Welding

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Welding

• Oxy-Acetylene, Arc, MIG, Spot, Ultrasonic.

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Oxy - Acetylene

• The basis of this process is using a very hot
  flame produced by burning acetylene gas in
  oxygen.
• This takes place in a blowpipe that is connected
  to the two cylinders of gases.
• The heat and characteristics of the flame can be
  changed by adjusting the size of the nozzle on
  the blowpipe and the gas supply from the
  cylinders, to suit the thickness of material.
• A pool of molten metal is created by the flame
  using a filler rod that is made from the same
  type of metal as that being joined.
• The rod is dipped into this pool and melted into
  the joint, fusing the metal together.
• To the right is a picture of the process.
• Compared with arc welding, welding speed
• is remarkably slow. It is not an efficient
  welding
• method, and is rarely used in production
  lines.

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Electric Arc

• An electric current (Between 10 and 120 amps)
  jumping from an electrode to the work piece is
  the heat source for this welding process.
• The current then returns via an earth clamp on
  the work piece back to the transformer in the
  main unit.
• The electrode also acts as a flux coated filler
  rod. The flux melts during the process to form a
  shield that prevents oxidation of the weld. The
  electrode or filler rod is also melted during the
  process, filling the joint, fusing the joint
  together.
• To the right is a picture of the process.
• As you can see, safety precautions such as
• wearing eye protection and gloves are
  essential
• to prevent injury.

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MIG (Metal Inert Gas)

• Very similar to electric arc welding, an arc is
  struck between a continuous wire electrode and
  the workpiece, fed through a torch. However, an
  inert gas such as argon is fed through the torch
  which forms a shield that prevents oxidation and
  slag forming around the weld.
• The continuous electrode can provide a filler rod
  through spray transfer or dip transfer. Spray
  transfer uses a high voltage and current by
  causing a continuous stream of metal droplets
  that enter the joint. This is suitable for fast
  welding of thick material. Dip transfer involves
  dipping the electrode into the molten weld pool
  which causes a short circuit and some of the
  filler rod to melt off. This creates less current
  and heat so is suitable for welding thin sheets
  of metal.
• MIG welding is generally replacing oxy-acetylene
• welding in industry and is becoming
  increasingly
• popular in production lines of cars using
  robots.
• Most metals such as aluminum, copper, carbon,
• alloy steels and titanium are used in this
  process.

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Spot

• Two electrodes sandwich two sheets of metal
  together. A current then flows from one electrode
  to the other, through the metal and joint. Most
  resistance to the current occurs at the joint,
  so very high temperatures are created along the
  joint line.
• This causes welding to take place. Repeated
  several times, a series of spot welds are
  created, as shown below. Within the copper
  electrodes, water flows in order to keep the
  temperatures down.
• Spot welding is used extensively in the
  manufacture of thin sheet steel, such as car body
  panels, in long mass production lines.

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Ultrasonic

• The energy required for ultrasonic welding comes
  in the form of mechanical vibrations. The welding
  tool (sonotrode) is pressed against the part to
  be welded and moves in a longitudinal direction.
  The part to be welded on remains static. Now the
  parts to be bonded are simultaneously pressed
  together. This causes a fusion of the parts
  without having to use additional material.
• When welding plastics, the rise in temperature in
  the bonding area is produced by mechanical
  vibrations introduced vertically and the friction
  of the surfaces of the parts rubbing together.
  Frictional heat is produced, melting the parts
  together. Joint quality is very uniform and
  constant, but joining areas have to be prepared
  beforehand.
• Whereas in plastic welding, high-frequency
  vertical vibrations are used, the joining of
  metals is an entirely different process. Unlike
  in other processes, the parts to be welded are
  not heated to melting point, but are connected by
  applying pressure and high-frequency horizontal
  vibrations.

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Bibliography

• Internet sites - www.googleimages.co.uk
• - www.ultrasonicwelding.c
  om
• Text books - D.T - Resistant materials