Edge Quality in Laser Cutting Metal

When it comes to metal fabrication, precision cutting is important for many projects. When edges need to be pristine and cut beyond the tolerance limits of many modern methods, lasers come to the rescue.

Laser cutting often provides the very highest precision and edge quality, but there are a few choices at play even when using lasers. Primarily, laser cutting utilizes pure gasses at the point of cutting to control reactions and remove impurities from the area that could mar or damage the cut edge.

In the vast majority of cases, oxygen or nitrogen is used for this purpose with varying benefits and trade-offs. In some cases, argon or other blended gasses  might be used instead.

 This leads to an important question. Which gas is appropriate for laser-cutting metals?

Oxygen

Oxygen is one of the most common gasses used for metal laser cutting because it does not require high gaseous pressures. Oxygen is a reactive gas, and heated by laser applications, the oxygen itself can do roughly half of the work involved in cutting metals.

Because of this, oxygen laser cutting tends to move slowly, but the lack of pressure keeps cutting costs relatively low.

 Ultimately, oxygen is the preferred gas for cutting steel when there is a little more freedom in terms of edge quality. Oxygen cutting does oxidize the edges of cut steel, and when such edges are intolerable, oxygen is not viable as a gas choice.

Oxygen also enables a lower power system to achieve thicker than standard cutting when it comes to highly reflective materials such as brass, bronze and copper. 

Nitrogen is the other most common gas used in laser cutting metals. In most cases, when edge quality has low tolerance limits, nitrogen is the gas of choice.

Nitrogen

Nitrogen is the other most common gas used in laser cutting metals. Nitrogen is an abundant gas and easy to source, but nitrogen cutting requires high gaseous pressures. The pressures ensure a high concentration of nitrogen at the cutting site, which is important because nitrogen is largely an inert gas.

 The low reactivity of nitrogen allows for faster (I wouldn’t say faster but maybe higher energy input with less heat effect, on our lower power systems pure N2 is actually slower than both shop air and oxygen cutting) laser cutting with most metals, and the lack of oxidation produces precise, clean edges of very high quality. In most cases, when edge quality has low tolerance limits, nitrogen is the gas of choice.

Argon

Argon is an expensive alternative to nitrogen. Argon is even less reactive than nitrogen, but it is far more expensive to source. The advantage of nitrogen is that it can cleanly cut metals in the few circumstances where nitrogen is prone to reactions.

 The most notable case is with titanium. When titanium is cut at a high enough temperature, nitrogen can react with the titanium and produce low-quality edges. This can be avoided by controlling laser intensity and cutting temperatures, or the system can employ argon to avoid reactivity and accommodate a wider range of cutting temperatures.

Argon/Helium Blend

The ideal gas for ultra high quality titanium cutting, blends anywhere from 25% He to 50%, the helium enables faster cut speeds and very clean edges, however higher laser energy levels are required to maintain a dross free cut. This is the most expensive assist gas blend, and should be used for small batch, or very high precision/high quality cut edges. 

High Pressure Compressed Air

The lowest cost of all assist gasses, high pressure shop air is a widely versatile choice for a broad range of materials and thicknesses. Ideal for higher speed aluminum and stainless steel processing with lower laser energy, makes it a very economical choice for less sensitive applications. 

A minimum pressure of 300 psi is required with exceptional cleanliness and a -40c dew point to avoid any cut contamination. This can cause issues with delicate features on thinner materials. This method of processing can cause minimal introduction of oxidation on cut edges as well, gray or off yellow edges on stainless steel are common.