang length, runout, deflection, force and stability. In comparison to a macro-milling process, it is very difficult to determine the micro-milling force and stability in such a small machining scale due to higher spindle speeds, runout and deflection of the tool point. In this paper, we have proposed a complete and practical model for micro-milling process, which includes dynamic tool deflection and establishment of a stability lobe diagram (SLD) with runout-dependent effect. First, a multi-sections discretization method combined with dynamic tests was employed to the tool holder and tool dummy so that the frequency response function (FRF) at tool point was identified. Two runout models were introduced with the corresponding parameters, and the instantaneous uncut chip thickness (IUCT) was obtained by numerical solution. Then the dynamic tool deflection was developed by the product of force decomposition and FRF at tool point. Finally, the interaction between feed per tooth, runout and dynamic tool deflection was studied, which led to the proposed SLD. The experiments demonstrated that tool deflection as well as runout affected the IUCT, and runout enabled the cutter pitch angle acting on the workpiece to change, which enhanced stability limits despite reducing machining accuracy. In addition, the increase of feed per tooth also contributed to the improvement of stability boundary.
Decreasing batch sizes lead to an increasing demand for flexible automation systems in manufacturing industries. Robot cells are one solution for automating manufacturing tasks more flexibly. Besides the ongoing unifications in the hardware components, the controllers are still programmed application specifically and non-uniform. Only specialized experts can reconfigure and reprogram the controllers when process changes occur. To provide a more flexible control, this paper presents a new method for programming flexible skill-based controls for robot cells. In comparison to the common programming in logic controllers, operators independently adapt and expand the automated process sequence without modifying the controller code. For a high flexibility, the paper summarizes the software requirements in terms of an extensibility, flexible usability, configurability, and reusability of the control. Therefore, the skill-based control introduces a modularization of the assets in the control and parameterizable skills as abstract template class methodically. An orchestration system is used to call the skills with the corresponding parameter set and combine them into automated process sequences. A mobile flexible robot cell is used for the validation of the skill-based control architecture. Finally, the main benefits and limitations of the concept are discussed and future challenges of flexible skill-based controls for robot cells are provided.
Due to the symmetrical flank configuration, herringbone gears have no resulting axial forces and a smaller tooth width than helical gears. Because of existing manufacturing limitations, currently only double helical gears with wide center space or assembled herringbone gears are applied. In the present work, a novel machining method for herringbone gears by power skiving is presented. For this purpose, tool and technology are designed using a mathematical process model and tested subsequently. It is shown that the process can produce the required geometry with significant improvements on productivity and accuracy. Additionally, the unused center area can be eliminated.
Process cooling is crucial to many manufacturing processes. To monitor the performance of a cooling tower, it was equipped with extensive sensors for internal and environmental data acquisition. The aim is to improve reactive and predictive maintenance by estimating the actual condition as well as predicting defective behavior of the cooling tower. We designed a method, which derives the degree of defect from data of the non-defective cooling tower. A concept drift detection approach was implemented, which monitors the model estimation error of a multilayer perceptron model. Increasing model estimation error indicates changing system behavior and increasing risk of failure.
Metals represent about the 60-70% of vehicles weight. At the End of Life, after the disassembly of dangerous and some re-usable and recyclable parts, metals are scrapped and melted, with significant energy consumption. Innovative cold-reforming and joining technologies, coupled with systems to retrieve material information, can allow a second life before melting through remanufacturing. This would open the way to new circular business models in automotive providing added-value to customers as well as new market opportunities for OEMs. This paper investigates the potential of these approaches, as the results of the European H2020 “CarE-Service” project.
Recent advances in the manufacturing industry have enabled the deployment of Cyber-Physical Systems (CPS) at scale. By utilizing advanced analytics, data from production can be analyzed and used to monitor and improve the process and product quality. Many frameworks for implementing CPS have been developed to structure the relationship between the digital and the physical worlds. However, there is no systematic review of the existing frameworks related to quality management in manufacturing CPS. Thus, our study aims at determining and comparing the existing frameworks. The systematic review yielded 38 frameworks analyzed regarding their characteristics, use of data science and Machine Learning (ML), and shortcomings and open research issues. The identified issues mainly relate to limitations in cross-industry/cross-process applicability, the use of ML, big data handling, and data security.
