Press Brake Safeguarding To Prevent Injuries

Including In-Depth Analysis of Light Curtains vs. Laser AOPD

Press brakes are unforgiving machines and a common source of workplace amputations of hands, fingers and arms. United States Department of Labor statistics indicate an average of 368 instances of amputations annually from press brake accidents. And these are only the reported accidents.

The primary reasons are access to the point of operation at the front of the machine, as well as reaching around the safety device to get to the point of operation at the ends of the machine. In addition, there are pinch points and hazardous motion created by the back-gauge system.

But the dangers don’t stop there. However well intentioned, fabricators often employ lower cost, used or refurbished press brakes where the primary controls and/or condition of the machine and safety system may be suspect. Plus, original equipment manufacturers (OEM’s) generally consider the point of operation aspect of the press brake safety system to be the end-user’s responsibility. The end-user may assure, incorrectly, that the machinery arrived into the shop ready for commissioning. Lastly, press brakes have always been operator intensive, sometimes involving multiple operators, and operator behavior is not always predictable. That is why it is good practice to make one operator the leader of the crew.

OSHA’s machinery and machine guarding regulations (29 CFR 1910 Subpart O) require one or more guarding methods to protect employees from exposure to hazardous machine energy during the operation of press brakes. There isn’t a great deal of detail to the OSHA regulations so fabricators in search of answers would be better served by turning to ANSI B11.3-2012 which covers safeguarding of power press brakes. The B11.3 adopted EN 12622 (European standard), giving it even more specific instructions to follow and minimizing any vague, grey areas.

ANSI B11.3 is the only safety system standard specifically applicable to power press brakes used in America, and it excludes mechanical power presses; hydraulic power presses, hand brakes; tangent benders; apron brakes; and other similar types of metal bending machines. It discusses hazards associated with the point of operation at length and identifies alternative guards and devices. For example, the ‘close proximity point of operation AOPD’ safeguarding devices, which we will discuss later in this blog, and a means of safeguarding referred to as ‘Safe Speed.’ We should note that ANSI B11.0-2015 recommends risk assessments of press brakes among other equipment, offered by Rockford Systems.

Today, there several ways to safeguard a press brake, some better than others. All have advantages and drawbacks.

The most basic type of safeguarding is a fixed and interlocked barrier guard coupled with two-hand controls. This is not a functional solution for fabricators as a work piece is hand held in close proximity to the point of operation during the braking process and can potentially whip up as bending is taking place.

Another approach are pull backs and restraints. Both are restrictive and have limitations and for that reason, operators dislike them. Both devices shackle the operator to a machine and restricts mobility. Yet another approach is the two-hand down/foot-through device. In some cases, this will work. However, this method raises ergonomic issues and it is very slow. Not what you want in a busy, production-driven fabrication shop.

A modern light curtain is a photoelectric presence-sensing device that protects against access into hazardous points and areas of the press brake. They can range from very compact to larger, more robust and resistant models that can withstand demanding ambient conditions. We should note that a stop-time measurement (STM) device is needed to calculate the safety distance on a regular basis, just as it is needed with two-hand controls.

Safety Light Curtains safeguard personnel using an LED transmitter and receiver. Any interruption of the plane of light by an object equal to/or larger than the “minimum object sensitivity” initiates an output signal. That could be a hand or a finger or a misplaced tool that will either cause the machine to stop or prevent a cycle until the blockage is removed. The operator must be outside the protected area through the entire stroke of the press brake ram. The safety distance between the light curtain and the machine depends on the application, the type of light curtain, and the machine’s stopping performance.

OSHA has a set of regulations for light curtains that are listed here:
1. The machine must be able to stop the movement of the ram anywhere in the stroke.
2. The stopping time of the ram must be known.
3. The stopping time of the ram must be monitored for deviation in stopping time on each stroke.
4. The minimum distance the light curtains can be located to the pinch point must be known.
5. The light curtains must be control reliable.
6. The machine stop circuit with which the light curtains are interfaced, must be control reliable.
7. The light curtains must be self checking for proper operation on each stroke.
8. There should be no easy way to disable the safety system without special tools.
9. If the safety system is disabled there should be a clear indication that it is disabled.
10. The operator and setup person should be properly trained in the operation of the safety system.

The newest entry into the press brake safety category is probably its most revolutionary, the Laser Active Optic Protective Device, more commonly referred to as the AOPD. Four manufacturers now make AOPD systems including LazerSafe™ a partner of Rockford Systems. Inclusion of Laser AOPD technology in the B11.3 is a welcome addition to the standard that now gives press brake manufacturers, dealers and users a clear guideline to implementing this technology safely. (B11.3 sub-clause 8.8.7 – Close Proximity Point of Operation AOPD Safeguarding Device)

The biggest advantage of AODP is that operators can hand-hold piece parts up close to the dies, while using a foot-switch to actuate the machine-cycle, which is almost impossible to safely accomplish using a light curtain. Another advantage is for larger piece parts with tall side-legs that would be difficult when using a vertically mounted light curtain for safeguarding. For those familiar with using light curtains, those two situations often require excessive “Channel Blanking” which “yes” allows for production of those parts, but often lets the hands and fingers to reach too close to the dies.

