Transcript Production Technology

U3PEA01: PRODUCTION TECHNOLOGY
PREPARED BY
G.JEYAKUMAR
AUTOMOBILE ENGG DEPT
UNIT I
Casting Process
Casting
Refractory mold  pour liquid metal  solidify, remove  finish
• VERSATILE: complex geometry, internal cavities, hollow sections
• VERSATILE: small (~10 grams)  very large parts (~1000 Kg)
• ECONOMICAL: little wastage (extra metal is re-used)
• ISOTROPIC: cast parts have same properties along all directions
• Casting Process;
• Casting is the process of pouring molten metal
into the previously made cavity to the desired
shape and allow it to solidify.
• The following are the basic operations of
casting process
– Pattern making
– Melting the metal
– Pouring it into a previously made mould which
confirms to the shape of desired component.
• Pattern
• A pattern is an element used for making
cavities in the mould, into which molten
• metal is poured to produce a casting.
• Requirements of a good pattern, and
pattern allowances.
– Secure the desired shape and size of the casting
– Simple in design, for ease of manufacture
– Cheap and readily availableLight in mass and
convenient to handle
– Have high strength
• Pattern materials
– Wood
– Common metals such as Brass, cast Iron,
Aluminium and white metal etc.
– Plastic
– Gypsum
– Pattern allowances
– Shrinkage allowance
– Machining allowance
– Draft allowance
– Shake allowance
•
Distortion allowance
•
•
•
•
•
•
•
•
Different types of patterns
Split or Parted Pattern
Loose Piece Pattern
Draw backs
Gated Patterns.
Match Plate pattern
Cope and Drag Pattern
Sweep Patterns.
• MOULD PREPARATION
• Green sand mould :
• A green sand mould is composed of mixture
of sand, clay and water.
• Dry sand mould :
•
Dry sand moulds are basically green sand
moulds with 1 to 2% cereal flour and 1 to 2%
pitch.
• Materials used in mould preparation
• Silica sand, Binder, Additives and water
• .
•
•
•
•
•
•
•
Various properties of moulding sand .
Permeability
Strength or CohesivenessRefractoriness.
Plasticity or flowability
Collapsibility
Adhesiveness.
Co-efficient of Expansion
• Different moulding sand test procedures.
• The following tests have been recommended
by B.I.S.
• 1. Moisture content test
• 2. Clay content test
• 3. Permeability test
• 4. Fineness test or Sand grain size test (Sieve
analysis)
• 5. Strength test
• 6. Mould hardness test.
• CORE MAKING
• Core
• is a body made of refractory material (sand or
metal, metal cores being less frequently used),
which is set into the prepared mould before
closing and pouring it, for forming through
holes, recesses, projections, undercuts and
internal cavities.
• Core Prints. Core prints are the projections
on a pattern and are used to make recesses
(core seats) in the mould to locate the core
• Casting
• Factors to be considered for selecting a
furnace for a job
• Capacity of molten metal
• Melting rate and temp armature control
desired, Quality of melt required
• Method of pouring and types of product
contemplated.
•
• Cupola Furnace operation
• The cupola is the most widely used furnace in
the foundry for melting ferrous and nonferrous metals and alloys. A cross-section of a
cupola is shown. A cupola is a shaft furnace of
cylindrical shape erected on legs or columns.
The cupola shell is made of steel plate 8 or 10
mm thick. The interior is lined with refractory
bricks to protect the shell from getting overheated. The charge for the cupola consists of
metallic materials, fuel and fluxes.
Different Casting Processes
Process
Advantages
Disadvantages
Examples
Sand
many metals, sizes, shapes, cheap
poor finish & tolerance
engine blocks,
cylinder heads
Shell mold
better accuracy, finish, higher
production rate
limited part size
connecting rods, gear
housings
Expendable
pattern
Wide range of metals, sizes,
shapes
patterns have low
strength
cylinder heads, brake
components
Plaster mold
complex shapes, good surface
finish
non-ferrous metals, low
production rate
prototypes of
mechanical parts
Ceramic mold
complex shapes, high accuracy,
good finish
small sizes
impellers, injection
mold tooling
Investment
complex shapes, excellent finish
small parts, expensive
jewellery
Permanent
mold
good finish, low porosity, high
production rate
Costly mold, simpler
shapes only
gears, gear housings
Die
Excellent dimensional accuracy,
high production rate
costly dies, small parts,
non-ferrous metals
gears, camera bodies,
car wheels
Centrifugal
Large cylindrical parts, good
quality
Expensive, few shapes
pipes, boilers,
flywheels
Sand Casting
Sand Casting
cope: top half
drag: bottom half
core: for internal cavities
pattern: positive
funnel  sprue 
 runners  gate 
 cavity 
 {risers, vents}
Sand Casting Considerations..
(d) taper
- do we need it ?
