Process And Quality Evaluation Research On Self-Piercing Riveting For Dissimilar Metal Aluminum/Steel

The trend of lightweight aimed at reducing fuel consumption and emission of the automobile has become inevitable. The mixed use of Al-alloy and advanced high-strength steel (AHSS) is one of the most important means that can solve this problem well. Self-piercing riveting (SPR), as a cold forming process, is a desired method that can join dissimilar metals effectively. However, the research and application of SPR process on local automotive industry is just in a primary stage, especially lacking the study of parameter optimization and online quality evaluation.In this paper, by the orthogonal experimental design is used to optimize the process parameters of Aluminum AA6061 and AHSS DP590. And based on the force and displacement curve, an online monitoring method is proposed. The contents of this paper are list as follow:(1) Process parameters optimization: To achieve the goal of process parameters optimization of self-piercing riveting, the orthogonal experimental design is used to study two sheet combinations, AA6061-T6+DP590 and AA6061-T6+DP780. Die diameter, die height and rivet length is selected as factors. Under different process parameters, experiment data of undercut, bottom thickness, Remaining thickness and tensile shear strength is collected and analyzed, by using the range analysis method and variance analysis method. The influence of factors on the quasi-static strength of the joints is studied. Results show that, undercut and tensile shear strength is directly proportional, and the rivet length is the most significant factor of the tensile shear strength of joint. Based on the influence law, concluded the optimum process parameters of these two matching cases.(2) Online quality evaluation: Herein, the dynamic variation laws between the riveting force and displacement signal during the riveting process are studied, via some experiment under the typical defect conditions like poor fit up, different riveting direction, different sheet thickness and different sheet strength. Results show that, through the study of the evolution of curves, some characteristic points can be used to classify these four defect conditions. The characteristic points are the start-inflection point and the piercing-inflection point of the force-time curve, the start point and the end point of the displacement-time curve. By extract these characteristic values and set up windows of eigenvalue, the quality of riveted joint can be judged. In this theory, Force-time/displacement-time characteristic value method is proposed, and it can be used to provide guidance on online monitoring and process improvement.