Process development for the efficient production of SMA springs

SMA are thermosensitive materials that change their geometry depending on the temperatures and further show elastic properties in certain temperature ranges. Due to these characteristics, springs made of SMA are of particular importance, as large forces and strokes can be realized at precise switching temperatures as well as large reversible expansions. In particular, the self-sufficient mode of operation, i.e. activation by the ambient medium, predestines SMA springs for self-regulating applications, for example in the field of thermal management. However, the production of FG springs is relatively complex compared to conventional springs, as tools are required for heat treatment after winding.

The project aims to develop a new manufacturing process for SMA springs. The desired process is characterized by no need for a tool during forming and heat treatment. Compared to the state of the art, this results in a reduced process chain that allows efficient production of wire components with shape memory. In contrast to conventional spring materials, the complex material behavior of shape memory alloys requires a simulation-based analysis of the specific process. Using finite element models, permanent deformations in the component can be predicted to enable heat treatment without tools by specifically adjusting the degree of deformation.  In practical tests, springs are produced both with and without tools in order to compare the two processes. The performance of the realized springs is evaluated on a test bench. The results on the influence of the process parameters on the spring characteristics are then used in the modelling and an optimized process design.