Joining Processes Welding

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Joining Processes Welding
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• Joining is an important process in manufacturing
• For products impossible to manufacture in a
  single piece
• Many product are cheaper to fabricate as many
  individual components and join later
• Many product have to be dissembled for repairs
• Automobile assembly
• Electronic devices etc

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• Different parts of a product might have different
  design requirements
• It is cheaper and practical to transport
  assemblies to site before assembling it.e.g.
  machines,home products

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Classification of joining processes
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• Liquid state Process
• Usually involves fusion resulting due to melting
  of metal particles Filler metals
• E.g. Oxy-Fuel Welding, laser welding, chemical,
  electrical, optical
• Solid State process
• Ultrasound,friction,explosion
• No filler metal is used here
• Joining occurs due to external pressure and heat
  source.

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• Liquid Solid State process
• Braze metal, Soldering, Adhesive bonding
• Liquid metal applied to solid base metals to join
  parts
• Mechanical means
• Fasteners, bolts, nuts screws, seaming etc
• Easy to dissemble.

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• Types of Welding
• Based on filler metals
• Autogenous
• No filler metal, electrode acts as filler metal
• Homogenous
• Filler metal used is same as base metal
• Heterogeneous
• Filler of different metal, soldering, brazing
  etc.

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• Important factors governing fusion welding
  process
• Characteristic of heat source
• Nature of filler material
• Heat flow characteristics in the joint
• Gas metal / slag metal (reaction in the fusion
  zone)
• Cooling of the fusion zone with associated
  contraction, residual stresses and crystal changes

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• Principles of fusion welding
• Metallurgically there are three distinct zones
• Fusion zone
• Heat affected unmelted zone
• Unaffected original part

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• Arc Welding
• Consumable electrode first developed in mid 1800
• Heat developed by electric energy
• Arc between tip of the electrode and the work
  piece to be welded
• Uses both AC/DC power supplies
• Temperature 5000-30000 C ,very high!!

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• Shielded metal arc welding
• Most common and versatile method,electrodes are
  thin long sticks
• Heat melts the electrode, base metal and coating
  on the electrode,all of this weld in the weld
  bead
• Current AC or DC(sheet metals etc)
• Electrodes can be
• Straight polarity ( electrode -ve) DCSP Work
  Piece is positive
• Reverse polarity (electrode ve) DCRP

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Shielded metal arc welding (SMAW)

• About 50 of all large scale industrial welding
  operations use this process.

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• Arc Welding (contd.)
• Current ranges between 50-300 amps.
• Power 10 KW
• Choice of electrodes,current, power etc depends
  upon the metal to be welded
• Advantages
• Simple
• Versatile
• Small variety of electrodes
• Few basic equipment
• Used in ship building, pipe lines,construction,
  fabrication etc.

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• Welding practices
• Can be used to weld both ferrous and nonferrous
  material
• Economical for lt 0.25 inch

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• Submerged Arc Welding ( SAW)
• Welding arc is shielded by a granular flux
  consisting of lime,silica,manganese oxide,calcium
  fluoride
• Flux insulates weld area,allows deep thermal
  penetration
• Prevents spatter and spark over molten metal
• Shielded glass etc is unnecessary
• 300 2000 Amp
• Speed 5 m/min
• Thick plate welding 4 to 10 times more weld
  material than SMAW.
• Carbon, allow, stainless steel etc

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Submerged Arc Welding
Unfused flux is recovered and reused
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• Gas metal arc welding (GMAW)
• Also known as metal inert gas welding
• Weld area is shielded by an external source or
  inert gas
• Argon,CO2 , or mixture
• Multiple layers can be applied without cleaning
  surface
• Three types of GMAW processes
• Spray transfer spray small droplets High DC
• Pulsed Arc.
• Globular transfer using pressure Thick Metals
• Short circuiting individual droplets, 50/s
• Consumable electrode wires of 1/16 to 3/8 inch
  diameter
• 600-2000 A (AC/DC) at 440 V

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• Advantages
• Quality of weld is very good
• Good ductility and toughness
• Uniform properties in weld

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• Flux core arc welding (FCAW)
• Tubular electrode filled with flux
• Electrodes usually 1/16 to 3/32 inch diameter
• Combines good feature of Shield metal arc welding
  and gas metal arc welding (electrode feeding
  feature)
• We can alloying element in the flux
• Can be automated

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Flux Cored Arc welding Process
This process is similar to gas metal arc welding
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Summary

• Liquid Welding
• Solid Welding
• Liquid-solid welding
• Arc welding Fusion welding Consumable
  electrode
• Shielded Metal Arc Welding (SMAW)
• Submerged Arc Welding (SAW)
• Gas Metal Arc Welding
• Flux cored arc welding