面曝光快速成形关键技术及研究现状

全面介绍了面曝光快速成形关键技术、应用及研究现状,指出了其优势和存在的问题;阐述了面曝光快速成型系统组成、掩膜生成方法及关键器件工作原理,分析了LCD作为快速成型掩膜生成器件的失效原因,重点比较了LCD、DMD掩膜生成器件的分辨率、可靠性以及对快速成型的适用性;探讨了掩膜曝光快速成形过程中,树脂曝光固化引起翘曲变形的原理,介绍了改善翘曲变形的方法;最后,根据以上分析以及掩膜生成关键器件的发展现状,提出了面曝光快速成形技术的发展趋势。     

面曝光快速成形系统制作工艺参数的优化研究

应用田口方法的信噪比(SN)对液面曝光辐照度、曝光时间、液面等待时间及面收缩补偿系数4个主要影响面曝光快速成形的因素进行了优化试验研究。采用自由度为26的L27(313)形式的正交表,通过实验得到各个因素不同水平对应的制作零件尺寸误差的信噪比。实验结果的直观分析和方差分析表明:面收缩补偿系数、液面曝光辐照度、面收缩补偿系数与液面曝光辐照度的交互作用及液面等待时间对制作精度有显著影响;面收缩补偿系数与液面等待时间之间的交互作用对制作精度有一定的影响。针对面曝光快速成形系统,得出了以曝光平面内的制作精度为优化目标的制作参数的最佳组合。试验结果表明:在最佳的制作工艺参数条件下,曝光平面内的制作误差在±10μm范围内,显著提高了面曝光快速成形制作精度。     

微细光成型固化工艺参数优化

为了分析紫外光对液态光敏树脂进行曝光固化成型过程中工艺参数对固化物的形状和精度的影响,根据自行研制的实验系统的大量数据,对线形固化中的主要工艺参数进行了分析和优化。结果表明,在单层液态树脂膜厚30 μm,曝光光束功率0.15 μW,扫描速度15 μm/s以及工作距650 μm时能够得到具有较高精度线宽和线高的固化直线段,利用优化的工艺参数,成功实现了三维微小实体结构的成型制造。     

[材料成形中的数字化与智能化产品设计]6016铝合金汽车典型结构件固溶成形工艺研究

以某车型铝合金汽车后风挡下横梁为研究对象，利用PAM-STAMP软件进行了一步固溶成形和分步固溶成形工艺分析。通过优化关键工艺参数如摩擦因数和成形温度，结合相应的工艺实验，建立了工艺仿真模型；通过对测量路径上壁厚分布的实验值与数值模拟值进行误差对比分析，判断成形工艺合理性。结果表明：汽车后风挡下横梁采用一次成形方式容易在中间形变突变处造成开裂或减薄现象，随着摩擦因数增大，最小厚度急剧减小；相比一次成形方式，采用分步成形方式，最小减薄率减小了4.67%，回弹量减小了40.21%，温度与摩擦因数对最小厚度的影响较小；经时效处理后进行力学性能检测，铝合金汽车后风挡下横梁抗拉强度达到308 MPa，表明采用固溶成形工艺是可行的。     

面曝光固化快速成型曝光时间的参数优化研究

面曝光快速成型是光固化成型领域快速高速发展的一种工艺,曝光时间是成型工艺中的关键参数之一,对于成型质量有直接关系:若曝光时间过短,正在固化的树脂层硬度不够,在重力的的作用下会使其下落,进而影响下层树脂的固化,一层影响一层,最终使得逐层固化的树脂精度不高,导致制件变形较大;若曝光时间过长,正在固化的树脂硬度会比较高,但是其收缩也会比较明显,同时会在固化层和树脂槽之间会产生真空,真空力会使打印金属平台上升时所产生的拉力增大,容易造成固化层脱落遗留在树脂槽中,导致打印物件制造失败。通过比较不同曝光时间下样品的凝胶含量和双键转化率两大指标,确定样品随着曝光时间的增加固化程度也在不断增加;然后通过比较不同曝光时间下样品的拉伸储能模量,发现样品随着曝光时间的增加力学性能也随之增强。通过综合比较固化程度、成型力学性能、成型精度三大因素,确定整体成型最佳曝光时间。通过两个分层试验验证了前述最佳曝光时间的合理性。     