(e) core prints, chaplets
- hold the core in position
- chaplet is metal (why?)
chaplet
Mold
cavity
(f) cut-off, finishing
Shell mold casting
- metal, 2-piece pattern, 175C-370C
- coated with a lubricant (silicone)
- mixture of sand, thermoset resin/epoxy
- cure (baking)
- remove patterns, join half-shells  mold
- pour metal
- solidify (cooling)
- break shell  part
Expendable Mold Casting
- Styrofoam pattern
- dipped in refractory slurry  dried
- sand (support)
- pour liquid metal
- foam evaporates, metal fills the shell
- cool, solidify
- break shell  part
Plaster-mold, Ceramic-mold casting
Plaster-mold slurry: plaster of paris (CaSO4), talc, silica flour
Ceramic-mold slurry: silica, powdered Zircon (ZrSiO4)
- The slurry forms a shell over the pattern
- Dried in a low temperature oven
- Remove pattern
- Backed by clay (strength), baked (burn-off volatiles)
- cast the metal
- break mold  part
Plaster-mold:
good finish (Why ?)
plaster: low conductivity => low warpage, residual stress
low mp metal (Zn, Al, Cu, Mg)
Ceramic-mold:
good finish
high mp metals (steel, …) => impeller blades, turbines, …
Investment casting (lost wax casting)
(a) Wax pattern
(injection molding)
(d) dry ceramic
melt out the wax
fire ceramic (burn wax)
(e) Pour molten metal (gravity)
 cool, solidify
[Hollow casting:
pouring excess metal before solidification
(b) Multiple patterns
assembled to wax sprue
(c) Shell built 
immerse into ceramic slurry
 immerse into fine sand
(few layers)
(f) Break ceramic shell
(vibration or water blasting)
(g) Cut off parts
(high-speed friction saw)
 finishing (polish)
Die casting
- a type of permanent mold casting
- common uses: components for
rice cookers, stoves, fans, washing-, drying machines,
fridges, motors, toys, hand-tools, car wheels, …
HOT CHAMBER: (low mp e.g. Zn, Pb; non-alloying)
(i) die is closed, gooseneck cylinder is filled with molten metal
(ii) plunger pushes molten metal through gooseneck into cavity
(iii) metal is held under pressure until it solidifies
(iv) die opens, cores retracted; plunger returns
(v) ejector pins push casting out of ejector die
COLD CHAMBER: (high mp e.g. Cu, Al)
(i) die closed, molten metal is ladled into cylinder
(ii) plunger pushes molten metal into die cavity
(iii) metal is held under high pressure until it solidifies
(iv) die opens, plunger pushes solidified slug from the cylinder
(v) cores retracted
(iv) ejector pins push casting off ejector die
Centrifugal casting
- permanent mold
- rotated about its axis at 300 ~ 3000 rpm
- molten metal is poured
- Surface finish: better along outer diameter than inner,
- Impurities, inclusions, closer to the inner diameter (why ?)
Typical casting defects
UNIT II
WELDING PROCESS
Fusion Welding Processes
Consumable Electrode
SMAW – Shielded Metal Arc Welding
GMAW – Gas Metal Arc Welding
SAW – Submerged Arc Welding
Non-Consumable Electrode
GTAW – Gas Tungsten Arc Welding
PAW – Plasma Arc Welding
High Energy Beam
Electron Beam Welding
Laser Beam Welding
Welding Processes
Welding
Welding is defined as an
localized coalescence of metals,
where in coalescence is obtained
by heating to suitable temperature,
with or without the application of
pressure and with or without the
use of filler metal.
Different welding processes.
•
•
•
•
•
•
•
•
•
Fusion Welding, Brazing & Soldering
Solid State Welding
Chemical, welding
Electrical Resistance
Diffusion, Explosion
Mechanical
Cold Friction Ultrasonic
Oxyfuel gas, hermit welding
Electron Beam, Laser Beam,Plasma arc welding
Gaswelding.
Gas welding is a group of
welding processes where in
coalescence is produced by heating
with a flame or flames with or
without the application of pressure
and with or without the use of filler
material.
SMAW – Shielded Metal Arc Welding
Welding Processes
• Consumable electrode
• Flux coated rod
• Flux produces protective gas around weld pool
• Slag keeps oxygen off weld bead during cooling
• General purpose welding—widely used
• Thicknesses 1/8” – 3/4”
• Portable
Power... Current I (50 - 300 amps)
Voltage V (15 - 45 volts)
Power = VI  10 kW
Electric Arc Welding -- Polarity
Welding Processes
SMAW - DC Polarity
Straight Polarity
Reverse Polarity
(–)
(+)
Shallow penetration
(thin metal)
AC - Gives pulsing arc
- used for welding thick sections
(+)
(–)
Deeper weld penetration
GMAW – Gas Metal Arc Welding (MIG)
Welding Processes
• DC reverse polarity - hottest arc
• AC - unstable arc
Gas Metal Arc Welding (GMAW) Torch
• MIG - Metal Inert Gas
• Consumable wire electrode
• Shielding provided by gas
• Double productivity of SMAW
• Easily automated
Groover, M., Fundamentals of Modern Manufacturing,, p. 734, 1996
GMAW
• An arc welding process that uses an arc
between a continuous filler metal electrode and
the weld pool to produce a fusion (melting)
together of the base metal
• The process is used with a shielding gas
supplied from an external source without
pressure.
