WELDING

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WELDING

• Definition Material joining process. Two parts
  connected at their contacting surfaces by
  suitable heat and pressure.
• Many welding processes are accomplished by heat
  alone, some others by heat and pressure, and some
  with pressure only.
• In some welding operations a filler material is
  used.
• Welding operation usually applied to metals but
  also used for plastics.

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Technological and commercial importance

• Provides a permanent joint, welded parts become a
  single entity.
• Welded joints can be stronger than the parent
  material.
• Economical way to join components in terms of
  material usage and fabrication costs.
• No need for factory environment.

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Limitations

• Manually applied, therefore high labor cost.
• Need high energy causing danger
• Not convenient for disassembly.
• Defects are hard to detect at joints.

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Types of welding processes

• We can divide welding processes into two major
• groups
• Fusion welding Use heat to melt the base metals.
  Usually a filling material is added to provide
  strength to the welded joint. If no filling
  metals used, it is called autogenous weld. Most
  widely used techniques belongs to this category.

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Types of welding processes(cont.)

• 2) Solid-state weldingJoining process is
  provided by pressure alone or pressure and heat
  together. When the pressure is used alone, the
  heat is below the melting point.

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Some groups in fusion welding category

• Arc welding(AW) Heat is accomplished by electric
  arc.
• Resistance welding(RW) Heat is generated by
  electric resistance.
• Oxyfuel gas welding(OFW)Mixture of oxygen and
  asetylene used to produce a hot flame for melting
  the base metal and filler metal(if used). Most
  widely used.
• Electron beam welding(EBW)
• Laser beam welding(LBW)Better method than EBW,
  since laser can be shaped and directed optically,
  no vacuum is necessary, and quality becomes
  better.

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Cont.

• 6) Thermit Welding (TW)Thermit Welding
  usually uses the exothermic reaction of a mixture
  of iron oxide and aluminum powder or other
  similar mixtures to weld or repair large forgings
  and castings, and join pipes and railroad rails.
• The parts are aligned and a ceramic or sand
  mold is built around the joint to be formed. The
  thermitic mixture reaction is initiated with a
  special compound (an oxidizing agent) heating
  quickly to the desired temperature which melts
  the ends of the parts to be joined. After the
  weld cools, excess material is removed by
  machining, grinding, or other cutting methods.
• Note that, last 3 methods involves reactions
  between metals.

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Arc Welding
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Resistance welding
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Oxyfuel gas welding
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Electron beam welding
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Laser beam welding
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Thermit Welding
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Some groups in solid state welding category

• Diffusion welding(DFW) Two parts are held
  together under pressure at elevated temperature.
• Friction welding(FRW) By heat of friction
  between two surfaces two parts joined.
• Ultrasonic welding(USW)Moderate pressure between
  two parts hold together and an ultrasonic
  oscillation frequency send through in the
  direction parallel to the surface of contact.
• Forge welding(FOW) Heat and pressure applied.
  First the item is heated and hammered.
• Cold welding(CW)Only pressure is applied.
• Explosion Welding (EXW)A layer of explosives
  placed between layers of materials.

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Diffusion welding
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Friction welding
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Ultrasonic welding
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Forge welding
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Cold welding
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Explosion Welding
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Commercial operations that use welding

• Construction of buildings, bridges, etc.
• Piping, storage tanks, pressure vessels, etc.
• Ship building.
• Aircraft, aerospace industry.
• Railroads.

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Weld joint

• There are 5 basic joint types in welding
• Butt joint Two materials are in the same plane,
  joined from the edges.
• Corner jointThe corners of two materials form a
  right angle and joined.
• Lap joint Two parts overlaps.
• Tee joint One part is perpendicular to the
  other, making a T shape.
• Edge joint Edges of the two materials joined.

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Weld Joints
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Types of weld

• Fillet weld Used in T joints,corner joints, lap
  joints.
• Groove weldUsed in butt joints.
• Plug weld Used in lap joints.
• Slot weld Used in lap joints.
• Spot weld Used in lap joints.
• Seam weld Used in lap joints.
• Flange weldUsed in edge joints.
• Surfacing weldNot a joining process, it is used
  to increase the thickness of the plate, or
  provide a protective coating on the surface.

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Fillet Weld
Slot and Plug Weld
Groove weld
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Spot weld
Seam weld
Flange weld