Types of Molds (advantages vs. disadvantages) Flashcards
(25 cards)
3 Types of Sand Casting
- Green Sand Mold
- Cold Box Mold
- No Bake Mold
Type of Mold destroyed after each use
Expendable Mold
Sand Casting Advantages
- Most Widely Used
- Inexpensive
- resistant to elevated temps
- good permeability to allow gases to escape
What is Green Sand Mold
Refers to the mold obtaining moisture during pouring
- Least expensive
- Good re-usability
- moisture can cause defects
What is Cold Box Mold
Uses organic or inorganic binders blended into the sand to chemically bond grains for higher mold strength
- Better dimensional accuracy than green mold
- More expensive
What is No-Bake Mold
Synthetic liquid resin is mixed with sand (bonded with no heat added)
- Allows for complex geometries
- Fair dimensional accuracy
Shell Mold Casting Advantages
Mold Walls are smooth resulting in
- Sharper Corners
- Thinner sections
- Low resistance to flow
Shell Mold Casting Disadvantages
-High cost of metal patterns
BUT!
- No need for finishing or machining due to smooth finish
- several castings can be made in a single mold
Plaster-Mold Casting Advantages
Made of plaster (talc and silica flour in water)
- High dimensional accuracy
- Cools slower (uniform grain structure)
Plaster-Mold Casting Disadvantages
Very low permeability (traps gases)
Limited max temperature
Ceramic Casting Advantages
Same as Plaster mold except uses ceramic
- Suitable for High Temps
- Good dimensional accuracy
- Extremely high tolerances
Ceramic Casting Disadvantages
-Very expensive
Lost Foam Process
Uses Polystyrene pattern that evaporates among contact with molten metal
Lost Foam Advantages
- Cools very fast
- Very complex geometries can be produced
- Flask is inexpensive
- No removal of pattern
- easily automated
Lost Wax Process
Wax patterns can be joined into 1 mold making a ‘tree’
Lost Wax Advantages
- Significantly increases production rate
- Allows for extremely complex parts
- Good surface finish
Lost Wax Disadvantages
- Only for small parts
- Complicated and Expensive
Permanent Mold Castings
- Higher initial set up costs (bad for small production runs)
- Once set up, extremely economical for large runs
- Highly automated (less rejects)
2 types of Die Castings
Hot-Chamber
Cold Chamber
Hot-Chamber
Molten Metal is directly attached to machine
- High velocity of productivity
- Thermal damage occurs because continuously submerged in high temp alloys
Cold-Chamber
Metal is brought in from an external source
- Slower Production rate
- Can use higher melting point alloys
3 Types of centrifugal casting
True Centrifugal
Semi Centrifugal
Centrifuging
(All use internal forces caused by rotation to force Metals into cavities)
True Centrifugal Casting
- Great for hollow cylinder parts
- Impurities collect in inner region on axis of rotation
- Wall thickness is easily controlled by pouring amount
- High rate of productivity
Semi Centrifugal casting
-Mold is filled completely with molten metal through a central sprue