With its convenient operability and accuracy of simulation results, finite element software helps designers greatly shorten the R & D cycle of products and molds, fundamentally improve the R & D efficiency and save labor costs. At the same time, the numerical simulation results can directly reflect the possible problems in the plastic forming process, and provide guidance for the process scheme design of spur gear. However, the numerical simulation only approximately presents the metal plastic forming process in the virtual environment, which can not be 100% consistent with the actual. At this time, the process experiment of spur gear is particularly important. The process experiment provides an evaluation standard for checking the accuracy of numerical simulation results.
The cold extrusion process parameters of spur gear are optimized, the cold shaping mode of spur gear is selected, the corresponding shaping amount is determined, and the cold extrusion combined die is optimized. The above research starts with a single process and die. Therefore, this chapter carries out the composite forming process experiment of spur cylindrical gear for the purpose of verifying the forming effect and the accuracy of numerical simulation of continuous “cold extrusion + cold shaping” composite forming process of spur cylindrical gear. Through the process experiment, it is proved that the straight cylindrical gear produced by the continuous “cold extrusion + cold shaping” composite forming process has good forming quality and high forming precision, and the expected effect is obtained. It can stably and continuously produce the large modulus straight cylindrical gear that meets the design requirements.
This paper mainly carries out process experiments on the compound forming process of continuous “cold extrusion + cold shaping” of spur gear, designs, manufactures and assembles the dies respectively, and carries out corresponding extrusion pretreatment on the blank. After the experiment, the size, accuracy, metallography and hardness of the compound formed spur gear are tested, which can be summarized as follows:
① The cold extrusion die and shaping die in the composite forming process adopt three-layer combined die. After press fitting, the die core of the combined die is processed by “coarse wire cutting – fine wire cutting – EDM – polishing – manual grinding”. The tooth profile accuracy of the die is guaranteed to be grade 5, and the surface roughness reaches RA 0.2 μ m。 The cold extrusion die and cold shaping die are assembled with high-precision positioning mandrel and installed in a high-precision die base with guide post and guide sleeve. The extruded blank is hot forged into ring blank with solid bar. Before extrusion, it is spheroidized and annealed. The spheroidized body is rated as grade 6 and the hardness is in the range of 120 ~ 145hbs. After fine turning, it is subject to phosphorus saponification lubrication treatment.
② According to the measurement of the compound formed spur cylindrical gear, the minimum diameters of the upper and lower tooth tops are 74.40mm and 73.86mm respectively, which meet the requirements of subsequent turning outer circle. The outer convex of the lower end face is about 2mm and the concave of the upper end face is about 2mm, which is better than the spur cylindrical gear processed under the original process. The accuracy test of spur gear shows that the maximum total deviation of tooth profile is 12.2 μ m. The tooth profile accuracy grade of GB / t10095 is grade 6; The maximum total deviation of helix is 26.6 μ m. The accuracy grade of GB / t10095 tooth direction is grade 8, so the large module spur gear for truck can be processed and produced by compound forming process.
③ The metallographic and hardness tests of the compound formed spur gear show that the surface metal has a large amount of extrusion deformation, the ferrite grains are broken or distorted in varying degrees, the cold work hardening phenomenon is obvious, and the hardness value of the surface metal is large; The deformation of the core metal is small, the ferrite grains are extruded and deformed, but the grain boundary remains, the granular carbides gather at the grain boundary, and the hardness of the core metal is low.