The Heat Treatment Process Optimization Of Overloaded Motorcycle Frame And Thermal Stress Simulation

The whole cast is a developing direction of frame production for heavy load locomotive frame.The whole cast frame has good overall performance,but poor mechanical properties,and need the normalizing and tempering heat treatment.It is very necessary to determine the best heat treatment temperature to make the frame can have the best comprehensive mechanical properties.The thermal stress generated in the cooling process is the main causes for deformation,cracking and other defects.Optimizing the cooling mode of frame to reduce the thermal stress and short the cooling time,will directly improve the production quality and production efficiency of the frame.In this paper,the phase transformation points of the steel of frame and the temperature range of heat treatment are determined by the thermal expansion curve.To determine the best normalizing temperature of frame by normalizing microstructure and Brinell hardness test.After normalizing treatment under the best of normalizing temperature,take the termpering treatment for frame.Through observing the microstructure,hardness test and tensile test to determine the optimum tempering temperature of frame to ensure it has the best comprehensive mechanical properties.We use the ANSYS Workbench software to simulation the normalizing cooling process of frame,and take the indirect thermal structural coupling to calculate.In view of the complex of frame,and easily produce deformation in heat treatment process,the framework model and mesh were optimized.Reference the environment in heat treatment processing to set up the initial and boundary condition parameters.The distribution of temperature and stress field in frame when it is cooling in the air cooling is firstly simulated,and the relationship between the thermal stress and the temperature distribution is analyzed.In order to reduce the heat stress and short the cooling time,the heat transfer area on the surface of frame is divided into several parts,combined with different cooling rate into six different cooling optimization schemes,and then determine the best way of cooling structure by comparison.Through the above works,we get the following results:(1)the best normalizing temperature for frame is 900℃,with the maximum hardness of 180.7kgf/mm2;the best tempering temperature of frame is 590 ℃,the frame has the maximum strength and ductility product 19758MPa%;the hardness is 166.6kgf/mm2,the tensile strength is 555MPa and the elongation is 35.6%.(2)The optimized technology of heavy load locomotive frame is:When the top surfaces of middle axle box and traction beam are in 6m/s air cooling,the remaining area of frame is in air cooling,the cooling time is about 160min,the maximum thermal stress of frame has reduced up to 17.5%,the thermal stress distribution of the traction beam and middle axle box is reduced,and the stress concentration in the frame cooling is improved.