CMT Imports :. Process Selection Comparison Table

Process Selection Comparison Table

PROCESS	DESCRIPTION	METALS	LINEAR TOLERANCE	SURFACE FINISH (RMS)	MINIMUM SECTION THICKNESS	TYPICAL TOOLING COST	PROCESS ADVANTAGES
DIE CASTING	Molten metal is injected into steel (typical H13,8407,dievar mold steel) dies under pressure. The metal solidifies, the die is opened and the part ejected	Aluminum, Zinc and Magnesium	Standard +/- .010" to 1" then add +/- .001" / inch per NADCA publication #402	32-63 (Zinc); 63-250 (Aluminum)	.030"(Mg) to .060" (Aluninum)	$10000 to $300000	High volume, near net shape, minimal machining required, excellent casting detail, smooth finish.
PERMANENT MOLD	Molten metal is gravity poured in steel (typical H13 mold steel) molds. Sand cores can be used to form internal features. The mold is opened and the casting removed	Aluminum and Zinc	Standard +/- .015" to 1" then add +/- .002" / inch	150 -300	.188"	$10000 to $100000	All volume, able to cast internal features using cores, lower cost tooling.
LOW PRESSURE CASTING	In low-pressure casting, the furnace is pressurized whereby the molten aluminum is brought into the casting die through the riser tube. The die is filled by slowly climbing, controlled, and above all, constant pressure. The laminar filling process avoids the formation of oxidation, the onset of cold currents and the danger of air inclusions.	Aluminum	Standard +/- .015" to 1" then add +/- .002" / inch	150 -300	.188"	$10000 to $300000	All volume, able to cast internal features using cores, compressed structure,tensile strength and hardness is better than gravity casting, compression resistance and leakproof.
SAND CASTINGS	Treated sand is packed around a wood or metal pattern. Cores are added to form internal features. Molten metal is poured into sand molds. Molds are broken to remove the castings	All Metals	Standard +/- .030" up to 6", Add +/- .002" for every inch over 6	500-2000	.150"	$2000 to $40000	All volumes,able to cast complex internal passageways, low tooling cost, short tooling leadtime.
LOST FOAM	A metal mold is used to produce polystyrene foam patterns. Foam patterns are coated with a ceramic coating. Foam patterns are packed in loose sand. Molten metal is poured on to foam patterns. The foam pattern evaporates and is replaced by the metal.	Aluminum and Iron	Standard +/-.010" for 1 to 3" then add +/-.003" / inch	250- 1000	.150"	$10000 to $100000	Offers design flexibility. Complex shapes can be made when multiple patterns are glued together. No draft required.
INVESTMENT CASTING (LOST WAX)	A metal mold is used to produce wax patterns. Wax patterns are attached to a pouring tree. Trees are dipped in slurry to form outer shell. Wax is evacuated and metal is poured into cavity. Shell is broken and castings removed.	Aluminum and Steel	Standard +/- .005" to 3" then add +/- .003" / inch	63-250	.060"	$3500 to $25000	All volumes, near net shape, minimal machining, excellent surface finish, more design freedom.
MODIFIED SHELL MOLDING	A heated steel (typical H13 mold steel)pattern is placed over a ductile iron mold. A thin layer of shell sand is injected into the gap between pattern and ductile iron mold. The thin layer shell sand solidifies onto ductile iron mold after cooling.Mold closed and molten metal poured. Sand cores can be used to form internal features. Mold is opened, casting is removed, and ductile iron mold is cleaned before next use.	Gray and Ductile Iron	ISO 8062-3 DCTG Grade 8-12 Or Standard +/- .020" up to 6", Add +/- .002" for every inch over 6	500-1000	.12"	$10000 to $50000	Medium to high volumes, high yield rates, smoother casting surface, porosity free and closer tolerances than sand castings.
SQUEEZE CASTING (LIQUID FORGING)	Squeezer casting is a combination of casting and forging processes. An exact amount of molten meal is gravity poured into a die. Pressure is applied until the part solidifies. Cores can be used to create internal features.	Aluminum	Standard +/- .010" to 1" then add +/- .001" / inch per NADCA publication #402	90-500	.30"	$10000 to $300000	Medium to high volume. Low levels of porosity. More internal features can be cast using cores than die casting.
Metal Injection Molding (MIM?	Metal Injection Molding (MIM) is a metal working process that draws on two technologies — plastic injection molding and powdered metallurgy. Finely powdered metal (typically less than 20 micrometers) is mixed with a binder material to create a feedstock that is then fed into the cavities of a regular injection molding machine.	Stainless and Carbon Steels	Standard +/- .005" to 1" then add +/- .002" / inch	40 -252	.02"	$8000 to $15000	MIM allows for more design complexity – for example, thinner wall sections, sharper cutting points and tighter tolerances of up to +0.005" per linear inch – as compared to the investment casting process. In addition, MIM is better suited for the production of smaller parts that weight less than 20 grams, and that are less than 100 mm long.