Transcript Welding

Joining and Cutting
Processes
Fusion Welding Processes
• Fusion Welding involves heating two
materials above their melting
temperatures (electrically or chemically).
• Filler (rods) metals are added to the weld
area during the welding of a joint (supply
additional material to weld zone).
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Processes
Oxyfuel Gas
Arc
Consumed Electrode
Non-Consumed Electrode
Resistance
Solid State
Other – “High Energy”
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Oxyfuel Gas Welding
• Process that uses a fuel gas combined
with oxygen to produce a flame
• Typically used for structural sheet-metal
fabrication, automotive bodies, and
various repair tasks
• Most common fuels used - acetylene
(oxyacetylene).
• Manual operation, portable & flexible.Low
equipment cost.
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Torch
• allows for controlling and mixing
gases
Oxygen and fuel gas
cylinders
Cylinder Safety
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Caps on when moving
Secure to truck or wall
Keep upright (Acetylene) (1/7 Rule)
Hand over regulator when opening
Read labels – don’t rely on colors
Dangers of compressed oxygen
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Oxyfuel Gas Welding- Flame
Types
• Neutral Flame: 1:1 ratio (oxygen vs.
fuel).
• Oxidizing Flame: greater oxygen
supply (not for steels).
• Reducing (Carburizing) Flame: lower
oxygen supply (lower temperature)brazing.
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• Neutral - the oxygen and fuel gases
combine
• oxygen burns up the carbon and the
hydrogen in the fuel gas then releases
only heat and harmless gases
• flame temp is 5589 deg F.
Oxyfuel Gas Welding- Flux
• Retard oxidation of surfaces of the
parts being welded
• Dissolves/Removes oxides or other
substances
• Stronger joints
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Arc Welding Processes
(Consumable Electrode)
• Developed in the mid-1800s
• Heat obtained through electrical
energy
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Shielded Metal Arc Welding
(SMAW)
• Stick welding
• 50% of all large-scale industrial
welding operations- portable
process.
• Electric arc generated between tip of
coated electrode and the workpiece.
• Electrode coating produces a
shielding gas to protect from oxygen.
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Electric arc between flux
covered electrode and base
metal
7/21/2015
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SMAW (Cont.)
• (DCEN) electrode negative
• Workpiece positive, electrode negative.
• Sheet metals - shallow penetration, gap
joints.
• (DCEP) electrode positive
• Electrode positive, workpiece negative.
• Deeper penetration.
• (AC) Alternating current
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SMAW (Cont.)
• Thick sections, large electrodes at
max current.
• Manual, portable, and flexible. ACDC machines, low cost equipment
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Submerged Arc Welding
• Weld arc is shielded by a granular
flux.
• Flux is fed to weld zone by gravity.
• Flux covers molten metal which
prevents spatter, sparks, UV
radiation, or fumes.
• Flux is recovered.
• 4-10 times productivity of SMAW,
automatic, horizontal, low skill,
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Submerged Arc
Underwater SMAW
• use well insulated electrode holder
and special water proof covered
electrodes
• because of rapid cooling - use
stringer beads not weaving
• short arc length and DCEN
• poor visibility - use #4 or #8 lens
• communication system
• normally have 80% of the tensile
strength and 50 of the ductility of
normal welds
Gas Metal Arc Welding
(GMAW)
• Formerly MIG (Metal Inert Gas).
• Argon, helium, carbon dioxide, or
mix (Shield the arc to prevent
oxidation).
• Wire fed automatically through
nozzle into arc.
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GMAW (Cont.)
• Rapid, economical, twice SMAW
productivity.
• Most production done today
• Can be automated (robots), low skill,
DC, medium cost equipment.
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Flux Cored Arc Welding
(FCAW)
• Same as GMAW but electrode is tubular
and filled with flux.
• Automatic feeding of wire (like GMAW).
• Uses no external gas source
• Fast growing
• Thin to thick sections.
• Can be automated (robotics), DC, medium
cost.
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Electrogas Welding
• For welding butt joint edges vertically in
one pass.
• Metal deposited between two pieces
joined – space enclosed by copper shoes
sliding upward with weld
• Also around pipe
• 1/2” to 3” thickness.
• Usually automated, High equipment cost.
• For welding bridges, pipes, tanks, ships
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Electrogas - use shielding gas - flux
cored wire fed in joint
• arc
maintained
between
electrode and
weld
Electro-slag Welding
• Similar to EGW.
