Power press is a kind of industrial equipment that mainly used to shear, punch, form, or assemble metal or other material by means of tools or dies attached to slides.
They can be designed mechanical power press machine, hydraulic power press machine or pneumatic power press machine.
Divided by the ways they are powered, the machine tools can be categorized in to three types:
Tools and dies of mechanical power presses are mounted on a slide or ram. In general conditions, they would be moved away from the stationary bed containing the lower die.
When the elements arrive to the right place, the upper and lower dies would press together to punch, shear or form the workpiece.
Invented by Joseph Bramah, hydraulic power press machine is also as known as the Bramah Press.
This kind of press machine is powered with hydraulic cylinders to generate a compressive force, which is equivalent of a mechanical lever.
Basically, the hydraulic press depends on Pascal's principle which claims that pressure throughout a closed system is constant. Therefore, when the pistons that gearing with the cylinder works, the dies would meet and form the workpieces.
This kind of power press machine forms workpieces by the pressure comes from air compressors. Compared with the hydraulic power press, it does not have so much strength to provide the press like the hydraulic type does. However, pneumatic power press machine gains the property of quick operating and cleanliness.
From different working styles, power presses can be divided into:
- Full Revolution (Positive Clutch)
This machine would not be stopped once it is started. It would complete the whole working cycle of lowering and raising of the slide or ram.
During the working progress, there are no ways to stop the machine. Moreover, sensors would not work on this kind of power presses. In other words, this machine is dangerous.
Thus, for safety purpose, operators work with this machine should be protected by fixed guards or mechanical interlock guards during the whole working progress.
- Part Revolution (Friction Clutch)
The working progress of this machine could be shut down anytime in any of the steps. Compared with the full revolution, the part revolution is safer.
On this kind of power press machines, sensors would be a guard for operators. Therefore, operators working with this machine would not face so many risks compared with operators working with a full revolution version power press machine.
● Insert workpiece and start operation
Unavoidably, operators need to “interact” with the press machines. In this step, strain injury often occurs if the operators do not be careful enough.
When handling sheet metal into the machine, they should ensure that the machine is not working at that time.
Moreover, it is required to press the starting button after they completely take out their hands from the machine and put down the safety guards.
Nowadays, some operators would use mechanical aids, like automated material handling or robots, to hand the materials into the press machine.
● Entanglement when Placing Workpiece
When placing workpieces, deep cuts or amputation and crush injuries might occur if the operators’ clothes or arms being accidently involved into the machines.
To prevent this, it is suggested to do the protection below:
1. Use static fixed guards to separate the machine and operators.
2. Fit interlock safety devices that can stop the press machine’s movement immediately when opened.
3. Use sensors or emergency stops to ensure the machine could be stopped once the accident occurs.
4. Use light curtains with fixed and interlocked guards on part revolution power presses.
5. Use two handed controls as a back-up system.
● Contact impact or entanglement during operation
When the machine is working, it is highly possible that the operators’ clothes or accessories would be involved into the machines if they keep too close. It would result in deep cuts or amputation, crush injuries, bruising, and fractures.
Therefore, it is necessary to cover the controllers well to prevent accidental start-up.
● Maintenance, Cleaning and Repairs
When cleaning this machine tool, it should be careful and ensure the power is off that there are no any powers can operate the press machine. Otherwise, deep cuts, amputations, bruising, fractures might be caused.
This machine tool is useful. At the same time, it contains dangerous conditions. Sometimes, the accidents would be resulted in operating without carefulness.
It is often heard from news that operators hurt by the power press machines. Crushing injuries, amputations, and even death are damage the carefulness operating would cause. Among all the progression, die setting and troubleshooting are the two most dangerous process to do.
Therefore, operators working with power press machines should equip with the personal protective equipment (PPE) including ear protection, eye protection, hand protection, and foot protection.
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