Model of Curvature of Crankshaft Blank during the Heat Treatment after Forging

Abstract

The manufacturing process of large crankshafts is affected by undesirable bending of the shaft blank at the heating and heat treatment stages, as well as at the forging step. In line elimination of the shaft blank bending is a time consuming and expensive operation. Identification of reasons of the shaft bending and identification of possibilities of avoiding this bending is an important theoretical and practical problem. In previous works, the Authors developed the finite element model and applied this model to optimization of the forging process and to predict microstructure evolution. The model was extended to predict bending of shaft and applied in the present work to simulate the influence of various parameters of forging on shaft bending.The work is devoted to further extension of the model by including deformation of the crankshaft during heat treatment after forging. The model estimates the contribution of the elastic-plastic deformation, including thermal expansion and dilatometric effect due to transformations, on the deformation and bending of the shaft. This process generates also residual stresses. The aim of the paper was to simulate phenomena occurring during heat treatment. A program based on the finite element method was developed to solve the three-dimensional thermal and mechanical problems. Shaft material model was developed and the elastic-plastic characteristics were implemented in the FE code. Heat exchange with the cooling medium and the dependence of thermal properties on temperature and heat of phase transformations were accounted for in a solution of the thermal problem. Dilatometric tests were performed to supply data for identification of the phase transformation model during cooling. The results of calculations of bending of shaft during the process of heat treatment, as well as the distribution of residual stresses and strains are presented in the paper. The calculations were performed for several modes of the heat treatment. Parameters affecting bending of the shaft were identified.