In machining operations, a wide variety of materials are used—including those known as difficult-to-machine materials. These refer to materials with poor machinability, often resulting in rapid tool wear, reduced machining efficiency, and challenges in achieving desired surface quality.
Categories of Difficult-to-Machine Materials
1. High-Strength Steels
Common Examples: Quenched steels (e.g., 4340, H13), high-hardness alloy steels (e.g., D2, M2).
Key Properties: High hardness (HRC 45+), tensile strength exceeding 1000 MPa. These properties generate significant heat and friction during cutting, accelerating tool wear.
2. Stainless Steels
Common Examples: Austenitic (304, 316), martensitic (410, 420), and duplex (2205) stainless steels.
Key Properties: High toughness, low thermal conductivity, and tendency to work-harden. These often cause built-up edge and tool chipping.
3. High-Temperature Alloys
Common Examples: Nickel-based alloys (Inconel 718, Hastelloy), titanium alloys (Ti-6Al-4V), cobalt-based alloys (Stellite).
Key Properties: Excellent high-temperature strength and corrosion resistance. They generate extreme cutting heat, leading to diffusion wear and reduced tool life.
4. Composite Materials
Common Examples: Carbon fiber-reinforced polymers (CFRP), glass fiber-reinforced plastics (GFRP).
Key Properties: Anisotropic structure and abrasive fibers. These cause accelerated tool wear and can result in delamination or burring.
5. High-Hardness Non-Ferrous Metals
Common Examples: Hard aluminum alloys (e.g., 7075), high-silicon aluminum (e.g., A390), beryllium copper.
Key Properties: Softer than steel but often contains abrasive particles (e.g., silicon), which cause rapid abrasive wear on cutting tools.
Why are these materials difficult to Machine？
▶High Hardness: Materials like hardened steels impose high cutting forces, leading to chipping and rapid tool wear.
▶Low Thermal Conductivity: Seen in titanium and stainless steels, this causes heat to concentrate at the tool edge, resulting in thermal cracking and deformation.
▶Work Hardening: Materials such as austenitic stainless steels and nickel-based alloys harden during machining, increasing tool wear.
▶Chemical Reactivity: Titanium alloys, for example, can react with tool materials, causing built-up edge and diffusion wear.
▶High Toughness: Nickel-based alloys and high-strength steels resist fracture, increasing cutting forces and promoting tool failure.
▶Abrasive Wear: Composites and high-silicon aluminum contain hard particles that abrade the cutting tool like sandpaper.
How to Improve Machinability？
1. Select the Right Tool Material
CBN: Best for high-hardness steels (HRC 50+).
PCD: Ideal for high-silicon aluminum and composites.
Coated Carbide (e.g., TiAlN, AlCrN): Recommended for stainless steels and high-temperature alloys.
2. Optimize Cutting Parameters
Reduce feed rate to extend tool life.
Adjust cutting speed based on material—higher for some, lower for others.
3. Use Effective Cooling Methods
Apply coolant or high-pressure air cooling to manage heat and prevent thermal damage.
4. Apply Special Edge Treatments
Use tools with large rake angles and sharp edges to reduce cutting forces and improve finish.
By understanding the properties of difficult-to-machine materials and implementing these strategies, manufacturers can enhance tool performance, achieve better surface quality, and improve overall machining efficiency.
