Effect of variations of riveting process on the quality of riveted joints

Abstract

This thesis presents a study of the effect of controllable riveting parameters, mainly squeeze force, rivet length, rivet diameter tolerance, hole countersunk depth and hole diameter tolerance, on the quality of formed rivet. The quality of a formed rivet is determined by the geometry of its head formation and the extent to which the hole is filled. The study determines maximum allowable tolerance on drilled hole in a 0.064” thick aluminum sheet for a 1/8” rivet. The study is performed using finite element simulation of the riveting process. Theoretical relations between squeeze force and formed rivet head geometry derived in this study is used to validate the finite element model. Statistical design of experiment is employed to analyze the simulation data of riveting and determine the effect of individual factors, their interactions and relationship with the quality of formed rivet head. The results demonstrate that the correct formation of rivet head geometry depends upon all the factors studied. However, correct geometry of rivet head is not enough to determine the quality of a riveted joint, because the countersunk rivet head does not expand enough to fill up the hole completely, thereby creating a gap and leading to a loose rivet. The gap increases with the increase in tolerances in drilled hole, limiting its allowable tolerances to 0.006”. The length of rivet has no significant effect on the gap formation. To ensure the elimination of gap formation, an alternate procedure with reduced countersunk depth is studied, which allows for increased allowable tolerance in drilled hole. Results show that with as little as 0.01” reduced countersunk depth, the allowable tolerances on drilled hole could be increased to 0.03”, without compromising on the quality of the joint.