Cutting Tool Materials: Properties and Characteristics
Item 3.1: Properties of Cutting Tool Materials
Hot Hardness: Ability to maintain hardness and resist deformation at high temperatures.
Toughness: Ability to absorb energy before breaking.
Ductility: Ability to deform plastically without fracturing.
Mechanical Impact Resistance: Ability to absorb impact energy without cracking.
Wear Resistance: Resistance to erosion from contact with other materials.
Thermal Impact Resistance: Ability to withstand rapid temperature changes.
Hardness: Resistance to penetration or scratching.
Characteristics of Cutting Tool Materials
Common Materials: High-speed steels, cobalt alloys, uncoated carbides, coated carbides, ceramics, polycrystalline cubic boron nitride, diamond.
Key Properties: Hot hardness, wear resistance, cutting speed, cost (desirable); toughness, impact resistance (compromises).
High-Speed Steel (HSS)
Properties: High toughness, good wear resistance, relatively inexpensive.
Suitable for: Large positive rake angles, interrupted cuts, low-stiffness machine tools, complex tools, drills, taps, and gears.
Limitations: Low cutting speeds due to poor hot hardness.
Types: M-series (molybdenum), T-series (tungsten).
Cobalt Alloys
Properties: Lower toughness than HSS, good wear resistance, better hot hardness than HSS.
Suitable for: Roughing cuts, deep continuous cuts, high feed rates.
Limitations: Not ideal for finishing or interrupted cuts.
Uncoated Carbides
Properties: High modulus, high hardness over a wide temperature range, high thermal conductivity, low thermal expansion, relatively inexpensive.
Comparison: Similar toughness and impact resistance to HSS and cobalt alloys, but with better hot hardness and higher cutting speeds.
Types: Tungsten carbide (WC), titanium carbide (TiC).
Coated Tools
Features: Reduced friction, increased wear resistance, improved hot hardness and impact resistance.
Common Coatings: TiN, TiC, TiCN, Al2O3.
Coating Methods: Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD).
Ceramics
Types: Alumina-based (Al2O3), silicon nitride-based.
Properties: High abrasion resistance, high hot hardness, chemical stability.
Limitations: Brittleness, high cost.
Cubic Boron Nitride (cBN)
Properties: Second hardest material after diamond, excellent wear resistance.
Diamond
Properties: Hardest known material, low friction, high wear resistance.
Cutting Fluids
Purpose: Reduce friction and wear, cool the cutting area, remove chips, protect the machined surface.
Types: Oils, emulsions, semi-synthetic emulsions, synthetic fluids.
Application Methods: Flood cooling, mist cooling, high-pressure systems.
Tool Wear and Failure
Factors Affecting Wear: Cutting speed, tool geometry, process parameters, machine tool characteristics.
Types of Wear: Cratering, tip wear, notching, chipping.
Tool Condition Monitoring
Direct Methods: Optical measurements, contact sensors.
Indirect Methods: Acoustic emission, force, acceleration sensors.