Gear grinding is one of the most accurate finishing methods for producing high-precision gears. It can achieve gear accuracy grades from Grade 7 to Grade 4. Although gear grinding requires expensive equipment, skilled operators, and has relatively high production costs, it offers significant advantages over other finishing methods such as gear shaving and gear honing.
Compared with shaving and honing, gear grinding can machine hardened gears while providing better correction of errors from previous machining operations. It also compensates for distortion caused by heat treatment, resulting in higher dimensional accuracy and improved gear quality.
To achieve these results, selecting the right gear grinding wheel is essential for maintaining both machining accuracy and surface finish.
Choosing the Right Gear Grinding Wheel
1. Abrasive
When grinding hardened alloy steel or high-speed steel gears, the gear grinding wheel should use white aluminum oxide (WA), pink aluminum oxide (PA), or a blend of both abrasives.
2. Wheel Hardness
The harder the gear material, the softer the gear grinding wheel should be. Form grinding wheels have a relatively large contact area with the workpiece, making them more likely to generate heat, so a slightly softer wheel is recommended. However, the wheel should not be too soft, as profile accuracy must still be maintained. For dry grinding, a softer wheel is also preferred because of reduced heat dissipation.
3. Grit Size
The grit size of the gear grinding wheel should be selected according to the required gear accuracy and surface finish. Higher precision and lower surface roughness generally require finer abrasive grits.
4. Bond Type
A vitrified bond is commonly used because of its stable grinding performance. For high-speed grinding applications, a specially formulated vitrified bond designed for high-speed operation is recommended.
When selecting these specifications, factors such as gear accuracy requirements, production efficiency, and grinding machine capability should all be considered. If both high accuracy and large stock removal are required, using one gear grinding wheel for rough grinding and another with a finer grit and different hardness for finish grinding is often the best solution.
Balancing the Gear Grinding Wheel
Because gear grinding is a high-precision process, proper balancing of the gear grinding wheel is critical. An unbalanced wheel can cause vibration, reduce surface finish, lower machining accuracy, and even shorten the service life of the grinding machine.
The gear grinding wheel should undergo two stages of static balancing. After the first static balance, perform rough dressing, followed by a second static balance before finish dressing. For worm grinding wheels, which are larger and heavier, dynamic balancing is also required to ensure high gear accuracy and excellent surface quality.
Most modern CNC gear grinding machines are equipped with automatic dynamic balancing systems on the wheel spindle. Even so, two careful static balancing procedures are still recommended for the gear grinding wheel.
If a new gear grinding wheel requires significant dressing, it should first be roughly dressed on the grinding machine before static balancing is carried out.
