1. Materials Science Overview

Wood

• Hardwood: Oak, Maple, Walnut, Mahogany, Ash, Hickory, Birch, Teak
  • Easy to cut in a lathe.
  • Thick pieces: CNC cut (greater than 3mm)
  • Thin pieces: Laser cut (less than 3mm)
  • MDF with resin burns in laser cut
  • Good surface properties
  • Engravement possible
• Softwood: Pine, Spruce, Cedar, Cypress, Redwood
  • Better to laser cut
  • Upcut and downcut choice for surface finish

Plastics

• Thermosetting polymers: Resin and curing agents react chemically
  • Curing process hardens material
  • Process is irreversible
  • Not recyclable
  • Examples: Epoxy, Vinyl ester, Polyester
• Thermoplastic polymers: Amorphous or semi-crystalline
  • Can be remelted and reformed
  • Recycling changes material properties
  • Examples: Polyamides, Polyethylene, PLA, ABS, PC
• Elastomeric polymers: High stretchability
  • Examples: TPU, Vulcanized Rubber

Ferrous Alloys: Iron (Fe) + Carbon (C) = Steel

• Cementite (Fe3C): Hard and brittle inter-metallic compound
• Carbon Content and Classification
  • Low Carbon Steel (C < 0.15%):
    • Good weldability and ductility
    • Drawn tubes, thin sheets, wire rods
    • Surface hardening possible for wear resistance
  • Mild Steel (C: 0.15-0.3%):
    • Structural work
    • Weldability up to 0.25% C
    • Forgings, stampings, sheets, plates, bars, rods, tubes
  • Medium Carbon Steel (C: 0.3-0.7%):
    • Stronger and better wearing properties
    • Railway axles, rotors and discs, wire ropes, marine shafts, agricultural tools
  • High Carbon Steel (C: 0.7-1.3%):
    • Harder when quenched
    • Used in cold conditions (less than 150°C)
  • Cast Iron (C > 1.7% up to 4%):
    • Lower melting temperature, easy to cast
    • Cooling rate dictates type: Gray, White, Malleable, Ductile cast iron
• Above 2% carbon, it is considered cast iron. Cooling rate and other alloying elements are important

Steel Alloys

• Less than 2% carbon and other alloying elements
  • Ferritic Stainless Steel (0.15% C, 6-12% Cr, 0.5% Ni):
    • Magnetic, cannot be hardened
    • Food processing plants, dairy equipment
    • Low price
  • Martensitic Stainless Steel (0.15-1.25% C, 12-18% Cr):
    • Hardening possible, but reduces corrosion resistance
    • Surgical knives, bolts, nuts, screws, blades
  • Austenitic Stainless Steel (0.08-0.2% C, higher nickel content):
    • 18/8 Steel: 18% Cr, 8% Ni, 1.25% Mn, 0.75% Si
    • High corrosion resistance
    • Chemical plants, household utensils
    • High price
  • Tool steels (cut steel at high speeds):
    • Retain hardness at elevated temperatures (600°C): Red Hardness
    • High-Speed Steel (HSS): 18% Tungsten (expensive, T-series)
    • HSS: 6% Tungsten, 6% Molybdenum (M-series)
    • Super HSS: 10% Cobalt, 20% Tungsten
  • Special Steel Alloys
    • Manganese Steels:
      • Wear resistant
      • Used in railway points and crossings
    • Nickel Steels:
      • Corrosion resistance
      • Non-magnetic, low thermal expansion coefficient
      • Used in turbine blades, internal combustion engine valves
      • With chromium, increased UTS and IZOD strength
    • Silicon Steels:
      • Around 3% Silicon decreases magnetic hysteresis
      • Used in transformers, electric machines
      • Silico-manganese steels for springs

Heat Treatment of Carbon Steels

• Improve mechanical properties:
  • Heat up to a homogeneous temperature
  • Controlled cooling rate is critical
• Types of Heat Treatment:
  • Annealing:
    • Heating rate is not decisive
    • Around 3 minutes per millimeter thickness for even temperature distribution
    • Softening material through slow cooling
    • Relieves internal stresses
    • Increases ductility (grain growth)
  • Normalizing:
    • Same heating as annealing, but cooling in still air (faster)
    • No softening, but internal stresses relieved ("normalized" to zero)
  • Hardening:
    • Rapid cooling (quenching) in water/oil mixture
    • Requires high carbon content (greater than 0.25%)
    • Creates hard, but brittle material
  • Tempering:
    • Heated to 150-600°C and cooled slowly
    • Reduces brittleness of hardened material
  • Case Hardening:
    • Used for dead mild steel (low carbon)
    • Heat in charcoal for several hours to introduce carbon to the surface
    • Creates a hard surface (1-2mm) with a soft, tough interior

