Mask Projection Stereolithography Research Articles

Carbon scaffold with controllable small pore structure based on mask projection stereolithography

Mask Projection Stereolithography (MPSL), due to its high printing resolution, is suitable for fabricating porous polymer architectures that are used as carbon scaffold precursors. In the present work, a carbon scaffold with a controllable small porous structure was fabricated by MPSL. A polymer lattice structure used as the carbon scaffold precursor was first fabricated by MPSL. Sodium chloride was selected as the granular support, and nano-silica particles were introduced into the granular support so that sodium chloride could easily fill the lattice structure. A carbon scaffold with controllable low shrinkage (41.3%) and a small porous structure (skeleton thickness=~40 µm and pore size=~300 µm) was obtained by pyrolyzing the polymer lattice structure in the granular support, and subsequently, it was processed by hydrofluoric acid (HF). The unprocessed and HF-processed scaffolds were both composed of simple substance carbon, and silicon oxide particles embedded on the unprocessed scaffold were cleaned by HF. Finally, the compressive properties of the scaffold were examined. The fracture appearances of the scaffold under the application of compressive forces parallelly and vertically to the stacking direction were different, and compressive properties in vertical to the stacking direction were superior to those in parallel to the stacking direction. Therefore, it can be inferred that the proposed method is effective in fabricating multi-scale carbon scaffolds with small controllable porous structures based on stress analysis to obtain optimum mechanical properties, which makes it a promising material for many applications.

Tilting separation simulation and theory verification of mask projection stereolithography process

Purpose This study aims to accurately simulate the tilting separation process of mask projection stereolithography (MPSL) and verify the tilting theory. Design/methodology/approach The finite element separation models of MPSL 3D printing process were established. The established models simulated both tilting and pulling-up separation process by changing the constraints and boundary conditions. The bilinear cohesive curves were used to define the separation interface. The stress distribution of the cured part and FEP film at different times during the whole separation process was extracted. Different orientations of pulling-up and tilting were also compared for stress distribution. The stress change was analyzed for the center and edge points of the upper surface of cured part. Findings The results showed that the stress increased with the separation speed, and the stress at the edge position of exposure area was greater than the internal position. The tilting traction stress distribution was affected by the exposure area function and the velocity distribution. Alternation of the exposure area function changed the cohesive stiffness. The non-coincidence of the calculated traction stress with the input bilinear cohesive curve reflected the influence of the material properties and the separation methods. The high-speed side of tilting had fast separation and high traction stress. Originality/value This study proposes a technical method for simulation tilting separation and verified the tilting theory. The cohesive zone model was proved applicable to the tilting traction stress calculation.

A Novel Manufacturing Technique of Thin-wall Ceramic BASE Tube by Mask Projection Stereolithography

A Novel Manufacturing Technique of Thin-wall Ceramic BASE Tube by Mask Projection Stereolithography

A double mask projection exposure method for stereolithography

Mask Projection Stereolithography (MPSL) is an additive manufacturing technology that allows direct fabrication of complex parts from liquid resin. However, the present MPSL systems cannot meet the requirements of high accuracy and large building envelope at the same time. In order to solve this problem, a Double Mask Projection Stereolithography (DMPSL) system combining two projection modules is proposed based on Digital Micromirror Device. The Large Envelope Projection (LEP) module with a building envelope of 55 mm × 41 mm offers a pixel size of 53.8 μm to achieve large building space. In order to improve the local feature accuracy, the high accuracy features are fabricated by the High Accuracy Projection (HAP) module with a building envelope of 6.8 mm × 5.1 mm, offering a pixel size of 6.6 μm. The calibration and alignment of the system were implemented. The samples for shape and dimension accuracy tests were fabricated by DMPSL, respectively. The results indicated that the shape and dimension accuracy of the features requiring high accuracy was significantly improved. In addition, to overcome the poor mechanical properties at the splicing interface, the effects of splicing shape and overlapping width on the mechanical properties were studied. It was found that the poor mechanical properties can be improved by using straight line splicing strategy with overlapping width of 10 or 20 pixels, which makes DMPSL useful for producing parts that can be directly used in stress environments.

Modeling and visualization of layered curing conversion profile in ceramic mask projection stereolithography process

Ceramic mask projection stereolithography can be used for printing delicate ceramics through a layer-stacking process. However, the layered printing results in the introduction of layered anisotropy and defects along the layers in the printed parts. An in-depth investigation of the layered properties of curing conversion in the green parts is essential for improving the part quality. In this study, analytical, numerical, and experimental methods were used to characterize the curing conversion of a mask-exposed ceramic slurry. Visualization of the curing conversion profiles was achieved through optical microscopic observation of partially debound green parts. The results showed that the curing conversion in the green body was step-like and non-uniform between and within layers, because of the attenuation of UV light. The largest difference in the curing conversion appeared at the layer bonding interface. Uniform curing conversion should be achieved to reduce the layered properties of printed ceramics.

