The precision forging of spiral bevel gear is carried out under the environment of high temperature and high pressure, and the existence of friction between die and blank is very unfavorable to the forming of forging. In order to make the metal filling die chamber more smoothly, reduce the forging deformation force, prevent die sticking and clamping, reduce the wear of working part of forging die and prolong the service life of die, It is very necessary to fully lubricate the die in the precision forging process of spiral bevel gear. The lubricant used shall meet the following requirements:
1) It has good lubrication performance at high forming temperature and can effectively reduce the friction between spiral bevel gear blank and die bore.
2) It can effectively prevent the heat exchange between the spiral bevel gear blank metal and the die, prevent the early failure caused by the thermal fatigue of the die, and prolong the service life of the die.
3) Good demoulding performance ensures that the formed forging can be smoothly detached from the die bore without adhesion with the die.
4) It does not corrode the blank metal, mold and forming equipment of spiral bevel gear, does not pollute the environment, is easy to clean, safe and convenient to use and has good economy.
At present, the most widely used in the hot precision forging of spiral bevel gear is water-based graphite, which can fully meet the stringent requirements of lubricant performance for hot die forging. Compared with lubricants such as engine oil and oil-based graphite, the use of water-based graphite can prolong the service life of the die by more than half.
The main components of water graphite are graphite, release agent, high temperature wetting agent, carrier and other additives. Among them, graphite has hexagonal flake crystal structure. In the crystal, the bond bonding force of carbon atoms at different levels is very weak, while the bond force between carbon atoms at the same layer is very strong, so it shows a good compressive lubrication effect; Because the main chemical component of graphite is carbon, it has stable chemical properties and does no harm to human body; At the same time, the price of graphite is relatively low and the economy is good. The carrier of water agent graphite is mainly water, and the price of water is low, easy to obtain and no pollution. In addition, the water with high vaporization heat can take away part of the heat in the vaporization process, which can achieve the purpose of cooling the mold.
When using water graphite lubricant, the control of its dose has a great impact on the lubrication effect, but its impact is not linear. When the dose reaches a certain value, the reuse of too much lubricant has little impact on the lubrication effect, which will only cause the waste of lubricant. Fig. 1 shows the relationship curve between friction coefficient and lubricant thickness.
When spraying water agent graphite to cool the mold, its effect is greatly related to the injection pressure and the injection amount per unit time. The relationship curve is shown in Figure 2. Increasing the injection amount per unit time is more effective than increasing the injection time; In addition, high injection pressure can disperse the hot steam around the die.