Finite Element Simulation Study On Bending Process Of Large-caliber Thick-wall Tube By Induction Heating

Induction heating bending process is an advanced forming technology for manufacturing high-performance bent tube,which has been widely applied in gas pipeline,building industry and mechanical equipment manufacturing.However,defects such as inner arc wrinkling,outer arc thinning and radial section distortion may easily occur to tube wall during bending process.It has become a challenging issue to control and improve the forming quality of large-caliber thick-wall bent tube.The induction heating bending process of a large-caliber thick-wall bent pipe is a complex process integrating geometry,physics and boundaries as a whole,and enjoys deformation behaviors such as multi-physics coupling,unsteady state,multi-parameter and non-isothermality.It is difficult to comprehensively analyze the process only by using theoretical analysis,test method or finite element method.Therefore,the bending processed of a large-caliber thick-wall bent pipe by induction heating are investigated deeply in this study by combining test method,theoretical analysis and finite element modeling.The main work and results are as follows:3D finite element models for tube induction heating and bend forming is established based on COMSOL Multiphysics.Based on this 3D finite element model,key modeling issues such as"electromagnetism-heat"and"thermo-mechanical"coupling,boundary conditions processing and mesh generation are addressed;the effect of air boundary-induced electromagnetic wave on induction heating is avoided;and the bending of tube blank under stable electromagnetic induction heating conditions is realized.In addition,the effectiveness of the 3D finite element model is validated by experiments,showing that the simulation results are consistent with the experiment results.Thermal simulation experiment of X60 different temperatures.The deformational behavior during induction heating bending process of large-caliber thick-wall tube is analyzed based on constructed finite element model.Results show that the stress neutral layer occurred between inner surface and outer surface of tube wall along peripheral direction under bending moment.The circumferential plastic strain at deformation zone is small,and deformation mainly occurs along radial and axial directions;then as moving out of deformation zone,circumferential plastic strain gradually increases with the proceeding of bending process,while the plastic strain along the other 2 directions remains unchanged.The ovality of head part is larger than that of bottom part,and the largest ovality occurs at the area between middle point and bottom.The influence rule of key technological parameters to the forming quality of bent tube is investigated.Results show that when the bending radius is set to 2D₀,wrinkling occurs to inner arc of tube wall;with the increase of bending radius,the ovality and wall thickness change rate of tube both decreases;with the increase of induction coil width,the ovality and wall thickness change rate of tube both decreased,and wrinkling occurs to inner tube wall when the induction coil width reaches 82cm;with the decrease of temperature at induction heating zone,the wall thickness changes significantly,and the ovality increases;when the temperature of tube wall is within 851?-905?,wrinkling occurs to inner tube wall;with the increase of advance rate,the ovality gradually increases,deformation inhomogeneity becomes poorer,and wall thickness change rate is reduced;when the advance rate is 54mm/min,significant wrinkling occurs to inner tube wall while significant collapsing occurring to the middle part of tube.Orthogonal test analysis is carried out with three most important parameters as variables.Results show that the bending radius has a significant impact on ovality,inner arc thickening rate and outer arc thinning rate;the heating width has significant impact on ovality;the advance rate has no significant impact on these three indexes.In comprehensive consideration of ovality,wall thickness change rate and deformation inhomogeneity during induction heating bending process,the optimal processing parameters are set as heating width of 60mm,advance rate of 40mm/min and bending radius of 3.5D₀.