Numerical Simulation Of Flexible-bending Of Tubes And Its Process Parameters Analysis

Tubes have been widely used in the automotive,high-speed rail,aerospace and other fields due to its advantages of lightweight,high specific strength and ability to absorb impact energy.Forming quality of tubes is of great significance to the development of industry.Flexible-bending process can form parts with different shapes only by adjusting the position and angle of the bend die.Flexible-bending process has the advantages of short production cycle,wide application range and low cost compared with the traditional bending process.Finite element simulation can be used to predict the geometry of tube,distribution of stress and strain and possible defects of tube in bending process,and then we can optimize the process parameters.In this paper,flexible-bending process of tube is analyzed by the finite element analysis software ABAQUS.Effects of the clearance between tube and the bend die;friction coefficient and wall thickness on the forming is discussed.The defects of deformation of thin-walled tube in the bending process were predicted and the relative solution was put forward and validated by simulation.Moreover,three-dimensional forming of tube was carried out and effects of forming speed and friction coefficient on the forming quality of the transition zone were studied.The main contents and results of this paper are as follows:1.The principle of flexible-bending process was introduced;the unique advantages of flexible-bending process in modern industry were described.The finite element model of flexible-bending of tube is established,and the initial conditions such as grid division and element selection in the model are explained.2.Effects of some parameters such as the clearance between the guide and the tube blank,the friction coefficient on the bending results were studied.Results show that with the same die offsetting,the larger the clearance between the guide and tube,the larger the bending radius of tube;the larger the clearance between the bend die and the tube,the larger the bending radius of tube;the existence of the clearance will affect the forming precision and the forming range of the equipment;reducing the clearance between the bend die and tube can reduce the ellipticity of the forming parts and improve the forming quality;the larger the friction is,the bigger the thrust of the pusher and the force applied on the bend die in the bending process;the clearance between tube and the guide and between tube and the bend die should be minimized under the premise of ensuring the smooth forming of tube.3.Effects of wall thickness of tube on the forming were studied.The results show that the greater the wall thickness,the greater the change rate of the wall thickness and the smaller the ellipticity of the forming part;to form the thin-walled tube,deformation of tube wall occurred due to compression of the bend die.The defect can be eliminated by increase the contact area between tube and the bend die.4.The continuous three-dimensional bending of tube was carried out and effects of primary parameters such as moving speed of the bend die on bending results have been investigated.The results show that,if the tube does not move when the die moves,stress concentration and depression of tube appears in the transition region and the cross-section of the tube is flattened;pushing the tube while the bend die is moving can improve the stress state of tube;within a certain range,increasing the feeding speed or reducing the moving speed of the bend die can improve the stress and strain distribution and reduce the degree of wall depression;reducing the friction coefficient can improve the stress distribution of tube,reduce the degree of wall depression and improve the quality of the forming farts.5.Three-dimensional tube with the angle between two adjacent bending segments at 90° was obtained through flexible bending process and effects of tube feeding and die movement on quality of the forming parts was studied.The results indicate that pushing the tube during the movement of the bend die to the initial position can alleviate the pressure of the bend die and the guide on the tube;with a certain range,increasing the feeding speed or reducing the speed of the bend die can reduce the deformation of cross-section of the tube and improve the quality of forming parts.