Laser cutting machine nozzle design

When use from nozzle side ventilation with certain pressure Pn ( Gage pressure rated Pg) Gas, according to the nozzle pressure, from the outlet nozzle, after a certain distance to reach the surface of the workpiece, cutting pressure Pc, says the pressure, after the expansion of gases to the atmosphere pressure Pa. Research shows that with the increase of the Pn, airflow velocity increases, the Pc is also increasing. Can use the following formula: n = 8. 2d2( Pg + 1) V - L/mind - gas velocity MmPg - nozzle diameter Nozzle pressure ( Gage pressure) The bar for different gas pressure threshold, when the nozzle pressure exceeds this value, the airflow is normal oblique shock wave, transition from subsonic to supersonic gas flow rate. The threshold value freedom with Pn, Pa ratio and gas molecules ( n) Two factors: such as oxygen, air n = 5, so the threshold Pn = 1 bar x ( 1. 2) 3. 5 = 1. 89bar。 When the nozzle pressure higher Pn/Pa = ( 1 + 1 / n) (1 + n / 2 Pn； 4bar） Normal oblique shock wave, air sealing into normal shock, cutting pressure Pc drop, air velocity to reduce, and the workpiece surface vortex, weaken the effect of air flow to remove molten material, cutting speed. So the taper hole with small end round hole of the nozzle, the nozzle of the oxygen pressure is often under 3 bar. Laser cutting machine laser cutting steel, oxygen and focused laser beam is through the nozzle to cut CaiLiaoChu, thus forming a beam. Of the airflow into the incision are basic requirements of the gas flow, higher speed, so that make incisions enough oxidation material adequately exothermic reaction; With enough momentum to molten material injection blow out. Therefore, in addition to the beam quality and its control directly affect the quality of cutting, the design of the nozzle and air flow control ( Such as nozzle pressure, workpiece position in the air, etc. ) Is also very important factors. The laser cutting machine with nozzle USES the simple structure, namely a small round hole taper hole with end. Usually by experiment and error method to carry on the design. Because the nozzle is generally made of red copper, smaller volume, is quick-wear part, often need to change, so there is no fluid mechanics calculation and analysis.