Casting 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 Casting See: for descriptions of: Die casting Sand casting Investment casting etc.
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 : 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 : 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 : Metal: Aluminum Process: Die Cast Weight: 19 lbs Size: Large(over 12X12) Market: Automotive Description: Lower crankcase
Examples of cast parts: Metal: Zinc Process: Die Cast Weight: oz Size: Very Small(1X1) Market: Computer/Electronics Description: A shielded cable header for housing electrical connector pins
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.) 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 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
Deformation 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
Sheet metal forming : Involves : punching, bending, stretching Must avoid necking, tearing, etc. Formability Minimum ratios to which a sheet can be bent 1 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 Alloys
Powder 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 forming See, Electro-forming Physical vapor deposition (PVD) or Chemical vapor deposition (CVD) used for IC processing ; MEMS Composites lay up or winding Speciality methods : - A heat exchange tube bundle being sprayed with a tungsten carbide-cobalt coating.