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MEC 322 > Rolling, forging & extrusion > Flashcards

Rolling, forging & extrusion Flashcards

1
Q

What is rolling

A

it is a bulk deformation processes, where there is plastic deformation

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2
Q

How much waste does bulk deformation make?

A

no wastage of material

generally cold is net shape
hot is near net shape

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3
Q

what are bulk deformations performed as

A

cold(room temp), warm(heated), and hot work (very high heat)

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4
Q

How do u choose which operation is best

A

bigger the deformation higher the heat

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5
Q

what are the pros and cons of hot working

A

PROS
less force required, fill the micro cracks, and makes more ductile

CONS
accuracy, tolerence and surface finish is poor

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6
Q

what are the pros and cons of cold working

A

PROS
better finish and accuracy, much stronger final product

CON
requires ALOT of force

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7
Q

what happens in a rolling processes

A

length increases significantly and width mildly increases

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8
Q

what happens to the initial and final velocity in a rolling processes

A

output velocity is much higher than input velocity

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9
Q

what are the 5 rolling mill configurations

A
  1. two-high (two opposing rolls)
  2. three high (work passes in both directions)
  3. four high (backing rolls support smaller work rolls)
  4. cluster-mill (multiple backing rolls on smaller rolls)
  5. tandem rolling mill (sequence of two high mills, velocity is synchronized and increases)
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10
Q

what are the two types of two-high rolling mills

A
  1. non reversing mill
  2. reversing mill (reduces times required)
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11
Q

what does a backup roll do

A

supports the work roll and saves it from deformation,
(goes in the opposite direction)
also reduces contact area so less force required

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12
Q

what are the 2 roles of rolls

A
  1. pull the work into the gap between by friction
  2. squeeze the work to reduce its cross section (shrinks it)
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13
Q

what is the 2 rolling processes divided to

A
  1. flat rolling
  2. shape rolling
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14
Q

what are defects in flat rolling

A
  1. roll and material stick (hot)
  2. bending of rolls (deformed material)
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15
Q

the thicker the material… (velocity)

A

lower the velocity

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16
Q

how is bending of rolls compensated for

A

by applying camber (deforming the roll to give the shape u want)

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17
Q

what are the two types of camber

A
  1. insufficient camber (not enough roundness)
  2. over cambered (too much roundness
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18
Q

grain structure of hot and colds role

A

hot role is smaller and more random
cold role is bigger and more aligned

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19
Q

What is the roll called for thread rolling

A

a die

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20
Q

do you use cold or hot rolling for thread rolling

A

cold rolling because the deformation is small and because it needs to be strong

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21
Q

machined thread vs. roll thread

A

machine thread grain is straight and not for mass production and roll thread is more curved, better, and better for mass production

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22
Q

what condition is ring rolling generally done in

A

hot rolling

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23
Q

what is a cavity in rolling

A

the void when creating tubes in rolling

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24
Q

what is a mandrel used for

A

to shape the cavity

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25
Q

the higher the forces (work), the _____ material hardening

A

more

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26
Q

what types of forging of metals are there

A

cold and hot forging

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27
Q

what are the advantages/ disadvantages of hot and cold forging

A

same as cold and hot rolling

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28
Q

is forging used for high or low volume

A

used for high volume production because it is expensive

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29
Q

grain shapes between casting, machining, and forging

A

casting - random dots
machining - straight line dots
forging - clean and follow shape of product

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30
Q

what size shape is forging used for

A

big and small!!

31
Q

is forging expensive or cheap

A

expensive $$$$ and high quality (high volume manufacturing)

32
Q

what are the 3 groups of forging

A
  1. open die forging
  2. impression die forging
  3. closed die forging
33
Q
  1. open die forging
A

used for simple shapes, material can flow around, any type of force application

34
Q

what does friction do in open die forging

A

allows for easy flow at center and restricted flow at the edges -> causing “barelling or “pankacking” (more deformation at center)

35
Q

friction in cold vs hot forging

A

coefficient of friction is much higher in hot forging (so barrelling effect is more in hot forging)

36
Q

when height to diameter ratio is high what happens to the barrelling effect

A

the barreling effect is more

37
Q
  1. impression die forging
A

die contains cavity or impression that is imparted to workpart
(Metal flow is constrained so that flash is
created)

38
Q

is impression die forging one step process?

