Best Methods for Cutting Steel Plates

What’s the most effective way to cut steel plates? The answer: it depends. Several factors need consideration such as the application, the required speed, and the thickness of the steel plate or sheet metal. Once these are evaluated, you can choose from four main methods to cut steel plates on CNC machines.

Choose From Oxy-Fuel, Plasma, Laser, or Waterjet Cutting Techniques

Oxy-Fuel Cutting (Flame Cutting) Oxy-fuel cutting, also known as flame cutting, is the oldest method for cutting mild steel. It is generally a simple process with relatively cheap equipment and consumables. Oxy-fuel torches can cut very thick steel plates, mostly limited by the amount of oxygen that can be delivered. This method can handle steel plates up to 36-48 inches thick, but most shapes are cut from plates 12 inches thick or less.

For material over 1 inch thick and as thin as 1/4 inch, flame cutting is a solid choice. It’s relatively slow, reaching speeds of about 20 inches per minute on 1-inch thick material. However, productivity can be easily boosted by integrating multiple torches simultaneously.

Properly adjusted, oxy-fuel torches can produce smooth, straight metal surfaces. There’s slight slag on the bottom edge and a slight rounding at the top edge due to the preheat flame. This surface finish is suitable for applications where no further treatment is needed.

Plasma Arc Cutting Plasma arc cutting is another excellent method for cutting mild steel. It’s much faster than oxy-fuel but with slightly lower cut quality.

The best edge quality is achieved with material thicknesses between 1/4 inch to 1.5 inches. Beyond this range, overall cut quality begins to degrade, although the smoothness of edges and dross performance remain good.

Compared to oxy-fuel, plasma equipment is costly. A complete system requires a power supply, water cooler (for systems over about 100 amps), gas controls, torch leads, interconnecting hoses, cables, and the torch itself. Depending on your application, the increased productivity might justify the extra cost.

Laser Cutting Laser cutting is ideal for cutting mild steel up to 1.25 inches thick. Beyond 1 inch, everything must be precise for reliable operation, including the material (laser-grade steel), gas purity, nozzle condition, and beam quality.

Although slower, laser cutting offers extreme accuracy, producing a narrow kerf and allowing for very precise contours and small holes. The cut edge quality is excellent, with minimal kerf and dross; edges are sharp and square with almost no slag.

Laser cutting machines are highly automated and reliable, enabling “lights out” operations. You can load a steel plate, hit start, and come back to find hundreds of parts cut and ready for unloading.

Waterjet Cutting Waterjet cutting is another excellent method for cutting mild steel, ensuring smoothness and precision possibly surpassing laser cutting, with no thermal distortion.

Moreover, there’s no thickness limit for waterjet cutting, though practical limitations make cutting over 6-8 inches thick impractical due to the length of time and tendency for water divergence.

The primary drawback of waterjet cutting is its cost. Initial equipment costs are usually higher than plasma but lower than laser. However, operational costs are higher due to the use of garnet abrasive.

Choosing the Best Method to Cuting Steel Plates

Consider these steps:

1. Thickness:

   • Use laser cutting for steel thinner than 0.080 inches.
   • Use plasma or laser for steel up to 0.125 inches.
   • Use waterjet, plasma, or laser for steel up to 0.250 inches.
   • Use oxy-fuel for steel thicker than 8 inches.
   • Use oxy-fuel or waterjet for steel thicker than 2 inches.
   • Use plasma, oxy-fuel, or waterjet for steel over 1.25 inches.

2. Precision and Cut Quality:

   • Most steel fabrication can utilize plasma cutting; however, be aware of the lower edge quality.
   • If you can’t tolerate heat-affected zones from oxy-fuel, plasma, or laser, opt for waterjet cutting.

3. Production Efficiency and Costs:

   • Opt for waterjet when production efficiency is paramount.
   • Choose oxy-fuel if low initial and operational costs are crucial.

4. Other Considerations:

   • Can you tolerate occasional slag on the bottom of the plate? If not, choose waterjet or laser.
   • Is a perfect round hole necessary in secondary processing? If so, opt for waterjet or laser.

If you’re unsure about the best method for cutting steel plates, you’re not alone. Many manufacturers and steel service centers experiment with different processes to find the best fit for specific materials, often equipping their machines with multiple cutting processes and additional tools like angle grinders. Trial and error often determine the most suitable process for specific steel types