International Journal of Mechanical Sciences 44 (2002) 773–792 A new method of preform design in hot forging by using electric eld theory S.R. Lee, Y.K. Lee, C.H. Park, D.Y. Yang * Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology-KAIST-ME3214, 373-1 Kusong-dong, Yusong-gu, Daejeon 305–701, South Korea Received 17 August 2000; received in revised form 3 January 2002 Abstract The preform design in metal forging plays a key role in improving product quality, such as ensuring defect-free property and proper metal ow. In industry, preforms are generally designed by the iterative trial-and-error approach. This approach, however, leads not only to the increase of signicant tool cost but also to the extended down-time of the production equipment. It is thus necessary to reduce time and man power through an eective method of preform design. In this paper, the equi-potential lines designed in the electric eld are introduced to nd an appropriate preform shape. The equi-potential lines generated between two conductors of dierent voltages show similar trends for the minimum work paths between the undeformed shape and the deformed shape. Based on this similarity, the equi-potential lines obtained by the arrangement of the initial and nal shapes are utilized for the design of the preform, and then the articial neural network is used to nd the range of initial volume and potential value of the electric eld. ? 2002 Elsevier Science Ltd. All rights reserved. Keywords: Preform; Hot forging; Electric eld; Neural network; Finite element method 1. Introduction Forging is a process which makes a desired shape through changing the material shape by com- pressive force. In die forging, the workpiece is compressed by upper and lower dies and then lled into the die cavity shape. Forging in multiple stages can improve the process and material properties such as reduced press loads, reduced wear of the dies, more uniform deformation, etc. In the conven- tional die design, trial-and-error approaches are often employed for determining the preform or the intermediate die shapes, the number of stages, and the process conditions. In order to reduce time * Corresponding author. Tel.: +82-42-869-3214; fax: +82-42-869-3210. E-mail address: dyyang@mail.kaist.ac.kr (D.Y. Yang). 0020-7403/02/$ - see front matter ? 2002 Elsevier Science Ltd. All rights reserved. PII:S0020-7403(02)00003-6