GMAW – Gas Metal Arc Welding (MIG)
Welding Processes
• DC reverse polarity - hottest arc
• AC - unstable arc
Gas Metal Arc Welding (GMAW) Torch
• MIG - Metal Inert Gas
• Consumable wire electrode
• Shielding provided by gas
• Double productivity of SMAW
• Easily automated
Groover, M., Fundamentals of Modern Manufacturing,, p. 734, 1996
SAW – Submerged Arc Welding
Welding Processes
• 300 – 2000 amps (440 V)
• Consumable wire electrode
• Shielding provided by flux granules
Gas Metal Arc Welding (GMAW) Torch
• Low UV radiation & fumes
• Flux acts as thermal insulator
• Automated process (limited to flats)
• High speed & quality (4 – 10x SMAW)
• Suitable for thick plates
http://www.twi.co.uk
GTAW – Gas Tungsten Arc Welding (TIG)
Welding Processes
Current I (200 A DC)
(500 A AC)
Power  8-20 kW
• a.k.a. TIG - Tungsten Inert Gas
• Non-consumable electrode
• With or without filler metal
• Shield gas usually argon
• Used for thin sections of Al, Mg, Ti.
• Most expensive, highest quality
Friction Welding (Inertia Welding)
• One part rotated, one stationary
• Stationary part forced against rotating part
• Friction converts kinetic energy to thermal energy
• Metal at interface melts and is joined
• When sufficiently hot, rotation is stopped
& axial force increased
Welding Processes
Resistance Welding
Resistance Welding is the coordinated application of electric current and
mechanical pressure in the proper magnitudes and for a precise period of
time to create a coalescent bond between two base metals.
• Heat provided by resistance to electrical current (Q=I2Rt)
• Typical 0.5 – 10 V but up to 100,000 amps!
• Force applied by pneumatic cylinder
• Often fully or partially automated
- Spot welding
- Seam welding
Welding Processes
Resistance Welding
• Heat provided by resistance to electrical current (Q=I2Rt)
• Typical 0.5 – 10 V but up to 100,000 amps!
• Force applied by pneumatic cylinder
• Often fully or partially automated
- Spot welding
- Seam welding
Welding Processes
Diffusion Welding
Welding Processes
• Parts forced together at high temperature
(< 0.5Tm absolute) and pressure
• Heated in furnace or by resistance heating
• Atoms diffuse across interface
• After sufficient time the interface disappears
• Good for dissimilar metals
• Bond can be weakened by surface impurities
Kalpakjian, S., Manufacturing Engineering & Technology, p. 889, 1992
Soldering & Brazing
Metal Joining Processes
Soldering & Brazing
• Only filler metal is melted, not base metal
• Lower temperatures than welding
• Filler metal distributed by capillary action
• Metallurgical bond formed between filler & base metals
• Strength of joint typically
– stronger than filler metal itself
– weaker than base metal
– gap at joint important (0.001 – 0.010”)
• Pros & Cons
– Can join dissimilar metals
– Less heat - can join thinner sections (relative to welding)
– Excessive heat during service can weaken joint
LASER BEAM WELDING
High Energy Density Processes
Laser Beam Welding (LBW)
shielding
gas nozzle
(optional)
Laser beam
Plasma plume
Plasma
keyhole
Molten
material
workpiece motion
Keyhole welding
High Energy Density Processes
Focusing the Beam
Heat
treatment
Surface
modification
Welding
Cutting
Advantages
Weld penetration, mm
12
6 kW CO2
10
2 kW Nd:YAG
8
6
4
2
0
1
3
5
7
Welding speed, m/min
• Single
pass
weld
penetration up to 3/4”
in steel
• High Travel speed
• Materials need not be
conductive
• No filler metal required
• Low
heat
input
produces
low
distortion
• Does not require a
vacuum
0.1.1.2.1.T4.95.12
Soldering
Metal Joining Processes
Soldering
Solder = Filler metal
• Alloys of Tin (silver, bismuth, lead)
• Melt point typically below 840 F
Flux used to clean joint & prevent oxidation
• separate or in core of wire (rosin-core)
Tinning = pre-coating with thin layer of solder
Applications:
• Printed Circuit Board (PCB) manufacture
• Pipe joining (copper pipe)
• Jewelry manufacture
• Typically non-load bearing
Easy to solder: copper, silver, gold
Difficult to solder: aluminum, stainless steels
(can pre-plate difficult to solder metals to aid process)
PCB Soldering
Metal Joining Processes
Manual PCB Soldering
• Soldering Iron & Solder Wire
• Heating lead & placing solder
• Heat for 2-3 sec. & place wire
opposite iron
• Trim excess lead
PCB Reflow Soldering
Automated Reflow Soldering
Metal Joining Processes
SMT = Surface Mount Technology
• Solder/Flux paste mixture applied to PCB using screen print or similar
transfer method
• Solder Paste serves the following functions:
– supply solder material to the soldering spot,
– hold the components in place prior to soldering,
– clean the solder lands and component leads
– prevent further oxidation of the solder lands.
