In short: Oxy-fuel cutting, also called flame cutting or torch cutting, cuts steel by burning it. A flame of fuel gas and oxygen heats a spot on the plate to its ignition temperature, a jet of pure oxygen is then switched on, the hot iron oxidizes almost at once, and the stream blows the molten oxide out of the cut. It works on carbon and low-alloy steel, and it goes through plate far thicker than any laser or plasma system in a typical shop.
The weak end is thin material. On sheet and medium plate the torch is slow to start, leaves a wide kerf and puts enough heat into the part to bend it, and that is the work a fiber laser has largely taken over.
How Oxy-Fuel Cutting Works
Look at the end of a cutting tip and you will see a ring of small holes around one larger hole in the middle. The outer ring feeds a mix of fuel gas and oxygen that burns as the preheat flames. The center bore carries oxygen alone, opened by a lever on a hand torch or a valve on a CNC machine.
First the preheat flames are held on the steel until the surface glows bright red. That is the ignition temperature, and it sits well below the point where steel melts. When the cutting oxygen opens, the iron at that spot reacts with it and turns to iron oxide, and the reaction releases heat of its own. That heat, helped by the preheat flames running just ahead of the cut, carries the reaction down through the full thickness as the torch moves along.
Iron oxide melts at a lower temperature than the steel around it, so the oxygen stream flushes it out of the kerf as slag. This is why oxy-fuel is described as a chemical process rather than a melting one. The flame only brings the steel to the point of burning; the oxygen does the cutting.
Fuel Gases
Acetylene
Acetylene burns hotter with oxygen than any other common fuel gas, above 3,000 °C at the inner cone. It brings plate up to ignition temperature quickly and pierces fast, which is why it stays the usual choice for hand torches, thinner plate and bevel work. It also costs the most per hour, and its cylinders need careful handling.
Propane, propylene and natural gas
These burn cooler at the tip but give off more of their heat in the outer flame, which suits long runs in heavy plate where the torch spends most of its time cutting rather than starting. Piercing takes longer. Plate shops running several torches through a full shift often choose them on cost, and natural gas piped in from the mains does away with cylinder changes.
Which Metals It Can Cut
Mild steel and low-alloy steel cut well because they meet both conditions the process depends on: the metal must reach ignition before it melts, and its oxide must melt at a lower temperature than the metal itself so the jet can clear it.
Stainless steel fails the second test. The chromium in it forms an oxide that melts far hotter than the steel and seals the surface, so the reaction stops. Aluminum behaves the same way, and copper conducts heat away too quickly to hold ignition temperature. Those metals go to plasma, a fiber laser or a waterjet, which cuts without heat at all.
Carbon content matters too. Once it rises past roughly 0.3 percent, cut edges can harden as they cool, and higher-carbon and many alloy grades need the plate preheated and cooled slowly so the edge does not crack.
Where Oxy-Fuel Still Earns Its Place
Heavy plate is its home ground. Cutting speed drops off only gradually as thickness rises, so a torch that works through 50 mm of steel can, given the right tip and enough oxygen, carry on through plate several hundred millimeters thick. Nothing else in a fabrication shop comes close.
The kit is simple. A hand torch needs two cylinders, regulators and hoses and no electricity, which keeps it on demolition sites, in shipyards and on farms. On a CNC gantry, several torches can run side by side from one program, cutting identical parts out of one large plate at the same time.
Heavy weld preparation is the other stronghold. Torches set at an angle in a bevel head produce the joint angle as they travel, and on thick structural sections that is often the cheapest way to get a prepared edge; our guide to weld-prep bevels sets out how the angle and land are chosen.
Where It Falls Short
Starting a cut takes time. On thick plate the torch can sit preheating for a long stretch before it pierces, and piercing deep plate throws slag back up at the tip, so operators start from the plate edge whenever the nest allows it. Rust, mill scale and paint all lengthen the preheat, and a clean plate starts noticeably sooner.
The heat goes everywhere. A wide heat-affected zone runs down the full depth of the edge, and on thinner plate the part bows as it cools. Below about 6 mm, keeping a long strip straight with a torch is a constant fight.
A torch-cut edge has to be read rather than assumed. A good face shows fine drag lines running almost straight down. Lines that sweep sharply backward mean the torch moved too fast or the oxygen pressure was low. A rounded, melted top edge points to too much preheat or too slow a travel speed, and slag fused hard to the bottom edge usually comes from the same speed or pressure balance being off. Grinding any of that away is labor added to every part.
Tolerances are looser than plasma or laser and the kerf is wider, so small holes and fine detail are out of reach.
Oxy-Fuel or Fiber Laser for Plate
Most shops split the work by thickness and by how busy the part is. On plate within what a fiber source cuts in one pass, a laser wins on speed, edge quality and finishing time, and single-pass capacity for every power level is set out on our high-power fiber laser cutters page. Past that, oxy-fuel is the tool. Plasma falls between the two, and our look at how hot a plasma arc runs covers what that does to an edge.
Plate weight is rarely what stops a laser. The worktable on our 4020 sheet metal laser cutting machine is rated for up to 3,800 kg, while a full 4 × 2 m sheet of 25 mm steel weighs a little over 1,500 kg. The bed takes heavy plate with room to spare, so the limit you will meet first is source power, not the table.
Busy parts are where the gap opens widest. A torch has to preheat and pierce at every hole, while the head on the 4020 moves between features at up to 70 m/min along its X and Y axes and pierces in a moment. The more holes and slots a part carries, the further ahead the laser gets.
If you burn plate today, send us the grades and thicknesses you cut most often with a typical part drawing, and we will sort out which parts a fiber laser would take off the torch table and which should stay on it. Show us the plate you burn
Common Questions
Is oxy-fuel cutting the same as flame cutting?
Yes, flame cutting, torch cutting and gas cutting all name the same oxygen and fuel gas process.
Can an oxy-fuel torch cut stainless steel?
Not in the normal way. The chromium oxide that forms needs far more heat to melt than the steel does and blocks the reaction, so stainless is cut with plasma, a waterjet or a fiber laser instead.
How thick can oxy-fuel cut?
Much thicker than any other thermal process. With a heavy-duty tip and a large enough oxygen supply, plate several hundred millimeters thick can be cut, and thin sheet is actually the harder job for a torch.
Why is the top edge of my cut rounded?
Too much preheat or too slow a travel speed. Turn the preheat flames down once the cut is running, raise the speed in small steps until the drag lines lean back only slightly, and check that the tip is at the right height above the plate.
Is oxy-fuel cheaper than laser cutting?
The equipment costs far less, and on very thick plate the running cost per meter is low. On thin and medium plate with many features, a fiber laser usually comes out cheaper per part once slower cutting and edge grinding are counted.
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- Show us the plate you burn, the grades and thicknesses you cut most often and a typical part drawing.
