In-process monitoring in laser welding of automotive parts

Abstract

Spectral study was carried out to characterize laser induced plasma plume in terms of temperature and electron density in CO2 laser welding of mild steel sheet (0.8 mm thickness). The size and local properties of the plasma plume were determined by means of the Abel inversion technique and CCD camera observation. It was found that the height of the hot plasma core was very small, less than 0.5 mm. The maximum electron density in the plasma plume was approximately 1017/cm3 where the absorption loss of CO2 laser beam via inverse Bremsstrahlung was negligible in the plasma plume. In-process monitoring system using multi photo sensors with different aiming angles was developed to monitor CO2 laser welding of automotive parts, and effects of welding parameters including laser power, welding speed, flow rate of shielding gas and focal position were determined on the light intensity emitted from the welding zone. It was demonstrated that weld defects such as underfill and pits in lap and butt weld joints for aut...