Nozzle Design and Airflow Control Technology: When laser cutting steel, oxygen and a focused laser beam are directed through a nozzle to the material being cut, forming an airflow stream. The basic requirements for this airflow are a large flow rate and high velocity entering the cut to ensure sufficient oxidation for a full exothermic reaction in the cut material; simultaneously, sufficient momentum to eject the molten material. Therefore, besides the quality and control of the laser beam directly affecting the cutting quality, nozzle design and airflow control (such as nozzle pressure and the workpiece's position within the airflow) are also crucial factors.
Laser cutting nozzles employ a simple structure: a conical bore with a small round orifice at the end. Design is typically done using experimental and error-based methods. Since nozzles are generally made of copper, are small in size, and are easily damaged parts requiring frequent replacement, fluid dynamics calculations and analyses are not performed. During operation, gas at a certain pressure Pn (gauge pressure Pg) is introduced through the side of the nozzle; this pressure is called the nozzle pressure. The gas exits from the nozzle outlet, travels a certain distance to the workpiece surface, and reaches its cutting pressure, called the cutting pressure Pc. Finally, the gas expands to atmospheric pressure Pa. Research shows that as Pn increases, the airflow velocity increases, and Pc also increases continuously.