September 16, 2010
A tube bender can be considered a collection of power presses and, as such, it needs more than just a few conventional barriers between the operator and the machine. Safety mats, interlocked switches, emergency-stop switches, and interlocked side plates are a few of the safety devices available to machine tool manufacturers.
Over the last 40 years or so, most tube benders sold in the U.S. have been equipped with a certain level of safeguarding to prevent operator harm. However, guarding an operator from injury 100 percent of the time is not always easy. After all, a modern tube bender can be considered a collection of synchronized power presses, all intended to form a tube into an infinite number of programmable shapes.
For example, consider a hydraulic clamp and a hydraulic pressure die, which commonly are found on typical CNC tube bending machines. Both devices can be considered power presses, and it’s no secret that a power press can develop enough force to cause an injury. To minimize the hazards, machine tool builders now must install protective systems that go beyond the traditional physical barriers.
CNC tube benders are intended to move automatically after a cycle is initiated. Usually a cycle initiates when an operator presses a set of dual palm switches that conform to an OSHA standard (see Figure 1).
Some end users demand that the operator maintain contact with both of the palm switches the entire time the machine is moving. Good practice demands an additional device, such
Physical guards that cover sprockets, chains, belts, and other moving parts also are expected. In addition, emergency-stop switches should be located within easy reach of the operator.
A common electrically interlocked guard found on most tube benders involves one or more side plates mounted to a swing (see Figure 2). These side plates are guards that protect an operator from the rotational motion of a swinging bend head as a bend is being formed. This rotating arm is a powerful press that can impart harm to an operator if used without care. This is where the guard plates come into play. If activated, they stop the motion of the bend head. Without this type of guarding, a tube bender usually is considered unsafe to operate.
Moreover, the interlocked switches should be the forced guided type and fail to a safe condition. Thus, a component failure, loose wire, or broken wire breaks a circuit and causes the bend head motion to stop.
Chain guards, safety mats, emergency-stop switches, and other such devices are considered essentials on modern CNC tube benders. Furthermore, another layer of protection can be employed to prevent collisions. For example, low-air-pressure switches can be used to prevent a machine from operating if the line pressure drops too much. This, in turn, can prevent unexpected machine motions, thereby preventing a potential injury. The same is true for the motion of certain dynamic devices found on a tube bender. For example, it should be the job of the software to ensure that the servo-controlled carriage (see Figure 3) does not run into the back end of the pressure die.
Likewise, the software should ensure that the pressure die does not try to wipe out the carriage. In short, it is the job of the software to prevent a motion that would lead to a collision.
All machine tools need preventive maintenance to extend the life of the machine. A good software package will alert an operator as to what needs inspection over the life of the machine. Adhering to proper inspection and maintenance procedures means that maintenance personnel must have access to all areas of the machine, and this is when an electrically interlocked guarding system can come into play. Such a system includes electrical boxes; the interlock prevents personnel from making contact with high voltage. Furthermore, safeguards such as a padlock and lockout tags always should be used when maintenance is required inside an electrical enclosure. In addition, touchproof devices, which commonly are found inside electrical boxes, can help to ensure personnel do not come in contact with high voltage.
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