Partial heating as a new method for increasing the strength of clinch joints of thin-walled elements

The following article concerns an innovative method for increasing the strength of clinch joints. The possibility of strengthening joints by heating sheet from the side of the die prior to the joining process is presented. Extensive experimental tests were conducted and supported by numerical simulations. It was demonstrated that increasing the temperature of the bottom component prior to deformation increases the shear strength by 17%, and cross tensile strength, even by 53%. Low-carbon, non-alloy steel with a simple composition was purposefully chosen for tests, which rules out phase transitions in the material based on the Fe-C chart. Conducted material tests, microscopic examinations and microhardness tests unambiguously proved that the increase in joint strength is mainly the result of the improved geometry of formed joints and 25% higher strain hardening of the bottom sheet. Therefore, the presented method can successfully be applied for the joining of a broader group of thin-walled materials.