Tolerance verification for sheet metal bending: Factors influencing dimensional accuracy of bent parts

The dimensional accuracy of bent sheet metal parts is influenced by many factors and possible sources of inaccuracy such as the sheet material, machine, and material handling. This paper addresses the issue of tolerance verification for sheet metal bending by analytically and experimentally exploring the associations between each of these factors and the achievable dimensional accuracy of bending operations. Making use of the GUM method for quality assessment, in a first step, the influencing factors on the angular and linear dimensions of the parts are listed. The influences of these factors on each type of dimension are subsequently determined by geometry analysis. Secondly, special experimental setups were designed and experiments were conducted with industrial machines to establish the statistical characteristics of these factors. Therefore, the dominant factors determining the dimensional variations of the bending operations were fully identified and quantified. The result of this study can be used to predict the error range and thus the scrap ratio for the process. The developed methodology allows to point out possible improvements in the process plan, and most importantly, to predict the achievable dimensional accuracy of complex bent parts.