Push-bending Method Development Of Tube With Small Bending Radius Based On Elastic Filling Medium

The thin-walled tube with small bending radius has the advantages of light weight,large strength and space saving,and has a very broad application prospect in the fields of aviation,aerospace,automobile and so on.Wrinkling in the inner side,thinning of the outer wall,distortion of the cross section and short straight section at both ends of the bend are the common quality defects in tube bending,which seriously restrict the development and application of tube bending technology.In this paper,a new method of push bending forming is proposed,which uses polyurethane filling block as filling medium and controls the internal pressure by designing the geometric size and arrangement of polyurethane filling block.By bending the 5A02 aluminum tube with an external diameter of 40 mm and a wall thickness of 1mm with a double relative bending radius(R / D = 1;R is the bending radius and D is the outer diameter of the tube),it is found that the forming method can effectively improve the forming defects of the tube,improve the forming quality and reduce the energy consumption.This forming method not only enriches the modern pipe plastic processing technology,but also has practical guiding significance and reference value for the application of small bending radius tube parts in modern aviation and other industrial fields.The main research contents and achievements of this paper are as follows:This paper introduces the principle of tube push bending forming based on elastic filling medium,and analyzes the stress of tube bending process and several important influencing factors of tube bending forming.It also introduces the measurement method of basic mechanical property parameters of tube and material parameters of polyurethane filling block,and provides model parameters for subsequent finite element simulation.ABAQUS 6.14 finite element software is used to establish the push bending finite element model of small bending radius tube based on elastic filling medium.Based on the results of finite element simulation,the influence of the diameter,thickness,total length and arrangement of polyurethane rubber fillers on the stress-strain and wall thickness distribution of bend forming is studied firstly;then,the influence of the lubrication mode of the tube blank on the forming quality of the bend is discussed,and a new method of using differential lubrication to divide the outer surface of the tube blank to improve the straight end pushing amount of the bend is proposed.The results show that the optimal diameter of polyurethane rubber filler is 37 mm,the thickness of the polyurethane rubber filler in contact with the punch is 20 mm,and the thickness of the other 12 polyurethane rubber filler is 10 mm;the regional differential lubrication of tube blank can not only avoid wrinkling and improve the forming length of straight end push out,but also effectively improve the uneven wall thickness distribution.The push bending equipment of small bending radius tube is developed,the push bending die is designed,the test platform is built,and the push bending experiment of small bending radius tube based on elastic filling medium is carried out.In order to optimize the forming quality of the tube with small bending radius,PTFE thin film,molybdenum disulfide spray and fluorosilicone grease are used to lubricate different areas of the outer surface of the tube to optimize the forming quality of the small bending radius tube.The accuracy of the simulation results is verified by comparing the quality of the elbow formed by the experiment with the results of the finite element simulation.