Thermal Analysis for Resistance Welding of Large-Scale Thermoplastic Composite Joints

Abstract

The need for effective and reliable joining methods continues to grow as the use of thermoplastic composites becomes widespread. It is now possible to join largescale components with the development of an automated sequential resistance welding process. The thermal history generated by the heating element placed at the interface between adherends determines the quality and performance of the welded joint. This article presents a thermal analysis for the resistance welding of large-scale components that overcomes the limitations of previous models. To simulate welding of the interface, a heat generation term was incorporated that accounts for the Joule heating of graphite fibers in the heating element. A parametric study was conducted to investigate the influence of welding parameters and assess the uniformity of interface temperatures. Components were joined by the resistance welding process to obtain experimental verification. Regions of localized overheating where potential current leakage may occur were identified as a function of process parameters. Insights on promoting more uniform heating for the resistance welding process are discussed.

On avoiding thermal degradation during welding of high-performance thermoplastic composites to thermoset composites

“…Temperature beneath a PEEK coating layer with variable thickness (applied on a CF/PEEK adherend) for a typical resistance welding process with 90 kW/m 2 constant input power. The temperature at the welding interface is considered to be 400°C (based on Holmes & Gillespie 1D heat transfer model [12]). operative values of the machine with the booster/sonotrode configuration used, i.e.…”

“…1 and 2 are based on the material properties for CF/PEEK and PEEK provided in Ref. [12] and, therefore, they just offer an approximate result for thermoplastic to thermoset welding.…”

“…An approximate quantification of the influence of heating time on the temperature beneath the thermoplastic coating layer, and thus on the surface of the CF/epoxy adherend closest to the welding interface, can be obtained through the one-dimensional heat transfer model proposed by Holmes and Gillespie in Ref. [12] for resistance welding of carbon-fibre (CF) reinforced polyether-ether ketone (PEEK) composites. The model considers that a neat PEEK layer is placed between the heating element and the thermoplastic substrates (for the original resistance welding process considered by the authors), which makes it suitable for an approximate analysis of temperatures developed during welding of adherends with thermoplastic coating layers.…”

“…different heat inputs) when the temperature at the welding interface is 400°C (based on Holmes & Gillespie 1D heat transfer model[12]). …”

Science of Weld: Adhesive Joints

“…While methods such as adhesive bonding and mechanical fastening have been used in the past to join dissimilar materials [7] work in this area is now moving towards less labor intensive methods, geared more toward automation [6,34,39,40]. Neither adhesive bonding nor mechanical fastening is particularly well suited for inline application with the substrate fabrication methods.…”