Investigation and Correction of Surface Distortion in Dies With Typical Depression Features

Surface distortions are frequently introduced into Class “A” surfaces during various sheet metal forming operations such as drawing, trimming, and flanging. The origins of these surface distortions have not been well understood. The scope of this research is to investigate the distortion that occurs in the draw operation and to find effective and practical corrective methods. Five geometric parameters are first identified to represent typical depression features in automobile outer panels. Experimental dies are then designed to reflect various combinations of these five geometric parameters with the assistance of numerical simulations to ensure that the dies can make parts free of major defects such as splits and wrinkles. Surface distortions are observed in our stamping experiments and various techniques are used to measure and record the distortions for further mathematical analysis. Historical data of strains and deflections in distortion areas are collected through real-time measurement. The effects of three geometric parameters on distortion are analyzed using a full factorial DOE model. A geometry morphing program based on UG-NX platform is developed. The program is used to morph the die face in the distortion areas. Finally, three approaches that aim to correct distortions are tried out and the die morphing proves to be a practical and effective method.