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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.

The purpose of this study was to determine the adequacy of butt and T-shape welds in predicting the burst strength of realistic nylon 66 parts. This study assessed the effects and interactions of vibration welding process parameters using a central composite design of experiment on selected part geometries. The results confirm that butt-welded plaques exhibit higher weld strengths under tensile load than T-welded plaques and simple cup-plaque parts. These latter two welds were typically 50% weaker than butt welds. A comparison of weld strengths suggests that the lab-scale T-joint geometry more closely models more complex vibration welded parts.

Discontinuously reinforced thermoplastic composites are used in a wide variety of automotive applications due to their excellent mechanical properties and low processing cost. The mechanical properties of these short/long fiber reinforced materials can be improved by using continuous fibers. However, processing these continuously reinforced composites is more difficult due to the inextensible nature of the fibers. It is possible to combine the ease of processing of discontinuously reinforced thermoplastics with the superior mechanical properties of continuously reinforced materials by creating a hybrid part. The two different materials can be married using a number of technologies such as overmoulding and joining. In this research, vibration welding is used to join polypropylene reinforced with continuous glass fibers to other polypropylene compounds. Lap and T-style joints have been made using an instrumented linear vibration welder.

The objective of this study was to compare mechanical properties of lab-scale vibration welded test specimens with those of a complex automotive component using several different materials. Different laboratory specimens (butt, Tee, cup-plate with/without flash trap) were made under different vibration welding conditions (weld pressure, meltdown) and then tested in tension. The tensile properties of the specimens were then compared with the burst pressure results from a prototype air intake manifold. 30% glass reinforced nylon 66 and polypropylene compounds were used. The lab scale specimens and manifolds showed similar trends: (i) all parts failed at the weld; (ii) increased weld pressure generally caused decreased weld strength (iii) meltdown was observed to have little effect on part strength (iv) the ratio of lab specimen strength to burst strength was comparable but not equal for the materials tested. Flash traps significantly affect weld strength when over filled.

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.

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.

Resistive Implant Welding (RIW) is a technology that has the potential to join large thermoplastic automotive components. It involves placing an electrically conductive implant between two parts that are mated under pressure. Heat, dissipated at the interface by direct current, causes melting, flow and ultimately welding to occur. This research examines the RIW of long-glass-fiber reinforced polypropylene (LGF-PP) to continuous-glass-fiber reinforced polypropylene (CGF-PP) using a stainless steel mesh-implant. The effects of welding time, applied current, and weld pressure on the temperature near the mesh, meltdown and the compression-shear strength of the welds were assessed. The results show that it is possible to attain shear strengths of the order of 20 MPa under optimized welding conditions. The meltdown and strength correlate well with a semi-empirical lumped parameter dependent on weld-time, current squared and pressure.