Printed solder paste on a printed circuit board (PCB)
• PCB assembly then heated in “Reflow” oven to melt solder and secure connection
Brazing
Metal Joining Processes
Brazing
Use of low melt point filler metal to fill thin gap between
mating surfaces to be joined utilizing capillary action
• Filler metals include Al, Mg & Cu alloys (melt point
typically above 840 F)
• Flux also used
• Types of brazing classified by heating method:
– Torch, Furnace, Resistance
Applications:
• Automotive - joining tubes
• Pipe/Tubing joining (HVAC)
• Electrical equipment - joining wires
• Jewelry Making
• Joint can possess significant strength
Brazing
Metal Joining Processes
Brazing
Use of low melt point filler metal to fill thin gap between
mating surfaces to be joined utilizing capillary action
• Filler metals include Al, Mg & Cu alloys (melt point
typically above 840 F)
• Flux also used
• Types of brazing classified by heating method:
– Torch, Furnace, Resistance
Applications:
• Automotive - joining tubes
• Pipe/Tubing joining (HVAC)
• Electrical equipment - joining wires
• Jewelry Making
• Joint can possess significant strength
Welding defects
•
Misalignment (hi-lo)
Undercut
Underfill
Concavity or Convexity
Excessive reinforcement •
Improper reinforcement •
•
Overlap
Burn-through
Incomplete or Insufficient
Penetration
• Incomplete Fusion
• Surface irregularity
•
•
•
•
•
•
•
•
•
– Overlap
• Arc Strikes
Inclusions
– Slag
– Wagontracks
– Tungsten
Spatter
Arc Craters
Cracks
–
–
–
–
–
–
–
Longitudinal
Transverse
Crater
Throat
Toe
Root
Underbead and
Heat-affected zone
– Hot
– Cold or delayed
• Base Metal
Discontinuities
– Lamellar tearing
– Laminations and
Delaminations
– Laps and Seams
• Porosity
–
–
–
–
Uniformly Scattered
Cluster
Linear
Piping
• Heat-affected zone
microstructure alteration
• Base Plate laminations
• Size or dimensions
UNIT III
MACHINING PROCESS
Machine Tool
• Lathe
• Lathe is one of the oldest and perhaps most
important machine ever developed.The job to
be machined is rotated and the cutting tool is
moved relative to the job. This is also called as
turning machines.
Types of lathe
• Limited or low-production Machines. The
lathes included in this category are: engine
lathe (centre lathe), bench lathe, tool room
lathe and speed lathe.
• Medium-production Machines. Turret lathes
and duplicating (or tracer controlled) lathes.
• High-production Machines. Semiconductor
automatic and automatic lathes.
Lathe
• Main parts of a lathe.
• Bed, Head stock, tail stock & carriage., saddle, apron,cross
slide, compound rest ,spindle lead screw,
•
•
•
•
Size /capacity of lathe
Lathe size is specified by length of the bed and swing dia
Swing =2xHeight of centres from the bed slide way.
The size can also be specified by which max dia of the
component turned over the bed, and max length of the
component that can be held between centres.
Lathe operations
• Lathe is versatile machine
• Lathe is called as versatile machine because of the following
many operations unlike in other machines where the
operations are limited.
• Turning, Facing, Step turning, Boring, Thread cutting, Uunder
cutting,chamferring,counter
boring,internal
threading
boring.parting off,knurling,drilling,reaming
Turret and capstan lathe
• Turret lathe
• It is medium production lathe and semi automatic lathe to make parts in
great quantities to close tolerances and faster. In which tail sock is
replaced with a turret slide hexagonal shape in which six tools can be
mounted in six faces of the turret, tool post is replaced by a square cross
slide which can hold four tools,two more tools can be mounted on the rear
cross slide.Operations like turning, drilling, boring, reaming, threading
cutoff etc can be formed in this machine by proper tool setup.
• The work is held in the chuck or by collet. All centre lathe operations camn
be performed in this lathe
• Capstan lathe
• In this machine the turret is carried on a ram which moves longitudinally
on a saddle positioned and clamped on the ways of the bed at any desired
position. The lathe which is used for small
• and medium component. All the operation performed in turret lathe can be
performed in this machine.
Shaper,planer and slotter
The main function of shapers,
planers and slotters is the
machining of flat surfaces by
means of straight line reciprocating
single point cutting tools similar to
those used in lathe operations.
HORIZONTAL SHAPER
• Advantages of a shaper.
• The shapers have got the following advantages.
• The single point cutting tools used in shapers are
inexpensive, these tools can be easily grounded to any
desired shape.
• The simplicity and ease of holding work, its easy
adjustment, and the simple tool give the shaper its
great flexibility.
• Shaper set up is very quick and easy and can be
readily changed from one job to another.
• Thin or fragile jobs can be conveniently machined on
shapers because of lower cutting forces.
• Ram drive mechanisms of a Slotters.
• Hydraulic Drive, Variable Speed Reversible
Motor drive, Slotted disc mechanism
• Uses of Vertical Shaper / Slotter
• Internal machining of blind holes.
• Work requiring machining on internal sections
such as splines, keyways, various slots and
grooves and teeth.
• Cutting of teeth on ratchet or gear rings which
require primarily rotary feed.
• Machining of die, punchet, straight and curved
slots.
Drilling Process
• The drilling process is an extensively used
machining operation by which through or blind
holes are cut or originated in a workpiece. The
drilling tool is called a “drill” which is a multipoint ctting tool. The hole is produced by
axially feeding the rotating drill into the
workpiece which is held on the table of the
drilling machine.
Milling Process
• Milling is the process of removing excess
material from a work piece by rotating cutting
tool called milling cutteris a multi pint cutting
tool having the shape of teeth arranged on the
periphery or on end face or on both.
•
•
•
•
•
•
Types of milling process
Up & down milling operation
Up milling process
Cutter is rotating in opposite direction of feed
Down milling process
Cutter is rotating in the same direction of feed
• Advantages of Planers.
• Larger work can be handled as compared to
shapers and millers.
• Capable of taking much heavier cuts as
compared to shapers and millers.
• There are no overhanging parts such as a ram.
So there is no work or tool deflection or
distortion.
• The work is mounted on a table which is
supported throughout its entire movement. So,
a maximum support is obtained.
