Process and unit for. plasma-arc working with a gas mixture based on hydrogen, nitrogen and/or argon

A process for the plasma-arc working of at least one workpiece, in which:

• (a) a plasma torch is supplied with an electric current and with a gas mixture containing hydrogen and at least one compound chosen from nitrogen and argon,
• (b) a plasma jet obtained by the ionization of at least part of said gas mixture containing hydrogen and at least one compound chosen from nitrogen and argon by said electric current is delivered by means of said plasma torch, wherein:
• the concentration of hydrogen in the gas mixture containing hydrogen and at least one compound chosen from nitrogen and argon is greater than 0% by volume and less than 50% by volume,
• said gas mixture is obtained by the addition of a defined amount of hydrogen to a gas containing at least one compound chosen from nitrogen and argon, said addition of hydrogen being carried out immediately before the gas mixture containing hydrogen and at least one compound chosen from nitrogen and argon is introduced into said torch, and
• the amount of hydrogen is defined according to at least one parameter chosen from the thickness of the workpiece, the grade of the constituent material of the workpiece, the desired work rate and the intensity of the electric current.