Article

Effect of printing strategies on forming accuracy and mechanical properties of ZrO2 parts fabricated by SLA technology

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Abstract

Stereolithography (SLA) is a commonly used ceramic 3D printing technology which is capable of accurate and industrial production. Based on this technology, ZrO2 ceramics were prepared using different laser power in the presented work. The forming capability of laser on the printed sample at three-dimensional directions was investigated by combining the Gauss beam and Beer-Lambert model. Besides, the dimension variety and shrinkage after printing, debinding, and sintering were studied, and the scaling factors were further determined. The dimension shrinkage of the stratified surface outnumbers that of the laser scanned surface. Therefore, the printing direction has a significant influence on the dimensional accuracy. The weight, density, and porosity of the designed ceramics using different laser power were analyzed as well. It was found that the weight of parts after the debinding process can be reduced by 97.6% of the total deduction of the weight, while the density of parts in sintering process was increased by 86.9% of the total increase of the density. It should be highlighted that the ZrO2 ceramic gears and integrated bearing with the relative density of 97%, hardness of 13.1 GPa, fracture toughness of 5.62 MPa·m1/2, and flexural strength of 1044 MPa, were obtained using the optimum laser power of 360 mW.

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... In this context, several works (not only using LCM) focused their objective in the influence of the printing parameters on the final features of the 3D printed pieces [4][5][6][7][8]. However, in the last years, the interest for the development of photosensitive ceramic slurries is growing [9][10][11][12][13][14][15][16], and the comparison between different methodologies to prepare them is receiving high attention [17]. ...
... ZrO 2 [14,18,19] and Al 2 O 3 -ZrO 2 [20] materials are two of the ceramics widely used to optimise the 3D printing procedure and the subsequent thermal treatment because of their high interest in the medical/prosthetic field [21]. For such applications, to know the limitations depending on the orientation of the part is mandatory due to the different movements or forces that the ceramic part should resist without neither deterioration nor breaking down. ...
Article
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Lithography based Ceramics Manufacturing (LCM), i.e., Digital Light Processing (DLP) is one of the Additive Manufacturing (AM) techniques that is being widely used for the production of ceramic parts. Additionally, the development of photocurable slurries and the influence of the printing parameters on the fabricated parts properties are also receiving high attention. In this work, ZrO2 and ATZ materials were used as a case of study to evaluate the flexural strength of the fabricated parts, using our own developed UV-curable slurries. The influence of the tensile edges shape of the bars, tilting speeds, layer thickness and printing direction were evaluated, obtaining the highest flexural strength values for the 200 μm round shape bars, faster tilting speeds, 25 μm layer thickness and printing in the Z direction for ZrO2 and in the Y for ATZ.
... 35,36 Previous studies also dealt with the role of process parameters related to resin shrinkage and, as a consequence, on the dimensional accuracy of parts. 37,38 The layer height 39 and build orientations [40][41][42] are demonstrated to be key factors to determine the accuracy of printed parts. ...
... In particular, the combined effects of the layer thickness and build orientations are not completely documented. This kind of study has not been applied to the characterisation of embedded microchannels and build orientations, [38][39][40][41][42] for which dimensional accuracy of transversal sections plays a key role. Therefore, the present work analyses the combined effects of nominal dimensions, the layer height and build orientations on the manufacturability and accuracy of MFDs produced by SL. ...
Article
Lab-on-a-Chips integrate a variety of laboratory functions and embed microchannels for small fluid volume handling. These devices are used in medicine, chemistry, and biotechnology applications but a large diffusion is limited due to the manufacturing cost of traditional processes. Additive Manufacturing offers affordable alternatives for the production of microfluidic devices, because the fabrication of embedded micrometric channels is enabled. Stereolithography gained particular attention due to the low cost of both available machines and suitable polymeric materials to be processed. The main restriction to the adoption of this technique comes from the obtainable dimensional accuracy that depends not only on design, but also on process set-up. Firstly, the paper analyses theoretically the physics of stereolithographic processes and focuses on main phenomena related to microchannel manufacturing. Then, specific experimental activities are designed to investigate the combined effect of design and process parameters on the achievable dimensional accuracy of embedded microchannels manufactured through a commercial desktop stereolithography apparatus. In particular, the combined effect of channel nominal dimensions, build orientations and the layer thickness on the obtainable accuracy is examined by referring to a benchmark geometry. The collated experimental data showed that a number of combinations are successful. Besides, the experimental activity revealed that appropriate combinations of design, build orientation and manufacturing parameters can overcome the dimensional limitations reported in previous studies. Both binary logistic regression models to predict the manufacturability of microchannels and linear regression models to estimate the achievable accuracy for those geometries that can be produced successfully are developed.
... Thereafter, a debinding procedure was performed to remove the organic constituent [15]. The process involved gradual heating from 20 • C to 200 • C at a rate of 0.2 • C/min and holding for 2 h, gradual heating from 200 • C to 300 • C at a rate of 0.1 • C/min and holding for 2 h, gradual heating from 300 • C to 550 • C at a rate of 0.2 • C/min and holding for 2 h, and finally, gradual heating from 550 • C to 1150 • C at a rate of 2 • C/min and holding for 1 h [19]. After debinding, sintering was performed by gradual heating from 25 • C to 1150 • C at a rate of 3 • C/min and then from 1150 • C to 1450 • C at a rate of 2 • C/min. ...
... After debinding, sintering was performed by gradual heating from 25 • C to 1150 • C at a rate of 3 • C/min and then from 1150 • C to 1450 • C at a rate of 2 • C/min. The specimens were held at the sintering temperature (1450 • C) for 2 h and then cooled to room temperature at a rate of 3 • C/min [19]. According to the manufacturers, the shrinkage of SM and SLA ceramics is approximately 20% and 23%, respectively. ...
Article
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The present study comprehensively compared the microstructure, flexural strength, and fracture toughness of zirconia ceramics prepared via two different methods, subtractive milling (SM) and stereolithography (SLA). Disc- or rectangular-shaped zirconia specimens (Prettau (SM) and 3DMix Zirconia (SLA)) were prepared following each manufacturer’s instructions and polished. The microstructures of the two different zirconia specimens were studied by scanning electron microscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, and electron backscattered diffractometry. The flexural strength and fracture toughness based on the indentation fracture method were measured for the two different zirconia ceramics. A greater number of small pores and smaller grains were found in the SLA specimen than in the SM specimen. The crystal structure and microstructure analysis revealed that both ceramics had a similar phase composition to each other. No significant differences in flexural strength (p = 0.242) or fracture toughness (p = 0.101) were detected between the two ceramics. The mean flexural strength of the SLA-fabricated zirconia as well as the SM zirconia satisfied the class 5 criteria (>800 MPa) in the ISO 6872 standard.
... When the laser power was adjusted from 0.3 to 0.45 W and the laser scanning speed was also increased to 750 mm·s -1 , the flexural strength of ceramics was improved from 622 to 978 MPa, and the density has been at a high level (98.3%-98.7%). Fu et al. [84] further studied the changes in density and performance of ceramic parts obtained by different laser powers. Within a certain range, the combination between adjacent layers is linearly related to the laser power. ...
... (a) Changes in density of ceramic parts after printing and sintering, and (b) relative density and porosity of sintered parts as a function of laser power (reproduced with permission from Ref.[84], © Elsevier Ltd and Techna Group S.r.l. 2019). ...
Article
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Three-dimensional (3D) printing technology is becoming a promising method for fabricating highly complex ceramics owing to the arbitrary design and the infinite combination of materials. Insufficient density is one of the main problems with 3D printed ceramics, but concentrated descriptions of making dense ceramics are scarce. This review specifically introduces the principles of the four 3D printing technologies and focuses on the parameters of each technology that affect the densification of 3D printed ceramics, such as the performance of raw materials and the interaction between energy and materials. The technical challenges and suggestions about how to achieve higher ceramic density are presented subsequently. The goal of the presented work is to comprehend the roles of critical parameters in the subsequent 3D printing process to prepare dense ceramics that can meet the practical applications.
... Diverse techniques contribute to thriving ceramic additive manufacturing. These include material jetting (MJ) process, subdivided into the direct inkjet printing (DIP) method [13,14] and the hybrid drop-on-demand material jetting (DODMJ) system [15]; direct ink writing (DIW) process, categorized as the ceramic on-demand extrusion (CODE) technique [16,17], the 3D gel-printing (3DGP) method [18,19], and the novel extrusion-based AM process [20]; digital light processing (DLP) technology [21][22][23][24][25][26][27]; stereolithography (SLA) [28][29][30][31]; selective laser melting (SLM) [32]; selective laser sintering (SLS) [33]; laser engineered net shaping (LENS) [34,35]; fused deposition modeling (FDM) [36,37]; and binder jetting (BJ) [38]. ...
