Effects of part-to-part gap and the variation of weld seam on the laser welding quality

Abstract

Laser welding is an emerging joining technique for automotive industry. Due to the complex process, the control of laser welding quality problem such as spatter, porosity, and undercut is not easy. Traditional mechanical testing of weld is time consuming, costly, and inefficient for on-line monitoring of laser welding quality. In this regards, this thesis aims to estimate the laser welding quality in a non-destructive way by using the geometry of top weld seam of weldment. The most challenging task which is covered in this thesis is the estimation of the tensile shear strength in a non-destructive way. Experimental analysis reveals that the existence of two types of correlation in the variation of weld seam and tensile shear strength in the laser welding of galvanized steel: (1) positive correlation exists between the log-transformed average width of the top weld seam and maximum tensile shear strength, and (2) negative correlation exists between the variation of the width of top weld seam and maximum tensile shear strength. These correlations exist only when top weld seam having non uniform seam boundary. However, weld seam having uniform seam boundary do not have sufficient evidence of the correlation between the variation of weld seam and tensile shear strength. The reason for this is due to the high value of standard deviation of the average width of the top weld seam. Width of weld seam is more responsible for tensile strength rather than variation of weld seam.