Welding Continued

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Welding Continued
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Quiz 3 Name________

• What is
• SMAW
• SAW
• Describe Gas Metal Arc Welding?
• What is Heat-affected Zone?

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Electroslag Welding(ESW)

• 600 A at 40-50 V
• 2 in to 36in
• Travel speed 0.5 1.5 in/min
• Arc is created
• Flux is added and melted by arc
• Electrode submerges in molten slag and arc is
  extinguished
• Used for heavy structural steel, Pressure vessels
  etc.

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• Advantages
• Can weld thick sections (1in)
• Specific welded metal characteristics can be
  achieved without problem by adding alloys to flux
  core
• Easy to automate like GMAN

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Electrogas Welding(EGW)

• Used for welding vertical sections
• 750 A(cored) 400 A (solid)
• Inert gas

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• Used for aluminum,magnesium, titanium alloys
• Produces high quality weld
• Consumable electrode may produce variations in
  arc while tungsten arc is very consistent

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Electrodes

• For arc welding process electrodes are described
  by
• Strength of deposited weld
• Current (AC/DC)
• Type of coating
• Identified by letter code/color code
• Dimensions are usually 150-460 mm( 6-18 inch)
• Selection of electrode depends on
• Section
• Current
• Diameter of electrode
• ANSI standard or SAE standard

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Electrode Coating

• Clay like material (silicate binders,powdered
  oxides, cellulose etc)
• Coating is for
• Stabilizing arc
• Produce gases which acts as shield
• Control electrode melt rate
• Protect molten metal by acting as flux
• Alloying element
• AC process
• Potassium silicate binder
• Lower ionization potential
• DC process
• Sodium silicate binder

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Filler Materials

• Bare or coated with flux
• Flux protects the weld surface from being
  oxidized by creating gaseous shield
• Can also be used to remove oxides and other
  substances from the workpiece
• Slag created by flux also creates protection for
  molten metal

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• Non Consumable Electrode
• Uses tungsten electrodes
• Shielding gas is applied

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Gas tungsten Arc welding(GTAW)

• Also known as TIG(Tungsten inert gas welding)
• Filler metal is applied from a wire source
• Argon/helium produce inert environment
• May also be done with fillers for close finish

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Atomic Hydrogen Welding(AHW)

• Arc between two tungsten electrodes or two carbon
  electrodes
• Hydrogen atmosphere

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Plasma Arc Welding(PAW)

• Plasma is ionized hot gas (equal quantity of
  electrons and ions)
• Temperature is 60000F
• Arc is initiated between tungsten electrode and
  orifice (Thermal Spraying)
• Electrode and Workpiece (Transferred arc)
• Very concentrated heat
• High speed welding(5-40 in/min)
• Used for butt and lap joint

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Principles of arc welding

• Arc
• Voltage
• Current
• Length
• Type of power supply
• Type of electrode
• Shield gas
• Joint
• Design
• Preparation
• Pre heat post heat

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Cathode Anode in an Arc
Anode Space
Arc Column
Cathode Space
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Stability Amount Of sputter

• Depends on mode of metal transfer
• Gravity
• Upward
• Downward
• Surface tension
• Electromagnetic interaction
• Hydrodynamic action of plasma
• Density
• Size of metal

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Arc Characteristics

• Voltage reduces up to a value of 50 Amp and
  increases after that
• Arc is constant diameter, less resistance for
  arc, low voltage

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• Lets designate voltage drop
• V 4020l
• V A Bl
• A electrode drop
• B voltage drop at the arc column of length l
• A,B depend on electrode , power source etc
• Points D and B create stable arc

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How can we find optimum power

• Power P VI for given length
• Determine V for given arc length l1 , l2 etc
• Find I1, I2 from previous graph characteristics
  graph

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Resistive Welding

• Heat required is produced by means of electric
  resistance between members to be joined
• H(heat) I2Rt
• Heat in Joules
• I (current) in Amperes
• R(resistance) in Ohms
• T(time of current flow) in seconds.

