Appropriate hardness effectively improves the cost-effectiveness of grinding wheels

Choosing the appropriate hardness of the grinding wheel is the key to ensuring grinding efficiency, processing quality, and wheel life. The hardness of a grinding wheel does not refer to the hardness of the abrasive particles themselves, but to the degree to which the bonding agent (binder) holds the abrasive particles firmly.

Simply put:

• Hard grinding wheel: The abrasive particles are not easily detached. Suitable for light grinding force, small contact area, high precision, and hard materials.
• Soft grinding wheel: The abrasive grains are relatively easy to fall off, and new sharp abrasive grains can be exposed in a timely manner (with good self sharpening properties). Suitable for situations with heavy grinding force, large contact area, soft materials, and high heat dissipation requirements.

 

The following are the main considerations and guidelines for selecting the hardness of grinding wheels:

1. Hardness of workpiece material:

• Hard materials (such as quenched steel, hard alloys, ceramics): abrasive particles are prone to becoming dull. A softer grinding wheel is needed to allow the passivated abrasive particles to fall off in a timely manner, exposing new sharp abrasive particles to avoid burning the workpiece and generating vibration. Otherwise, blunt abrasive particles will generate heat through friction, leading to burns.
• Soft materials (such as low-carbon steel, aluminum, copper, plastic, wood): The abrasive grains are not easily dull, but they are prone to clogging (chips embedded on the surface of the grinding wheel). We need a harder grinding wheel to keep the abrasive particles for a longer period of time and reduce clogging. Grinding soft materials with a soft grinding wheel can be inefficient and more prone to clogging due to premature detachment of abrasive particles.
• Resilient materials (such as stainless steel, high-temperature alloys, titanium alloys): prone to clogging and burning. Usually, a moderately soft grinding wheel is required to ensure good self sharpening, timely discharge of chips, and heat dissipation.

 

2. Grinding method and contact area:

• Small contact area (such as cylindrical grinding, tool grinding, blade grinding, narrow groove grinding): The heat dissipation at the grinding point is relatively easy, and the grinding force is relatively concentrated. A harder grinding wheel can be used to achieve better shape retention and accuracy.
• Large contact area (such as flat grinding, internal circular grinding, centerless grinding guide wheel, wide grinding wheel grinding): The grinding area has difficulty dissipating heat, which can easily generate a large amount of heat and blockage. A softer grinding wheel is needed to ensure self sharpening, timely heat dissipation, and avoid clogging.
• Cutting in grinding: With a large contact area, a softer grinding wheel is required.
• Longitudinal feed grinding: The contact area is relatively small, and a harder grinding wheel can be used.

 

3. Grinding process requirements:

• Rough grinding/large surplus grinding: high grinding force, high metal removal rate, and high heat generation. We need a softer grinding wheel to ensure good self sharpening and heat dissipation.
• Fine grinding/small allowance grinding/high-precision grinding: The grinding force is small, requiring good shape retention, stable size, and high surface smoothness of the grinding wheel. We need a harder grinding wheel.
• High efficiency grinding: usually requires a softer grinding wheel to maintain a sharp cutting edge, but also to balance the wear rate of the grinding wheel.
• Low roughness requirement: A hard and uniformly structured grinding wheel is required to avoid premature detachment of abrasive particles and affect surface texture

 

4. Grinding wheel linear speed:

• A higher linear speed of the grinding wheel will reduce the force borne by a single abrasive grain, which is equivalent to the grinding wheel becoming a little harder. Therefore, during high-speed grinding, it is sometimes necessary to choose a slightly softer grinding wheel than the conventional speed to compensate and ensure self sharpening.

 

5. Machine tool rigidity and condition:

• Good rigidity and low vibration of machine tools: softer grinding wheels can be used to fully utilize their self sharpening advantages.
• Poor rigidity and high vibration of machine tools (such as old ones): It is necessary to use harder grinding wheels to avoid premature abnormal detachment of abrasive particles due to vibration, which may affect the grinding effect and wheel life.

 

6. Cooling conditions:

• Good cooling (sufficient and effective grinding fluid) can remove heat, reduce the risk of burns, and allow for the use of slightly harder grinding wheels.
• Poor cooling conditions (dry grinding, insufficient or unsatisfactory coolant): It is necessary to choose a softer grinding wheel and rely on self sharpening to dissipate heat.

