Determination of strain rate at laser shock forming

Abstract

Laser shock forming is a new high speed forming process based on TEA-CO₂-laser induced shock waves. In former publications laser shock forming was already presented as a process, which can be used for deep drawing, stretch drawing and cutting of thin copper and aluminium sheets. The process utilizes an on a target surface initiated plasma shock wave, which leads to the sheets forming. Several pulses can be applied at one point in order to achieve a high forming degree without increasing the energy density beyond the ablation limit. During the process, pressure peaks in the range of some MPa can be achieved. In order to classify the process in the framework of high speed forming processes, the temporal varying deformation velocity due to different materials have been identified based on a stretch drawing process by using different pulse energies. Consequently, a high speed measurement system based on the shadowing effects is designed and its suitability is shown. The maximum strain rate of 1450 s^-1 meets one of the criteria for the classification of laser shock stretch drawing as a high-speed forming process.