Forming Limit and Fracture Mode of Microscale Laser Dynamic Forming

The microscale laser dynamic forming (LDF) process is a high strain rate microfabrication technique, which uses a pulse laser to generate high pressure by vaporizing and ionizing an ablative coating, and thus produces complex 3D microstructures in thin foils. One of the most important features of this technique is ultrahigh strain rate (typically $106–7s−1$⁠), which is theoretically favorable for increasing formability. However, due to the lack of measurement techniques in microscale and submicroscale, the formability of workpieces in LDF is hardly studied. In this article, experiments were carried out on aluminum foils to study the forming limits and fracture of thin films in LDF. The deformation depth was measured by an optical profilometer and the formed feature was observed using a focused ion beam and a scanning electron microscope. Meanwhile, a finite element model based on a modified Johnson–Cook constitutive model and a Johnson–Cook failure model was developed to simulate the mechanical and fracture behaviors of materials in LDF. Experimental results were used to verify the model. The verified model was used to predict the forming limit diagram of aluminum foil in LDF. The forming limit diagrams show a significant increase in formability compared with other metal forming processes.