TRANSFORMATIVE

Question 1

Define transformative process and give some examples

Answer 1

• changing the shape of a material without removal or additions
• metal casting, forging, rolling, extrusion

Question 2

Advantages of casting?

Answer 2

• complex shapes with internal cavity
• very large parts can be produced
• process is economically competitive with others

Question 3

Equation relating area and height of sprue?

Answer 3

A1/A2 = sqrt(h2/h1)

Question 4

Equation for molten metal velocity in casting?

Answer 4

v = c * sqrt(2gh)

Question 5

What Reynolds number is desired in casting?

Answer 5

BELOW 20,000

Question 6

Examples of expendable mould casting?

Answer 6

sand casting, evaporative (foam), shell mould, investment

Question 7

Examples of permanent mould casting?

Answer 7

die casting, centrifugal casting

Question 8

Equation for true strain / stress?

Answer 8

true strain: natural log of FINAL LENGTH / ORIGINAL

true stress: P/A with A being instantaneous area NOT original A.

Question 9

Define forging?

Answer 9

compressive forces shape a workpiece through a die

Question 10

Advantage of forging?

Answer 10

grain structure can be controlled so forged parts have good strength and toughness

Question 11

Info about cold forging?

Answer 11

• higher forces required
• must be ductile enough to not crack
• good surface finish and dimensional accuracy

Question 12

Info about hot forging?

Answer 12

• lower forces
• lower quality surface finish and lower dimensional accuracy

Question 13

What processes are usually done after forging?

Answer 13

Usually forges are heat treated and machined to be finalised

Question 14

Define open\flat die forging?

Answer 14

solid workpiece compressed between two flat dies

Question 15

Define impression/closed die forging?

Answer 15

• 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

Question 16

Define flat rolling?

Answer 16

thickness of a metal strip is reduced between powered rollers

Question 17

Equation to estimate power of rolling?

Answer 17

Power (in kW) = (2piFLN) / 60,000
N in rpm

Question 18

Define extrusion?

Answer 18

Cylindrical billet is forced through die to create a desired cross section

Question 19

Define symbols in rolling force equation:
F = L * w * Yavg

Answer 19

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.

Question 20

How would you calculate the time taken for a certain thickness of a cast to cool?

Answer 20

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

Question 21

Define casting?

Answer 21

Pouring molten metal into a mould cavity, letting it solidify and removing from the mould

Question 22

What is draft angle in forging?

Answer 22

Draft is the angle or taper on the sides of a forging. Draft is necessary for releasing the forging from the dies.