1. ME 437 - Session #5 Selection of term projects
Assignment#4 : Review of manufacturing processes
Presentations of PDS work
Material selection
Questions on material science review

2. Term Projects Let us select 3 projects
Each project would have 5 teams of size 2 working on them
Desired characteristic
Consumer-type products, or common applications
Simple: Not too many components
Some plastic parts, some metal parts
Some off-the-shelf components

3. Projects Nut cracker Cat/Dog feeder Fish feeder Rock tumbler
Envelope licker
A bike rack for automobiles
A device to test shear strength of wood dowels
Device to test effect of vibration on light bulbs
A battery-operated home lifter (or car jack).
An easy-to-install tire traction device.

4. Material Selection Criteria
Most designers select materials with equal consideration of:
Properties
Availability
Cost

5. Availability Is the material available in the desired form?
Can it be obtained in a month?
Do we have to order 100,000 lbs?
Is the material available from multiple suppliers?
Does a particular material impose time delays in part manufacturing?

6. COST The primary factor in material selection in industry.
Comparative cost of engineering metals per pound.
Cost per volume may be a better choice. The following table is $/in3 .
Hook design: Tungsten
In school: Properties important / cost no issue
In industry: Cost also very important

7. Cost Factors Cost of material in relation to the production cost.
The production volume?
The anticipated service life?
Manufacturability cost (Fabricability)
Machinability
Formability
Weldability
Castability
Tolerances / Surface finish

8. Designer’s Repertoire
Carbon steels
Cast irons
Alloy steel
Tool steels
Stainless steels
Aluminum alloys
Nickel alloys
Copper alloys
Titanium alloys
Magnesium alloys
Ceramics
Plastics
Composites

9. Materail Selection Plain carbon steels have very poor hardenability.
Cold finished steels (1006 to 1050) can come in various tempers (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.

10. 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 but can not be easily welded without 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.

11. Alloy Steels High Strength Low Alloy Steels (HSLA)
Used for Structural applications
Stronger than plain carbon steels (40-80 ksi yield)
Not heat treatable
Corrosion resistant (not as much as stainless steel)
Good weldability (low carbon content)
Good formability
Applications: (ASTM 242) structural bars, plates.

12. Alloy Steels Ultra-strength steels
High strength and reasonable toughness.
Used for heavily loaded machine parts.
4340 and 4140 are most common
Hard to weld but machinable
18% nickel maraging steel
Very high strength ( ksi)
Good weldability
Very expensive

13. 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:
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 inch.

14. Example
Based on the operational requirements, time constraint, and cost, the following selection factors have been established:
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

15. Example [From Budinski]

16. Solution ideas What kind of material Must be hardenable to 30 HRC
Metal?
Plastic? Low stiffness
Ceramic? Low impact strength
Composites?
Must be hardenable to 30 HRC
Hardenable steels 1050 or 4340/4140
High fatigue strength
AISI 4340 or 4140
Must be surface treated (nickel plating)