The principle of forward extrusion forming process of spur gear is shown in the figure. Under the action of extrusion punch, the metal blank is extruded from the concave mold cavity to obtain the required tooth shape parts. The blank generally adopts hollow cylindrical ring blank or solid cylindrical bar. During extrusion, the flow direction of the metal is consistent with the movement direction of the punch. Under the action of the extrusion punch, the metal mainly flows along the tooth direction of the tooth concave die to complete the filling and forming of the tooth shape in the die forming area.
J. H. song, Y. T. IM and others designed and developed a set of computer-aided design system, which is applied to the development of forward extrusion process and die design of spur gear. By inputting the basic parameters of spur gear in the user interface, such as modulus, number of teeth, pressure angle, displacement coefficient, design contact ratio and bending strength capacity of the product, the effective data of limiting extrusion ratio of tooth top and tooth root and limit forming load on die design can be obtained. The spur gear is formed by forward extrusion. Due to the friction resistance between the blank metal and the die cavity, the flow velocity of the surface metal of the blank and the core metal is inconsistent. The flow velocity of the surface metal of the blank is less than that of the core metal, resulting in shrinkage on the upper end face of the spur gear and collapse on the lower end face.
Xue Song, Feng Zhixin and others correctly divided the forward extrusion deformation region of spur gear into 9 regions by using the upper bound element method, established a simplified mathematical model of each region, analyzed the metal flow law of each region, and carried out experimental verification. The mathematical model basically conforms to the metal flow law during forward extrusion, and the error of calculation results is small. A convenient and correct method for calculating the forward extrusion load of spur gear is proposed. The surface profile of the extrusion die is composed of three characteristic areas: die entry area, deformation area and shaping area.
Chen Wei, Wang Yang and other researchers believe that the die insertion angle of the female die is the key process parameter affecting the forward extrusion forming of spur gear. When the die insertion angle is small, the outer and central layers of the blank metal flow evenly, the flow velocity difference is small, and the dead zone of deformation is the least. With the increase of the die angle, the greater the flow velocity difference between the surface layer and the central layer of the blank metal, and the dead zone of deformation increases gradually. The research shows that the reasonable die insertion angle is 40 ° ~ 66 °. The deformation area of the die is a streamline complex three-dimensional surface. The shape of the deformation area, the streamline transition design of the deformation area and shaping area and the manufacturing accuracy grade of the die are the key and difficult points of the forward extrusion technology of spur gears. Because the deformation rate can not be too large in the process of material extrusion, as well as the constraints of concave mold cavity manufacturing and equipment extrusion capacity, at present, the forward extrusion process of spur cylindrical gear is only applied to the production of spur cylindrical gear with small modulus and small geometric size.