November 7, 2011
How press maintenance and safety intertwine.
Various factors must work in harmony to create a safety-conscious stamping environment. The press must be used and maintained properly, as should its safety systems. You should know how to use personal protective equipment (PPE), undergo safety training, and know how to identify hazards. Ignoring any of these factors, in fact, can create a hazardous workplace.
Metal stamping presses are designed for specific applications. Many machine designs are in use, but most of today’s stamping presses are of the gap-frame, straight-side, or transfer-press variety. Each press also is designed for specific tonnage requirements, bed areas (die spaces), stroke, and speed (strokes per minute). As long as you use machinery within specific design limits, the safety systems included in the machine—other than the point-of-operation guarding—generally will meet safety requirements.
But when you operate any machine outside of the design specifications, machine safety can be quickly compromised. Overtonnage and speed changes are some of the most common violations that can lead to an unsafe condition. Unless your machine comes equipped with accurate tonnage monitoring devices, you really do not know exactly what load is being generated within the machine. If you have a 400-ton die installed in a 500-ton press, you may be overloading the machine.
Various elements affect the die’s tonnage requirements, one being die height settings. Say you decrease the die space to make a good part; in reality, that means, “I will get a good part if I hit it harder.” Anytime you hit the workpiece harder and exceed the machine’s tonnage rating, you create a safety hazard. And, of course, you always risk mechanical failure if an overload occurs.
Die positioning is another critical factor. Metal stamping presses are designed for distributed loading. If you have a 300-ton, two-point machine, you do not have 300 tons of pressure available at all points within the die space. If you move the die to the right or left sides under the connection assemblies, as shown in Figure 1, you have only about 60 percent of the machine tonnage available. So if this machine is designed for a 300-ton load capacity, and you move the tool under one connection assembly, you have only about 180 tons of pressure available. This means that if you put a 250-ton die in a 300-ton press in the wrong position, you will overload your machine.
Metal stamping press safety regulations protect against many hazards, which is why these regulations are so critical. When an accident occurs, everyone loses; this includes the injured individual, of course, but it also includes the entire company, which undergoes a significant loss in production.
Press controls are designed with cross-checking circuits that prevent unintentional machine actuation. In addition, point-of-operation guarding—properly sized, installed, and maintained—will enhance machine safety. Most operations maintain these controls at a reasonable level. But other safety system elements commonly are overlooked.
For instance, is there a safety cable that ties the motor to the press frame? Are there guards over the top of all open counterbalance cylinders that shield against mechanical failure of the machine? Are the clutch and brake assemblies excessively worn?
Every press comes with an operator station, but presses may have several operators, including people loading and unloading. Everyone must have a set of palm buttons, unless light curtains are protecting these additional operators.
As long as the flywheel is turning, the machine has stored energy. If that energy releases, the machine can cycle, and you might be in harm’s way. Say a toolmaker lies on his back, on a piece of cardboard placed over the lower die shoe, to polish tooling marks out of the upper die shoe—and works with the flywheel turning. If the press were accidentally cycled, he would be killed. Is saving a little time worth risking your life?
For this reason, any time an operator, die setup, or maintenance person works inside the die space, a die block must be there to protect that individual against unintentional machine actuation. Also, when servicing a machine, never climb down inside the crown or around any other pinch point, unless the slide is either blocked on location or is at bottom dead center.
You also should know how to identify hazards around the press. Sharp objects, including steel parts and coils, can create significant tripping hazards.
Many break the safety rules by failing to wear one of the simplest forms of PPE: safety glasses. Is it worth it? What would your family do if you couldn’t see? Hearing protection also is a challenge. If you enjoy music and talking with family and friends, use proper hearing protection when you’re in elevated-noise areas. If you can’t hear something you need to hear, you can always remove the protection long enough to hear what you need to, then put it on again. Protect your hearing; you can’t replace it.
Also, most metal components have sharp edges. You must handle these parts during the workday, of course. Simply wearing gloves and forearm shields can greatly reduce the frequency of cuts.
When working on a press, safety harnesses are a must. Anyone can slip. If you are 6 feet off the ground or on the edge of the machine pit and are focused on a certain press component, you can easily fall—and the landing is always hard. There is no soft place to land in a stamping environment.
Finally, wear safety shoes. Most stamping operations involve heavy components, and safety shoes can shield the pain. Some may think that when a heavy component falls on them, steel toes will damage their feet. Think logically about this: If the object that falls on you is heavy enough to crush the steel toe of your shoe, your feet would be in serious trouble—with or without steel toes.
Lockout/tagout procedures have come a long way in creating safer work environments. The law requires that employees be properly trained on the machinery they are required to operate. Sometimes management considers training an additional cost, so they don’t spend as many resources as perhaps they should.
Consider one automotive supplier that purchased a new 600-ton stamping press and had just finished the installation. The first production run was made on the evening shift. An operator who was not fully trained was assigned to set up the machine for production, which included installing a stamping die in the press. The operator opened the press and inserted the tool in the die space. He proceeded to install 2-inch parallels over the upper die shoe without checking the die-space setting. He cycled the press, holding the palm buttons, and had a 2-in. interference because the tool required no parallels. The press crashed, causing major damage to a $1.2 million machine (see Figure 2).
Consider another situation involving a service technician who climbed down inside the press crown. The machine was turned off and locked out, but the slide was not at bottom dead center—nor was the slide blocked. While the service technician was inside of the crown, the brake slipped and the gear train rotated, allowing the slide to fall to bottom dead center. The technician lost his life.
This shows just how critical safety is when it comes to machine maintenance. Take care to protect machinery and, most important, your workers from all hazards. Not only does proper safety training for operators and maintenance personnel increase throughput and help eliminate unscheduled downtime, this kind of training saves lives. That in itself makes it well worth the investment.
STAMPING Journal® is the only industrial publication dedicated solely to serving the needs of the metal stamping market. In 1987 the American Metal Stamping Association broadened its horizons and renamed itself and its publication, known then as Metal Stamping. Print subscriptions are free to qualified stamping professionals in North America.