Numerical Research Of Multi-point 3D Hot Stretch-bending Process For Titanium Alloy Profiles

The three-dimensional(3D)stretch-bending structural parts of titanium alloy profiles have the characteristics of light weight,high structural strength,and smooth geometric shape,so they are increasingly used in the production of high-speed vehicles.At room temperature,titanium alloy materials have the characteristics of high yield strength,narrow plastic deformation range,easy cracking,and large springback.Therefore,titanium alloy profiles are generally processed by hot forming.In order to achieve the bending forming of this kind of parts,a multi-point 3D hot stretch-bending process was developed,in which the self-resistance heating method is adopted for forming of titanium alloy profiles.The 3D bending of the profile is achieved by superimposing of the bending deformation in the horizontal and vertical directions.For this process,with the goal of achieving high-efficiency and high-quality three-dimensional hot stretch-bending,this paper uses theoretical analysis and numerical simulation methods to analysis the forming procedure of TC4 titanium alloy profiles in multi-point 3D hot stretch-bending process.The influence law of the process parameters was studied,the research details as follows:The principles and forming steps of the multi-point 3D hot stretch-bending process was introduced at first,the thermal-mechanical coupling effect in the process of hot stretch-bending process is analyzed.Based on the unidirectional hot tensile test data of TC4 titanium alloy samples,the high temperature mechanical properties parameters of TC4 titanium alloy were obtained.Based on the rheological behavior,the Arrhenius high temperature constitutive relationship of TC4 titanium alloy was established.The correlation coefficient value is 0.97583,and the average absolute relative error value is 8.64%,which provides material parameters for numerical simulation.The ABAQUS software was used to establish the simulation model of multi-point 3D hot stretch-bending process of TC4 titanium alloy profile,and the setting of key modeling steps such as analysis steps,boundary conditions,element types and meshing were introduced respectively.Based on the simulation results,a springback prediction model is established.By numerical simulation,the distribution characteristics and laws of the profile temperature field and stress field in the forming process are described,and springback is used to evaluate the forming accuracy.The influence of forming temperature,mold temperature,pre-stretching and supplementary stretching on the forming results is investigated.The heat conduction betweenthe profile and the multi-point die is the main factor affecting the temperature change of the molded part.The higher the initial temperature of the multi-point mold,the more uniform the temperature field distribution of the molded part;the higher the initial temperature of the profile and the multi-point mold,the distribution of stress on the profile is more uniform,and the more springback of the profile gradually decreases with increasing temperature.Pre-stretching and post-stretching play an important role in reducing springback.With the increase of pre-stretching and post-stretching,the springback of the profile shows a decreasing trend.Based on the analysis results,the influence relationship of each process parameter on the forming quality is obtained,which provides a reference for the subsequent research of the multi-point3 D hot stretch-bending test.In this paper,the numerical research of the multi-point 3D hot stretch-bending process for TC4 titanium alloy profiles is conducted,the influence law of various process parameters on the forming quality is quantified,which lays the foundation for the design of the subsequent multi-point 3D hot stretch-bending process and equipment.