What Is The Best Way To Cut Steel Plate – Elena
Oxy-fuel, Plasma, Laser, or Waterjet
There are many ways to cut mild steel plate. Some of which are suiteble for automation some are not. And some are suiteble for thinner plate, some for thicker. Some are fast, some are slow. Some are low-cost, some expensive. And some are accurate, some are not.
Oxy-Fuel Cutting
Oxy-fuel torch cutting, or flame cutting, is by far the oldest cutting process, we can use on mild steel. We generally view as a simple process, and the equipment and consumables are relatively inexpensive. An oxy-fuel torch can cut through very thick plate, limited primarily by the amount of oxygen that can be delivered. It is not unheard of to cut through 36, or even 48 inches of steel using an oxy-fuel torch. However, when it comes to shape cutting from steel plate, the vast majority of work is on 12 inch thick plate and thinner.
When adjusted properly, an oxy-fuel torch delivers a smooth, square cut surface. There is little slag on the bottom edge, and the top edge is only slightly rounded from the preheat flames. This surface is ideally suiteble for many applications without further treatment.
Oxy-fuel cutting is ideal for plates thicker than 1 inch. But we only can use all the way down to about 1/4 inch thick plate, with some difficulty. It is a relatively slow process, topping out around 20 inches per minute on 1 inch material. Another benefit of oxyfuel cutting is that you can easily cut multiple torches at once, increasing productivity.
Plasma Cutting
Plasma arc cutting is a great process for cutting mild steel plate, offering much higher speeds than oxy-fuel cutting, but sacrificing some edge quality. That is where plasma is tricky. Edge quality has a sweet spot that, depending on cutting current, generally ranges from about 1/4 inch up to 1.5 inches. Overall edge squareness starts to suffer when the plate gets really thin, or really thick (outside of the range), even though the edge smoothness and dross performance may still be quite good.
Plasma equipment can be pricy when compared to an oxy-fuel torch, since a complete system requires a power supply, water cooler (on systems over about 100 Amps), a gas control, torch leads, interconnecting hoses & cables, and the torch itself. But the increased productivity of plasma vs. oxy-fuel will pay for the cost of the system in no time.
You can plasma cut with multiple torches at once, but the additional cost factor usually limits this to two torches. However, some customers do choose multiple three to four plasma systems on one machine. But these customers are usually high-end manufacturers who cut the same parts to support a production line.
Laser Cutting
The laser cutting process is suitable for cutting mild steel from gauge thickness up to about 1.25 inch. Beyond the 1 inch barrier, everything has to be just right to make it work reliably. Including the material (laser grade steel), gas purity, nozzle condition, and beam quality.
Laser is not a very fast process, because on mild steel it is basically just a burning process that uses the extreme heat of a focused laser beam instead of a preheat flame. Therefore, the speed of the chemical reaction between iron and oxygen can limits that speed. Laser is, however, a very accurate process. It creates a very narrow kerf width, and therefore can cut very precise contours and accurate small holes. Edge quality is usually very, very good, with extremely small serrations and lag lines, very square edges, and little to no dross.
The other great thing about the laser process is the reliability. The consumable life is very long, and machine automation very good. So that many laser cutting operations can be done “lights-out”. Imagine, loading a 10’ x 40’ plate of 1/2” steel on the table, pressing the “Start” button, then going home for the evening. When you come back in the morning, you could have hundreds of parts cut and ready to unload.
Due to the complexity of the beam delivery, CO2 lasers do not lend themselves to cutting with multiple heads on the same machine. However, with fiber lasers, cutting with multiple heads is possible.
Waterjet Cutting
It also does a very nice job of cutting mild steel, giving a smooth and extremely accurate cut. Waterjet cutting accuracy can exceed that of laser cutting, because the edge smoothness can be better, and there is no heat distortion. Similarly, laser and plasma cutting methods will not limits the thickness of the waterjet. The practical limit on waterjet cutting is around 6 to 8 inches. Due to the length of time to cut that thickness, and the tendency of the water stream to diverge.
The cost of operation is the drawback to waterjet cutting. Up front equipment costs are usually a little higher than plasma. Due to the high cost of an intensifier pump, but not as high as laser. But the cost-per-hour to run waterjet is much higher, primarily due to the cost of the garnet abrasive that goes into the cut.
Waterjet cutting also lends itself to cutting with multiple heads. We can do this with a temporary make-up pump. But each additional cutting head requires additional water flow that either requires a larger pump or a smaller orifice.