... As tabulated in Table 1, the flexural strength of the NPJ-produced part was unfavorable compared with that of parts fabricated by other technologies. SLA [29,31] and SLM [32] resulted in flexural strengths that are noticeably advanced, and DIP [14], DLP [23,24], and FDM [36,37] resulted in flexural strengths that are slightly higher. As the flexural strength of 3D printed ZrO 2 ceramics is strongly dependent on the defects, it can be inferred that there were defects within the NPJ-fabricated zirconia sample affecting the flexural strength. ...
Article
Additive manufacturing has received tremendous attention in the manufacturing and materials industry in the past three decades. Zirconia-based advanced ceramics have been the subject of substantial interest related to structural and functional ceramics. NanoParticle Jetting (NPJ), a novel material jetting process for selectively depositing nanoparticles, is capable of fabricating dense zirconia components with a highly-detailed surface, precisely controllable shrinkage, and remarkable mechanical properties. The use of NPJ greatly improves the printing process and increases printing accuracy. An investigation into the performance of NPJ-printed ceramic components evaluated the physical and mechanical properties and microstructure. The experimental results suggested that the NPJ-fabricated ZrO2 cuboids exhibited a high relative density of 99.5%, a glossy surface with minimum roughness of 0.33 μm, a general linear shrinkage factor of 17.47%, acceptable hardness of 12.43 ± 0.09 GPa, outstanding fracture toughness of 7.52 ± 0.34 MPa m1/2, comparable flexural strength of 699 ± 104 MPa, dense grain distribution of the microstructure, and representative features of the fracture. Subsequently, the exclusive printing scheme that achieved these favorable properties was analyzed. The innovative NanoParticle Jetting™ system was shown to have outstanding potential for additive manufacturing.
... The design of tooth profiles is no longer limited to the involute profiles generated by gear hobbing or shaping. Furthermore, different kinds of materials can be used for the additive manufacturing of gears with different kinds of metallic and non-metallic materials, such as polymers, ceramics, metals, nanocomposite materials, etc. [27][28][29][30]. With the improvement of precision and productivity, 3D printing will become the preferred method for the manufacture of special-shaped non-generated gears. ...
... The tooth surfaces of the pinion and gear are formed by the spiral motion of their transverse tooth profiles along their contact curves. The mentioned spiral motion should be coordinated with the law of motion expressed in Equation (1) , are given by Equation (28). The subscripts 1 and 2 represent S 1 of the pinion and S 2 of the gear, respectively. ...
Article
Full-text available
Helical gears are widely used in powertrain systems. The computerized design of a new type of non-generated external helical gears based on critical control points at the transverse tooth profile is presented. The entire tooth profile is divided into different parts including the active tooth profile and fillet by control points. Involutes, circular arcs and Hermite curves are defined between two critical control points and smoothly connected with each other at those control points. The parametric equations for the tooth surfaces are derived considering the position of the mentioned control points. The basic design parameters and equations of the geometric sizing are proposed. The contact patterns, variation of the maximum stresses and peak-to-peak level of loaded transmission errors for six cases of design of the proposed new geometry of helical gear drives are studied with two cases of traditional helical gear drives as a reference, including gears with and without microgeometry modifications. One case of an external helical gear drive designed with a combination of a circular arc and an involute to form the active tooth profile for both the pinion and the gear shows a much lower maximum bending stress and similar lower peak-to-peak level of loaded transmission errors with respect to the other cases of design. The proposed design method of tooth profiles based on critical control points lays the foundation for the topological optimization of helical gear drives.
... Generally, the studies on accuracy include bulk structures, walls, or gaps. Fu et al. [18] studied the influence of the laser power on the dimensional accuracy of SLA of bulk products, concluding that the length and width increased with the increase of the laser power due to the increase of the light scattering [18]. A study of printability and lateral accuracy of holes and walls with lithography-based AM showed holes down to 200 μm could be fabricated, but those smaller than 500 μm would have a large deviation from the CAD design [19]. ...
... Generally, the studies on accuracy include bulk structures, walls, or gaps. Fu et al. [18] studied the influence of the laser power on the dimensional accuracy of SLA of bulk products, concluding that the length and width increased with the increase of the laser power due to the increase of the light scattering [18]. A study of printability and lateral accuracy of holes and walls with lithography-based AM showed holes down to 200 μm could be fabricated, but those smaller than 500 μm would have a large deviation from the CAD design [19]. ...
Article
Digital Light Processing (DLP) technology demonstrates the potential for manufacturing parts with complex structures for various engineering applications. The purpose of this study is to evaluate Al2O3 ceramic slurry preparation techniques, establish optimal processing window and assess the manufacturability and dimensional accuracy of lattice structures with CAD strut diameters of up to 500 µm. Two preparation techniques of the ceramic slurry were investigated. The slurry with the pre-treated powder showed appropriate rheological and photopolymerization behaviour. Full factorial Design of Experiments (DOE) was conducted to generate an experimental plan and assess the influence of the printing parameters on the dimensional accuracy. Analysis of Variance (ANOVA) revealed the exposure time, the exposure power, and the interaction effect of both had a significant influence on the dimensional accuracy of lattice strut diameters. The excess cure width was found to be dependent on the feature size, the energy dose and the layer thickness.
... Recently, ceramic materials can be widely used in various fields such as ceramic cutting tools, biomedical implants because of their good chemical and physical properties [1,2]. Stereolithography 3D printing technology has been widely used in the preparation of complex alumina (Al 2 O 3 ), Zirconia (ZrO 2 ) and hydroxyapatite (HAP) ceramic parts because of its rapid prototyping [3][4][5][6][7]. Zhou et al. [8] prepared a defect-free alumina ceramic cutting tool with Vickers hardness of 17.5 GPa and relative density of 99.3% via stereolithography, liquid desiccant drying and two-step debinding process. ...
Article
In this paper, the UV curable ZrO2-Al2O3 composite ceramic pastes based on SLA-3D printing technology were synthetized firstly, and the corresponding ceramic green bodies were 3D printed, and finally the ZrO2-Al2O3 composite ceramic parts were manufactured by a subsequent debinding and sintering process. Our work focuses on the investigation of the microstructure, hardness and fracture toughness of the printed ZrO2-Al2O3 composite ceramics sintered at different maximum sintering temperature and holding time. In case of the sintering temperature of 1500 °C and holding time of 60 min, the actual density, hardness and fracture toughness of the ceramics can reach 3.75 g/cm³, 14.1 GPa and 4.05 MPa⋅m1/2, respectively. If the sintering temperature is higher than 1500 °C, the abnormal grain growth can occur, resulting in some more reductions in the mechanical properties of ceramics; while when the sintering temperature is lower than 1500 °C, the lower driving force makes the grains not fully developed, resulting in a low density of ceramics and worse mechanical properties. With the increase of holding time, the sintering driving force is promoted, making for the grain growth. However, when holding time is more than 60 min, the actual density of ceramics almost remains unchanged, and the mechanical properties of ceramics are not able to be improved further.
... The development of additive manufacturing, such as 3D printing, provides a great possibility of free design for non-generated gear tooth surfaces. The materials for additive manufacturing of gears include polymers, ceramics, metals as well as nanocomposite materials, which are all used for gear design [19][20][21][22]. The active design of the meshing line function also provides a convenient way of gear design, such as the design of pure rolling gear mechanisms for parallel-axis transmissions, intersecting-axis transmissions, and rack and pinion transmissions [23][24][25][26][27][28]. ...
Article
The computerized design of non-generated double circular-arc helical gear drives with different combinations of transverse pressure angle based on the active design of the meshing line function is presented. The application of different transverse pressure angles for the double circular-arc tooth profiles is discussed and the parametric equations for the driving and driven gear tooth surfaces are derived. The meshing performance and mechanical behavior are studied in terms of the achieved contact patterns and the evolution of the contact and bending stresses for nine cases of design. The results show that one of the cases of design of double circular-arc helical gear drives considering a combination of transverse pressure angles of 25 and 15 degrees for the convex and concave circular-arc profiles of the pinion shows better mechanical performance with respect to the other combinations of different transverse pressure angles. The proposed geometry of non-generated gears is appropriate for manufacturing by injection molding or additive manufacturing for plastic, ceramic, metal as well as nanocomposite gears.
... The as-fabricated 3Y-TZP has a relative density of 98.8%, Vickers hardness of 13.1 GPa, fracture toughness of 4.6 MPa m 1/2 , flexural strength of 616 MPa, which are much better than those fabricated by other AM processes and close to those from the conventional process. Fu et al. [172] derived the optimum laser power as 360 mW for the SLA processing of zirconia ceramic parts, and the corresponding properties are 97% relative density, 13.1 GPa hardness, 5.62 MPa m 1/2 fracture toughness and 1044 MPa flexural strength. By combining SLA method with gelcasting, the flexural strength and fracture toughness of zirconia-based allceramic teeth could reach 1170 MPa and 19.0 MPa m 1/2 [107]. ...
