CFIGURE 3 A lead-in cut is sized to
the width of nearby slots so that it can
aid in the destruction of interior scrap.
CFIGURE 4 A cluster cut nests similar parts together in one area of the sheet.
CFIGURE 5 Software can help determine where to place parts to avoid tipped
parts or parts that fall between the grids.
Compare laser manufacturing to
punching and notice how interior
scrap is managed. By definition, the
punching process eliminates a portion
or all of the interior scrap. Once a
punching machine finishes with the
interior holes on a nest of parts, the
equipment operator will be left with a
sheet that is manually sheared or
tabbed portions that require a manual
“shake and break” sequence.
Punch/shear combination machines
were developed to eliminate many, if
not all, manual operations in the
punching process.
The greatest hurdle in eliminating
manual part separation in laser processing is managing both the interior
(see Figure 3) and the exterior scrap.
No other single concern in automating laser cutting comes close to the
challenge posed by developing an efficient means to separate scrap from finished parts.
Software Makes
Clean Sorting a Reality
create a final product that may look
like a “box” or help to reduce points or
notches within the bordering scrap
regions. Sorting software should not
impede the nesting ability to rotate
parts and optimize sheet utilization.
Technology, Nesting
Approaches Make a
Difference as Well
If an unloading device is capable of
rotating the part liberated from the
sheet and stacking the piece in routine
fashion, it helps to create optimal
nesting with optimal unloading.
Couple that feature with dual-head
unloaders, and fabricators can have
two pickup cycles with one pass, effectively optimizing unloading cycles and
increasing the odds of balancing laser
cutting with unloading throughput.
Dual-head unloading devices also
lend an advantage with large parts.
The two heads work together to pick
the large pieces and remove them
consistently.
In the case of very small parts being
cut, a group or cluster of parts can be
produced. The small parts are tabbed
into a blank and unloaded in one
cycle, to speed up manual separation
later. Small-part clusters also may be
paired with a larger part or placed in a
larger scrap window to help optimize
sheet utilization (see Figure 4).
Nesting pairs are often parts with
numerous holes or parts just too narrow to unload by themselves. The
parts may have “partner” pieces in the
material and thickness specs that
allow the parts to be tabbed together
and unloaded as one. Software can
index the part count correctly for real-time invoice update quantities.
Common-line cutting is an obvious advantage when sorting parts off a
laser cutting machine. Minimal scrap
is inherent in this process. Critical factors when dealing with common-line
cutting are the sequencing of the cuts
in the common line shared by parts
and the software’s ability to implement or abandon the common-line
approach as the application requires.
Finally, when permissible, total
skeletal destruction is possible, which
leaves the unload table bare of scrap
and full of laser-cut parts. In these
cases, the software intelligence to
destroy the interior scrap and exterior
skeleton truly positions automated
part unloading as a must-have tool in
any lean laser cutting operation.
In the end, what is the best scenario for laser cutting and automated
sorting? A fabricator cuts blanked-to-size parts and relies on nesting software that promotes common-line cutting. This is not reality, however. It is
for that reason that such sophisticated
software must evolve to make laser-cut
part sorting automatic and a practical
reality. ■
Liz Kautzmann is product manager, laser
technologies, Salvagnini America Inc., 27
Bicentennial Court, Hamilton, OH 45015,
513-874-8284, www.salvagnini.com.
A Check List of Parts-Sorting Issues
Here is a list of issues to keep in mind that might affect a move to automated
parts sorting:
• Over time, deterioration of the grids in the laser cutting machine bed may
cause microwelds to occur where raw material usually rests or where it comes
in contact with too much of the lower grid supports. As the laser travels along
the resting zones, the molten steel can’t be expelled properly, resulting in a
partial weld along the cutting line of the sheet in contact with the grid support. Although the microweld is not very strong, it becomes a cause for concern when it disrupts the consistency of the unloading device by causing it to
require multiple “picks” to free the part and break the weld. Preventive maintenance is vital to any laser’s performance, whether automated or manual.
Software developments to assist the
sorting devices can lead to a dramatic
advantage and may result in more
consistent automated part sorting.
Just as in a carefully orchestrated
chess match, each calculated maneuver must have a detailed and accurate
reply—not only to anticipate subsequent movements, but also to plan for
the final stages of the match.
Fabrication is no different.
It is imperative to keep in mind
that many of the challenges associated
with material handling after laser cutting may not occur on each nest.
Software thus needs to be able to
anticipate certain problems, respond
effectively to each occurrence, and be
flexible enough to address different
scenarios.
Take, for instance, free part nesting. Free part nesting refers to the
addition of perimeter cuts that either
• Also instrumental in consistent, automated processing is the assignment
of the unloading device pickup locations. In some systems, the assignment
may be manual and, therefore, time-intensive. In an automatic installation,
it’s desirable, if not mandatory, to have the gripping device (suction or magnetic) assigned automatically within either the nesting software or system
software. Calculating the optimal lifting locations is not always transparent;
the center of gravity, potential areas where tipping may occur (see Figure 5),
grid placement, and other factors all combine to influence consistent part
retrieval. Powerful software algorithms must be implemented to ensure the
unloading device has this capability.
• When the material thickness exceeds 7 gauge (0.179 in. or 4. 5 mm),
unloading must occur in such a way so it doesn’t pinch or trap the part within either the remaining nest or the scrap left on the table. Part binding can
occur if the lifting force is not delivered consistently or perpendicular to the
unloading surface.
• Placement of critical perimeter cuts outside the main geometry must be
factored into the nesting pattern to free parts from places where interference
may occur. Perimeter cuts are designed to liberate the laser-cut part from
scrap regions that may conflict with consistent unloading.
The FABRICATOR | An FMA Publication
March 2007 | www.thefabricator.com
• In some cases, eliminating all scrap on the table by evacuating it through
the conveyor under the table is required. Software should determine the precise number of cuts necessary to “tile” the larger regions of interior and exterior scrap so the resulting pieces will fall through the grids or table supports,
leaving just the processed parts staged for automatic unloading. Blanked-to-size raw material and common-line cutting mesh with this feature to enhance
sorting performance.
