A Preliminary Study On Integral Winding Forming Process Of Thin-Walled Conical Step Tube

The conical stepped tube is a tube formed by connecting conical tubes between different diameter circular tubes at both ends,and is widely used for various fluid transportation.The current manufacturing process is mainly made up of piecewise winding,then re-welding and assembling.There is a lack of smoothness of the pipe wall,poor integrity,and low production efficiency.The overall winding forming process can overcome these deficiencies,but changes in the geometric parameters of the transition site will directly determine whether the product has wrinkles,cracks and other defects.This article takes a certain type of automotive muffler parts as an example to study the related issues of the overall winding process of thin-walled conical stepped tubes.A two-step forming scheme was proposed and preliminarily explored for parts with given sizes(diameter at both ends,length of conical tube)and wall thickness.It was found that the transition between the small-diameter tube and the conical tube on the opposite side of the patchwork was prone to wrinkling.A three-step forming scheme of “arching forming?U-forming?O-forming” was proposed;the corresponding molds were designed,in which the arch forming and U-forming molds used blanking blocks,O-forming mold adopts the structure of horizontal movement upper die and mandrel;the numerical simulation test of the forming process was carried out with Dynaform software.The results show that the forming process of the arch bridge is the key to controlling the wrinkling,and the integral punching mode has a bad effect,and the piecewise differential punch forming is used to reduce the wrinkle defect.In order to deeply explore the effect of the difference in diameter at both ends on the forming quality,the ratio of the diameter at both ends was taken as 0.75,0.60,and 0.50.The numerical simulation experiments were carried out with the integral punch and piecewise differential punch respectively,which proved that the diameter ratio at both ends was smaller,the more easy to wrinkle.The difference in the thinning of the workpiece caused by the two punches is not significant.When the diameter ratio is less than 0.60,the splicing edge of the transition between the small diameter tube and the conical tube is easy to be crack,and the smaller the diameter ratio is,the more severe the fracture trend is.The method of expanding the bulging deformation of the flat plate improves the mold structure so that the molding can be achieved at a smaller diameter ratio(minimum to 0.4).In order to explore the influence of several factors on the forming quality of conical stepped tubes,three representative factors,the blank holder force F,the transition cone angle ?,and the difference between the actual length of the truncated cone slope and the theoretical length,? L,were selected for the orthogonal test.the study.The maximum thickening rate of sheet metal thickness is taken as qualitative index,and the wrinkling condition and the size of the undeformed area are used as quantitative indicators to set up 9 groups of orthogonal test combinations.Through the range analysis,it is concluded that the primary and secondary order of the influence of the three factors on the forming process is ? ?? L?F.