BFIGURE 1 Any press brake safety evaluation should consider factors such as the application, part geometry, tooling, and brake type.
many operators just turn off the curtain.
Typical practice has been to allow the
operator to turn off the light curtain as
long as he uses another safeguard, be it
a two-hand control, pullback device,
physical guard, or something else. But
quite often the operator doesn’t use any
guard at all.
This doesn’t point blame at the operator. The reality has been that, until
relatively recently, many press brake
safeguards have been intrusive, and
often they’ve significantly slowed production.
Laser-based Protection
A A Safety Advice
One safeguard (not) for all
Press brake safeguarding requires a holistic approach
By Christopher King
Press brakes are one of the most versatile machine tools on the fabrication floor. Shops continually add new
tools, from specialized die sets, hemming tools, and flattening dies, to tools
for piercing, notching, and punching.
This has done wonders for the machine tool’s flexibility and efficiency,
but it also has made the press brake
one of the most challenging machine
tools to safeguard properly.
For years safety professionals, insurance representatives, and various other
inspectors realized that the technology
available for safeguarding devices was
either not practical for press brakes or
created its own hazards. For instance,
operators can become tangled in restraints, harnesses, and pullbacks, and
even lose control of the part. Other
times those evaluating press brakes didn’t have a clear understanding of the
technology. In the past the inspectors
saw how people operated the machines, witnessed the great variety of
parts going into them, and recognized
there was no practical way to apply
general-purpose safeguards and protect
operators for everything they needed to
do at the brake.
New safeguarding technology has
changed matters for the better. Be-
tween light curtains, laser-based systems that travel with the ram, two-but-ton control, and other guards, almost
any brake situation can be effectively
and reliably safeguarded with minimal
reduction in productivity.
Still, no one safeguard does it all.
OSHA inspectors look at press brake
safety holistically, and companies
should do the same (see Figure 1). It is
not about this light curtain or that
laser-based traveling system, foot pedal
usage and placement, two-hand control, restraining systems, or other
guarding devices; it’s about choosing
the best elements for the application
and designing a system so the safeguards work together to create a safe
environment for the operator.
Odd-shaped parts also can cause
light curtain issues, because certain
flanges may block the light curtain at
the wrong times, so the curtain must be
deliberately ignored to complete the
job. This can lead to “muting abuse” in
which the operator, for convenience
and efficiency, tells the system to mute
high in the stroke, so high that it ignores most obstructions and ceases to
function as a safeguard. “Blanking
abuse” happens when operators tape off
a series of optics on the curtain so it ignores side flanges, multiple bend progressions, and other procedures. Finally,
This changed with the advent of laser-based safety systems. Certain systems
(see Figures 2 and 3) mount directly
on either side of the ram; emit a beam
just below the punch tip; and monitor
the machine’s performance, including
its stopping distance and travel speed.
If an operator’s finger crosses the beam
while a pinch-point hazard exists, the
machine stops.
These beams also can be set up to
mute certain portions of the beam automatically. In a box bend, for instance,
the operator positions the flanges to
the side of or behind the tooling. The
laser system, drawing from information
in the part program, knows which areas
to mute to account for those flanges,
and which areas to keep active
throughout the brake cycle.
Certain laser-based, close-proximity safeguards watch the operation at a
much higher level than light curtains
or two-hand-control devices can. This
Wrong Guard,
Unsafe Operation
Using the wrong safeguard can be just
as bad as no safeguard at all. For instance, safety distance requirements
have meant light curtains—which emit
infrared beams in front of the work
area—must be installed a significant
distance from the pinch point, a measurement that varies depending on the
reaction time of the machine. To bend
small parts, operators may have to close
the tooling to a ¼-inch opening or less,
when the curtain mutes, and insert the
part. Or, more commonly, they just by-pass the curtain altogether.
CFIGURE 2 Laser-based safety systems travel with the ram, allowing for safe brake operation
when bending small parts. The system also monitors brake performance during operation to ensure the brake maintains a consistent stopping distance.
The FABRICATOR® | An FMA Publication
www.thefabricator.com | November 2009