Accurate printing of a zirconia molar crown bridge using three-part auxiliary supports and ceramic mask projection stereolithography

Abstract Zirconia ceramic is a widely used material for dental restoration. Stabilized zirconia all-ceramic teeth have excellent mechanical properties, biocompatibility, and aesthetic properties. At present, the CAD/CAM technique for zirconia all-ceramic dental prosthesis leads to low material efficiency and high tool wear. Although restorations fabricated using additive manufacturing are gaining attention, it is still very challenging to obtain accurate shapes and proper mechanical properties in zirconia restorations. In this investigation, a type of three-part auxiliary support was adopted and added to the occlusal surface to fabricate a typical molar crown bridge. A ceramic solid content of 40 vol% acrylic-based slurry was prepared, and a molar crown bridge was fabricated using mask projection stereolithography. The experimental results showed that the average dimensional error of the printed green body was ±150 μm. The density of the sintered ceramic parts was 6.026 g/cm3, and the three-point bending strength was 541 ± 160 MPa, which is higher than that of human dentin (160 MPa), but lower than that of CAD/CAM zirconia (900–1200 MPa). Although the proposed process still needs to be optimized to improve the mechanical properties and reliability of the crown bridge, the mask projection process combined with the adopted three-part auxiliary supports are capable of individualized manufacturing of complex zirconia crown bridges.

Effects of soft-start exposure on the curing characteristics and flexural strength in ceramic projection stereolithography process

Ceramic mask projection stereolithography (CMSL) is an additive manufacturing (AM) technology which is capable of implementing delicate structural designs of ceramic parts. Studies have shown that soft-start exposure mode has an effect on the polymer properties of the cured resin, such as conversion degree, curing speed etc. However, the effect of soft-start exposure on CMSL process has not received much attention. In this investigation, soft-start exposure was compared with constant exposure. The results showed that the soft-start exposure reduced the critical exposure energy (maximum reduction of 48.2%) of the slurry. The feature dimensional error of soft-start exposure was smaller than constant exposure by 25–45%. The soft-start exposure also had an effect on the strength of sintered parts. The bending samples fabricated by soft-start exposure had higher Weibull moduli (maximum increase of 47.2%), indicating that soft-start exposure stabled the curing process.

Rapid multi-material 3D printing with projection micro-stereolithography using dynamic fluidic control

Mask projection stereolithography is a digital light processing-based additive manufacturing technique that has various advantages, such as high-resolution, scanning-free parallel process, wide material sets available, and support-structure-free three-dimensional (3D) printing. However, multi-material 3D printing with mask projection stereolithography has been challenging due to difficulties of exchanging a liquid-state material in a vat. In this work, we report a rapid multi-material projection micro-stereolithography using dynamic fluidic control of multiple liquid photopolymers within an integrated fluidic cell. Highly complex multi-material 3D micro-structures are rapidly fabricated through an active material exchange process. Material flow rate in the fluidic cell, material exchange efficiency, and the effects of energy dosage on curing depth are studied for various photopolymers. In addition, the degree of cross-contamination between different materials in a 3D printed multi-material structure is evaluated to assess the quality of multi-material printing. The pressure-tight and leak-free fluidic cell enables active and fast switch between liquid photopolymers, even including micro-/nano-particle suspensions, which could potentially lead to facile 3D printing of multi-material metallic/ceramic structures or heterogeneous biomaterials. In addition, a multi-responsive hydrogel micro-structure is printed using a thermo-responsive hydrogel and an electroactive hydrogel, showing various modes of swelling actuation in response to multiple external stimuli. This new ability to rapidly and heterogeneously integrate multiple functional materials in three-dimension at micro-scale has potential to accelerate advances in many emerging areas including 3D metamaterials, tissue engineering, and soft robotics.

Process Optimization of Oxygen-inhibition-based Ceramic Mask-projection Stereolithography

Process Optimization of Oxygen-inhibition-based Ceramic Mask-projection Stereolithography

Influence of boundary masks on dimensions and surface roughness using segmented exposure in ceramic 3D printing

Mask projection stereolithography can be used to fabricate complex ceramic parts layer by layer through the photopolymerisation of ceramic suspensions. The broadening or lateral overcure of the curing shape occurs because of light scattering effects. Achieving a better dimension and strength quality by adjusting light energy delivery in the boundary mask area has been insufficiently investigated thus far. In this study, the conventional mask was segmented into boundary and interior masks. The exposure time and power of the boundary mask (two pixels wide) were varied to investigate the effects of segmented exposure. The segmented exposure constrained the dimension errors to a width of within two pixels for a feature dimension of less than 1200 µm. It further smoothed the lateral surface of the green part to achieve Ra values of below 6 µm. Moreover, enhancing the boundary mask increased the flexural strength and Weibull modulus to 248 MPa and 11.1, respectively. The results indicate that segmented exposure can potentially be used in complex lattice ceramic structures.