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• Total resistance is the sum of
• Resistance of the electrode
• Workpiece-electrode contact resistance
• Resistance of the individual parts to be welded
• Workpiece-workpiece contact resistance
• Resistance should be low
• High current is required usually because of poor
  resistance

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• Effect of high thermal conductivity in aluminum
  and copper
• More current required
• Dissimilar metals can be welded

Low volt. High Amp
Low amp. High volt
Functional Sketch of a transformer
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Spot Welding

• Weld electrodes 0.25 0.375 in diameter
• Most commonly used resistance welding
• Mechanical or pneumatic press

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Seam Welding

• Electrodes or wheels
• Intermittent spot or continuous seam
• Cans or Gasoline tanks

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Flash Butt welding (FW)

• Diameter 0.05 to 3 inches
• Joining pipes tubular shapes
• Usually automated

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Resistance projection Welding
Electrode Copper cooled with water
Mesh Welding
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High frequency resistance weld

• Similar to seam welding except that high
  frequency current usually 450Khz is used
• Used for tube welding from sheet
• Also induction heating method

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Stud welding Sequence of Operations

• Used for welding bars, threaded rods and various
  fasteners on metal plates

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• High Intensity Welding
• Electron Beam Welding (EBW)
• High velocity narrow-beam electrons
• Kinetic energy of electrons is converted to heat
  as they strike work piece
• High focused beam usually in vacuum, deep
  penetration in vacuum
• Any metal can be welded
• Very small heat affected zone
• Depthwidth 101 to 301
• Very high weld speed 200 mm/sec or 40 ft/min
• Distortion and shrinkage in the weld area is very
  low

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Laser Beam Welding

• Utilizes High power Laser beam
• Beam can be focused accurately
• 8 ft/min to 250 ft/min
• Useful for deep and narrow welds
• Al, Ti, Cu, Super alloys, Ferrous etc

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• Oxy-Fuel gas welding
• Melting and fusion ( coalescing of metals by
  means of heat)
• Filler metals may or may not be used, used to
  supply additional material to weld zone
• Oxy-Fuel gas welding designates any process in
  which oxygen is mixed with fuel gas to create
  heat

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Schematic diagram of oxy welding
Neutral Flame
Carburizing Flame
Oxidizing Flame
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• Common gas welding Process
• Acetylene Fuel
• C2H2 O2 -gt 2CO H2 heat
• 2CO H2 1.5 O2 -gt 2 CO2 H20 heat
• Temperature up to 6000 F can be produced by
  this method
• Ratio of C2H2 / O2
• 11 neutral flame
• 1gt1 oxidizing flame
• Not good for steel but ok for Cu or Cu alloy
• 1 lt 1 reducing or carburizing flame
• results in lower temperature,
• Applications brazing, soldering

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• Other fuels
• Methyl acetylene propadiene, used for low melting
  point applications such as lead,thin wall
  sections
• Figure of different flames

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Thermit Welding(TW)

• Brand name trademark
• This is a welding process where heat produced due
  to reaction between metal oxides and metallic
  reducing agents is used
• Used for welding steel and cast iron
• Finely divided iron oxide (Fe3O4) Aluminum oxide
  (Al2O3) iron and aluminum

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Chemical equations in TW

• Fe3O4 2 Al Fe Al2O3 heat
• 3 FeO 2 Al 3 Fe Al2O3 heat
• Fe2O32Al 2Fe Al2O3 heat
• Weld thickness from 0.5in to 3 in
• Steel, Aluminum , Titanium alloys

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• Reaction is started by magnesium fuse to special
  compounds of peroxide,chlorates or chromates
  known as oxidizing agents
• Heat 3200C (5800 F)
• Oxides of copper,nickel chromium and manganese
  are also used for thermit welding

Joining two cast iron pipes
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Summary of Fusion Welding

• Electro slag/Electro gas
• Non-consumable - Plasma welding using Tungsten
  Electrode
• Voltage/Current graph arc length types of
  metal transfer stable arc etc
• Resistance welding spot, seam weld, Projection
  weld etc
• EBW, LBW advantages
• Gas welding, Thermit welding