Injection bonding of structural components with fast-curing two-component PUR-systems

Abstract

When someone joins large structural components, the importance of the joining technology increases. Well-known joining processes such as welding and classic adhesive bonding reach their limits with respect to cycle times and tolerances. A new two-component polyurethane injection process based on the reaction in mold technology, offers an alternative and has the potential to reduce costs and compensate tolerances. The objective of this paper is to characterize and evaluate this process for potential applications so that it is possible to set the parameters as necessary. The example that was chosen for this research is the battery housing for electric vehicles. The advantage that this process does not only join the parts within seconds, but also will seal or fill long gaps if necessary, makes it particularly interesting for the industry. Classic adhesive technology applies the adhesive on one part, then takes the second part for the joining process, grouts the adhesive to a defined gap and afterwards, it still has to cure in a geometrically-defined tool. The PUR injection process fixes the two components in a tool with a defined gap and afterwards, injects the PUR that then reacts in the gap and joins the two parts within seconds. The adhesion and as well the rheology decreases with an increase in crosslinkings. These two parameters are therefore described relative to time and temperature. A steep increase in viscosity is detected after just a few seconds. With higher adherend temperatures the increase in viscosity appears earlier and steeper. The property for adhesion to the surface is decreasing the longer the PUR takes to hit the surface. These dependencies are described in this paper to develop a reproducible application process with a battery housing for electric vehicles as a case study.