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 an electric arc via a gas that is blown via a nozzle at high pressure, inducing the gas to develop into plasma and creating a focused flame that reaches temperatures of 50,000 degrees Fahrenheit. Automated plasma cutting systems are classified as either conventional or precision (high-definition), based on the characteristics of the cutting flame. Precision plasma systems are designed for producing parts to tighter tolerances, achieving faster cut rates, and producing less kerf and bevel than conventional plasma systems. The cost of these units may also be significantly more than conventional plasma systems. It is therefore extremely vital that you 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. This really is often the result of manufacturers not finding the time to understand the buyer’s requirements, having a small or single-product type of machines, limited OEM use of power sources, and/or deficiencies in industry/application knowledge. These manufacturers will often sell with an emphasis on lowest price as laser fabric pattern fabric flatbed cutter opposed to cheapest of ownership, highlighting the strong point of the plasma system or the machine without regard to the limitations of the other. The most effective precision plasma power source available won’t provide users with the desired cut quality and accuracy when it is not mated to a suitable base machine.
There are many types of plasma shape cutting machines available on the market today. The most frequent machines are bridge or gantry style machines created from either fabricated steel or extruded aluminum. Construction of the machine is incredibly important in accordance with your application. Machines made of extruded aluminum are generally considered to be hobbyist or artisan machines and most appropriate when performing a limited number of cutting or when cutting light gauge materials. The plasma and oxy-fuel cutting processes create large levels of heat that is retained in the materials being cut and may cause deflection or warping of aluminum machine components traveling on the hot cutting surfaces, greatly effecting accuracy and cut quality. Fabricated steel machines are strongly recommended for any kind of continuous cutting process, cutting of plate steel, and where auxiliary oxy-fuel torches might be used. Auxiliary heat shields may also be available to help expand protect the machine and components from extreme heat conditions.
Cutting machines can be found 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 very well in conventional plasma applications. The benefit of the extra precision made available from two-motor dual-side drive systems won’t be realized in conventional plasma applications because of the limitations in the precision of the traditional plasma cutting process itself. Two-motor dual-side drive systems can provide the accuracy and performance required to achieve optimal results from an accuracy plasma process.
Sizing of the motors and gear boxes in accordance with the mass of the machine can be extremely important. Undersized motors and gearboxes won’t be able 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 system that ties together most of the functionality and features of the machine and plasma source. There are basically two classes of controls applied to these types of machines today. Most industrial applications use industrial PC-based control systems such as those produced by Burny or Hypertherm. These units have user-friendly touchscreen display control panels and are housed in enclosures that will endure the harsh environments they operate in. Smaller machines of the hobbyist or artisan types often utilize standard PCs with I/O cards to manage the drives and plasma systems. Industrial based controls are strongly recommended for any application, were created for industry specific requirements, are less susceptible to the typical PC problems, but could be cost prohibitive in smaller applications.
Another important, and often overlooked, feature to think about when selecting a device could be the construction of the rail system. Plasma cutting machines produce and reside in a harsh environment. It is therefore important that the components utilized in the construction of the rail system be robust enough to exist in this environment. All rail surfaces ought to be made of hardened materials and cleaned frequently so that they do not become pitted and gouged by the splatter of molten steel that may inevitably fall on them. Self-cleaning wheels may also be a recommended feature to keep the wheels clean between regular preventive maintenance (PM) cycles. Sizing of the rails should also be robust enough to avoid deflection as the machine travels across them.
The combination of most of the above factors results in the precision and accuracy of a system. Unlike other mechanical machining processes, it is difficult to assign a regular tolerance to plasma cutting processes. Many manufacturers will strongly promote the truth that their machines have positional accuracy of +/-0.007 in. and repeatability of +/-0.002 in.. The truth is that just about any machine available on the market can hold tolerances that far exceed the tolerance and convenience of the plasma cutting process itself. There are numerous factors that may influence the cut quality you’ll achieve in 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 give you cut examples of your parts or parts that closely approximate the parts you will soon be cutting, made on a machine/plasma combination that is comparable to what you’re looking at. This will give you the most realistic representation of what you may anticipate from a specific machine/plasma combination and the plasma cutting process itself.