Conceptual%20Designs

1
Conceptual Designs

2
Most Commonly used Metals

• Plain carbon steels
• Available in all structural forms, thin sheets,
  coated or uncoated, cold formed, hot rolled, and
  free machining.
• Use 1006 to 1020 for parts requiring severe
  forming or welding. Bolts, nails, automobile
  body panels, brackets, appliance housing, machine
  bases.
• Use 1030 to 1060 for parts requiring higher
  strength w/o heat treatment. Use only if welding
  is not required.
• Use 1040 to 1060 for parts requiring surface
  hardening by flame or induction methods.
• Use 1080 to 1095 for small parts requiring
  through hardening. Springs, hammers.

3
Materail Selection

• Plain carbon steels have poor hardenability.
• Cold finished steels (1006 to 1050) can come in
  various forms (hard to skin rolled). They can be
  strengthened up to 100 with cold working.
• Cold finished parts are stronger, have better
  surface finish, are more dimensionally accurate.
  But, they have less ductility, cost more, are
  dimensionally less stable in machining, and loose
  their strength if welded.
• High sulfur steels are ideal for machining (AISI
  1112) as the chips break up easily. High sulfur
  content, however, causes weld cracking.

4
Material Selection

• Alloy steels
• AISI 4340 or 4140 (Through hardening grades)
  Have excellent strength and toughness. Available
  in most forms in hot rolled form. Designed for
  high hardenability. Best suited to high stress
  machine parts - gears, cams, shafting, piston
  rods, bolts, dies, keys, bending rolls. They can
  be finish machined and can be welded with
  special precautions.
• AISI 8620 or 9310 (carburizing grades) These
  steels are designed for case hardening
  requirements. Deep cases can be created and
  hardened using carburizing. Used when high wear
  resistance is required. Suitable for gears,
  racks, cams, and sliding surfaces.

5
Alloy Steels

• High Strength Low Alloy Steels (HSLA)
• Used for Structural applications
• Stronger than plain carbon steels
• Not heat treatable
• Corrosion resistant (not as much as stainless
  steel)
• Good weldability (low carbon content)
• Good formability
• Applications structural forms, bars, plates.
• ASTM A36 (most popular), A242

6
Alloy Steels

• Ultra-strength steels
• High strength and reasonable toughness.
• Used for heavily loaded machine parts.
• 4340 and 4140 are most common
• Harder to weld but machinable
• Maraging steels

7
Alloy Steels

• 18 nickel maraging steel
• Maraging steels are carbon free iron-nickel
  alloys with additions of cobalt, molybdenum,
  titanium and aluminium. The term maraging is
  derived from the strengthening mechanism, which
  is transforming the alloy to martensite with
  subsequent age hardening.
• Very high strength (200-300 ksi)
• Good weldability
• Very expensive

8
Cast Irons

• Grey cast iron (ASTM A 48 grades 20-60)
• Easy to cast (excellent fluidity)
• Low cost
• Low toughness, brittle, no shock resistance
• High compressive strength
• Not appropriate for parts highly stressed in
  tension.
• Low to medium tensile strength
• Excellent machinability
• Superb vibration damping property
• Not easily weldable
• Low stiffness (30 to 60 of steel)

9
Cast Irons

• Gray cast iron additional properties
• Excellent metal-on-metal wear resistance
• Good corrosion resistance in all media
• Ductile iron (ASTM 536, grade 5 60-40-18)
• Easy to cast/low cost.
• Much better toughness than gray iron.
• Stiffness is about 70 of steel
• Yield strengths range from 40 o 90 ksi
• Similar to gray cast iron in other properties

10
Aluminum Alloys

• General properties
• Lightness 1/3 of steel
• Good thermal and electrical conductivity
• High strength/weight ratio
• Weldable (most alloys)
• Atmospheric corrosion resistance (will not rust)
• Excellent machinability
• Can be die cast
• Good formability
• Non-magnetic
• Non-toxic (pots and pans - 25 of all usage)