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An overview of press brake safeguarding

The emergence of new laser-based camera vision systems changes how fabricators can approach safety at the point of operation

Figure 1
Press brake operators experience a greater risk of injury if they are working with small parts that require them to have their fingers close to the point of bending.

Press brakes are unforgiving machines and a frequent cause of workplace injuries. The U.S. Department of Labor reports that press brakes cause more than 350 amputations per year. And those are only the reported accidents.

With such risk at stake, most would expect manufacturers to be strongly committed to press brake safeguards, but that’s not really the case. As reported in Safety + Health magazine, a lack of machine guarding is consistently on OSHA’s top 10 most cited violations report, moving from No. 9 in 2015 to No. 8 in 2016.

In 2016 alone, 88 percent of the total number of OSHA machine guarding violations were classified as “serious,” meaning there is a substantial probability that death or serious physical harm could result and the employer knew or should have known of the hazard.

The fines for these violations are more than $7 million each year. Of course, the actual price tag for an injury is much higher than simply the OSHA citation. Its indirect costs must be taken into account, such as damage to facilities or equipment, medical expenses, lawsuits, lost productivity, and replacement personnel.

Why Are Press Brakes So Dangerous?

No matter its age, a press brake presents a unique set of dangers. The primary dangers are access to the point of operation at the front of the machine (see Figure 1) and reaching around the safety device to get to the point of operation at the ends of the machine. (In the U.S., press brake manufacturers often consider the point of operation to be the end user’s responsibility and therefore do not install required guarding. In Europe, when a machine leaves its point of manufacture, it is shipped with the guarding already in place.) In addition, pinch points and quick-moving backgauges also pose risks to press brake operators.

But the dangers don’t stop there. Fabricators sometimes employ used or refurbished press brakes on which the primary controls and the general condition of the machines and safety systems may be suspect. Fabricators may not have anyone on staff that has safeguarding competency, so serious shortcomings can be overlooked or ignored. Press brakes have always been operator-intensive, sometimes involving multiple operators, and their behavior is not always predictable. That is why it is good practice to make one operator the leader of the crew.

For a list of basic safety procedures, see the Golden Rules of Press Brake Operation sidebar.

The two safety codes that matter most in press brake operation are OSHA 29 CFR 1910 and ANSI B11.3-2012. The ANSI B11.3 standard is the far more specific of the two. Plus, with the recent adoption of the European 12622 standard in the latest version, the updated B11.3 has largely removed many of the vague parts of the original standard. U.S. standards often adopt European standards to augment or clarify an existing OSHA or ANSI standard.

ANSI B11.3 is the only safety system standard specifically applicable to power press brakes used in the U.S. It excludes mechanical power presses, hydraulic power presses, hand brakes, tangent benders, apron brakes, and similar metal bending machines. It discusses hazards associated with the point of operation at length and identifies alternative guards and devices. For example, it discusses modern press brake safeguarding concepts such as close-proximity, point-of-operation AOPD safeguarding devices (AOPD stands for active optoelectronic protective device) and working at safe speeds.

It should be noted that ANSI B11.TR3 recommends risk assessments of press brakes and other equipment. Risk assessments have proven over time to be the best and more comprehensive approach to establish an effective safety system. They should be performed when new machinery is installed, refurbished presses are put into commission, existing machinery has been upgraded, or work processes have changed in the bending area.

Figure 2
Physical barriers (top), restraints (middle), and two-button operation are some of the more traditional means of press brake safeguarding.

In addition, the risk assessment needs to be done after an accident or serious incident as part of an investigation. In general, it is good practice to perform a risk assessment every three years, even if no changes have been recorded.

Basic Press Brake Protection Options

Several options are available to safeguard a press brake. Some are better than others.

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

Pull-backs and restraints are another physical protection approach. Both are restrictive and have limitations. For that reason, operators hate them. Both devices shackle the operator to a machine and restrict mobility.

Yet another approach is the two-hand down/foot-through device. (The two hands have to be placed palms down onto two pads and the foot pedal has to be engaged before the ram comes down.) In some cases, this will work. However, this method raises ergonomic issues, and it is very slow. This is not what fabricators want in a busy, production-driven shop.

Figure 2 provides a glimpse at these more traditional safety measures.

Electrosensitive Protection Device Spotlight

The next level of safeguarding available to fabricators centers around electrosensitive protection devices. The most familiar safety tool in this category is the light curtain.

Light curtains started as a simple product detection device before evolving into a more complete machine guarding product. Early safety light curtains used incandescent lamps strung together with a corresponding line of light detectors—basically a reflector. Today they are photoelectric presence-sensing devices that protect against access into hazardous points and areas.

