Scaled Management Systems

Programmed logic control (PLC) operation


A metalworking company identified a trapping hazard on its 100-ton mechanical press during hot forging of brass components. There were two trapping spaces identified, one being created by a ram-driven piercing punch as it entered the die, and the second when the two halves of the vice die closed. Mistakes in order of operation have caused many serious accidents with presses.

Operators were required to reach near the trapping space with tongs and place a hot slug into the vice die. This operation required two hands to hold the set of tongs.


The press was modified and an air-operated interlocked guard was installed to prevent entrapment of the operator. This guard worked in conjunction with the clutch mechanism.

The press cycle included a PLC device to ensure the correct order of the guard and the operation of the ram. The controller ensured the programme maximised operator safety. The cycle of operation is as follows: –

  1. Treadle – close guard, close vice, open guard
  2. Place slug manually
  3. Treadle – close guard, ram / punch operation open vice, open guard
  4. Manually remove formed part

The interlocked guard was supplemented by fixed side and rear guards as well as a treadle cover to ensure it totally complied with health and safety regulations.

There can be other types of hazards associated with some hot metal presses. Heat stress and noise may also need to be considered. Noise attenuating surfaces and heat reflecting materials may be built into the safety guards.

Hierarchy of Controls:



  • The incorporation of a PLC device to control the order of operation has created a sophisticated guard.
  • There has been a reduction in incidents and injuries.