Investigation of Hot Forging Die to Improve its Life

Abstract

One of the established processes wherein metal is plastically deformed with the help of temperature and pressure is hot forging, either with closed or open die. In closed die hot forging, the dies are subjected to the high temperature and contact pressure. The die cost ranges from 10% to 15% of the cost of the whole forging process, so die cost plays an important role in the overall process cost. To increase the profit by reducing the forging cost it is necessary to improve the die life and material utilization in the closed die hot forging process. The selection of die material is based on its ability to retain the hardness and toughness at elevated temperature. One among them is chromium die steel, which can retain its hardness up to 4250 C. The die life is not only depending on the material used but also on the process parameters like preform size, number of blows, forging force, temperature, coefficient of friction and so on. To enhance the lifecycle of a die the die stress and forging force should be minimized during the closed die hot forging process. The preform size and shape have a strong influence on the die stress and forging force. For the economical forging, it is necessary to optimize the preform volume. For estimating the volume of the preform, it is required to consider the volume of the finished part, the scale and the volume of flash. Burning loss and machining allowances are also to be considered to produce high quality forged parts. It is very difficult to accurately calculate the volume requirement for the preform and it is impractical and uneconomical to do the sample try-outs on the shop floor. Now a day s finite element analysis (FEA) is used very effectively for the simulation of the closed die hot forging process to optimize the preform volume and to reduce the forging force and effective stress of preform leading to economical forging. Most forging operations are of a non-steady-state type in terms of metal flow, stresses and temperatures. These variables vary continuously during the p