 

 

Representation method for hardness grade of grinding wheel

• Commonly used letter representations, roughly from soft to hard: A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z.
• The letter sequence and specific correspondence of different standards (such as GB national standard, JIS Japanese standard, ANSI American standard, etc.) may vary slightly, and specific standards should be referred to.
• It is also represented by numbers (such as 1 being the softest and the larger the number, the harder it is).

 

Summary of Selection Principles (Quick Reference)
When choosing a softer grinding wheel (such as G-K)
When choosing a harder grinding wheel (such as L-T)
Workpiece material is hard (quenched steel, hard alloy, ceramic)
Workpiece material soft (low-carbon steel, aluminum, copper, plastic, wood)
High toughness of workpiece materials (stainless steel, high-temperature alloys, titanium alloys)
Requires high shape accuracy/smoothness (precision grinding, forming grinding)
Large contact area (flat grinding, internal circular grinding, wide grinding wheel)
Small contact area (outer circle grinding, tool grinding, blade grinding)
Rough grinding/large cutting depth/large feed rate
Fine grinding/small cutting depth/small feed rate
The machine tool has good rigidity and low vibration
Poor rigidity and high vibration of machine tools
Poor cooling conditions (dry grinding, insufficient cooling)
Good cooling conditions (sufficient and effective coolant)
High speed grinding (to be compensated)
Avoid rapid wear of the grinding wheel
Require high grinding efficiency (maintain sharpness)
Require high durability of the grinding wheel

 

Common problems and directions for hardness adjustment

• Workpiece burn: The grinding wheel may be too hard ->try a softer level.
• Serious blockage of grinding wheel: The grinding wheel may be too soft ->try harder (for soft materials), or check cooling and dressing (for hard/tough materials).
• There are vibration patterns/ripples on the surface of the workpiece: the grinding wheel may be too soft (due to excessive shedding of abrasive particles causing imbalance), or the machine may vibrate ->try a slightly harder grinding wheel and check the machine condition.
• The grinding wheel wears out too quickly: the grinding wheel may be too soft ->try harder (but be alert to the risk of burns).
• Low grinding efficiency: The grinding wheel may be too hard (dull and not self sharpening) or too soft (premature detachment of abrasive particles) ->Adjust the direction based on the workpiece material and phenomenon. For hard materials, low efficiency is often due to being too hard; For soft materials with low efficiency, it is often due to being too soft or blocked.
• Unstable workpiece size/shape: The grinding wheel may be too soft (worn out quickly) ->try harder. 

 

Important Note

• 1. There is no absolute standard: The above guidelines are basic principles, and actual selection needs to be tested and optimized based on specific operating conditions (machine tools, workpieces, processes, coolant, etc.). Different manufacturers and operating habits may choose grinding wheels with different hardness for the same workpiece.
• 2. Initial selection: If unsure, you can start with moderate hardness (such as J, K, L) and then adjust towards softer or harder directions based on the grinding effect (burn, smoothness, efficiency, wear).
• 3. Consulting suppliers: Grinding wheel manufacturers usually have extensive application experience and provide recommended hardness for specific materials and processes. Provide them with detailed working condition information as much as possible.
• 4. Grinding wheel dressing: The hardness of the grinding wheel also affects the frequency and method of dressing. Soft grinding wheels require more frequent dressing to maintain their shape.
• 5. Balance other parameters: The selection of hardness must be comprehensively considered with parameters such as abrasive type (corundum, silicon carbide, CBN, diamond), particle size, binder type (ceramic, resin, rubber, metal), and microstructure (degree of tightness).

 

Summary of selection process:

1. Identify the workpiece material (hard/soft/tough).

2. Determine the grinding method (contact area size? Coarse/fine grinding?).

3. Evaluate the working conditions (rigidity of the machine tool, cooling effect, linear velocity).

4. Based on the core principles (hard/large contact/rough grinding/good cooling ->soft; soft/small contact/fine grinding/poor cooling ->hard), preliminarily select the hardness range.

5. Conduct trial grinding and observe the effect (surface quality, burns, blockages, efficiency, wear).

6. Adjust the hardness according to the problem (burn ->softer; blockage/wear faster ->harder; vibration pattern ->inspection or slightly harder; low efficiency ->analyze the cause and adjust).

7. Optimize confirmation and consult suppliers if necessary.

Quanzhou Huice New Material Co.,Ltd. provides high-quality diamond CBN grinding wheels with stable performance and high cost-effectiveness, which can perfectly replace diamond grinding wheels produced in Europe.