Simulation And Experiments Of Hot Gas Forming Technology For Thin-wall Tube

Reducing weight of vehicle is the effective way for energy-saving and emission reduction in the process of vehicle use.The high strength and high toughness metal materials was applied in reducing weight.Most of the thin wall parts of traditional cars were cold formed by hydraulic forming technology at room temperature.However the deformability of advanced high strength steel(AHSS)at room temperature was very poor and easy to crack.The accuracy of the dimension was poor and the forming force was very large.Therefore the room temperature hydraulic forming method was not effective to meet the requirements of the AHSS thin-walled hollow parts manufacturing.This paper presents a method of hot metal gas forming,which is used to solve the problems such as large forming force,great springback,low dimensional accuracy and easy cracking at room temperature.By this method,the ideal effect of weight reducing and safety improving were achieved with effectively power consumption.The main work contents are shown as following:(1)Manufacturing process of high pressure gas forming for thin-wall tube was designed.In the forming dies,the AHSS thin-walled blanks were heated and bulged to the desired forms.The forming temperature was above the austenite phase transform point,and the forming medium was nitrogen with high pressure.After forming,the blanks were quenched by water cooling dies and supercharged atmosphere to increase the strength of the blanks up to 1400MPa.The dimensions and shapes of the tubes were uniform with high yield ratio.(2)The control system of high pressure gas forming was designed and developed.According to the technological requirements,the temperature closed-loop model,pressure closed-loop model and the axial feed fed amount of the materials were developed.(3)The high pressure gas forming process for thin-wall tube was simulated.High temperature mechanical properties of ultra-high strength steel 22MnB5 was obtained by high temperature tensile test.The data were utilized to fit the constitutive equation.The numerical simulation of the high pressure thermal forming of thin wall tube was carried out by using the finite element software.The relationship between the bulging rate,wall thickness,temperature and air intake velocity were obtained.(4)The experiments of high pressure gas forming for thin-wall tube were studied.Experiments had been carried out with stainless steel and ultra-high strength steel.The conclusion of the simulation was verified.The fracture morphology and the microstructure changes of the bulging tube were analyzed by means of scanning and metallographic analysis.