Making the Cut: An Oxy Fuel Outfit Versus a Plasma Cutter
Chances are if you are considering a welder purchase, you have put some thought toward what type of cutting system you will need. The choices are fairly limited outside of the traditional saws and abrasive cutting equipment that have speed and capacity limits. Oxy Fuel Cutting and Plasma cutting both offer faster and larger capacity cuts while providing acceptable cut quality. It can be difficult to make a choice between the two. However, there are some distinct differences that can make the push toward one system or the other.
Oxy Fuel cutting (OFC) uses two gases (always oxygen, and usually acetylene) that combine and burn in a high temperature reaction to rapidly oxidize and "burn" the metal away. This process is good for cutting low carbon steels. Unfortunately aluminum and most stainless steel cannot be cut with the cutting process. Even small systems are good for cutting up to two inch thick plate steel. The cut is fairly smooth, but the kerf can be quite large and much metal can be wasted. The most common fuel used is Acetylene, though other fuels such as propane, MAPP, propanol, and other gases can be substituted. Acetylene gives the most thermal value when mixed and burned with pure oxygen. This allows shorter preheat times and faster cuts. Some torch systems allow the use of several different gases without major equipment changes other than the cutting tip.
Some Oxy-Acetylene may not support other fuels without major changes to the equipment. Oxy-Acetylene also offers a bonus feature of being able to weld different metals including steel and even aluminum together with a special welding tip. Other Oxy-fuels don't reach the required temperature to properly join most metals. Brazing can be done with alternative fuel torch systems, because the temperature required to braze is much lower. Soldering can be done with almost all fuel choices. Though limited to cutting mainly steel, it is effective for use in heating most metals for tempering and bending/straightening operations. Portability is only limited by size of the gas cylinders selected. Small cylinders can be bought in a portable pack, and larger ones can be leased. Due to governmental regulations, most companies will only lease the largest cylinders. Refill of personally owned cylinders when the gases are depleted can be problematic, especially when exchanging or refilling them at a company other than where the cylinders were originally purchased. Tank lease can run fifty to eighty dollars per cylinder per year. Many companies charge a higher price to refill customer owned cylinders as well. Every few years, the tanks must be tested as well, creating an additional expense. Leased or rented cylinders are usually maintained by the company that owns the cylinders and all testing is kept up by them. A drawback to using Oxyfuel systems is tank storage and management. Acetylene can pose a danger if not properly handled. It is held stable by dissolving the gas into a solution of Acetone, and a porous honeycomb material inside the cylinder. The gas is released as it is depressurized. Operating pressures must be carefully monitored as pressures over 15 psi, makes the gas unstable and dangerous. Oxygen cylinders and other gas cylinders pose risk by dropping or damaging. A tank with a broken valve can become a missile that can deliver deadly results. As long as the cylinders are handled properly and kept capped when not in use, any risk can be reduced.
Plasma Arc Cutting (PAC) can be used to cut virtually any metal, including stainless and aluminum. The high temperature flame exceeds 10,000 degrees Fahrenheit. The flame exits at supersonic speeds, making quick clean work. Accurate cuts can be made easily without special equipment. Almost anyone can learn to use a plasma cutter with very little instruction. Initial purchase cost for a typical plasma cutter is much higher than the usual investment required for Oxy-fuel equipment. Also, a plasma cutter requires a suitable air compressor to supply the ionizing gas to create the plasma. Demand is quite high, so a larger compressor will need to be purchased. On average, for most small plasma units, a minimum of 30 gallons and over 5 cubic feet per minute output at 90 psi will be required. Air dryers are a must. Dry air is essential to plasma cutting and must be considered as part of the maintenance price to operate. Electricity requirements must also be considered. Most plasma cutters capable of cutting more than sheet metal thicknesses will require 240V, and up to 70 amps. Inverter plasma cutters such as the Everlast PowerPlasma series reduce power consumption, though and lesson power demands over transformer based cutters. Consumables are also part of ongoing cost, with price ranging from ten to more than twenty dollars for a full set. Improper use and abuse can reduce consumable life to make it an expensive option. Most plasmas are limited in practical cutting thicknesses. Many companies offer a "real" cut range, and a maximum severance cut. Be sure to evaluate the real range when buying the unit as your base guideline. Most plasma cutters are not intended to make extended cuts at the severance cut thickness. With that said, most plasma cutters that would appeal to a small shop or homeowner will offer a real cut range under three quarters of an inch, not meeting the thickness of cut offered by even the smallest oxy-fuel systems.
Whichever cutting system you choose, both systems have limitations. No single cutting system will meet all cutting and welding needs. Most people eventually realize that both are needed. Carefully consider what kind of financial commitment you are able to make and what type of cutting process lends itself best to your shop environment.