Copper based bi-metallic tooling for high pressure die casting using direct metal deposition

In high pressure die casting (HPDC) cooling time greatly affects the total cycle time. As thermal conductivity is the main governing factor, a higher thermal conductive die material allows faster extraction of heat from the casting, thus resulting in shorter cycle time and higher productivity. This thesis presents a novel approach to replace a conventional steel die by a bi-metallic die made of copper alloy in which the cavity surface is coated with a protective layer of tool steel using laser based additive manufacturing technology, Direct Metal Deposition (DMD) for high pressure die casting application. Results obtained from the finite element heat transfer analysis showed that bi-metallic die offered superior thermal performance compared with monolithic steel die. However, the main challenge lies in the deposition of tool steel on copper alloy due to the very different material properties of these two materials. Over the past decade, researchers have demonstrated interest in tribology and prototyping by the laser aided material deposition process. Laser aided DMD enables formation of a uniform clad by melting the powder onto a substrate material to form desired bimetallic component. Thus, the principal objective of this research is to investigate the feasibility of deposition of a protective tool steel layer on copper alloy substrate material to form bi-metallic structure using DMD technology for HPDC tooling. Heat transfer analysis, process and material characterization, tooling fabrication and industry evaluation have been investigated in this research to attain the stated aim. The following outcomes have been achieved from this thesis in order to develop an effective bi-metallic tooling for HPDC industries- Reduction of cycle time by employing bi-metallic die compared to that of tool steel for improvements to productivity of existing processes in HPDC; Establishment of feasibility of the application of DMD technique to deposit protective tool steel clad on completely different material i.e. copper alloy substrate; Investigation of microstructural characteristics of the DMD deposited tool steel clad on copper alloy substrate; Evaluation of mechanical properties namely, bond strength and fracture toughness of the bi-metallic structure; Analysis of thermal fatigue behaviour of the bi-metallic structure under conditions analogous to high pressure die casting environment; and Fabrication and performance evaluation of bi-metallic core pin in a semiindustrial high pressure die casting machine. The outcomes of this research offer innovative technologies based on leading edge research in laser based rapid tooling development for enhancing productivity and reducing lead time in die casting industry. This research has the potential to directly impact multi-million dollar die-casting industry through improved process efficiency, reduced cycle time and lower cost of component processing.