Cold extrusion process is a production technology with high precision, high efficiency, high quality and low consumption, which is widely used in the mass production of small and medium-sized forgings. Compared with the traditional die forging process, it can significantly improve the quality and accuracy of forgings, significantly improve the working environment of workers, save materials as high as 30% ~ 50% and energy consumption as high as 40% ~ 80%.
T. A. Dean et al. Introduced an example of forming spur gear by “push through” cold extrusion. The uneven defects on the upper end face of the gear are caused by the violent non-uniform flow of metal. However, this technology is still in the laboratory trial production stage. If you want to carry out mass industrial production and application, there are still many technical difficulties to be overcome.
Xia Dengyu used the curve and surface modeling function of three-dimensional software to establish the mathematical model of cold extrusion cavity on the basis of flow function theory. The accurate parametric modeling of cold extrusion cavity solves the error caused by manual point repair. The accurate finite element model of extrusion cavity can ensure more accurate simulation results.
Liu Quankun, Li Dongsheng and others used NURBS surfaces to construct a streamlined concave model cavity, and numerically simulated the cold extrusion process of spur gear by using three-dimensional large deformation rigid plastic finite element method. The interface friction model is modified and designed to refine the mesh redrawing process, and more accurate simulation results are obtained. The extrusion forming of streamlined concave mold cavity can significantly reduce the sudden change of deformation, improve the uniformity of metal flow and improve the filling of corner metal.
Song Yanping and Yang Shibin designed a set of simple dies and completed the cold extrusion experiment of spur gears. The surface quality of the formed parts is good, the tooth profile of the spur gear is fully filled, and the accuracy can reach about it8. The test shows that the strength and bending fatigue life of cold extrusion gear are significantly improved compared with cutting gear, and the heat treatment deformation is greatly reduced. It is more suitable for working under the working conditions of high frequency impact and heavy load.
Meng Yajun, Qu Xinhuai, Zhao Han and others designed the pre forging cavity of cold extrusion die for spur gear based on flow curve and equal section theory. The streamlined tooth root transition design ensures that the metal always flows close to the extrusion cavity wall during extrusion molding, and the tooth profile constant section transition design improves the filling capacity of the tooth top. The effects of blank magnification factor on die wear, impact load and filling performance are analyzed. When the magnification factor is 1.06, it is the best molding parameter of cold extrusion concave die cavity.
Zhang Meng used finite element software to simulate and analyze the influence of important parameters such as modulus, number of teeth and transition fillet radius on the cold extrusion forming of spur gear. When the modulus increases by 0.5, the load will be doubled accordingly. The more the number of teeth, the better the filling effect. When the number of teeth is greater than 30, the load will increase sharply, which is not suitable for radial cold extrusion. During cold extrusion forming of spur gear, the elastic deformation of prestressed inner and outer ring is in the order of 10-5, which can be ignored. The elastic deformation of die and parts is the key factor affecting the forming accuracy of spur gear.