Plasma cutting has become widespread due to the precision and quality of the cut, but traditional gas cutting remains utilized in a variety of processes.
Oxygen cutting retains prevalent usage for applications necessitating a high degree of mobility and maneuverability, notably for cutting thick steel billets.
Both methods confer respective benefits and limitations: material thickness, cut quality, maneuverability, and component cost constitute select considerations when determining the optimal selection. An examination of the relative merits of each process ensues below.
Metal cutting systems
Metal cutting constitutes a ubiquitous procedure across numerous welding applications, spanning fabrication workshops to hobbyist garages. Prominent metal cutting methodologies include plasma cutting and gas-oxygen cutting. While both confer respective benefits and limitations, the optimal selection remains contingent on several factors, including metal composition and thickness, job site locale, accessible energy sources, and cost.
Gas-oxygen torches have historically maintained popularity for field-based metal cutting owing to formidable portability. However, contemporary technological advancements have engendered enhanced transportability in plasma implementations as well. Subsequent sections delineate fundamental principles underlying each process and salient considerations when determining the most appropriate system for the application at hand.
Plasma cutting basics
Plasma cutting involves the use of ionized gas to cut metal. This plasma comprises a mixture of gases transformed into a high-velocity jet by an electric arc, achieving temperatures between 5,000-30,000°C. Plasma generation occurs by imparting energy, typically electrical, to a neutral gas stream – often compressed air. This energy is introduced within the chamber between the electrode and nozzle (primary consumable components), ionizing the gas. Resultant pressure differential propels this electrically conductive plasma through the nozzle aperture, yielding a compressed jet. Greater energy input corresponds to heightened arc temperatures and thus, improved cutting performance and efficiency.
Plasma torches facilitate cutting and gouging operations. Average handheld systems can cut metal up to approximately 3 centimeters thickness. Plasma cutting requires a compressed air source and electricity – considerations for mobility. However, ongoing size and weight reductions of plasma machinery – now as light as 9 kilograms – continue to improve portability. Additionally, power availability rarely impedes construction site usage, equipped with engine-driven welders and generators.
7 advantages of plasma cutting over oxygen cutting
1. Better cutting quality
Plasma cutting yields cuts with minimized scale formation, warping, and heat-affected zones. The highly concentrated energy creates narrow kerfs, reaching approximately 2.5 mm for 20 mm thick workpieces.
Plasma cutting mitigates distortion in thin sheet metals while providing smooth edges absent swelling or dross. This facilitates economical cutting schemes and welding unmachined structures.
2. More parts per unit of time
Despite excluding oxy fuel preheating and secondary machining, plasma cutting systems demonstrate clear productivity advantages over oxyfuel through substantially higher speeds.
High plasma cutting productivity arises from expedited processing across material thicknesses, abbreviated piercing times, and rapid torch deactivation.
3. Production cost reduction
The cost per workpiece associated with plasma cutting is lower compared to oxyfuel cutting due to the high production rate and even distribution of operating expenses. Specifically, plasma cutting enables the rapid production of numerous workpieces per hour, allowing fixed costs to be allocated across a large output volume. Additionally, plasma-cut edges typically require little to no secondary processing, further reducing per-part costs.
Modern plasma cutting offers extended consumable life, increased cutting speeds, and sufficient cut quality to minimize unit costs by up to 50% compared to conventional oxyfuel methods. Technological improvements in plasma power supplies, torch designs, and automation contribute to heightened productivity and competitive per-workpiece expenditures versus alternate cutting approaches.
4. High profitability
Plasma cutting is arguably one of the most cost-effective methods of thermal cutting currently available. The profitability of plasma cutting machines stems from reduced operating costs and improved productivity, as well as from minimizing or even eliminating secondary machining operations.
5. Easy to operate
One advantage of plasma cutting is that there is no need to regulate the gas supply or control the chemical reaction of combustion, unlike processes such as oxyfuel cutting. Plasma metal cutting machines are designed for contact cutting of sheets; therefore, no effort is required by the operator to maintain an optimal standoff distance between the torch and the workpiece.
The cutting parameters of automated plasma systems can be input and controlled with minimal actions, further streamlining equipment operation. Since contact cutting eliminates the need for standoff regulation and plasma cutting does not involve monitoring gas flows, manual plasma cutting systems have a shorter learning curve, allowing factory workers to become productive in less time.
6. Increased flexibility
Plasma technology can cut any conductive metal, including mild steel, aluminum, stainless steel, copper, and most other metal varieties. Unlike plasma, oxyfuel cutting relies on a chemical reaction between oxygen and iron, thus it is only suitable for low-carbon mild steel.
