Study Of Centripetal Forward And Backward Combined Extrusion Process Based On Hollow Billet

Aluminum and aluminum alloys have wide application prospects and important positions in the fields of aviation,aerospace,nuclear industry and weapon industry because of their advantages of low density,high strength,corrosion resistance and good formability.At the same time,the innovative development technology of aluminum and aluminum alloy is also listed as the key development of national defense science and technology and the basic technology with strategic position.Parts with pad flanges such like hubs can be seen everywhere in real lives.As combined extrusion parts,the traditional use of solid blanks often has the problem of large extrusion load,and subsequent machining is more complicated.Therefore,based on the existing research,this paper proposes a centripetal forward and backward combined extrusion process based on hollow billet,and studies its process.In this paper,the kinematic allowable velocity field of centripetal forward and backward combined extrusion based on hollow billet is established by studying the metal flow law of this process,and the calculation formula of compound extrusion pressure is derived by using the upper bound method.According to the finite element theory,the numerical simulation model of combined extrusion was established.The variation of combined extrusion force under different extrusion temperature,extrusion speed,die fillet radius and friction coefficient was simulated by Deform-3D software.The results show that the extrusion force decreases with the increase of extrusion temperature,increases with the increase of friction coefficient,increases with the increase of extrusion speed,and decreases with the increase of die radius.In addition,the orthogonal experiment was used to evaluate the extrusion load and strain uniformity coefficient Ci.The optimum process parameters were selected as extrusion temperature470 °C,extrusion speed 1mm/s,die fillet radius 5mm,and the friction coefficient should be minimized.The combined extrusion experiment was carried out by 1250 T extruder to produce the hub forming parts.The experimental results show that the theoretical calculation values of the extrusion force are larger than the numerical simulation values and the experimental measured values,and the errors are within 10 %,which proves the accuracy of the upper bound theory and the calculation formula.The microstructure and mechanical properties of different positions of the extruded parts were analyzed.The strength and hardness of the forward extrusion part and the backward extrusion part were better than those of the flange part due to the fibrous grains.After solution and aging treatment of the extruded alloy,the microstructure of the alloy is further changed,the precipitated phase is re-precipitated around the grain boundary,and the mechanical properties of the formed part are further improved.The strengthening effect of the precipitated phase particles is the main reason.