Influence of Punch Velocity on Spring Back in Micro Forming

In macro forming it is already known, that the punch velocity has an influence on the deep drawing process. This influence is considerably induced by the velocity dependent friction behavior between sample and tool. A further influence is the strain rate dependent forming behavior of the material. In micro range, the influence of punch velocity on the deep drawing process could, due to the size effects, be different from that in macro range, for example the spring back behavior. In this article the influence of punch velocity on the spring back behavior in micro deep drawing is investigated using strip drawing test with two different widths (1 mm and 2 mm). Experiments with aluminum strips with a thickness of 50 µm were performed with punch velocities ranged from 1 mm/s to 1000 mm/s. The strain behavior, which occurs with different punch velocities are investigated on the basis of microsections. The spring back of all samples was measured by an optical measurement system and compared with each other. From the reported work it can be concluded, that with increasing punch velocity the spring back of the complete system is increasing, while the spring back at cup wall stays constant. As reasons can be cited mass inertia effects due to the high velocities and the velocity dependent friction.