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University of Nevada Las Vegas |
MEG426/626 Manufacturing Processes |
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Department of Mechanical Engineering |
Fall Semester 2000 |
Mold Casting Progresses
Two common mold casting processes:
Expendable mold casting
: with single-use molds/single-use patterns, and single-use molds/multiple-use patterns.Permanent mold casting
: multiple-use molds.
A. Expendable mold casting:
Sand casting: by far the most popular of the casting processes, use ordinary sand (silica, zircon, or olivine) as the primary mold material.
Sand conditioning:
1). Refractoriness: the ability to withstand high temperatures.
2). Cohesiveness: the ability to retain a given shape when packed into a mold.
3). Permeability: the ability to permit gases to escape through it.
4). Collapsibility: the ability to permit the metal to shrink after it solidifies and ultimately to free the casting by disintegration of the surrounding mold.
The Making of Sand Molds (expendable):
1). Jolting machine,
2). Squeezing machine,
3). Shell Molding: many molds are made by the shell-molding process, which offers better surface finish than can be obtained with ordinary sand molding (jolting and squeezing).
B. Basic Permanent Mold Casting Processes
Permanent mold casting uses metal molds (steel or cast) instead of sand molds as which is used in expendable mold casting.
Mostly is used for low-melting-point alloys.
Slush casting: the metal is permitted to remain in the mold only until a shell of the desired thickness has formed. The mold is then inverted and the remaining liquid metal is poured out.
To make statures, toys out of lead, zinc, and tin.
Low-pressure casting: low pressure is used to draw the liquid metal into the cavity.
Advantage: clean molten metal is introduced into the mold, better part proprieties.
Vacuum mold casting: a vacuum is used to draw the molten metal into the mold cavity.
Die casting: is to use high pressure (1000-50,000 lb/in2) to force the metal into the cavity.
Hot-chamber die-casting is used for low-melting point metals such as zinc, tin, and lead.
Advantage: high production rate, 15 cycles per minute.
Cold-chamber die-casting is used for high-melting point metals such as aluminum, brass, and magnesium alloys.
Created by Dr. Wang