New Mechanical Methods to Join Sheets in Lap and Butt Configuration and Analytical Model to Predict and Improve Clinching Joint Strength

Abstract

Mechanical joining of sheets has many advantages over other joining methods in terms of wide variety combination of similar, dissimilar and non-metallic material sheet joining. In conventional SPR joining, the rivet and sheet materials are different, which causes problem in recyclability and corrosion. In study of new proposed method called Single Material SPR (SMSPR) joining, the aluminum sheets are joined using rivet made from the same material. In this method, since rivet needs to pierce through the first (top) sheet and flare in the second (bottom) sheet, rivet need to be higher strength than the sheets. To achieve required strength difference between sheet and rivet, the sheets are heated to a higher temperature and rivet is maintained at room temperature. The combination of temperature, ram speed, rivet and die profile are studied to obtain Single Material SPR (SMSPR) joint strength close to the conventional method. The mechanical joining methods including clinching and SPR are for lap joining, there is no technique for mechanical butt joining hence, a new method Self-Lock Butt Riveting (SLBR) is studied. The rivet and die dimensions play important role in achieving the strength close to the SPR joining method. For quick evaluation of clinching joint strength under cross tensile and lap shear loading conditions analytical method is necessary. Proposed analytical model is validated by conducting experiments on changing flange diameter, and is able to predict strength without greatly losing accuracy. Apart from quick evaluation the model offers greater understanding of joints behavior under various loading condition. Parameters (friction and wrap angle) identified in analytical model is used to increase lap shear strength without losing much of cross tensile strength by changing surface roughness