Table of Contents
Safety is and must always be your first, foremost and primary
concern! Even with all of the modern safety devices available the
press brake is a very dangerous machine. The loss of fingers, hands
arms is still a very real possibility. Especially, if you, the
operator, are not paying attention!
There are many safety related questions that should be
answered: Will the stops flip out of the way in time? Will the
ram come open far enough to get the formed piece? Is the backgauge going to crash into the tooling?
We'll start with the video an old government film from the 1940's;
it's fun to watch, but remember, basic shop safety has not changed.
The rules are still the same.
Toward the end of this chapter on press brake
and general safety we'll take a look individual
safety practices, but first well take a look at safety issues related
specifically to press brakes beginning with the mechanical press
The Mechanical Press Brake
The mechanical press is one of the most dangerous; it moves really
fast, moves only in one direction and has to complete the stroke.
average mechanical press is also capable of producing 150% of
at dead bottom of stroke.
Dead Bottom is where the
driven the eccentric to its lowest point; Top Dead Center
is at the highest point. On mechanical style presses the open height
and shut heights are fixed.
It is best practice to cycle the ram to just past
"top dead center" and pause. Bring the ram down slowly and come to
a complete stop .250-inches above the material, or less, what we now call the Mute Point.
Adjust the workpiece against the stops, and using the inertia
of the flywheel, slowly finish the bend, returning to
any point past top dead center,
When operating a flywheel driven mechanical press brake attention needs to be paid to "ram drift". If the ram
has not been brought
back up to, or past top dead center, there is a chance the ram could
start to drift down the wrong direction before the clutch re-engages. Even when
the clutch and brake assembly is in
adjustment there is a time lag between the brake's release and the
clutch engagement; this is the drift and it could lead to startling the operator and possibly
to an injury.
Also note that flywheel driven press brakes CANNOT
REVERSE THE STROKE! Regardless if fingers or hands
are caught, THE STROKE HAS
TO BE COMPLETED !!
Some machines were retrofitted at the power switch
so the electric motor could
be reversed. Even then, it takes a few minutes for the flywheel to wind down and than wind back up
before moving the ram in the opposite direction. And, the mechanical press brake has one speed, fast!
trying to operate any mechanical press
brake new to you, practice feathering the
pedal; learn to stop and control the speed.
A modern press brake
overall is a much safer machine (circa 2013). With light guards, CNC controls,
reversibility at any point in
the stroke, etc. However, some modern machines have
pinch points that the older press brakes
A pinch point is defined
two ways, one that relates to you and
the other, the press. On the press brake "pinch point" refers to the
point where the material is pinched between the punch and
die under a light load. The other is a place on the machine that can pinch you,
whether it's between the workpiece and the machine or between
different parts of the machine such as a forming robot.
Nonetheless, if operated in accordance with State and Federal
rules (OSHA) and with a little
common sense, injuries can become rarer. When they
do happen quite often it's operator inattentiveness or error.
Over Tonnage and
Tooling is the next safety concern. American style planed tooling
, as a
general rule, is relatively soft by tooling standards.
This tool steel is a high quality carbon
with a mean hardness of approximately 30 Rockwell-C throughout.
These tools are many times, flame hardened on the working surfaces for
Should you accidentally over-tonnage this style of
tooling, there would be a very
loud bang and a chunk of tooling most often fell to the floor; good reason for steel toed boots!
tooling, whether European, American or New Standard are
quite different; they are hardened to an average of
70 Rockwell-C. When these tools are overloaded, they tend explode with
some force and will throw shrapnel!
The tool shown in figure 3 is a precision ground,
single V-die that was over-loaded.
The tool exploded and the smaller piece, four inches long, razor
sharp flew 80-feet downrange and collided with the wall 6-foot from the floor; enough
Because of the importance of proper tooling selection, applied tonnages
and installation, you may not be aware of the real dangers that exist. First,
and foremost, you need to pay special attention; Press Brake safety is a common sense issue. Most accidents
are caused by operator inattentiveness or lack of
With that, lets start with safe tooling installation. Before any tooling
can be installed, the ram must be locked into the
position; the ram is in its most extended position.
Once the press is locked into that position and the ram can no longer close any tighter, the
tooling can safely be slid into the press. The gap between the ram and the bed should be just enough to allow
easy installation, but not so much as to allow the tooling to fall out.
Not all tooling can be loaded universally into any press brake.
Some can be
loaded correctly only one way.
The best way to envision if you are installing the tooling correctly is
to look at the tooling from the end view and check where the power is flowing, figure
Pressure flow through the tool on the left is incorrect and could be the
cause of serious bodily injury, not to mention the damage to the
press brake itself. Note the power flow and the force from the
forming are passing right by each other.
The tool set to the right shows a
ground tooling set installed
correctly. Notice how the power flows
through the tooling.
Of the three different forms of press brake tooling; New
Standard, European, and American Planed, Standard American
tooling is completely reversible as far as power flow is
concerned. But, the tooling can lose its center in the die, figure 5.
Non-safety note: It will also change the relationship from the
backgauge to the bend line.
European Precision Ground tooling is completely reversible as to
center, figure 6, but it can be installed wrong, figure 4.
Also check to make sure that the tooling
angles match correctly and are appropriate for the type of
forming that you are attempting, figure 7.
the punch and die angles need to match or the punch angle needs
to be less than the included die angle. For example, a 90° die
can use a 90° or an 88° punch.
When the tools are mismatched, best case, you get an ugly part;
worst case, you blow up the tooling.
Special care also needs to be taken to ensure that the total
applied tonnage does not exceed the abilities of the tooling or the
press brakes have placards placed on and around the machine. The
purpose, of course is to warn you about some aspect of the brake
at the point where it is most appropriate, for example, to warn
you of pinch points or electrocution hazards. Be sure you have read
them and read the manual that came with the machine. Figure 8,
courtesy of Amada USA, is a good example of the placards and
placement on the press.