Article
Full-text available
In recent years, additive manufacturing (AM) has emerged as a type of efficient manufacturing technology for building ceramic prototypes with increased dimensional accuracy, improved time efficiency, and reduced cost. A wealth of research works have been conducted to uncover the underlying formation mechanism of zirconia ceramic parts manufactured by AM processes and to improve the performance of the parts. In spite of the achievements, there are still some unresolved issues, such as porosity, cracks, coffee staining, which impede the adoption of AM processes for zirconia part manufacturing. This paper aims to review the recent research efforts on zirconia ceramic manufactured using AM techniques. The existing works are mainly categorized in terms of the different AM preparation methods and the applications. More importantly, the challenges and opportunities related to AM of zirconia products are discussed. As such, this review provides not only a comprehensive survey of the existing research, but also an insightful discussion regarding the potential research in the future. Innovations are expected to be stimulated for many critical industrial applications.
... It uses a projector to selectively expose an entire cross-sectional slice from CAD software on the photosensitive resin surface at each given time, which shows faster build speeds than early stereolithography technology in which the surface of the resin is scanned by a laser beam [9]. By now, numerous researches concerning slurry preparation, optimization of processing parameters and heat treatment about the stereolithography fabrication of many kinds of oxide ceramics, such as Al 2 O 3 [10][11][12][13][14][15], ZrO 2 [16][17][18][19][20], ZTA [21][22][23], SiO 2 [24][25][26], and other ceramics with light color [27][28][29][30] have been widely reported. However, the photo-shaping method of non-oxide ceramics (often in deeper color) still faces tough challenges. ...
Article
Full-text available
Among a series of 3D printing techniques, stereolithography provides a new route to produce ceramic architectures with the advantages of high-precision and short cycle time. However, up to now the stereolithography of non-oxide ceramics still face complex and difficult problems. This work focused on the analysis of rheological and curing ability of Si3N4 photocurable slurries. The effects of monomer type, coarse silicon powder, solid loading and ambient temperature on the rheological behavior were intensively studied. The relationships between powder characteristic (involving refractive index, absorbance and the introduce of coarse silicon powder), monomer type and curing ability were discussed in detail. It is expected that this study may benefit the development of Si3N4 or other non-oxide ceramic slurries for stereolithography.
... Borlaf et al. [9] developed the ZrO 2 and ATZ materials through additive manufacturing technique and analysed their flexural strength through 4-point bending test. X. Fu et al. [10] printed the ZrO 2 ceramics parts through Stereolithography process and studied the mechanical properties. Result showed that the mechanical properties of the printed parts can be improved through optimal laser power. ...
Article
In recent years, additive manufacturing (or) 3-Dimensional (3D) printing is applied to denture materials widely. However, there is no proper technique or standard for testing the material properties such as Young’s modulus and Poisson’s ratio that are directly related to the strength of denture materials. This research focuses on the use of laser ultrasound technique, ultrasonic microscopy, and ultrasonic C-scanning imaging system to explore the material properties and acoustic parameters of human teeth and additive manufactured teeth. In addition, defect detection is performed on the additively manufactured teeth to provide the relevant information to help the dentists. Firstly, we used ultrasonic microscopy to obtain the surface wave velocity of the denture material and obtained the elastic coefficient of the material through the principle of wave propagation. Secondly, the laser ultrasound technique was performed on denture material in a non-destructive way, and the inverse calculation procedure was applied to obtain the elastic coefficient of the denture material. Finally, the elastic coefficient was obtained from the three-point bending test, and the correctness of the back-calculation results of ultrasonic microscopy and the laser ultrasound was verified. Results showed that the elastic coefficient obtained by the laser ultrasonic combined with the inverse calculation was comparable with the three-point bending test, with the error value within 5%. The comparison error between the ultrasonic microscopy and the three-point bending test was within 15%. Besides, the ultrasonic C-scanning system can detect the defects with an accuracy of less than 0.2 mm. Therefore, this research has successfully measured the material properties, acoustic parameters, and defect detection of dentures through non-destructive ultrasonic testing. It demonstrates considerable potential in dental medical measurement and can provide effective methods for the testing and manufacturing of denture materials.
... The defects observed in SLA-produced ZrO 2 ceramics were agglomerates, delaminations, cracks caused by differential shrinkage and insufficient layer bonding, pores due to air bubbles present in the slurry during printing, and post-processing induced damage [41,42,47,49,59,[67][68][69][70]. Mechanical properties and the reliability of the sintered ceramics were often anisotropic, related to weaker connections between the layers in the building direction, pores, agglomerates or due to surface defects caused by post-processing [41,42,47,69,70]. ...
Article
The possibility of additive manufacturing of ceramics has been reported widely in scientific literature. This study investigates the potential of direct inkjet printing or material jetting of 3Y-TZP ceramics by assessing the microstructure and mechanical properties of the sintered printed parts. The technique allows to print in layers of 10.5 µm, with an as-printed green density of 58% and nearly fully sintered density of 6.03 ± 0.1 g/cm³ (99.7% TD). The dimensions of the green and sintered parts were highly accurate but showed an anisotropic roughness in function of the building direction, mainly due to the support structures. The biaxial bending and 4-point bending strength of the sintered material was found to be substantially higher in the XY direction than in the building (Z) direction. SEM and X-Ray computed tomography revealed the presence of delamination cracks, agglomerates and spherical pores, which were identified as fracture origins on fractured surfaces.
... The stereolithography (SLA) is traditionally considered a promising additive manufacturing technique for polymer based on the polymerization reaction between monomer and oligomer activated by ultraviolet (UV) [1−5]. Recently, it has attracted intensive attention on additively manufacturing ceramic, including Al 2 O 3 [6,7], ZrO 2 [8], and Si 3 N 4 ceramics [9,10] due to its capability of high precision and complex geometric shapes. However, it is still a main challenge to sinter dense ceramics with comparative mechanical properties to counterparts by conventional dry pressing technique. ...
Article
Combining sintering additive with field assisted sintering, stereolithographical dense Si3N4 ceramics was successfully fabricated. Owing to a large amount of polymer during the stereolithography, the green parts have the characteristics of low powder loading and high porosity. Adjusting the process parameters such as sintering temperature and soaking time can effectively improve the density of the specimens. The stress exponent n of all specimens is in a range of 1 and 2, which is derived from a modified sintering kinetics model. The apparent activation energy Qd of stereolithographic Si3N4 ceramics sintered with applied pressures of 30 MPa, 40 MPa, and 50 MPa is 384.75, 276.61 and 193.95 kJ/mol, respectively, suggesting that the densification dynamic process is strengthened by raising applied pressure. The grain boundary slipping plays a dominating role in the densification of stereolithographic Si3N4 ceramics. The Vickers hardness and fracture toughness of stereolithographic Si3N4 ceramics are HV10/10 (1347.9±2.4) and (6.57±0.07) MPa·m1/2, respectively.
... Zirconium oxide (ZrO 2 ) is another structural ceramic with excellent mechanical property, low thermal conductivity, and good biocompatibility [35]. FU et al [36] prepared zirconia with different laser power through SLA. The research results show that the process parameters have a significant influence on the dimensional accuracy of the parts, but the improvement of mechanical properties mainly depends on the cracks and density controlling during the debinding process. ...
Article
Additive manufacturing (AM), also known as 3D-printing (3DP) technology, is an advanced manufacturing technology that has developed rapidly in the past 40 years. However, the ceramic material printing is still challenging because of the issue of cracking. Indirect 3D printing has been designed and drawn attention because of its high manufacturing speed and low cost. Indirect 3D printing separates the one-step forming process of direct 3D printing into binding and material sintering, avoiding the internal stress caused by rapid cooling, making it possible to realize the high-quality ceramic component with complex shape. This paper presents the research progress of leading indirect 3D printing technologies, including binder jetting (BJ), stereolithography (SLA), and fused deposition modeling (FDM). At present, the additive manufacturing of ceramic materials is mainly achieved through indirect 3D printing technology, and these materials include silicon nitride, hydroxyapatite functional ceramics, silicon carbide structural ceramics.
