The three forming process schemes will be comprehensively evaluated and analyzed from the three aspects of material utilization, production efficiency and process feasibility, and the best process scheme will be determined. In terms of material utilization: the forming scheme of spur gear I forms parts, the tooth top collapse angle of the lower surface is serious, and the blank can not be fully formed, and a large amount of cutting allowance is reserved. The forming schemes 2 and 3 of spur gear adopt continuous extrusion to form the external teeth. In the forming process, the lower blank provides a certain back pressure for the forming of the upper blank, which effectively improves the filling effect of tooth profile and reduces the machining allowance of spur gear. However, when forming internal teeth in the second forming scheme of spur gears, flanging occurs on the upper end face of the part’s internal hole and reaming occurs on the lower end face, which reduces the effective tooth profile length of internal and external teeth and increases the machining allowance. The third forming scheme of spur gear only needs to ensure the effective tooth profile length of external teeth formed by continuous extrusion. Compared with the first and second forming schemes of spur gear, the material utilization rate is higher.
In terms of production efficiency: the method of simultaneous extrusion of internal and external teeth in scheme 1 and the method of finishing external teeth and forming internal teeth in scheme 2 reduce the forming process and relatively improve the forming efficiency. The male and female dies for the simultaneous shaping of internal and external teeth in scheme I and scheme II have tooth structure, which require high guiding accuracy of the equipment and complex installation and disassembly of the die. It will take a lot of time to change the die, which will seriously affect the production efficiency. In the second forming scheme of spur gear, the tooth punch is used to form the internal teeth, so the through finishing die can not be used for rapid extrusion forming. After finishing, the parts must be pushed out of the finishing concave model cavity through lower ejection. The third forming scheme of spur gear adopts the method of continuous extrusion for the formed outer teeth, and the method of rapid extrusion by through finishing die for the formed inner teeth. Moreover, the male and female dies have no relative position requirements, and the die installation and disassembly are convenient and fast, which can ensure high production efficiency.
In terms of process feasibility: in the process of simultaneous extrusion of internal and external teeth in the forming scheme of spur gear, due to the large blank deformation and severe metal flow during the forming of external teeth, the internal teeth have serious plastic deformation, and the local area is even completely closed, which can not meet the original design intention of one-step forming of external teeth and internal teeth. The second and third schemes of spur gear forming adopt continuous extrusion to form the external teeth. The external teeth have good forming quality, relatively simple die structure and high production efficiency. In the second straight tooth spur gear forming scheme, after finishing, the parts rest at the bottom of the finishing die. At this time, the minimum distance between the part tooth surface and the die should remain unchanged. However, when the internal tooth punch goes down to form the internal teeth, the minimum distance between the finished tooth surface and the die has changed significantly, as shown in the figure.
The finished tooth surface has small plastic deformation, and the accuracy of spur gear has been damaged, which can not meet the original design intention of finishing external teeth while maintaining the accuracy of spur gear and forming internal teeth. The third forming scheme of spur gear is to form the external teeth by continuous cold extrusion, then improve the gear accuracy by cold finishing, and finally form the internal teeth of involute spline by broach, which is feasible in theory.
The comprehensive comparative analysis shows that the material utilization rate of the third spur gear forming scheme is high, the continuous extrusion and push finishing forming mode can ensure high production efficiency, and the forming process scheme is feasible in theory. Therefore, the third spur gear forming scheme is selected as the best forming process scheme for follow-up research.