A detailed look at various grades of carbide cutting tools, focusing on their composition, properties, and applications:
1. Cemented Carbide
Composition:
- Made from tungsten carbide (WC) particles bonded with a metallic binder, typically cobalt (Co) or nickel (Ni).
- Common ratio: 70–97% tungsten carbide and 3–30% cobalt.
Properties:
- Hardness: High hardness, excellent wear resistance.
- Toughness: Good toughness due to cobalt binder, making it resistant to chipping and cracking.
- Thermal Conductivity: Good heat dissipation, enabling higher cutting speeds.
- Strength: Strong under compressive loads but less resistant to tensile stress.
Applications:
- General-purpose machining (e.g., steel, stainless steel).
- Heavy-duty cutting operations.
- High-speed machining due to excellent thermal stability.
2. Ceramic Cutting Tools
Composition:
- Primarily made of aluminum oxide (Al₂O₃) or silicon nitride (Si₃N₄).
- May be reinforced with zirconia (ZrO₂) or mixed with titanium carbide (TiC).
Properties:
- Hardness: Extremely high hardness, even at elevated temperatures.
- Toughness: Lower than cemented carbide, making it prone to chipping.
- Thermal Resistance: Excellent high-temperature stability and oxidation resistance.
- Chemical Stability: Resistant to chemical reactions with metals.
Applications:
- High-speed finishing operations.
- Machining hard materials like cast iron and high-strength alloys.
- Not suitable for interrupted cuts due to brittleness.
3. Cermet (Ceramic-Metal Composite)
Composition:
- Made from ceramic particles (e.g., TiC or TiN) bonded with metallic materials (e.g., nickel or cobalt).
Properties:
- Hardness: Intermediate between ceramics and cemented carbides.
- Toughness: Higher toughness than ceramics but less than cemented carbide.
- Thermal Conductivity: Moderate, reducing thermal shock resistance.
- Wear Resistance: High resistance to wear, especially in finishing applications.
Applications:
- Finishing and semi-finishing of steel and stainless steel.
- Applications requiring a smooth surface finish.
- Not ideal for roughing or interrupted cuts.
4. Polycrystalline Diamond (PCD)
Composition:
- Sintered layer of diamond particles bonded to a carbide substrate.
Properties:
- Hardness: Extremely high hardness, second only to natural diamond.
- Wear Resistance: Exceptional wear resistance, especially for abrasive materials.
- Thermal Conductivity: Excellent heat dissipation, reducing tool wear.
- Chemical Reactivity: Poor performance with ferrous materials due to carbon diffusion.
Applications:
- Machining non-ferrous materials (e.g., aluminum, copper, composites).
- High-precision applications requiring a superior finish.
- Not suitable for cutting steel or high-temperature alloys.
5. Cubic Boron Nitride (CBN)
Composition:
- Cubic form of boron nitride bonded to a carbide substrate.
Properties:
- Hardness: Very high, second only to diamond.
- Thermal Resistance: Outstanding thermal stability.
- Wear Resistance: Excellent for cutting hard and abrasive materials.
- Chemical Stability: Works well with ferrous materials, unlike PCD.
Applications:
- Hard turning and milling of hardened steel.
- Cutting high-temperature alloys.
- High-speed machining with long tool life.
Summary Comparison Table
| Grade | Hardness | Toughness | Thermal Stability | Wear Resistance | Key Applications |
|---|---|---|---|---|---|
| Cemented Carbide | High | High | Good | High | General-purpose machining; high-speed cuts |
| Ceramic | Very High | Low | Excellent | High | High-speed finishing; cast iron machining |
| Cermet | Medium | Moderate | Good | High | Finishing/semi-finishing of steel |
| PCD | Extreme | Moderate | Excellent | Exceptional | Non-ferrous machining; precision cutting |
| CBN | Very High | Moderate | Outstanding | High | Hardened steel; high-temp alloys |
Key Considerations for Selection
- Material to be Machined: Choose PCD for non-ferrous, CBN for hardened steels, ceramics for cast iron, etc.
- Type of Machining: For roughing, cemented carbides are better. For finishing, cermets or ceramics excel.
- Cutting Speed and Temperature: High-speed machining benefits from ceramics or PCD.
- Cost and Tool Life: PCD and CBN are expensive but offer exceptional tool life.