Enhancement of the connection strength of flat-clinch joints by alternative process concepts

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The objective of the proposed project is the enhancement of the connection strength of flat-clinch joints by developing alternative process concepts and load-capable design concepts. By means of load-capable design concepts, it is possible to determine the application-related requirements concerning the connection strength (tensile strength, shear strength, torsional strength) of flat-clinch joints. Based on the knowledge gained, the optimal joining geometry and the required process parameters are derived. Furthermore, a novel simulation approach - the numerical computation using mesh-free methods - is used for enhancing the accuracy of the 3D simulation of flat-clinch joints as well as reducing the computing time.By using non-rotationally symmetric tool geometries, the torsional strength is increased compared to flat-clinching with a circular punch. Because of the irregular tool cross section, the interlocking between the metal sheets is expected to be irregular as well. During the project, different tool geometries will be developed for producing torsion-proof flat-clinch joints with high resistance to tensile and shear stress.By inserting local joining elements, the tensile strength and shear strength of conventional flat-clinch joints with circular punch geometries will be increased. Cylindrical blanks are inserted into the flat-clinch joint and subsequently formed in mainly radial direction. This second process step leads to an increased interlocking between the metal sheets and thus to an increase of the tensile strength. Furthermore, the bottom thickness, at which the joining element is inserted, will be investigated. By choosing a higher bottom thickness during the first process step (conventional flat-clinching), the punch-sided metal sheet undergoes less thinning, resulting in a higher neck thickness. During the second process step, the forming of the joining element leads to an interlocking that is comparable to the interlocking of conventional flat-clinching. Because of the higher neck thickness, the shear strength of the flat-clinch joint is higher as well. The aim of the investigations is to develop an understanding of the related joining mechanisms to detect the proper bottom thickness for inserting the joining element as well as the optimal geometry and material of the joining element depending on the thickness and material of the metal sheets.