Ultrasonic consolidation of thermoplastic composite prepreg for automated tape layup

Abstract

There is an industry need to manufacture advanced thermoplastic composite parts faster, cheaper and with less waste as interest in these materials continues to grow. For example, although hot gas torch heating is a well-established method for bonding and consolidating thermoplastic 'prepreg' in automated tape layup (ATL), researchers are looking at other polymer welding methods (laser, infrared and ultrasonic heating) to improve the process. This thesis focuses on benchmarking the capabilities of one of these methods, ultrasonic consolidation, against the industry standard process for consolidating thermoplastic composites, i.e. thermal pressing (welding). To accomplish this, 3-point beam bending tests were conducted on specimens made with both methods using a custom-designed experimental apparatus, and flexural strength and modulus results were used as an objective comparison. Ultrasonic welding proved to be more effective in welding PET/Carbon composite tape than thermal welding; specifically, a maximum increase of 65.4% flexural stiffness was observed. Contrarily, flexural stiffness of ultrasonically welded HDPE/Glass composite samples was as much as 36% lower than thermally welded ones. The quasi-isotropic samples exhibited very similar results. The results show that given suitable process parameters and a compatible thermoplastic composites system, ultrasonic consolidation of prepreg composite tape can be as effective as current thermal methods. In addition, a simple transient conduction model used to predict temperature rise in the thickening laminate compared favorably to experimental results.