Download Material Selection - Web Services Overview

Selection Criteria
• Most designers select materials with equal
consideration of:
– Properties
– Availability
– Cost
Properties
• Mechanical
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Yield strength (ductile) / Ultimate strength (brittle)
Fatigue (endurance limit)
Stiffness or rigidity (modulus of elasticity)
Hardness (Rockwell, Brinell)
Impact strength (fracture toughness)
Toughness (sharpy test)
Ductility (% reduction is area)
Hardenability
Creep (elevated temperature properties)
High/Low temperature properties
Wear characteristics
Properties
• Physical
– Density
– Electrical properties
– Thermal properties
(conductivity)
– Magnetic
– Melting point
– Thermal expansion
– Flamability
– Optical
• Chemical
– Corrosion resistance
– Oxidation resistance
– Toxicity
– Resistance to radiation
– Resistance to elements
• Dimensional
– Dimensional stability
– Surface finish
Availability
• Important questions:
– Is the material available in the desired form?
• Gage 10 sheets of 304L stainless steel?
– If not available, can it be obtained?
– Do we have to order 100,000 lbs?
– Is the material available from multiple
suppliers?
COST
• The primary factor in material selection in industry
• Comparative cost of engineering metals per pound
Material
Cast irons
Carbon steels
Low alloy steels
Aluminum
Copper alloys
Stainless steels
Magnesuim
Tool steels
Nickle alloys
Price $
.15
.25
.30
.60
.80
1.25
1.5
1.75
4.00
Material
Cobalt
Titanium
Tungsten
Silver
Beryllium
Gold
Price
12
17
30
75
200
6100
COST
• Cost per volume may be a better choice.
The following table is $/in3
Material
Cast irons
Carbon steels
Low alloy steels
Magnesuim
Aluminum
Copper alloys
Stainless steels
Tool steels
Nickle alloys
Price $
.04
.07
.09
.10
.10
.22
.35
.50
1.25
Material
Titanium
Cobalt
Beryllium
Silver
Gold
Price
2
4
15
31
4257
Other Cost Factors
• What is the cost of material in relation to the
production cost or selling price?
– Is it orbiting satellite, B1 bomber, or a hammer?
• What is the production volume?
– A one of a kind design, or graden weisel?
• What is the anticipated service life?
– A toy is expected to last for a year or two, low quality
gears and other components do fine.
– Tooling materials for a one-year production can wear
more quickly
Other Cost Factors
• Manufacturability (Fabricability)
– If considerable machining is required, it may well be
more economical to choose a more expensive material
with higher machinability rating than a lower cost
material with lower machinability.
– Some materials can not be machined at all (ceramics).
– A “non-common” metal may require more lead time,
different tooling and set up, or special techniques for
fabrication.
– Only softer materials with good formabilty can be
easily formed.
Manufacturability
• The size and weight of a part can limit its formability.
• Part size and geometry limit parts fabricated with PM
technology
• Materials to be heat treated for strength must have
sufficient hardenability.
• Materials that require heat treatment may have to go
through further processes.
• Hot rolled materials may require further processing.
• Cold-rolled materials may distort when machined
• Casting processes have weight, wall thickness, size,
accuracy, surface finish, and material limitations.
Manufacturing
• Parts fabricated by welding require good material
weldability.
• Most metals can be welded but with a wide range of
methods and very different costs. Low alloy steels cost the
least, high strength steels cost more, and tool steels are
most expensive to weld.
• Some materials require pre and post-weld heat treatment.
• Welding induces distortion in parts, further processing may
be required.
• It is difficult to join aluminum and steels together.
Designer’s Repertoire
• Know about the properties of a few carbon steels
– 1010, 1030, 1050, 1080, B1112
• Know about the properties of a few cast irons:
– Class 20, Class 60, Ductile 60-45-18
• Know about the properties of a few alloy steel:
– 4140, 4340, 9310
• Know about the properties of a few tool steels:
– 01, A2, D2, S1, H13, M2
• Know about the properties of a few stainless steels:
– 304, 304, 316,420,440C, 17-4 PH
Designer’s Repertoire
• Know about the properties of a few Aluminum alloys:
– 3003, 5052, 6061, 7075
• Know about the properties of a few nickel alloys:
– Monel, Inconel
• Know about the properties of a few copper alloys:
– C36000 yellow brass, C52100 phosphor bronze
• Know about the properties of a few titanium alloys
• Know about the properties of a few Magnesium alloys
Designer’s Repertoire
• Know about the properties of a few ceramics:
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Aluminum oxides
Silicon nitride / Silicon carbide
Cemented carbides
Carbon products
Ceramic coatings (Chromium oxide, Tungsten carbide)
• Know about the properties of a few plastics:
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Polyethylene / Polyimides / Polyamides
Polycarbonate
PVC /ABS
Nylons
Elastomers
Example
• Suppose a designer has created a drawing for a shaft of a
hypothetical device. The list of operational conditions
have been determined as follows:
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1.25” diameters are to fit ball bearings
The shaft is subjected to maximum shear stress of 10 ksi
There is possibility of moderate shock load
Small end must resist damage from frequent removal of a keyed
gear.
– There are no inertial requirements.
– Surface roughness to be 32 micro inches max.
– Diameters must be concentric to 0.001 inch.
Example
• Based on the operational requirements, time constraint, and
cost, the following selection factors have been established:
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Hardness of at least 30 HRC
Fatigue strength of 30 ksi
Impact strength must be high
Stiffness must be high
The part must not rust in 50% RH room air.
Must be dimensionally stable.
Parts are needed in one week.
Three units are required.
Expected service life is 5 years
Example