... Key words: zirconia ceramic; stereolithography; accuracy; debinding; sintering 氧化锆陶瓷具有良好的力学性能,生物相容性 以及耐腐蚀性等特点,在医疗修复领域,尤其是牙 科修复领域得到了广泛应用 [1][2][3][4] 。传统的全锆冠制造 方法主要是利用数控机床铣削氧化锆 [5] 。但是该方 法有以下缺点 [5][6] :对刀具的硬度和耐磨性要求很高, 制作成本昂贵;铣削过程中会使牙冠表面引入各种 微裂纹或缺陷,降低修复体强度;加工时浪费大量 材料。 陶瓷增材制造技术,基于离散、堆积原理,被 广泛用于定制化程度高、结构复杂的陶瓷制件 [7] 。 其中, 光固化陶瓷增材制造技术具有制作分辨率高、 制造精度高和表面质量好等特点 [7][8] ,特别适合固化 氧化锆陶瓷浆料制作义齿素坯。光固化增材制造技 术可分为扫描光固化(Stereolithography, SL)和投影 光固化(Digital light processing, DLP),其中 SL 工艺 多采用紫外激光器为光源, 其波长短, 输出能量高, 穿透陶瓷浆料的深度深,适合高固相的氧化锆陶瓷 成形。基于以上优点,国内外众多学者对氧化锆陶 瓷的 SL 工艺进行了大量研究。Zou [9][10] 等利用 SL 设备打印了体积百分比 55%固相含量的氧化锆陶瓷 膏料,其综合力学性能达到传统等静压成形工艺的 水平,但是未见其打印精度的相关报道。王文俊 [11] 等利用 SL 设备打印了氧化锆全瓷冠,但是其尺寸 稳定性和可重复性欠佳。Sun [12] ...
... For ME applications, the review paper by Mohamed et al. covers a comprehensive look at the history of research and array of parameters that influence a specimen's mechanical strength [72]. Fu et al. published a research paper on VAT printing strategies, examining forming accuracy and mechanical properties [73]. Lastly, a review of PBF of aluminum powders by Olakanmi et al. outlines pertinent research and the current state of technology for 3D printed metal parts [74]. ...
Article
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Advances in 3D printing are leading to a wealth of excitement around the topic; designers, engineers, and hobbyists alike are looking to utilize the technology to improve upon existing designs and produce new components that perform better than a traditionally manufactured part. In this respect, additively manufactured parts offer a neat solution to problems of geometric limitations, small production economics, and rapid design cycle fulfillment. Though promising in capability, the variety in 3D printing methods and the inherent limitations of each can be difficult for new users to comprehend effectively when exploring whether or not the technology may work for them. It is in the best interest of the additive manufacturing community that the technology, though rapidly developing, be well understood so that adoption is easier and more widespread. The purpose of this paper, therefore, is to present an evaluation tree specific to additive manufacturing, that will assist new users of the technology when assessing manufacturing methods for their application. The evaluation tree is focused on providing a high-level technical overview of the engineering decisions required for AM adoption, a current gap in the research. A detailed review of the dominant 3D printing types and recommendations are given for the user’s future considerations. Three case studies have additionally been provided at the end of the paper to demonstrate the use of the evaluation tree. The goal of this paper is to aid in the further adoption of 3D printing, while providing valuable general information and technical considerations for new users.
... The curing depth is defined as the depth (or thickness) of a cured layer obtained by one scan of laser beam across a thin layer of paste. Although many ceramics, such as alumina, zirconia and hydroxyapatite have been printed by SLA-based 3D printing method [30][31][32], successful SLA printing of Si 3 N 4 cellular ceramics with complex geometries is not well demonstrated yet, mainly due to the strong UV absorbance and the high refractive index (n: 2.1) of Si 3 N 4 powders which limit the curing depth of the paste [33]. It has been reported that the curing depth of the Si 3 N 4 paste with 30-45 vol% solid load is only ~20-50 μm when exposed to 0.25-1.0 ...
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Si3N4 cellular ceramics with large thickness/length ratio (up to ∼12.0) have been successfully prepared by stereolithography 3D printing with highly viscous (viscosity >10.0 Pa‧s at 30 s⁻¹ shear rate), self-holding pastes. Due to the high viscosity and low curing depth of the paste, structural defects are commonly found in the printed honeycombs or lattices and anisotropic surface roughness is present. The structural defects can be reduced by aligning the lattice orientation at 45° relative to the paste recoating direction to reduce shear stress concentration at the cured part beneath. The resultant honeycombs and simple cubic lattices with density of ∼1.5–1.6 g/cm³ exhibit compressive strength as high as 1.1 GPa and 290.7 MPa, respectively. The specific compressive strength of honeycombs increases from 298.6 to 681.7 MPa‧cm³/g with the ceramic volume fractions increase from 0.19 to 0.52, surpassing that of many other ceramic honeycombs and lattices with similar density reported so far. The controlling factors governing the defect formation, surface finish and mechanical properties of the printed cellular ceramics are discussed thoroughly.
... These actions allowed to attain a maximum RD of 95.2 % using a raw alumina powder with 5 μm mean particle size. Table 7, the VP category is the AM processing route with highest number of experiments reported in literature, with an overall number of 140 entries distributed as 79 entries for SLA [15,23,66,69,71,97,112,118,183,186,263,277,294,343,358,377,378,[386][387][388][389][390][391][392][393][394][395][396][397][398][399][400][401], 58 for DLP [46,49,62,68,70,100,102-104, 106-109,111,135,137,145,146,185,354,356,357,402,403] and 3 entries for LCM [98,228,344]. Since LCM has the basic principles of DLP, the results for the first technology are included in DLP in Table 7. ...
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The current need to develop Additive Manufacturing (AM) processes capable of producing defect-free, fully-dense functional ceramics could benefit from the knowledge consolidated throughout the years in conventional processing. This review provides an up-to-date status of AM fabrication of dense alumina, zirconia and their composites, in comparison with reference values published during 20 years of research on powder pressing and colloidal-based technologies. A systematic literature search on conventional methods and AM selected 1706 papers and, after screening, 344 papers included 1313 different experiments reporting relative density and mechanical properties (flexural strength, elastic modulus, hardness and fracture toughness) of the final ceramics. The associations between experimental processing conditions, densification and, subsequently, mechanical performance were evaluated in powder- and suspension-based technologies. The research evolution in the fabrication of these ceramics over the last two decades is also summarized, highlighting the most used AM technologies for each material and the place of functional ceramics in recent and future market perspectives. Furthermore, future insights in the fabrication of functional ceramics are identified, to guide researchers and commercial players in drawing scientific and industrial novelties for developing new business strategies, key decision-making and road mapping to make the AM market of functional ceramics a reality.
... However, it is generally recognized that the interlayer (i.e. the contact surface between two consecutive layers) and related defects in SLA and DLP technologies provide the main contribution to failure [20]. Therefore, the fracture surface of the samples submitted to bending tests were further characterized by FE-SEM, as shown in Figure 13 for The same images show a different roughness of the printed surface, which can be responsible of the difference in mechanical properties, too, as suggested by Fu et al. [28]. For the XZ samples, the surface under tension is very smooth because it was in contact with either the building platform or the printing plane and thus it could be considered almost defect free. ...
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In this research, we report a novel approach to fabricate complex-shaped aluminum nitride (AlN) ceramics via digital light processing (DLP)-based stereolithography. The rheological behaviors, curing kinetics, and mechanical properties were investigated. Compared to unmodified AlN powders, AlN powders modified by stearic acid and oleic acid showed better wettability with resin. The excess cure widths, cure depths, and depth sensitivities of the AlN suspensions with modified powders were decreased. However, their critical energy was increased because of the increased absorbance of the modified AlN powders. Finally, complex-shaped AlN ceramic parts were fabricated by DLP with sintered-body relative densities exceeding 99% of the theoretical density. The flexural strength and hardness of the sintered sample were 398 ± 10.4 MPa and 10.47 ± 0.08 GPa, respectively, indicating prospective applicability in the industry.
Chapter
Additive manufacturing (AM) has attracted increasing attention from the scientific community due to its huge potential to fabricate ceramic components without the use of expensive tooling. In addition, it has a layer-by-layer building principle, making it a suitable candidate for the creation of geometrically complex, functionalized, customized architectures that could not be realized at all, or could only be produced at great cost, using conventional technology. However, there has been a slower industrial adoption of additively manufactured ceramic components compared to polymers and metals. Several limitations must be addressed to extend the widespread adoption of AM by industrial end-users. This study provides a review covering the current state of the AM of advanced ceramics, culminating in a comprehensive evaluation of both the advantages and the limitations of each AM process and emphasising the achievements of advanced ceramics and ceramic matrix composites made using AM in terms of characterization and applications. The outcome is the provision of guidelines for ceramicists for optimal AM process selection considering a given material, and most suitable ceramic materials for AM specialists considering a specific application. Furthermore, this chapter also presents case studies illustrating the advantages of ceramic AM.
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Nowadays it is possible to produce ceramic parts with solid and complex shapes with rapid and efficient shaping and sintering techniques. In this paper, 3mol% yttria stabilized zirconia (3Y-TZP) dense and lattice parts were shaped by Digital light processing method (DLP) and densified by conventional (CV) and microwave (MW) sintering. 3Y-TZP samples were MW sintered up to 1550 °C with different heating rates (10, 30, and 50 °C/min) for the dense samples and 30 °C/min for the lattice samples. Controlled thermal cycles with a homogenous heating and no thermal runaway was reached. CV sintering was carried out at 10 °C/min up to 1550 °C. No inter-layer delamination was detected after sintering by the two methods. Both dense and lattice MW-sintered samples reached high final densities (equivalent to obtained values with CV-sintered samples, i.e., ≥98% T.D.), but exhibited a lower average grain size than CV-sintered materials. The different architectures between dense and lattice samples resulted in a different specific absorbed power: the power absorbed by the dense sample is lower than that absorbed by the lattice one meaning that this sample architecture heats up easily.
