Journal of Materials Processing Technology 145 (2004) 21–26 Improvement of initial blank shape for intricate products using slip line field M.H. Parsa a,∗ , P.H. Matin b , M.M. Mashhadi c a Department of Metallurgy and Materials Engineering, Faculty of Engineering, University of Tehran, P.O. Box 11365-4563, Tehran, Iran b Mechanical Engineering Department, Oakland University, Rochester, MI 48309, USA c Department of Mechanical Engineering, Faculty of Engineering, University of Tehran, P.O. Box 11365-4563, Tehran, Iran Received 13 October 2000; received in revised form 1 April 2003; accepted 1 July 2003 Abstract Conventional methods were used for constructing the slip lines around the die opening. A curve was drawn in order to establish the periphery of the initial blank and calculate the distance between the beginning and the end points, using the constructed slip lines. This distance was defined as the error distance parameter “d” which indicated the errors in calculations. The effects of die opening shape and drawing depth on the error distance “d” were investigated. For eliminating such an error, a modified method for drawing periphery of the initial blank has been introduced and its effectiveness on the calculated results have been shown. © 2003 Elsevier B.V. All rights reserved. Keywords: Slip line field; Initial blank shape; Deep drawing 1. Introduction For producing the intricate shape products using deep drawing method, it is very important to predict the initial shape of the blank as accurate as possible. Besides this, the estimation of the force required for production of the parts can be helpful in choosing suitable tools and equipment in shop floor. It is for this reason that many researchers have used various methods in order to establish the best possible technique [1–12]. The currently applied methods vary from simple calculations to very sophisticated techniques such as various proposed FEM procedures. The slip line field is an acceptable method, among var- ious proposed methods. Besides its application for simple shapes, it has been developed to predict the initial shape of blank for production of two level bottoms [13], shells with reentrant [14] and double cylindrical shells [15]. Predicted initial blank shape and its deformation force can be used for making trail blank and doing experimental work or they can be used as an initial data for further calculations such as finite element method for simulation of next deformation processes. Developed techniques based on the slip line field method may be fast but depends on the applied method. ∗ Corresponding author. E-mail address: mhparsa@ut.ac.ir (M.H. Parsa). Some errors may arise which increase the amount of the initial blank shape’s approximation (decreasing accuracy). These errors not only affect the calculated deformation force but also influence next steps results. So, every attempt for reducing these errors has direct effect on increasing the ac- curacy of the final results. By using such an idea, in this paper some techniques will be introduced for increasing the accuracy and efficiency of the methods based on the slip line for predicting the initial blank shape and the force required for deformation of the blank. After analyzing the reasons for such errors arising during the calculation of the initial blank, a criterion for measuring the amount of error will be introduced. In the next step some procedures for minimization of the errors will be examined. Finally a technique will be introduced for dividing the blank area into network with equal areas. It can also be utilized for determining the flow lines and calculating the deformation force. 2. Theory In the following the assumptions and applied method pro- posed by other researches for construction of the slip lines around the die cavity will be explained briefly first. Then 0924-0136/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0924-0136(03)00858-6