Study Of Thick-wall Tube Open-die Cold Extrusion With Mandrel Technology

Thick-walled tube is an important manufacturing mechanical parts in a great demandand for a wide range of applications. Most of the required thick-walled pipe in theproduction would meet the using requirements only after a lot of machining, which resultsin low efficiency and material consumption. Therefore, the study on the efficient, low-costmanufacturing method of thick-walled tube has important theoretical significance andgreat economic benefits.In this paper, a lot of the system research on the process parameters related of thethick-walled tube open-die cold extrusion with mandrel technology by a combination ofcombining theoretical modeling, numerical simulation and experimental study.On the basis of preliminary studies, the open-die cold extrusion with mandrel wasanalyzed by dividing into the three kinds of deformation, reducing outer diameter with thesame inner diameter, expanding inner diameter with the same outer diameter and neckingouter diameter with expanded inner diameter. And the critical process parameters weredefined: deformationε, mold cone angle (cone angle of the die 2α, mandrel coneangle2α') coefficient of frictionμ, billet original thickness to diameter ratiot 0D0, theyield strength of materialσs.The open-die cold extrusion with mandrel was simulated and analyzed. The metaldeformation process was intuitively divided into the unreformed stage, deformation stageand the deformation stage. The failure form of extrusion was simulated when parameterswas not correctly selected, and the measurement of the upsetting value was determined inthe verification experiment. The trajectory of the metal particles which was simulated ingood agreement with the theoretical analysis of flow lines.As the simulation results is discrete, a large of systematic theoretical studies arecarried out in this paper. The comprehensive analysis methods of forming theory is createdfor open-die cold extrusion with mandrel.Based on the theory of fluid mechanics, stream function method was introduced firstlywhich is a rigorous theory of kinematically admissible velocity field to determine thecontinuous deformation flow model. The establishment of a continuous velocity fieldmodel in kinematics was performed by the introduction of stream function and the use ofvelocity boundary conditions and constant volume. strain rate field was obtained based onthe relationship between the strain rate field and velocity field. A unified expanding power calculation formula was deduced using the upper limit method for open-die cold extrusionof the thick-walled tubes with mandrel, including the three kinds of deformation, reducingouter diameter with the same inner diameter, expanding inner diameter with the sameouter diameter and necking outer diameter with expanded inner diameter. The quantitativeanalytic solution was established between the force and energy and the impact forceparameters, the relationship of the force and energy was obtained in the combinations ofcertain parameters. The best mold half cone angle range was detemined:α_opt(α′_opt)=6°¹2°,and the key parameters of the mold design was obtained.According to the instability criterion for thick-wall tube forming by open-die coldextrusion with mandrel, the theoretical criterion model for maximum deformation degreeis obtained for the three kinds of deformation, reducing outer diameter with the same innerdiameter, expanding inner diameter with the same outer diameter and necking outerdiameter with expanded inner diameter. Based on the theoretical maximum deformationdegree model, the variation law of maximum deformation degree in combinations of theparameters is investigated. Whent₀ / D₀ = 0.15,μ=0.03, the max value of the maximumreduction in reducing outer diameter with the same inner is up to 41%. Compounding theis up to 36% in expanding inner diameter with the same outer diameter, which filled theblank of no available data in formulating open die cold extrusion with mandrel.Based on the theoretical and simulated parameters range, targeted, feasibilityexperimental program was designed. A series of typical experiments is conducted and thetheoretical result was verified by experiments. The verification results show that: themaximum relative error of the theoretical calculations and experimental results is less than10%, and the accuracy of theoretical calculations is proved.The extrusion process of the typical part billet with material saving and efficient in ahydraulic cylinder bracket was developed initially by the application of research resultsand related data, and extrusion dies was designed. By the self-developed special extrusionmachine, the successful extrusion of the connecting column billet was realized whichprovides guidance and reference for formulating process of the relevant parts of open diecold extrusion.