切割头喷嘴安装在加工头前端，有助于控制辅助气体的流速和流量进而会影响到激光切割机的切割质量。

激光光束的能量在反应气体(O2)中加热材料至高于母材燃点的温度

Energy from the laser beam heats the material (mild steel) to above the ignition temperature in the reactive gas (O2).

Fe+½O2→FeO

（氧化反应形成氧化铁）

Combustion-process Fuels the Burning of Iron Oxide

一旦切缝形成，材料就会从近乎垂直的切前面(薄的熔融层)被移除，切割过程中母材对激光能量的吸收主要是在这一层熔融层。受热材料的气化，底部喷渣，材料的热传导和熔化都会造成切割过程中热量的流失和损耗，因此为了满足加工效率，激光功率，工艺参数，切割头光学配比和喷嘴的选择就变得尤为重要。

Once the kerf has been opened, material removal is from a nearly vertical erosion front (thin molten layer). Absorption of laser energy is predominantly at this liquid layer during the cutting processing. The layer loses heat by vaporisation, by ejection of liquid material at the lower surface, by conduction and by melting of solid material as the cut advances. In order to ensure the quality of the workpiece and the efficiency of the process, the selection of the proper conditions is very important, such as laser power, cutting parameters, cutting head and nozzle.

切割条纹-当切割速度较慢时会造成切缝两边局部过多的热量沉积，从而导致断面条纹粗糙甚至会出现烧边现象。

Striations-The slow cutting speed will cause the local thermal accumulation，which will lead to rough striations even side burns.

切割速度快（左图）切割速度慢（右图）

喷嘴在激光切割中起着非常重要的作用，它的主要目的是将辅助气体释放到切割材料表面和切缝中，使在切割过程中产生的熔融状和气化的母材被排走，留下一个干净的切口。

The nozzle is very important in laser cutting. Its main purpose is to deliver a gas jet such that the heat generated by the laser beam (and the resulting melt & vapour) is blown away, leaving a clean cut.

如果喷嘴设计和维护不当，加工精度不够，就会造成气体的流速减弱，气流方向变得不稳定从而影响切割过程中材料的移除最终导致切割效果不理想。

If the nozzle is poorly designed (& maintained), the gas jet will not have the required velocity or directional stability to remove the molten material. 

目前主要有两种喷嘴设计: “低速喷嘴” (气体流速小于音速) 和“高速喷嘴” (气体流速接近音速) 。影响喷嘴性能的因素有切割头腔体气压，喷嘴直径，喷嘴内部形和喷嘴出口形状。

There are two basic designs: ‘Low Speed’ (gas velocity less than speed of sound) and ‘High Speed’ (velocities around the speed of sound). There are many factors that affect nozzle performance nozzles, such as chamber pressure , nozzle diameter, internal shape, nozzle exit shape and nozzle material.

低速喷嘴 VS 高速喷嘴

Low Speed Nozzle VS High Speed Nozzle

低速喷嘴

Low Speed Nozzle

Laval高速喷嘴

Laval High Speed Nozzle

为什么要选择高速喷嘴？

Why high speed LC nozzles?

有些材料如不锈钢和铝合金很难保证切割断面底部完全没有毛刺，因为它们的熔融态金属具有很强的粘性，因此在气流流速很低的情况下不易被移除，在断面底部重凝固形成毛刺。

Some materials such as stainless steel and aluminium alloy are difficult to cut because their molten material is viscous and cannot be easily removed with low gas speeds. 

高速喷嘴的工作原理与火箭和喷气发动机的排气原理相同，对进入喷嘴的气体有加速的作用，因此高速喷嘴对于粘性材料的切割能产生更好的效果。

High speed nozzles work on the same principle as a rocket or jet engine exhaust. The gas expands, pressure drops and the gas velocity accelerates to the design velocity at the nozzle throat region and accelerates to the supersonic gas velocity at the nozzle exit. The design velocity is determined by throat area, exit area, gas pressure, atmospheric pressure, nozzle inter shape and nozzle length.

而如果使用普通低速喷嘴，工件表面会气压随着切割高度的变化而产生较大的波动，导致切割效果不理想。

The gas pressure along the axis of the jet can vary a great deal with changing of the stand-off distance in the low speed case and variation in pressure on the work-piece surface will affect the ability of the gas jet to remove molten material at the cut front.

断面质量与喷嘴的关系

Relationship between Surface Quality and Nozzle

喷嘴温度：温度上升影响陶瓷环电容值从而造成跟随不稳定，连续生产时断面质量不可控。

Nozzle temperature: The high temperature of the nozzle will affect the capacitance of the ceramic ring and cause the instable stand-off distance, which will lead to the uncontrollable cutting quality during the production.

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