Experimental and Numerical Investigation of Deformation Behaviours of Copper Sheet in Multi-Pulse Microscale Laser Dynamic Flexible Forming
Z-B. Shen, L. Zhang, Y-Y. Lin, K. Liu, G-Y. Zhou, Y. Wang, P. Li, J-D. Zhang, H-X. Liu and X. Wang
Microscale laser dynamic flexible forming (μLDFF) is a new kind of high velocity forming (HVF) process, in which the desired microfeatures can be obtained under the action of laser shock. The forming depth of workpiece depends primarily on laser power density, so the high laser power density is used to form deep microfeatures. The fracture will occur when the forming velocity imparted by the high power density exceeds the critical forming velocity. To overcome this problem, single pulse µLDFF is extended to multi-pulse µLDFF in this work, and multipulse free forming experiments were carried out. The forming depth increases with the number of laser shocks, and the first laser shock make a major contribution to the total forming depth. The roughness of the unconstrained surfaces increases with the number of laser shocks. A three-dimensional (3-D) finite element method (FEM) model is also built to simulate the multiple laser shocking process, and the predicted 3-D surface morphology are compared with the experimental results to validate the accuracy of the simulation model. The 3-D comparisons results indicate that geometric inaccuracy occurs, which may be due to multiple shocks of the high velocity air flow induced by the high velocity deformation of workpiece under atmospheric condition. In addition, the unconstrained surface roughening may, in turn, affect the geometry of workpiece. With the increase of the times of laser shocks, the loading mode varies from plane/plane impact to curved surface/curved surface impact. The deformation behaviours of workpiece under the different loading modes are characterized.
Keywords: Nd:YAG laser, copper sheet, microscale laser dynamic flexible forming (μLDFF), multiple pulse, free forming, surface roughening, geometric inaccuracy, loading mode, finite element method (FEM)