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Questions and Answers
Which of the following materials is classified as a machinable ceramic?
What is the recommended depth of cut when milling Macor?
What is the primary characteristic of hard ceramics like Zirconia?
Which milling tools are suggested for milling Macor?
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What is the cutting speed range for milling Macor?
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What process normalizes internal stresses in materials without softening?
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What is the main purpose of tempering in metallurgy?
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What is the carbon content needed to produce a hard and brittle piece through hardening?
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Which material is primarily used as a coating for steel to provide corrosion resistance?
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What happens to the carbon content of dead mild steel during case hardening?
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Which alloy contains 70% copper and 30% zinc, suitable for deep drawing applications?
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Which bronze is specifically known for its fluidity in fine casting due to phosphorus addition?
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What mixture gives cupro-nickels their extreme corrosion resistance?
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Which aluminum alloy includes a significant percentage of copper for higher strength?
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Which nickel-based superalloy is recognized for its high-temperature applications?
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Which of the following statements about hardwood is NOT true?
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What is the primary characteristic of thermosetting polymers?
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Which type of steel is characterized by its high carbon content and brittleness after hardening?
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What distinguishes thermoplastic polymers from thermosetting polymers?
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Which steel alloy is known for its non-magnetic properties and corrosion resistance?
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Which manufacturing method is best suited for cutting softwood?
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What process is used to increase the ductility of steel by heating and slow cooling?
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Which property of high carbon steel enables its use in cold conditions?
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What type of materials are commonly used as matrix materials in composites?
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In terms of strength and wear resistance, which type of steel is commonly used for railway axles and agricultural tools?
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What is a common application for manganese steels?
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What effect does heating steel followed by slow cooling have during the annealing process?
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Which material is best suited for 3D printing applications?
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Study Notes
Engineering Materials
-
Wood:
- Hardwood (oak, maple, walnut, mahogany, ash, hickory, birch, teak):
- Easy to cut in a lathe
- Multiple passes needed for CNC cut
- Thicker than 3 mm CNC cut, thinner than 3 mm laser cut
- Good surface properties, engravement possible
- Softwood (pine, spruce, cedar, cypress, redwood, plywood, balsa):
- Better to laser cut
- Upcut and downcut choice for surface finish
- Hardwood (oak, maple, walnut, mahogany, ash, hickory, birch, teak):
Plastics
-
Thermosetting Polymers:
- Resin and a curing agent form a chemical reaction during hardening
- Not possible to revert the process, not recyclable
- Examples:
- Epoxy, vinyl ester, polyester
- Matrix material in composites (carbon reinforced, aramid reinforced, glass reinforced)
-
Thermoplastic Polymers:
- Amorphous or semi-crystalline
- Remelting and reforming possible
- Recycling changes properties
- Examples:
- Polyamides (PA 6, PA 6.6, PA 11, PA 12)
- Polyethylene (LDPE, HDPE, PET)
- PLA, ABS, PC
-
Elastomeric Polymers:
- Very high stretchability
- Examples: TPU, vulcanized rubber
Ferrous Alloys
-
Steel (Iron + Carbon):
- Inter-metallic compound cementite (Fe3C) is hard and brittle
-
Low carbon steel: C < 0.15%
- Good weldability and ductility, drawn tubes, thin sheets, wire rods
- Surface hardening for wear resistance