Laser AOPD protects the point of hazard whereas light curtain systems restrict operator access to the point of hazard. Operators can hand-hold piece parts up close to the dies with AOPD, while using a foot-switch to actuate the machine-cycle. This is virtually impossible to safely accomplish using a Light Curtain. But that doesn’t make AODP perfect for every application. AOPD systems are well suited for applications such as box bending, bending with flanges, or where light curtain effectiveness is diminished due to excessive blanking or muting.

There are advantages and drawbacks to both systems. And we would stress that it is not an “either-or” situation between light curtains and AODP. The two can be used, and often are, on the same machine. Light curtains provide for die configurations that the AODP won’t handle like compound bends, for instance. This is done to ensure that safeguarding is provided for all die setups. For die setups where neither light curtains or AOPD can offer effective safeguarding, but the part can be fixture in place, that is it does not require hand-support, a two-hand control can be used for safeguarding.

The diagram below sums up the two systems.

Press Brake Safeguarding Basics

Press Brakes are currently a hot topic in the “Machine Safeguarding” arena. OSHA regulations consider press brakes to be a 1910.212 machine, saying to the employer; “one or more methods of machine guarding shall be provided to protect the operator and other employees in the machine area from hazards such as those created by point of operation, in-going nip points, rotating parts, flying chips, and sparks” … 1910.212 requirements are good place to start, but they leave out the details of exactly how to go about safeguarding any particular machine. Therefore, a reference to an ANSI Standard like B11.3 on press brakes is often used to identify specific safeguarding alternatives. ANSI B11.3 may however need some help from ANSI B11.19 on safeguarding methods, to provide a complete picture of how to go about protecting people.

Older press brakes, like those manufactured in the mid-1980’s and before, were mechanical (flywheel-type) machines, some of which are still in use today. Because the stopping times on mechanical press brakes are long, equally long light curtain safety-distances result, making that safeguarding device impractical in many cases.

Press brakes manufactured after the mid-1980’s are much more likely to be hydraulic. Hydraulic press brakes allow for a wider variety of safeguarding options than mechanical press brakes do, and offer faster stopping-times, resulting in closer safety-distances where light curtains or two-hand controls are used.

A common method of safeguarding press brakes is with a vertically mounted infra-red light curtain. Hydraulic press brakes allow for short stopping times so that a light curtain can be mounted relatively close to the dies.

Two-hand controls on press brakes are often used in the sequence-mode of operation where the actuators bring the machine down and stop before the dies close, allowing just enough die-space to feed the part. The part is placed in the remaining die-opening, then a foot-switch is used to make the bend and return the machine to its full-open position.

Safety distance is required for both light curtains, and two-hand controls. That distance must be calculated with a stop-time measurement (STM) device on a quarterly basis. STM readings must be documented to show safety inspectors.

ANSI B11.3 which was updated in 2012, offers two completely new categories of protection for hydraulic press brakes: Active Optical Protective Devices (lasers) and Safe Speed Safeguarding. Active Optical Protective Devices (AOPDs) detect hands and fingers in a danger area. The biggest attraction for AOPDs are for jobs where the operator must hand hold small parts up close to the dies. A unique feature of AOPDs is that that they are designed to be mounted with zero safety distance, unlike light curtains that must be mounted at a calculated safety-distance, as outlined in ANSI B11.3. Safe Speed Safeguarding is based on a ram speed of 10mm per second or less, providing that speed is carefully monitored. Again, these two new methods of protection can only be applied to hydraulic press brakes (and potentially Servo-Drive Press Brakes).

The Lazersafe® Sentinel Plus is the most advanced guarding solution available designed specifically for hydraulic press brakes. The Lazersafe ties directly into the machine’s existing hydraulic and electric control circuits, providing a Category 4 solution. The Lazersafe is CE rated and allows machine operators to hold workpieces within 20mm of the point of operation. Encoder feedback ensures that the speed and position of the tooling is continuously monitored, and a 4.3” HMI provides machine operators immediate feedback of all vital functions. The Lazersafe Sentinel Plus is compatible with a wide variety of machines and tooling types, material thickness and easily allows for box shapes to be formed.

The backs of press brakes cannot be left wide open. Two hazards exist often exist here. The first is reaching the dies from the back. The second is the possibility of a multi-axis back gauge moving and creating pinch points. As to exactly what is required on the back of equipment often depends on local OSHA interpretation. The very least, an awareness barrier, like a railing, chain, or cable with a “Danger” or “Warning” sign, complete with Pictograms, not just verbiage. (see photo)

For local OSHA interpretations that won’t accept awareness barriers, a full perimeter guard may be the answer for the back of a press brake. That guard can either be bolted into position, or if it’s movable, an electrical interlock switch can be installed to make sure it stays closed.

As with any industrial machine, Lockout/Tagout on Press Brakes must strive for “Zero Energy State” to and within each piece of equipment using both locks and tags.

Also mentioned in the ANSI standard is die safety blocks; please see our related blog post on “Demystifying Die Safety Blocks”.

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