Laser-based powder bed fusion as an additive manufacturing process allows the integration of sensors at any location within the manufactured part. This allows for manufacturing smart parts that can be integrated into complex structures for monitoring applications, as they can perform in-situ measurements. Especially, monitoring of force and torque is gaining increasing interest. However, a proper strain transmission from the mechanically loaded part to the embedded strain sensing element must be ensured, as the performance of such sensors is strongly dependent on it. In this work, we present an approach for additively manufactured deformation elements in a disruptive manner with integrated strain gauges using a steel plate as measuring element carrier. In order to evaluate the strain transmission, and, thus, the performance of the additively manufactured deformation elements, we compare them to a conventionally manufactured deformation element with identical geometry. The strain gauges are applied after manufacturing at locations with a proper strain, which are determined by a finite element analysis. Loading these additively and conventionally manufactured prototypes with 15 N results in only 0.1 % linearity and 0.2 % hysteresis error. Furthermore, a nearly linear temperature behavior of manufactured prototypes with a TK <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> of up to 0.3 %/10 K and a TK <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> of up to 0.6 %/10 K is achieved. These results confirm that a proper strain transmission is ensured within the additively manufactured deformation elements, making them competitive with conventionally manufactured deformation elements. Thus, the disruptive manufacturing process introduced is suitable for fabricating structural integrated force sensors based on strain gauges.
Modeling forms the basis for optimal control of complex technical processes in the context of industry 4.0 development and, hence, for high product quality as well as efficient production. For the mechanical joining process of self-pierce riveting with 11 input and 5 output variables, two modeling approaches based on (1) experimental data and (2) FEM computer simulation are outlined and performed. A physical modeling approach is ruled out due to the high problem dimensionality and complex nonlinear dynamic relationships between input and output variables. Alternatively, data-based approaches lead to Artificial Intelligence (AI) model designs. The experimental approach is cost- and resource-consuming; therefore, only a relatively small data set can be collected. Here, we present results from experimental trials that serve as representatives and are generalized by a description with high-dimensional parametric membership functions (fuzzification). The fuzzification procedure is also applied to the FEM computer simulation results. In principle, it can provide an arbitrarily large database. However, consequently, time- and computational effort increase considerably. Both data sets form the basis for parallel model building using the AI method of local fuzzy pattern models, which can be used to describe highly nonlinear input-output relationships by error-minimizing partitioning. Finally, the comparison of the results of the two modeling approaches is outlined. Finally, a coupled modeling strategy and future model adaptation are proposed.
In safety-critical human-machine interaction the allocation of users’ attention and the communication of key system information is crucial. Haptic feedback is a promising addition to visual and audio feedback as the latter communication channels are often heavily used in human-machine interaction. Mid-air haptic (MAH) feedback systems have shown to increase immersion, improve the usability of gesture-based interactions and thus might be beneficial for communicating system information in safety-critical environments. Ultrasound feedback systems are at the focus of current research as they deliver high resolution and instantaneous feedback. They come with two major drawbacks: limited interaction space and weak feedback intensity. Although having a lower resolution, feedback systems providing MAH feedback via air vortex rings promise to be better suited for interaction scenarios that require adaptive interaction spaces and high feedback intensities. In this paper, we explore air vortex rings as an alternative to ultrasound-based MAH feedback systems for communicating critical information. We present a vortex generator design that provides a wide interaction space and enables more complex feedback design. We evaluated MAH feedback within a user study (N = 21) using an integrated dual-task design within take-over requests in autonomous driving scenarios. Reaction time was measured to quantify objective performance. Participants further rated the subjective perceivability of the haptic feedback. We observed similar objective performance of vortex rings compared to ultrasound, visual and audio feedback. Qualitative data shows mixed results: feedback via vortex rings felt more intrusive and in part unpleasant to participants but was perceived to have a higher intensity. An expert workshop was conducted to gain insights on feedback design for vortex ring systems and to identify further application areas and research goals.
For applications of the chemical, gas and oil industry duplex stainless steels are mostly used due to good corrosion resistance and mechanical properties. These performances are archived by a microstructure of ferrite and at least of 30 % austenite. To ensure the properties, the energy per unit length EL of the welding process must be suitable adjusted for duplex stainless steels. In this context, one-layer laser beam-submerged arc hybrid welding processes were developed for butt joints of duplex stainless steel S31803 (t = 16 mm). In this study, the metallurgical and mechanical properties of weld seams are investigated by metallographic analysis, tensile test and Charpy impact test depending on EL. All weld seams meet the requirement of at least of 30 % austenite, but the weld seams achieve the highest impact energy of 131 kJ by using a lower EL of 1740 kJ/min. This is caused by finer microstructure.