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High density zirconia (ZrO2) parts with 3 mol% yttrium oxide (3Y-TZP) have been successfully fabricated using a novel additive manufacture technology of powder extrusion printing (PEP). The optimized parameters for the PEP fabrication of ZrO2 ceramic parts were determined with the orthogonal experiment. The microstructure, phase evolution, surface quality and mechanical properties of the as-prepared ZrO2 ceramic parts were systematically characterized and analyzed. The high density (98.6%) ZrO2 part was composed of submicron cellular grains without any discernible pores and cracks. The XRD analyses showed that the phase of sintered specimen was t-ZrO2. TEM results revealed that the grains of t-ZrO2 exhibited irregular polygonal morphologies with clear trigeminal grain boundary and minor m-ZrO2 existed with dislocation and stacking faults. Affected by the printing dimensions, the samples showed anisotropic character of surface quality, with the roughness of 9 μm and 46 μm for the horizontal (X–Y) and vertical (X-Z) surfaces, respectively. The compressive strength was also anisotropic with 1088.7 ± 241.8 MPa and 850.8 ± 110.8 MPa for the X–Y and X-Z surfaces, respectively. Additionally, the hardness and flexural strength of parts were 1486 ± 87 HV and 495 ± 11.8 MPa, respectively. Finally, a series of ZrO2 parts with complex geometries were produced to demonstrate the capability of PEP for fabricating geometrically complex ceramic parts.
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Vat photopolymerization (VP) is one of the most remarkable additive manufacturing techniques today, and has been used for a variety of applications, from materials research to product manufacturing. The main challenge with VP is the limited choice of compatible materials, which motivates significant interest in VP material development. We provide a brief overview of the materials that are currently accessible via VP and highlight recent advances in the field. We also provide perspective on expanding the library of materials compatible with VP using in‐situ material synthesis. This article is protected by copyright. All rights reserved.
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Digital Light Processing (DLP) is attracting high interest thanks to the possibility to prepare dense or complex ceramic parts starting from a photosensitive ceramic slurry. ZrO2 and Al2O3 are the most studied ceramic materials for DLP, while few studies deal with their composites in spite their wide range of applications. In this work, three alumina-zirconia composites (at 15, 50 and 85vol% of ZrO2) were prepared by mixing ready-to-use ZrO2 and Al2O3 slurries. The mechanical and physical properties of the composites prepared via DLP technique were investigated and compared to those of neat alumina and zirconia materials used as a reference. For each composite, the sintering temperature was optimized on the ground of final density and microstructural development, with the aim to achieve a target density (i.e. ρ > 98.5%TD), while keeping a fine microstructure. The composites were characterized by quite homogeneous microstructures, with a good distribution of the two phases, in line with the materials prepared by conventional techniques. Flexural strength, elastic modulus and Vickers hardness of fabricated alumina-zirconia composites ranged between 415-843 MPa, 188-318 GPa and 15-21 GPa, respectively. These results show that the well-known microstructure-properties relationship, which dominates the conventionally fabricated materials, also plays an important role in stereolithography processed samples. In fact, once optimized the fired densities and the microstructures, the 3D-printed alumina-zirconia composites reached mechanical properties higher than almost all previous investigations for the same composites fabricated by stereolithography, and in most cases even higher than those of conventional composites of analogous compositions.
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The mechanical properties of 3D printed alumina ceramics are degraded due to the micro anisotropy, interlayer interface defects and microporous characteristics. In order to improve its mechanical properties, solid phase sintered, liquid phase sintered and solid-liquid phase sintered alumina (Al2O3) ceramics were prepared by Vat photopolymerization 3D printing technology, respectively. In the experiment, Al2O3 was used as the main material to study the effects of TiO2 solid phase additive, MgO-SiO2 liquid phase additives and TiO2-MgO-SiO2 solid-liquid phase additives on Al2O3 ceramics sintering behavior and mechanical properties, so as to improve the sintering density and mechanical properties of alumina ceramics. The best composition ratio and sintering temperature were determined by shrinkage, relative density, Raman, XRD and SEM characterization. Under optimal sintering conditions, The comprehensive properties of Al2O3 ceramics prepared by liquid phase sintering are more balanced. And has excellent mechanical properties. The flexural strength reached 317 ± 34 MPa and the Vickers hardness up to 1250 ± 102 HV30. Thus, nine types of truss structures are prepared to study their mechanical properties. By changing the structure types, the order of compressive strength is FCC > BCC > DLS. By changing the number of units, the order of compressive strength is 3 × 3 × 3 units >2 × 2 × 2 units >1 × 1 × 1 units. The Al2O3 ceramics prepared by the liquid phase sintering exhibit excellent mechanical compression properties and energy absorption capacity. The FCC structure of 3 × 3 × 3 units can reach 23.2 ± 1.7 MPa compressive strength.
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The aim of this study is the evaluation of powder injection molding (PIM) binder compositions for the material extrusion (MEX) additive manufacturing of zirconia parts. Four commercial PIM binder compositions were selected and mixed with 45 vol% of yttria-stabilized zirconia powder. Due to the brittle characteristic of the obtained ceramic feedstocks, a screw based pellet printing head was used for printing dense zirconia structures. To compare 3D printing performance, additionally a commercially available zirconia filament was used in this study. Application of PIM binder compositions was limited either due to phase separation during processing, poor printing performance or delamination during solvent debinding. Only one of the PIM based feedstock compositions could be successfully printed, debound and sintered. A ring-on-ring setup was used to investigate the equibiaxial flexural strength after sintering for both pellet and filament printed disks. For benchmarking, cold isostatic pressed (CIP) ceramic discs were fabricated by commercial, ready-to-press, zirconia powder. The ring-on-ring results showed a low Weibull modulus (3<m<5) for all samples, regardless of the manufacturing process. Fractography on selected samples demonstrated, that the origins of failures are close to the area of the loading ring which indicates an uneven stress distribution along the contact area between the setup and the sample. The pointwise stress concentration is the reason for the immature failure of the samples and the low Weibull modulus. The characteristic strength and 90% confidence intervals were used to compare the strength of ceramic samples produced via additive manufacturing and CIP. Almost similar mechanical properties were obtained for the CIP pressed (σ0 = 657 MPa) and filament printed (σ0 = 531 MPa) samples. However, a lower strength was obtained by the pellet printed samples based on commercial PIM Binder (σ0 = 203 MPa). Fractography analysis indicated poor fusion of printed layers for the samples produced with PIM binder composition as the main reason for poor mechanical performance.
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Ceramic vat photopolymerization has been one of the promising three-dimensional printing technologies for personalized zirconia crown with high dimensional accuracy and surface topography. However, insufficient material stability and complex procedure about auxiliary supports limit the application based on low viscosity slurry. In this work, we developed a photocurable ceramic paste, in which the high static viscosity and high yield stress characteristics allowed it to exhibit sufficient anti-settling and self-supporting capabilities. The rheological characteristics of the as prepared paste were measured by stress-controlled rheometer, and conformal contactless support was designed including top conformal structure without contact with the crown and appropriate empty layer. The 3D precision of crown was evaluated by laser scanning confocal microscope and optical surface scanner. In addition, mechanical properties and biocompatibility of sintered samples were systematically evaluated. The results demonstrated that the yield stress of the ceramic paste approached around 600 Pa, and integrate morphology at the bottom of the crown with the contactless supported zone was observed. 3D deviation between the printed crown scan data and the reference model was reduced within the range of 40 to 70 μm. Finally, the flexural strength and fracture toughness of the sintered zirconia ceramics reached 1117 MPa and 7.76 MPa⋅m1/2, respectively, as well as good biocompatibility by the lack of cytotoxicity and hemolytic reaction. The results indicate an important practical significance for the development of vat photopolymerization printing technology of viscoelastic paste and conformal contactless support strategy to realize the integrated manufacturing of ceramic crowns.
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The computerized design of non-generated pure rolling internal helical gear drives with combined transverse tooth profiles based on the active design of the meshing line function is presented. The application of different combinations of curves, namely circular arcs and involutes, to form the gear active tooth profiles is discussed. The parametric equations for tooth surfaces and the basic design parameters and equations of geometric sizing are proposed. The meshing performance and mechanical behavior are studied in terms of the contact patterns, maximum contact and bending stresses and peak-to-peak level of loaded transmission errors compared with a design of internal helical gear drive with corrected fillet. The combination of a circular arc and an involute connected at the pitch point to form the active tooth profile for both the pinion and the internal gear shows reduced maximum contact and bending stresses and lower peak-to-peak level of the loaded function of transmission errors. The proposed design of combined tooth profiles will contribute to lower the noise and vibration of the proposed gear drives, increase the endurance and life of the gear drive, and lower the heat generation due to pure rolling conditions of the achieved bearing contact.