Most fabricators are familiar with light curtains because they have probably seen them in the form of yellow bars on the front of the press brake (see Figure 3). This type of system comprises a light curtain transmitter and receiver. They are wired into a safety monitoring relay and a pair of magnetic motor starters, which are part of the machine’s control circuit. A light curtain creates a sealed work area using beams of invisible infrared light that are spaced about 20 mm apart. If the operator reaches through the protected area, this press will either stop moving, or it will not begin the next cycle until he pulls his hand away.

Safety light curtains also can 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, a finger, or a misplaced tool. This causes the machine to stop, or it doesn’t allow a cycle until the blockage is removed. 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.

Figure 3
Light curtains, which many have undoubtedly seen positioned on each end of a press brake’s bed, cover a large work area and stop the ram should someone’s hand enter the work area.

With this type of setup, parts can bend up to the light curtain’s sensing field. In this case, it stops the cycle before it’s finished. One of two things can be done to prevent this from happening:

  • Just before the upper die touches the part, the light curtain can be automatically shut off for the balance of the cycle. This is referred to as muting. This is safe and recognized by ANSI B11.19.
  • If the light curtain is equipped with a floating blank feature, the part can bend up through the sensing field without stopping the cycle. This allows the light curtain to be active throughout the entire light curtain cycle, upstroke and downstroke. Floating blanking is usually selective for one or two beams, depending on the thickness of the part being bent. Simply put, if the operator is not blocking more than one or two beams at a time, as the workpiece swings up as it’s formed, the light curtain still functions, and the workpiece itself presents a barrier to the point of operation so that the machine operator can’t get his hands where they don’t belong.

OSHA has a 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.
  • The operator should have no easy way to disable the safety system without special tools.
  • If the safety system is disabled, the operator should have a clear indication that it is disabled.
  • The operator and setup person should be properly trained in the operation of the safety system.

Laser Focus on Safety

The newest entry into the press brake safety category is the AOPD. This gives operators close proximity to the point of operation (see Figure 4). An AOPD is best suited for applications in which a box is being formed or a workpiece has flanges and in which the light curtain effectiveness is diminished because of excessive blanking or muting.

AOPDs were invented in 1998. Laser AOPDs primarily were used in the European Union. In 2003 laser AOPDs started coming into use in the U.S. as a retrofit for existing press brakes. Laser AOPD has since become a standard system for many press brakes, both on imported machines and those manufactured locally. Inclusion of laser AOPD technology in the B11.3 standard is a welcome addition. It gives dealers and users a clear guideline to implement this technology safely. (More specifically, B11.3 subclause 8.8.7, “Close Proximity Point of Operation AOPD Safeguarding Device” addresses this subject.)

The biggest advantage of an AOPD is that operators can handle pieces up close to the dies while using a footswitch to activate the machine cycle. This is almost impossible to accomplish safely while using a light curtain. Another advantage is for larger piece parts with tall side legs, which are difficult to form on a press brake with vertically mounted light curtains. Those familiar with using light curtains on press brakes know that these two situations often require extensive channel blanking, which does allow production of those parts, but often lets the operator’s hands and fingers reach too close to the dies.

Light Curtains or AOPD?

Laser AOPDs protect the point of hazard. Light curtain systems restrict operator access to the point of hazard (see Figure 5). The AOPD’s design lets operators hold piece parts up close to the dies, while using a footswitch to actuate the machine cycle. This is virtually impossible to accomplish safely using a light curtain, but that doesn’t make AOPD perfect for every application.

In some instances, light curtains and AOPD can be used together, often on the same machine. Light curtains accommodate die configurations that the AOPD can’t, such as compound bends. Using both methods ensures that safeguarding is provided for all die setups.

For die setups in which neither light curtains nor AOPDs can offer effective safeguarding but the part can be fixtured in place and does not require hand support, a two-hand control can be used. Even basic press brake protection systems still have their place in today’s modern world.

Don’t Forget the Training

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 to 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.

Golden Rules of Press Brake Operation

  • Keep work area clean, orderly, and free of oil, grease, and scrap.
  • Use work supports, mechanical assists, or helpers when loading and unloading parts or heavy sheets.
  • Wear personal protective equipment, such as gloves and goggles. Never wear loose clothing, wristwatch, and rings when operating machinery to avoid being dragged into the danger area.
  • Never leave the machine running unattended.
  • Keep hands away from all moving items, such as the ram. Avoid trip hazards with the footswitch and cord.
  • Always lock out/tag out before doing maintenance, no matter how small.
  • Never use damaged dies.
  • Never attempt to tamper with wiring or bypass the safety control. When finished, position the ram at the bottom of the stroke, lock out, and tag out.