You also need to be aware
that there are different levels of
Indicates an imminently hazardous situation, which if not
avoided can lead to serious injury or death.
Indicates a potentially hazardous situation, which if not avoided can lead
to injury or death.
Indicates a potentially hazardous situation, which
result in a minor or moderate injury.
The mute point is set at .250-inches above the material
thickness, and it is required that it be used. According to OSHA
guidelines, the press is closed to the mute point before any
part of your body is to get within 4-inches of the pinch point. At that point you can adjust the workpiece against the
backgauge and complete the bend.
The pictures shown in figures 9 and 10 show this concept. If the
press is not brought to the mute point a finger or hand can slip
between the punch and die, figure 9. Set at the
mute point, no part of your body can enter the die
Figure 9 Figure 10
Unfortunately, too many operators put way too much faith in
electronic safety devices. Light curtains work very well when
used properly. Always trusting the safety device rather than
practicing safety, thinking the device will protect you making
the mute point and other safety measures unnecessary, is the kind
of thinking that leads to injuries.
The idea behind a light guard is this: the ram must stop
movement before the operator can get part of the body in
between the punch and die. Light curtains are set several inches
from the front of the machine; if the beam is broken, the ram
stops. If the press cannot be stopped in time the light curtains
will continue to be moved further back from the front of the press until it
This is one of the reasons a mechanical press brake cannot be
adequately guarded. By the time the light curtains are far
enough from the front of the brake to meet the guarding
requirements, they make the mechanical
press brake functionally impractical.
Point of operation guarding
only guards the pinch point making
press brake guarding practical. These come in several forms:
cameras, two or three laser beams, even thermo-graphic
The following video shows an example of point of operation
guarding courtesy of
Never interrupt someone or allow yourself to be interrupted when operating
If you are drowsy walk away.
Dry run the program/press before using any material. No matter how good an operator thinks
he or she is, this is one thing that
should be done religiously before starting any job.
- When two or more people are working together on the same press brake,
only one should be in charge. This duty should never be
It should always be the operator in charge that makes sure that the
is clear of the press before beginning the bending process.
- Never apply pressure against the backgauge. Only a light
touch is necessary to produce a good part. Pushing against the back gauge
with unnecessary force sets the operator in the position of "leaning" into
the machine. One slip and you’re on your way into the dies. It also is an
inconsistent method of forming, as you cannot push equally time and time
- Have you ever given any thought to what happens if you get a
body part between the punch and die? It is not pleasant for
Look at figure 11, it is a picture of a finger sized pork bone
that has been formed; crushed beyond any repair regardless of how good your
doctor is. Now look at figure 12;
that is bone
marrow smashed from within the bone.
A good way to remember safety around the press
brake or any machine is this:
"The Press Brake does not like
you and will bite you badly the first chance it gets."
These figures are meant to show just what is
going to happen to the bone in your finger should you ever get one
caught in the press brake. If the splintering in
figure 12 isn't
enough to make you think safety, maybe the bone marrow (dark
spots) in the bottom of the die in figure 12 will help.
- Caution should always be used when reaching around behind
the tooling; make sure the backgauge has stopped
moving and is in position. If the backgauge moves while your hand is there, it could get smashed, figure 13.
- Always reach around or walk around behind the press brake, figure
Never reach between the punch and die sets for any reason.
- Never put any part of your body between the punch and die!
- Never let your fingers or a body part come between your workpiece and
the machine. Never hold your workpiece over the top of a previous bend,
- Keep your face and upper body out of the way for
workpiece movement. This will keep you from getting slapped in the chin or
face, figure 16.
Bad Safety Practices
It needs to be stated clearly; if there is a safety device
present on your press brake you are required to use it with no
exceptions!" The next three figures show three different
safety issues: one operator installed, one management ignored,
and one, that is management approved.
Kick-toe pedal, has a tab at the back of the pedal that must
first be moved with a light tap of your toe to release the foot
pedal and allow it to be depressed. In this
picture you can see that the operator
used a wire tie to hold the tab back out of the way, figure 17.
The safety device has been disconnected!
In this photo the Emergency Stop Switch has been covered up with
a piece of metal and taped in place. This was done to over 20
press brakes in one facility.
This is another example of a disconnected safety device; the
difference between this one and the first example? This one
last example is a down foot pedal that has been tapped and drilled
so that a bar could be added. The purpose was to allow the operator
to invoke the press at any point along the length of the bed without
the need to lift a foot up and under the protective cowling for the
factory foot bar.
Again, another example of disengaging the safety device on over 20 presses, but this
approval, figure 19.
What is the point? You are never to operate any
machine with the safety device disconnected! And, you cannot be
forced to run one that has that done to it.
The company featured in figure 19 is no longer in business in
part from the OSHA visit, one that found the press brake physically
modified; the fine was horrendous.
If and when you see something like these examples, correct it.
Remove the wire tie, remove the E-stop block or remove the
extra addition to the foot pedal. They're your body parts and they do not grow back. If
you operate a machine with the guarding altered, removed or
disengaged, you will assume some if not all of the responsibility.
You may not even have a worker's compensation claim; you may not even
get the hospital
Best advice... DON'T DO IT!
Some of you may remember Bozo the Clown and for
kids he's great, but a Bozo or someone like him does not belong in a shop
Depending on the incident, maybe you warn him once. Maybe
you fire him on the spot. Either way his ilk does not belong on the shop
A shop clown will at some point cause severe injury to you
or your co-workers.
Do not tolerate this guy!
Press Brake Safety courtesy of
Asma LLC reviews safety
from a slightly different perspective.
Press Brake Safety