Model of Curvature of Crankshaft Blank During Heat Treatment, Accounting for Phase Transformations

Abstract

The manufacturing process of forging of large crankshafts is affected by bending of the shaft during heat treatment, as well as at the forging step. For this reason, analysis of the curvature of the shaft at various stages of the technology is needed. This paper deals with the modeling of elastic–plastic bending of crankshafts during heat treatment after forging. Present work is dedicated to heat treatment after forging. The aim of the paper is to develop a model and finite element (FE) software to simulate the elastic–plastic deformation of the shaft due to thermal expansion and dilatometric effect caused by phase transformations. Shaft material model is developed and the elastic–plastic characteristics are implemented in the FE code. Heat exchange with the cooling medium, dependence of thermal properties on temperature, and heat of phase transformations are accounted for in a solution of the thermal problem. Dilatometric tests are performed to supply data for identification of the phase transformation model. The method of estimation of the curvature of the shaft with one design variable is proposed. This allows to perform optimization of heat treatment in order to reduce the curvature of the shaft. The calculations are performed for several modes of the heat treatment. It is shown that in the presence of phase transformations, cooling process is accompanied by a three‐time changing of stress sign and the direction of bending of the crankshaft, which is due to the nonlinearity of thermal deformation during the phase transformations.