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The preparation of high solids loading Al2O3 paste is of great significance for improving the properties of ceramics formed by UV-curing. However, the solid contents of alumina slurry used by digital light processing (DLP) and traditional alumina paste for stereolithography (SLA) are both less than 80 wt%. With increase in solid content, the viscosity of paste increases sharply, and rheological property deteriorates. In this study, ceramic paste containing 85 wt% (62 vol%) Al2O3 was prepared for SLA-3D printing of ceramics, and more than 85 wt% solid content was achieved by dispersant and other additives. Effects of different dispersants on rheological and curing properties of Al2O3 ceramic paste were studied. At room temperature, the viscosity of 85 wt% Al2O3 ceramic paste was 51733 mPa s at shear rate of 30 s⁻¹. A novel method was proposed to control curing deformation of parts during printing. As-manufactured ceramic did not show any cracks by naked eye and exhibited excellent mechanical properties, with three-point bending strength of 540 MPa, fracture toughness of 4.19 MPa m1/2, Vickers hardness of 16 GPa, surface roughness of 0.463 μm, and density of 3.86 g/cm³.
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Composite ceramics of stabilizer oxide coated ytterbia-samaria costabilized zirconia (1.5Yb1.5Sm-TZP) and 24-32 vol% of tungsten carbide as an electrically conductive dispersion were manufactured by hot pressing at 1300-1400 °C for 2 h at 60 MPa pressure. The materials were characterized with respect to microstructure, phase composition, mechanical properties and electrical discharge machinability by die sinking. Materials with a nanocomposite microstructure and a strength of up to 1700 MPa were obtained. An attractive toughness of 6-6.5 MPa√m is achieved as 40-50% of the zirconia transformed upon fracture. The materials show fair material removal rates of 1 mm³/min in die sinking. Smooth surfaces indicate a material removal mechanism dominated by melting.
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UV-curable different-colored 3Y-ZrO2 ceramic nanocomposite resins with a ceramic content of 50 vol% were prepared for supportless stereolithography 3D printing. Based on the correlation between the solubility parameters of UV-curable organic resin systems and the rheological behaviors of highly loaded ceramic nanocomposites, the physical properties of the different-colored 3Y-ZrO2 ceramic nanocomposite resins, such as photocurability, viscosity, flowability, and printability, were optimized for a supportless 3D printing process. Thus, white, pink, yellow, and gray 3Y-ZrO2 ceramic nanocomposite resins with optimum physical properties were prepared. The different-colored 3D-printed 3Y-ZrO2 objects sintered at 1450 °C for 180 min exhibited a high relative density of more than 99.90% and a high flexural strength of more than 930 MPa, which are comparable to those of commercial 3Y-ZrO2 manufactured by a conventional ceramic process. In addition, gear-shaped objects with different-colored layers of ceramic resins were successfully manufactured by continuous 3D printing and simultaneous sintering. This study paves the way for innovation in the manufacturing of ceramic products by 3D printing as an alternative to the traditional ceramic process.
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Most of the presently known thermosensitive shape-memory polymers suitable for 4D printing have insufficient mechanical strength and thermal stability that restricts their potential areas of application. Here, new photosensitive compositions (PSCs) based on aromatic heterochain polymers – poly-N,N′-(m-phenylene)isophthalamide (MPA) or poly-2,2′-(p-oxydiphenylene)-5,5′-dibenzimidazole (OPBI) – for DLP printing are proposed. Thermal post-curing and supercritical carbon dioxide (scCO2) are used for post-processing of the structures. During the scCO2 treatment the removal of unreacted monomeric component (N,N-dimethylacrylamide) and its uncrosslinked oligomers is accompanied by the preservation of the initial degree of crosslinking. The more stable shrinkage is observed for the combined post-processing method (T°+scCO2) in the case of OPBI-PSC and after the heat treatment for MPA-PSC specimens. The method of post-processing and the nature of the heterochain polymer strongly affect the mechanical properties and thermal resistance of the structures. The tensile strength has the maximum value after the thermal post-treatment (101.1 ± 7.1 and 78.4 ± 5.1 MPa of OPBI-PSC and MPA-PSC, respectively). The intense destruction of the materials is observed at 393 and 408 °C for MPA-PSC and OPBI-PSC, respectively. Moreover, the 4D-printed structures exhibit excellent shape memory performance at transition temperatures >100 °C, thus have a great potential for the use in aerospace, robotics, sensorics. FREE TO READ https://onlinelibrary.wiley.com/doi/epdf/10.1002/admt.202100790
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Stereolithography (SL) 3D printing of ceramic materials is a promising forming technology to prepare denture with complex shape in the dental field. But the SL formed parts often have inferior mechanical properties than traditional forming method, and the debinding process is time assuming, limiting the clinical application of the technology. In this paper, a novel fluorapatite (FAp) glass-ceramics samples were fabricated through SL 3D printing based on self-made glass-ceramic powders. The effect of laser power and scanning speed on mechanical properties and tribological properties of FAp glass-ceramics were investigated. Phase compositions and microstructure of specimens were characterized by X-ray diffractometer and scanning electron microscope. The microhardness, flexural strength, elastic modulus and tribological performances of the SL samples were tested and compared with that of traditional dry pressing formed samples. The results showed that with the appropriate laser parameters and a relatively short debinding time, the SL formed glass-ceramics had microhardness, flexural strength, and elastic modulus of 772.05 Hv, 205.97 MPa, and 97.06 GPa, respectively, which exceeded that of traditional formed samples. The results reveal that it is possible to efficiently obtain FAp glass-ceramics with excellent mechanical and tribological performance by SL 3D printing process with appropriate parameters.
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Dense hydroxyapatite (HA) bars were fabricated using digital light processing. The roles of HA median particle size (MPS), curing depth-to-layer thickness ratio (CD/LT), and debinding process on the printing/debinding flaws and flexural strength of the sintered parts were investigated. Commercial HA was milled for different times to provide powders with an MPS ranging from 0.3 to 2.7 μm. Thermal debinding led to delamination and vertical cracks, which decreased with increasing MPS; the minimum value required to fabricate specimens with appreciable flexural strength was 0.9 μm. At a given MPS (2.7 μm), the CD/LT varied between 1.4 and 3.3, indicating a progressive disappearance of the above major flaws. Finally, the positive effect of water debinding prior to thermal debinding on reducing crack formation was demonstrated. After optimisation, the bars achieved a strength of >100 MPa, which is the highest value among dense HA fabricated using lithography-based techniques.
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Cellular ceramic structures (CCSs) have promising application perspectives in various fields. Recently, additive manufacturing (AM), usually known as three-dimensional printing (3D printing), has been increasingly adopted to produce CCSs. Usually, the structural properties of additively manufactured cellular ceramic structures (AM-CCSs), i.e., lightweight characteristics, load-bearing capacity, toughness, unconventional properties, are traditionally investigated. Interestingly, AM technologies have a significant advantage in achieving the structure-function integration for CCSs. Functional properties, e.g., electromagnetic property, acoustic property, thermal property, of CCSs can be achieved during the structural design synchronously. In this review, firstly, the AM technologies for CCSs are comparatively introduced. Then, structural AM-CCSs are summarized. After that, structure-function integrated AM-CCSs are further introduced in detail. Finally, challenges and opportunities towards structure-function integrated AM-CCSs are forecasted. This review is believed to give some guidance for the research and development of CCSs.
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This review focuses on the advancements in additive manufacturing techniques that are utilized for fabricating bioceramic scaffolds and their characterizations leading to bone tissue regeneration. Bioscaffolds are made by mimicking the human bone structure, material composition, and properties. Calcium phosphate apatite materials are the most commonly used scaffold materials as they closely resemble live bone in their inorganic composition. The functionally graded scaffolds are fabricated by utilizing the right choice of the 3D printing method and material combinations to achieve the requirement of the bioscaffold. To tailor the physical, mechanical, and biological properties of the scaffold, certain materials are reinforced, doped, or coated to incorporate the functionality. The biomechanical loading conditions that involve flexion, torsion, and tension exerted on the implanted scaffold are discussed. The finite element analysis (FEA) technique is used to investigate the mechanical property of the scaffold before fabrication. This helps in reducing the actual number of samples used for testing. The FEA simulated results and the experimental result are compared. This review also highlights some of the challenges associated while processing the scaffold such as shrinkage, mechanical instability, cytotoxicity, and printability. In the end, the new materials that are evolved for tissue engineering applications are compiled and discussed.