Cylindrical Grinding Machine
• The cylindrical grinder is a type of grinding
machine used to shape the outside of an object.
The cylindrical grinder can work on a variety
of shapes, however the object must have a
central axis of rotation. This includes but is not
limited to such shapes as a cylinders an ellipse
a cam, or a crankshaft
Rolling
Important Applications:
Steel Plants,
Raw stock production (sheets, tubes, Rods, etc.)
Screw manufacture
• Cylindrical grinding is defined as having four
essential actions
• The work (object) must be constantly rotating
• The grinding wheel must be constantly
rotating
• The grinding wheel is fed towards and away
from the work
• Either the work or the grinding wheel is
traversed with the respect to the other.
• While the majority of cylindrical grinders
employ all four movements, there are grinders
that only employ three of the four actions.
•
•
•
•
Grinding operations
Outside diameter grinding
ID grinding
Plunge grinding
Abrassive Jet Machining (AJM)
• In abrasive et machining method, the material is
removed form the surface or a Workpiece, by
impinging a focused jet of fine abrasive particles
carried by a compressed gas which imparts kinetic
energy to the stream of fine abrasives. The stream
leaves through a nozzle at a velocity of the order of
300 m/s and strikes the surface of the Workpiece,
producing impact loading on it. plastic
deformation or micro-cracks occur is the vicinity
of the impact. Due to repeated impacts, small chips
of material get loosened and fresh surface gets
exposed to the jet.
Ultrasonic Machining (USM)
• Ultrasonic machining is a kind of grinding
method. An abrasive slurry is pumped between
tool and work, and the tool is given a high
frequency, low amplitude oscillation which, in
turn, transmits a high velocity to fine abrasive
particles which are driven against the work
piece. At each stroke, minute chips of material
are removed by fracture or erosion.
Electrical Discharge Machining
• It has long been recognized that a powerful spark,
such as at the terminals of an automobile battery, will
cause pitting or erosion of the metal at both the anode
and cathode. This principle is utilized in Electric
Discharge Machining (EDM), also called spark
erosion. If anode and cathode are of the same
material, it has been found that greater erosion takes
place at anode (positive electrode). Therefore, in
EDM process, work is made the anode and the tool is
the cathode (negative electrode).
Electro Chemical Machining
• In ECM, the principle of electrolysis is used to remove
metal from the workpiece. The principle of electrolysis
is based on Faraday’s laws of electrolysis which may
be stated as: “The weight of substance produced during
electrolysis is directly proportional to the current which
passes, the length of time of the electrolysis process and
the equivalent weight of the materials which is
deposited”. ECM is just the reverse of electroplating
(which also uses the principle
Plasma Arc machining or Plasma Jet
Machining (PAM or PJM
• We know that all gases burning at high
temperatures are ionized gases. In plasma arc
machining, the gases are isonized by placing
an arc across the path of gas flow. The gas
molecules get dissociated causing large
amounts of thermal energy to be liberated.
This generates temperatures of the order of
16500C, which are than utilized in removing
metal by melting and vapourization. Figure
shows a schematic view of PAM.
Electron Beam Machining
• In electron beam machining (EBM), electrons emitted by a hot
surface and accelerated by a voltage of 10 to 50 kV are
focused to a very small areas on the workpiece. This stream of
high energy electrons possess a very high energy density (of
the order of 104 kW/mm2) and when this narrow stream strikes
the work piece (by impact), the kinetic energy of the electrons
is converted to powerful heat energy which is quite sufficient
to melt and vaporize any material. Even though, it can
penetrate metals to a depth of only a few atomic layers the
electron beam can melt metal to a depth of 25 mm or more.
The electron beam which travels at about half to three- fourth
the velocity of sound is focused on the workpiece by electrostatic or electro-magnetic lenses.
•
• EBM is done in a high vacuum chamber to eliminate
the scattering of the electron beam as it contacts the
gas molecules on the work piece. Figure shows
schematic view of EBM.
• Since a continuous beam loses considerable heat by
conduction through the work piece, a pulsed beam at
a frequency of less than 100 cps is used in electron
beam machining. This consists of repeatedly striking
the electron beam on the work piece for a few milliseconds and then turning it off for a certain period of
time.
Laser Beam Machining
• A Laser (Light Amplification by Stimulated
Emission of Radiation) is a device which
produces a beam of light Laser light can be a
very powerful source of power. In LBM,
exceedingly high electromagnetic energy
densities (of the order of 105 kW/mm2) are
focused on the surface of the work piece (in
air or vacuum) to remove metal by melting
and evaporation.
Rolling Basics
Sheets are rolled in multiple stages (why ?)
tf
to
Vf
to
tf
Vf
Vo
Vo
stationary die
Screw manufacture:
rolling die
thread rolling machine
Reciprocating flat thread-rolling dies
UNIT IV
FORMING PROCESS
Forming process
• Hot working :
• The Metal working process which is done
above recrystallaisation temperature is known
as hot working.
• Cold working:
• The metal working process which is done
below recrystallaisation temperature is known
as cold working.
• Hot working :
• The Metal working process which is done
above recrystallaisation temperature is known
as hot working.
• Cold working:
• The metal working process which is done
below recrystallaisation temperature is known
as cold working.
• Recrystallaisation temperature.
