Axial Low Pressure Forming Process Of 5A03 Aluminum Alloy Bellows

Metal bellows is the core elastic element of expansion joint,which is widely used in various fields.Metal bellows are usually manufactured by hydroforming.But with the increase of the size of the formed bellows,the performance requirements of Hydroforming Equipment and the cost of die increase sharply.Based on this,in view of the difficulty of forming bellows with large diameter and small thinning requirements,this paper proposes an axial low pressure forming process combined with the principle of hydroforming.The core idea is that the bending deformation of the tube blank was produced by the mould axial feeding under the support of gas internal pressure,so as to fill the waveform required by the cavity forming.In this paper,U-shaped bellows of 5A03 aluminum alloy was studied as the main research object and an experimental setup was designed and assembled for axial hydro-pressing process of metal bellows.The finite element simulation and the experiment were used to analysis the mechanism and influencing factors of various defects in the forming process of metal bellows were analyzed the mechanism and influencing factors of various defects in the forming process of metal bellows,the influence of different process parameters on the forming quality of metal bellows as well as the forming quality of metal bellows with different types of corrugations.The defect forms in the forming process of U-shaped metal bellows were given and the mechanism of different defects and the reasonable range of parameters required to restrain the defects were revealed by numerically simulating the deformation behavior and stress state of the material in the forming process of bellows.The results show that the collapse in the area of the round corner is caused by the excessive axial circumference of the deformation zone of the metal bellows greater than the unfolded length of the waveform.The axial circumference of the deformation zone depends on the initial internal pressure and the axial feed rate,and it is proportional.The wrinkling in the area of the round corner is caused by the small radius of the round corner of the die and the insufficient internal pressure,which the tube blank not to fully fit the die and usually occurs in the middle of the forming process.The undercut defect is caused by the parting surface located at the wave crest and the inner fillet r on the moving die is 0.When r is 0.5mm,the undercut defect disappears.The fracture is mainly caused by the unreasonable matching between the forming internal pressure and the axial feed.The forming quality of U-shaped metal bellows is characterized by the shape accuracy and wall thickness distribution after forming.Based on the reasonable range of different parameters obtained from the defect analysis,the maximum distance between the metal bellows and the die when the moving die is closed,the thickness change of the root of the waveform and the wave height change after unloading were taken as the characterization.The influence rules of different parameters on the shape accuracy of the metal bellows as well as the wall thickness distribution of the metal bellows were studied.The optimal process parameters and springback compensation scheme were determined.And the U-shaped metal bellows with inner diameter of340 mm,diameter reduction rate of 23.5% and maximum wall thickness reduction rate of 10.8% were obtained.Finally,the forming quality of different types of metal bell ows under the same conditions was studied.Through comparison,it was found that the wall thickness distribution of three types of bellows is similar.For rebound,S-shaped bellows is larger than U-shaped bellows and square bellows is smaller than U-shaped bellows.At the same time,by analyzing the influence of different parameters on the fillet radius of square metal bellows,the minimum fillet radius of square metal bellows under the existing conditions is 3.1mm.