Numerical Simulation Calculation Of The CNC Thermal Bending Process Of Ti75 Alloy Tube

Titanium alloys have been widely used as liquid and heat-transfer tubes in the field of aviation,aerospace,shipbuilding,etc.,because of their high strength,light mass,corrosion resistance and so on.During the bending process of the high strength titanium alloy tube,the wall thickness of the outer surface on the tensile side became much thinner,while the one of the inner surface on the compression side became much thicker,and even wrinkles and other quality defects may appear.Especially in high temperature environment,these defects are more likely to appear,seriously affecting the geometry,accuracy and use of the pipe.Therefore,it is the key premise to improve the forming quality of pipe in high temperature environment to explore the forming law of tube,which has important guiding significance for the research of high temperature forming of tubes.In this paper,the Ti75 alloy tube with a size of ?38 mm × t4 mm was used.The microstructure and mechanical properties in different process states were studied by the optical microscope observation and high temperature stretch performance testing,respectively.These data were provided for the simulation calculation.3D modeling software Creo and finite element analysis software ABAQUS were used to investigate the effects of temperature,boost speed and bending rate on the forming quality of titanium Ti75 tube bending in high temperature environments.Because heat and force are involved in the model,finite element simulation uses sequentially coupled thermal stress analysis.The temperature field of the model was analyzed firstly,and the results were used for stress field analysis.The stress field was analyzed firstly using the finite element orthogonal simulation analysis,and the primary and secondary factor influence on the on forming quality,which are the temperature,bending rate and boost rate,were investigated.And then,the optimal process parameters were determined by using finite element simulation optimization parameters.Finally,the reliability of the simulation results was verified through the actual experiment.The main findings are as follows:(1)The aggregation and coarsening of the beta phase for the as-cast Ti75 alloy could be observed.,and the grain boundary is clear.These are the characteristics of the as-cast structure.After heat treatment(Annealing conditions: 880?,120 min,air cooling),the grain boundary of the beta phase disappeared,and the dark-gray beta phases are uniformly distributed in the bright-white alpha phase.A large number of small alpha grains small were distributed in the matrix.The results of the high temperature stretch testing shows that: in the same temperature environment,the ascast specimen exhibits a high tensile strength and a low break elongation,while the asannealing specimen has a relatively higher break elongation as well as good plastic forming performance which is the best choice for the tube material.(2)The radiation and circulating heats with a temperature difference of less than 10? have a small effect on heat transfer in this model.Thus,the heat was considered to be transferred by contact.Such that,the node temperature of the tube bending deformation area after preheating is the same as the mold temperature.Under the actual forming condition,the warm-up time was set for 12 s.(3)The boost rate has the most significant effect on the forming quality of tube.When the value is equal to 1,the tube forming quality is better,the optimal forming temperature is 450?.On the premise of meeting the requirements for use,choosing a shorter bending time can obtain relatively good forming quality,and improve production efficiency.(4)When other conditions are timed,as the bending angle increases,the wall thickness thickening rate,thinning rate and elliptical degree are gradually increased.When the bending angle is greater than 50 degrees,the cross-sectional deformation rate tends to the stage of platform stability.As the bending rate decreases,the section deformation rate gradually approaches the quasi-static forming quality.And when the forming temperature is 450 oC,the bending rate has little effect on Ti75 thermal bending,and the forming defects are relatively small.(5)Through the thermal bending experiment,the validity of the finite element model established in this paper and the reliability of the simulation results were verified,which further proves that the results of this paper are instructive to the actual production.