Factors affecting the joint strength of ultrasonically welded polypropylene composites

Abstract

Ultrasonic welding of thermoplastic composites has become an important process in industry because of its relatively low cost and resultant high quality joints. An experimental study, based on the Taguchi orthogonal array design, is reported on the effect of different processing factors on the joint strength of ultrasonically welded composites, including weld time, weld pressure, amplitude of vibration, hold time, hold pressure, and geometry of energy director. Three materials were used in the study: virgin polypropylene, and 1 0 9 4 0 and 30% glass-fiber filled polypropylene composites. Experiments were carried out on a 2000-Watt ultrasonic welding unit. After welding, the joint strength of the composites was determined by a tensile tester. For the factors selected in the main experiments, weld time, geometry of energy director and amplitude of vibration were found to be the principal factors affecting the joint properly of ultrasonically welded thermoplastic composites. Glassfiber fdled polymers required less energy for successful welding than the non-filled polymer. The joint strength of welded parts increased with the fiber content in the composites. In addition, a triangular energy director was found to weld parts of the highest strength for virgin polypropylene and 10% glass-fiber filled polypropylene composites, while a semi-circular energy director was found to weld the highest strength parts for 30% glass-fiber filled composites.T o whom correspondence should be addressed energy director, which has the smallest cross section and therefore the highest strain, heats, melts, and flows to fill the interface with molten polymer and to fusion bond the parts (3).Up to the present, some research work has been done in the ultrasonic welding of thermoplastics. Benatar et d. (4, 5) completed research in both near-field and far-field welding of different thermoplastics, including polystyrene, ABS, polyethylene and polypropylene. They proposed a lumped parameter model to predict the heating rates and energy dissipation of the ultrasonic welding. Michaeli and Korte (61 used a statistic regression method to analyze experimentally the welding process of thermoplastics. Gerdes et al. (7) completed a finite element analysis of plastic part failure during ultrasonic welding. He and Benatar (8) studied the effects of amplitude and pressure control 132

Fusion Bonding/Welding of Thermoplastic Composites

“…The resulting rapid solidification of crystalline polymers prevents interface wet-out, causing brittle welds [30]. At butt joints and lap shear joints, the ultrasonic vibration occurs perpendicular to the contact areas (see Figure 12) [4,30,31]. Figure 11.…”

Ultrasonic welding of advanced thermoplastic composites: An investigation on energy‐directing surfaces

“…However, to concentrate ultrasonic heating at the welding interface, energy directors (EDs), that is, artificially made asperities in the form of resin protrusions, are required on the surfaces in order to be welded. Energy directors play an important role in the welding process and their morphology, size, and configuration affect the quality of the resulting welds 2,3…”

Hot embossing precise structure onto plastic plates by ultrasonic vibration

“…In ultrasonic vibration of thermoplastics, heat is generated when the plastic is subjected to cyclic strain. The power dissipated depends upon the loss modulus of the polymer and the cyclic strain amplitude [13]:…”