How many kilowatts does your fiber laser need?

For most job shops cutting mild steel up to about 12 mm (1/2 in) and thin stainless, a 3 to 6 kW fiber laser covers the work. Move to 9 to 12 kW or more when you cut thick stainless or aluminium every week, need nitrogen-quality edges on plate, or the laser is your bottleneck.

Laser power is the first number on every fiber laser quote, and the easiest one to overspend on. A 12 kW machine will cut anything a 6 kW machine cuts, and faster. The real questions are whether your parts need that, and whether the rest of your shop can keep up with it.

Can you cut at the maximum thickness every day?

Not comfortably. Manufacturers publish a maximum thickness for each power level and material. Treat that figure as the upper limit the machine can cut with a good setup, good material and patience, not as the thickness you want to run all day. Near the maximum, cutting speed drops, piercing takes longer, edges get rougher and small setting changes matter more. Most shops plan everyday work comfortably below the headline figure. How far below depends on the part and on the edge quality your customers accept.

Published figures also vary between manufacturers for the same power class, which is why the table below gives ranges rather than single numbers.

How thick can a 3, 6, 12 or 20 kW fiber laser cut?

At the published maximum, roughly 16 to 20 mm of mild steel at 3 kW, 20 to 25 mm at 4 to 6 kW, 25 to 35 mm at 9 to 12 kW and 30 to 50 mm at 20 to 24 kW. Stainless and aluminium figures are lower on smaller sources and close the gap as power rises. These ranges come from published manufacturer cutting charts and datasheets. They are a starting point for a conversation, not a guarantee for any specific machine, so always ask for the cutting chart of the exact model and laser source you are quoted.

Laser power	Mild steel	Stainless steel (nitrogen)	Aluminium (nitrogen)
3 kW	16 to 20 mm	8 to 12 mm	6 to 10 mm
4 to 6 kW	20 to 25 mm	12 to 25 mm	12 to 25 mm
9 to 12 kW	25 to 35 mm	20 to 40 mm	20 to 30 mm
20 to 24 kW	30 to 50 mm	30 to 50 mm	30 to 40 mm

Typical manufacturer maximums, not guaranteed values (25 mm is about 1 in). Thick mild steel is normally cut with oxygen; on higher-power machines, thinner mild steel is often cut with nitrogen or clean dry air. Some manufacturers sell thick-plate packages or special processes that push the maximum well above these figures.

Speed: where extra power actually goes

On thin sheet, more power mostly means more speed. Published cutting charts give straight-line speeds like these:

Laser power	1 mm stainless (nitrogen)	3 mm mild steel
3 kW	15 to 25 m/min	3 to 5 m/min
6 kW	30 to 45 m/min	8 to 12 m/min
12 kW	50 to 70 m/min	15 to 20 m/min
20 kW	60 to over 80 m/min	35 to 45 m/min (nitrogen or air)

Those are straight-line speeds, and gas, nozzle and edge-quality settings differ between charts. Corners, small holes and pierces slow the machine no matter how much power it has, so on a nest of small, detailed parts doubling the power gains less than the chart suggests. The benefit also flattens as power climbs: going from 3 to 6 kW is usually a bigger jump in daily output than going from 12 to 20 kW on the same work. For small, precise parts in thin sheet, a compact machine such as the Gweike LF1390, an enclosed 1300 x 900 mm laser offered from 500 W to 3 kW, can make more sense than a large high-power bed.

Assist gas changes cost and edge quality

The gas you cut with affects running cost and edge finish as much as the source does.

	Oxygen	Nitrogen	Compressed air
Typical pressure	Low, around 1 bar (15 psi)	High, about 10 to 20 bar (145 to 290 psi) depending on thickness and nozzle	High, similar to nitrogen
Edge	Oxide layer that may need removing before painting or welding	Clean, bright and oxide-free	Darker, greyish edge
Usual use	Thick mild steel	Stainless, aluminium and visible mild steel parts	Thin and mid-range mild steel, stainless and aluminium
Supply	Cylinders, liquid dewars or a bulk tank	Cylinders, dewars, a bulk tank or an on-site generator	Dedicated high-pressure compressor with drying and filtration
Running cost	Low: little gas, because the burning reaction adds heat to the cut	Highest: high pressure and far more flow	Lowest gas cost once the compressor is installed

Ordinary shop air is not a substitute: it can damage the cutting head. An on-site nitrogen generator only pays off with steady, high consumption. Ask every seller for gas pressure and consumption at your typical thicknesses, because two machines of equal power can have very different running costs depending on how you plan to cut. Our fiber laser assist gas guide goes deeper into supply options.

Bed size

Match the bed to the sheets you buy and the longest part you cut. A 3000 x 1500 mm bed, often called a 3015, takes a 5 x 10 ft sheet and is the common starting point. Larger formats such as 4000 x 2000 mm and 6000 x 2500 mm suit shops that buy bigger sheets or cut long parts. A bigger bed costs more, takes more floor space and needs more extraction, so buy it for real parts, not for flexibility you may never use. Most production lasers have an exchange table so one sheet loads while the other cuts, as on the 3 x 1.5 m Gweike LF3015GA; plan floor space for it and for any loading automation.

When is a higher-power fiber laser worth it?

When thick material, a laser bottleneck or two-shift automation mean the extra speed will actually be used. Typical cases:

• You regularly cut stainless or aluminium above roughly 10 to 12 mm and want nitrogen-quality edges.
• The laser is your bottleneck and most jobs are long cuts in mid-thickness plate.
• You run two shifts with loading automation, so faster cutting is not wasted waiting for an operator.
• You want to cut mild steel with air or nitrogen at thicknesses where a smaller source would force you onto oxygen.

More power is harder to justify when most of your work is thin sheet with detailed parts, when bending or welding downstream is the real bottleneck, or when your electrical service would need a major upgrade (see 600 V power for imported machines). Higher-power sources also draw more electricity, need bigger chillers and cost more to repair. Many frames are offered across a wide power span, for example the HSG G3015H from 3 kW up to 30 kW, so you can often choose the source separately from the machine.

Look beyond the source

Compare the cutting head and whether it has automatic focus, the nesting software and its licence terms, the chiller, and the extraction and filter unit (our guide to fume extraction and laser safety covers that side). Also ask whether another process fits part of your work better: a tube laser for tube and profile, or a plasma table for thick mild steel where tolerances are looser and cost per metre matters more than edge finish. The fiber laser vs plasma comparison sets out that trade-off.

Checklist

• List your top 20 parts by volume with material and thickness.
• Mark the thickest material you cut every week, not once a year.
• Decide which edges must be oxide-free.
• Note your sheet sizes, your longest part and the floor space, including the exchange table.
• Check your electrical service and where a compressor or gas supply would go.
• Ask for the cutting chart, gas consumption and included options for every machine quoted.

Send us your parts list when you request a quote; we quote the machine together with freight, installation and operator training.