Measures to Effectively Reduce Gear Transmission Noise in Gear Reducers

To ensure that gear reducers pass factory testing, it is essential to address the issue of intermittent high noise levels. Tests using the ND6 precision sound level meter indicate that low-noise gear reducers register 72.3 dB(あ), meeting factory standards, while high-noise gear reducers reach 82.5 dB(あ), failing to meet the requirements. Through repeated testing, analysis, and experimental improvements, it has been concluded that comprehensive management across all production stages is necessary to effectively reduce gear transmission noise. Below are detailed measures to achieve this goal:

1. Controlling Gear Precision

Achieving precise gear manufacturing is fundamental. Based on practical experience, the following standards should be adhered to:

• Gear Precision Standards: Gear accuracy must meet GB10995-887 level 7–8.
• High-Speed Gears: For gears with a linear speed above 20 m/s, the gear pitch tolerance, radial runout of the gear ring, and gear alignment tolerance must consistently achieve level 7 precision.
• Additional Considerations: Gear teeth must be chamfered, and care must be taken to avoid root bulges.

2. Ensuring High-Quality Raw Materials

High-quality raw materials form the foundation for manufacturing superior products. Common materials like 40Cr and 45 steel used in gear production must undergo rigorous quality assurance measures:

• Chemical Composition Analysis: Ensures consistency in material properties.
• Grain Size Measurement: Determines the material’s structure.
• Purity Assessment: Evaluates inclusions and impurities.

These processes ensure proper heat treatment adjustments and improved gear machining quality.

3. Preventing Heat Treatment Deformation

Heat treatment is a critical stage that significantly affects gear performance. The following measures should be implemented:

1. Normalizing and Quenching :
   • Soften steel parts to facilitate cutting operations.
   • Eliminate residual stress.
   • Refine grains to improve mechanical properties.
   • Prepare the microstructure for final heat treatment.
2. Process Controls :
   • Ensure uniform furnace temperature and use appropriate fixtures to allow even heating and cooling.
   • Prevent stacking of parts during heat treatment.
3. Drilling Post-Treatment: Weight-reduction holes should be drilled after heat treatment to maintain structural integrity.
4. Final Heat Treatment: High-frequency quenching minimizes deformation while providing gears with:
   • High strength and hardness on the surface.
   • Adequate plasticity and toughness at the core.

4. Guaranteeing Gear Blank Precision

The accuracy of gear blanks directly impacts overall gear performance. The following measures are recommended:

• Dimensional Accuracy: Gear hole size deviations should center around ±0.003 to ±0.005 mm. Components outside this range must be classified and handled accordingly.
• Runout Tolerances: End face and radial runout tolerances must meet level 6 standards, within a range of 0.01–0.02 mm.

5. Enhancing Gear Cutting Processes

Precision gear cutting is critical to reduce noise levels. Key steps include:

• Inspection of Purchased Tools: Gear cutting tools must meet AA-grade standards.
• Tool Sharpening: Tools must be checked for:
  • Radial alignment of cutting edges.
  • Accumulated pitch errors.
  • Parallelism between tool faces and bore axes.
• Tooth Profile Adjustments: Increase the tooth height coefficient by 0.05–0.1m to reduce root interference. Use chamfered hobs for gears with module M = 1–2.
• Deburring and Chamfering: Eliminates burrs and sharp edges to improve engagement.
• Equipment Maintenance: Cutting machines must undergo annual precision checks and timely repairs.

6. Promoting Civilized Production Practices

Approximately 30% of gear transmission noise originates from burrs and dents. Proactive measures include:

1. Protecting Gear Parts :
   • Apply specialized plastic covers immediately after machining to prevent damage.
   • Store and transport gears with protective covers.
2. Gear Honing :
   • Reduces surface roughness.
   • Removes burrs.
   • Prevents dents during operation.

7. Adopting Alternative Materials and Surface Treatments

Innovative materials and processes can further reduce gear noise:

1. Powder Metallurgy: Produce gears using powder metallurgy, followed by high-frequency quenching.
2. Malleable Cast Iron: After machining, gears can undergo soft nitriding treatment.
3. Advanced Materials: Use 40Cr steel with post-machining treatments like soft nitriding or copper plating.

Comprehensive Summary

Addressing gear transmission noise requires a holistic approach:

• Material and Heat Treatment: Form the backbone of noise reduction strategies.
• Gear Blank Precision: Provides foundational accuracy.
• Gear Precision: Serves as the critical factor.
• Civilized Production Practices: Establish a supportive environment for consistent quality.