For continuous radial immersion milling operations, the dominant mode shape becomes difficult to determine when stiffness of the tool and workpiece are comparable, and this can pose a great challenge for ensuring machining processes stability. In this paper, we propose a rapid method to obtain time-varying modal parameters of the workpiece by combining experimental measurements with the receptance coupling method. Firstly, the contact parameters between the workpiece and vise were identified by a so-called dynamic coupling matrix. Then the mode shapes and the time-varying natural frequency of the workpiece were determined using the modal parameters of workpiece. Finally, the stability lobe diagrams (SLDs) were computed using the modal parameters and then were validated by undertaking immersion milling experiments. The experiments showed a more conservative and practical SLD for general workpiece under continuous radial immersion, where the workpiece mode had not always dominated the machining process. Based on the proposed method, we also explored two modifications in form of additional cylinder masses and passive support, to suppress chatter. Both modifications were effective in enhancing the minimum boundary of the conservative SLD, and the modification of passive support worked better. Although the modification of the workpiece could improve the stability boundary, it indirectly affected the dynamics of the milling tool through the interaction area between the workpiece and milling tool.
In machining, tool wear is one of the main influence factors for the resulting quality of the product. Several wear mechanisms have to be addressed to prevent unwanted deterioration of the tool integrity. For aluminium alloys, adhesion of the workpiece material on the cutting tool is one of the most challenging wear mechanisms. Engineering surface microtopographies has been proved as a convenient strategy to tackle this issue. Particularly, the direct laser interference patterning (DLIP) technique enables the integration of periodic structures on the micrometer or sub-micrometer scale. In this study the structuring of tungsten carbide with different cobalt content is presented. The interference of two laser beams leads to periodic line-like structures with a spatial period of 5.5 µm. A maximum structure depth of 2.2 µm is reached by controlling the processing parameters. Moreover, the wettability of the structured samples was analyzed by contact angle measurements with selected cooling lubricants, revealing a hydrophilic behavior with a decreased contact angle of 10°. This work gives an insight into the possibilities of structuring tungsten carbide materials with a picosecond laser source in combination with an innovative beam shaping setup from the point of view of an analysis to explore the formation of structured surfaces and their wetting behavior with cooling lubricants.
Motivated by a routing problem faced by banks to enhance their encashment services in the city of Perm, Russia, we solve versions of the traveling salesman problem (TSP) with clustering. To minimize the risk of theft, suppliers seek to operate multiple vehicles and determine an efficient routing; and, a single vehicle serves a set of locations that forms a cluster. This need to form independent clusters—served by distinct vehicles—allows the use of the so-called cluster-first route-second approach. We are especially interested in the use of heuristics that are easily implementable and understandable by practitioners and require only the use of open-source solvers. To this end, we provide a short survey of 13 such heuristics for solving the TSP, five for clustering the set of locations, and three to determine an optimal number of clusters—all using data from Perm. To demonstrate the practicality and efficiency of the heuristics, we further compare our heuristic solutions against the optimal tours. We then provide statistical guarantees on the quality of our solution. All of our anonymized code is publicly available allowing extensions by practitioners, and serves as a decision-analytic framework for both clustering data and solving a TSP.
In acetabular dysplasia, the cartilaginous roof on the acetabular side does not fully cover the femoral head, which may lead to abnormal stress distribution in both the femoral head and pelvis. These stress changes may have implications to the adjacent sacroiliac joint (SIJ). The SIJ has a minimal range of motion and is closely coupled to the adjacent spine and pelvis. In consequence, the SIJ may react sensitively to changes in stress distribution at the acetabulum, with hypermobility-induced pain. The purpose of this study was to investigate the stress distribution of the SIJ in acetabular dysplasia, and to gain insight into the cause and mechanisms of hypermobility-induced pain at the SIJ. Finite element models of pre- and postoperative pelves of four patients with acetabular dysplasia were created and analyzed in double leg standing positions. The preoperative models were relatively inflare, the sacral nutation movement, SIJ cartilage equivalent stress, and the load on the surrounding ligaments decreased with increased posterior acetabular coverage. Acetabular morphology was shown to affect the SIJ, and improvement of the posterior acetabular coverage may help normalize load transmission of the pelvis and thus improve the stress environment of the SIJ in acetabular dysplasia.
