In recent years, achieving high gear accuracy has become a paramount priority in ensuring optimal performance across various applications. For instance, the automotive industry is undergoing a significant transformation with the rapid adoption of electric vehicles (EVs). Projections indicate that EVs could account for approximately 42% to 58% of global car sales by 2030. 

In EVs, noise reduction is a significant concern. The absence of an internal combustion engine makes other noises, such as gear noise, more noticeable. The precision of gears is crucial in minimizing this noise, and grinding processes play a major role in achieving the necessary accuracy.This article explores two key grinding methods—Gear Generation Teeth Grinding and Profile Teeth Grinding delving into their principles, applications, and guidance on selecting the appropriate method for specific scenarios.

Based on the comparison above, we can determine the most suitable grinding method for our part by considering factors such as production volume, gear design complexity, precision requirements, and cost efficiency.

Generation Gear Grinding

When designing and manufacturing gears with generation teeth grinding, key factors such as gear geometry, material selection, and critical decisions about machine choice, fixture design, and heat treatment methods are crucial to optimize the process for quality, performance, and cost-effectiveness.

1. Machine Selection- 

• Based on Gear Data (Max Diameter, Module, Max Length etc.)
• Max Allowable Grinding Wheel Diameter, Speed 
• Max Rotary table load
• Automation: No of spindles (2), If high volume production to save loading- unloading time.

2. Fixture Selection- 

• Hydraulic (Cost high, Shorter time)
• Mandrel (Low Cost, Longer time compare to Hydraulic)

Fixture directly impact on process parameters, so choose fixture according to volume.

3. Stock Allowance Per Flank-

• Depends on deformation after Heat Treatment.
• Finalize stock allowance based on module and tip diameter of part.

The theoretical stock allowance per flank typically ranges from 0.10 mm to 0.50 mm. If heat treatment (HT) causes significant deformation, a deformation factor should be applied based on the extent and shape of the part. For example:

• Solid gears tend to have less deformation during HT.
• Thin-walled parts experience higher deformation during HT.

Adjust the deformation factor accordingly to ensure that an adequate stock allowance is maintained for grinding.

4. Number of Strokes-

• Larger stock allowance requires more passes.
• In some cases, multiple passes help manage the wear of the grinding wheel, ensuring consistent cutting performance.

Typically, the last 1–2 passes are reserved for finish grinding, where a reduced feed rate is used. This approach ensures a finer surface finish and achieves the desired precision without excessive material removal.

5. No of Start- In generation grinding, the number of starts on the grinding wheel refers to how many cutting edges are actively engaged during the process. Here’s how to decide:

• Single-start: Used for fine grinding or high-precision applications where surface finish and profile accuracy are critical. This setup provides better control but slower material removal.
• Multistart – Choose a number of starts that does not evenly divide the number of teeth on the gear.

Example-      No of Teeths= 27, No of Start= 2 or 5

6. Process Parameters- After determining the above variables in the grinding process, the next step is to set the process parameters accordingly. (Grinding worm RPM & Feed)

• Larger Tip Diameter: Requires lower RPM to avoid excessive heat and wear.
• Smaller Tip Diameter: Requires higher RPM to achieve the desired cutting speed and material removal.
• Larger Module (larger teeth): Needs lower RPM to maintain proper cutting conditions.
• Smaller Module (finer teeth): Needs higher RPM for efficient material removal.

7. Dressing & Dresser type- In gear generation grinding, selecting the right dressing tool is essential for achieving high-quality results. 

Double Radius Form Roll                                       Single Taper Disc                                  Double Taper Disc                        Composite Diamond Roll                                   Profile Diamond Roll

The Double Taper Disc is widely used due to its high precision, longer life, and stability, making it ideal for consistent dressing and superior surface finishes. The dressing cycle and grinding wheel RPM should be selected based on the dresser type and desired part quality. Proper selection ensures optimal performance, tool longevity, and a high-quality finish.

Note: Ensure the use of appropriate process parameters to prevent common issues such as grinding burns and chatter marks on gear teeth.

