Study On Flow Forming Process Of Thin-walled Cylindrical Parts With Grid Inner Ribs

Thin-walled cylindrical parts with grid inner ribs are important shell parts in aerospace field.This structure can improve the stiffness of components and meet the requirement of lightweight design.Through flow forming process,this kind of parts can be integral formed.The formed parts have the advantages of good comprehensive mechanical properties and high reliability.However,there are some problems in the forming process,such as insufficient forming height of ribs due to insufficient plastic flow of blank material along the thickness direction,and difficult demoulding of formed parts due to the restriction of formed grid ribs,which seriously affect the application and popularization of flow forming process in the forming of thin-walled cylindrical parts with grid inner ribs.Taking a thin-walled cylindrical part with grid inner ribs as an example,the calculation method of theoretical rib height in flowing forming,the simulation of flowing forming of thin-walled cylindrical parts with grid inner ribs and related experiments are studied in this paper.The main research contents are as follows:(1)Study on theoretical rib height calculation method in flow formingThe rib height has a great influence on the structural rigidity and bearing capacity of the ribbed structural parts and is one of the main design parameters of the parts.The stress state of the blank material at the rib position is deduced.According to the principle of volume invariance of plastic deformation and the assumption of plane strain,and based on the slab method,the theoretical rib height calculation method is proposed.The influence of blank thickness reduction and blank wall thickness on the forming height of ribs is studied.It is found that with the increase of thickness reduction,the height of grid rib increases.When the blank wall thickness is less than the groove depth of the mandrel,the height of the grid rib almost increases linearly with the increase of the blank wall thickness.When the blank wall thickness is larger than the groove depth of the mandrel,the height of the grid rib increases little with the increase of the blank wall thickness.(2)Simulation study on flow forming of thin-walled cylindrical parts with grid inner ribsA simulation model of flow forming for thin-walled cylindrical parts with grid inner ribs is established.Combining with the simulation results,the formability of formed parts is discussed,and the stress distribution and material flow characteristics of the rib positions are emphatically analyzed.With the increase of the thickness reduction,the equivalent strain of the formed part increases obviously,and when the thickness reduction increases to 45%,crack defects appear on the outer surface of the formed part corresponding to rib transition positions.The stress distribution of transverse rib positions is more uniform than that of longitudinal rib positions.The material stress distribution is not uniform,and the equivalent strain is relatively large at the crack defect positions.The radial and axial flow of material in grid rib positions is the main reason for forming grid ribs.Combining with the simulation results,the accuracy of the theoretical rib height calculation method is verified.(3)Experimental study on flow forming of thin-walled cylindrical parts with grid inner ribsA module type combined mandrel for flow forming of thin-walled cylindrical parts with grid inner ribs is designed,and rapid demoulding of formed parts is realized.Flow forming experiments of thin-walled cylindrical parts with grid inner ribs under different process parameters are carried out.The effects of thickness reduction and feed rate on forming quality of parts are evaluated and discussed.Under the experimental conditions,when the wall thickness reduction is 45% and the feed rate is 0.5mm/r,high and uniform grid ribs can be formed,and there is no crack defect on the surface of the formed part.In order to improve the forming height of ribs,a set of silicone O-rings are added to restrain the axial flow of cylindrical blank material.This research provides theoretical guidance and technical support for the engineering application of flow forming of thin-walled cylindrical parts with grid inner ribs.