Replacing grinding with turning is a process decision, not a tool decision. Cermet makes the substitution practical over a defined band of hardness, geometry and volume, and beyond that band grinding or CBN remains the right answer. This page sets out the conditions and the trade-offs.
What turning instead of grinding means
In a conventional sequence a hardened part is turned oversize, heat treated and then ground to final size. Turning instead of grinding removes the grinding operation by holding the final size and finish on the lathe, in one setup, on the same machine that produced the part.
Cermet is the material that makes this economic in the softer part of the hardened range. The catalogue describes cermet as achieving a good surface finish that replaces grinding with turning and milling, with outstanding life in finishing and in stable semi-finishing.
The conditions that make cermet turning viable
- Workpiece hardness up to HRC45 for carbon and alloy steel; harder material calls for CBN
- A stable operation without heavy interruption, since cermet toughness limits it
- Finishing depths of cut, in line with the catalogue values: for example 0.05-0.6 mm with the G-grade NP chipbreaker
- A machine with enough rigidity and speed to run the finishing pass at the recommended Vc
- Cooling managed as either dry cutting or full flood, never partial
- A part geometry that suits a single-point turning pass, such as a shaft, ring or bushing
Comparing the two processes
The comparison below is qualitative because the outcome depends on the part, the machine and the volume. It reflects how the two processes differ in structure rather than a claim about a specific part.
| Dimension | Grinding | Cermet turning |
|---|---|---|
| Process steps | Turning, heat treatment, grinding | Turning, heat treatment, finish turning |
| Setup and flexibility | Dedicated machine, wheel and dressing cycle | Same lathe, quick insert change, easy to change part |
| Surface finish | Very fine, with controlled waviness | Fine, good enough to remove the grinding step in the cermet range |
| Dimensional consistency | High, but sensitive to wheel wear | High, driven by insert tolerance and edge wear |
| Geometry freedom | Limits on internal and interrupted forms | Turning can reach forms that are awkward to grind |
| Tooling | Wheel, dressing, coolant and swarf handling | Insert plus holder |
| Cooling | Wet grinding in most cases | Dry cutting is practical with cermet |
| Typical volume | High volume on controlled geometries | Low to high volume with frequent part changes |
Surface finish, accuracy and the bearing example
The clearest documented example in the catalogue is bearing ring machining. Cermet forming inserts are used on bearing machining tools to turn the raceway and related forms directly. The catalogue reports that this approach raises turning productivity by about 20%.
In the same case, because the turned form is closer to final size, the grinding stock is reduced and the grinding stroke is shortened, which raises productivity in the grinding operation by an average of about 10%. The gain therefore comes from two sides: a faster turning step and a lighter grinding step, rather than from deleting grinding entirely.
Boundaries - where grinding still wins
- Hardness above about HRC45, where cermet is outside its stated range and CBN becomes the candidate
- Heavy interrupted cuts and roughing, where cermet's toughness is insufficient
- Very tight waviness and roundness requirements that a ground surface achieves more predictably
- Thin or flexible parts where turning forces cause deflection
- Duplex stainless steel and high-silicon aluminium, both of which the catalogue excludes from the cermet range
How to run a substitution trial
Start with one finishing pass on a part you already grind. Set the depth of cut and feed inside the catalogue window for the chipbreaker you have chosen, and set Vc inside the published range for the steel type. Run dry or under full flood cooling.
Measure finish and size over a full edge, then compare cost per part against the ground route. If the finish holds and the edge life is stable, extend the trial to the whole family of parts. If chipping appears, the operation is probably outside the cermet band and the correct move is a harder or tougher grade, or CBN.
FAQ
Can cermet turning replace grinding on hardened steel?
For carbon and alloy steel up to about HRC45 in stable finishing conditions, yes. Above that hardness cermet is outside its range and CBN is the material to evaluate. In every case the substitution should be proven on the actual part.
Does hard turning need coolant?
Cermet is well suited to dry cutting because of its oxidation resistance and hot hardness. If coolant is used, it should be full flood; intermittent or misted cooling creates the rapid temperature change that causes thermal cracking in a low-conductivity material.
What finish can be expected from cermet turning?
The catalogue states that cermet achieves a surface finish good enough to replace grinding with turning and milling in precision and stable semi-finishing conditions. The exact value depends on the part, the chipbreaker and the feed, and should be confirmed on a trial.
Related
- Cermet Cutting Tools: Complete Guide to Grades, Geometries and Applications
- Cermet vs Carbide vs CBN: Choosing a Cutting Tool Material
- Cermet Insert Troubleshooting: Causes and Fixes for Common Failures
- KT20 vs KCT25: A Cermet Grade Selection Guide
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