A Brief Introduction To Gear Profile Modification

I. Why Is Gear Profile Modification Necessary? (Purposes and Imperatives)

1. Elastic Deformation: During power transmission, slight elastic deformation occurs in gear teeth, shafts, and bearings. This causes the root of the driving gear tooth to "over-cut" into the tip of the driven gear tooth (known as "interference"), resulting in impact, vibration, and noise.

2. Manufacturing and Installation Errors: Gears themselves have minor pitch errors and tooth profile deviations. During installation, there may be center distance errors and misaligned axes. These errors disrupt the ideal meshing state.

3. Thermal Deformation: Heat generated during system operation causes thermal expansion of the gearbox and gears, altering the original meshing conditions.

• Tooth Tip Edge Contact: Intensified meshing impact.

• Stress Concentration: Excessively high contact stress at the tooth tips and roots.

• Increased Vibration and Noise: Compromised transmission stability and comfort.

• Reduced Efficiency: Energy loss due to additional friction and impact.

II. Main Types of Modification

1. Tooth Profile Modification - Modification Along the Tooth HeightIt involves altering the tooth profile shape within the end plane perpendicular to the gear axis. The main types include:

• Tip Relief: The most commonly used tooth profile modification method, which involves appropriately thinning a small portion of the involute tooth profile near the tooth tip. Its purpose is to compensate for base pitch errors and gear tooth deformation, avoid tooth tip edge contact as well as meshing-in and meshing-out impacts, and ensure smooth transmission.

• Root Relief: Thinning the root of the gear at the area corresponding to the tooth tip of the mating gear. Its purpose is to prevent interference between the tooth tip of the mating gear and the root of the current gear, also facilitating a smooth transition during meshing.

• Crowning Modification: Shaping the tooth profile into a slight drum shape with the middle part slightly protruding. Its purpose is to compensate for gear eccentric loading and installation errors, enabling the load to be better concentrated at the middle of the tooth surface and avoiding edge stress concentration.

2. Tooth Trace Modification - Modification Along the Tooth WidthIt refers to modifying the tooth surface shape in the direction parallel to the gear axis. The main types include:

• Tooth End Relief: Appropriately thinning both ends of the gear tooth along the tooth trace direction. Its purpose is to compensate for shaft and gearbox deformation as well as gear helix errors, prevent stress concentration at the tooth ends, and improve the load distribution on the tooth surface.

• Tooth Crowning Modification: Shaping the tooth surface into a slight drum shape along the tooth width (bulging in the middle and lower at both ends). As the most effective tooth trace modification method, it can significantly compensate for eccentric loading caused by shaft torsional deformation and installation misalignment, concentrating the contact pattern at the middle of the tooth surface and improving load-carrying capacity and service life.

III. How to Achieve Gear Profile Modification? (Manufacturing Methods)

1. Modified Gear Grinding: The most accurate and commonly used method. On a CNC gear grinding machine, the movement trajectory of the grinding wheel is controlled through software programming to directly grind the required modified tooth profile. It is the preferred method for achieving complex modifications (such as crowned teeth).

2. Modified Gear Shaving: For gears with soft tooth surfaces, a modified shaving cutter can be used for shaving, transferring the modification amount to the gear tooth surface.

3. Modified Gear Honing: Similar in principle to gear shaving, a modified honing wheel is used for finishing heat-treated gears. It not only improves surface quality but also achieves a certain degree of modification.

Conclusion