Nozzle design and control technology
naky
www.diecastingpartsupplier.com
2015-09-11 13:54:32
Laser cutting steel, oxygen and focused laser beam is irradiated through a nozzle at the cut material, thereby forming a stream bundle. The basic requirements of the air flow is cut the gas flow into the larger, higher speed, so that sufficient oxidation makes the cut material sufficiently exothermic reaction; while there will be enough momentum to blow the molten material injection. So in addition to the quality of the beam and its control directly affects the cutting quality, the nozzle design and airflow control (such as nozzle pressure, the workpiece location in the gas stream) is also very important factors. Today laser cutting nozzle using a simple structure, namely a tapered hole with a small hole end. Usually trial and error approach to design. Because the nozzle is generally used copper manufacturing, smaller, is wearing parts, often need to be replaced, so do not be computational fluid dynamics and analysis. When you use from the nozzle side leads to a certain pressure Pn (gauge pressure of Pg) of gas, said nozzle pressure, is ejected from the nozzle exit, after a certain distance to the surface, its pressure, said cutting pressure Pc, the last expansion of the gas to atmospheric pressure Pa. Studies show that with the increase of Pn, air flow rate increases, Pc are increasing
Using the following formula: V = 8.2d2 (Pg + 1)
V- gas flow rate L / min
d- nozzle diameter mm
Pg- nozzle pressure (gauge pressure) bar
V- gas flow rate L / min
d- nozzle diameter mm
Pg- nozzle pressure (gauge pressure) bar
To further improve the laser cutting speed, according to the aerodynamics, increase the nozzle under pressure without a positive shock, design and manufacture of a zoom-type nozzle, namely Laval (Laval) nozzle. To facilitate the manufacture of the structure of FIG. 4 may be employed. University of Hannover Laser Centre use 500WCO2 laser, lens focal length 2.5〃 using orifice nozzle and Laval nozzle were tested separately, Figure 4. The test results shown in Figure 5: each represent NO2, NO4, NO5 nozzle at different oxygen pressure, as a function of the cut surface roughness Rz of the cutting speed Vc. As can be seen from the figure that the nozzle orifice NO2 Pn is 400Kpa (or 4bar) cutting speed can reach 2.75m / min (steel plate thickness of 2mm). NO4, NO5 two kinds of Laval nozzle in Pn as 500Kpa to 600Kpa cutting speeds up to 3.5m / min and 5.5m / min. It should be noted that the cutting pressure Pc is a function of the distance of the workpiece and the nozzle. Since the oblique shock wave reflection border several times in the air flow, so that the cutting pressure changes periodically.