Hard Turning vs Grinding: When Cermet Turning Replaces Grinding

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.

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.