How To Cutting Metal Sheet Plate

How To Cutting Metal Sheet Plate

There are many ways to cutting sheet metal plate, but it will depends on the metal cutting jobs precision and speed, you can choose the best way for you sheet metal cutting jobs!

Someof which are suited for automation some are not. Some are suited 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. This article takes a quick look at the four primary methods used on CNC shape cutting machines, compares each processes strengths and weaknesses, and then gives a few criteria that can be used to decide which process is best for your application.

Oxy-Fuel Cutting for metal sheet cutting

Oxy-fuel torch cutting, or flame cutting, is by far the oldest cutting process that can be used on mild steel. It is generally viewed as a simple process, and the equipment and consumables are relatively inexpensive. An oxy-fuel torch can cut through very thick metal 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 done 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 suited for many applications without further treatment. 

Oxy-fuel cutting is ideal for plates thicker than 1 inch, but can be used 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 great thing about oxy-fuel cutting is that you can easily cut with multiple torches at once, multiplying your productivity.

Plasma Cutting Machine

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 I just mentioned), 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 opt for as many as three or four plasma systems on one machine, but those are usually high-end manufacturers who cut a high volume of the same parts to support a production line.

Fiber Laser Cutting with fast speed and accurate

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 is limited by the speed of the chemical reaction between Iron and Oxygen. 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 Machine

Waterjet cutting 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. Also, waterjet is not limited in thickness the way laser and plasma cutting are. 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 drawback to waterjet cutting is the cost of operation. 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, and this can even be done with a single intensifier pump. But each additional cutting head requires additional water flow that either requires a larger pump or a smaller orifice.

Sheet Metal Cutting Shears

Sheet Metal Cutting Shears, the first cousin of the venerable press brake, are commonly referred to as the “back bone” of the fab shop. (Maybe we should bump up the status of the shear to “little brother” to the press brake.) From light-duty fab shops to medium-duty fab shops to the heaviest of heavy-duty fab shops, one thing is identical in each operation: they all get their material in sheets. Sheets of this, sheets of that, every type and size of metal that can practically be moved, comes in a sheet. That makes the shear a pretty popular machine tool around a shop of any size.

In a rather unusual way, one could compare the metal shear to (of all things) a band saw! What’s the connection there? In the fab shop, the shear is typically the first machine to touch the material as it was received from the mill, right? You have to cut down the sheet of material to the needed part size to proceed with the production process. Likewise, in the chip making business, where either solids or tubes or shapes are being cut, the band saw is the first machine to touch that industry’s raw material. So, although they both do drastically different things, in a way they are the same, as producers of the first cut part in the production process.   

Sheet metal guillotine, metal guillotine, metal shear, metal shears, sheet metal shears, shear machine. People from all walks of life call the venerable old shear many different names, but they all mean the same thing. A stand-alone machine that will cut its maximum capacity every time you hit those buttons, and do it faster than any other machine in the shop.