• Weld begins at part bottom, molten slag
extinguishes arc.
• Heat then produced continuously by elect.
Resist. of molten slag
• Very thick sections - 2” to 36”.
• High cost of equipment.
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Vertical joint - arc started
between electrode & bottom
Electrodes
• Strength of deposited metal.
• Type of coating.
• Size (1/16 to 5/16 in diameter).
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Electrode Classifications
• E6011-A1
• E - arc welding electrode
• 60 – 60,000 psi min. tensile strength
• 1 – next to last digit – position
• 11 – last two digits together, type of
covering and current to be used
• A1 – alloying elements
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Electrode Coatings
• Clay like material.
• Silica binders and powdered
materials (Oxides, carbonates,
fluorides, metal alloys, cellulose)
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Electrode Coatings (Cont.)
1. Stabilize the arc.
2. Generate a gas shield.
3. Control rate at which the electrode
melts.
4. Act as a flux to protect weld (from
oxidation).
5. Add alloying elements to joint ie.
Protect from becoming brittle).
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Arc Welding (NonConsumable Electrode)
• Gas Tungsten-Arc Welding (GTAW)
• Plasma Arc Welding (PAW)
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Gas Tungsten-Arc Welding
(GTAW)
• Formerly TIG (Tungsten Inert Gas).
• Shielding gas is supplied from an
external source. Argon or helium
(high cost).
• Filler metal is supplied from filler
wire.
• Tungsten electrode is not consumed.
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GTAW-NCE (Cont.)
• Good for thin parts, high quality
welds. Used for welding aluminum,
magnesium, titanium, and refractory
metals.
• all positions, AC-DC, medium
distortion, portable equipment,
medium cost of equipment.
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Plasma Arc Welding
• Argon and helium.
• Arc is hot ionized gas (60,000 degrees °F).
• Transferred- workpiece is part of circuit.
• Non-transferred- Arc between tungsten
electrode and nozzle.
• High energy, deep penetration, stable arc,
less thermal distortion, high speed, > ¼”
thick material, high skill, medium cost of
equipment.
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Separate shielding gas
protects the welding or
cutting process
Resistance Welding
Processes
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Spot
Seam
Projection
Stud
Flash
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1.) Resistance Spot Welding
• Uses pressure and resistivity of parts
to form nugget.
• Must be clean but not oxide free
• Used for sheet metal parts
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Spot - most common
Two pieces fused with small
nugget
2.) Resistance Seam
Welding
• Like spot welding but with rollers.
• Continuous or “roll spot welding”.
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two wheeled electrodes
travel over metal - current
passes through them
can produce intermittent
seam of overlapping spots
for leak proofing
Seam welding I-Beams
3.) Resistance Projection
Welding
• High elect resistance developed at
joint by embossing projections on
surfaces to be welded
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form projections with dies
current passes through two
pieces and is concentrated
at bumps
4.) Resistance Stud welding
• Similar to flash welding
• Threaded rod or hanger welded to
flat plate
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Stud
• no drilling or punching holes in
structure
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5.) Resistance Flash
welding
• Also Called “Upset Welding”
• Heat generated from arc as ends of
two bars or sheets begin to make
contact and develop an electrical
resistance at the joint
• After heating occurs and metal
softens, an axial force is applied.
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generally used to weld the
butt ends of two pieces
parts are held in two clamps
with ends together
high current passed
between them
• high resistance causes small arcs to
occur between uneven surfaces
adv: fast and no pre cleaning of surfaces
Solid State Welding
• Processes in which joining takes place
without fusion of the workpiece, thus no
liquid (molten) phase is present in the
joint.
• Clean surfaces in atomic contact under
pressure and maybe heat (increases
diffusion) form bonds and produce a
strong joint.
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Solid State Welding
• Cold Welding
• Ultrasonic Welding
• Friction Welding
• Explosion Welding
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1.) Cold Welding
• Surfaces degrease, wire brush, or
wiped to remove oxide smudge.
• Roll bonding or hot roll bonding
(cladding).
• Processes takes advantage of
materials solubility (soft, ductile
materials)
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Tool can be hand,
pneumatic, or hydraulic
• dies must be designed to impose
proper pressure for different metals
2.) Ultrasonic Welding
• Sonotrode oscillates 10-75 kHz
• Contact causes plastic deformation.
