A state-of-the-art digital light processing 3D printing material and process for production of investment casting sacrificial patterns

熔模铸造（IC）是制造近净形金属零件的最古老和最通用的方法之一。集成电路可以提供具有复杂几何形状，薄壁，极好的表面光洁度和高尺寸精度的零件，能够制造不同行业中使用的大多数金属材料。然而，集成电路方法的主要缺点是开发周期长，模具制造成本高。具体来说，在高价值制造业中，快速开发、低订单量、短产品生命周期、几何复杂性和定制设计的需求最高，传统的熔模铸造方法非常昂贵且速度缓慢。然而，增材制造（AM）通过减少IC中使用的牺牲模式的生产前置时间和成本来改变这一缺点。模式可以通过AM技术直接生产，完全消除了对注塑工具和注射过程的需求，这通常占产品开发成本的三分之一和开发前置时间的一半。对于定制产品，如生物医学植入物，这些估计甚至更高。在众多增材制造方法中，还原光聚合是一种在光照下选择性固化液态光树脂的方法，以其低成本、优异的分辨率和高扩展性而闻名。数字光处理（DLP）是一种还原光聚合技术，在这种技术中，部件的整个横截面一次光固化，使该过程比其他技术更快。本文将研究这种增材制造技术及其在集成电路中的应用。虽然材料喷射和立体光刻印刷方法在集成电路应用中已经研究了很长时间，但目前很少有学术文献和有限的工业报告使用DLP系统来生产成本效益高、快速和准确的集成电路图案。因此，需要定义一种方法来开发一套工艺和材料，以便在铸造模式生产中广泛使用DLP方法。然而，挑战在于开发树脂混合物，打印工艺和处理/组装程序，以提供以下内容：1)印刷和印刷后过程中的最小收缩；2)印刷过程中残余应力最小，避免印刷后变形；3)花样烧尽后灰分最小；4)烧尽过程中热膨胀最小，避免IC陶瓷模具开裂和断裂；5)最佳打印分辨率、表面光洁度和几何印刷适性；6) AM-IC图案的最佳处理和存储条件，以及在需要时将陶瓷芯嵌入AM-IC图案的最佳方法。本研究旨在设计，验证和验证DLP系统和材料，以实现IC模式的最高铸造性，尺寸和几何精度以及成本效益。为了实现这一目标，定义了以下目标：-开发一种方法，以更好地研究和理解燃烧AM-IC模式以及燃烧过程中的热膨胀和气体膨胀。它可能包括物理和计算机辅助有限元模拟方法。-修改光固化树脂材料和DLP 3d打印工艺，通过减少打印和打印后的收缩和残余应力，以达到最佳的尺寸精度和几何可打印性，从而最大限度地减少/控制打印和打印后阶段的零件变形。-通过在树脂中加入添加剂，改进辞去混合材料，调整图案去除操作来提高去除图案的工艺能力，以防止损坏陶瓷模具。开发和验证一种方法，以最好地存储，处理和组装AM-IC图案，并在保持其尺寸精度和功能的同时将陶瓷芯装入图案中。

Investment Casting (IC) is one of the oldest and most versatile methods of manufacturing near net shape metal parts. IC can deliver parts with intricate geometries, thin walls, superb surface finish, and high dimensional accuracy with an ability to manufacture most metallic materials used in different industries. However, the main shortcoming of IC method is its rather long development lead-time and high toolmaking cost. Specifically, in high-value manufacturing where fast development, low order quantities, short product life cycles, geometrical complexities, and customised designs are in highest demand, conventional investment casting method is prohibitively expensive and slow. However, additive manufacturing (AM) is set to change this shortcoming by reducing the production lead time and cost of sacrificial patterns used in IC. Patterns can be directly produced by AM techniques to entirely eliminate the need for the injection moulding tools and the injection process, which often comprise up to one-third of the product development cost and up to half of the development lead-time. These estimations are even higher for customised products such as biomedical implants.Among many AM methods, Vat Photopolymerization process in which a liquid photo-resin is selectively solidified under light illumination, is known for its low cost, excellent resolution and high scalability. Digital Light Processing (DLP) is one of the Vat Photopolymerisation techniques in which the whole cross-section of the part is light cured at once making the process faster compared to other techniques. This AM technique and its application in IC will be studied in this research.Research GapAlthough material jetting and stereolithography printing methods have been long studied in IC applications, there is currently little academic literature and limited industrial reports on using DLP systems to produce cost effective, fast and accurate IC patterns. Thus, one needs to define a methodology to develop a set of processes and materials to enable a wide use of DLP method in the casting patterns production. However, the challenges are to develop a resin mix, print process and handling/assembling procedure to offer the following: 1) minimum shrinkage during printing and post printing processes; 2) minimum residual stress during printing process to avoid deformations after printing; 3) minimum ash-content after pattern burn-out process; 4) minimum thermal expansion during burn-out process to avoid cracking and breaking IC ceramic mould; 5) best print resolution, surface finish and geometrical printability; 6)best handling and storing conditions for AM-IC patterns and best method to embed a ceramic core into an AM-IC pattern when needed. Aims and objectivesThis research aims to design, verification, and validation of a DLP system and material to achieve the highest castability, dimensional and geometrical accuracy, and cost effectiveness for IC patterns.To achieve this aim, the following objectives are defined:- To develop a methodology to better study an understand burning AM-IC patterns and thermal and gas expansion during burn-out process. It may include physical and computer-aided finite element simulation methods.- To modifying the photocurable resin material and the DLP 3D-printing process to achieve the best dimensional accuracy and geometrical printability by reducing the shrinkage and residual stress during printing and post-printing, in order to minimise/control deformation of the part during print and post-print stages. - Enhancing pattern removal process capability by introducing additives to the resin, improving resign mix materials, and adjusting the pattern removal operations, in order to prevent damage to the ceramic mould. - Develop and validate a method to best store, handle and assemble AM-IC patterns and to fit the ceramic cores inside the patterns while maintaining its dimensional accuracy and functionality.