Continuous Cross-section Pipe Hydraulic Expansion Study

The continuous cross-section tube is differential thickness tube,which is made by welding tube process by Tailor Roll Blank.The TRB tube has a transition zone and no wall thickness mutation compared with the tailor welded tube.The TRB tube in the process of hydraulic bulging change rule of transition zone,influence law of parameters of transition zone on forming performance,influence law of different parameters of tube on tube billet deformation coordination and un-axial filling expansion stepped tube was studied.The hydraulic bulging model of TRB tube with different parameters is established to study the changed law of the transition zone in process of hydraulic expansion.The influence of length,thickness difference and length ratio of transition zone on moving volume and elongation of transition zone and max thinning rate of pipe is studied.The results show that the length of transition zone of 60 mm is a cut-off point in the trend of change.The movement volume and maximum reduction rate decreases with speed is reduced quickly before then slow with length of transition zone increases,the change is not obvious when the length of transition zone is greater than 60 mm.The elongation is increased before then decreases and the max is 0.22 mm when length of transition zone is 60 mm.The thickness difference of 1.5mm is a cut-off point in the trend of change.The movement volume and max reduction rate increases with thickness of wall increases.The moving volume increases fast and max reduction rate increases slowly and quickly but it increases faster when thickness difference is greater than 1.5mm.And the elongation is trend of decreases.The movement quantity and the max decrease rate is trend of decreases with length ratio increases.The elongation is decreases then increases and the min is-0.03 mm when length ratio is 1 and the transition zone is compressed.The influence of length ratio is more complicated than the difference between the length and thickness of the transition zone.A tailor-rolled blank(TRB)tubes hydraulic account FEM for different transition zone parameters is established.The new way for discrete irregular transition zone is proposed.The influence of TRB tubes transition curve,thickness difference and length of transition zone on expansion property is studied.Based on result of the numerical simulation,the BP neural network prediction model was established and the predicted results will be compared with the numerical simulation results to verify the accuracy of the predicted results.The result indicates that the parameters have different effects on the expanded performance,but have a significant influence on the maximum forming height,the max difference reached 6.47 mm and min is 2.88 mm.The concave arc transition curve has the worst forming performance and the max difference for forming height is 2.88 mm.The increase of transition zone is conducive to bulging,but the forming performance decreases rapidly with the increase of thickness and the height difference of thickness is 8.22 mm.The single set of predicted value is within the margin of error,so the prediction model can be used to predict the expansion of TRB tubes in other transition zone parameters.The free expansion model of TRB tube of different parameter is established to realize the effect of TRB tube parameters on deformation coordination.The influence law that length of transition zone,thickness ratio and length ratio on deformation coordination,thin tube limit bulging and max expansion of thick tube was studied.The results show that the deformation coordination,the limit bulging and the max expansion are increases first then decreases with length of transition zone increases,deformation coordination reached a max value of 0.362 and limit expansion of the max value of 9.32 mm and max expansion of the max value 3.43 mm when length of transition zone is 40 mm.The deformation coordination decreased rapidly with thickness ratio increases but limit expansion is the change process of rapidly increasing,slowly increasing and decreasing and max expansion increases first then decreases.The limit expansion is 9.48 mm when thickness ratio is 2 and the max expansion is 3.76 mm when the thickness ratio is 1.5.The deformation coordination slowly decreases and then increases rapidly with length ratio increases and the min value is 0.178 when length ratio is 1.The limit expansion is increased rapidly first then increases slowly when length ratio is larger than 1.7 and max expansion is increased slowly first then increases rapidly when length ratio is larger than 1.A tailor-rolled blank(TRB)tubes hydraulic bulging FEM for un-axial filling expansion stepped tube is established.The influence of the length of transition zone,length of expansion zone of TRB tubes and thickness of design wall for stepped pipe on thickness distribution of final forming part was studied.And axial asymmetric stepped tube was simulated of forming.The result indicates that the max difference between min wall thickness of forming part and the thickness of design wall is 0.109 mm,which is 5.45% of the thickness of design wall.The max difference between max wall thickness and design wall thickness is 0.117 mm,which is 5.85% of the thickness of design wall.The max difference in the shape of axial asymmetric step tube is 4% and 4.88% of the thickness of design wall respectively.Therefore,the wall thickness distribution is considered to be uniform.The difference of wall thickness and between min wall thickness and the thickness of design wall is increase with the increase of thickness of design wall.The extreme difference reaches 0.109 mm and 0.042 mm respectively,which has the greatest influence on the wall thickness distribution.The wall thickness difference is increases with the increase of length of the transition zone,and the difference between min wall thickness and design wall thickness decreases rapidly when the length of the transition zone is less than 30 mm,then the change is not obvious.The length of the expansion zone is similar effect law to the two wall thickness difference,and the difference is small.