Non-Ferrous Alloys

• Copper:
  • Corrosion resistance, best conductor
  • Wire drawn, sheet beaten
  • Alloyed with: Zinc (brass), Tin (bronze), Nickel (cupro-nickels)
• Aluminum:
  • Corrosion resistance, good conductor
  • Ductile and malleable (thin sheets, cables)
  • Alloyed with Magnesium for improved properties
• Tin:
  • Resistant to acidic conditions
  • Low melting point, used in solders
• Zinc:
  • High corrosion resistance
  • Coating for steel (galvanized steel)

Non-Ferrous Alloys (Continued)

• Brass:
  • Cartridge Brass (70% Cu, 30% Zn): Deep drawing cartridges
  • Admirability Brass (70% Cu, 29% Zn, 1% Sn): Ship fittings
  • Muntz’s Metal (Cu, 40-45% Zn): Condenser tube, heat exchanger, preheater
  • Naval Brass (60% Cu, 39% Zn, 1% Sn): Ship fittings
• Tin Bronze (up to 10% tin):
  • Increases strength and hardness
  • Too much tin creates brittle intermetallic compound Cu3Sn
  • Phosphor Bronze (0.5% phosphorous): Better fluidity for fine casting
  • Leaded Bronze (less than 2% Lead): Better machinability, self-lubricating
  • Gun-metal (88% Cu, 10% Sn, 2% Zn): Bearing bushes, glands, pumps
  • Bell-metal (20-25% tin): Cymbals
• Other
  • Silicon Bronze (1-4% Si to copper): Extreme corrosion resistance (boilers, marine fittings)
  • Manganese Bronze (55-60% Cu, 40% Zn, 3-5% Mn): Ship propellers
• Special Alloys
  • Cupro-nickels (copper and nickel): Extreme corrosion resistance (thermocouples, resistors)
  • Aluminum Alloys (L-M series, mixed with Magnesium for strength): Extrusions in profiles
  • Duraluminum (Al, 4% Cu, 0.5% Mg, 0.5% Mn):
  • Nickel Alloys:
    • German Silver (60% Cu, 30% Ni, 10% Zn): Household Devices
    • Inconel (Nickel-chromium-based superalloy): High temperature, corrosive applications (gas turbine blades, Formula 1 exhaust systems)
      • Alloy 625: Inconel 625, Chronin 625, Altemp 625, Haynes 625, Nickelvac 625 Nicrofer 6020 and UNS designation N06625
      • Alloy 600: NA14, BS3076, 2.4816, NiCr15Fe (FR), NiCr15Fe (EU), NiCr15Fe8 (DE) and UNS designation N06600.
      • Alloy 718: Nicrofer 5219, Superimphy 718, Haynes 718, Pyromet 718, Supermet 718, Udimet 718 and UNS designation N07718

Ceramics

• Hard, brittle, corrosion resistant, sometimes insulating material
• Machinable Ceramics: (Soft)
  • Macor: Excellent electrical and thermal insulator, machinable with carbide tools
  • Shapal: High thermal conductivity and mechanical strength
  • Boron-Nitride: High heat capacity, thermal conductivity, low dielectric constant
• Hard Ceramics (Tough, difficult to cut)
  • Zirconia: High hardness, wear resistance, high fracture toughness
  • Silicon Carbide: Extremely hard, exceptional thermal shock and impact resistance.

Macor, Characteristics and Milling

• Macor:
  • Excellent electrical and thermal insulator
  • Machinable with carbide tools
• Milling Macor:
  • Typical head speeds: 1000-1500 RPM
  • Chip load: 0.05mm per tooth
  • Depth of cut similar to turning
  • Climb milling prevents material pull-off from the edge
  • Recommended milling tool: Carbide or equivalent, two or four flute, helical cutters
  • Avoid using rouging or chipbreaker mills
• Milling Macor Speeds and Feeds:
  • Cutting speed: 23-35 SFPM (1-1.4 meters per minute)
  • Feed rate: .002" per tooth (.05mm per tooth)
  • Depth of cut: .15-.2" (4-5mm)