Research On Extrusion Of Internal Threads In Titanium Alloy Deep Small Blind Holes With Different Lubrication

With the development of modern precision machinery in the direction of lightweight,miniaturization and ultra-high strength of alloys,high-strength alloy micro-sized parts have been widely used in various fields.Titanium alloy has high strength,good rigidity,good corrosion resistance and high thermal strength,and can still maintain mechanical properties at low temperature.Because of its excellent mechanical properties and biocompatibility,it has been widely recognized and used in automobile parts,aerospace parts,energy equipment and modern biomedicine.However,the elastic modulus of titanium alloy is small,and the springback amount is large in the process of material processing.It is difficult for cutting fluid to enter,the cooling lubrication is poor,and the torque is unstable in the process of processing,which easily leads to the fracture of the tap.In order to improve the machining quality and forming efficiency of threaded connectors,it is a common method to produce internal threads by plastic extrusion in aerospace,modern medicine,energy and other internal thread parts.It is of great significance to systematically study the extrusion processing of internal threads in deep holes of titanium alloy.In this paper,Ti-6A1-4V is used as workpiece material,and the extrusion forming process of deep and small blind hole internal thread(M1.2,H=4mm)is systematically studied by combining experimental research with finite element simulation,so as to deeply understand the extrusion forming process of titanium alloy deep and small internal thread,thus providing a basis for the optimization of process parameters.The main research contents and conclusions are as follows:Firstly,under the condition of dry extrusion,the experiments of internal thread extrusion of titanium alloy blind holes with bottom hole diameter of 1.1mm and 1.09mm were carried out with different spindle speeds,and the internal thread extrusion of bottom hole diameter of 1.1mm was numerically simulated with Deform.The results show that the torque decreases with the increase of spindle speed in the range of 50-2000r/min under dry extrusion condition.The optimum spindle speed is 1500r/min and 2000r/min,and the crack at the crest gradually decreases,but the thread surface finish is poor and the depth of hardened layer decreases.At the same spindle speed,the extrusion torque can be effectively reduced by using 1.1 mm diameter of bottom hole compared with 1.09mm,and the thread profile and quality obtained are better;When the diameter of the bottom hole is 1.1mm,and the rotating speed of the spindle is in the range of 50r/min-2000r/min,the simulated torque decreases,the equivalent stress at the tooth shape decreases,the equivalent strain increases and the temperature increases.Secondly,under the condition of castor oil lubrication,experiments on internal thread extrusion processing of titanium alloy blind holes with bottom hole diameters of 1.1mm,1.09mm and 1.07mm were carried out by using different spindle speeds,and the internal thread extrusion processing of different bottom hole diameters at the same spindle speed was numerically simulated by using Deform.The results show that in castor oil lubrication environment,the torque decreases with the increase of spindle speed in the range of 50-2000r/min.When the diameter of the bottom hole is 1.1 mm and 1.09mm,the extrusion torque obtained by lubricating with castor oil cutting fluid is lower than that obtained by dry extrusion,the thread morphology and tooth shape quality are improved,and the depth of hardened layer is increased At the same spindle speed,the torque decreases with the increase of bottom hole diameter,and the thread morphology and tooth shape quality improve;At the same spindle speed,the simulated torque increases as the diameter of the workpiece bottom hole decreases.The equivalent stress and strain at the tooth shape are increasing and the temperature is increasing.At last,under the lubrication condition of MoS2 nanoflow cutting fluid,the experiments of internal thread extrusion processing of titanium alloy blind holes with bottom hole diameter of 1.09mm and 1.07mm were carried out with different spindle speeds,and the internal thread extrusion processing with bottom hole diameter of 1.09mm under the same spindle speed and different lubrication environment was numerically simulated with Deform.The results show that under the lubrication environment of MoS2 nano-flow cutting fluid,the torque decreases with the increase of spindle speed in the range of 50-2000r/min;Under the same bottom hole and spindle rotation speed,compared with dry extrusion and castor oil lubrication,MoS2 nano-flow cutting fluid lubrication environment has the lowest extrusion torque,higher internal thread tooth shape quality,good surface finish and large hardened layer depth at high rotation speed;Under the same bottom hole and spindle speed,when the lubrication environment is MoS2 nanoflow cutting fluid,the simulated extrusion torque is the lowest,the equivalent stress at the tooth shape is the smallest,and the equivalent strain is the largest.