• When a metal is heated and deformed under
mechanical force, an energy level will be
reached when the old grain structure starts
disintegrating, and entirely new grain structure
(equip axed, stress free) with reduced grain
size starts forming simultaneously.
This
phenomenon is known as recrystallaisation,
and the temperature at which this phenomenon
starts called recrystallaisation temperature.
• Advantages of hot working:• Very large work pieces can be deformed with
equipment of reasonable size
• Strength of the metal is low at high temperature.
Hence low tonnage equipments are adequate for hot
working.
• Gra in size can be controlled to be minimum.
• Advantages of cold working:• Surface defects are removed.
• High dimensional accuracy.
• Cold working is done at room temperature, no
oxidation and scaling of the work material occurs.
Drawing.
• Drawing is a cold working process in which the work
piece is pulled through a tapered hole in a die so as to
reduce its diameter. The process imparts accurate
dimensions, specified cross – section and a clean
excellent Quality of surface to the work.
• Degree of drawing (RA).
• The degree of drawing is measured in terms of
“reduction of area” which is defined as the ratio of
the difference in cross – sectional area before and
after drawing to the initial cross sectional area
expressed in percent.
•
Drawing
Similar to extrusion, except: pulling force is applied
stock (bar)
die
wire
F (pulling force)
Commonly used to make wires from round bars
• DRAWING
• Drawing is a cold working process in which
the work piece (wire, rod or tube) is pulled
through a tapered hole in a die so as to reduce
its diameter. The process imparts accurate
dimensions, specified cross section and a
clean and excellent quality of surface to the
work. The process may appreciably increase
the strength and hardness of metal.
Rolling.
• Rolling is the process in which the metals and alloys
are plastically deformed into semi-finished or
finished condition by passing these between circular
rolls. The main objective in rolling is to decrease the
thickness of metal.
• The faster method is to pass the stock through a
series of rolls for successive reduction, but this
method requires more investment in equipment.
• Tube drawing
• Tubes which are made by hot metal working,
processes are finally cold drawn to obtain
better surface finish and dimensional
tolerances, to enhance the mechanical
properties of the pipe, and to produce tubes of
reduced wall thickness.
Types of rolling mills
•
•
•
•
Two high rolling mill
Three high rolling mill
Four-high rolling mil
Multiple –roll mills
Forging.
• Forging may be defined as a metal working
process by which metals and alloys are
plastically deformed to desired shapes by the
application of compressive force. Forging
may done either hot or cold.
Forging
[Heated] metal is beaten with a heavy hammer to give it the required shape
Hot forging,
open-die
Stages in Closed-Die Forging
[source:Kalpakjian & Schmid]
Stages in Open-Die Forging
(a) forge hot billet to max diameter
(b) “fuller: tool to mark step-locations
(c) forge right side
(d) reverse part, forge left side
(e) finish (dimension control)
[source:www.scotforge.com]
• Basic Forging Operations
•
•
•
•
•
•
•
•
•
•
•
. Upsetting
Heading
Fullering
. Drawing down
Edging
. Bending
Flattening
. Blocking
Cut – off
Piercing
Punching
Quality of forged parts
Surface finish/Dimensional control:
Better than casting (typically)
Stronger/tougher than cast/machined parts of same material
[source:www.scotforge.com]
Extrusion.
• Extrusion may be defined as the manufacturing
process in which a block of metal enclosed in a
container is forced to flow through the opening
of a die. The metal is subjected to plastic
deformation and it undergoes reduction and
elongation during extrusion.
Extrusion
Metal forced/squeezed out through a hole (die)
[source:www.magnode.com]
Typical use: ductile metals (Cu, Steel, Al, Mg), Plastics, Rubbers
Common products:
Al frames of white-boards, doors, windows, …
• Direct Extrusion:
• eated billet is placed in the container. It is pushed by ram
towards the die. The metal is subjected to plastic deformation,
slides along the wall of the container and is forced to flow
through die opening.
• Ram movement = Extruded material movement.
• Indirect Extrusion:• In this type of extrusion, the extruded material movement is
opposite to that of ram movement. In indirect extrusion there
is practically no slip of billet with respect to container walls
FORGING HAMMERS
• Pneumatic forging hammer
• Hydraulic presses Direct – drive hydraulic
presses
• Accumulator – driven hydraulic presses
Sheet Metal Processes
Raw material: sheets of metal, rectangular, large
Raw material Processing: Rolling (anisotropic properties)
Processes:
Shearing
Punching
Bending
Deep drawing
Shearing
A large scissors action, cutting the sheet along a straight line
Main use: to cut large sheet into smaller sizes for making parts.
Punching
Cutting tool is a round/rectangular punch,
that goes through a hole, or die of same shape
F  t X edge-length of punch X shear strength
crack
(failure in shear)
t
Punch
piece cut away, or slug
sheet
die
die
clearance
Punching
Main uses: cutting holes in sheets; cutting sheet to required shape
nesting of parts
typical punched part
Exercise: how to determine optimal nesting?
Bending
Body of Olympus E-300 camera
component with multiple bending operations
component with punching,
bending, drawing operations
[image source: dpreview.com]
Typical bending operations and shapes
(a)
(b)
Sheet metal bending
Planning problem: what is the sequence in which we do the bending operations?
Avoid: part-tool, part-part, part-machine interference
Bending mechanics
Bending Planning  what is the length of blank we must use?
