Research On Hydroforming Technology Of Automobile Exhaust Pipe With Variable Cross-section

Exhaust pipe is a kind of hollow component with complex cross-section structure characteristics.It has many functions,such as exhaust catalysis,noise reduction and shock absorption,displacement compensation,etc.it is widely used in automobile industry,even in chemical industry,aerospace,mechanical and electrical fields.The traditional processing method of exhaust pipe is usually formed by block stamping and then welding.This process has many problems,such as many processes,low efficiency and poor forming quality.As a kind of modern advanced plastic forming technology,hydroforming is a kind of soft die forming technology,which can significantly improve the forming ability and quality of parts.Through the integral forming of hydroforming process,the production process can be reduced,the secondary operation(such as welding,connection and assembly)can be avoided,the number of parts and dies can be reduced,and the part design with lower cost can be realized.In order to solve the overall manufacturing problem of the exhaust pipe of a passenger car with a large cross-section rate of change,this paper takes 439 ferritic stainless steel pipe as the research object and adopts the hydroforming process to produce automobile exhaust pipes.In order to guide the actual production process design,finite element Simulation is used as an analysis tool to analyze the hydroforming process of the exhaust pipe.The specific research content is as follows:Based on the Dynaform finite element analysis software,a finite element model of the hydroforming process including clamping,refilling,forming,and shaping was established,and combined with experiments,the effects of multiple process passes and key process parameters on the forming quality were studied.According to the law,the design increased the number of process passes and optimized the hydroforming loading path,and carried out the design of a forming die.The results show that the loading path has a significant effect on the wall thickness distribution and thinning rate of the exhaust pipe.The optimized forming pressure,shaping pressure,and axial feed displacement are obtained by the response surface method,and the maximum thinning rate of the part obtained by the optimized parameter simulation can be reduced to 15.3%.After the second pass optimization,the maximum thinning rate is reduced to 5%.After the third pass optimization,the maximum thinning rate is 5.2%,and the cumulative maximum thinning rate of the three-pass forming is reduced to23.7%,thereby reducing the risk of forming cracks.The maximum thinning rate of automobile exhaust pipe formed by the well-designed one-time forming mold in this paper is 18.792%.Compared with the original three-pass forming process,the improved one-time forming mold effectively reduces the maximum thinning rate and improves the parts Formability.