Manufacturing methods Flashcards
Representation of surface finish
Ra = surface roughness average low = smooth high = rough
Advantages and disadvantages of open die forging
better fatigue resistance
continuous grain flow and finer grain size
increased strength
machining required to achieve desired dimensions
not capable of forming close tolerance and high precision parts
Advantages and disadvantages of closed die forging
no material limitation
better surface finish
no post machining required
internal grain structure formation increases the tightness and strength of the final product
dimensions with tight tolerances can be achieved
uneconomical for short runs due to the high cost of die production
Sand casting
It involves pouring molten metal into a cavity-shaped sand mould where it solidifies. After the metal has cooled to room temperature, the sand mould is broken open to remove the casting.
Gravity casting
gravity feeds molten substance into mould
quicker than sand casting
useful when making large batches
more efficient
more expensive
Pressure casting
changes in grain structure as molten material is under pressure
Cores
sheet metal forming
deep drawing abilities
cheap to get low batch numbers
Laser casting
quick
cheap
easy
efficient
Considerations with laser cutting
tiny cracks occur around the material
crack propagation can occur throughout the material
Water-jet cutting
no microscopic cracks noisier more time consuming better edge finishes more expensive than laser cutting
Advantages and disadvantages of sand casting
cheap
quick
simple
not suitable for dimensions with close tolerances
low mechanical properties due to the coarse grain structure as a result of the slow cooling rate
Advantages and disadvantages of pressure casting
good surface finish
close dimensional accuracy
good mechanical properties
efficient in large batch production
high setup costs makes pressure casting inefficient for short runs
Lathe
rotates a workpiece about an axis to perform various tasks such as cutting, sanding or turning
Milling machine
shape, flat/irregular shapes
Cutter collets
hold workpiece still
Injection moulding
molten material injected into a cavity/mould
used to make thermoplastics, thermosets and elastomers
useful for making large batches, quick, simple components
Common materials used in injection moulding
polypropylene nylon polyester polycarbonate polystyrene ABS
Sintering and 3D printing
allow complex parts to be made
low strength, expensive
Investment casting
A wax pattern is manufactured for the process which is then coated with a refractory ceramic material
once the ceramic material has hardened, it takes the shape of the casting
the wax is then melted out and molten metal is poured into the cavity.
Once the metal solidifies, the metal cast is broken out
Advantages and disadvantages of investment casting
allows casting of extremely complex parts
good surface finish
high dimensional accuracy with very low tolerances
efficient
complicated process and relatively expensive
limits on size
