Forming Law And Parameter Optimization Of NC Bending Of Dissimilar Bimetallic Composite Tube

Because of its high performance,low cost and worked in the harsh service environment,dissimilar bimetallic composite tube is increasingly used in the fields of petroleum,ocean,nuclear energy,transportation and national defense.the NC rotary draw bending is the preferred processing technology of tube bending,which is an important component in the pipeline system.However,in the process of bending,it is easy to appear defects such as outer arc side thinning and cracking,inner arc side thickening and wrinkling,section distortion,while it is different in properties of base and cladding tube and the existence of bonding interface,the bending mechanism is more complex and the control is more difficult.These problems seriously restrict the improvement on forming quality and bending process properties of NC winding parts of dissimilar bimetallic composite tube.For this reason,in this paper,the NC rotary draw bending of 20#/T2 tube is studied systematically and deeply by using the finite element simulation method and the experimental and theoretical methods.The conclusions are as follows:(1)A 3D finite element models on NC rotary draw bending of dissimilar bimetallic composite tube was established,and the key problems such as geometric model establishment,boundary condition treatment,meshing and mass scaling were solved.the reliability of the finite element model was verified by experiments.(2)Based on the finite element model,the deformation behavior of dissimilar bimetallic composite tube in NC bending process was analyzed.It is found that the tube begins to deform about 20 °before the bending tangent point,and ends when it reaches the bending tangent point;the deformation degree of the outer arc side is greater than that of the inner arc side,and the strain neutral layer moves toward the inner arc side;there is a stress discontinuity on the bonding interface,but there is no strain discontinuity.The difference of material properties and the existence of bonding interface between base cladding tubes can decrease the change of wall thickness,but have little effect on the distortion of cross section.(3)With the increase of the relative bending radius,the wall thickness change rate and section distortion is basically decrease with the characteristics of linear;with the increase of mandrel protrusion,the wall thickness reduction rate and the section distortion is decreases; with the increase of pressing speed,the wall thickness reduction rate and the section distortion is slightly decreases.(4)The thickness thinning defect of outer arc side wall can be decreased by increasing the gap between composite tube and mandrel or reducing the gap between composite tube and bending die or pressing block,or reducing the friction coefficient between composite tube and mandrel or increasing the friction coefficient between pressing block and composite tube.Reducing the clearance between composite tube and bending die and mandrel,or increasing the friction coefficient between composite tube and bending die,the friction coefficient between composite tube and anti-wrinkle block,and the friction coefficient between composite tube and mandrel can reduce the thickening of outer arc side tube wall.reducing the gap between composite tube and bending die,pressing die and mandrel,or increasing the friction coefficient between tube and bending die,pressing block or reducing the friction coefficient between tube and mandrel can reduce the degree of cross-section distortion of curved tube.(5)the four most significant process parameters in the forming process,the amount of mandrel protrusion,the gap between the composite tube and the mandrel and the bending die,and the friction coefficient between the mandrel and the composite tube are selected as design variables for orthogonal experimental analysis.Considering the distortion and wall thickness change rate of heterogeneous dissimilar bimetallic composite tube,the optimum process parameters are determined as follows: 3mm for mandrel protrusion,0.15 mn for clearance between mandrel and composite tube,0.05 mm for gap between mandrel and bending die,and 0.05 for friction coefficient between mandrel and composite tube.