What does assist gas do in laser cutting?
When the laser beam heats the material enough to melt or react, the assist gas helps to remove material from the cutting kerf. The gas can also affect the amount of heat applied, the speed of the process and the surface and edge quality achieved. This means that the choice of gas is not a detail at the margin, but an important parameter in the whole cutting process.
In practice, gas is selected based on several factors: material type, material thickness, speed requirements, requirements for oxide-free cut surfaces and how the part will be used after cutting. For some jobs, low cost is most important. For others, getting a clean edge suitable for welding, painting or other post-processing is more important.
Oxygen in laser cutting
Oxygen is often used to take advantage of the extra heat generated when the oxygen reacts with the material during cutting. This reaction can provide high process energy and is suitable in many cases for cutting carbon steel. Oxygen enhanced cutting is well known in laser cutting because it can be effective in coarser materials or when the process window requires extra thermal support.
The disadvantage is that oxygen normally produces an oxidized cut surface. This can affect the next stage of production, for example if the part is later to be welded, painted or treated with high demands on clean edges. Therefore, oxygen is not always the right choice when post-processing places high demands on surface quality immediately after cutting.
Nitrogen in laser cutting
Nitrogen is an inert gas, which means that it does not drive the same type of chemical reaction in the cutting zone as oxygen does. Instead, it is mainly used to blow out the molten material while protecting the cut surface from oxidation. The result is often a cleaner and more neutral edge, making nitrogen a common choice when the part is going on to, for example, welding, assembly or surface treatment.
Nitrogen is often associated with high quality in the cut, but it also requires the right pressure, the right parameters and a functioning process set-up. For many applications in stainless steel, aluminum and thinner sheet metal, it is a very relevant option when you want to prioritize finish and minimize oxide formation.
Compressed air in laser cutting
Compressed air has become an increasingly interesting option in many productions, especially where reasonable edge quality is to be combined with lower gas costs. Several machine manufacturers describe compressed air as a way to maintain high productivity while reducing costs significantly compared to pure nitrogen cutting. For example, AMADA states that compressed air cutting can reduce the cost of assist gas by over 70% compared to the traditional use of nitrogen in some applications.
However, compressed air is not always used where the highest possible cut quality is required. The result depends very much on the material, material thickness and quality requirements. For the right application, compressed air can be a very effective option, but it must be assessed in relation to the function of the part and the requirements of the next production step. For example, the BLM describes that in some cases, high-pressure air can provide productivity on par with nitrogen, but at a lower cost.
Thor Ahlgren's offer in laser cutting
At Thor Ahlgren, it is more relevant to talk about the type of laser cutting they offer than to highlight assist gases as a stand-alone service. The company works with figure cutting in sheet metal, 2D laser cutting in flat sheet metal, tube laser cutting and complementary CNC machining. They also describe that they often produce, for example, shims and pulse wheels with high dimensional accuracy, especially in thinner sheet metal, and that the process is combined with post-machining for the right fit or surface finish if necessary.
This makes Thor Ahlgren a relevant partner for companies that need laser-cut sheet metal parts with good repeatability and the ability to move on to the next stage of production, rather than for those who are specifically looking for a supplier that profiles itself in assisted gas as a separate specialist area. Instead, their website highlights production experience, process breadth and the ability to combine laser cutting with other manufacturing steps.
Executive summary
Laser cutting with assist gas is an important area in modern manufacturing. Oxygen is used when you want to utilize reactive heat in the cut, nitrogen when you want a clean, low-oxide edge, and compressed air when you are looking for a cost-effective balance between quality and productivity. The best option always depends on the material, the thickness of the material and the end result requirements.