酚醛树脂/石墨模压成型复合材料双极板的制备与性能

以石墨与酚醛树脂粉料为原料通过低温热模压成形工艺制备低成本酚醛树脂／石墨复合材料双极板，对材料的力学性能与导电性能进行了研究。结果表明：酚醛树脂含量是影响复合材料导电性能与力学性能的主要因素，酚醛树脂含量低于20％时，材料具有较高的导电性能；提高固化温度与固化压力，可以提高材料的抗弯强度，但材料的导电性能明显降低；适中的固化压力与固化温度有利于材料具有较好的力学性能与导电性能。     

辊弯成形力影响因素作用的机理分析

为研究成形力影响因素，根据定半径成形法建立了6道次辊弯成形的仿真模型。通过实验测量了不同板材每道次的成形力和同一板材变形后弯角区相同位置的硬度，分析了立边长度、加工硬化、板厚对成形力的影响。结果表明，成形力随板宽的增加有不显著的增大趋势；成形力与板厚的平方近似成正比；成形力与弯角区硬度呈现相同的变化规律。     

熔融挤压堆积成形的原型精度分析

从分层叠加制造的基本原理出发，通过几何运算，建立了用于分析原理性误差的理论公式。该公式适用于ＲＰ技术的各种工艺方法，具有普遍意义；通过成形实验，探讨了几咱不同聚合物材料的成形精度规律。结果表明，试件的实测结果与理论值吻合。同时发现，当采用结晶型材料，由于其具有较大的线收缩率，将造成较大的尺寸误差。     

考虑可靠度的成形极限曲线建立方法

实验获得板材成形极限的方法是通过对不同加载路径下获得的极限应变点进行拟合,从而得到成形极限曲线。将百分回归分析理论应用到成形极限实验数据点的曲线拟合方法中,利用该方法可以对成形极限曲线的百分位值进行分析和预测,可以在给定的实验可靠度和置信度下,根据实际需要调节曲线的位置,同时为给定极限应变点分布带的上下限的确定提供理论依据。     

缩口件不同过渡段形式的变形机理研究

研究缩口件过渡段变形成形机理。将宏观塑性理论的能量法及矢量分析解法相结合，建立了缩口件不同过渡形式的克服总能量的理论模型，通过对不同过渡形式的铜管缩口实验，验证了理论模型的准确性，此外，依据所建立的理论模型，分析了不同过渡形式对成形的影响，可知，直线段过渡所克服阻力最小，凹圆弧过渡所克服阻力最大，在此基础上，给出了缩口件过渡优化策略，并通过实验验证了策略的有效性。得到的变形规律可为精密缩口工艺控制提供了方法和依据。     

Development of micro-stereolithography technology using a UV lamp and optical fiber

Micro-stereolithography technology makes it possible to fabricate free-form three-dimensional (3D) microstructures using a focused UV beam with a very small focal diameter to solidify a UV-curable liquid photopolymer. Generally, expensive UV lasers and complex optical systems are required. However, in this study, we developed a more economical and simpler micro-stereolithography technology using a UV lamp as a light source and optical fiber as the light delivery system. We conducted photopolymer solidification experiments to examine the characteristics of the developed micro-stereolithography apparatus. To achieve an adequate solidification width and depth, a photostabilizer was mixed with a conventional photopolymer and then tested. The developed apparatus could be used to fabricate 3D microstructures by modifying the fabrication conditions for a given photopolymer. Several 3D microstructures were fabricated.     

Micro-stereolithography photopolymer solidification patterns for various laser beam exposure conditions

