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70 Cards in this Set
- Front
- Back
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categories of casting processes
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1. expendable molds
2. permanent molds 3. composite molds |
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expendable molds
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sand, plaster, mold is made from pattern, mold is expendable, pattern is either expendable or reusable
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permanent molds
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made of metals that maintain strength at high temps, metal conducts heat which can impact the microstructure and grain size
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composite molds
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made of 2 or more materials,
ex: sand, graphite, metal, have permanent and expendable portions |
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sand casting
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most prevalent way of casting metals
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sand casting process
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a. placing a pattern in sand to make an imprint
b. incorporating a gating system c. removing the pattern and filling the mold cavity with molten metal d. allowing the metal to cool e. breaking away the mold f. removing the casting |
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types of sand
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naturally bonded, synthetic
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naturally bonded
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bank sand
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synthetic
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lake sand, preferred
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factors important in selection of sand for molds
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fine grain enhances mold strength but lowers permeability (where fluids and gases penetrate through pores), good collapsibility
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collapsibility
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good collapsibility allows casting to shrink while cooling to avoid defects in the casting (hot tearing, cracking)
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types of sand molds
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green-sand, cold-box, no-bake
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green molding sand
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mix of sand, clay, water,
cheapest and most common, sand can be recycled |
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skin-dried [method]
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mold surfaces are dried, by storing the mold in air or by drying it with torches,
for large castings |
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cold-box mold
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binder are blended into sand to bond the grains chemically and make stronger,
more expensive, more dimensionally accurate |
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no-bake mold
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synthetic liquid resin is mixed with sand and mixture harden at room temp
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cold-setting processes
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no-bake, cold-box
called because they bond without heat |
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major features of sand molds
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1. flask
2. pouring basin 3. sprue 4. runner system, gates 5. risers 6. cores 7. vents |
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flask
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supports mold, 2 piece molds have cope on top and drag on bottom
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parting line
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separates cope and drag
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sprue
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through which molten metal flows downward
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runner system
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has channels which carry molten metal from sprue to mold cavity
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gates
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inlets into mold cavity
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risers
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-supply molten metal to the casting as it shrinks during solidification
-types: blind riser, open riser |
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cores
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inserts made of sand and placed in the mold to form hollow regions or otherwise define the interior surface of the casting, used on outside to form lettering or deep external pockets
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vents
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placed in molds to carry off gases produced when molten metal comes into contact with the sand in the mold and core, also exhaust air from mold cavity as molten metal flows into the mold
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patterns
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used to mold the sand mixture into the shape of the casting
wood, plastic, metal |
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parting agent
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coating on patterns to facilitate removal of casting from molds
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one-piece patterns
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for simple shapes, low-quantity production,
wood, inexpensive |
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split patterns
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two-piece patterns, each part forms a portion of the cavity, for complicated shapes
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match-plate patterns
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common type of mounted pattern in which two-piece patterns are constructed by securing each half of one or more split patterns to the opposite sides of a single plate
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core prints
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recesses added to the pattern to locate and support the core and provide vents for gases to escape
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chaplets
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metal supports, used to anchor the core in place
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vertical flaskless molding
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a. halves of pattern form vertical chamber wall against which sand is blown and compacted
b. mold halves are packed horizontally, with parting line oriented vertically, and moved along a pouring conveyer |
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sandslingers
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fill flask uniformly with sand under high-pressure stream, used to fill large flasks, operated by machine
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impact molding
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sand is compacted by a controlled explosion or instantaneous release of compressed gases, method produces molds with uniform strength and good permeability
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vacuum molding
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V process, for high surface detail, large, flat, castings
1. pattern is covered tightly with a thin sheet of plastic 2. flask is placed over the coated pattern and is filled with dry, binderless sand 3. a second sheet of plastic then is placed on top of the sand 4. a vacuum action compacts the sand 5. take away the pattern 6. both halves are assembled 7. when the metal has solidified, the vacuum is turned off and the sand falls away, releasing the casting |
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shell molding
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for small mechanical parts requiring high precision
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precision casting
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consists of shell molding, ceramic-mold and investment casting
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plaster molding
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mold is made of plaster of paris mixed with water then poured over the pattern and allowed to set
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antioch process
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molds are dehydrated in an autoclave then rehydrated in air, increases permeability
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ceramic-mold casting
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similar to plaster-mold process except uses refractory mold materials suitable for high-temp applications
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shaw process
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ceramic facings are backed by fireclay to give strength to the mold
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evaporative-pattern casting
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uses polystyrene pattern which evaporates upon contact with molten metal to form a cavity for the casting
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advantages of evaporative-pattern casting
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simple, inexpensive, capable of producing complex shapes, minimal finishing operations required, can be automated
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investment casting
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lost-wax process, produces office equipment
1. inject wax or plastic pattern 2. eject pattern 3. pattern assembly (tree) 4. slurry coating 5. stucco coating 6. completed mold 7. pattern melt-out 8. pouring 9. shakeout 10. pattern |
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where does the term "investment" derive from?
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that fact that the pattern is invested (surrounded) with the refractory material
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semipermanent-mold casting
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uses easily collapsable sand cores that allow you to have intricate internal cavities
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slush casting
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makes hollow castings with thin walls, uses principle that a solidified skin develops in a casting and becomes thicker with time
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pressure casting
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molten metal is forced upward by gas pressure into a graphite to metal mold
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die casting
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molten metal is forced into the die cavity at pressures ranging from .7 to 700 MPa
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types of die casting machines
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cold-chamber, hot-chamber
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hot-chamber process
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uses piston which forces certain volume of metal into the die cavity through a gooseneck and nozzle
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cold-chamber process
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molten metal is poured into the injection cylinder at room temp, then the metal is forced into the die cavity at pressures from 20 to 70 MPa
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insert molding
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process of die casting pins and shaft integrally, like placing wooden sticks in popsicle prior to freezing
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heat checking
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surface cracking from repeated heating and cooling of the die
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semicentrifugal casting
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used to cast parts with rotational symmetry
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centrifuging
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mold cavities of any shape are placed a certain dist from the axis of rotation, molten metal is poured from the center and forced into the mold by centrifugal forces
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which 2 casting processes incorporate both casting and forging?
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squeeze casting, semisolid-metal forming
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squeeze-casting
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liquid-metal forming, involves solidification of molten metal under high pressure, uses die, punch, ejector pin
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semi-solid metal forming
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metal (consisting of liquid and solid) is stirred so that all of the dendrites are crushed into fine solids
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thixoforming
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means viscosity decreases when agitated
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crystal-pulling method (Czochralski process)
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a seed crystal is dipped into molten metal and pulled out slowly while being rotated
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floating-zone method
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induction coil heats polycrystalline silicon resting on a crystal while moving upward
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amorphous alloys
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metallic glasses
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melt spinning
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alloy is melted by induction in a ceramic crucible, then propelled under high gas pressure against a rotating copper disk, which chills the alloy rapidly
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splat cooling
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rapid chilling
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chill block
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rotating copper block
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melting furnaces
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electric-arc, induction, crucible, cupolas, levitation melting
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foundaries
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where casting operations are carried out
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