By Je; Lee
Photographers love rooster tails, those spark plumes a plasma torch makes as it starts to pierce thick plate—an iconic image of heavy industry getting to work. Anyone managing a heavy-plate cutting
operation, though, could certainly do without them. Flashy rooster tails
don’t show “America’s manufacturer getting the job done,” but instead
shows plasma consumables wearing faster than they should. Shop managers like to see plasma torches cutting, not piercing. After all, cutting is
where the money is made.
From this demand came the fabrication industry’s early combination plate cutting machines, those that had not only plasma and oxyfuel
torches, but also hard tooling like drills and (more recently) mills. Introduced several decades ago, these plate cutting combo machines were
developed to solve the piercing conundrum.
Today these systems have advanced to become plate cutting’s Swiss
Army knife. In this sense, their main function has evolved. They’re now
more than just about avoiding or minimizing the pierce, though it’s still
an important variable in the overall equation. It’s now about minimizing
handling, eliminating secondary operations, and increasing part flow velocity, from raw stock to the next application downstream.
At first these machines simply o;ered drilling capability alongside plasma
and oxyfuel cutting. Instead of dealing with a lengthy pierce cycle that was
hard on torch consumables, fabricators now could drill a pilot hole, then
edge-start with the cutting torch.
This also opened up new nest layout possibilities, particularly in very
heavy plate (such as 2 in. thick), in which a plasma pierce would be di;cult,
time-consuming, or just impossible. In these plates, programmers
incorporated edge starts from the plate edge and perhaps some chain
cutting from one part profile to the next, so the torch wouldn’t have to
stop and repierce during the cut.
Of course, that edge-starting requirement limits the nest layout possibilities. A programmer might have to end up with a smaller remnant—so
small that it might make sense to just cut it up for scrap rather than save
it. An integrated drill frees the programmer to place pilot holes wherever
needed to maintain an optimal, e;cient, material-saving nest layout.
The drilling of pilot holes was a big reason behind the early successes
of these combo machines, but it wasn’t the only reason. The ability to add
drilled features was an added benefit. The machine could also add small
holes with high depth-to-width ratios that were di;cult or impossible for
conventional plasma torches to achieve. Sometimes fabricators needed
to cut larger holes that, because of their tight tolerances, required
machining. And they needed holes of various sizes, some of them with
From this came combo machines with not only an oxyfuel and plasma
torch, but also a cutting head with a rotating turret that held about a
half-dozen tools. It could hold conventional twist drills of various sizes
as well as tapping and similar cutting tools. Next came the demand for
larger holes that, in turn, required larger drill bits on larger machines
with high-horsepower spindles, now with through-spindle coolant deliv-
ery, to handle the increased torque and heat.
Chamfering and milling, including helical milling of pockets and slots,
were the next logical steps. Consider a large cut part with an interior
8-in.-wide hole with extremely tight edge tolerances and a chamfer. Conventionally, the plasma would cut the profile, and the operator would
then move the piece to a vertical machining center that would mill and
chamfer the edge to the required tolerance.
» The drilling, chamfering, milling, tapping, and plasma cutting these workpieces
required were all performed on one machine.
» Bevel cutting remains one of the most complex plasma arc cutting operations.
The potential of
Milling, drilling, tapping, chamfering,
thermal cutting—all on one table