DIE SURFACE DESIGN OPTIMIZATION ACCOMMODATING SPRINGBACK ASSISTED BY AN AUTOMATIC SURFACE GENERATOR Waluyo A. Siswanto 1 * , Badrul Omar 2 1 Advanced Dynamics and Vehicle Safety (AdVeS), Dept. Eng. Mechanics, University Tun Hussein Onn Malaysia 2 Dept. Engineering Mechanics, University Tun Hussein Onn Malaysia (UTHM)b ABSTRACT: One of manufacturing problems in sheet metal forming is springback. This elastic recovery occurs when unloading the formed part off the tooling dies, resulting in shape inaccuracies. Optimizing the geometry surfaces of the tools can be used to accommodate the springback, so that after the unloading process, the formed part meets the target shape. This paper presents an optimization method to modify the geometry surfaces of the tooling dies based on springforward simulations assisted by an automatic surface generator during the process. In the optimization cycle, new sets of upper and lower die surfaces are required. An automatic surface generation method based on normal vector has been developed to create new finite elements of the new surfaces. The normal vector calculation of the deformed elements after springback generates new upper and lower surfaces with uniform gaps. The new generated elements can be used directly during the optimization cycle. For testing and verification purposes, the method is applied in various complicated surfaces. The test results show that this method is able to generate a uniform gap in a corner with 90 degrees angle, without discontinuity in any elements. The application in optimization to minimize the springback is conducted in hat- shape problem. The result shows that the automatic mesh generator works effectively during the optimization cycle. The distortion error after springback can be significantly minimized. KEYWORDS: Sheet Metal Forming - Springback - Springforward - Optimization - Mesh Generator 1 INTRODUCTION Sheet metal forming processes are extensively used in au- tomotive industry to produce various components of car bodies. The stamping products, however, have a very common distortion problem (springback) due to an elas- tic recovery when the forming punch is removed off the tools. The springback problem is then becoming very cru- cial when the requirement of the shape accuracy is in- creased. Many efforts have been done to eliminate the springback problem. In general, their approaches can be classified into two main groups. The first one is reducing the springback effect by properly selecting some design parameters, which may affect the sheet material flow. The configurations of drawbeads, radius of curvatures, draw- bead forces and blank holder forces are very important pa- rameters. An appropriate choice of these may reduce not only the distortion due to the elastic springback, but also wrinkling and fracturing defects, at the same time. The methods have been discussed in [1–3]. The basic geome- try of the tooling dies in this group is based on the desired shape of the formed-part. Even though the distortion can be minimized, the springback is always present. The sec- ond group is reducing the springback effect by modifying the tooling surfaces geometry to compensate the spring- back. In this method, iterative numerical simulations * Corresponding author: UTHM - 86400 Parit Raja - Batu Pahat, Jo- hor, Malaysia. Email: waluyo@uthm.edu.my are required to predict the unloading shape deformations, based on various tooling surfaces. Amongst researchers who have contributed to this category are Karafillis [4, 5], Wu[6] and Shu [7]. In iterative optimization, after the springback simulation a new die surface is usually redefined following the spring- forward shape of the formed part. When the surface of the part is not too complicated, the method introduced by L.Wu et al. [6] which is a translation of the formed part can be successfully implemented. However this transla- tion method cannot create a consistent gap generated by a translation vector in punch moving direction. Another method based on displacement calculation during the iter- ative optimization has been introduced by Gan and Wag- oner [8] which performed better compared to optimization involving springforward calculation. This paper presents an automatic mesh generator to create a numerical method in compensating the springback by using an inverted springback prediction so called spring- forward to optimize new tooling geometry surfaces. The normal vector algorithm is a refined version of the previ- ous version, Siswanto et al. [9]. It can create a consistent gap between lower and upper dies generated from spring- forward part.