Abstract
Infrared welding technology is currently used in the automotive industry to assemble very complex composite shapes made of short glass fiber reinforced polymers. Such applications are targeted more towards short joining times than towards the optimization of adhesive properties. Through this work, the authors joined their efforts on the experimental investigation of driving mechanisms and their optimization, enabling the welding of high-performance materials typically selected for aeronautics applications. The thermal field through the thickness and on the surface was investigated. The best configuration of the LM-PAEK/C laminate presented a single lap shear (SLS) strength of 43.5 MPa with a standard deviation of 0.7 MPa compared to a strength of 24.9 MPa with a standard deviation of 2.3 MPa obtained with the welding configuration without insulation. These results highlight the major effect of a thermal gradient during infrared welding. It is specific to infrared welding to observe that the major resulting defects are located not at the interface area but inside the composite substrate, where voids, generated during the heating step, are unable to be reconsolidated during pressure application. The impact of the decompaction behavior on the thermal gradient was studied through a MATLAB© implemented 1D numerical model, developed internally and called “LysIR”.
Highlights
Infrared welding is a sequential welding process composed of four main steps
A set of five microscopic images is reconstructed for each infrared heating sample from 8 s to 24 s heating time
Deconsolidation is triggered by the Experimental investigation and optimization of thermal gradients by infrared welding release of the internal residual stress contained in the reinforcement weave [2], which is generated during laminate manufacturing
Summary
Infrared welding is a sequential welding process composed of four main steps (Cf. Fig. 1). Two thermoplastic composite (TPC) parts are positioned on the upper and lower welding tools. Phase I consists of heating up the TPCs until deconsolidation starts. During this phase, no morphological change such as void content variation is considered. Phase II starts when deconsolidation voids appear on the first layer of the TPC and is finished when the IR lamps switch off. Phase III covers the change-over operation, where the mobile heating frame moves back and where the upper and lower tools move up to make intimate contact with both TPC welding parts. Phase IV consists of applying the pressure and cooling down mainly by thermal conduction through the TPC and welding tool.
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