JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008 - 50

FEATURE “Automotive” Induction welding: an automated joining process for composites For the manufacture of large complex parts, joining is an important step in the process chain. The joining process is therefore subject to stiff requirements. Robotized induction welding is a highly flexible, automated joining process for dissimilar materials that allows joint debonding and continuous quality control. polymer matrix in the joining zone. The components to be welded are submitted to an alternating electromagnetic field. When there are electrically conductive loops in the component, e. g. with carbon-fibre reinforcements, eddy currents are induced, resulting in efficient, localized heating directly in the laminate. Glass-fibre reinforcements are electrically non-conductive and additional susceptors, e.g. metal grids, have to be applied to convert the magnetic energy into thermal energy. In the case of ferromagnetic materials, hysteresis effects contribute further to heating. Figure 1 shows the basic principle of inductive heating of composites. 1- LARS MOSER, RESEARCHER, MANUFACTURING SCIENCE 2- PETER MITSCHANG, RESEARCH DIRECTOR, MANUFACTURING SCIENCE 3- ALOIS K. SCHLARB, MANAGING DIRECTOR, RESEARCH DIRECTOR, MATERIAL SCIENCE INSTITUT FÜR VERBUNDWERKSTOFFE GMBH, KAISERSLAUTERN Induction welding Components for the aerospace or transportation industry are typical applications for fibre-reinforced thermoplastic polymer composites. These components often require the production of large, complex structures that are normally composed of substructures, often from dissimilar materials. The process chain includes a joining step such as mechanical joining, adhesive bonding, or welding. In many cases, the production of composite structures is labour intensive and costs more than similar metal parts. Therefore, there is great demand for cost-effective production and automation. Robotized induction welding is a joining process that targets these needs. It has been adapted to industrial robots, allowing highly flexible automated production for both continuous or spot welds. Similar and dissimilar material combinations such as composites to metals can be welded. The process is capable of joining a variety of geometries, including three-dimensional curved structures. The joint is produced sequentially, allowing welding of different joint and part geometries without using component-specific tools. For repair purposes, the joint can be debonded, enabling substitution of components. In case of design alternations or product variations, reprogramming the control software and matching fixtures facilitate fast adaption of changes. Fig. 1: Basic principle of induction welding (schematic). Process fundamentals Induction welding utilizes inductive heating for melting the The most relevant parameters for inductive heating are coupling distance, field frequency, coil current, and inductor geometry. Reinforcement properties such as geometry or the electrical properties of the welding susceptor also influence the heating behaviour. Once the welding zone has been heated, the joint has to be consolidated under pressure and cooled, either actively using a cooling medium such as compressed air, or passively by convection. Up to now, the standard two-dimensional continuous induction welding process has been state of the art. In this process, the welding unit, consisting of induction coil and consolidation roller, is fixed and the joint is produced sequentially, making it necessary to translate the component during the welding process. Figure 2 shows the process conduct, the processing direction of jec composites magazine / No45 November-December 2008

JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #45 - November/December 2008