If you are a first time buyer or have existing installations of plasma and/or oxy-fuel shape cutting systems, continuous advancements in technology and an increasing landscape of low-cost manufacturers and integrators has clouded the automated plasma shape cutting machinery landscape.
Plasma cutting is the result of introducing a power arc through a gas that is blown through a nozzle at high pressure, inducing the gas to become plasma and producing a focused flame that reaches temperatures of 50,000 degrees Fahrenheit. Automated plasma cutting systems are classified as either conventional or precision (high-definition), on the basis of the characteristics of the cutting flame. Precision plasma systems can handle producing parts to tighter tolerances, achieving faster cut rates, and producing less kerf and bevel than conventional plasma systems. The price of these units can also be significantly greater than conventional plasma systems. It’s therefore extremely important to properly match the design cutting machine with the appropriate plasma cutting system.
One of the most common and costly pitfalls buyers encounter is when manufacturers or integrators mismatch machines and power sources. That is often the result of manufacturers not making the effort to know the buyer’s requirements, having a limited or single-product type of machines, limited OEM usage of power sources, and/or deficiencies in industry/application knowledge. These manufacturers will then often sell with a focus on lowest price rather than cheapest of ownership, highlighting the strong point of the plasma system or the machine without regard to the limitations of the other. The best precision plasma power source available will not provide users with the desired cut quality and accuracy if it is not mated to an appropriate base machine.
You can find many types of plasma shape cutting machines available on the market today. The most common machines are bridge or gantry style machines produced from either fabricated steel or extruded aluminum. Construction of the machine is incredibly important relative to your application. Machines made of extruded aluminum are normally regarded as being hobbyist or artisan machines and most appropriate when carrying out a limited level of cutting or when cutting light gauge materials. The plasma and oxy-fuel cutting processes create large amounts of heat that is retained in the materials being cut and could cause deflection or warping of aluminum machine components traveling on the hot cutting surfaces, greatly effecting accuracy and cut quality. Fabricated steel machines are highly recommended for any type of continuous cutting process, cutting of plate steel, and where auxiliary oxy-fuel torches might be used. Auxiliary heat shields are often available to further protect the machine and components from extreme heat conditions.
Cutting machines are available with a variety of drive systems including single-side drive, single-motor dual-side drive, and true two-motor dual-side drive systems. A well constructed single-side drive system or single-motor dual-side drive system will perform well in conventional plasma applications. The benefit of the excess precision made available from two-motor dual-side drive systems will not be realized in conventional plasma applications as a result of limitations in the precision of the standard plasma cutting process itself. Two-motor dual-side drive systems will give you the accuracy and performance required to reach optimal results from an accuracy plasma process.
Sizing of the motors and gear boxes relative to the mass of the machine can be extremely important. Undersized motors and gearboxes will not have the ability to effectively change the direction of the mass of the machine at high traverse and cut speeds, resulting in un-uniform cut quality and washed-out corners. This not merely affects the cut quality, but will even lead to premature mechanical failures.
The CNC control is the unit that ties together all the functionality and top features of the machine and plasma source. You can find basically two classes of controls applied to many of these machines today. Most industrial appli Oscillating knife digital fabric cutter cations use industrial PC-based control systems such as for instance those produced by Burny or Hypertherm. These units have user-friendly touchscreen display control panels and are housed in enclosures that can endure the harsh environments they operate in. Smaller machines of the hobbyist or artisan types often utilize standard PCs with I/O cards to regulate the drives and plasma systems. Industrial based controls are highly recommended for just about any application, are designed for industry specific requirements, are less prone to the conventional PC problems, but can be cost prohibitive in smaller applications.
Another important, and often overlooked, feature to consider when selecting a machine may be the construction of the rail system. Plasma cutting machines produce and reside in a harsh environment. It’s therefore critical that the components used in the construction of the rail system be robust enough to exist in this environment. All rail surfaces should really be made of hardened materials and cleaned frequently in order that they don’t become pitted and gouged by the splatter of molten steel that will inevitably fall on them. Self-cleaning wheels will also be a proposed feature to help keep the wheels clean between regular preventive maintenance (PM) cycles. Sizing of the rails must also be robust enough to avoid deflection as the machine travels across them.
The mixture of all the above factors results in the precision and accuracy of a system. Unlike other mechanical machining processes, it’s difficult to assign a regular tolerance to plasma cutting processes. Many manufacturers will strongly promote the fact their machines have positional accuracy of +/-0.007 in. and repeatability of +/-0.002 in.. The truth is that more or less any machine available on the market can hold tolerances that far exceed the tolerance and convenience of the plasma cutting process itself. There are many factors that will influence the cut quality you will achieve on your parts including: the characteristics of the part itself, power settings, consumables, gases used, material type, gauge/thickness of material, part layout on plate, etc.. Ask producer to offer you cut samples of your parts or parts that closely approximate the parts you is likely to be cutting, made on a machine/plasma combination that is comparable from what you are looking at. This will provide you with the most realistic representation of what you may anticipate from a specific machine/plasma combination and the plasma cutting process itself.
