Research On The Hydroforming Process Of The Automotive Sub-frame And Its Parameters Optimization

Recently,with the increasing environment deterioration and energy crisis,the need of automobile environment protection and energy saving is rising and energy reduction is becoming a primary challenge for the automobile industry.Thus,the weight lightening of the automobile components is one of the most important subjects in this field.Generally,the main methods to realize weight lightening are using light materials and realizing structure weight lightening by applying advanced manufacturing technology.As a forming technology with high efficiency in weight lightening,hydroforming is becoming one of the most important forming technologies due to its high forming quality,high material utilization and the ability to produce products with light weight and high strength.But,this technology is still immature in China so far.To help changing the current situation which has high cost and is resource-wasting due to the application of trail-and-error method in actual producing,this dissertation studied the forming process of a sub-frame offered by an automobile manufacturing enterprise by forming tests and finite element simulation.As a result,the forming defects including crack and crinkle were optimized.The main contributions of this work are as following:(1)Based on the commercial software AUTOFORM,the finite element model was developed and the following simulation of hydroforming process for the sub-frame was conducted according to the predetermined parameters.The simulation results verified the crack and crinkle defects in actual producing.(2)The effect law of friction factor on the forming quality of hydroformed automotive sub-frame was studied by using controlling variable method and numerical simulation.To minimize the friction in the process test,the film-wrap process was carried out on the preforming product.Then a qualified final product was obtained.(3)The processing parameters of the hydroforming for the sub-frame were further optimized by the combination of central composite experimental design method and response surface method.Subsequently,the optimal initial yield strength,sizing pressure and axial feedings were determined to be 34.9MPa,89.36 MPa and 19 mm,respectively.(4)The effects of die surface and friction factor on the forming property of sub-frame were discussed.The maximum thinning rate was further decreased by increasing the radius of the lateral fillet on the third corner in the mold to 15 mm.(5)The optimized forming parameters and model were applied in the actual producing,and a qualified product was finally obtained,which revealed that the stability problem of the product quality was solved fundamentally.