Analysis and validation of high-power laser machining with variable defocus for thick steel plates without assistant gas

This study aims to explore the feasibility of defocused laser cutting of thick steel materials without assistant blowing gas, as a basic research on applying laser technology to cut wellhead pipes at long distances at oil and gas drilling rescue sites. The influence of different defocus amounts on the cutting effect was analysed through laser cutting experiments on 20 mm thick 20CrNiMo steel plates under different defocus amounts. In addition, the research developed a novel cutting method, utilising optimised process parameters to achieve efficient cutting of 170 mm thick steel plates without the need for auxiliary blowing gas. The research results reveal the impact of defocus amount on the cutting performance of thick steel and verify the technical feasibility of cutting thick steel without auxiliary gas blowing. This study provides an important reference for defocus cutting technology and its industrial application in unassisted blowing gas laser cutting of thick steel plates.