Many welding jobs involve a metal cutting step, whether in the fabrication shop or on a jobsite.
Two popular metal-cutting processes are plasma arc and oxy-fuel cutting. Both systems have advantages and disadvantages, so determining the best fit depends on numerous factors, including the type and thickness of the metal being cut, location of the job, power resources available and cost.
Oxy-fuel torches have long been a popular choice for cutting metal in the field due to portability benefits. However, technology advancements are making plasma a more portable option. Learn more about the basics of each process and factors to consider in choosing one for your application.
Plasma is an ionized gas that conducts electricity, created by adding energy to an electrically neutral gas. The energy is electricity and the gas is typically compressed air. Both elements combine in a chamber between an electrode and nozzle, causing the gas to become imbalanced, creating plasma gas. Air pressure forces the plasma gas through the nozzle, creating a concise constricted flow that is electrically conductive. The more energy added via the plasma cutter, the hotter the plasma arc becomes, providing more cutting capacity and efficiency.
Operations use plasma cutters for cutting and gouging, with the average hand-held system capable of cutting a maximum metal thickness of about 1 inch. Plasma typically requires a source for compressed air and electrical power. These are issues to consider when the application requires portability, though the reduced size and weight of plasma machines — with some smaller machines weighing about 20 pounds — make them a more portable option than ever. Also, the need for electrical power is not an issue on many jobsites, where engine-driven welder/generators are commonly available.
With oxy-fuel cutting, an oxygen/fuel gas flame preheats the steel to its ignition temperature. A high-powered oxygen jet is then directed at the metal, creating a chemical reaction between the oxygen and the metal to form iron oxide, also known as slag. The high-powered oxygen jet removes the slag from the kerf.
When using oxy-fuel torches, the type of fuel gas used may influence cut quality, preheating times and metal thicknesses. Cutters most frequently use four basic fuel gases in combination with oxygen for this process: acetylene, propane, propylene and natural gas. Operations typically choose fuel gases according to the cutting application, cost, heat output and oxygen consumption.
However, there are several factors to keep in mind regarding oxy-fuel cutting systems.
Operations normally use oxy-fuel torches for cutting only ferrous metals or those containing iron, such as carbon steel. For the most part, they are not used for cutting cast iron, aluminum or stainless steel.
And while oxy-fuel torches aren’t dependent on primary power or compressed air, they do require purchase of gas.
Cost considerations likely also will come into play when making the decision between an oxy-fuel torch vs. a plasma cutter. The initial investment in a plasma cutter is typically more expensive than an oxy-fuel system. However, oxy-fuel torches involve an ongoing cost for the necessary gases, which plasma cutters don’t require.
When choosing between plasma and oxy-fuel cutting tools, ask yourself: what metal do I cut most often, and what is the thickest metal I will cut? If the job consistently requires cutting thicker metals, the time and money saved by quickly cutting through thick metal with an oxy-fuel system makes a difference. On the flip side, if precision cutting of stainless steel and aluminum is important, a plasma system is the way to go.
The bottom line: Oxy-fuel torches and plasma cutters have a place in most metal-processing applications, and many operations will benefit from having both systems in their arsenal.
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