Climate change, critical material shortages and environmental degradation pose an existential threat to the entire world. Immediate action is needed to transform the global economy towards a more circular economy with less intensive use of fossil energy and limited resources and more use of recyclable materials. Recyclable materials and manufacturing techniques will play a critical role in this transformation. Substantial advancements will be needed to achieve a more intelligent materials design to enhance both functionality and enhanced sustainability. The development of hybrid materials combining functionality at macro and nano scales based on organic and inorganic compounds, that are entirely recyclable could be used for tremendous applications. In this mini-review, we provide the reader with recent innovations on hybrid materials for application in water, energy and raw materials sectors. The topic is very modern and after its deep study we propose a creation an international research centre, that would combine the development of hybrid materials with green manufacturing. We have highlighted a framework that would comprise critical themes of the initial research needed. Such a centre would promote sustainable production of materials through intelligent hybridisation and eco-efficient, digital manufacturing and enable a circular economy in the long term. Such activities are strongly supported by current environmental and economical initiatives, like the Green Deal, REPower EU and digital EU initiatives.
Despite all progresses made so far, in‐stent restenosis (ISR) is still a vital problem during angioplasty and stenting with permanent stents. Therefore, the effects of micro‐blasting on laser power bed fusion (LPBF) manufactured biodegradable Fe‐based stents with regard to surface topography and its effect on smooth muscle cell (SMC) adherence, which could be interpreted as an early hallmark for ISR, are characterized. The LPBF‐processed Fe‐30Mn‐1C‐0.025S stents are micro‐blasted with spherical glass beads and angular corundum particles. On the micro scale, the partially molten particles on the stents are significantly reduced after the surface treatments, especially after micro‐blasting with glass beads. Angular corundum particles lead to a rougher surface on the nanoscale as demonstrated by SEM and AFM analysis. With the aim to reduce migration and proliferation of SMC, which contribute to ISR after stenting, the interactions of micro‐blasted stent surfaces with SMC are assessed by fluorescence microscopy. Both micro‐blasted surfaces reduce SMC adhesion and change SMC morphology compared to the as‐built state as well as to commercially available 316L stents. In conclusion, micro‐blasting treatment shows a high potential for the post‐processing of additively manufactured, biodegradable stents due to the reduction of the surface roughness and possible beneficial effect regarding ISR. This article is protected by copyright. All rights reserved.
Replicating the mechanical behavior of human bones, especially cancellous bone tissue, is challenging. Typically, conventional bone models primarily consist of polyurethane foam surrounded by a solid shell. Although nearly isotropic foam components have mechanical properties similar to cancellous bone, they do not represent the anisotropy and inhomogeneity of bone architecture. To consider the architecture of bone, models were developed whose core was additively manufactured based on CT data. This core was subsequently coated with glass fiber composite. Specimens consisting of a gyroid-structure were fabricated using fused filament fabrication (FFF) techniques from different materials and various filler levels. Subsequent compression tests showed good accordance between the mechanical behavior of the printed specimens and human bone. The unidirectional fiberglass composite showed higher strength and stiffness than human cortical bone in 3-point bending tests, with comparable material behaviors being observed. During biomechanical investigation of the entire assembly, femoral prosthetic stems were inserted into both artificial and human bones under controlled conditions, while recording occurring forces and strains. All of the artificial prototypes, made of different materials, showed analogous behavior to human bone. In conclusion, it was shown that low-cost FFF technique can be used to generate valid bone models and selectively modify their properties by changing the infill.
The alteration in mechanical properties of posterior pelvis ligaments may cause a biased pelvis deformation which, in turn, may contribute to hip and spine instability and malfunction. Here, the effect of different mechanical properties of ligaments on lumbopelvic deformation is analyzed via the finite element method. First, the improved finite element model was validated using experimental data from previous studies and then used to calculate the sensitivity of lumbopelvic deformation to changes in ligament mechanical properties, load magnitude, and unilateral ligament resection. The deformation of the lumbopelvic complex relative to a given load was predominant in the medial plane. The effect of unilateral resection on deformation appeared to be counterintuitive, suggesting that ligaments have the ability to redistribute load and that they play an important role in the mechanics of the lumbopelvic complex. Alterations in sacrospinous and sacrotuberous ligament stiffness have substantial influence on pelvis kinematics. This influence appears nonlinear. There seems to exist a certain prestrain on both ligaments. Transection of the ligaments is related to alterations in particular at the lumbosacral transition and within the innominate bone.
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224 members
Thomas Mäder
  • Functional Integration and Systems Integration
Markus Bergmann
  • Business Unit Forming Technology
Mohamad Bdiwi
  • Cognitive Human Machine Systems
Welf-Guntram Drossel
  • Dresden Branch of the Institute
Sebastian Hensel
  • Business Unit Car Bodies and Cell Structures
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Prof. Dr.-Ing. Welf-Guntram Drossel
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