-
Mild steel: 0.15% < C < 0.3%
- Structural work, weldability up to 0.25% C
- Forgings, stampings, sheets, plates, bars, rods, tubes
-
Medium carbon steel: 0.3% < C < 0.7%
- Stronger and better wearing properties, railway axles, rotors, discs, wire ropes, marine shafts, agricultural tools
-
High carbon steel: 0.7% < C < 1.3%
- Hardened by quenching, used in cold conditions (< 150°C)
-
Cast iron: C > 1.7% (up to 4%)
- Lower melting temperature, easy to cast
- Gray, white, malleable, ductile cast iron based on cooling rate and other alloying elements
Steel Alloys
-
Ferritic Stainless Steel: 0.15% carbon, 6-12% chromium, 0.5% nickel
- Magnetic, no hardening possible
- Food processing plants, dairy equipment, low price
-
Martensitic Stainless Steel: 0.15-1.25% carbon, 12-18% chromium
- Hardening possible but reduces corrosion resistance
- Surgical knives, bolts, nuts, screws, blades
-
Austenitic Stainless Steel: 0.08-0.2% carbon, higher nickel
- 18/8 steel: 18% chromium, 8% nickel, 1.25% manganese, 0.75% silicon
- High corrosion resistance, chemical plants, household utensils, high price
-
Tool Steels: Cut steel at high speeds
- Maintain hardness at elevated temperatures (red hardness)
- High Speed Steel (HSS):
- 18% tungsten (T-series, expensive)
- 6% tungsten and 6% molybdenum (M-series)
- 10% cobalt, 20% tungsten (Super HSS)
Heat Treatment of Carbon Steels
- Improves mechanical properties
- Temperature increase and waiting time for homogeneous temperature are crucial
- Cooling rate is the most critical factor
-
Types of heat treatment:
- Annealing: Heating and slow cooling, relieves internal stresses, increased ductility
- Normalizing: Heating and cooling in still air, relieves internal stresses
- Hardening: Rapid cooling (quenching), increases hardness but can make material brittle
- Tempering: Heating to 150-600°C and slow cooling, reduces brittleness
- Case hardening: Hardening the surface of mild steel by diffusion of carbon
Non-ferrous Alloys
-
Copper: Corrosion resistance, best conductor, wire drawn, sheet beaten
- Alloyed with zinc (brass), tin (bronze), and nickel (cupro-nickels)
-
Aluminum: Corrosion resistance, good conductor, ductile, malleable, thin sheets, cable drawn, cans
- Alloyed with magnesium for better properties
- Tin: Resistance to acidic conditions, low melting point, used in solders
- Zinc: High corrosion resistance, used as coating for steel (galvanized steel)
Brass
- Cartridge brass: 70% Cu + 30% Zn, deep drawing
- Admirability brass: 70% Cu + 29% Zn + 1% Sn, ships fittings
- Muntz’s metal: Cu + 40-45% Zn, condenser tube, heat exchanger, preheater, etc.
- Naval brass: 60% Cu + 39% Zn + 1% Sn, ships fittings
Tin Bronze
- Up to 10% tin added for increased strength and hardness
- Too much tin creates brittle intermetallic compound Cu3Sn
- Examples:
- Phosphor bronze (added phosphorous for better fluidity in fine casting)
- Leaded bronze (added lead for better machinability, self-lubricating)
- Gun-metal (88% Cu + 10% Sn + 2% Zn, bearing bushes, glands, pumps)
- Bell-metal (20-25% tin, used in cymbals)
Other Non-ferrous Alloys
- Silicon bronze: 1-4% Si to copper, extreme corrosion resistance, boiler and marine fittings
- Manganese bronze: 55-60% Cu + 40% Zn + 3-5% Mn, ship’s propellers
- Cupro-nickels: Extreme corrosion resistance, thermocouples, resistors
-
Aluminum alloys:
- L-M series: Mixed with magnesium, higher strength, used in extrusions
- 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 and corrosive applications (gas turbine blades, Formula One exhaust system)
Ceramics
- Hard, brittle, corrosion resistant, sometimes insulating
-
Machinable ceramics:
- Macor: Excellent electrical and thermal insulator, machinable with carbide tools
- Shapal: High thermal conductivity and excellent mechanical strength
- Boron-Nitride: High heat capacity, thermal conductivity, low dielectric constant
-
Harder ceramics:
- Zirconia: High hardness, wear resistance, high fracture toughness
- Silicon carbide: Extremely hard, excellent thermal shock and impact resistance
Macor
- Excellent electrical and thermal insulator
- Machinable via carbide tools
- Milling speeds and feeds:
- Cutting speed: 23 to 35 sfpm (1 to 1.4 meters per minute)
- Feed rate: 0.002"/tooth (0.05mm/tooth)
- Depth of cut: 0.15" to 0.2" (4 to 5 mm)
- Carbide or equivalent tools, two or four flute and helix milling cutters
- Climb milling prevents material being pulled off the edge
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Description
Test your knowledge on various engineering materials, including wood and plastics. Explore the differences between hardwood and softwood, as well as thermosetting and thermoplastic polymers. This quiz will help you understand the properties and applications of these materials in engineering.
