Bulk Deformation

Question 1

What are the four types of bulk deformation?

Answer 1

Forging, Rolling, Extrusion, Drawing

Question 2

What is Forging?

Answer 2

Production of discrete parts with a set of dies and compressive forces, usually done at elevated temperatures. Equipment and labour costs are high

Question 3

What is Rolling?

Answer 3

Production of flat sheets and foils and high speeds with good surface finish High equipment costs with low labour cost

Question 4

What is extrusion?

Answer 4

Production of long lengths of solid or hollow products with constant cross sections that can be cut

Question 5

What is Drawing?

Answer 5

Production of long rod, wire, tubing with round or other cross section. Usually thinner than extrusion with a good surface finish

Question 6

What is extrusion?

Answer 6

Production of long lengths of solid or hollow products with constant cross sections that can be cut (pushing)

Question 7

What is Drawing?

Answer 7

Production of long rod, wire, tubing with round or other cross section. Usually thinner than extrusion with a good surface finish (pulling)

Question 8

Why choose plastic deformation?

Answer 8

Offers structural and mechanical advantages over cast and machining.
plastic deformatiom after casting reduces prosity in casting and orients grains in favourable directions.
makes parts strongers than just cast.
residual stresses maybe an issue

Question 9

Forging Temps

Answer 9

Cold forging ( T/Tm 0.6)
T/Tm = 0.5 = recrystallization temperature

Question 10

Open die forging (Aka Upsetting)

Answer 10

part placed between 2 flat dies (platens)
reduce height through compression
usually done for simple shapes
friction andheat transfer causes barelling.
lubrication and vibration can reduce friction

Question 11

Open die forging (Aka Upsetting)

Answer 11

part placed between 2 flat dies (platens)
reduce height through compression
usually done for simple shapes
friction andheat transfer causes barelling.
lubrication and vibration can reduce friction

Question 12

Impression Die Forging

Answer 12

workpiece takes the hape of the die cavity.
material flow outward will cause flash
many die cavities is progressively used to get from rough to fine parts.
dimensional accuracy are highly dependent on the process (0.5- 1% of size)

Question 13

Importance of Flash

Answer 13

Consists of excess material
Aids in allowing the cavity to fill fully and create fine details
Inhibits the material from flowing out of the die
Increases die pressure substantially.

Question 14

Closed Die Forging

Answer 14

No flash
Entire blank is used in the part.
Accurate material amounts is critical to avoid pressure build up.
More accurate that impression die forging and does not need as many finish operations

Question 15

Other Forging Operations

Answer 15

Heading - upsettting a single end of a blank - ie bolt head
Piercing - internal feature within a forging - high aspect ration
Edging and Fullering - spreading material to different areas. edging - increase in cross section. fullering - decrease in cross section

Question 16

Other Forging Operations

Answer 16

Roll Forging - create grooves and features using rolling dies,
Coining - very high pressure - 5- 6 times the flow stress, good surface quality and fine detail
Skew Rolling - Axis of rolling are not parallel

Question 17

Forging Equipment

Answer 17

Mechanical Presses
Screw Presses
Hydraulic Press
Hammers

Question 18

Mechanical Presses

Answer 18

Uses a crank to apply force (10MN)

Question 19

Screw Presses

Answer 19

Force transfer through a vertical screw (280 MN)

Question 20

Hydraulic Presses

Answer 20

Constant slow speed

Question 21

Hydraulic Presses

Answer 21

Constant slow speed operation (730 MN)

Question 22

Hammers

Answer 22

Potential energy of a ram. Good for hot forging due to high speed of stroke (1100 MN)

Question 23

Hammers

Answer 23

Potential energy of a ram. Good for hot forging due to high speed of stroke (1100 MN)

Question 24

Forging Dies

Answer 24

• Made from hardened steel to create fine detail
• Maybe with or without gutters for oen or closed die forging
• Comes in a set to fulfill many pressing operations

Question 25

Defects in Forging

Answer 25

Buckling
Cold Shuts
Grow Flow Patterns

Question 26

Buckling

Answer 26

Duringt he forging of a thin cross sections it is possible for the blank to buckle and create overlaps in the final piece

Question 27

Cold Shuts

Answer 27

Around tight radii, the material could fold over itself producing a cold shut. Reduces fatigue life dramatically

Question 28

Grain Flow Patterns

Answer 28

Grains may orient themselves perpendicular to the surface exposing end grains. Contaminants can attach and cause corrosion.

Question 29

Grain Flow Patterns

Answer 29

Grains may orient themselves perpendicular to the surface exposing end grains. Contaminants can attach and cause corrosion.

Question 30

Open Die Forging Ideal Case

Answer 30

Uniform deformation,

frictionles platens and unixial compression

Question 31

Open Die Forging Realistic Case

Answer 31

Barelling occurs from friction between the blank and platen causin uneven deformation.

Assume - uniform deformation with friction

Question 32

Yield Critera

Answer 32

complicated stuff when materials yield - like dislocations move, grains slide

approximations - Von Mises and Tresca

Question 33

Von Mises

Answer 33

Shear Yield Stress (K)
K = sigmaY/(3)^(1/3)

2*sigmaY^2 = (sigma1 - sigma2)^2 +(sigma2-sigma3)^2+ (sigma3 - sigma1)^2

Question 34

Tresca (Max Shear Stress)

Answer 34

sigmaMAX - sigmaMIN = sigma Y

K = sigmaY/2

Question 35

Plain Strain

Answer 35

when epsilon2 = 0;
Von Mises-
sigma2 =( sigma3+sigma1)/2

Yield Criteria = sigma1 -sigma3 = 1.15*sigmaY

Question 36

Friction Hill equations

Answer 36

Distribution of die pressure, used to calculation average die pressure