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的工艺概念和承载能力设计概念来提高平接接头的连接强度。通过具有承载能力的设计概念，可以确定与应用相关的要求，即连接强度(拉伸强度、剪切强度、扭转强度)。根据所获得的知识，得出了最佳连接几何形状和所需的工艺参数。此外，还采用了一种新的模拟方法--无网格数值计算方法，提高了平面联接三维模拟的精度，缩短了计算时间；由于采用了非旋转对称的刀具几何形状，与圆形冲头的平面联接相比，扭转强度得到了提高。由于刀具横截面不规则，预计金属板之间的联锁也将是不规则的。在该项目中，将开发不同的工具几何形状，以生产高抗拉和抗剪应力的抗扭平扭连接。通过插入局部连接元件，将提高传统圆形冲头几何形状的平扭连接的抗拉强度和剪切强度。圆柱体毛坯被插入到平卡箍接头中，随后主要沿径向成形。这第二个工艺步骤导致金属板之间的联锁增加，从而增加了抗拉强度。此外，还将研究插入连接件的底部厚度。通过在第一个工艺步骤(传统的平压)中选择较高的底部厚度，冲头侧面的金属板经历较少的减薄，从而导致较高的颈部厚度。在第二工艺步骤中，接合元件的形成导致可与传统平压接合的互锁相媲美的互锁。由于颈厚较大，平接接头的抗剪强度也较高。研究的目的是加深对相关连接机制的了解，以确定插入连接元件的合适底部厚度，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.