Plasma Cutting and Its Effect on Plasma Cutting and Its Effect on Mild Steel Mild Steel

Brad Rush Mynda Songer Eliot Speed

Background of Plasma Arc ProcessBackground of Plasma Arc Process

In 1941 the U.S. defense In 1941 the U.S. defense industry was looking for a industry was looking for a way to join light metals, way to join light metals, from this came Tungsten from this came Tungsten Inert Gas (TIG) weldingInert Gas (TIG) welding

It was found that by It was found that by passing a gas through the passing a gas through the TIG arc that metal could be TIG arc that metal could be cut by gas in a plasma cut by gas in a plasma statestate

TIG and plasma arc TIG and plasma arc processes were created for processes were created for the aerospace industry, the aerospace industry, primarily for aluminum primarily for aluminum which is difficult to weld by which is difficult to weld by other processes and other processes and difficult to cut with a torchdifficult to cut with a torch CNC Plasma Cutting Machine,

1980

How a Plasma Cutter WorksHow a Plasma Cutter Works An arc is used to An arc is used to

ionize the gas around ionize the gas around a high voltage arca high voltage arc

This ionized gas is This ionized gas is superheated by the superheated by the arc to plasmaarc to plasma

In the plasma state, In the plasma state, the gas is at 30,000˚F, the gas is at 30,000˚F, reducing the steel to a reducing the steel to a molten state, allowing molten state, allowing the stream of gas to the stream of gas to push it out of the cutpush it out of the cut

Effect of Plasma Cutting at Effect of Plasma Cutting at Different AmperagesDifferent Amperages

We examined the microstructure of ¼” thick 1018 We examined the microstructure of ¼” thick 1018 mild steel that was cut at different amperagesmild steel that was cut at different amperages

The steel was cut at 15, 22.5, and 30 ampsThe steel was cut at 15, 22.5, and 30 amps The three samples were mounted and polished, The three samples were mounted and polished,

and the microstructures were examined and and the microstructures were examined and photographedphotographed

15 Amp Cut15 Amp Cut• This amperage was too low for the thickness of steel, so the cut This amperage was too low for the thickness of steel, so the cut

that was made was slowthat was made was slow• The sample was heated to around 1200˚F, annealing the steel The sample was heated to around 1200˚F, annealing the steel

in the heat affected zone (HAZ)in the heat affected zone (HAZ)• The annealed steel can be seen by the lighter region in the 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 pearliteand near the edge of the steel, which is ferrite and pearlite

Heat Affected Zone Border Edge of Steel

22.5 Amp Cut22.5 Amp Cut• The amperage was correct for this cut, so the annealed region, or 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 heatHAZ, 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 Only the edge was heated to around 1200˚F as seen in the

photographphotograph• The dark region is ferrite and martensite due to the austenization and 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 slow cooling, while the light region is ferrite and pearlite, since it is unaffected by the cutunaffected by the cut

Edge HAZ Border

30 Amp Cut30 Amp Cut• The amperage for this cut was too high and created a larger HAZ, even though the The amperage for this cut was too high and created a larger HAZ, even though the

speed of the cut was greaterspeed of the cut was greater• The edge and some of the interior was all heated to around 1200˚F 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 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 regioncut, as in the 22.5 amp cut the ferrite and pearlite region is the unaffected region

HAZ Border Edge

ConclusionConclusion

At 22.5 amps, the steel has the At 22.5 amps, the steel has the smallest HAZ, as this is the correct smallest HAZ, as this is the correct amperage to cut ¼” mild steelamperage to cut ¼” mild steel

The plasma cutter can cut steel The plasma cutter can cut steel about 10 times faster than a about 10 times faster than a reciprocating sawreciprocating saw

Best cutting tool for light metals, Best cutting tool for light metals, especially as an alternative to an especially as an alternative to an oxy-acetylene torchoxy-acetylene torch