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

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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.