Simulation Analysis And Experimental Research Of The Forminng Process By Continuous Resistance Heating

The traditional hot forming technology is difficult to satisfy the real time demand because of high energy consumption, low material utilization and long production cycle. On the other hand, new material get a still higher demand on the matal forming technology because of the special properties of temperature sensitive, narrow forming range and complex phase transition during forming. The hot forming technology by continuous resistance heating is one of the advanced and filled with hopes technologies in the furture, which heats the billet in the dies during the whole forming process in order to keep the billet as the higher temperature. The troditional forming technology and the continouos heating technology has been combined. It have advantages of low forming force, low energy consumption, and can avoid the increase of produation cost due to repeated heating.The hot forming technology by continuous resistance heating can heating the billet to the forming temperature in the die prior forming by the resistance heating and continue heating it during forming. The resistance heating is the ideal continuous heat source for it has characters such as high heat efficiency, simple device, convenient control and so on. The more imporatant thing is which can improve the metal platstic deformation by the exist of current field. Howerer, the forming process by resistance heating is compex, which include heat transfer theory, material science, computer control technology and so on. Many influencing factors and the complex relations each other serevely obstructed the futher development of the hot forming technology by continuous resistance heating. In the paper, based on the previous studies, the die structure has been classify and the experiments of the 42CrMo4 upsetting have been contacted by the independent designed experimental system. Finally, an axis-symmetric electro-thermo-mechanical model has been developed to analyze a hot-forging process by direct resistance heating.The mold structure of continuous resistance heating has been dedived into four kinds: 1) Non-contact of the electrode and billet; 2) Directly contact of the electrode and billet; 3) Part-contact of the electrode and mold and billet. The mold system has four subsystems: heating, temperature control, forming and isolation system. The upsetting experiment device for 42CrMo4 bar has been designed with the first mold structure.The forming process is consist of two parts: heating inside mold before forming and forming during resistance heating.The parameter,material property,mold structure and aluminium alloy buffer,which influence temperature and temperature field distribution of billet and forming force and forming process,have been studied. And the reasons of defect have been researched and solution has been put forward.It is hard to further study with traditional experiments because the continuous resistance heating forming process is a nonlinear complex of electric conduction, thermal conduction and plastic deforming. The coupling simulation of electric, thermal and force can not be inplemented at present. This article separately calculate the electric-thermal coupling and thermal-force coupling and then calculate sequential coupling of them and finally build the finite element model of electric-thermal-force coupling for the continuous resistance heating forming. Comparing the results of simulation and experiments, contacting resistance model built in electric-thermal coupling effectively reflect influence of contacting resistance to temperature, in which the resistivity has an inverse relation with temperature of contact surface. The veracity of math model has been validated and the distribution of temperature, current density and stress and strain has been obtained. The results have provided contion to complicated part's continuous resistance heating forming and further optimization. In order to keep the billet temperature constant during the continuous resistance heating process, the control of current strength is the key point which decides the results of this method. In this article, Latin hypercube sampling method and quadratic polynomial has been used to build a decimal quadric form approximate model for heating current and billet temperature, and then genetic algorithm has been used to optimize the current intensity, and finally obtained the heating current curve which could maintain the billet temperature varying within 12oC.