Nozzle and Gas Pressure

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A nozzle is a cone-shaped tip with a channel that directs the laser beam. The diameter of the nozzle orifice depends on the thickness and density of the material being processed.

The capacitive sensor's contact closes directly on the nozzle (usually through a ceramic insulator). The sensor generates signals that maintain the prescribed standoff distance between the nozzle and the workpiece during operation.

Nozzle materials

Nozzles are made of copper, which dissipates heat well and retains its capacitive properties at high temperatures. They are often chrome-plated to prevent molten metal droplets — blown out of the cut zone — from sticking to the nozzle surface. When droplets adhere, the optimum distance between the nozzle and the workpiece is lost, so non-plated nozzles need to be replaced more often.

Nozzle design types

Single (single-layer) nozzles are used to deliver nitrogen and inert gases for cutting stainless and other high-alloy steels, aluminum, titanium, zinc, and brass.
Double (double-layer) nozzles are used for oxygen cutting of low-alloy steels. Inside the nozzle there is an insert that delivers two different gases. The inner stream is pure oxygen (99.999 %), while the outer stream shields the oxygen jet from atmospheric air. The shielding is necessary because air contaminants alter the combustion parameters and therefore the machine's performance.

Choosing the orifice diameter

Nozzles are selected in inverse proportion to the gas pressure used.

The outlet orifice diameter is selected based on the thickness of the metal being cut. As material thickness increases, so does the nozzle orifice diameter.

The orifice diameter also affects the cross-section, velocity, and shape of the gas jet. The larger the diameter, the higher these values, the more efficiently the melt is removed, and the faster the cut.

There is no point in quoting specific figures (nozzle diameter), because in each individual case the values depend on power, focal length, standoff distance, and other parameters.

The slightest intrusion of atmospheric or other gases changes the combustion parameters and therefore the machine's performance. That is why the outer gas layer acts as a protective "sheath" for the inner gas column.

Nozzle functions

When the orifice is properly centered on the laser beam, the nozzle performs the following functions:

Protects the lens from dust, spatter, and foreign particles; directs the laser beam precisely into the cut zone.
Delivers the assist gas to the cut zone with flow control. This improves edge quality and prevents the formation of beads.
Ensures coaxial alignment of the gas jet and the laser beam.
Blows the melt out of the cut zone — melt formed when the laser heats the metal to its melting point.
With oxygen, an oxidation reaction occurs with the laser-heated metal. The heat released raises the temperature in the cut zone, increasing both cutting speed and the maximum cuttable thickness.
Nitrogen and inert gases (argon, helium) displace atmospheric air — which contains oxygen — from the cut zone. This prevents oxidation of the material. Cut edges remain clean and smooth, eliminating the need for mechanical descaling.
Cools the cut edges, preventing thermal distortion of the material.

Some versions are chrome-plated; the purpose of the coating is to prevent molten droplets blown from the cut zone from sticking.

The nozzle is one of the consumable parts of a laser machine. It is part of the laser cutting head and prevents rapid oxidation or scorching of heated surfaces.

Assist gas

The assist gas is sprayed coaxially with the laser beam to protect the lens from contamination and hot spatter; in some cases — when oxygen is used — to react with the metal and blow the molten slag out of the lower part of the cut zone; with stainless steel, it cools the metal and blows it out.

Gas pressure

Assist-gas pressure determines how effectively slag is blown out and therefore directly affects the final laser-cut quality.

Different metals require different optimum gas pressures. If the pressure is too low, the molten material cannot be ejected in time and sticks to the back side of the cut edge.

If the pressure is too high, it weakens the cutting capability of the laser beam, making the kerf wider and rougher.

Effect of assist gas on piercing

At low gas pressure, piercing is more difficult and the cycle time increases.
At excessively high gas pressure, the pierce point melts excessively and a large molten spot forms.

For this reason, piercing pressure on thin sheet is higher than on thick sheet.

Nozzle geometry

Gas pressure and the distance from the metal to the nozzle (standoff) are very important factors in laser cutting — they affect cut quality.

Fluctuations in the pressure gradient and lateral force on the cutting front are detrimental to slag removal by the gas jet, which leads to deterioration of cut quality.

Check the nozzle geometry a couple of times per day; if it is deformed, replace the nozzle immediately. A reminder: the nozzle is a consumable.

Nozzle types

Type A "Skirt". Standard truncated-cone tip. Named for its visual resemblance to a skirt. Poorly suited for cutting closely spaced contours (it tends to ride up onto the neighboring edge). Its advantage is that the sensor has significantly more time to prevent a probable collision of the nozzle with the cut edge.
Type B "Sombrero". Named for its visual resemblance to the Mexican hat. The cone is taller with shallow side-wall angles. Excellent for cutting closely spaced contours (does not ride up onto the neighboring edge). The drawback is that the sensor has significantly less time to react and prevent a collision with the cut edge, which can damage the coating or the ceramic ring.
Type C "Sombrero-parabola" (half-sombrero), high-speed. A sombrero with parabolic walls — a modification of the sombrero design whose geometry lets it smoothly "flow around" obstacles and avoid collision with the cut edge. High-speed nozzles are an intermediate option between classic nozzles and the sombrero. The parabolic profile gives the capacitive sensor more reaction time. Like the sombrero, high-speed nozzles allow cutting parts with closely spaced contours, but they perform worse than the sombrero in that respect.
Type D "Sombrero-arrow". A nozzle with a rounded tip, suitable for blanks up to 0.3 mm thick. Unlike a flat-head nozzle, this type does not drag the metal sheet along for the first few millimeters after retraction, and cutting accuracy is preserved. The shape prevents the sheet from "sticking" to the nozzle when the cutting head lifts.

Sombrero-type nozzles are mainly used on machines above 4 kW. However, the drive for material savings is pushing this type into machines above 1 kW.

Nozzle mounting face

For all the types above, the mounting face cross-section can be hexagonal or round. Hexagonal models can be used on machines with automatic nozzle changers. Without automation, either shape works.

It is important to understand that each shape has its own pros and cons.

Using the right nozzle shape helps avoid damage to the ceramic, sheet shifting, reduced cutting efficiency, and lower cut quality.

Popular brands

WSX — Chinese equivalent of the part from German manufacturer Precitec (Light Cutter). Compatible with most cutting head models. Material: high-quality copper. Available in single- and double-layer versions.
Raytools. Heavy-duty nozzles. Various sizes are produced depending on the task. Not compatible with IPG Precitec heads.
Unimach. Nozzles from a Russian manufacturer. Rated for high gas pressure. Material: copper alloy with chrome plating. Air blow-down for cooling.
Tag. Copper cylindrical nozzles for hand-held laser cutting of mild and stainless steel and aluminum.
IPG Photonic — copper conical part with chrome plating and a sharp tip. High precision. Designed for standard and micro-cutting. Compatible with Precitec, WSX, and other heads.
Bodor. Single- and double-layer nozzles, with or without chrome plating. High laser and gas precision. Long service life.