Theoretical Prediction And Experimental Verification Of Thermal And Mechanical Loading Of Multi-layer Metal Hot Forging Die

Compared with other tools or molds,hot forging dies have shorter service life because of the worse working environment in the forging process.Studies in recent years have showed that,the multi-layer metal forging die,whose cladding materials and structures designed according to the die's temperature distribution,can effectively improve the service life.And in this paper,the studies of the theory,that calculating thermal-mechanical stress of the multi-layer metal forging die,will provide the scientific reference for the selection,design and preparation of a multilayer metal forging mold's coating material.Firstly,on the foundation of the FGM(Functionally Gradient Materials)plate's homogeneous and forging die's thermal-mechanical stress analysis theory,the theoretical formulas of calculating thermal-mechanical stress of the multilayer metal forging die,including the differential equations of temperature field,thermal stress and thermal-mechanical stress calculation theory,was preliminarily established.Secondly,with MATLAB,the mathematical analysis values of the study object were acquired by the theory of calculating thermal-mechanical stress of the multi-layer metal forging die;and with the ABAQUS,the simulated values,as the reference,were obtained.By temperature collection equipment,ultrasonic frequency induction heating equipment and resistance furnace,the temperature of selected measuring points was measured;with Gleeble3500,the thermal strain of selected measuring points was measured.Then the Mathematical analysis values of the selected measurement points were compared with the simulated ones and observed ones of them to verify the accuracy of the theoretical formulas.Finally,the feasibility and effectiveness of using the theoretical formulas to predict the temperature change and the maximum thermal stress of the mould was studied.The accuracy of the theoretical formulas was preliminary verified by the results.Though,there were errors between the mathematical analysis values and the simulated and observed ones,the variation trend of the mathematical analysis values was in agreement with that of the observed and simulated ones.The absolute error of the mathematical analysis ones of the temperature and that of the simulated values was not more than 40? and the relative error was about 7%.The absolute error of the mathematical analysis ones of the temperature and that of the observed values was not more than 50? and the relative error was about 15%.The absolute error between the mathematical analysis values of thermal stress and the simulated values was 70 MPa and the relative error was about 30%.But in engineering calculation,the error can be reduced.The thermal strain of the observed values was a little higher than that of the simulated ones.The relative error between the thermal strain of the observed values and that of the simulated ones was less than 5%.And the trends of them were consistent with each other.The absolute error between the mathematical analysis values of the equivalent stress and that of the simulated values was about 170 MPa and the relative error was about 25%.However,the absolute error between the mathematical analysis values of the equivalent stress of Mold A and that of Mold B was 10 MPa,which was consistent with the absolute error between the simulated values of them.Using the theoretical formulas and taking the simulated values of ABAQUS as a reference standard,the temperature distribution and the maximum thermal stress of the study object was predicted.The theoretical deduction values of temperature were in agreement with the simulation results.And the absolute error between them was less than 40? with the relative error being less than 7%.But,the absolute error between the theoretical deduction maximum thermal stress and the simulated one was about 60 MPa with the relative error being about 24%,which can be reduced by improving the accuracy of thermal parameter data.The results showed that it was feasible and effective to design the multi-layer metal forging die by the theoretical formulas or mathematic analysis.