Diagonal cutting pliers are manufactured using drop forging, tempering (including induction hardening) and plastic injection moulding processes.
A chunk (billet) of metal is heated and roughly shaped using open-die drop forging machinery. Large rams are dropped onto the metal while a worker moves the piece around to create the rough shape of a handle and jaw.
The worker then places the billet on the anvil in the lower die (also known as a mould) of a closed-die drop forge. The die is shaped like a lever and jaw of diagonal cutting pliers. A ram with another die drops onto the billet forcing the metal into the shape of the tool.
The shaped piece is placed in a press which cuts off the excess metal.
Once the piece has cooled, the blades are ground and sharpened.
Two pieces are fitted together with a rivet, which is set in place using heat and pressure. The rivet is ground down so it is flush (level) with the surface of the pliers.
The diagonal cutting pliers are tempered to harden the metal. This involves heating them up to a high temperature and then ‘quenching’ them in oil to cool them down quickly.
Induction hardening is used to harden the surface of the blades even further. This process uses an alternating electromagnetic field to heat small areas of a tool, in this case the blades, before quenching them.
The pliers’ surfaces are ground to produce a smooth finish and the plastic handles are added over the top of the metal levers. This is done by dipping the handles into liquid vinyl once or twice and allowing the plastic to set or by using the injection moulding technique.
The injection moulding technique is where a metal diagonal cutting pliers piece is placed in a mould with a cavity around the handles. Plastic granules are heated to form a liquid and pressure from the drive unit forces the plastic into the cavity.
The plastic cools and the tool is removed from the mould. If the handles are made of two plastics then this process is repeated in a new mould. This is called ‘overmoulding’ because one plastic is moulded over the top of the other. The second material is usually a softer plastic or a rubber which forms rubbery grips to increase user comfort.
