the processing time and energy efficiency of metal or composite bonding operations is improved by heating the lay - up preform of the structure in an induction heating press where energy goes primarily to heating the workpieces rather than to heating the tooling or being lost to the environment . the bonding process is especially beneficial for joining thermoplastic composites , but it also can be used with metals or thermosets . preferential heating at the bondline is achieved by using shims to define the bondline and to define bead regions that have relief from contact with the susceptor envelope because of the thickness of the shims in the bondline regions .