Three-dimensional thermo-viscoplastic finite element analysis of hot forging

Abstract

In order to design forging processes effectively and to prevent the defects, analysis of the processes is essential, for the die design and the die manufacture. For the complex problems, numerical method are commonly used for the modeling of forging processes. The effectiveness of the finite element method has long been proved for the prediction of metal flow and defects, forging load, stress and strain distributions, temperature gradients and tool distortion. Since materials at the elevated temperature are usually rate-sensitive, analysis of hot forging requires two considerations; the effect of the rate-sensitivity of materials and the coupling of the metal flow and heat transfer analysis. The material behavior that exhibits rate-sensitivity is called viscoplastic. A three-dimensional thermoviscoplastic finite element formulation is presented considering the heat transfer. An efficient three-dimensional finite element code of the workpiece and the die has been developed for the simulation of hot forging. The finite element method and the boundary element method are employed for the analysis of the heat transfer. The boundary element method is one of the efficient methods for the transient heat trasfer analysis, because element nodes are fined only on the extemal surface and intermal unknowns are not required. To show the effectiveness of the three-dimensional thermo-viscoplastic finite element method, forging processes which are useful in the industry such as cogging process and turbine blade forging are analyzed. Simulation of the cogging process focuses on the influence of various cogging paramenters on centerline consolidation such as die shape, die width ratio and temperature gradient of ingot. In turbine balde forging, the forging experiment was carried out in the laboratory condition and compared with the computation. It has been shownd that the results of the experment and the computation are in good agreements in forging load, temperature distribut...