week 3: transformative manufacturing

Question 1

definition and advantages of metal casting

Answer 1

pouring molten metal into a mould cavity
produces intricate shapes in one piece

advantages:
- complex shapes with internal cavities
- large parts
- economically competitive

Question 2

molten metal flow - what is used to ensure adequate flow

Answer 2

riser gated casting
risers serve as reservoirs and supply molten metal as the casting shrinks in solidification

Question 3

rate of flow for incompressible liquids

Answer 3

volume flow rate (Q) = cross sectional area (A1) x average velocity (v1) = A2v2

Question 4

velocity of molten metal leaving gate

Answer 4

v = friction factor (c) x sqrt(2gh)

where h is distance between sprue base to the liquid metal height

Question 5

solidification time

Answer 5

solidification time = C x (V/A)^n

where C is the constant that reflects the mould materials, metal properties and temp
n is value between 1.5 and 2 usually taken as 2

Question 6

mechanics of metal forming: what is true stress?

Answer 6

ratio of the load P to the actual or instantaneous cross sectional area A

stress = P/A

Question 7

mechanics of metal forming: true strain

Answer 7

true strain = ln(l/l0)

Question 8

metal forging definition

Answer 8

workpiece shaped by compressive forces applied through various dies

Question 9

open die forging - definition

Answer 9

solid workpiece between two flat dies and reduced in high by compression ( die surfaces may have shallow cavities)

Question 10

open die forging force eq (Yf, mu, r, h)

Answer 10

Yf - flow stress
mu - coefficient of friction
r - instantaneous radius
h - instantaneous height

Question 11

closed die forging - definition

Answer 11

workpiece takes the shape of the die cavity while being forged between two shaped dies
carried out at elevated temp to lower required forces and attain enhanced ductility

Question 12

closed die forging - draft angle

Answer 12

draft angle needed to facilitate removal
- upon cooling forging shrinks radially and longitudinally, so internal draft angle (7-10 degrees) larger than internal (3-5 degrees)

Question 13

rolling - definition / description

Answer 13

• strip of thickness h0 enters the roll gap and is reduced in thickness by a pair of rotating rolls
• surface speed of the rolls is Vr, the velocity of the strip increases from entry value v0 as it moves through roll gap and is highest at exit, Vf
• relative sliding between the roll and the strip along the arc of contact
• friction needed by dissipates energy

Question 14

rolling - force calc variables (L, w, Yavg)

Answer 14

L = strip contact length
w = width
Y avg = average true stress