Bend allowance, Lb = (R + kT)
This section is
under extension
T = Sheet thickness
Neutral axis
L = Bend length

This section is
in compression
Ideal case: k = 0.5
R = Bend radius
Real cases: k = 0.33 ( R < 2T) ~~ k = 0.5 (R > 2T)
Bending: cracking, anisotropic effects, Poisson effect
Bending  plastic deformation
Engineering strain in bending = e = 1/( 1 + 2R/T)
Bending  disallow failure (cracking)  limits on corner radius: bend radius ≥ 3T
effect of anisotropic stock
Poisson effect
Exercise: how does anisotropic behavior affect planning?
Bending: springback
T
Final
R
i
i
Rf
Initial
f
How to handle springback:
3
R
RY 
RY 
(a) Compensation: the metal is bent by a larger angle i  4 i   3  i   1
Rf
 ET 
 ET 
(b) Coining the bend:
at end of bend cycle, tool exerts large force, dwells
coining: press down hard, wait, release
Deep Drawing
Tooling: similar to punching operation,
Mechanics: similar to bending operation
punch
blank holder
blank
punch
punch
punch
part
die
die
(a)
die
die
(b)
(c)
die
(d)
Examples of deep drawn parts
Common applications: cooking pots, containers, …
(e)
Sheet metal parts with combination of operations
Body of Olympus E-300 camera
component with multiple bending operations
component with punching,
bending, drawing operations
[image source: dpreview.com]
UNIT-5 Powder Metallurgy
Example Parts
Basic Steps In Powder Metallurgy
(P/M)
•
•
•
•
•
Powder Production
Blending or Mixing
Compaction
Sintering
Finishing
Powder
Production
• Atomization the most
common
• Others
– Chemical reduction of
oxides
– Electrolytic deposition
• Different shapes
produced
– Will affect compaction
process significantly
Blending or Mixing
• Can use master alloys, (most commonly) or elemental powders
that are used to build up the alloys
– Master alloys are with the normal alloy ingredients
• Elemental or pre-alloyed metal powders are first mixed with
lubricants or other alloy additions to produce a homogeneous
mixture of ingredients
• The initial mixing may be done by either the metal powder
producer or the P/M parts manufacturer
• When the particles are blended:
– Desire to produce a homogenous blend
– Over-mixing will work-harden the particles and produce variability in
the sintering process
Compaction
• Usually gravity filled cavity
at room temperature
• Pressed at 60-100 ksi
• Produces a “Green”
compact
– Size and shape of finished
part (almost)
– Not as strong as finished part
– handling concern
• Friction between particles
is a major factor
Isostatic Pressing
• Because of friction between particles
• Apply pressure uniformly from all
directions (in theory)
• Wet bag (left)
• Dry bag (right)
Sintering
• Parts are heated to ~80% of
melting temperature
• Transforms
compacted
mechanical bonds to much
stronger metal bonds
• Many parts are done at this
stage. Some will require
additional processing
Sintering ctd
• Final part properties
drastically affected
• Fully sintered is not always
the goal
– Ie. Self lubricated bushings
• Dimensions of part are
affected
Die Design for P/M
• Thin walls and projections create fragile tooling.
• Holes in pressing direction can be round, square, D-shaped,
keyed, splined or any straight-through shape.
• Draft is generally not required.
• Generous radii and fillets are desirable to extend tool life.
• Chamfers, rather the radii, are necessary on part edges to
prevent burring.
• Flats are necessary on chamfers to eliminate feather-edges on
tools, which break easily.
Advantages of P/M
• Virtually unlimited choice of
alloys,
composites,
and
associated properties
– Refractory materials are popular
by this process
• Controlled porosity for self
lubrication or filtration uses
• Can be very economical at large
run sizes (100,000 parts)
• Long term reliability through
close control of dimensions and
physical properties
• Wide latitude of shape and
design
• Very good material utilization
Disadvantages of P/M
•
•
•
•
Limited in size capability due to large forces
Specialty machines
Need to control the environment – corrosion concern
Will not typically produce part as strong as wrought
product. (Can repress items to overcome that)
• Cost of die – typical to that of forging, except that
design can be more – specialty
• Less well known process
Financial Considerations
• Die design – must withstand 100
ksi, requiring specialty designs
• Can be very automated
– 1500 parts per hour not uncommon for
average size part
– 60,000 parts per hour achievable for
small, low complexity parts in a rolling
press
• Typical size part for automation is
1” cube
– Larger parts may require special
machines (larger surface area, same
pressure equals larger forces involved)
Extrusion
• Raw materials in the form if thermoplastic pallets,granules,or
powder, placed into a hopper and fed into extruder barrel.
• The barrel is equipped with a screw that blends the pallets and
conveys them down the barrel
• Heaters around the extruder’s barrels heats the pellets and
liquefies them
Screw has 3-sections
• Feed section
• Melt or transition section
• Pumping section.
• Complex shapes with constant cross-section
• Solid rods, channels, tubing, pipe, window frames,
architectural components can be extruded due to continuous
supply and flow.
• Plastic coated electrical wire, cable, and strips are also
extruded
Pellets :extruded product is a small-diameter rod which is
chopped into small pellets
Sheet and film extrusion :
Extruded parts are rolled on water and on the rollers
Extruder
Fig : Schematic illustration of a typical extruder for plastics, elastomers, and composite materials.
