Transcript Nonconsumable Electrode Consumable Workpiece

Nonconsumable Electrode
Consumable Workpiece
William “Quin” Underwood
10-29-08
Topics of Interest:
• Nonconsumable Electrode
▫ GTAW, or TIG
▫ Plasma Arc
▫ Carbon Arc
 Twin Carbon Arc
• Consumable Workpiece
▫ Stud
 Drawn Arc Stud Welding
 Capacitor Discharge Stud Welding (CD)
▫ Percussion
Definitions:
• Arc length: The distance from the electrode along the workpiece opposite
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the direction of welding.
Arc Voltage: the amount of voltage present between the electrode and the
workpiece.
Consumable Electrode: An electrode that conducts electricity to the arc
but also melts into the weld as a filler metal.
Gas shielding: A layer of inert or slightly reactive gas provided by the
electrode. Shielding gas protects the weld puddle and arc from atmospheric
contamination.
Weld puddle: The small area of molten metal that forms during welding.
The cooled weld puddle forms the permanent joint.
Nonconsumable Overview
• Also known as ARC welding.
• Discovered in the 1800’s with the discovery of the electric arc.
• Uses power supply (AC or DC) to create an electric arc between electrode
and base material. This melts the workpiece at the welding point.
• Sometimes protected by shielding gas.
• Arc welding is widely used because of low running costs and a wide variety
of applications.
• Arc welding really took its stride in WWII.
▫ Allowed the US to repair ships quickly.
▫ British constructed a ship, the Fulagar, with an entirely welded hull.
GTAW
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Gas Tungsten Arc Welding.
Otherwise known as TIG.
Perfected in 1941.
Uses nonconsumable tungsten electrode to produce weld.
Weld arc is protected from atmospheric contamination by a shielding gas.
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Usually Argon.
Needs a constant current welding supply.
Allows the user great control.
Usually a stronger or higher quality weld.
More complex and harder to master.
Slower than most welding types.
GTAW
Operation
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Often considered most difficult of all welding procedures.
Must maintain short arc length and great care is required to prevent contact between the electrode and
workpiece.
Must feed a filler metal into the weld area with one hand while manipulating the welding torch in the
other.
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To strike welding arc, a high frequency generator provides a path for the welding current through the
shielding gas, this allows arc to be “struck” when separation between the workpiece and the electrode is
app. 1.5 – 3mm.
If you bring the electrode and workpiece in contact in can contaminate the weld and the workpiece.
Once an arc is struck you move the torch in small circles to create a welding pool, then you move along
the welding line, and the filler metal is added manually as needed.
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Thin materials don’t always need a filler material. Most often edge, corner and butt joints.
If using a aluminum filler material you must take great care to maintain some distance from the arc while staying inside
the gas shield. If you are to close the filler rod will melt. If to far away it will become contaminated.
At completion of the weld the arc current is usually gradually reduced.
GTAW Currents
• Can use Positive or Negative direct current or an Alternating current.
• PDC
▫ Positively charged ions flow from the tip of the electrode, heating the workpiece,
Helps remove oxide layers from the surface of workpiece. It produces a shallow,
wide weld with minimum heat input.
• NDC
▫ Causes a stream of electrons to collide with the surface, creates lots of heat.
Produces a deep, narrow weld.
• Alternating
▫ Best of both worlds. Has a cleaning effect and also imparts lots of heat.
GTAW Applications
• Aero Space industry is one of the prime users.
▫ Extensively used in space vehicle's.
• Good for thin workpieces.
• Small diameter thin walled tubing (bicycle's).
• Used on aluminum and magnesium.
• Used to weld spent nuclear fuel canisters before burial.
• Used when maximum weld quality is needed.
▫ Must maintain clean workpiece. Free from oil, moisture and dirt.
GTAW Pros & Cons
• Pros:
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Concentrated arc.
No slag, sparks or splatter.
Little smoke or fumes.
Good for thin martial's.
Will weld more metal and metal alloys than any other process.
Wide assortment of filler material can be used.
Highly resistant to corrosion and cracking.
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Slower travel speeds.
Hand eye coordination is a must.
Bright UV rays, mostly causes sunburns.
Equipment costs can be higher.
Overexposure can cause skin cancer.
GTAW Pictures
How to TIG Weld
Plasma Arc Welding
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Also known as PAW.
Very similar to GTAW.
Introduced in 1964.
Uses a plasma gas which is heated
and ionized so it becomes electrically
conductive.
• Uses this plasma to transfer an
electric arc to the workpiece.
• The metal that is to be welded is
melted by the intense heat of the arc.
• PAW is an advancement over GTAW.
Plasma Operation
• Uses a tungsten electrode but uses
plasma gas to make the arc.
• Electric arc is forced between an
electrode and the workpiece.
• Key diff. between GTAW and PAW is
that in PAW, by positioning the
electrode within the body of the torch,
the plasma arc can be separated form
the shielding gas envelope.
• Plasma is then forced through a fine
bore non-consumable copper nozzle
which constricts the arc and then the
plasma exits the orifice at high
velocities (approaching the speed of
sound) and at a temp around 20,000
C.
PAW Pros & Cons
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Deep narrow penetration is achievable.
Can be used to weld all metals that are wieldable with GTAW.
Greater arc stability allows much longer arc length (stand off).
Affords greater control and improved weld quality.
Can be used in miniature or precision applications.
Can be used on a wider range of material thicknesses.
Wide variety of applications from strip metal to aircraft blades.
Long electrode life.
Can operate with low amperage (down to .1 amps).