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The present study demonstrates the possibility of fabricating zirconia parts with a complex shape and internal architecture using a low-cost stereolithography-based technique. One of the critical steps in ceramics stereolithography is the preparation of a photo-curable slurry with properties that fulfill specific requirements, such as having a low viscosity, high solids loading and appropriate curing characteristics. Slurries with different acrylic monomers and ceramic fillers were studied concerning their rheological and curing behavior. New formulations based on mono- and tri-functional acrylic monomers revealed the following excellent rheological properties: The viscosity of the mono-/tri-acrylate-based slurry with 75 wt.% of zirconia was 1.6 Pa·s at 30 s−1. Zirconia stabilized with 3 mol.% yttria was found to be more favorable than zirconia with 8 mol.% yttria for slurry preparation, because of its lower surface area and higher tapped density. It was shown that the cure depth of the suspensions was suitable for printing objects with a 50 µm layer thickness, good interlayers connection and surface finishing.
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PURPOSE The purpose of this study was to compare the cutting method and the lamination method to investigate whether the CAD data of the proposed inlay shape are machined correctly. MATERIALS AND METHODS The Mesial-Occlusal shape of the inlay was modeled by changing the stereolithography (STL). Each group used SLS (metal powder) or SLA (photocurable resin) in the additive method, and wax or zirconia in the subtractive method (n=10 per group, total n=40). Three-dimensional (3D) analysis program (Geomagic Control X inspection software; 3D systems) was used for the alignment and analysis. The root mean square (RMS) in the 2D plane state was measured within 50 µm radius of eight comparison measuring points (CMP). Differences were analyzed using one-way analysis of variance and post-hoc Tukey's test were used (α=.05). RESULTS There was a significant difference in RMS only in SLA and SLS of 2D section (P<.05). In CMP mean, CMP 4 (−5.3±46.7 µm) had a value closest to 0, while CMP 6 (20.1±42.4 µm) and CMP 1 (−89.2±61.4 µm) had the greatest positive value and the greatest negative value, respectively. CONCLUSION Since the errors obtained from the study do not exceed the clinically acceptable values, the lamination method and the cutting method can be used clinically.
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This paper describes an efficient method of fabricating high-performance ceramic (HPC) parts by using solvent-based slurry stereolithography (3S) and sintering. In this study, zirconia was used as the structural material, methyl alcohol was used as the solvent, a waterborne inorganic pigment was used as the dispersant, and a visible-light-curing resin was used as the organic binder for forming the slurry. The slurry was photocured using a visible-light projector for layer-by-layer deposition in an enclosed cabinet to form a three-dimensional object. The obtained green part was sintered at high temperatures (up to 1600 °C) so that it densified and formed a rigid body. Thus, an HPC part with high material strength could be produced. A complete system was developed for producing complex zirconia ceramic parts with a high level of precision without the necessity of generating support structures for the overhang features. The system was determined to achieve a very fine-detailed shape (30 μm). The mechanical properties of the obtained zirconia parts, such as flexural strength, density, and average roughness, were also investigated in this study.
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Ceramic processing to fabricate 3D complex ceramic structures is crucial for structural, energy, environmental, and biomedical applications. A unique process is ceramic stereolithography, which builds ceramic green objects from CAD files from many thin liquid layers of powder in monomer, which are solidified by polymerization with a UV laser, thereby "writing" the design for each slice. This approach directly writes layers in liquid ceramic suspension and allows one to fabricate ceramic parts and products having more accurate, complex geometries and smooth surfaces. In this paper, both UV curable materials and processes are presented. We focus on the basic material principles associated with free radical polymerization and rheological behavior, cure depth and broadening of cured lines, scattering at ceramic interface and their corresponding simulation. The immediate potentials for ceramic AM to change industry fabrication are also highlighted.
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Direct inkjet printing is a versatile additive manufacturing technology to produce complex three-dimensional components from ceramic suspensions. By successive printing of cross-sections, the sample is built up layer by layer. The aim of this paper is to show the different possibilities of direct inkjet printing of ceramic suspensions, like printing of oxide (3Y-TZP, Al2O3, and ZTA) or nonoxide (Si3N4, MoSi2) ceramics, featuring microstructures, laminates, three-dimensional specimens, and dispersion ceramics. A modified thermal inkjet printer was used and the ink replaced by aqueous ceramic suspensions of high solids content. The suspensions were processed in an attrition mill or agitator bead mill to reduce the grain size <1 μm to avoid clogging of printhead nozzles. Further significant parameters are rheological properties (viscosity and surface tension) and solids content which were adjusted to the requirements of the printheads. The printed and sintered samples were analysed by SEM. Mechanical properties of 3Y-TZP samples were examined as well by use of the ball-on-three-balls test. The biaxial flexural strength of 3Y-TZP specimens was up to 1393 MPa with a Weibull modulus of 10.4 for small specimens (3 × 4×0.3 mm3).
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The photopolymerization of suspensions of ceramic powders in monomer solutions is the fundamental step in several rapid prototyping forming techniques based on photocuring. Exposure to an UV dose of energy E causes the monomer to be polymerized to a certain cure depth, with the relation between cure depth and energy dose dependant on two properties of the photosuspension, the sensitivity and the critical energy dose. We present simple models for sensitivity in terms of the attenuation of the UV beam by absorption and scattering, and demonstrate the applicability of the model with experimental data for a UV laser, UV lamps and direct spectrophotometry. We also present a model for the critical energy dose in terms of the relative number of photo-generated radicals and the concentration of inhibitors.
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This paper focused on the influence of ingredients of silica suspensions and laser exposure on curing behavior of the highly concentrated aqueous silica suspensions. As a basic building unit, single cured lines were regarded as research objects to characterize the curing behavior of aqueous ceramic suspensions. The cured width and depth were characteristic parameters of single cured lines and measured with a digital optical microscope. The relationships between two characteristic parameters and ingredients of highly concentrated aqueous ceramic suspensions and laser exposure were investigated. The cured depth and width of single cured lines increased with the ceramic mean diameter and monomer concentrations. The cured width of single cured lines decreased with the solid content, but the cured depth increased with the solid content for silica suspensions. The cured depth and width of the single cured line all decreased with the laser scanning speed. The experimental results show that the ingredients of ceramic suspensions and laser exposure all have great influence on curing behavior of the highly concentrated silica suspensions, which indicates that the formula is an intrinsic factor on the curing behavior of ceramic suspensions and laser exposure is an exterior factor. KeywordsStereolithography–Ceramic suspensions–Scattering–Curing behavior
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The Ceramic On-Demand Extrusion (CODE) process is a novel additive manufacturing method for fabricating dense (~99% of theoretical density) ceramic components from aqueous, high solids loading pastes (>50 vol%). In this study, 3 mol% Y2O3 stabilized zirconia (3YSZ) specimens were fabricated using the CODE process. The specimens were then dried in a humidity-controlled environmental chamber and afterwards sintered under atmospheric conditions. Mechanical properties of the sintered specimens were examined using ASTM standard test techniques, including density, Young's modulus, flexural strength, Weibull modulus, fracture toughness, and Vickers hardness. The microstructure was analyzed and grain size measured using scanning electron microscopy. The results were compared with those from Direct Inkjet Printing, Selective Laser Sintering, Lithography-based Ceramic Manufacturing (LCM), and other extrusion-based processes, and indicated that zirconia specimens produced by CODE exhibit superior mechanical properties among the additive manufacturing processes. Several sample components were produced to demonstrate CODE's capability for fabricating geometrically complex ceramic components. The surface roughness of these components was also examined.
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Zirconia (ZrO2) ceramic bars with three different printing sizes were fabricated by a stereolithographic (SLA) 3D-printing process and subsequent sintering. An anisotropic character of the ceramics surface quality was observed. The surface roughness of the horizontal surface was below 0.41μm, whereas it reached 1.07μm along the fabrication direction on the vertical surface. The warpage and flatness were utilized to measure the dimensional accuracy of the 3D printed ZrO2. Furthermore, it was evaluated that the warpage and flatness were below 40μm and 27μm, respectively, even if the printed size of ceramic bar reached 3mm × 4mm × 80mm. In addition, the flexural strength, the fracture toughness, the hardness and the density of ZrO2 ceramics can reach to 1154 ± 182MPa, 6.37 ± 0.25MPam1/2, 13.90 ± 0.62GPa and up to 99.3%, respectively. Moreover, the effects of scanning paths and printing size on properties of the sintered ZrO2 samples were analyzed. The anisotropic character of surface quality was related to the various scanning paths. The warpage and flatness of 3D printed ZrO2 bars were apparently affected by the various printed sizes. Also, the effects of special microstructure on the mechanical properties of sintered ZrO2 samples were investigated.