Injection molding
Fig : Injection molding with (a) plunger, (b) reciprocating rotating screw, (c) a typical part made from
an injection molding machine cavity, showing a number of parts made from one shot, note also
mold features such as sprues, runners and gates.
• Similar to extrusion barrel is heated
• Pellets or granules fed into heated cylinder
• Melt is forced into a split-die chamber
• Molten plastic pushed into mold cavity
• Pressure ranges from 70 Mpa – 200 Mpa
• Typical products : Cups, containers, housings, tool
handles,
knobs,
electrical
and
communication
components, toys etc.
Injection molding
• Injection
molds
have
several components such as
runners, cores, cavities,
cooling channels, inserts,
knock out pins and ejectors
3-basic types of molds
• Cold runner two plate mold
• Cold runner three plate
mold
• Hot runner mold
Fig : Examples of injection molding
Injection Molding Machine
Fig : A 2.2-MN (250-ton) injection molding machine. The tonnage is the force applied to keep
the dies closed during injection of molten plastic into the mold cavities.
Process capabilities :
• High production rates
• Good dimensional control
• Cycle time range 5 to 60 sec’s
• Mold materials- tool steels, beryllium - Cu, Al
• Mold life- 2 million cycles (steel molds)
10000 cycles ( Al molds)
Machines :
• Horizontal or vertical machines
• Clamping – hydraulic or electric
Blow molding
• Modified extrusion and Injection Molding process.
• A tube extruded then clamped to mold with cavity larger
than tube diameter.
• Finally blown outward to fill the cavity
• Pressure 350Kpa-700Kpa
Other Blow Molding processes
• Injection Blow molding
• Multi layer Blow molding
Fig : Schematic
illustration of (a)
the blowmolding process
for making
plastic beverage
bottles, and (b)
a three-station
injection blowmolding
machine.
Rotational Molding
• Thermo plastics are thermosets can be formed into large
parts by rotational molding
• A thin walled metal mold is made of 2 pieces
• Rotated abut two perpendicular axes
• Pre-measured quantity of powdered plastic material is
rotated about 2-axes
• Typical parts produced-Trash cans, boat hulls, buckets,
housings, toys, carrying cases and foot balls.
Rotational
Molding
Fig: The rotational molding
(rotomolding or
rotocasting) process.
Trash cans, buckets, and
plastic footballs can be
made by this process.
Thermoforming
•
Series process for forming thermoplastic sheet or film over a mold by applying
heat and pressure.
•
Typical parts : advertising signs, refrigerator liner, packaging , appliance housing,
and panels for shower stalls .
Fig : Various Thermoforming processes for thermoplastic sheet. These processes are
commonly used in making advertising signs, cookie and candy trays, panels for shower
stalls, and packaging.
Compression molding
•
Pre-shaped charge ,pre-measured volume of powder and viscous mixture of liquid
resin and filler material is placed directly into a heated mold cavity.
•
Compression mold results in a flash formation which is a n excess material.
•
Typical parts made are dishes, handles, container caps fittings, electrical and
electronic components and housings
•
Materials used in compression molding are thermosetting plastics & elastomers
•
Curing times range from 0.5 to 5 mins
3- types of compression molds are
•
•
•
Flash type
Positive type
Semi-positive
Compression
Molding
Fig : Types of compression
molding, a process
similar to forging; (a)
positive, (b) semi
positive, (c) flash (d) Die
design for making
compression-molded
part with undercuts.
Transfer molding
• Transfer
molding
molding is an improvement if compression
• Uncured thermosetting material placed in a heated transfer
pot or chamber, which is injected into heated closed molds
• Ram plunger or rotating screw feeder forces material into
mold cavity through narrow channels
• This flow generates heat and resin is molten as it enters the
mold
Typical parts : Electrical & electronic components, rubber and
silicone parts
Transfer molding
Fig : Sequence of operations in transfer molding for thermosetting plastics. This
process is particularly suitable for intricate parts with varying wall thickness.
Casting
Conventional casting of thermo plastics :
• Mixture of monomer, catalyst and various
additives are heated and poured into the
mould
• The desired part is
polymerization takes place.
formed
after
Centrifugal casting :
• Centrifugal force used to stack the material
onto the mold
• Reinforced plastics with short fibers are used
Fig : Casting
Cold forming
•
Processes such as rolling ,deep drawing extrusion closed die forging ,coining and rubber
forming can be used for thermoplastics at room temperatures
•
Typical materials used : Poly propylene, poly carbonate, Abs, and rigid PVC
Considerations :
•
•
Sufficiently ductile material at room temperature
Non recoverable material deformation
Solid Phase forming
•
Temperatures from 10oc to 20oc are maintained, which is below melting point
Advantages :
• Spring-back is lower
• Dimensional accuracy can be maintained
Calendaring and Examples of Reinforced
Plastics
Fig : Schematic illustration of calendaring,
Sheets produced by this process are
subsequently used in thermoforming.
Fig : Reinforced-plastic components for a Honda
motorcycle. The parts shown are front and
rear forks, a rear swing arm, a wheel, and
brake disks.
Sheet Molding
Fig : The manufacturing process for producing reinforced-plastic sheets. The
sheet is still viscous at this stage; it can later be shaped into various products.
Examples of Molding processes
Fig : (a) Vacuum-bag forming.
(b) Pressure-bag
forming.
Fig : Manual methods of
processing reinforced
plastics: (a) hand layup and (b) spray-up.
These methods are
also called open-mold
processing.
THE END