Improving mechanical joining by increasing tool velocity

In this article, the possibilities for improving the joining process of self piercing solid rivets and self piercing nuts by increasing tool velocity are demonstrated. Thereby, the focus is put on the joining process of high strength steel sheets. Proper and reliable joining of these steels presents a major challenge for mechanical joining techniques. In the conventional joining process, where tool velocities well below 1 m/s are common, different problems during the joining process caused by the high strength of the steel sheets can occur. At the punch riveting process undesirable material flow or unwanted burr development can occur, and at the setting process of self piercing nuts a deformation of the nuts is possible. These problems can be reduced significantly by using elevated tool velocity. In the present paper, characteristics of the joining process at conventional and elevated tool velocity are investigated. The influence caused by different tool velocities within the joining process is shown by cross section- and process force analysis. In the cross section analysis of the mechanical joints it is demonstrated that the quality of connections can be improved significantly due to the usage of elevated tool velocity. The process force analysis of the high speed joining process shows an oscillating progression of tools and joining elements.