530.352 Materials Selection530.352 Materials Selection

Lecture #31 Material ProcessingMonday November 22nd, 2004

Processing Results in :Processing Results in :

Materials

Shape and size

Tolerance

Roughness / Surface finish

Precision

Primary Forming Processes :Primary Forming Processes :

Casting

Pressure molding

Deformation processing

Powder methods

Special methods

CastingCasting

Liquid poured into a mold and solidified• metals cool, thermosets react

Gravity fed (or low P) - requires low viscosity

Mold shape and design are crucial• no thin walls, no keyed in shapes

Types of CastingTypes of Casting

See: http://www.efunda.com/processes/processes_home/process.cfm for descriptions of:

•Die casting•Sand casting•Investment casting •etc.

Examples of cast parts :Examples of cast parts :

Metal: Aluminum Process: Die Cast Weight: 14.6 lbs Size: Large(over 12X12) Market: Automotive Description: Transmission Gear Case

Examples of cast parts :Examples of cast parts :

Metal: Magnesium Process: Die Cast Weight: 90 grams Size: Medium(3X3 to 12X12) Market: Computer/Electronics Description: Military Hand Held Radio Housing

Examples of cast parts :Examples of cast parts :

Metal: Zinc Process: Die Cast Weight: 0.39 lbs Size: Medium(3X3 to 12X12) Market: Automotive Description: Police/Commercial Spot Light Hsng.

Examples of cast parts :Examples of cast parts :

Metal: Aluminum Process: Die Cast Weight: 19 lbs Size: Large(over 12X12) Market: Automotive Description: Lower crankcase

Examples of cast parts:Examples of cast parts:

Metal: Zinc Process: Die Cast Weight: 0.244 oz Size: Very Small(1X1) Market: Computer/Electronics Description: A shielded cable header for housing electrical connector pins

Examples of cast parts:Examples of cast parts:

Metal: Aluminum Process: Die Cast Weight: xx Size: Medium(3X3 to 12X12) Market: Sports/Recreation Description: wankel snowmobile engine rotor housing

Casting (cont.)Casting (cont.)

sand, ... shell, plaster, investment ... die casting $ / part price $$$$ / part

one offs #’s batches low tolerance and finish high

slip casting–ceramics

Types of Casting

Pressure moldingPressure molding

Casting of high viscosity liquids• thermoplastics and glasses

Requires considerable pressure

Die must withstand :• pressure, temperature, wear

Types of molding :• pressure, transfer, injection, blow

Pressure moldingPressure molding

Deformation processingDeformation processing

Forging , Rolling, Extrusion, Drawing

Hot (T > 0.55 Tmelt) - lower strength and recrystallization

– bigger shape changes

– poorer finish

Warm (0.35 Tm < T < 0.55 Tm) - recovery not recrystallization

Cold (T ~ Room T) - strengthen through work hardening

– smaller shape changes

– better finish

ForgingForging

ForgingForging

RollingRolling

Wire drawingWire drawing

ExtrusionExtrusion

Deep drawing:Deep drawing:

Sheet metal forming :Sheet metal forming :

Involves :• punching , bending, stretching

Must avoid• necking, tearing, etc.

Formability• Minimum ratios to

which a sheet can be bent1 x thickness (good) 4 x t (average)

Cast alloys• solidified in near-net shape

• segregation often leans to microstructural inhomogeneities

• does not require expensive shaping, forming and machining processes

Wrought alloys• shaped from large ingots

• hot/warm/cold working evens out inhomogeneities

• cold working strengthens an alloy

Cast vs. Wrought AlloysCast vs. Wrought Alloys

Powder methodsPowder methods

Pressing and sintering fine particles• cold pressed and sintered (T ~ 0.8Tm)• “die pressing” - pressed in a heated die • “HIPing” - hot isostatic pressing

Pluses• economical, can use for ceramics and other brittle / hard to

form materials.• Provides homogeneity

Limits• part sizes and purity

Spray formingSee, http://www.aws.org/wj/nov02/feature.html

Electro-forming

Physical vapor deposition (PVD) or Chemical vapor deposition (CVD)• used for IC processing ; MEMS

Composites • lay up or winding

Speciality methods :Speciality methods :

- A heat exchange tube bundle being sprayed with a tungsten carbide-cobalt coating.