Stainless steel is difficult to glue, but permanent glue connections are often only possible with pretreatment. Delo and the Institute for Production Technology and Materials Testing at the Ulm University of Applied Sciences have now found that stainless steel bonds are almost as durable after intensive laser pretreatment as after the Saco process.

So far, wet-mix or tribochemical methods such as sandblast coating (Saco) have been used for stainless steel bonding. Recently, however, the pretreatment with a laser (1064 nm wavelength) has also come into focus, as it has some advantages over Saco. This reduces ongoing costs in the process, making it easier to implement inline processes and selective treatments. The partners have investigated how different laser intensities affect the surface topology of stainless steel 1.4301). An 2K polyurethane adhesive was used for joining, the effectiveness of the surface treatment was checked by means of tensile shear tests.

The laser-pretreated samples exhibit simulated aging resistance at the highest processing intensity, achieving nearly as high tensile shear strength as the Saco samples. For this, however, a certain minimum intensity must be achieved. With increasing intensity of the laser treatment, there is a growing oxidation of the surface. The increasing energy input also causes the near-surface areas melt and shortly thereafter cool down quickly through the heat conduction into the sample interior. Only at higher intensities, in which larger areas of the surface are melted, it comes to the described improvements, especially in the aging resistance of the bond.