TRANSFORMATIVE Flashcards
Define transformative process and give some examples
- changing the shape of a material without removal or additions
- metal casting, forging, rolling, extrusion
Advantages of casting?
- complex shapes with internal cavity
- very large parts can be produced
- process is economically competitive with others
Equation relating area and height of sprue?
A1/A2 = sqrt(h2/h1)
Equation for molten metal velocity in casting?
v = c * sqrt(2gh)
What Reynolds number is desired in casting?
BELOW 20,000
Examples of expendable mould casting?
sand casting, evaporative (foam), shell mould, investment
Examples of permanent mould casting?
die casting, centrifugal casting
Equation for true strain / stress?
true strain: natural log of FINAL LENGTH / ORIGINAL
true stress: P/A with A being instantaneous area NOT original A.
Define forging?
compressive forces shape a workpiece through a die
Advantage of forging?
grain structure can be controlled so forged parts have good strength and toughness
Info about cold forging?
- higher forces required
- must be ductile enough to not crack
- good surface finish and dimensional accuracy
Info about hot forging?
- lower forces
- lower quality surface finish and lower dimensional accuracy
What processes are usually done after forging?
Usually forges are heat treated and machined to be finalised
Define open\flat die forging?
solid workpiece compressed between two flat dies
Define impression/closed die forging?
- workpiece is forced between 2 shaped dies and takes the shape of the cavity
- done at high temps to increase ductility and reduce force required
Define flat rolling?
thickness of a metal strip is reduced between powered rollers
Equation to estimate power of rolling?
Power (in kW) = (2piFLN) / 60,000
N in rpm
Define extrusion?
Cylindrical billet is forced through die to create a desired cross section
Define symbols in rolling force equation:
F = L * w * Yavg
L = sqrt(R (h0 - hf) ) where R = roll radius, h0 = originial thickness, hf = rolled thickness
w = width of strip
Yavg = average of 2 yield stresses - 1 is the unrolled yield stress, the other is the yield stress under the true strain value.
How would you calculate the time taken for a certain thickness of a cast to cool?
Calculate how long it takes for the entire cast to cool, then take away the thickness of the shell, perform same calculation and subtract them
Define casting?
Pouring molten metal into a mould cavity, letting it solidify and removing from the mould
What is draft angle in forging?
Draft is the angle or taper on the sides of a forging. Draft is necessary for releasing the forging from the dies.
