Optimal method for auto-body closure panel fitting using Hausdorff distance criteria

Auto-body closure panel-fitting positions at the final stage of body-in-white (BIW)’s hierarchical assembly. It is such a critical process that contributes greatly to automotive dimensional integrity and quality. Poor fitting results in unsatisfied gap width and flushness that would cause functional problems and make adverse effect on vehicle quality perceived by customers. Although this problem has been studied by several authors in the past, two aspects still require further research. One is the improvement of fit quality measure suitable for complicated contours of closure panel and body opening’s profile. The other is the effect of weld-induced distortion during fitting process. In this paper, a novel computer-aided approach is proposed to address these above two problems. Firstly, panel fitting is mathematically modeled as a relative position optimization between panel and body opening which adopts translation and transposition parameters in homogeneous transformation as independent variables. Hausdorff distance between two continuous closed panel curves is firstly employed as the measure to evaluate the fitting quality of panel-opening profile contour. Secondly, since hinge axis plays important role for panel-opening relative position, its deviation from nominal design intent could not be neglected. After obtaining weld-induced hinge distortion using numerical analysis for these subassembly process, deviation of closure panel profile contour from design stage is calculated by homogeneous transformation during optimization and factors resulting from this physical thermal effects on gap width and flushness are taken into account and compensated. For the reason that the panel-fitting optimal function contains more than three variables, it is not suitable for applying algorithm with gradient descent or direct search. Genetic algorithm is used to search optimal fitting variables in a global and parallel way. Case study of certain car door fitting shows that the proposed method can effectively improve panel-fitting quality and accuracy.