The Study Of Backward Extrusion Process For Ti-Ni Alloy Tube

TiNi alloy has the strong point of high strength, low density, high-temperature resistance etc. It is widely used now, especially, the application of Ti-Ni shape memory alloy joints have a broad prospect in the military and civilian industry. In a hot-working process, TiNi alloy changes in shape with higher resisting force, lower thermal conductivity, larger temperature difference between inner and surface billet, uneven deformation , so it is difficult to apply the ordinary perforated pipe forming extrusion process to TiNi alloy tubes.Using the Finite Element software DEFORM-3D,the paper makes a Thermo-Mechanical Coupling numerical simulation on the hot backward extrusion process of theφ44×10.5(mm)TiNiNb alloy tubes, and analyses the changing rules of the Extrusion force, mandrel tension and the temperature filed during the extrusion process.About the confirming the deformation parameter of the hot backward extrusion forming experiment of TiNiNb tubes, the paper applies the single-factor techniques. Based on the Thermo-Mechanical Coupling numerical simulation, the paper analyses the relation of the shaping-changing parameters including extrusion force and the extrusion angle of die, length of the calibrating strap, die, preheating temperature of the extrusion container and the billet, the extrusion spreed and the friction coefficient, on the basis that at the exit point of the die the tube's temperature is lower than the metal eutectic melting point and ascertains the main shape-changing parameters, it also gives a reasonable range.All the parameters are about the extrusion angle of die, preheating temperature of the billet , the pressure speed, and the friction coefficient,Based on the results of the numerical simulation, the paper establishes the quantitative relationship of extrusion force, heating temperature of the billet, and extrusion speed with hydraulic extrusion press's peakload as limit. It also ascertains the quantitative relationship of the temperature of the tubes at the exit point of the die, the heating temperature of the billet and the extrusion speed. the paper makes an Extrusion female die about the TiNiNb alloy tubes and establishes reasonable extrusion conditions ofφ44×10.5(mm)TiNiNb alloy tubes in experiment.The paper ascertains the best combination of the main technological parameters and structural parameters of die.That is, under the condition of lubrication, the extrusion angle of die, preheating temperature of the billet , the extrusion speed, should be 120°,950℃and 50 mm/s respectively. By making the hot backward extrusion forming experiment about tubes on the three sunstances---lead(Ph),45steal, and TiNiFe alloy, the paper verifies the feasibility of the best assembly parameters.