A

no, it cant be done in one step (many processes)

39
Q

what is flush in forging

A

the excesses material only in impression forging

40
Q

what is the 2 purposes of the flush

A
  1. constrains material to fill die cavity
  2. holds in excesses material
41
Q

too much flush requires…

A

more force

42
Q
  1. closed die forging
A

amount of material needed need to be known because there’s no place for extra (or adding more) material

can be used for complex shapes (no excesses material)

43
Q

used for big or small deformation (closed die forging?)

A

generally small deformations, but can be complex
i.e coins

44
Q

what is upsetting and heading

A

a forging process used to make heads of nails and bolts (form of open die forging)

45
Q

how is swaging done

A

rotating dies that hammer the workpiece radially inward as the work piece is fed into the die

46
Q

Two main types of forging materials/tools

A
  1. press
  2. hammer
47
Q

Main things that can go wrong during forging process

A
  1. improper shapes due to little material
  2. too much extra material
48
Q

3 types of presses

A
  1. hydraulic press (high force low speed)
  2. mechanical press (crank & knuckle joint)
  3. screw press
49
Q

3 types of hammers (more vibration)

A
  1. gravity drop hammer
  2. power drop hammer
  3. counterblow hammer
50
Q

What is extrusion of metals

A

pushing through die opening to make the shape u want

51
Q

what is drawing of metals

A

pulling though die opening to make the shape u want

52
Q

can you use hot and cold working for extrusion

A

yes done in cold and hot

53
Q

what is relief angle

A

the angle needed so the die doesn’t touch the work piece

54
Q

what is butt

A

the small porion of billet (workpiece) that can never be romved ~ gets stuck in die (lol it’s in the butt crack)

55
Q

what is a mandrel and why is it needed

A

its attached to the ram (thing that pushes) and is needed to make a hallow object

56
Q

what is hot and cold extrusion further classified as

A
  1. direct (forward)
  2. indirect (reverse/backward)
57
Q

what are the 2 limits of indirect extrusion (backwards)

A
  1. lower rigidity of hollow ram
  2. difficulty in supporting extruded product as it exits
58
Q

what is dead zone controlled by

A

controlled by friction (changes by changing the geometry of die and whether it is hot or cold working)
hot working gives more dead zone

59
Q

is dead zone good or bad?

A

bad, we dont want it

60
Q

what are dead zones?

A

dead zones are areas in the container where material flow is zerp

61
Q

relationship between complexity of shape and force

A

simple chape = less force,
complex shape = more force

62
Q

can you use hot and cold working for drawing

A

no. generally done in cold

63
Q

what is cold drawing further classified as

A
  1. bar (large diameter, single step)
  2. wire (small diameter, multi step)
64
Q

area reduction in drawing formula

A

r = (Ao - Af)/Ao

r = area reduction in drawing
Ao = original area of work
Af = final area of work

65
Q

what is a wire drawing process

A

many drawing machines with multiple draw dies (4 - 12) separated by accumulating drums

66
Q

what do the drums (capstan) do

A

they provide proper force to draw wire stock through up stream die

67
Q

what is annealing

A

it is used between dies to relieve work hardening

68
Q

Pros and Cons of Wire Drawing

A

PROS
- length
- surface finish

CONS
- multiple dies and take up roles

69
Q

What are the 3 preparations of work for drawing

A
  1. annealing (increase ductility ~ stretch not crack)
  2. cleaning (clean to avoid damage to work surface and die)
  3. pointing (reduce diameter of starting end to allow insertion through draw die)
70
Q

what do lubricants do

A

reduce friction during drawing and reduces temperature

71
Q

what are the three lubricants

A
  1. wet drawing (completely in oil)
  2. dry drawing (coated, passing through box with oil)
  3. coating (wire/bar is coated with soft metal that acts like lubricant)
72
Q

what type of metal can be used as a lubricant

A

copper or tin

73
Q

what is the rule for max reduction per pass

A

max draw stress has to be less than yield strength of existing metal

74
Q

as reduction increases, the draw stress ________

A

increases
(draw stress is required to draw aka force)

MEC 322 (3 decks)

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