36 ■■■
Cover Story
BAutomated parts removal helps to
eliminate the non-value-added aspects
of laser cutting, but a closer look at
nesting is necessary to get the most efficiency from the automated operation.
CFIGURE 1 Heat generated during
the laser cutting process can create “
ribbons” that may cause head crashes or
inaccurate height sensing. Nesting software can ensure these thin parts rest on
the grid and do not tip up.
By Liz Kautzmann
In the world of sheet metal fabrication, intelligent fabricating with a
laser cutting machine can lead to
increased productivity and flexibility and reduced setup and tooling
costs—as well as faster design and
prototype turnaround.
The laser’s versatility, whether you
run one or 1,000 pieces, makes it a
powerful weapon in the highly competitive battle for manufacturing market
share, especially when many companies are in search of labor savings and
are sourcing fabricated goods from offshore facilities. Running the laser in a
lean manufacturing environment where
just-in-time principles and single-piece
part flow help to minimize waste makes
CFIGURE 2 Unloading one sheet of cut parts on top of another can lead to
scratched parts.
a fabricating operation a formidable
competitor in the world market.
A fabricator must reduce non-value-added phases in manufacturing,
limit production costs, and maximize
production efficiency if it is to survive.
This can be achieved by not starving
the laser and by considering automation of parts removal, but the latter
requires a more in-depth discussion.
Don’t starve the laser. Lasers
employ impressive acceleration rates
and sophisticated control of laser
energy to deliver quality parts quickly.
The operational challenge is to balance laser processing time with loading and unloading of the system.
A far too familiar sight is seeing a
laser sitting idle—starving—while an
employee removes parts from the
unload area and stages the next sheet
for cutting to resume. Every moment
the laser is waiting is a missed opportunity. The cost associated with the
pursuit of competitive manufacturing
keeps going up.
Whenever the laser is idle, high-speed part processing is not possible.
The principal advantage of the laser
cutting machine is nullified. That’s
why the goal of modern laser cutting
should be to limit production stops to
spark-to-spark time—the time production is stopped after the final spark
of sheet current to the first spark of sheet
next.
Consider automated parts
removal, but keep an eye on unloading parts. Unloading laser-cut parts
poses an interesting set of challenges:
• Laser cutting is a thermal operation, and as material is being
processed, stress relieving can occur
and long, thin strips of scrap can bow
above the sheet or curl under the
parts. If the scrap region between parts
bows up, it can cause the laser head to
“track” an incorrect surface height
from the previously processed item,
instead of the true dimension of the
current part.
• Internal pieces of scrap can tip or
rest between grids and interfere with
speedy removal of the material once
laser cutting is finished. Tip-ups and
ribbons of scrap are commonplace in
laser cutting (see Figure 1).
• Perimeter notches and contours
can cause binding points that may interfere with the efficient removal of parts.
Automation can help reduce starvation time by delivering raw sheets
and removing the processed nests.
However, unless the previously listed
challenges can be solved or mitigated,
the shop floor will continue to experience problems in achieving consistent, uniform stacking. If any of these
problems occur, employees must
unload and stack processed sheets in a
timely manner, or the bottom sheets
could be damaged as successive nests
are placed on top of one another (see
Figure 2). Of course, if manual part
unloading is necessary, part identification, part sorting, and scrap disposal
also must be manual operations.
It’s Time to Sort
Parts Automatically
How can manufacturers spend hundreds of thousands of dollars on equipment to eliminate manual processes
and then saddle the equipment with
manual delays? Sorting parts automatically must occur if laser cutting is to
be incorporated into a lean manufacturing environment.
The laser has the advantage of
being able to cut virtually any geometry. However, after laser cutting is
completed, interior and exterior scrap
remains on the worktable along with
the finished parts. In essence, what
you see is what you get.
The FABRICATOR | An FMA Publication
www.thefabricator.com | March 2007
