Advanced Process Chains for Prototyping and Pilot Production based on Direct Rapid Soft Tooling

Abstract

In precision engineering, fast and economic prototyping and pilot production is essential for industrial manufacturers. Additive manufacturing, considered a potential key player for such tasks, comes with a number of unique advantages as well as significant drawbacks. On one hand, additive manufacturing enables the use of different design rules, fast production, and manufacturing in advanced materials such as photopolymers. On the other hand, material choices are limited when compared to mature technologies such as injection molding. Advancement in material science as well as printing technology have led to the establishment of Direct Rapid Soft Tooling (DRST), the direct manufacturing of tools for injection molds by additive manufacturing technologies such as light reactive photopolymer curing. The focus of this thesis is to establish the foundation for implementation of DRST into precisionengineering process chains satisfying industrial requirements. At the time of this research, the performance of a single DRST insert is reported to enable the production of up to low three-digit numbers of injection molded parts. Available print materials usually allow either high accuracy or high temperature resistance. Heat deflection, wear, and accuracy are among the key challenges. In addition, production based on injection molding with DRST inserts is challenging to predict. Injection molding parameters such as cycle time or injection pressures are significantly different to conventional injection molding production. This research focuses on analyzing the most critical aspects of the DRST process chain including achievable precision and accuracy, design, simulations, and economic as well as environmental consequences. Premanufacturing considerations included the modeling and comparison of different manufacturing process chains for establishinga method to choose the most appropriate one. Three different DRST insert designs were developed comprising numerous geometric features to test the process chains for their capabilities to conform to precision engineering requirements, including a satisfactory insert lifetime, surface quality including realization of submillimeter structures, and dimensional accuracy. Thermal simulations were used to predict cycle times, to quantify and locate temperature peaks, and to compare performance to conventional injection molding production with metal inserts. Life Cycle Analyses were conducted to determine the environmental impact. A cost model for DRST inserts printed using light reactive photopolymer curing was developed to calculate the economic consequences. Lifetime was extended by an order of magnitude when a DRST insert printed ina ceramic-plastic composite was still intact after the production of 10 000 parts in ABS. Material reinforcement by carbon fibers prolonged the lifetime of a DRST insert up to more than 2 500 parts. The environmental impact of DRST inserts was found to be significantly lower than that of metal inserts for production in the lower three-digit numbers. The economic benefits were found to be significant with savings between 73% and 91% in a production scenario of 100 injection molded parts. The thermal simulations were in good agreement with the measurements during experiments and provided valuable information about cycle time optimization and heat transfer throughout the injection molding cycle. Vat photopolymerization enabled the generation of parts containing submillimeter surfaces, both in direct printing as well as in injection molding process chains with DRST inserts. This research contributes to a better understanding of process chains based on DRST for the production of polymer parts, thereby facilitating their implementation in industrial manufacturing. New additive manufacturing materials as well as the improvement of existing ones led to a significant improvement of insert lifetime. In certain circumstances, process chains based on DRST can enable high precision production of polymer parts including microstructure surfaces. Implementing DRST process chains can significantly save time and reduce costs as well the environmental impact.