Sheet Metal Forming

Question 1

Phases of Stress-Strain Curve

Answer 1

1. Elastic Region
2. Plastic Region
3. Necking Region
4. Failure

Question 2

Properties of elastic region

Answer 2

Increases linearly with strain – Slope is E
No permanent deformation; returns to original shape after unloading

Question 3

Yield Stress on curve

Answer 3

Point where material shifts from elastic to plastic
Can determine with .2% offset
(Dislocations form in crystal lattice)

Question 4

Ultimate strength on curve

Answer 4

maximum stress a part will see before failure

Question 5

Stress =

Answer 5

F/A_o

Question 6

True Stress =

Answer 6

F/A_t
A_t :Area that varies w/ time

Question 7

Unloading

Answer 7

When load is removed the material will follow an unloading curve parallel to linear elastic portion

Question 8

Spring back is proportional to …

Answer 8

(Elastic energy/total energy)
Elastic and total energy is found as area under the curve

Question 9

MBR assumptions(5)

Answer 9

1. All deformations take place in zone defined by alpha(a) and R
2. Metal has same behavior in tension & compression
3. The neutral axis does not change in L
4. The metal outside NA becomes thinner, and inside becomes thicker
5. metal is isotropic and homogenous

Question 10

Methods for single curved parts

Answer 10

1. Bending
   a. Air bending
   b. Bottoming (V-Die bending)
   c. Wipe Bending
2. Roll Bending
3. Roll Forming

Question 11

Strain =

Answer 11

(delta_L/L_o)
delta_L: Change in L
L_o: original L

Question 12

True strain

Answer 12

ln( eps_n + 1)
eps_n : nominal strain

Question 13

poisson’s

Answer 13

eps_1 = eps_2 = -v*eps_3
v=Poisson’s ratio
between .25 & .35

Question 14

plastic poisson’s

Answer 14

v = .5
eps_1 + eps_2 + eps_3 = 0

Question 15

What does a FLD diagram do?

Answer 15

shows viable combinations for of strain when biaxial stress is applied
Plots true strain

Question 16

Methods for Double Curved Parts

Answer 16

1.Panel Beating
2.Deep drawing
3.Matched die forming
4. Rubber forming
5. hydroforming