Rolling, forging & extrusion Flashcards
What is rolling
it is a bulk deformation processes, where there is plastic deformation
How much waste does bulk deformation make?
no wastage of material
generally cold is net shape
hot is near net shape
what are bulk deformations performed as
cold(room temp), warm(heated), and hot work (very high heat)
How do u choose which operation is best
bigger the deformation higher the heat
what are the pros and cons of hot working
PROS
less force required, fill the micro cracks, and makes more ductile
CONS
accuracy, tolerence and surface finish is poor
what are the pros and cons of cold working
PROS
better finish and accuracy, much stronger final product
CON
requires ALOT of force
what happens in a rolling processes
length increases significantly and width mildly increases
what happens to the initial and final velocity in a rolling processes
output velocity is much higher than input velocity
what are the 5 rolling mill configurations
- two-high (two opposing rolls)
- three high (work passes in both directions)
- four high (backing rolls support smaller work rolls)
- cluster-mill (multiple backing rolls on smaller rolls)
- tandem rolling mill (sequence of two high mills, velocity is synchronized and increases)
what are the two types of two-high rolling mills
- non reversing mill
- reversing mill (reduces times required)
what does a backup roll do
supports the work roll and saves it from deformation,
(goes in the opposite direction)
also reduces contact area so less force required
what are the 2 roles of rolls
- pull the work into the gap between by friction
- squeeze the work to reduce its cross section (shrinks it)
what is the 2 rolling processes divided to
- flat rolling
- shape rolling
what are defects in flat rolling
- roll and material stick (hot)
- bending of rolls (deformed material)
the thicker the material… (velocity)
lower the velocity
how is bending of rolls compensated for
by applying camber (deforming the roll to give the shape u want)
what are the two types of camber
- insufficient camber (not enough roundness)
- over cambered (too much roundness
grain structure of hot and colds role
hot role is smaller and more random
cold role is bigger and more aligned
What is the roll called for thread rolling
a die
do you use cold or hot rolling for thread rolling
cold rolling because the deformation is small and because it needs to be strong
machined thread vs. roll thread
machine thread grain is straight and not for mass production and roll thread is more curved, better, and better for mass production
what condition is ring rolling generally done in
hot rolling
what is a cavity in rolling
the void when creating tubes in rolling
what is a mandrel used for
to shape the cavity
the higher the forces (work), the _____ material hardening
more
what types of forging of metals are there
cold and hot forging
what are the advantages/ disadvantages of hot and cold forging
same as cold and hot rolling
is forging used for high or low volume
used for high volume production because it is expensive
grain shapes between casting, machining, and forging
casting - random dots
machining - straight line dots
forging - clean and follow shape of product
what size shape is forging used for
big and small!!
is forging expensive or cheap
expensive $$$$ and high quality (high volume manufacturing)
what are the 3 groups of forging
- open die forging
- impression die forging
- closed die forging
- open die forging
used for simple shapes, material can flow around, any type of force application
what does friction do in open die forging
allows for easy flow at center and restricted flow at the edges -> causing “barelling or “pankacking” (more deformation at center)
friction in cold vs hot forging
coefficient of friction is much higher in hot forging (so barrelling effect is more in hot forging)
when height to diameter ratio is high what happens to the barrelling effect
the barreling effect is more
- impression die forging
die contains cavity or impression that is imparted to workpart
(Metal flow is constrained so that flash is
created)
is impression die forging one step process?
no, it cant be done in one step (many processes)
what is flush in forging
the excesses material only in impression forging
what is the 2 purposes of the flush
- constrains material to fill die cavity
- holds in excesses material
too much flush requires…
more force
- closed die forging
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)
used for big or small deformation (closed die forging?)
generally small deformations, but can be complex
i.e coins
what is upsetting and heading
a forging process used to make heads of nails and bolts (form of open die forging)
how is swaging done
rotating dies that hammer the workpiece radially inward as the work piece is fed into the die
Two main types of forging materials/tools
- press
- hammer
Main things that can go wrong during forging process
- improper shapes due to little material
- too much extra material
3 types of presses
- hydraulic press (high force low speed)
- mechanical press (crank & knuckle joint)
- screw press
3 types of hammers (more vibration)
- gravity drop hammer
- power drop hammer
- counterblow hammer
What is extrusion of metals
pushing through die opening to make the shape u want
what is drawing of metals
pulling though die opening to make the shape u want
can you use hot and cold working for extrusion
yes done in cold and hot
what is relief angle
the angle needed so the die doesn’t touch the work piece
what is butt
the small porion of billet (workpiece) that can never be romved ~ gets stuck in die (lol it’s in the butt crack)
what is a mandrel and why is it needed
its attached to the ram (thing that pushes) and is needed to make a hallow object
what is hot and cold extrusion further classified as
- direct (forward)
- indirect (reverse/backward)
what are the 2 limits of indirect extrusion (backwards)
- lower rigidity of hollow ram
- difficulty in supporting extruded product as it exits
what is dead zone controlled by
controlled by friction (changes by changing the geometry of die and whether it is hot or cold working)
hot working gives more dead zone
is dead zone good or bad?
bad, we dont want it
what are dead zones?
dead zones are areas in the container where material flow is zerp
relationship between complexity of shape and force
simple chape = less force,
complex shape = more force
can you use hot and cold working for drawing
no. generally done in cold
what is cold drawing further classified as
- bar (large diameter, single step)
- wire (small diameter, multi step)
area reduction in drawing formula
r = (Ao - Af)/Ao
r = area reduction in drawing
Ao = original area of work
Af = final area of work
what is a wire drawing process
many drawing machines with multiple draw dies (4 - 12) separated by accumulating drums
what do the drums (capstan) do
they provide proper force to draw wire stock through up stream die
what is annealing
it is used between dies to relieve work hardening
Pros and Cons of Wire Drawing
PROS
- length
- surface finish
CONS
- multiple dies and take up roles
What are the 3 preparations of work for drawing
- annealing (increase ductility ~ stretch not crack)
- cleaning (clean to avoid damage to work surface and die)
- pointing (reduce diameter of starting end to allow insertion through draw die)
what do lubricants do
reduce friction during drawing and reduces temperature
what are the three lubricants
- wet drawing (completely in oil)
- dry drawing (coated, passing through box with oil)
- coating (wire/bar is coated with soft metal that acts like lubricant)
what type of metal can be used as a lubricant
copper or tin
what is the rule for max reduction per pass
max draw stress has to be less than yield strength of existing metal
as reduction increases, the draw stress ________
increases
(draw stress is required to draw aka force)