Micro-stereolithography is a novel micro-manufacturing process that fabricates 3D microstructures by solidifying the photopolymer using a UV laser in a layer-by-layer fashion. In this paper, variation in the photopolymer solidification pattern due to the scanning pattern and pitch of a focused laser beam was investigated experimentally. Also, experiments were conducted to determine the effects of the layer thickness on the solidification width and depth in multi-layer solidification. The experimental results were compared to numerical simulations. The results showed that a zigzag-shaped scanning pattern was faster and more stable than a crank-shaped pattern. It was also determined that the scanning pitch should be selected according to solidification depth and width for a given scanning pattern, and that the layer thickness has little effect on the solidification depth. Based on the results, several microstructures were successfully fabricated, such as a micro-tube with a helical separation wall and a microlink.Nomenclature P_L The power of the laser beam - The wavelength of the laser beam - f The focal length of the focusing lens - z The depth from the surface of photopolymer - V_S The scanning feed of the laser beam - W₀(z) The Gaussian half-width of the focused laser beam at a given depth z - E_C The critical exposure of the photopolymer - D_P The penetration depth of the photopolymer - W_{0 min} The Gaussian half-width at the focal point - R The Gaussian half-width of the laser beam that passes into the focusing lens - w The scanning width of the laser beam - L The solidified width of the photopolymer - h The solidified depth of the photopolymer - D₁ The layer thickness - D₂ The total solidified depth in a multi-layer solidification     

CURING PROCESS OF PHOTOPOLYMER RESIN BOND DIAMOND TOOLS

Analytical simulation and corresponding proof-test are adopted to study the principle of the curing process of photopolymer resin diamond tools. The influence of the diamond as abrasives in photopolymer resin owing to the absorptivity of the diamond for the UV light on the photopolymer resin curing process is discussed. Based on the above, a kind of diamond tool—dicing blade is selected to analyze the curing process of photopolymer bond diamond tools. An analytical model of curing process is developed and a correlation curve between the depth of polymerization of the photopolymer resin diamond tools and the exposure time to represent the curing process of photopolymer bond dicing blade. A test is done to proof-test the validity of the analytical model and the correlation curve. The simulated data fit the experimental results, which demonstrates the analytical models and numerical algorithm are of high reliability. The analytical simulation method could possibly be used to optimize the curing cycle and improve the quality of the photopolymers resin bond diamond tools.     

Curing Characteristics of the Photopolymer Used in the Solid Laser-Diode Plotter RP System

Most stereolithography (SL) processes employ ultraviolet (UV) or diode pumped solid state lasers to cure the associated photopolymer to build a 3D part. A UV or diode pumped solid state laser is more expensive in initial cost and maintenance than a semiconductor laser. A semiconductor laser is used in the solid laser-diode plotter (SLP) rapid prototyping system to cure a specific photopolymer (DF2000). The DF2000 photo-polymer is formulated from a based resin, hardening agent, and powder. The wavelength of the semiconductor laser used in the SLP system is 680 nm and is in the range of red colour light. In this work, the curing effect of the visible wavelength spectrums generated by a lamp on the DF2000 photopolymer was investigated, using differential scanning photo calorimetry (DSPC). The DSPC result indicates that the curing degree of the photopolymer using blue light is better than that when using red light. The result also seems showing that the shorter the wavelength, the better the curing effect of the photopolymer. Hence, a blue semiconductor laser (405 nm) or a shorter wavelength laser or even a higher-power lamp, instead of a red laser, can be employed to increase the curing degree of the photopolymer used in the SLP system. The quantitative effect of the SLP processing parameters on the curing degree of DF2000 photopolymer and the mechanical property of the SLP test specimen was studied using the Taguchi method. The results show that the mechanical property of a fabricated part is proportional to the curing degree of the photopolymer. The results also indicate that the scanning pitch of processing parameters is the most sensitive parameter of the SLP system affecting the curing degree and, hence, also affecting the mechanical property. Therefore, the curing characteristics of the photopolymer used in SLP system could be used as an index of the mechanical property of a fabricated part. Also, the employment of a shorter wavelength laser rather than red laser can further improve the part mechanical property and fabrication speed of the part.     