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Largely limited to automated systems.
Requires expensive and complex equipment.
Proper torch maintenance is critical.
Can not be used on magnesium.
Welding procedure is more complicated so skill level required is much higher.
Plasma Video
Carbon Arc Welding
• Also known as CAW.
• Produces a weld by
heating the two metals
with an arc between a
non-consumable carbon
(graphite) electrode and
the workpiece.
▫ This arc produces extreme
temperatures in excess of
3000 degrees.
• Oldest of the arc welding
processes.
• Not widely used today.
CAW Pros & Cons
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Low cost equipment and welding operation.
High level of skill is not required.
Easily automated.
Low distortion of workpiece.
• Cons:
▫ Unstable quality of weld.
▫ Carbon electrode contaminates weld material with
carbides.
▫ Out dated.
▫ Replaced by Twin Carbon Arc Welding.
Twin Carbon Arc Welding
• Similar to CAW but uses two
carbon electrodes instead of
one.
• Size of arc depends on the
distance between the 2
electrodes, the electrode
diameter and the welding
current.
• AC current is recommended.
• Workpiece is not part of the
electrical current.
▫ Can move arc anywhere without it
being extinguished.
Consumable Workpiece Overview
• Stud Welding.
▫ Two types of stud welding
 Drawn Arc Stud Welding
 Capacitor Discharge Stud Welding (CD)
• Similar to spot welding, where a bolt or a specially formed nut its
welded onto another metal part.
• Bolts may be automatically fed into the spot welder.
• Weld nuts generally have a flange with small nubs that melt to form
the weld.
• Studs have necked down, unthreaded area for the same purpose.
• Fast, reliable and accurate.
Drawn Arc Stud Welding
• A process by which a metal stud
is joined to a metal workpiece by
heating both parts with an arc.
• Permits strong one sided welds.
• Can produce a weld in as little as
.06 seconds.
• Wont mar the other side of the
workpiece.
• Provides a highly reliable
fastening for a wide variety of
applications.
• Allows almost any size or
configuration of metal stud to be
welded quickly.
• Uses DC power supply to create
arc.
DAS Applications
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Offers high structural integrity.
Leak poof.
Corrosion resistant.
Minimizes noise and vibration.
Used in:
▫ Automotive
 Heat shields, power steering, exhaust systems.
▫ Construction
 Bridges, piping.
▫ Furniture
▫ Ship building
 Hatches
3 Common DAS Techniques
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▫ Drawn stud arc welding:
 Flux stud is loaded into stud weld tool chuck, and a ferrule (a disposable
ceramic shield that contains the molten pool of metal) is placed over the end.
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▫ Short arc stud welding:
 Similar to drawn stud, does not use a flux load or ferrule. Offers the shortest
welding times of all the drawn arc stud-welding options.
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▫ Gas arc stud welding:
 It employ’s insert shielding gas with no flux or ferrule. Easier to automate.
However provides less fillet control and less depth of penetration in
comparison with the other 2.
DAS Pros
• Excellent welding success under a broad range of
conditions.
• Forms a bond that is stronger than the surrounding
metal.
• Can prevent unwanted tampering because bolt head is
not accessible.
• Takes less than a second.
• Very few manufacturing steps.
• Can weld on painted surfaces.
• Can be completed by a single worker.
DAS Pictures
Capacitor Discharge Stud Welding
• Used when appearance is
critical
• Permits the welding of
small diameter studs to
thin, lightweight materials.
• Weld cycle can be
completed in .01 seconds on
materials as thin as .5mm.
• Minimizes heat build up.
• Very little distortion or
burning.
CD Applications
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Used mainly for welding mild steel, stainless steel and aluminum.
Provides quick welds on lightweight or thin gauge materials.
Little to no distortion.
Can be used for:
▫ Jewelry
 Earrings and pins
▫ Hardware
 Brackets, cleats and tool handles
▫ Cookware
 Utensils, pots and pans
▫ Electrical components
2 Common CD Techniques
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▫ Contact CD Stud welding
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Stud is loaded into tool and put into contact with workpiece.
Energy is instantaneously discharged from capacitors through stud projection.
Ignition tip cant handle the current being discharged through it and it vaporizes.
This creates a gap that allows the arc to be formed.
Arc melts workpiece and the two workpiece are forced together.
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▫ Gap Stud welding
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Shorter weld times.
Higher current densities than contact stud.
Suited to cosmetic applications.
Produces very minimal backside marking.
CD Pros
• Precise repeatability.
• High integrity on thin materials.
• Allows welding of dissimilar materials.
▫ Weld penetration is so slight that metallurgical problems are prevented.
• Appealing one-sided welds with no reverse-side
dimples.
• High strength in light weight applications.
• Very fast.
CD Pictures
Stud Video’s
Contact
Gap
Percussion Welding
• Also known as PEW
• A type of resistance welding
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Uses heat from an arc, produced by rapid discharge of electrical energy.
The heat of the arc produced between them melts a shallow layer of metal on the surface of the
workpiece.
Then one of the workpieces is impacted against the other.
This extinguishes the arc, expelling oxides and forges the weld.
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In the welding of copper to molybendenum.
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For use in the manufacturing of power rectifiers
For making phone and electrical devices.
Attaching large area contacts to switch components.
Percussion Pros & Cons
• Pros:
▫ Welding of dissimilar metals such as copper to steel.
▫ Can weld metals with high melting points, i.e. Tungsten and
molly.
▫ Very short time cycles.
• Cons:
▫ Welding is typically dirtier and less smooth.