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Plasma Cutting and Its Effect on Mild Steel

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Plasma Cutting and Its Effect on Mild Steel Background of Plasma Arc Process In 1941 the U.S. defense industry was looking for a way to join light metals, from this ... – PowerPoint PPT presentation

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Title: Plasma Cutting and Its Effect on Mild Steel


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Plasma Cutting and Its Effect on Mild Steel
Brad Rush Mynda Songer Eliot Speed
5
Background of Plasma Arc Process
  • In 1941 the U.S. defense industry was looking for
    a way to join light metals, from this came
    Tungsten Inert Gas (TIG) welding
  • It was found that by passing a gas through the
    TIG arc that metal could be cut by gas in a
    plasma state
  • TIG and plasma arc processes were created for the
    aerospace industry, primarily for aluminum which
    is difficult to weld by other processes and
    difficult to cut with a torch

CNC Plasma Cutting Machine, 1980
6
How a Plasma Cutter Works
  • An arc is used to ionize the gas around a high
    voltage arc
  • This ionized gas is superheated by the arc to
    plasma
  • In the plasma state, the gas is at 30,000F,
    reducing the steel to a molten state, allowing
    the stream of gas to push it out of the cut

7
Effect of Plasma Cutting at Different Amperages
  • We examined the microstructure of ¼ thick 1018
    mild steel that was cut at different amperages
  • The steel was cut at 15, 22.5, and 30 amps
  • The three samples were mounted and polished, and
    the microstructures were examined and photographed

8
15 Amp Cut
  • This amperage was too low for the thickness of
    steel, so the cut that was made was slow
  • The sample was heated to around 1200F, annealing
    the steel in the heat affected zone (HAZ)
  • The annealed steel can be seen by the lighter
    region in the HAZ and near the edge of the steel,
    which is ferrite and pearlite

Heat Affected Zone Border
Edge of Steel
9
22.5 Amp Cut
  • The amperage was correct for this cut, so the
    annealed region, or HAZ, was very small due to
    the cut being the correct speed and heat
  • Only the edge was heated to around 1200F as seen
    in the photograph
  • The dark region is ferrite and martensite due to
    the austenization and slow cooling, while the
    light region is ferrite and pearlite, since it is
    unaffected by the cut

Edge
HAZ Border
10
30 Amp Cut
  • The amperage for this cut was too high and
    created a larger HAZ, even though the speed of
    the cut was greater
  • The edge and some of the interior was all heated
    to around 1200F
  • The HAZ contains ferrite and martensite due to
    austenization as in the 22.5 amp cut, as in the
    22.5 amp cut the ferrite and pearlite region is
    the unaffected region

HAZ Border
Edge
11
Conclusion
  • At 22.5 amps, the steel has the smallest HAZ, as
    this is the correct amperage to cut ¼ mild steel
  • The plasma cutter can cut steel about 10 times
    faster than a reciprocating saw
  • Best cutting tool for light metals, especially as
    an alternative to an oxy-acetylene torch
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