Ultrasonic Welding of Carbon Fiber Reinforced Composite With Variable Blank Holding Force

Energy directors (EDs) have been widely used in ultrasonic welding (UW) of polymers and polymer-based composites. They help concentrate the welding energy and localize the weld at the location where the EDs are present. However, the utilization of EDs increases manufacturing cost and time, especially for complex parts and structures. This paper presents a method for UW of carbon fiber reinforced composite without using EDs. A reusable annular clamp (called a blankholder) is used as part of the weld tool to apply a variable force (called blank holding force) on the composite sheets during the UW. The effect of the blank holding force (BHF) on the weld formation is investigated. The results show that the duration of the BHF had significant impact on the weld formation. There is a critical duration with which a localized weld can form. Suitable durations of BHF at different levels of welding energy are determined by experiments. The main function of the BHF is to create an initial melting area by improving the contact condition. The initial melting area will act as an ED to concentrate the welding energy, and therefore, promotes the formation of a localized weld.