I use skiving and roller burnishing for fast finishing of hydraulic cylinder bores. Skiving and roller burnishing is a combined process that cuts the bore to final size and then burnishes the surface in a single pass. It replaces honing on many applications and produces a mirror-like finish in less time.
How the Combined Process Works
The skiving head carries cutting inserts that remove the bulk of the stock. Behind the cutting inserts, a set of hardened rollers presses against the bore surface. The rollers apply high contact pressure that plastically deforms the surface peaks into the valleys.
The burnishing action work-hardens the surface layer to a depth of roughly 0.01-0.05 mm. Hardness increases by 10-30 percent in the surface layer, which improves wear resistance in service. The final surface finish lands between Ra 0.05 and 0.4 um depending on the starting condition and the material.
I have measured surface finishes as low as Ra 0.03 um on medium-carbon steel with a good skiving head and proper parameters. That is better than most honing operations can achieve consistently.
Stock Removal and Tolerance Capabilities
A key advantage of skiving is the amount of material it removes per pass compared to honing. Here is the comparison I use when deciding between processes:
| Parameter | Skiving + Burnishing | Conventional Honing |
|---|---|---|
| Stock removal per pass | 0.3-0.5 mm | 0.01-0.05 mm |
| Achievable tolerance | IT7 | IT6-IT7 |
| Surface finish (Ra) | 0.05-0.4 um | 0.1-0.8 um |
| Cycle time (300 mm bore) | 30-60 seconds | 2-5 minutes |
| Tool cost per part | Lower | Higher |
The burnishing rollers compress the surface by about 0.01-0.02 mm. The skiving inserts remove the rest. I set the skiving diameter so the total stock removal leaves 0.01-0.02 mm for the rollers to compress.
Materials That Respond Well to Burnishing
In my experience, materials with moderate ductility burnish best. The surface needs to deform without cracking. Materials above 45 HRC do not respond well because the surface cannot flow under the roller pressure.
| Material | Burnishing Result | Recommended |
|---|---|---|
| Medium-carbon steel (1045) | Excellent | Yes |
| Alloy steel (4140 annealed) | Excellent | Yes |
| Ductile iron (65-45-12) | Good | Yes |
| Gray iron | Fair | With caution |
| Stainless steel (304) | Good | Yes |
| Tool steel (O1 hardened) | Poor | No |
| Hardened steel (50+ HRC) | Poor | No |
I recently ran a job in 304 stainless steel for a food-grade hydraulic cylinder. The skiving and burnishing produced Ra 0.15 um consistently. The same bore would have taken three times longer with honing.
Tooling Design and Speed Parameters
The skiving head must be rigid. The cutting inserts experience radial and axial forces that can deflect the head if the fit in the bore is too loose. I use a head with carbide guide pads that maintain alignment in the bore.
Typical cutting parameters I run:
| Parameter | Typical Range |
|---|---|
| Cutting speed | 60-120 m/min |
| Feed rate | 0.2-1.0 mm/rev |
| Burnishing speed | 40-80 m/min |
| Burnishing feed | 0.1-0.3 mm/rev |
| Coolant pressure | 30-60 bar |
| Coolant type | Emulsion or neat oil |
The burnishing speed should be lower than the skiving speed. High burnishing speed generates heat that can cause the rollers to skid rather than roll, which leaves a torn surface.
When to Choose Skiving and Burnishing Over Honing
I use skiving and burnishing for hydraulic cylinder bores that need a sealing surface finish, typically for pneumatic or hydraulic piston applications. The process eliminates the need for honing on many applications, which saves time and tooling cost.
The cycle time advantage grows with bore depth. A 1-meter-long bore that takes 15 minutes to hone can be skived and burnished in under 2 minutes. For production volumes above 1000 parts per year, the tooling cost for a skiving head pays back quickly.
However, honing remains the better choice when the bore has interrupted cuts, keyways, or cross-holes. The burnishing rollers can be damaged by the sharp edges of an intersecting hole. For smooth, continuous bores, skiving and burnishing is faster and cheaper.
Key Takeaways
Skiving and roller burnishing is one of the most productive finishing processes for deep holes when the conditions are right. The process delivers a surface finish that rivals honing at a fraction of the cycle time. Material selection is critical, and I now check the hardness and ductility before quoting a skiving job. The combined process has saved my customers hours of cycle time and thousands of dollars in tooling costs.