The choice of die processing and material for gear precision forging

“One fire and two forging” form straight bevel gear. The tooth surface of the gear die is affected by the thermal impact of the high temperature gear billet. The temperature rises quickly. The forging temperature is higher than the temperature. After the forging dies, the water graphite is used for cooling and spray lubrication. The die needs to bear the alternating heat and cold load, and the working condition is very bad. Therefore, when precision forging bevel gear, the tooth die has the earliest failure and the shortest service life, which is the key part of precision forging bevel gear.

In order to improve the strength and life of the tooth die, we should not only consider the die material to improve the bearing capacity of the material itself, but also start from the die structure design to effectively use the die material and ensure the bearing capacity of the die. Therefore, the tooth shaped die is designed as a double-layer combined cylinder structure, the outer layer is a die sleeve, and the inner layer is a tooth shaped cavity die. The interference fit between the inner and outer layers not only saves the die steel, but also improves the rigidity, strength and die life, and reduces the production cost.

The tooth shaped die is designed as a double-layer combined cylinder structure, which will deform during the heat treatment of the die and the hot press fit between the die and the die sleeve. Therefore, generally, the die sleeve and the die module should be machined and heat treated respectively for press fit and assembly, and then the tooth shaped cavity part should be processed by the electrode gear. In order to ensure the machining accuracy of the tooth cavity, it is necessary to select a higher precision planer to machine the electrode gear. In order to reduce the surface roughness of the machined surface of the electrode gear and improve the dimensional accuracy of the cavity, it should be divided into three times of rough, medium and fine machining. The discharge intensity is from strong to weak, and the discharge gap is from large to small.

When the bevel gear is formed by “one heat and two forging”, the die is in contact with the high temperature billet, the die cavity is usually heated to 1 ℃, the metal flow is violent, the die cavity surface is very easy to wear, and the die must work under the condition of continuous and repeated heating and cooling, and the failure of the working part often occurs in the form of collapse, thermal wear, thermal fatigue and fracture. Therefore, the die material should have the following properties:

1) High strength and enough toughness

2) High temperature strength

3) Good tempering stability

4) Better thermal and cold fatigue properties

5) Good oxidation resistance and hot melt

6) High hardenability

7) Good cold and hot processing performance.

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