Precision near net shape forming of spiral gear belongs to less and no cutting technology. Due to its outstanding advantages such as material utilization, high productivity, low cost and good performance, countries all over the world attach great importance to this research, but it is mainly focused on the following forming methods:
(1) Extrusion precision forming process
Extrusion commonly used are forward extrusion, reverse extrusion and compound extrusion. According to the temperature, it can also be divided into hot extrusion, warm extrusion and cold extrusion. Due to high temperature, serious oxidative decarburization and low dimensional accuracy, the spiral gear process is rarely used.
(2) Traditional block forging
Block forging is an advanced manufacturing technology developed in the world in recent years. It is a kind of non flash die forging. The principle is to close the separable die and apply sufficient clamping force to the closed die, and then extrude the blank in the die bore from one or more directions with one punch or multiple punches. Foreign block forging technology has been widely used in the production of automobile parts.
(3) Floating die closed precision forging
In the traditional one-way extrusion mode, the upper punch goes down, the die and the lower punch are stationary, the main direction of material flow is downward, and the die moves upward relative to the workpiece, resulting in upward friction. The more materials filled into the cavity, the greater the friction, which makes many materials stay at the upper end of the workpiece and it is difficult to flow to the lower end of the workpiece, resulting in the upper end of the workpiece being filled first. In view of this filling defect, the floating principle of the die is proposed. The die adopts the floating structure to make the die move downward relative to the workpiece. The “effective friction” force between the workpiece and the die makes the material flow downward, which is conducive to the filling of the lower tooth end. Cheng Yu of Xi’an Jiaotong University and others made full use of the floating die theory and constrained diversion theory to systematically study the hole diversion, the die structure with mandrel and insert, and selected the best hole diameter, mandrel diameter and insert height dimension matrix when forming spiral gear. Jiang Hongzhi and Wan Pingrong carried out finite element simulation and Experimental Research on the precision forging process of hollow spiral gear by using the floating die structure, obtained the metal flow law and deformation mechanical characteristics of the precision forging process of hollow helical In the traditional one-way extrusion mode, the upper punch goes down, the die and the lower punch are stationary, the main direction of material flow is downward, and the die moves upward relative to the workpiece, resulting in upward friction. The more materials filled into the cavity, the greater the friction, which makes many materials stay at the upper end of the workpiece and it is difficult to flow to the lower end of the workpiece, resulting in the upper end of the workpiece being filled first. In view of this filling defect, the floating principle of the die is proposed. The die adopts the floating structure to make the die move downward relative to the workpiece. The “effective friction” force between the workpiece and the die makes the material flow downward, which is conducive to the filling of the lower tooth end. Cheng Yu of Xi’an Jiaotong University and others made full use of the floating die theory and constrained diversion theory to systematically study the hole diversion, the die structure with mandrel and insert, and selected the best hole diameter, mandrel diameter and insert height dimension matrix when forming spiral gear. Jiang Hongzhi and Wan Pingrong carried out finite element simulation and Experimental Research on the precision forging process of hollow spiral gear by using the floating die structure, obtained the metal flow law and deformation mechanical characteristics of the precision forging process of hollow spiral gear, and revealed the deformation mechanism of hollow spiral gear. The die is designed into four structures of floating and fixed forms when the convex die is plane and inclined respectively. The effects of different design schemes on metal flow and required load are studied. At the same time, the effects of friction on metal flow and load are discussed. The results show that when the convex die is inclined and the concave die is floating structure, it is most conducive to the filling of spiral gear cavity and the reduction of forming load.
(4) Powder metallurgy forging
In recent ten years, powder metallurgy, as a “advanced metallurgy” high and new technology, especially powder forging technology, can achieve the tooth profile without machining cutting teeth with less forming steps, which is equivalent to the usual forging process such as precision forging process, which has attracted extensive attention in the world. At present, the manufacturing technology of some new powder metallurgy structural parts for cars is only mastered and mass produced in a few countries such as the United States, Germany and Japan, which is still blank in China. However, in terms of forging spiral gears with powder, China has also built a powder hot forging production line for spiral gears for automobiles and tractors, and has entered the stage of batch production.