Research On Hot Forming Process Of Automobile Torsion Beam Based On Lightweight

The ultra-high strength steels are used for the manufacturing of the body structural parts of cars,which can increase the structure safety,and at the same time a significant reduction in weight is achieved.The hot forming as a new blank forming process combining the forming process with in-die heat treatment can overcome the difficulty of the spring back often encountered in cold forming and maintaining the accuracy of the geometric dimensions of the part.In this paper,the hot forming technology of torsion beam is studied systematically from the aspects of hot forming process,process parameters and microstructure.The main contents of this paper are as follows:(1)Based on the theory of heat conduction and strength analysis,the requirements for the design of mold cooling system are analyzed.The parameters such as cooling water flow rate,the radius of the cooling channel,the distance between the cooling water channel and the distance between cooling water channel and the mold surface are obtained.(2)By using the LS-DYNA software thermo mechanical module,the simulation of the thermal forming of the torsion beam is carried out by importing the key parameters of the material.The distribution of the temperature field and the microstructure are obtained.After the hot forming of the torsion beam,the maximum temperature of the part is 558K(285?)and the microstructure is ferrite;The minimum temperature is 316K(43?)and the microstructure is martensite.The lowest average cooling rate of the parts is 92.4?/S,which is greater than the critical martensite transformation rate 30?/S,and the martensite transformation can occur.The temperature distribution of the parts is related to the microstructure of the parts.(3)Through the hot forming of torsion beam,the microstructure,hardness and decarburized layer of different section are studied.The shape of the section has a direct influence on the temperature field distribution of the parts after hot forming,and the difference of the temperature change curves in different regions makes the microstructure of the different regions show different forms.After the hot forming,the microstructure of the parts is mainly martensite.And the bainite and ferrite transformation occurs in some regions with lower cooling rate.(4)Study on the hot stamping process parameters and optimization method,using orthogonal experiment and setting up the regression model,find the influence between the initial temperature of blank,stamping speed,initial temperature of mould,quenching time,the friction coefficient and minimum content of martensite.(5)Based on the finite element analysis software,the effects of hot and cold forming methods on the strength,stiffness,modal and frequency response of torsion beam are analyzed.The results show that under the same conditions,the hot forming can greatly improve the strength property of the torsion beam.But the forming method has no obvious influence on the stiffness,modal and frequency response.