Research On Optimization Of Extrusion Mandrel Structure Of Titanium Alloy Internally Threaded Tube

The development of high-corrosion-resistant,high-performance heat exchange threaded pipes to reduce leakage accidents due to corrosion in the marine environment is an urgent problem in the field of ocean engineering.Titanium alloy is known as a marine metal and is an ideal material to replace the copper alloy or stainless steel threaded pipe.However,the titanium alloy has poor plasticity,large deformation resistance,and the complex forming of internal threaded pipes has the characteristics of small thread tooth forming size and high precision requirements,which leads to difficult mold structure design and low mold trial success rate.Therefore,it is necessary to treat titanium alloy internal threads.The structural parameters of the pipe extrusion die are studied.In this paper,TA1 titanium alloy is used as the test material,and the titanium alloy internally threaded tube is used as the research object,and the structure of the extrusion die is designed.A simulation model of the initial extrusion die was established on the Deform-3D software platform.The extrusion process of the internally threaded pipe was numerically simulated by setting reasonable simulation parameters.The forming law of the metal material in the extrusion process was analyzed and discussed,including the internal the deformation of the threaded tube,the rheological law of the material in the mold cavity,combined with the extrusion test to verify the rationality of the mold structure design,the research shows that the uneven flow of the metal material during the extrusion process is a defect in the forming of the internal threaded tube the main reason.Aiming at the forming defects of TA1 titanium alloy internally threaded tube during the extrusion process,the system explored the influence of internal threaded mandrel thread rise angleφ₁,thread length L and angle of attackφ₂ on extrusion forming.Studies have shown that appropriately increasing the thread lift angle can make the overall flow rate more uniform,while increasing the thread lift angle can increase the accumulation of the blank at the front end of the mandrel,increase the tangential and radial strain,and reduce the axial tensile strain,which make the filling of the thread teeth more full;when the length of the mandrel thread is adjusted from 5mm to 10mm,the thread length has a greater effect on the balance of the metal flow rate.In addition,increasing the thread length mainly affects the tangential strain and the radial strain when the thread teeth are formed;the change of thread length and thread lift angle will inevitably cause the change of the extrusion force;the appropriate adjustment of the angle of attack of the mandrel will fine-tune the uniformity of the flow rate of the pipe wall.By using the response surface method,the thread length L,the thread lift angleφ₁ and the mandrel angle of attackφ₂ are used as design variables.VRD₁,VRD₂ and F are optimized target parameters,a multi-response regression model is established,and the interaction between design variables and target parameters is explored,the particle swarm algorithm is used to globally optimize by the established multi-response model,and finally internal thread mandrel the optimal parameters:thread length L=11mm,thread lift angleφ₁=30°,and angle of attackφ₂=96°.The optimized mandrel structure is compared with the initial threaded mandrel structure design,the VRD₁ of the pipe wall speed of the threaded pipe material head is reduced by 50.38%,and the VRD₂of the tooth part speed is reduced by 44.81%.The structure parameters of the mandrel were processed by die processing and extrusion test.The results showed that the thread lift angle of the internal teeth of the TA1titanium alloy internally threaded tube reached 19.8°,the tooth height dimension is0.98mm,which is close to the ideal value（1mm）and the quality was qualified.