Influence and Limits of Sintering Temperatures on the Movability of Shaft-To-Collar Connections Formed by Two-Component Micro Powder Injection Moulding

Two-component micro powder injection moulding (2C-MicroPIM) is a special variant of micro injection moulding. It enables the integration of two different functions in one micro assembly due to the combination of different materials. By 2C-MicroPIM it is possible to realise fixed and movable connections. For both applications, the two components have to be adapted well to each other. The adaptation has to cover the materials as well as the processes. In this context, especially the sintering process is of importance since the degree of shrinkage and physiochemical processes at the interface between both components determine either the formation of a fixed junction between the components or the formation of a gap. Both processes are temperature-dependent. Therefore, it can be assumed that by a certain temperature these processes can affect the interface in such a way that it may get in conflict with the formation of movable connections, i.e., there is a limiting temperature at which the components are not joined together. Above this temperature joining of the components occurs at least partially. For this study, shaft-to-collar connections were produced by 2C-MicroPIM. They consist of a gear wheel made of zirconia feedstock and an axle made of alumina feedstock. The 2C-MicroPIM process has influence on the characteristics of the micro parts, like functionality, density and mechanical properties. This work focuses on movability of the shaft-to-collar connection as the most important function. The sintering temperature required for movable connections constitutes important limits for the overall process. The aim of our presented work is to determine the limit temperature or temperature range at which movable connections cannot be formed due to the mentioned processes. Furthermore it was analysed if there is a smooth transition from movable connections to unmovable connections with increasing temperature or if this transition takes place within a small temperature range. Within a given temperature interval the portion of movable connections out of all sintered samples were counted for each peak temperature. The results showed that the number of movable connections decreases with increasing peak sintering temperature. Hence, production of movable connections has a limit with respect to sintering temperature. This temperature limit was found to be sharply defined at around 1,460–1,470°C.