• Temperature is 1/3 to 1/2 of melting
temperature (except in plastics).
• Suited for metallic dissimilar metals
and non-metallic materials (thin
parts).
• Can use roll transducer for seams.
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UT spot welds
UT seam welds with lateral
drive rollers
3.) Friction welding
• One component rotates at high speed
while other is stationary. Pressure contact
causes heating. Part must be stopped fast
to avoid shearing weld.
• Wide variety of materials, good joint
strength
• Solid bars up to 3” & tubes up to 10”.
• Surface speed 3000ft/min.
• Automated, low skill, high machine cost.
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Friction welding
4.)Explosion Welding
• Pressure generated by detonating a
layer of explosive placed over one of
the components.
• Causes wavy interface and cold
pressure welding by plastic
deformation.
• Good bond strength.
• Clad dissimilar metals.
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“Other” High Energy Welding
Processes
• involves concentrating a lot of
energy on a small spot
• produces deep narrow welds
• two processes include:
• Electron beam
• LASER beam
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Electron beam welding
(EBW)
• Electrons-focused, Vacuum required.
• High quality welds, very expensive
equipment
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Laser Beam Welding (LBW)
• Focused laser
• Good quality, little distortion, good
strength, ductile, non-porous.
• Automated,
• high equipment cost.
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Cutting
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Oxyfuel Gas Cutting
• Cuts mostly by oxidation
• For ferrous metals
• Rough surface, high distortion, can
cut underwater.
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Cutting
Alignment of torch tip
orifices with the kerf
• one orifice should proceed and one
should follow the cut
Plasma Arc Cutting (PAC)
• Highest temperatures
• Rapid cutting, good surface, narrow
kerf, popular with Robotics/Flexible
automation
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protects the welding or
cutting process
Transferred vs. Non
Transferred Arc
Lasers & Electron Beam
Cutting
• Accurate
• Wide variety of material
• Good surface, narrow kerf.
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Brazing, Soldering,
Adhesive Bonding, and
Mechanical Fastening
Processes
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Brazing
• Characteristics
• filler metal is placed at or between the faying
surfaces to be joined.
• temperature is raised to melt the filler metal but not
the work piece.
• Above 840 deg F.
• surface should be cleaned.
• Flux
• prevents oxidation.
• removes films from work piece surfaces.
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Soldering Characteristics
• solder fills joint by capillary action.
• use of soldering irons, torches,
ovens.
• lower temperature than brazing.
(below 840)
• Copper, Silver and Gold are easy to
solder while
• Aluminum and stainless steels are
not.
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Flux
• Inorganic acids or salts
• Zinc ammonium chloride solutioncleaning.
• Remove afterward to avoid corrosion.
• Non-corrosive resin based fluxes
• Electrical application.
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Adhesive Classifications
• Chemically reactive
• Pressure sensitive
• Hot Melt
• Evaporative or diffusion
• Film and tape
• Delayed tack
• Electrically and thermally conductive
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Adhesives Advantages
• Interface gives strength, sealing,
insulation, electrochemical corrosion from
dissimilar metals, reduces vibration and
noise.
• Distributes load, gives structural integrity
(no holes), improved appearance.
• Good for thin, fragile, and porous parts.
• Limited distortion because of low
temperature.
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Adhesives Limitations
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Service temperatures.
Possibly long bonding time.
Great care in surface preparation.
Difficulty in testing bonded joints
nondestructively.
• Limited reliability of adhesively
bonded structures during service
life.
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Mechanical Fastening
Characteristics
• Ease of manufacture.
• Ease of assembly and transportation.
• Ease of disassembly, maintenance,
replacement or repair.
• Ease on creating designs for movable
joints (hinges, sliding mechanisms,
adjustable components, fixtures).
• Lower over all cost of manufacture of the
product.
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Mechanical Fastening
Methods
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Threaded fastener.
Rivets.
Metal stitching or stapling.
Seaming.
Crimping.
Snap-in fasteners.
Shrink & Press fit.
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Thermoplastic Joining
• External heat sources
• Hot air, gasses, elect resist, lasers
• Internal heat sources
• Ultrasonic, Friction
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Thermoset Welding
• Threaded or molded inserts
• Mechanical fasteners (self tapping
screws)
• Solvent bonding
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