There are many factors affecting the quality of the gear, such as the quality of the material, the precision forging process, the blank heating process, the die structure, the machining accuracy of the tooth profile, the overall quality of the die, the heating of the blank, the control of the forging process, the control of the state of the die, After forging normalizing, turning, boring, spline broaching of semi-axle gears, as well as carburizing and quenching, grinding, etc. have different degrees of impact on the accuracy and performance of the gears. The following paper will discuss several major influencing factors.
1. Precision forging process of planetary gears and half shaft gears
The planetary gear and semi-axle gear precision forging process mainly has the following five kinds: one fire two forging, one fire two forging and cold pressing, one fire two forging and warming, hot forging and cold pendulum milling and cold extrusion forming. Among them, the hot forging and cold pendulum milling and cold extrusion forming precision precision forging gears have high precision and can reach ISO7-8. It is mainly used for precision forging of planetary gears and semi-axle gears for passenger cars and mini-cars. Jiangsu Pacific Precision Forging Co., Ltd. adopts the forming process of hot forging and cold pendulum milling. Jiangsu Spaceship Co., Ltd. adopts cold extrusion forming planetary gears and half shaft gears. Due to the large cold extrusion force, the cold extrusion process is difficult to apply to truck planetary gears and side gears.
The accuracy of a fire for two forging and cold precision gears can be controlled at ISO8-9, and FAW Special Vehicle Co., Ltd. uses this process to produce planetary and semi-axle gears for trucks. The application of a fire for two forging and warming is affected by the life of the thermo-precision die, and the application is limited to a certain extent. Since the two forging process of a fire does not have a coining process, the gear precision fluctuates greatly, generally in the ISO 8-12 class.
2. Heating of gear blanks
At present, most manufacturers use medium frequency induction heating for the gear blank. This process has a fast heating speed, which can effectively reduce the oxidation during the heating process of the blank, and the inert gas is introduced into the furnace, which further reduces the tendency of the scale generation of the blank. In addition, some manufacturers use gas or heavy oil to heat the gear blank, and in the furnace through the incomplete combustion of the fuel or the introduction of a reducing gas, the formation of a reducing atmosphere in the furnace suppresses the oxidation of the blank.
3. Precision machining of planetary gears and half shaft gears
The tooth die is the most important working part of the planetary gear and the semi-axle precision forging die. Generally, the structure of the die core and the outer casing is used to not only save the use of the die steel, but also the interference between the core and the jacket. The resulting pre-stress ensures the dimensional stability and die life of the precision forging. Hot forging die tooth cores are often made of H13 or 3Cr2W8V materials. H13 has the distinction of rolled material and electroformed remelting material. The material of electroforming remelting is more compact. There is no anisotropic property, and the performance is obviously better than that of rolled material. However, the price is higher, so the amount of rolled material is more. Since the thermal toughness of 3Cr2W8V is not as good as that of H13, the thermal fatigue resistance under the same conditions is not as good as that of H13, and the crack propagation speed is faster. The cold-rolling and cold-squeezing die tooth-shaped cores are generally made of high-speed steel materials, and mass production tends to be hard alloy materials. The forging process and heat treatment process of die steel, especially high-speed steel, have a great influence on the life of the die. The forging temperature range of high-speed steel die blank is small, and it needs to be repeatedly drawn. The general forging ratio is not less than 4, so the forging is particularly difficult. If the operation is not proper, the mold life is very low. In addition, the quality of high-speed steel heat treatment has a great impact on the mold. The hardness is high and easy to crack; the hardness is low, and the tooth mold is easily deformed. Under normal circumstances, the hardness of the tooth-shaped mold material H13 is 48-52HRC, and the hardness of 3Cr2W8V is 48-52HRC.
The main processing method of the tooth mold cavity is formed by electrode electric discharge machining. The machining process and machining accuracy of the mold electrode determine the accuracy of the mold and therefore play a vital role in the accuracy and quality of the part. At present, foreign countries have begun to try to directly process the tooth-shaped cavity by the hard milling process after the hardening of the tooth die core. However, the tool cost is too high, and the cavity cavity precision limits the processing efficiency of the die, so it has not been widely used.
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