A 3D Printable Thermal Energy Storage Crystalline Gel Using Mask-Projection Stereolithography.

Most of the phase change materials (PCMs) have been limited to use as functional additions or sealed in containers, and extra auxiliary equipment or supporting matrix is needed. The emergence of 3D printing technique has dramatically advanced the developments of materials and simplified production processes. This study focuses on a novel strategy to model thermal energy storage crystalline gels with three-dimensional architecture directly from liquid resin without supporting materials through light-induced polymerization 3D printing technique. A mask-projection stereolithography printer was used to measure the 3D printing test, and the printable characters of crystalline thermal energy storage P(SA-DMAA) gels with different molar ratios were evaluated. For the P(SA-DMMA) gels with a small fraction of SA, the 3D fabrication was realized with higher printing precision both on milli- and micro- meter scales. As a comparison of 3D printed samples, P(SA-DMAA) gels made by other two methods, post-UV curing treatment after 3D printing and UV curing using conventional mold, were prepared. The 3D printed P(SA-DMAA) gels shown high crystallinity. Post-UV curing treatment was beneficial to full curing of 3D printed gels, but did not lead to the further improvement of the crystal structure to get higher crystallinity. The P(SA-DMAA) crystalline gel having the highest energy storage enthalpy was developed, which reached 69.6 J·g−1. Its good thermoregulation property in the temperature range from 25 to 40 °C was proved. The P(SA-DMAA) gels are feasible for practical applications as one kind of 3D printing material with thermal energy storage and thermoregulation functionality.

3D Printable Energy Storage Crystalline Gels Using Mask-Projection Stereolithography

Phase change materials (PCMs) are considered one of the most reliable latent heat storage and thermoregulation materials. In this paper, a vinyl monomer is used as phase change material to synthesize gel. Using the light-induced polymerization 3D printing technique, we synthesize the energy storage gel and shape it on 3D printers at the same time. iBox Nano and Lumi Forge are used to print our crystalline gels through mask-projection stereolithography. By adjusting layer thickness, exposure time and first layer settings, gels are shaped into several formations successfully. Infrared images, DSC and WAXS test indicate the printed objects have phase transition behaviors and can provide energy storage capacity. Also, the effects of monomer ratios on phase change enthalpy and phase transition temperature are investigated.

Using total specific cost indices to compare the cost performance of additive manufacturing for the medical devices domain

The label additive manufacturing, also known as three-dimensional printing, serves as an umbrella term for a number of technologies designed to deposit product geometries directly from build materials and digital design information. However, as a relatively recent addition to the spectrum of manufacturing processes, the relationship between process type, system characteristics and cost performance is still broadly unclear for several technology types. To address this gap, the current research develops comprehensive and robust additive manufacturing cost models for two less-studied polymeric additive manufacturing technology variants, material jetting and mask projection stereolithography. Despite sharing the fundamental principle of photopolymerization, the operating processes of both systems are markedly different. This is reflected in the constructed cost models, which incorporate process maps to capture ancillary process elements, ensure efficient capacity utilisation through optimised build volume packing and approximate the expected cost impact of build failure. On this basis, this article estimates a set of specific cost indices reflecting the overall total cost performance of the investigated systems in an example application from the medical devices domain. Specific cost results range from £2.01 to £1.19/cm3 deposited on the Objet Connex 260 system and from £1.59 to £1.00/cm3 of material deposited on the Perfactory system. These results are discussed in the context of similar cost indices extracted from the empirical engineering literature. This article shows that next to increases in build speed, improvements in overall process automation and process stability are needed to enhance the commercial proposition of the investigated technology variants.

Fabrication of β-TCP Scaffold with Pre-Designed Internal Pore Architecture by Rapid Prototyping of Mask Projection Stereolithography

The aim of this study was to present a direct fabrication technique of β-tricalcium phosphate (β-TCP) scaffolds by a bottom-up mask projection stereolithography (MPSL) technology, which provided an excellent control of the internal pore architecture. The debinding and sintering schemes of β-TCP were determined by TG-DSC analysis, the scaffolds with designed pore architecture were obtained. The physical properties of β-TCP scaffolds were investigated including pore morphology , size and pore distribution, the crystal phase and chemical composition of sintered β-TCP were measured. Results indicated that the β-TCP scaffolds fabricated with a pore size of 0.4-0.7mm, a porosity of 58.50% and an average compressive strength of 20.92MPa met the requirements of bone scaffold. The effectiveness of degradation and cell proliferation of β-TCP scaffold were also evaluated, the results showed that β-TCP scaffolds had some certain degradability and bioactivity, which may stimulates bone tissue repair and regeneration.

