As the core component of power transmission, the reliability of the planetary gear system directly determines the life of mechanical equipment under extreme loads and high-speed operation. The collaborative innovation of material science and precision manufacturing processes has given modern planetary gears durability and stability that surpass traditional designs.
1. Special alloy steel: the cornerstone of fatigue resistance and deformation resistance
Planetary gears often use carburized alloy steel (such as 20CrMnTi, 17CrNiMo6), whose surface hardness can reach HRC 58–62, and the core maintains HRC 30–35 toughness, balancing wear resistance and impact resistance. Vacuum degassing smelting technology controls the oxygen content below 15ppm, reduces non-metallic inclusions, and increases the bending fatigue strength to 1,200–1,500 MPa. For example, the sun gear in the wind power gearbox is double quenched (930°C carburizing + 820°C secondary quenching), and the tooth surface contact fatigue life exceeds 1×10⁷ cycles.
2. Powder metallurgy process: a breakthrough in microstructure homogenization
The density of powder metallurgy gears manufactured by atomization powder making-cold isostatic pressing-sintering process can reach 7.4-7.6 g/cm³ and the porosity is less than 0.5%. Adding 2-3% copper or nickel as a binder phase can form a diffusion-strengthened layer when sintered at 1,200°C, which increases the bending strength of the tooth root by 30%. This process is particularly suitable for micro planetary reducers, and the tooth profile accuracy is stable at ISO 5 level (error ≤8μm), avoiding stress concentration caused by traditional cutting.
3. Surface modification technology: the ultimate line of defense against friction and wear
Physical vapor deposition (PVD) coatings such as CrAlN (chromium aluminum nitride) can reduce the surface friction coefficient from 0.12 to 0.05 and maintain lubricity at high temperatures of 200°C. Laser surface cladding technology can generate a 0.2–0.5mm thick Stellite 6 alloy layer on the tooth surface, with a microhardness of HV 1,100, and a 4-fold increase in resistance to abrasive wear. For space robot arm gears, MoS₂ solid lubricant film ensures 10⁹ revolutions of oil-free operation in a vacuum environment.
4. Collaborative optimization of precision manufacturing and heat treatment
CNC forming gear grinding machines (such as KAPP VX300) use CBN grinding wheels to achieve a tooth surface roughness of Ra 0.4μm, and with shaping processes (such as drum teeth and topological trimming), the transmission error is controlled within 1 arc minute. Carburizing heat treatment uses a low-pressure vacuum furnace, with a carbon potential fluctuation of ±0.05% and an effective hardened layer depth tolerance of ±0.1mm, avoiding grain boundary oxidation caused by traditional gas carburizing.
5. Assembly accuracy and residual stress control
The planetary carrier is manufactured using investment casting, and the planetary hole position error is compressed to φ0.01mm with a three-coordinate measuring machine (CMM). The prestressed assembly technology uses liquid nitrogen to cool the shaft (-196°C), so that the surface compressive stress generated by the interference fit reaches 300-400MPa, inhibiting the initiation of fretting fatigue cracks.