Investigating the use of Fused Deposition Modeling as Energy Director application method for Ultrasonic Welding of Thermoplastic Composites

Abstract

The joining of high performance Thermoplastic Composite (TPC) structures by Ultrasonic Welding (USW) is considered a promising alternative for mechanical joining or adhesive bonding methods. The process is fast, clean, and highly automated. In the USW process, an intermediate, unreinforced polymer layer is required at the weld interface to concentrate the heat generation at this weld interface and is called the Energy Director (ED). This research investigates a new method to manufacture and apply this ED at the weld interface, being Fused Deposition Modeling (FDM).

With FDM, complex products can be manufactured directly from a Computer Aided Design (CAD) model, without additional mould or special tooling required. The goal is to simultaneously manufacture and adhere a dedicated ED geometry on a consolidated TPC substrate with FDM, such that no additional fixation step of the ED is required before welding. The new technique is successfully applied with a PEEK (Polyether ether Ketone) ED and a consolidated CF/PPS (Carbon fibre/Polyphenylene Sulfide) substrate. The deposited ED has sufficient bonding with the substrate that it remained fixated during handling prior to and during the weld process. This resulted in a successful weld, having similar strength and quality as found with welds having a loose, flat film as ED.

A challenge encountered in using FDM as manufacturing method of the EDs, is a non-uniform thickness distribution occurring in the ED. Additional research on the influence of a variation in thickness is done, where it is found to reduce the overall single Lap Shear Strength (LSS), and divide the fracture surface of a single weld in two areas welded to different weld stages.