Development and parametric study of a water-jet assisted underwater laser cutting process

The conventional underwater laser cutting process usually utilizes a high pressure gas jet along with the laser beam to create a dry condition in the cutting zone and eject out the molten material. This causes a lot of gas bubbles and turbulence in water, and produces aerosols and waste gas. This may cause contamination in the surrounding atmosphere, while cutting the radioactive components. In order to minimize this effect, a water-jet assisted underwater laser cutting technique has been developed using a high power fiber laser. A high velocity coaxial water-jet has been employed in place of gas-jet to remove the molten material through the kerf. Some amount of water vapour bubbles is formed at the laser–metal–water interface; however, they tend to condense as they rise up through the surrounding water. AISI 304 stainless steel sheet of maximum 1.5mm thickness was cut at 1.4m/min cutting speed with the present setup at 1800W CW laser power, and the resulting average kerf-width was about 0.75mm. The heat convection by water jet and the scattering of laser beam by vapour were found to influence significantly the energy efficiency of the cutting process. The effects of various processing parameters on the cutting performance were investigated. The energy efficiency improved at higher cutting speeds. An energy balance model with various loss mechanisms included has been also developed. ► A new method of water-jet assisted underwater laser cutting is reported. ► This process causes less water turbulence and aerosols in surrounding atmosphere. ► This process may be attractive for underwater cutting of radioactive components. ► Heat convective loss by water jet affects the process efficiency. ► A lumped heat capacity model accounting different losses is also presented.