Gear surface strengthening technology

Surface hardening treatment, such as surface quenching, shot peening and laser surface strengthening, can obtain the surface hardening layer, but only when the surface hardening layer reaches a certain depth can the surface strength and fatigue resistance of the gear be improved.

Surface quenching:

The most commonly used are high frequency quenching and flame quenching. The hardness, strength and toughness obtained by surface quenching of automobile gears can meet the requirements, and has the advantages of not easy oxidation, small decarburization and deformation, high productivity and so on. However, the biggest weakness of this process is that the tooth root is prone to stress concentration, tooth breakage is easy to occur in use, and the hardness distribution of the tooth surface is uneven.

Shot Peening:

Shot peening can form a layer of residual compressive stress on the gear surface, counteract the tensile stress caused by alternating load, and can significantly improve the bending fatigue strength. The research shows that after shot peening, the bending fatigue limit of carburized gear is generally increased by 20 ~ 30%, and the contact fatigue limit is generally increased by 5 ~ 7%. However, after shot peening, the gear can not be heated at a temperature above 190 ℃, which will also reduce the machining accuracy and surface roughness of the gear. When the parts are subjected to alternating stress at room temperature and high temperature for a long time, the effect of shot peening will gradually disappear.

Laser surface strengthening treatment:

Steel for automobile gears, axles and other materials has strict requirements for surface hardness and wear resistance. The traditional surface quenching process has some shortcomings, such as low production efficiency, easy deformation of material surface, post-treatment after quenching and so on. Laser quenching is to use the laser beam with high energy density (104 ~ 105W / cm2) to scan the material, so that the surface temperature of the irradiated metal or alloy rises above the phase transformation point and below the melting temperature at a very fast speed. When the laser beam leaves the irradiated part, due to the effect of heat conduction, the cold metal cools it rapidly and carries out self cooling quenching (the cooling speed can reach 104 ~ 106 ℃ / s), so as to realize the surface transformation hardening of the workpiece. The high energy density stress wave produced by laser quenching makes the metal surface layer produce stress elastic-plastic deformation, increase dislocation density, improve hardness and fatigue properties. It can significantly improve the surface hardness and wear resistance of metal parts. At the same time, the core of the material still maintains good toughness, so that the parts have good wear resistance, impact resistance and high-temperature fatigue resistance, which can double the service life of the parts. Researchers found that the fatigue life of 7475 – t761 and 30CrMnSiNi2A can be increased by 89% and 74% respectively after laser shock.

Laser quenching has the unique advantages of fast cooling speed, short process cycle, no need for external quenching medium, small workpiece deformation, clean working environment, no need for gear grinding and other finish machining after treatment, and the size of the treated gear is not limited by the size of the treatment equipment.

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