Flexible automation of clinching and adhesive bonding of sheet metal parts

Adhesive bonding and mechanical joining techniques have developed rapidly in recent years and they have become more common joining techniques in sheet metal product industry. New joining techniques have become more popular because increasingly used precoated sheet materials are difficult to weld. New joining techniques can also be applied as well for precoated as for uncoated sheet metal materials. VTT Manufacturing Technology in cooperation with IVF has carried out a research project of flexible automation of joining techniques for sheet metals. The project consisted of flexible automation of mechanical joining and adhesive bonding of sheet metal parts. The joining techniques studied can be applied to supplement each other. The shape of a typical clinching tool is limiting the applications, because the tool must reach to both sides of the joint like in spot welding. Adhesive bonding without jigs can be used only for parts that are locking each other when joined. If no constructive locking appears the parts are kept steady in a jig or the parts are secured by clinching or riveting. The adhesive is also a sealing of the joint. The research equipment was developed and built in the laboratory of VTT, consisting of a robot with linear track, clinching equipment, adhesive bonding equipment, a flexible jig, a ventilation system and tables for loading and unloading of sheet metal parts. The demands for joint design and the economic effects of different joining techniques were studied. Five industrial case products were studied considering the utilization of clinching or adhesive bonding instead of spot welding or arc welding. The results of the studies show that clinching and adhesive bonding are possible to be automated flexibly. Existing sheet metal products usually need some re-design when a new joining method is applied. Sufficient joint strength for most sheet metal products can be produced by clinching or adhesive bonding. Joining costs depend very much on jig costs. Clinching reduces remarkably the lead time of adhesive bonded parts and reduces also jig costs. Clinching and adhesive bonding are very suitable joining techniques for several material combinations, especially for thicknesses less than 3 mm.