Design of nozzles for automatic fiber laser cutting machine manufacturers

The nozzle used for laser cutting of automatic fiber laser cutting machine manufacturers adopts a simple structure, that is, a tapered hole with a small round hole at the end. Usually design with experiment and error method. Since the nozzle is generally made of red copper, the volume is small, and it is a vulnerable part that needs to be replaced frequently, so fluid mechanics calculation and analysis are not performed a. When in use, a gas with a certain pressure Pn is introduced from the side of the nozzle, which is called the nozzle pressure, and it is sprayed from the nozzle outlet and reaches the surface of the workpiece after a certain distance. The pressure is called the cutting pressure Pc, and finally the gas expands to the atmospheric pressure Pa. Research work has shown that with the increase of Pn, the air flow rate increases, and Pc also continues to increase. There are different pressure thresholds for different gases. When the nozzle pressure exceeds this value, the airflow will be normal. In order to further increase the cutting speed of clear light, according to the principle of aerodynamics, before the shock wave of increasing the nozzle pressure, the air flow rate will change from The speed of sound transitions to supersonic speed. The normal oblique shock wave of the airflow turns into a positive shock wave, the cutting pressure Pc decreases, the airflow speed decreases, and a vortex is formed on the surface of the workpiece, which weakens the effect of the airflow to remove the molten material and affects the cutting speed. Therefore, a nozzle with a tapered hole and a small round hole at the end is used, and the oxygen nozzle pressure is often below 3 bar.

Manufacturers of fully automatic fiber laser cutting machines design and manufacture a zoom-type nozzle, namely Laval nozzles, without generating positive shock waves. The laser center of the University of Hannover, Germany uses a 500WC02 laser with a lens focal length of 2.5The relationship between the surface roughness Rz of the incision and the cutting speed Vc under high oxygen pressure. It can be seen from the figure that the NO 2 small hole nozzle can only reach 2.75m/min when the Pn is 400Kpa (or the cutting speed can only reach 2.75m/min (carbon steel plate thickness is 2mm). Due to the multiple reflections of the oblique shock wave on the boundary of the airflow, the cutting pressure star periodically changes. 0.5~1.5mm, the cutting pressure Pc is large and stable, which is a commonly used process parameter for cutting handles in industrial production.