Matching of Cutting Tool Materials with Workpiece Mechanical, Physical, and Chemical Properties for Optimal Machining Performance
1. Mechanical Property Match Between Cutting Tools and Workpieces
The matching problem regarding mechanical properties primarily involves the alignment of tool materials' strength, toughness, and hardness with those of workpiece materials. Different tool materials are suitable for machining different types of workpiece materials based on their mechanical properties.
- The hardness sequence of tool materials is: diamond > cubic boron nitride (CBN) > ceramic > carbide > high-speed steel (HSS).
- The bending strength order is: HSS > carbide > ceramic > diamond and CBN.
- The toughness ranking is: HSS > carbide > CBN, diamond, and ceramic.
High-hardness workpiece materials require tools with higher hardness; the tool material's hardness must be above 60HRC and greater than that of the workpiece. The higher the hardness of the tool material, the better its wear resistance. For instance, when the cobalt content in carbides increases, the strength and toughness rise while hardness decreases, suitable for rough machining; conversely, reduced cobalt content enhances hardness and wear resistance, ideal for finish machining.
Tools with excellent high-temperature mechanical properties are particularly suited for high-speed cutting. Ceramic tools' superior high-temperature performance allows for much higher cutting speeds—up to 2 to 10 times faster than carbides.
2. Physical Property Match Between Cutting Tools and Workpieces
Different physical properties of tools, such as high thermal conductivity and low melting point in HSS, high melting point and low thermal expansion in ceramics, and high thermal conductivity and low thermal expansion in diamond tools, dictate their suitability for different workpiece materials. When machining materials with poor thermal conductivity, use tools with better thermal conductivity to efficiently dissipate heat and reduce cutting temperature. Diamond's high thermal conductivity and heat diffusion rate ensure quick heat dissipation and minimal thermal deformation, crucial for precision tools requiring high dimensional accuracy.
- The heat resistance temperatures: diamond at 700–800°C, PCBN at 1300–1500°C, ceramic at 1100–1200°C, TiC(N)-based carbide at 900–1100°C, WC-based ultra-fine grain carbide at 800–900°C, and HSS at 600–700°C.
- Thermal conductivity order: PCD > PCBN > WC-based carbide > TiC(N)-based carbide > HSS > Si3N4-based ceramic > Al2O3-based ceramic.
- Thermal expansion coefficient sequence: HSS > WC-based carbide > TiC(N) > Al2O3-based ceramic > PCBN > Si3N4-based ceramic > PCD.
- Thermal shock resistance ranking: HSS > WC-based carbide > Si3N4-based ceramic > PCBN > PCD > TiC(N)-based carbide > Al2O3-based ceramic.
3. Chemical Property Match Between Cutting Tools and Workpieces
This refers to the compatibility between tool materials and workpiece materials concerning chemical affinity, chemical reactions, diffusion, and dissolution. Different tools suit different workpiece materials based on these chemical properties.
- The anti-adhesion temperature (with steel) ranking: PCBN > ceramic > carbide > HSS.
- Oxidation resistance temperature order: ceramic > PCBN > carbide > diamond > HSS.
- Diffusion intensity (for steel): diamond > Si3N4-based ceramic > PCBN > Al2O3-based ceramic. Diffusion intensity (for titanium): Al2O3-based ceramic > PCBN > SiC > Si3N4 > diamond.
4. Rational Selection of CNC Tool Materials
Generally, PCBN, ceramic, coated carbide, and TiCN-based carbide tools are appropriate for the CNC machining of steels and other ferrous metals. Conversely, PCD tools are suitable for machining aluminum, magnesium, copper, their alloys, and non-metallic materials.
