The laser welding of copper using the integrated keyhole and weld pool model and continuous CO2 and Nd:YAG lasers

Abstract

The laser welding of materials like stainless steel is a successful and well established process. If instead materials like copper and aluminium are used, the thermophysical properties of these materials may produce difficulties. Here, the welding of copper has been studied experimentally and by means of a mathematical model, using a continuous CO2 laser beam of high intensity without precoating the surface of the copper specimen. A successful laser welding process can be earned out by the careful coupling of the laser beam to the weld specimen with a suitably designed gas jet and shielding gas system. The experiments carried out mainly concentrated on the use of 7 and 9 kW of continuous total laser power with N2 as the jet gas and helium as the shroud gas, though some experiments employed argon with N2 as the shroud gas. Laser welding with a continuous CO2 beam was found to break down at translation speeds above about 30 mm s−1. The thickness of the copper sheet was 3.25 mm. This paper clarifies the nature of the underlying fundamental physical processes responsible. The possibility that the gas jet and shroud configuration leads to an enhancement of the inverse bremsstrahlung absorption process in the keyhole at its mouth and in the associated nearby region of the plasma was analysed. If instead a pseudo continuous Nd:YAG laser were to be used, no inverse bremsstrahlung absorption process would be expected to arise in the keyhole or the plume region near its mouth. The entire absorption of laser energy would arise from Fresnel absorption on the walls of the keyhole and its values would be enhanced over that for the CO2 case as a result of the dependence of Fresnel absorption on wavelength. This paper presents an interaction of experiment and theory in discovering the part played by fundamental physical processes in the welding copper with continuous lasers.The laser welding of materials like stainless steel is a successful and well established process. If instead materials like copper and aluminium are used, the thermophysical properties of these materials may produce difficulties. Here, the welding of copper has been studied experimentally and by means of a mathematical model, using a continuous CO2 laser beam of high intensity without precoating the surface of the copper specimen. A successful laser welding process can be earned out by the careful coupling of the laser beam to the weld specimen with a suitably designed gas jet and shielding gas system. The experiments carried out mainly concentrated on the use of 7 and 9 kW of continuous total laser power with N2 as the jet gas and helium as the shroud gas, though some experiments employed argon with N2 as the shroud gas. Laser welding with a continuous CO2 beam was found to break down at translation speeds above about 30 mm s−1. The thickness of the copper sheet was 3.25 mm. This paper clarifies the natu...