Laser cutting is a modern metal manufacturing process that has transformed sheet metal part production. But what actually happens when a laser beam meets a steel plate? How do kilowatts, cutting speed and cutting gas affect the result? This article walks through the technical side of laser cutting in practical terms.
Modern industrial laser cutting machines use fiber laser technology. Unlike older CO₂ lasers, the fiber laser beam travels through an optical fiber — much like internet data through a fiber optic cable.
The fiber laser wavelength (1 064 nm) is excellent for cutting metals — metal absorbs it more efficiently than CO₂ laser light. In practice this means faster cutting and lower energy consumption.
Fiber laser efficiency is approximately 30–40% from electricity to light, while CO₂ laser efficiency is only about 10%. This means significantly lower electricity bills for the same cutting power.
Laser power is expressed in kilowatts (kW). Power directly affects how thick material can be cut and how fast cutting happens.
More power = thicker material or faster cutting. A 12 kW machine cuts 20 mm steel at a speed that would take far longer — or simply not be possible — with a 3 kW machine.
Cutting speed drops significantly as thickness increases. Typical speeds with a 12 kW fiber laser on steel:
| Thickness | Speed (m/min) | Cutting gas | Notes |
|---|---|---|---|
| 1 mm | 30–50 | Nitrogen/air | Very fast |
| 3 mm | 10–20 | Nitrogen/air | Fast |
| 6 mm | 4–8 | Oxygen/air | Good quality |
| 10 mm | 2–4 | Oxygen | Takes more time |
| 15 mm | 1–2 | Oxygen | Slow, precise |
| 20 mm | 0.5–1 | Oxygen | Normal max in series production — technical max at 12 kW is ~40 mm but not practical |
Kerf is the width of the slot burned by the laser beam — typically 0.1–0.3 mm depending on thickness and power.
You don't need to account for kerf in your drawing — the cutting software compensates automatically using an offset setting. Holes are cut on the inner path and the outer contour on the outer path, so the finished part is the correct size.
The cutting gas has a major impact on cut quality and edge finish:
Oxygen reacts chemically with steel and produces additional energy — enabling thick steel cutting. The downside is an oxidised (dark) cut edge which usually needs grinding before painting or welding.
Nitrogen is an inert gas — it doesn't react with the material. The result is a clean, oxide-free cut edge that can be welded or painted directly. The downside is higher gas consumption and cost.
The most affordable option. Suitable for thin sheet (1–6 mm). Quality is slightly below nitrogen but sufficient for many applications.
Bending means forming a cut plate to the desired angle using a press brake. The upper tool (punch) presses down and the lower tool (die) shapes the bend.
The key factor in bending is bend radius — too small a radius can crack the material, too large won't hold its shape. For steel, the minimum radius is typically 1× the plate thickness.
💡 Design tip: If you're designing a laser-cut part that will be bent, remember the bend allowance — material stretches at the bend point, so the blank must be shorter than the finished part dimensions.
Laser cutting and welding often go hand in hand. Laser-cut parts are accurate and straight, making welding easier and the finished result higher quality. Precise dimensions mean parts fit together without extra fitting before welding.
The most common method for structural steel (S235, S355). MIG (Metal Inert Gas) uses inert shielding gas, MAG (Metal Active Gas) uses active gas such as CO₂ or mixed gas. MAG is more common for steel. Fast, affordable and works well with laser-cut parts. The weld is strong but not as neat as TIG.
TIG (Tungsten Inert Gas) is a more precise and slower method. The welder feeds filler wire by hand while holding the torch in the other — requires more skill. The result is a neat, precise weld with minimal spatter. Especially suitable for stainless steel and aluminium. The straight, precise edge from laser cutting significantly simplifies TIG welding as the joint geometry is consistent.
Two metal sheets are pressed between electrodes and a large current is passed — the metal melts and joins without filler material. Fast and affordable for thin sheet (0.5–3 mm). Common in automotive, appliance and thin sheet structures. Laser cutting can produce precise holes for spot weld points.
A laser can also be used for welding in addition to cutting. Laser welding is extremely precise and fast — the beam melts material in a narrow zone so heat input is minimal and distortion is low. Especially suitable for thin parts and applications where aesthetic finish is important.
Steel cut with oxygen gas has an oxidised edge — it must be ground or cleaned before welding, otherwise the weld won't bond properly and won't pass NDT inspection. Steel cut with nitrogen can be welded directly without pre-treatment.
When designing laser-cut parts that will be welded together, a few things are worth keeping in mind:
Joint geometry — laser cutting gives a straight, precise edge that is ready to weld. For butt welds, no separate bevel preparation is needed for thin plate (under 6 mm).
Fixtures — laser-cut precise jigs can hold parts in the correct position during welding. This improves repeatability in series production.
Heat input — welding heats the material and can cause distortion. For thin plate (under 3 mm) this is especially important to consider in the welding sequence.
| Topic | Practical meaning |
|---|---|
| Fiber laser | Fast, energy efficient, precise |
| Power (kW) | More = thicker material or faster cutting |
| Kerf | 0.1–0.3 mm material removed by laser |
| Oxygen gas | Thick steel, oxidised edge |
| Nitrogen gas | Clean edge, higher cost |
| Tolerance | ±2 mm with laser cutting |
| Bending | Remember bend allowance in design |
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