导电性光固化树脂结合剂锯片的研制

采用光固化树脂作为结合剂制作金刚石锯片是近年来快速制造领域里的一个新型制造工艺,针对各种材料进行的切割试验也验证该项技术的可行性和实用性。在使用过程中发现锯片的导电性是一个非常重要的性能要求。对高分子材料的导电性研究进行比较,分析几种不同的实现光固化树脂导电性的途径,找出适合光固化树脂结合剂锯片的有效方法。通过采用镀铜金刚石作为磨料并适量添加导电铜粉,利用试验手段调整配方,最终达到了在光固化树脂结合剂超薄锯片的制造中实现具有导电性的目的。     

Micro-rapid-prototyping via multi-layered photo-lithography

Rapid prototyping (RP) is widely used for part fabrication in the normal scale. For fabrication in micro-scale applications such as integrated circuit (IC), micro-electro-mechanical system (MEMS), methods such as surface and bulk machining are commonly used. This paper introduces a micro-fabrication technique using the RP principle, i.e., layered manufacturing, combined with mask-based micro-lithography, which is usually used in semiconductor industry. An ultraviolet (UV) excimer laser at the wavelength of 248 nm was used as the light source. A single piece of photo-mask carrying various patterns of multiple layers obtained from slicing a three dimensional (3D) micro-parts was employed for the lithography process. The preliminary results show that a certain RP photopolymer can be applied for the micro-RP, and solid layers with sharp edges can be formed from the liquid photopolymer identified. Using a unique alignment technique, a five layered gear of 1 mm in diameter has been successfully fabricated using the proposed method .     

SolTrack: an automatic video processing software for in situ interface tracking

High-Resolution in situ observation of solidification experiments has become a powerful technique to improve the fundamental understanding of solidification processes of metals and alloys. In the present study, high-temperature laser-scanning confocal microscopy (HTLSCM) was utilized to observe and capture in situ solidification and phase transformations of alloys for subsequent post processing and analysis. Until now, this analysis has been very time consuming as frame-by-frame manual evaluation of propagating interfaces was used to determine the interface velocities. SolTrack has been developed using the commercial software package MATLAB and is designed to automatically detect, locate and track propagating interfaces during solidification and phase transformations as well as to calculate interfacial velocities. Different solidification phenomena have been recorded to demonstrate a wider spectrum of applications of this software. A validation, through comparison with manual evaluation, is included where the accuracy is shown to be very high.     

Fabrication of suspended micro-structures using diffsuser lithography on negative photoresist

We report the results of diffuser lithography applied to a negative-type thick photoresist to fabricate 3-dimensional microstructures suspended on supports. When UV light passes through a diffuser film, the direction of the light is randomized because of the irregular surface of the diffuser. By exposing through a diffuser on a Cr-mask, a circular or an elliptical cross-section of exposed region can be formed on a spin-coated photoresist. When applied to a negative-type thick photoresist, diffuser lithography gives a 3-dimensional circular cross-section of the exposed and cross-linked regions, which could be used for making suspended microstructures. The size of the exposed region has been controlled by the dose of the UV light. The current study clearly shows that the depth of exposed region of photoresist is affected by the geometry of the pattern. By controlling the depth of the exposed region using different pattern size, beam structures suspended on the support structures could be fabricated by single exposure process. The characteristics of the diffuser lithography process were investigated on a negative type photopolymer, SU-8, with different doses of UV-light and different geometry.     

A combined additive manufacturing and micro-syringe deposition technique for realization of bio-ceramic structures with micro-scale channels

This article presents a novel rapid layered manufacturing approach based on a combined additive manufacturing (AM) process and a UV-based micro-syringe deposition (μSD) technique to be used in the fabrication of bio-ceramic structures with controlled micro-sized channels for bone and osteochondral tissue regeneration. In the proposed rapid manufacturing method, micro-scale sacrificial photopolymer networks are integrated within the manufactured part by depositing the photopolymer on selected bio-ceramic powder layers using an injection system. This AM–μSD method along with a post-processing protocol can potentially overcome current limitations of traditional powder-based AM approaches that are restricted in terms of complexity of internal architecture and feature size. For bone or osteochondral repair applications, the material system composed of the bio-ceramic and sacrificial photopolymer, along with the post-processing protocol, must ensure that the final implants are free from manufacturing residuals that could trigger an immune response post-implantation. In this study, calcium polyphosphate bio-ceramic was used as the substrate material based on prior art, polyvinyl alcohol solution was used as the powder binding agent, and ethoxylated (10 bisphenol A diacrylate) photopolymer solution was used as the sacrificial photopolymer element. Material characterization suggests that the proposed material system along with heat treatment protocol is suitable for the targeted applications where micro-scale channels within the implant are produced by AM–μSD.