Plasma Cutting and Its Effect on Mild Steel

4. 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 30,000˚F, 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 1200˚F, 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 ZoneBorder 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 1200˚F 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 1200˚F • 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