In bearing ring superfinishing, choosing the right honing stone is critical because it directly affects machining quality, production efficiency, and processing costs. Superfinishing is a low-speed, low-temperature, and low-pressure precision grinding process. Since the tool is not dressed during operation, it must maintain stable cutting and polishing performance throughout the machining process.
The main factors affecting performance include abrasive type, grit size, bond, structure, hardness, and hardness uniformity.
1. Abrasive Type
Common abrasives used for manufacturing honing stone include WA, GC, SC, WA/GC mixed abrasive, WA/SC mixed abrasive, and WA/C graphite abrasive.
In the bearing industry, WA/GC and WA/SC mixed abrasives are widely used because they provide a good balance between cutting ability and surface finishing performance.
2. Abrasive Grit Size
The grit size of micro abrasives ranges from W63 to W0.5. For bearing superfinishing applications, the commonly used range is W2.5 to W28.
Coarse grit provides stronger cutting ability and higher production efficiency, while fine grit produces a smoother surface with lower roughness. The selection should be based on the required surface quality and machining allowance.
|
Abrasive Grit Size (μm) |
W28 |
W20 |
W14 |
W10 |
W7 |
W5 |
|
Abrasive Particle Size (μm) |
28–20 |
20–14 |
14–10 |
10–7 |
7–5 |
5–3.5 |
|
Surface Roughness Ra (μm) |
0.10–0.15 |
0.08–0.12 |
0.05–0.08 |
0.025–0.05 |
0.02–0.025 |
0.012–0.025 |
|
Machining Allowance per Diameter (μm) |
12–16 |
10–12 |
8–10 |
6–9 |
5–8 |
3–5 |
3. Bond Type
The bond determines the strength, durability, and self-sharpening ability of the abrasive tool. Common bond types include vitrified, resin, glass-ceramic, polyethylene, and graphite.
For bearing superfinishing, vitrified bond is the most commonly selected because it offers stable performance, good wear resistance, and reliable abrasive retention.
4. Structure
The structure of a honing stone affects chip removal and grinding performance. A relatively open structure provides more space for holding grinding debris, helping prevent clogging and reducing scratches on the workpiece surface.
However, excessive porosity may cause rapid wear and reduce finishing performance. For bearing superfinishing, the structure grade is generally selected between 10 and 12, with a porosity of around 43%–49%.
5. Hardness and Hardness Uniformity
The hardness of a honing stone directly affects its self-sharpening ability. If the hardness is too low, abrasive grains may detach too quickly, making it difficult to achieve the required surface finish. If the hardness is too high, the working surface may become clogged and lose cutting performance.
Generally, harder workpiece materials require softer tools, while softer materials require harder ones. For bearing superfinishing, a hardness level around 50 HRC is commonly selected.
Hardness uniformity is another important factor. Uneven hardness of the honing stone can lead to inconsistent surface roughness and affect the dimensional accuracy of bearing rings. The hardness variation should generally be controlled within 3–5 HRC.
A properly selected honing stone can maintain a balance between cutting performance and polishing ability, helping achieve high-precision bearing ring surfaces with better consistency and efficiency.
