It is well known that stainless steel is difficult to bond, and durable bonded connections are often only enabled through pretreatment. DELO Industrial Adhesives and the Institute of Production Engineering and Materials Testing of the Ulm University of Applied Sciences have recently discovered that laser-pretreated stainless steel bondings are nearly as durable as after SACO pretreatment.
So far, mainly wet- or tribo-chemical methods, such as the SACO method (sandblasting and coating) have been used for stainless steel bondings. However, laser pretreatment (wavelength 1,064 nm) is coming to the fore as is has several advantages over SACO. Running costs in the process can be cut down, 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 (1.4301). A two-component polyurethane was used for bonding. The effectiveness of surface pretreatment was verified by tensile shear tests.
Intensive lasing is nearly as effective as SACO
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 SACE-pretreated specimens. For this purpose, however, a certain minimum intensity must be reached.
Increasing intensities of the laser pretreatment lead to a correspondingly growing oxidation of the surface. 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. Only at higher intensities, when larger areas of the surface are melted, the improvements described are achieved, mainly in terms of the aging resistance of the bonded connection.