STUDIES ON. DIMENSIONAL 'CHANGES AND DISTORTION IN MATERIAL DURING POST FORGING - FINISHING OPERATIONS

Abstract

Most of the machine assemblies are made of various forged components. Hence the performance of these machine assemblies will depend on the quality of the forged component. Dimensional accuracy of forged product is one of the most important factor which decides its quality. Here the attempt has been made to study various types of dimensional changes occurring during post forging finishing operations. As a formulation of this project, it is divided into two parts : literature review and case study. A case study has been done in a forge plant, BHEL (Hardwar). For this purpose, turbogenerator rotor is selected as an example. Heat treatment and machining are major post forging operations. Distortion and dimensional changes occur mostly during heat treatment. During this study, sagging and volumetric changes in the rotor were observed during precaution and quality heat treatment respectively. Sagging was due to the uneven support provided during heat treatment and was removed by rough machining, because the allowances given were large enough. Volumetric change or size change in the rotor was due to phase transformation taking place during quality heat treatment. This dimensional change was quantified and it was found that these changes were within tolerance limits and taken care of during finish machining. it was observed that most of the distortions can be avoided by providing proper support and fixtures and controlling heat treatment operations.