The Influence of Manufacturing Processes on Resistance Welded Fiber-Reinforced Thermoplastics (Masterarbeit)

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Abstract

Weldability is one of the main advantages of thermoplastic composites over the more widely used thermosets. Among the available techniques, resistance welding has proven to be one of the most promising one, thus attracting the interest of the aerospace industry. To date, research in resistance welding has focused on near-perfect laboratory materials, usually produced by hot-press (or compression moulding). Nowadays, innovative techniques for the production of large compo�nents are in development. It became necessary to evaluate whether the different quality of the components produced by these new techniques might affect the welding process differently compared to the traditional materials. In this project, the influence of the manufacturing process on the resistance welding of carbon fibre-reinforced LM-PAEK laminates is studied. To do so, two parallel experimental campaigns were conducted. In the first one, traditional laminates produced by hot-pressing (HP) were used; in the second campaign, laminates produced by the more scalable Automated Fibre Placement (AFP) technique were employed. The joint configuration is a single overlap design. Process parameters included pressure, internal temperature, current, residence time and cooling rate. The tests were organized following Design of Experiments (DOE) techniques. The welding quality was assessed through both destructive and non-destructive tests. It was noticed that the initial characteristics of the laminates such as consolidation can influence the heating process. In addition, all AFP laminates yielded before the joint itself, and at a lower load than the joints in the hot-pressed laminates group. The initial quality of the laminates is therefore a parameter that influences the mechanical behaviour of the joints significantly. Furthermore, it appeared that the welding process currently has little influence. However, optimization of the process parameters can considerably reduce the internal porosity of the laminates and could thus improve the fatigue strength of the joint.

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