Determination of friction law in dry metal forming with DLC coated tool

Frictional behaviour in dry metal forming is studied with a developed tribometer using aluminium specimens and a DLC coated tool. The ratio of flattened area by smooth tool surface starts to increase sharply after the occurrence of bulk plastic deformation. As deformation proceeds, the contact pressure and frictional stress on the flattened area decrease by following Coulomb's law, because once flattened surface leaves the tool surface. A friction law with a constant friction coefficient at low pressure and the associated frictional stress at high pressure is proposed and confirmed.