Document Sample
					Lesson Outcomes:

After today’s lecture, students are
  expected to:
• Differentiate many types of solid state
  welding processes; cold welding,
  Friction welding, Resistance welding,

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Solid-State Welding
Solid State Welding
• The process of joining takes place without
  fusion (melting) of the workpiece.
• There is no liquid (molten) phase present
  in the joint.
• The basic principle of solid state welding is
  when two clean surfaces are brought into
  atomic contact with each other under
  sufficient pressure, they form bonds
  (strong joint).
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Solid State Welding (cont.)
• Applying external heat improves the
  bond by diffusion.
• It may improve the strength of the
• Heat may be generated by friction.
• Filler metal is not added

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SSW Advantages over
Fusion Welding Processes

• If no melting, then no heat affected
  zone, so metal around joint retains
  original properties
• Many SSW processes produce welded
  joints that bond the entire contact
  interface between two parts rather than
  at distinct spots or seams

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SSW Advantages over
Fusion Welding Processes (cont.)

  • Some SSW processes can be used to
   bond dissimilar metals, without
   concerns about relative melting points,
   thermal expansions, and other problems
   that arise in FW.

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Cold Welding
• In the process, pressure is applied to
  the workpiece, through rolls.
• Prior to welding, the interface is
  degreased, wire-brushed, and wiped to
  remove oxide smudge.
• Cold welding can be used to joint small
  workpieces made of soft, ductile metals.

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Cold Welding (cont.)
• The pressure required for cold welding
  can be applied through a pair of rolls.
• Hence, the process is called roll

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Roll Bonding

 Schematic illustration of the roll bonding or
 cladding process.
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Cold Welding (cont.)
• The process can be carried out at
  elevated temperatures (hot roll
• E.g. cladding of pure aluminium over
  aluminium-alloy sheet and of stainless
  steel over mild steel, for corrosion

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Cold Welding (cont.)
• If joining of two dissimilar metals that
  are mutually soluble, brittle intermetallic
  compounds may form.
• These will produce a weak and brittle
• E.g. in the bonding of aluminium and
• The best bond strength is obtained with
  two similar materials.
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Friction welding
• The heat required for friction welding is
  generated through friction at the
  interfaces of the two components being
• In friction welding, one of the
  components remains stationary while
  the other is placed in a chuck or collet
  and rotated at a high constant speed.

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Friction welding (cont.)

• The two members to be joined are then
 brought into contact under an axial

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      Friction welding (cont.)


(a) Sequence of operations in the friction welding process:
  (1) Left-hand component is rotated at high speed.
 (2) Right-hand component is brought into contact under an axial force.
 (3) Axial force is increased; flash begins to form.
 (4) Left-hand component stops rotating; weld is completed. The flash can
 subsequently be removed by machining or grinding.
 (b) Shape of fusion zone in friction welding, as a function of the force
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 applied and the rotational speed.
Resistance Welding (RW)
• use a combination of heat and pressure
  to accomplish coalescence
• Heat generated by electrical resistance to
  current flow at junction to be welded

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Resistive Welding (cont.)
• Heat required is produced by means of
  electric resistance between members to be
      H(heat) = I2Rt
  –   Heat in Joules
  –   I (current) in Amperes
  –   R(resistance) in Ohms
  –   T(time of current flow) in seconds.
• Often modified by including a factor , K,
  which represents the energy losses through
  conduction and convection (K < 1).
     H(heat) = I2RtK
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Resistive Welding (cont.)

• Total resistance is the sum of
  – Resistance of the electrode
  – Workpiece-electrode contact resistance
  – Resistance of the individual parts to be
  – Workpiece-workpiece contact resistance
• High current is required usually because
  of poor resistance
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     Resistance Spot Welding

    (a) Sequence in
    resistance spot welding.

(b) Cross-section of a spot
weld, showing the weld
nugget and the indentation of
the electrode on the sheet
surfaces. This is one of the
most commonly used process
in sheet-metal fabrication and
in automotive-body assembly.

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• Two flat copper sheets (each 1.5 mm
 thick) are being resistance spot welded
 by the use of a current of 7000 A and a
 current flow time of 3 s. The electodes
 are 5 mm in diameter. Estimate the
 heat generated. Assume that the total
 resistance is 200 μΩ.

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Advantages and Drawbacks of
• Advantages:
  – No filler metal is required
  – High production rates are possible
  – Lends itself to mechanization and
  – Operator skill level is lower than for
    arc welding
  – Good repeatability and reliability
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Advantages and Drawbacks of
• Disadvantages:
  – High initial equipment cost
  – Limited to lap joints for most RW

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