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Two-component epoxy adhesives that cure at room temperature but are responsive to induction heating offer tremendous processing flexibility in the manufacture of hemmed closure panels. Using a two-component, hemmed closure panels can be induction heated to quickly cure the adhesive. Since two-components are generally very reactive, lower induction temperatures can be used and panel handling strength will still develop within minutes. Also, if panel deformation due to induction heat is a concern, or if spot induction coils are being used, two-component epoxy adhesives build strength with time at ambient temperatures, allowing parts to be handled within 3-4 hours after hemming. Experiments described here will illustrate the differences between single-side coils and L-coil induction heating systems. Other induction experiments will show the sometimes large differential between metal skin temperature and the temperature actually seen by the adhesive in the bondline.

As automakers continue their drive to reduce weight in vehicle structures, aluminum has received increased attention as a material of choice. Achieving the weight reduction that aluminum can provide without any loss in structural integrity has posed a distinct challenge. Structural adhesives are now playing an important role in reinforcing aluminum structures, and automakers are finding that adhesive-bonded aluminum structures meet or even exceed the torsional stiffness of welded steel. This paper describes two structural adhesives which address the particular needs of two distinct aluminum bonding applications. The first adhesive, 3M 5041, is a two-part (2K) induction-curable and room-temperature-curing epoxy adhesive designed for high-volume-production hem flange bonding operations on unprepared oily aluminum. The second adhesive, 3M 5042, is a heat curing one-part (1K) weld-bond epoxy adhesive developed for body structure bonding applications.