The flexibility and versatility of plasma cutting extends to other applications as well. For example, this technology can facilitate manual, guided, pipe, and coordinate table cutting. Furthermore, plasma systems enable gouging, marking, and cutting painted, rusted, and multi-layer overlapped metal sheets. While challenging with oxy fuel, plasma can perform both conventional and bevel cuts on metal grating.
7. Improved security
Plasma cutting systems utilize only compressed air to function, in contrast to oxygen cutting, which requires a mixture of oxygen and a fuel gas (acetylene, propane, propylene, or natural gas). Among these gases, acetylene is the most commonly used, as it provides a hotter flame and decreases piercing time. However, acetylene is an unstable and flammable gas that is sensitive to static electricity, as well as elevated pressure and temperature. As such, working with oxyfuel cutting equipment under these conditions cannot be considered entirely safe. The instability and flammability of acetylene highlights the potential hazards involved in oxygen cutting. In comparison, plasma cutting systems rely solely on compressed air, avoiding these risks and improving safety.
What is plasma cutting for?
Plasma cutting is performed on any type of conductive metal such as: non-ferrous metals, mild steel, aluminum and stainless steel. Mild steel cuts faster than alloys with a plasma machine.
Plasma cutting is ideal for cutting workpieces less than 25 mm thick. Plasma cutting is excellent for non-standard tasks, such as cutting metal foam: metal with a cellular structure, which is almost impossible to cut using oxyfuel cutting. Compared to mechanical means, plasma cutting is generally much faster and easier to perform non-linear cutting.
Fundamentals of Oxygen Gas Cutting
In gas-oxygen cutting, a burning gas preheats the steel to reach its ignition temperature. Subsequently, a powerful jet of burning oxygen is directed at the metal, which induces a chemical reaction between the oxygen and the metal to form iron oxide, also termed slag. The powerful jet removes the slag from the kerf.
When utilizing oxy-fuel torches, the quality of the cut, preheating duration, and thickness of the metal can be contingent on the type of fuel gas employed. In combination with oxygen, the four predominant fuel gasses most commonly utilized for this process are acetylene, propane, propylene, and natural gas. Fuel gasses are typically chosen based on the type of cutting, cost, heat output, and oxygen consumption.
Advantages and disadvantages of oxygen gas cutting
- Oxy-fuel systems are suitable for cutting thicker sheets of metal. A typical handheld oxy-fuel system is capable of cutting steel ranging from 15 to 30 centimeters in thickness. With the appropriate torch nozzle and mouthpiece selection, some oxy-fuel systems can cut steel even thicker than 30 centimeters. For steel over 3 centimeters thick, oxy-fuel torches generally offer higher cutting speeds compared to typical handheld 100-amp plasma cutting systems.
- Oxy-fuel cutting systems offer excellent portability for field use, as they do not require an electrical power source. Some compact oxy-fuel systems weigh approximately 15 kilograms. This allows operators to easily transport the oxy-fuel tanks, torch, and other system components to perform steel cutting in virtually any location.
- Extended length: oxygen torches can be extended lengths to keep the operator away from the heat, flame and slag generated during cutting. Most torch hoses are connected to a set of cylinders on a portable cart or to a stationary manifold system. The use of long hoses provides greater mobility.
- Process versatility: oxygen torches can perform cutting, welding, brazing, heating and gouging.
However, it has just as many disadvantages:
- As a result of strong heating, the cut parts can be deformed (especially from thin sheet metal).
- Sufficiently large cutting width, which requires certain allowances for marking work.
- Poor cut quality – edges are uneven with oxides and scale. Therefore, pre-treatment of edges is required before welding or other works.
- Quite high production cost of the oxy fuel cutting process.
However, there are several factors to consider when using oxy-fuel cutting systems: Oxy-fuel torches are typically only used to cut ferrous metals or metals containing iron, such as carbon steel. For the most part, they are not used to cut cast iron, aluminum or stainless steel.
And while oxy-fuel burners do not rely on primary energy or compressed air, they do require the purchase of gas.
When choosing between plasma and oxy-fuel systems, cost considerations are also likely to be a consideration. The initial investment in a plasma cutting system is usually more expensive than an oxyfuel system. However, oxy-fuel torches involve ongoing costs for necessary gases that plasma cutters do not need.
When choosing between plasma and oxy-fuel gas cutting tools, ask yourself: what metal do I cut most often and what are the thickest sheets to cut?
If the job consistently requires cutting thicker metal, the time and money saved by cutting thicker metal quickly with an oxyfuel system makes a difference. On the other hand, if precision cutting of stainless steel and aluminum is important, a plasma system is best.
Plasma and oxyfuel are used in most metalworking solutions, and many businesses would benefit from having both systems in their arsenal.