Press-Brake Safeguarding Matters
EP Editorial Staff | February 16, 2018
Today’s advanced technologies offer safer, more operator- and production-friendly solutions than earlier approaches.
Press brakes are unforgiving machines, and a frequent source of workplace amputations of hands, fingers and arms. Statistics from the United States Department of Labor (dol.gov, Washington) indicate an average of 368 instances of amputations annually from press-brake accidents. And these are only the reported accidents.
Press brakes have a long history of productivity and danger. Hammers were the tool of choice for any blacksmith until 1784. That was when Scottish inventor James Watt came up with concept of the “steam hammer.”
The building of the first steam hammer in 1840 marked a turning a turning point for manufacturing with steel. The downside of this industrialization, though, was safety: it was largely disregarded in the rush to use labor-saving machines and processes. Developments of press brakes and other machinery occurred within a legal and regulatory climate that diminished employer’s interest in safety. In the process, while highly effective production methods became commonplace, for various reasons they often were unsafe. Manufacturing operations have come a long way since then in terms of productivity and safety.
Older press brakes, i.e., those built prior to 1985, were mechanical or flywheel types. Stopping times were long, making modern safeguarding techniques such as light curtains impractical. After 1985, press brakes were hydraulic, allowing a wider variety of safeguarding options with faster stopping times. Still, regardless of their age, press brakes present a unique set of dangers.
The primary safety concerns with press brakes involve access to the point of operation at the front of the machine and reaching around the safety device to get to the point of operation at the ends of the machine. Pinch points and hazardous motion created by the back-gauge system are also problematic. But the dangers don’t stop there.
However well intentioned, machine fabricators often employ lower cost, used, or refurbished press brakes that can make the primary controls and/or condition of the machine and safety system suspect. Because personnel in such enterprises may not have safeguarding competency, serious shortcomings can be overlooked or ignored. Plus, original equipment manufacturers (OEMs) generally consider the point-of-operation aspect of the press-brake safety system to be the end-user’s responsibility. The end user, in turn, may incorrectly assume that the machinery arrived on-site in full operating condition for commissioning. Lastly, press brakes have always been operator-intensive technologies—sometimes involving multiple operators. Unfortunately, operator behavior is not always predictable. That’s why it is good practice to make one operator the leader of the crew.
Training should be completed before any employee or operator is allowed to work near the press brake, and the employer should maintain accurate records of all training. Employees should also be encouraged to report press-brake hazards and make suggestions related to safety. Refresher training should be conducted as needed.
It is also good practice to develop and enforce a written safety program, one that incorporates guidelines for operating all machinery and performing tasks. Employees should be given a copy and provided training that emphasizes safe operating procedures, limitations of equipment, use of guards, and hazard recognition and control. Employers should monitor employee compliance with all policies.
There are two sources of press-brake regulations: OSHA and ANSI. Of the two, ANSI is considered the more specific and modern.
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 presses. The B11.3 adopted EN 12622 (European standard), giving it even more specific instructions to follow and minimizing any vague, gray 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,including, for example, the “close proximity point of operation AOPD” safeguarding devices, discussed later in this article, and a means of safeguarding referred to as “Safe Speed.”
PRESS-BRAKE PROTECTION OPTIONS
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 held by hand in close proximity to the point of operation during the braking process can potentially whip up as bending occurs.
A second approach involves pull-backs and restraints. These types of devices are restrictive and have limitations—and operators hate them. Both shackle the operator to a machine and restrict mobility.
The two-hand, down/foot-through device is yet another approach. While this method will work in some cases, it raises ergonomic issues and is very slow.
Then there are light curtains and laser active-optic protective devices (AOPDs). They represent more advanced press-brake safeguarding options. The diagram in Fig. 1 shows how these technologies work.
SHEDDING LIGHT ON SAFETY
Light curtains started out as simple product detection devices, then developed into machine-guarding solutions. Early versions used incandescent lamps strung together with a corresponding line of light detectors. Presses were one of the first machine-safety applications where safety light curtains were used. A light curtain is a photoelectric presence-sensing device. It protects against access into hazardous points and areas. These solutions range from very compact to larger, more robust and resistant models that can withstand demanding ambient conditions. 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 in the vicinity of point-of-operation hazards. This is done with 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, and it causes the machine to stop or it doesn’t allow a cycle until the blockage is removed. To not initiate this output signal, 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 established the following set of regulations for light curtains:
• The machine must be able to stop the movement of the ram anywhere in the stroke.
• The stopping time of the ram must be known.
• The stopping time of the ram must be monitored for deviation in stopping time on each stroke.
• The minimum distance the light curtains can be located to the pinch point must be known.
• The light curtains must be control reliable.
• The machine stop circuit, with which the light curtains are interfaced, must be control reliable.
• The light curtains must be self-checking for proper operation on each stroke.
• There should be no easy way to disable the safety system without special tools.
• If the safety system is disabled there should be a clear indication that it is disabled.
• The operator and setup person should be properly trained in the operation of the safety system.
A LASER FOCUS ON SAFETY
The laser AOPD, is the newest entry in the press-brake-safety-solution arena. Invented in 1998 as an alternative to light curtains, the systems were first used in the European Union before coming to the United States as a retrofit solution for existing press brakes.
Today, these systems have become standard for many press brakes, on imported machines and those manufactured in the U.S. Because of their close proximity point of operation, laser AOPDs are best suited for applications such as box bending, bending with flanges, or where light-curtain effectiveness is diminished due to excessive blanking or muting. 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 for implementing this technology safely (see B11.3 sub-clause 8.8.7 – Close Proximity Point of Operation AOPD Safeguarding Device).
The biggest advantage of AOPD is that operators can hand-hold parts close to the dies, while using a foot-switch to actuate the machine-cycle—something that’s almost impossible to accomplish safely with a light curtain. Another advantage is seen in the machining of larger-piece parts with tall side legs, a task that would be difficult using a vertically mounted light curtain for safeguarding. Such applications often require excessive “Channel Blanking,” which often allows hands and fingers to become too close to the dies.
SELECT THE RIGHT SAFEGUARDING SOLUTION
Light-curtain systems restrict operator access to the point of hazard, whereas laser AOPD protects the point of hazard. But that doesn’t make AOPD perfect for every application. Nor is it an either-or situation between the two approaches. There are advantages and drawbacks to both systems. In fact, the two technologies can be used on the same machine—and often are.
For example, light curtains provide for die configurations, such as compound bends that a laser AOPD won’t handle. 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 machined in a fixture-in-place manner, i.e., without hand-support, a two-hand control can be used for safeguarding. The table at the top of this page sums up the two systems. EP
The ‘Golden Rules’of Press-Brake Use
Basic safety procedures bear repeating. The “golden rules” of press-brake use can save body parts and lives:
• Keep work area clean, orderly, and free of oil, grease, or scrap.
• Use work supports, mechanical assists, or helpers when loading and unloading parts or heavy sheets.
• Wear PPE, i.e., gloves, goggles: never wear loose clothing, wristwatches, rings, bracelets, and other items, when operating machinery to avoid being dragged into the danger area.
• Never leave machine running unattended.
• Keep hands away from all moving items (ram, work pieces). Avoid trip hazards with foot switch and cord.
• Always lockout/tagout (LO/TO) equipment before performing maintenance, no matter how small the task.
• Never use damaged dies.
• Never attempt to tamper with wiring or bypass safety control. When finished, position ram at bottom of stroke and LO/TO.
This information was provided by Carrie Halle, a vice president of Rockford Systems LLC, Rockford, IL. To learn more about these technologies and other machine-safeguarding solutions, visit rockfordsystems.com.