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The effect of laser welding parameters such as laser power, laser speed, working distance and weld pressure on the weld strength, microstructure and meltdown of modified T-joints were studied using a diode laser and a contour welding technique. Specimens made of 30% glass reinforced nylon 6 were used in this study. A regression model was fitted to the data based on a central composite experimental design. The model showed that low levels of laser power at lower laser speed gave the maximum weld strength. It was observed that increases in weld pressure had a negative effect on weld strength. Meltdown was found to increase proportionally to the line energy and weld pressure.

Laser transmission welding is a relatively new technique for joining thermoplastic components in the automotive industry. Laser energy is passed through a laser-transparent part and dissipated as heat in a laser-absorbent component. There is currently no standardized test to assess the strength of laser transmission welds made using thermoplastic materials. A properly-designed test allows the weld strength of the joint to be measured accurately and rapidly. This paper reports on a technique for measuring overlap shear strength. This study compares two weld orientations (weld line parallel and perpendicular to assembly loading) using polycarbonate, polypropylene, polyamide 6, polyamide 6 reinforced with 30% glass fibres and polyamide mXD6 reinforced with 50% glass fibres. Assemblies were made using a range of laser powers. In order to simulate industrial conditions, artificial gaps were also introduced between the transparent and absorbent parts.

In Laser Transmission Welding (LTW), a laser beam passes through a transparent part and is dissipated as heat in an absorbent material through the use of laser-absorbing pigments such as carbon black (CB). This energy is then conducted further into both parts. Melting and subsequent solidification occur at the interface causing a weld to form between the two parts. Gluing or welding structures to the back of automotive Class-A panels often results in the appearance of undesirable surface deformations on the Class-A side. Through control of the laser welding and material parameters, it may be possible to use contour LTW as a means of joining structures to the back of absorbent Class-A panels without creating these unwanted surface defects. A series of lap welds was made using a range of CB levels and laser powers. A profilometer was used to measure the size and shape of the defects generated on the surface of the black part. Two types of defects were observed: ribs and sink marks.