Research On Numerical Simulation On Process Of Internal Thread Formed By Cold Extrusion

Process of internal thread formed by cold extrusion has a great prospect in the thread processing onaircraft landing gear, high-speed train and many other applications working on high speed and dynamicload conditions because of its excellent forming accuracy, surface integrity and the improvement ofthread connection strength and fatigue life, which maintain the cold hardening state on the threadsurface after cold extrusion.Technology of internal thread formed by cold extrusion has been developedafter years of study, however, it still lacks of numerical simulation on it and needs to be strengthenedurgently. In this paper, the mathematical model of extrusion torque during the forming process is build,the rigid plastic finite element software DEFORM-3D is used for the numerical simulation on theprocess of internal thread formed by cold extrusion, and both are experimentally verified to lay thefoundation for further understanding the forming process, optimization and selection of the extrusiontap and process parameters, and to provide a new research tool for the process of internal thread formedby cold extrusion. The major work completed in this paper and the results achieved are as follows:(1) The forming mechanism of internal thread formed by cold extrusion is analyzed based on theelastoplastic deformation theory, and the force condition during the forming process is analyzed basedon it to derive the theoretical formula of contact stress and contact arc length in the extrusiondeformation area, and then to derive the theoretical formula of extrusion torque during the entireforming process of internal thread formed by cold extrusion. Comparative analysis of theoretical andexperimental extrusion torque curve under the same process parameters is found that the trend of thecurves are consistent and the error between them is small, and it can be used as the theoretical basis forfurther studying the mechanical analysis during the forming process of internal thread formed by coldextrusion.(2) The numerical simulation on process of internal thread formed by cold extrusion is carried outbased on the finite element model established by using of rigid plastic finite element softwareDEFORM-3D. The forming process of internal thread cold extrusion is truly reappeared to show thatthe finite element model built is valid and can be used as the basis for the further research and analysis.The distribution of effective stress and effective strain are analyzed to show that the effective stress andeffective strain during the forming process are concentrated on the deformation area in the thread ofworkpiece and other part of the workpiece is independent of the effects of compressional deformation.The metal flow velocity field during the forming process is also analyzed to show that the velocity fieldpresents a flow line along the tooth-shaped surface contour and the speed in the top of the thread are greater than other parts of the thread. Both of them are fully described that the metal material canflow into the tooth groove of the extrusion tap (the top of thread tooth) in which has smaller resistanceconstantly during the forming process. The extrusion torque and temperature during the formingprocess are also derived, and both of them are experimentally verified. Both of the extrusion torque andtemperature curve with time have the same change trends with their experiment and those of the errorare small to fully verify the validity of the model.(3) In order to reduce the extrusion torque and temperature during the forming process and toimprove the forming quality of the internal thread and the life of the extrusion tap, study on theinfluence law of process parameters include workpiece diameter, extrusion speed and coolant on theirextrusion torque and temperature by using numerical simulation base on its correctness and validityverified. The orthogonal experiment method is also used to optimize the process parameters during theforming process of internal thread formed by cold extrusion.(4) The displacement of vibration plate and the angular velocity of vibration rod and extrusion tapare derived by dynamic simulation using ADAMS software base on the testing device of low frequencyvibration used in the forming process of internal thread formed by cold extrusion. Numerical analysisof the nonlinear relationship among the amount of the reduction of friction coefficient and excitingforce, exciting arm and the extrusion speed are also carried out. It shows that when the frequency isfixed, the smaller the extrusion speed and the exciting arm, the greater the exciting force, the better thefriction reduction effect. Another mechanism on the friction reduction is studied: the instantaneousseparation between the workpiece and extrusion tap due to vibration making the original sealed coolantin extrusion tap groove can reenter the extrusion area. The affection relationship on the vibrationfrequency is also analyzed. Import the vibration into DEFORM-3D to carry on the numericalsimulation on internal thread formed by cold extrusion based on low frequency vibration, it shows thatthe forming process, the distribution of effective stress and effective strain and the metal flow velocityfield are similar with the traditional cold extrusion process by imposing the20Hz external vibration,however, the extrusion torque reduces to57.2%of original one, and the error between its numericalsimulation and experimental one is13.7%, which verify the correctness of the anti-friction theory in acertain extent.(5) The relationship among extrusion torque during the forming process and the structuralparameters of an extrusion tap is analyzed based on the mechanical model of extrusion torqueestablished and experimentally verified. Two set of optimal structural parameters of an extrusion tapare obtained respectively using total extrusion torque and single-tooth extrusion torque as the fitnessfunction by genetic algorithm, which show that the extrusion tap optimization to reduce the torque during the forming process is effective and lay the foundation for the further research of the experimentof internal thread formed by cold extrusion.