Laser pretreatment enables versatile stainless steel bonding

Until now, mainly wet- or tribo-chemical methods, such as the SACO method, have been used for stainless steel bondings. However, laser pretreatment, with a wavelength of 1,024nm, is coming to the fore as it offers several advantages over SACO. Running costs of the process can be cut, in-line processes are possible, and selective pretreatment is easier to implement.

In collaboration with DELO, the Ulm University of Applied Sciences investigated how dissimilar laser intensities influence the surface topology of stainless steel. A two-component polyurethane was used for bonding, and the effectiveness of surface pretreatment was verified by tensile shear tests.

At the maximum processing intensity, the specimens pretreated by a laser achieve tensile shear strength values after simulated aging, which are nearly as high as those of SACO-pretreated specimens. For this purpose, however, a certain minimum intensity must be reached.

Increasing intensities of the laser pretreatment lead to a corresponding increase in surface oxidation. In addition, the rising energy input also causes areas near the surface to melt and cool down quickly again through heat conduction to the specimen inside. The improvements described, in terms of the aging resistance of the bonded connection, are only achieved at higher intensities when larger areas of the surface are melted.