An experimental and numerical study of laser impact spot welding

A novel solid state spot welding technique is developed, which utilizes laser induced shock waves to accelerate the flyer plate towards the base plate to obtain spot joining of similar or dissimilar metal plates. As a kind of no-contact, cold, and low energy input process, laser impact spot welding of Al/Al and Cu/Al with different weld spot dimensions were achieved by using 3. mm and 5. mm laser spot diameters, respectively. The surface quality of the cold weld spots maintained good. However, the dimensions and the surface morphologies of the weld spots were greatly affected by the standoff distances. Flat and wavy interfaces with un-bonded regions at the centers of the metal plates were observed through metallographic analysis for the cross-sections of the weld spots. It was found that the wavelength and amplitude of the interfacial wave varied along the weld interface due to the dynamical change of the impact angle. The nanoindentation hardness values of the joint interface regions were measured to analyze the mechanical properties of the weld joints. In addition, the finite difference engineering package AUTODYN with Smoothed Particle Hydrodynamics (SPH) method was employed to simulate this welding process. It was shown that the opposite shear stress direction and effective plastic strain above a certain threshold in the studied materials should be essential to successfully achieve this novelly developed welding process.