Powder metallurgy manufacturing is a scientific discipline that uses metal and non-metal powders as raw materials and employs techniques such as compaction, sintering, and various post-processing methods to produce metallic components. This technology enables the fabrication of high-performance powder metallurgy products at relatively low costs. When applied to gear manufacturing, powder metallurgy can significantly reduce production costs.

Based on the principles of powder metallurgy forming and sintering mechanisms, this paper primarily focuses on the development and application of high-performance iron-based powder metallurgy helical gears.

The research is conducted in the following specific areas:

Research on High-Performance Iron-Based Powder Metallurgy Helical and Spur Gears. Based on the molding principles for powder metallurgy products with complex structures, this study explores various die design approaches for powder metallurgy helical gears. By establishing a mathematical model of helical gear manufacturing process parameters, the die designs are optimized to enhance the strength and precision of the gears. Furthermore, research is conducted on high-performance, low-cost iron-based powder metallurgy gear materials.

I. A Comparative Study on the Performance of Helical Gears and Spur Gears.

1. During gear meshing, straight-tooth gears follow the following principle: tooth engagement—force transmission achieved through pure involute rolling—tooth separation—transfer of force transmission to the next pair of teeth.

2. As can be seen from the above discussion, gear meshing is inherently intermittent. For involute gears, factors such as manufacturing tolerances and installation errors further exacerbate this characteristic of discontinuous transmission.

3. The use of involute tooth profiles is intended to achieve smooth transmission and a constant gear ratio. However, due to manufacturing tolerances, the sudden engagement and disengagement of teeth may induce transient impact forces within the mechanism.

4. Meshing principle of helical gears: They feature smooth, impact-free engagement and disengagement. In each engagement-disengagement cycle, the meshing and disengagement between each pair of teeth occur gradually. Unlike spur gears, helical gears do not experience any meshing impact, resulting in smooth operation and helping to maintain a constant transmission ratio.

5. In spur gears, the load-bearing surface of the teeth extends axially across the entire tooth width. In helical gears, although the load-bearing surface is also distributed axially, it does not cover the entire tooth width. Under identical conditions—such as the same module, number of teeth, and material—helical gears experience lower stress than spur gears.

Advantages of helical gears:

1) Excellent meshing performance. Smooth transmission, low noise, and minimal impact.

2) High overlap ratio. Each tooth shares the load evenly, enabling high-speed, heavy-load operation with stable performance.

3) Compact structure. Fewer equivalent teeth required.

II. Mold Design and Molding Principles

1. Mold design depends on the product’s shape, dimensions, density, height, and the equipment selected. To ensure dimensional consistency of mass-produced parts, molds must have a long service life and high precision. To manufacture high-quality molds, it is crucial to rationally select mold materials, heat treatment processes, and machining technologies. The core and cavity of the mold should be made from materials with excellent wear resistance; their heat-treated hardness should reach HRC 60 or higher, such as hard alloys YG15 and YG8, high-speed steels W18Cr4V, ASP60, or SKH-9. As for the upper and lower punch dies, they should exhibit good impact resistance and sufficient wear resistance; their heat-treated hardness should range from HRC 56 to 60, for example, alloy steels GCr15, 9CrSi, SKD11, or 3V.

2. Powder metallurgy forming involves placing loose metal powders or mixtures (powder compacts) into steel molds. Under the pressure exerted by the mold, the powder is compacted and maintained at a certain pressure; then, the pressure is released, resulting in a dense blank with a defined shape, size, density, and strength. Subsequently, the blank is ejected from the die.

III. Comparative Study of Raw Materials

Through process trials targeting different compositional materials—Fe-2.0Cu-0.8C, Fe-1.5Cu-0.6C-1.0Ni, and Fe-1.5Cu-0.6C-1.75Ni-0.5Mo—we investigated the pressing and sintering properties of various iron-based powder metallurgy gear materials, as well as the influence of alloy elements on the sintering performance of these materials.

Development of High-Performance Iron-Based Powder Metallurgy Helical Gears. Building on the aforementioned research, we successfully developed powder metallurgy helical gear products through material design, process optimization, and die design. The developed gears have smoothly passed bench tests and demonstrated significant social and economic benefits.