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

拟议项目的目标是通过开发替代工艺概念和可承载设计概念来增强平扣接头的连接强度。通过可载荷设计概念，可以确定与应用相关的平扣连接强度（拉伸强度、剪切强度、扭转强度）的要求。根据所获得的知识，导出了最佳连接几何形状和所需的工艺参数。在此基础上，提出了一种新的模拟方法——无网格法数值计算方法，提高了平面夹持关节三维模拟的精度，缩短了计算时间。通过使用非旋转对称的工具几何形状，与使用圆形冲头进行平夹紧相比，扭转强度增加了。由于不规则的工具横截面，金属板之间的联锁预计也是不规则的。在项目期间，将开发不同的工具几何形状，以生产具有高抗拉应力和剪切应力的抗扭平扣接头。通过插入局部连接元件，可以提高传统圆凸模平扣接头的抗拉强度和抗剪强度。圆柱坯料插入平压接头后，主要沿径向成形。这第二个过程步骤导致金属板之间的联锁增加，从而增加抗拉强度。此外，还将研究插入连接单元的底部厚度。通过在第一个工艺步骤中选择较高的底部厚度（传统的平夹紧），冲孔侧金属板的薄化程度较低，从而产生较高的颈厚。在第二工艺步骤中，连接元件的形成导致与传统平夹紧的联锁相当的联锁。由于颈厚较高，平扣接头的抗剪强度也较高。调查的目的是发展对相关连接机制的理解，以检测插入连接元件的适当底部厚度，以及根据金属板的厚度和材料确定连接元件的最佳几何形状和材料。

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.