Application of Powder Metallurgy in Gear Manufacturing

---

Gear manufacturing technology includes hobbing, milling, gear shaping, powder metallurgy pressing and other processes. Powder metallurgy gear is widely used in various automotive engines, which is very economical and practical in large quantities.

What is powder metallurgy
It is a process technology for manufacturing metal materials, composite materials and various products by forming and sintering metal or using metal powder (or mixture of metal powder and non-metal powder) as raw materials. Generalized powder metallurgical products industry includes iron tool, cemented carbide, magnetic materials and powder metallurgical products. In the narrow sense, the powder metallurgical products industry only refers to powder metallurgical products, including powder metallurgical parts (accounting for the vast majority), oil bearing and metal injection moulding products.

Advantage:
1. General powder metallurgy gear manufacturing processes are few.
2. When the gear is manufactured by powder metallurgy, the material utilization rate can reach more than 95%.
3. The repeatability of powder metallurgical gears is very good. Because powder metallurgy gears are formed by pressing with dies, under normal operating conditions, a set of dies can press tens of thousands to hundreds of thousands of gear blanks.
4. Powder metallurgy can integrate several parts.
5. The material density of P/M gears is controllable.
6. In powder metallurgy production, the roughness of the working surface of the die is very good in order to facilitate the stripping of the blank from the die after forming.

Disadvantages:
1. It is necessary to produce in batches. Generally speaking, more than 5000 pieces in batches are suitable for powder metallurgy production.
2. The size is limited by the pressing ability of the press. Press presses are usually several tons to hundreds of tons of pressure, the diameter is basically less than 110MM can be made into powder metallurgy;
3. Powder metallurgy gears are restricted by their structure. Because of the reasons of pressing and die, it is not suitable to produce worm gear, herringbone gear and helical gear whose helical angle is more than 35 degrees. Helical gears are generally recommended to be designed within 15 degrees.
4. The thickness of powder metallurgical gears is limited. The die cavity depth and press stroke must be 2-2.5 times the thickness of the gear. Considering the uniformity of the longitudinal density of the gear height, the thickness of powder metallurgical gear is also very important.

Technological characteristics
1. The density of products can be controlled, such as porous materials, good density materials, etc.
2. Fine grains, homogeneous microstructures and no segregation.
3. Near-form forming, the utilization ratio of raw materials is more than 95%.
4. Less or no cutting, cutting only 40-50%.
5. Controllable material components are beneficial to the preparation of composite materials.
6. Preparation of insoluble metals, ceramics and nuclear materials.

Basic process flow
1. Powder Making
Pulverizing is the process of making powder from raw materials. The common methods of pulverizing are oxide reduction method and mechanical method.
2. Mixture
Mixing is the process of mixing various required powders in a certain proportion and homogenizing them into billet powder. It can be divided into dry type, semi-dry type and wet type for different requirements.
3. Forming
Forming is the process of pressing a billet with a certain shape, size and density by loading a uniform mixture into a die. The forming methods are basically divided into pressure forming and non-pressure forming. Compression moulding is the most widely used in pressure moulding.
4. Vacuum Sintering
Vacuum sintering is a key process in powder metallurgy process. The formed compacts are sintered to obtain the required final physical and mechanical properties. Vacuum sintering can be divided into unit sintering and multicomponent sintering. Besides ordinary sintering, there are some special sintering processes, such as loose-packed sintering, melt-immersion sintering and hot-pressing sintering.
5. Post-processing
After sintering, various methods can be adopted according to the different requirements of products. Such as finishing, oil immersion, machining, heat treatment and electroplating. In addition, in recent years, some new processes such as rolling and forging have also been applied to the sintering process of powder metallurgical materials, and satisfactory results have been achieved.

Learn more: Powder Metallurgy Vacuum Sintering Furnace