Thesis Abstracts 2001
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Improving Vibration Weld Joint Strength through Process and Equipment Modifications
By: Capt. Brenda Tucker
Abstract
Vibration welding is an important process used to join thermoplastic components. Currently, under optimized low pressure welding, the weld strength of butt joints of unreinforced polymer can be equivalent to the strength of unwelded material.
However, for short glass fiber reinforced polymer, the optimized weld strength is significantly lower than that of unwelded material and is closer to the strength of the resin matrix. The cause of this lower strength is attributable to the unfavourable reorientation of the short glass fibers in the weld plane. This work examined the impact of various modifications to the existing vibration welding technology, with the objective of producing a more favourable orientation of fibers in the weld plane. If these fibers could be oriented more randomly, or, ideally, perpendicular to the weld plane, the tensile strength would significantly increase.
The modifications involved removal of the weld pressure in two different phases of the existing weld process; the introduction of an elongation of the welded region prior to cooling; and the oscillation of the welded region during welding. The latter caused the weld strength to be increased by as much as 20% at the higher weld pressures. The cause of this improvement was a more random orientation of fibers in the weld plane. The optimized strength of low pressure welding with the existing technology could not, however, be surpassed. A potential advantage of this oscillation process is that the optimum weld strength can be achieved at high weld pressures, without the disadvantage of the longer cycle time associated with low weld pressures. Patent protection for this development is currently being sought. Work was conducted using short glass fiber reinforced nylon supplied by Dupont Canada. The welding and testing was done on an instrumented laboratory vibration-welding machine located at the Queen's University Centre for Automotive Materials and Manufacturing. The mechanical testing was performed at Alcan International, Kingston Research and Development Centre.