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Stereolithography is an additive manufacturing process which makes it possible to fabricate useful complex 3D ceramic parts, with a high dimensional resolution and a good surface finish. Stereolithography is based on the selective UV polymerization of a reactive system consisting in a dispersion of ceramic particles in a curable monomer/oligomer resin. In order to reach a homogeneous polymerization in the green part, and to limit the risk of cracking and/or deformation during subsequent stages of debinding and sintering due to internal stresses, the influence of various fabrication parameters (laser power, scanning speed, number of irradiations) on the degree of polymerization was investigated. In addition, the impact of the irradiation of the subsequent upper layers onto the previously deposited and irradiated layers was evaluated. The degree of conversion was determined by Fourier Transform Infrared Spectroscopy (FTIR). Raman spectroscopy was also used and a brief comparison between these two methods is given.
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High-power direct laser deposition (HP DLD) was utilized to fast generate AISI 316L stainless steel parts with large size and excellent mechanical properties. In order to efficiently manufacture the stainless steel parts with high surface quality and dimensional accuracy, a dry milling finish was applied. During the DLD process, heat retaining powder was employed to prevent buckling deformation. The effect of building direction on the microstructure, mechanical properties and machinability of the stainless steel was investigated. It was found that the microstructure was homogeneous, at the building direction of 0°, while a number of larger dendritic grains were present in the microstructure, at the building direction of 90°. The tensile properties and hardness values at the building direction of 0° were higher than those at the building direction of 90°. For both building directions, the decrement in surface roughness and the increment in cutting force and tool wear, were observed with the increase in cutting speed. The cutting force, tool wear and surface roughness of the additive manufactured stainless steel at the building direction of 0° were relatively higher, which implies that the anisotropy in the machinability could be utilized to increase efficiency and reduce production cost.
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A dense defect-free alumina cutting tool was fabricated via stereolithography process. Different drying processes and debinding profiles were then tested and compared to find the optimal way for the preparation of the sintered body. The experimental results showed that using PEG400 as a liquid desiccant results in a lower deformation of the body compared to the natural drying process. Compared with vacuum debinding or air debinding, a two-step debinding process, which consisted of both a vacuum pyrolysis step and the following air debinding, is allowed to control the pyrolysis rate while suppressing the formation of defects in the alumina body. After optimization of the postprocessing, the relative density of the sample as high as 99.3%, and the Vickers hardness ∼17.5 GPa. These properties are similar to the properties of alumina bodies prepared via the conventional shaping method.
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Light scattering in photopolymerizable ceramic suspensions affects the resolution of photopolymerization processing methods; it is necessary to predict the cure width and cure depth at a given energy dose for a suspension with a known composition. The volume fraction of ceramic powder in the suspension or the refractive index (RI) contrast between the ceramic powder and the liquid solution was varied, measuring the quasi-Beer–Lambert suspension properties. For these suspensions, the depth and width attenuation and the depth and width critical energy doses were determined. The volume fraction of powder has no effect on the broadening depth; the solids loading can be varied without concern for increased scattering within the suspension. The broadening depth decreases with the logarithm of RI contrast. Suspensions with a small RI contrast are able to cure deep, narrow features without broadening.
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Through computer aided design, manufacturing and evaluation, various ceramics dendrites with spatially ordered micro cavities were successfully fabricated by utilizing stereolithography. Micrometer order ceramic lattices were propagated spatially in computer graphic space. Ceramics nanoparticles were dispersed in to photo sensitive liquid resins to obtain thixotropic slurries. The paste material was spread on a grass substrate by using a mechanical knife edge, and an ultra violet micro pattern was exposed to create cross sectional solid layer. After the layer stacking process, the obtained composite precursor was dewaxed and sintered in an air atmosphere. By the micro patterning stereolithography, solid electrolyte dendrites of yttria stabilized zirconia with spatially ordered porous structures were fabricated for fuel cell miniaturizations. Gaseous fluid profiles and pressure distributions in the formed ceramic lattices with various porosity percent were visualized and analyzed by a finite element method. Subsequently, alumina micro photonic crystals with a diamond lattice structure were fabricated. Electromagnetic wave properties were measured by using a terahertz time domain spectroscopy. A complete photonic band gap was exhibited, and a localized mode to select the wavelength was obtained by introducing a defect cavity.
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In this study, a new process for additive manufacturing (AM) of dense and strong ceramic objects is described. The lithography-based ceramic manufacturing (LCM) technique is based on the selective curing of a photosensitive slurry by a dynamic mask exposure process. The LCM technique is able to produce strong, dense and accurate alumina ceramics without virtually any geometrical limitations. With over 99.3% of a theoretical alumina density, four-point bending strength of 427 MPa, and very smooth surfaces, the LCM process distinguishes itself from other AM techniques for ceramics and provides parts with very similar mechanical properties as conventionally formed alumina.
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In our new approach—thermoplastic 3D printing—a high-filled ceramic suspension based on thermoplastic binder systems is used to produce dense ceramic components by additive manufacturing. Alumina (67 vol%) and zirconia (45 vol%) suspensions were prepared by ball milling at a temperature of about 100°C to adjust a low viscosity. After the preparation the suspension solidified at cooling. For the sintered samples (alumina at 1600°C, zirconia at 1500°C), a density of about 99% and higher was obtained. FESEM studies of the samples' cross section showed a homogenous microstructure and a very good bond between the single printed layers.
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When a photopolymerizable ceramic suspension is illuminated, the cured region is characterized by the cure width and cure depth. The cure depth follows a semilogarithmic behavior with increasing energy dose, as expected for Beer–Lambert absorption, and is described by the depth sensitivity (Sd) and depth critical energy dose (Ed). The excess cure width, which is the cured width beyond the incident illumination width, is also found to increase with the logarithm of energy dose. This quasi-Beer–Lambert behavior can be described by a width sensitivity (Sw) and width critical energy dose (Ew). The semilogarithmic dose dependence is demonstrated for ceramic suspensions containing silica, mullite, alumina, and zircon powders. Broadening can be quantified by the broadening depth (Db), which is the cure depth at which broadening begins to occur. It is shown that the broadening depth decreases with the logarithm of the normalized refractive index contrast between the powder and monomer solution.
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UV laser stereolithography is a rather new shaping technique that makes it possible the fabrication of complex 3D ceramic structures with a high dimensional accuracy. The green part is built through layer by layer photopolymerization of a light sensitive suspension.Polymerization is thus a critical step to control in this shaping technique. Photopolymerization, with the initiation, propagation and termination reactions, involves the mobility of reactive species and is then sensible to the rheology of the media. This study investigated the influence of the rheology of suspensions of silica particles in an acrylate oligomer and of the intergranular curable organic phase on the UV polymerization. In this respect, the effects of the powder concentration, the state of dispersion and of the dilution of the reactive oligomer on polymerization, are measured.In addition, the influence of the powder loading on the cure depth and cure width, which are respectively pertinent indicators of the reactivity of the suspension and of the dimensional accuracy of the green part, is evaluated.
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The photoinitiated polymerization of a commercial polyether acrylate oligomer with 2,2-dimethoxy-1,2-phenyl acetophenone (DMPA) as radical photoinitiator was studied by using real time infrared spectroscopy (RTIR). First, the effect of light intensity, photoinitiator concentration and reactive diluent (1,6-hexanediol diacrylate, HDDA) on reaction was investigated in homogeneous phase. The maximum conversion was obtained for 0.5wt% of DMPA and 10–15vol% of HDDA. Then, ceramic fillers (SiO2, Al2O3, ZrO2 and SiC) were added to the acrylate oligomer in order to be used later as reactive suspensions for stereolithography. The influence of the nature, size and concentration of these fillers on the kinetics and the final conversion was characterized. The index ratio between filler and organic matrix as well as the intergranular phase viscosity were found to be the main parameters governing the reaction in heterogeneous phase.
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Ceramic green bodies can be created using stereolithography methods where a ceramic suspension consisting of 0.40–0.55 volume fraction ceramic powder is dispersed within an ultraviolet-curable solution. Three ceramic materials were investigated: silica for investment casting purposes, and alumina and silicon nitride for structural parts. After mixing the powders in the curable solution, the ceramic suspension is photocured, layer by layer, fabricating a three-dimensional ceramic green body. Subsequent binder removal results in a sintered ceramic part. Three-dimensional objects have been fabricated from a 0.50 volume fraction silica suspension.
  • M Rosa
  • C Barou
  • V Esposito
M. Rosa, C. Barou, V. Esposito, Zirconia UV-curable colloids for additive manufacturing via hybrid inkjet printing-stereolithography, Mater. Lett. 215 (2018) 214-217.
Light Curing 3D Printing Technology of Liquid Resin, Xi'an University of Electronic Science and Technology
  • J Mo
J. Mo, Light Curing 3D Printing Technology of Liquid Resin, Xi'an University of Electronic Science and Technology, Xi'an, 2016 (In Chinese).
Shrinkaging Behaviour and Its Mechanism of Zirconia Ceramic during the Sintering, Doctor's thesis)
  • Z Peng
Z. Peng, Shrinkaging Behaviour and Its Mechanism of Zirconia Ceramic during the Sintering, Doctor's thesis), Wuhan, 2014 (In Chinese).