Profile Gear Grinding

To produce parts using profile grinding, it’s essential to focus on factors such as the part type and its geometry. Based on these, select the appropriate machine and grinding wheel type. Next, consider parameters like stock allowance, grinding approach, specific material removal rate (Qw), axial feed, and chip volume (Vw) to determine the optimal dressing cycle.

We will explore what needs to be adapted at each stage of the part during profile grinding.

1. Machine Selection- The selection of the machine should be based on the part geometry, grinding wheel size, and required accuracy to ensure precise grinding and optimal results. 
2. Selection of Grinding Wheel- The selection of a grinding wheel depends on factors such as the material type (harder materials need CBN or diamond), abrasive type (e.g., aluminium oxide for general use), grain size (finer for finishing, coarser for roughing), bond type (vitrified for precision, resinoid for flexibility), and wheel hardness (softer for hard materials). Additionally, consider the wheel shape, grinding process, and required surface finish. Proper wheel selection ensures efficient grinding and achieves the desired part quality.
3. Stock Allowance- In profile grinding, it’s essential to define the theoretical stock allowance and deformation factor based on the heat treatment process (e.g carburizing or nitriding). Stock allowance typically ranges from 0.1 mm to 0.7 mm, depending on factors such as the heat treatment process, tip diameter, module, and part geometry.

       4.    Material Removal Rate (Qw) – Depend on Module & Heat treatment method.

• Carburizing Parts: Material removal rate (Qw) ranges from 5-16 mm³/mm/sec.
• Nitriding Parts: Material removal rate (Qw) ranges from 5-9 mm³/mm/sec.

Module Consideration: The appropriate and adaptable Qw can be defined based on the module for efficient material removal.

       5.    Axial Feed- Based on factors like material type (softer materials allow higher feed), grinding wheel type (harder wheels need slower feeds), surface finish requirements (slower feed for finer finish), part geometry (complex shapes need slower feed), material removal rate (Qw), and machine stability. Balancing these factors ensures effective grinding while maintaining precision and part quality.

Feed ranging from- 4000- 5500 mm/min

      6.   Chip Volume- For the roughing cycle, higher chip volume (Vw) is used, influenced by factors like larger module, heat treatment, diameter, and face width to remove more material quickly. In the finishing cycle, lower chip volume is preferred to achieve a smooth surface finish, with smaller chip volumes influenced by smaller module, heat treatment, diameter, and narrower face width. Roughing focuses on efficient material removal, while finishing prioritizes precision and surface quality.

Roughing Vw – 2500-6000 mm3/mm

Finishing Vw= 200-350 mm3/mm

So based on decided chip volume we can calculate after how many no of teeth we can dress the wheel in each cycle by using below formula- 

Number of teeth’s ground until dressing cycle=   Vwae X Z

Vw= Chip volume (mm3/mm)

ae= Total radial infeed (mm)

Z= Face width of gear (mm)

7. No of Passes- Generally we followed the profile grinding by 2 passes (Roughing & Finishing)

Roughing Pass- We need to define no of strokes based on Rouging stock (from total stock we need to keep 0.04 to 0.05 mm for finish) rest we need to remove in roughing cycle.

Example= Total stock allowance= 0.34 mm

Roughing Stock= 0.295 mm⭢ Calculate Infeed normal per flank for roughing⭢ Qw X SinPressure angelX60Axial Feed⭢ Total Stock/Infeed stock = No of strokes in roughing.

For Example, Qw= 6

Pressure Angle= 25° (Radian= 0.436)

Axial Feed= 4500

Infeed Normal per flank= 6 x 0.436 x 60/ 4500= 0.034 mm

Roughing Strokes= 0.295/0.034= 9 strokes 

Finish Stock= 0.045 mm (here use 2 strokes max)

8.  Grinding Approaches – We need to determine the appropriate grinding approach based on the desired final quality of the part.

Once all the process parameters and approaches are set, we are ready to begin profile grinding. Before starting, ensure proper stone positioning to achieve optimal grinding contact and accuracy. It’s also essential to closely monitor the process to avoid issues such as grinding burn, which can affect part quality. Keeping track of factors like grinding wheel sharpness, coolant flow, and feed rates throughout the process will help prevent overheating and maintain surface integrity. By following these precautions and maintaining close control over the grinding process, you can achieve the desired profile with high precision and minimal defects.