Under What Circumstances Cannot Cermet Replace Cemented Carbide?

There are fundamental differences in mechanical properties between metal ceramics (Cermet) and cemented carbide (WC-Co). The toughness (impact resistance) and thermal shock resistance of metal ceramics are much lower than those of hard alloys. In the following scenarios, metal ceramics must not be used in place of cemented carbide; otherwise, it is highly likely to cause tool chipping, cracking, or even processing accidents:

1. In situations with impact loads or intermittent cutting

Typical scenarios: 

milling (especially side milling, chamfer milling), turning shafts with keyways or holes, rough machining of black skin surfaces of castings, drilling (entry/exit instant).

Reason: 

The flexural strength of metal ceramics is usually only 1/3 to 1/2 of that of hard alloys. The instantaneous impact force on the cutting edge when entering or exiting the workpiece will directly cause the edge to break, which cannot be absorbed by plastic deformation as hard alloys can.

2. Low rigidity processing systems or vibration environments

Typical scenarios: 

old machine tools (with large spindle runout), processing of slender shafts, suspended long boring bars, insufficient fixture rigidity, unstable workpiece clamping.

Reason: Metal ceramics are extremely sensitive to vibration. Minor tremors in the processing system may only cause slight wear on hard alloys, but in metal ceramics, they will rapidly evolve into macroscopic chipping.

3. Heavy-duty rough machining or large allowance cutting

Typical scenarios: cutting with a back rake depth (ap) > 3mm and feed rate (f) > 0.3mm/r.

Reason: The strength of metal ceramics cannot withstand huge cutting resistance. Under heavy loads, the blade base is prone to fracture, rather than normal wear.

4. Processing high-toughness, viscous materials

Typical scenarios: 

turning/milling titanium alloys (TC4), high-temperature alloys (Inconel 718), austenitic stainless steel (304), pure nickel.

Reason:

These materials have difficult-to-break chips and are prone to forming long rolls of chips that wrap around the tool. Although the chemical affinity of metal ceramics to these materials is low, the pulling force and adhesion of the chips will cause the edge to experience "peeling" failure, and its ability to resist plastic deformation is inferior to that of hard alloys.

5. Unstable coolant supply or dry rough machining

Typical scenarios: 

using water-based emulsion for large-flow cooling, intermittent cooling (such as manual pouring), dry rough machining.

Reason: 

Metal ceramics have poor heat conductivity and are sensitive to thermal stress. If the hot blade suddenly comes into contact with the coolant, a huge thermal gradient will generate "thermal cracks", accelerating tool failure. Hard alloys have good heat conductivity and stronger thermal shock resistance.

6. Low-speed, high-torque processing

Typical scenarios: 

tapping, reaming, low-speed turning.

Reason:

The advantage of metal ceramics lies in their red hardness and wear resistance at high speeds. At low speeds, their hardness advantage cannot be exerted, and instead, due to insufficient toughness, they are prone to micro-fracture at the edge, resulting in a decrease in processing accuracy.

As long as any of the keywords "impact", "vibration", or "heavy load" exist in the processing process, cemented carbide must be used; metal ceramics are only suitable for continuous, stable, and high-speed finishing and semi-finishing.