Oxygen-controlled bottom-up mask-projection stereolithography for ceramic 3D printing

To fabricate ceramic components with a complex structure, the bottom-up mask-projection stereolithography (MP-SL) technique is currently employed. However, a fracture or a defect is normally found because of the large separation force formed between the newly cured layer and the bottom surface of the slurry tank. Hence, to overcome this issue, an oxygen-permeable layer is integrated into the conventional MP-SL system for printing a β-TCP ceramic slurry in this study. The system is based on the fact that oxygen inhibits the photopolymerization process by consuming free radicals. The effects of the light exposure time and oxygen concentration on the curing depth and thickness of the oxygen-inhibition layer were investigated. Moreover, the separation forces were indirectly determined using a weight sensor. The results show that the oxygen-inhibition layer helped in reducing the separation force by 60% compared to that wherein oxygen is not employed. The solid loading could be increased by up to 44 vol% and the printable cross-sectional area by 5 times. In summary, the proposed oxygen-controlled bottom-up MP-SL technique helped in improving the ceramic printing efficiency and product quality.

3D Printing All-Aromatic Polyimides using Mask-Projection Stereolithography: Processing the Nonprocessable.

High-performance, all-aromatic, insoluble, engineering thermoplastic polyimides, such as pyromellitic dianhydride and 4,4'-oxydianiline (PMDA-ODA) (Kapton), exhibit exceptional thermal stability (up to ≈600 °C) and mechanical properties (Young's modulus exceeding 2 GPa). However, their thermal resistance, which is a consequence of the all-aromatic molecular structure, prohibits processing using conventional techniques. Previous reports describe an energy-intensive sintering technique as an alternative technique for processing polyimides with limited resolution and part fidelity. This study demonstrates the unprecedented 3D printing of PMDA-ODA using mask-projection stereolithography, and the preparation of high-resolution 3D structures without sacrificing bulk material properties. Synthesis of a soluble precursor polymer containing photo-crosslinkable acrylate groups enables light-induced, chemical crosslinking for spatial control in the gel state. Postprinting thermal treatment transforms the crosslinked precursor polymer to PMDA-ODA. The dimensional shrinkage is isotropic, and postprocessing preserves geometric integrity. Furthermore, large-area mask-projection scanning stereolithography demonstrates the scalability of 3D structures. These unique high-performance 3D structures offer potential in fields ranging from water filtration and gas separation to automotive and aerospace technologies.

Research of Control System for Mask Projection Stereolithography with Raspberry Pi

To reduce the space and cost of the control system of Mask Projection Stereolithography Apparatus (MPSLA), the control system of MPSLA based on Raspberry Pi is designed and implemented. The system with Raspberry Pi as the control core, Linux as the operation system, realizes the projection control of mask image and the motion control of platform by using Python program. When Raspberry Pi connects to the network via the Ethernet port, remote control function of the control system has been achieved for MPSLA with VNC. The control system provides MPSLA with some telecontrol function, such as Remote login, File remote transfer via FileZilla and Remote monitoring. The novel control system distinctly reduces the space and the cost of MPSLA.

Ceramics Fabrication Using Rapid Prototyping of Mask Projection Stereolithography

Ceramics Fabrication Using Rapid Prototyping of Mask Projection Stereolithography

Research on Worktable Control of the Mask Exposal Forming Machine

In view of the mask projection stereolithography of rapid prototyping technology, the hardware system of the mask exposal forming machine is constructed of a carriage, a resin tank, stepping motor, ball screw and other components. And its working principle is introduced. Based on googol motion control card, software control system is developed in VC6.0 environment, provides a human-computer interactive platform for operators. And the experiments show that the system can run reliably.

Tilting separation analysis of bottom-up mask projection stereolithography based on cohesive zone model

Compared with top-down stereolithography, bottom-up mask projection stereolithography can reduce the start filling volume of vat and is able to build components with high-viscosity materials. For general photosensitive materials, a separation process is required to detach the cured layer from the resin vat surface in order to accomplish the fabrication of current layer. The separation process can be achieved without damaging the part by utilizing appropriate platform motions including pulling-up, tilting and shearing, and covering inert film on the vat surface. The tilting separation is used in both industrial and academic area. However, there is a limited corresponding study compared with pulling-up separation. The mechanism of tilting separation and its effects on separation force and fabrication process are not clear. In this paper, an analytical model based on cohesive zone model was formed and a specialized experimental system was built. Experimental studies on the tilting effects on cohesive stiffness and fracture energy were conducted by collecting and analyzing separation force data. The results showed that changing exposure area function or the part fabrication orientation changed the cohesive stiffness, and increasing tilting separation velocity caused different increase in fracture energy when using different inert films. The results of this investigation can be used to choose the reasonable platform motion and process parameters by considering the part geometry and the characteristics of both inert film and materials.