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Dross-free laser cutting stainless steel

A project at TWI has demonstrated that a specially developed nozzle for laser cutting, in combination with a high pressure gas, will produce clean, dross free cut edges in 3mm stainless steel.

The prototype nozzle was developed to counteract the problem of dross and oxide formation which occurs during normal low pressure oxygen cutting because of the high viscosity of the chromium oxides formed. Previously the only way that dross and oxide-free edges could be obtained was by using high cut assist gas pressure. TWI found that apparently the gas was not channelled into the cutting slot efficiently. Consequently, the desired momentum and velocity for dross removal were not always achieved and gas was wasted.

A survey by TWI indicated that, because of the high costs from excessive gas consumption, this technique had not been widely adopted by industry. The cost of machining the dross and oxide layer after the component had been cut using the normal oxygen assist technique was considerably lower.

TWI developed the new nozzle to supply gas at a very high velocity. The molten metal can be blasted away from the cut once it is melted by the laser beam. The continuous and immediate removal of the molten metal, together with the cooling effect of the gas, prevents sideways heat transfer and the metal beyond the gas jet zone remains unaffected.

Studies continue into gas dynamics in the cutting region, both at the laser's nozzle tip and inside the cutting slot. After the first project attention turned to developing high pressure cutting nozzle tips so that gas consumption is reduced while the improved cut quality possible with high pressure cutting is maintained.

Dedicated high pressure nozzles have been developed for cutting stainless steel but the same process, principles and equipment, may be applied to cutting a wider range of materials including aluminium and titanium alloys.

For information about TWI’s capabilities please email contactus@twi.co.uk

Clean, dross-free edge in 3mm laser cut stainless steel (bottom). Comparison with cut surface exhibiting dross from conventional low pressure oxygen cutting (top)
Clean, dross-free edge in 3mm laser cut stainless steel (bottom). Comparison with cut surface exhibiting dross from conventional low pressure oxygen cutting (top)
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