Exam 2 Topics

Question 1

High required forces cause

Answer 1

increased equipment costs

Question 2

Why are K(Strength coefficient) and n(strength hardening exponent) usually found only in compression.

Answer 2

Necking limits the uniform strain in tension

Question 3

K and n are

Answer 3

strongly affected by microstructure

Question 4

Strain hardening through cold work (T«0,5Tm)

Answer 4

Dislocation Density increases, Yield Strength Increases, Ductility decreases, K increases, n decreases due to microstructural changes

Question 5

Annealing recovery (T=0.3-0.5Tm)

Answer 5

Dislocation rearrangement

Question 6

Annealing recrystallization (T>0.5Tm)

Answer 6

New Strain-Free grains form

Question 7

Hot work

Answer 7

T>0.5Tm

Question 8

What happens during hot work

Answer 8

Dislocation density low, little strain hardening, dynamic recovery results in low flow stresses (simultaneous dislocation propagation and softening during working)

Question 9

Advantages to hot work

Answer 9

High deformability, low flow stress, microstructure equilibrates

Question 10

Disadvantages to hot work

Answer 10

Requires heat, poor surfaces/dimensions, tool damage

Question 11

Steady State Processes

Answer 11

uniform deformation mode
all regions of the part must see the same deformation load

Question 12

Non-steady state processes

Answer 12

localized analysis

Question 13

Instantaneous flow stress

Answer 13

Non Steady state(forging)

Question 14

How is fracture delayed in bulk deformation

Answer 14

Hydrostatic pressure

Question 15

Name open die processes

Answer 15

Cogging-successive “bites”
Fullering- move material “away” from the center
Edging-move material “toward” the center
Ring upsetting
Piercing- p=sigmaf(d0/Dp)

Question 16

What must be considered in impression die forging

Answer 16

Shape to fill the die, corners radiused

Question 17

Properties of closed die forging

Answer 17

workpiece fully contained, no flash
Expensive so die design critical

Question 18

What is closed-die forging good for?

Answer 18

Dimensional tolerancing

Question 19

Process limitations for Impression and Closed die

Answer 19

Die pressures high
Shape needs to be removable

Question 20

Extrusion

Answer 20

Compression of workpiece into die(in container)
Hot or cold work
High Speed and Good accuracy

Question 21

What shapes are good for hot extrusion

Answer 21

solid, hollow, semi-hollow

Question 22

Drawing

Answer 22

Used for wire and tube
deformed in compression but has tensile forces
Typically a cold work process

Question 23

What forces are seen in rolling

Answer 23

force pulling strip in
force pushing back

Question 24

Sheet metalworking

Answer 24

Wrought alloys suitable
Deformation is primarily tensile
Surface finish is critical

Question 25

Crystallographic

Answer 25

Develops during thermo-mechanical treatment of original sheet -usually undesirable

Question 26

Mechanical Fibering

Answer 26

Elongated inclusions or second phase Always undesirable

Question 27

In the shearing process what is the quality of edge dependent on?

Answer 27

Clearance

Question 28

What needs to be done in bending?

Answer 28

Must induce plastic bending to be irreversible

Question 29

Springback

Answer 29

Stresses may be plastic at the outer surface while remaining elastic near the neutral line

Question 30

How to overcome springback

Answer 30

Overbend/High T Stretch Bend- tensile Counter Punch -compressive

Question 31

Deep Drawing

Answer 31

Minimal thickness change material drawn into the die must be rounded else shearing

Question 32

Limiting Draw Ratio

Answer 32

When draw force exceeds the force that the cup wall can support

Question 33

Approximation of Ideal (Long Chips)

Answer 33

Low speeds, low friction Speed increase T increase

Question 34

Chip formation

Answer 34

Segmented chips (sawtooth)- localized, repetitive heating Discontinuous Chips- High Adhesion/low speeds

Question 35

What is the secondary shear zone

Answer 35

Stationary metal attached to tool face(BUE)

Question 36

What are the aspects of machinability

Answer 36

Machinability index Tool life Tool wear Surface Finish

Question 37

What is to look for in machinable materials

Answer 37

Cutting w/ minimum energy Cutting w/ minimum tool wear Cutting w/ good surface finish The material must have low ductility, TS, BHN

Question 38

Disadvantages to multipoint operations

Answer 38

chisel point geometry Surface finish heat and wear prone

Question 39

What info is needed to machine

Answer 39

The machinability Shape/Finish Dimensions/Tolerancing

Question 40

Tool life for casting and bulk deformation

Answer 40

1000's of parts

Question 41

Tool life for machining

Answer 41

5-10 minutes

Question 42

How are tensile tests conducted

Answer 42

at low strain rates

Question 43

What process should be used for very fine grain size

Answer 43

Cold roll to reduce grain size, nucleation is generated. Anneal at a low temperature for a short period of time to prevent grain growth

Question 44

For a fracture toward the end of a draw in deep drawing what is a source of this problem

Answer 44

Insufficient blankholder pressure, results in wrinkling which can be ironed out Blankholder pressure should be increased

Question 45

Fracture in the beginning of a draw in deep drawing what is a source of the problem

Answer 45

excessive pressure decrease the pressure and use lubrication

Question 46

What is the draw force proportional to?

Answer 46

tensile strength