It's not a secret anymore

May 1, 1999
Advancements in plasma cutting technology have increased productivity, leading to more widespread use.

Advancements in plasma cutting technology have increased productivity, leading to more widespread use.

Operators avoid the time-consuming task of manually adjusting a plasma cutter to match available voltage using Miller-developed Auto-Line technology. Found on the Spectrum 2050, Auto-Line automatically senses the available voltage and directs the connection to any primary power level from 208 to 575 VAC on a single or three-phase circuit operating at 50 or 60 Hz.

Plasma cutters run off the auxiliary power of engine-driven welder/generators, eliminating the need for large, heavy transformers in the units. Shown is the Spectrum Lynx running off the Miller Bobcat engine-driven generator.

The rest of the world is now catching on to something that metal fabricators, manufacturers, and ship builders have known for years: Air plasma arc cutting makes quick, quality cuts on any conductive material. It's also well suited to piercing and gouging operations. In fact, today's advanced plasma cutters offer a number of additional benefits, including portability, adaptability, reliability, and versatility.

Much like TIG welding, plasma cutting is a process where an open arc is constricted by passing through a small nozzle from the electrode to the workpiece. But, for decades, plasma cutters contained transformers that made them heavy, bulky, and difficult to move.

Recently, however, advanced inverter technology has reduced the size and weight of these machines. For example, Miller's Spectrum 3080 plasma cutter, which is rated at 80 amp, weighs less than 75 lb. Despite its small size, it is capable of cutting mild steel and stainless steel from 1 1 /4 in. thick and aluminum up to 7 /8 in. thick. A conventional, transformer-based plasma cutter with the same amperage and cutting capability, on the other hand, weighs approximately 450 lb.

Another hassle of a conventional plasma cutter concerns electrical hook-up after moving it from one utility power source to another. This nuisance often has little or nothing to do with the plasma cutter or the quality of available utility power. Instead, problems stem from the need to match utility input voltage with the plasma cutter's requirements. Fortunately, advanced input power technology has greatly reduced, and in some cases, eliminated these hassles.

For years, operators needed to be sure that their plasma cutter would operate on the existing utility power supply voltage. Without the proper voltage match, the machine simply would not operate, or the machine would be severely damaged when started. Plasma cutter manufacturers initially circumvented the problem by offering multiple-voltage machines. These plasma cutters are typically designed to run off 230/ 460, 380, and 575 VAC, the common U.S. utility voltages.

The only drawback is that the plasma cutter has to be manually adjusted to match available voltage, a time-consuming task. Additionally, the plasma cutter's electronics are susceptible to catastrophic damage if the voltage is improperly configured.

To eliminate voltage compatibility issues, advanced electronic circuitry was introduced that lets the plasma cutter sense incoming power and automatically link to it, providing the correct configuration. For instance, Miller's Spectrum 3080's Auto-Link technology automatically links to 208, 230, or 460V input power. This eliminates the need to physically open the plasma cutter and link wires manually.

Another technological advancement is Miller's Auto-Line. Found on its Spectrum 2050, it lets the plasma cutter operate at any location, in any country. The plasma cutter automatically senses and then connects to any primary power level from 208 to 575 VAC on a single or three-phase circuit operating at 60 Hz. Auto-Line even works on the predominately European frequency of 50 Hz. An added benefit of the technology is its ability to handle fluctuations in the utility power supply, ensuring consistent cutting output.

In addition to improved power linking capabilities, evolutions in plasma cutting technology have made it possible to run plasma cutters from the auxiliary power of an engine driven welder/generator. For example, the Spectrum 2050 cuts up to 5 /8-in.-thick steel when plugged into a Miller engine-driven generator that provides at least 8,000 W of auxiliary power.

Miller's Spectrum Lynx unit operates off the company's Bobcat engine-driven generator by tap-ping into its transformer and auxiliary power, not utility power. Because the need for a transformer is eliminated, the result is a hand-held, portable unit that weighs less than 50 lb and has the capability to cut up to 3 /4 in. mild steel and 5 /8 in. aluminum.

Unique design and advanced electronics boost reliability
Plasma cutters traditionally work in dirty environments where airborne dirt and other contaminants are commonplace. Dirt buildup leads to overheating, and metal filings and salt deposits can cause the control board to short circuit. To combat this, Miller introduced a two-pronged approach that minimizes unwanted contaminants — Wind Tunnel Technology and Fan-On-Demand.

This combination incorporates a tunnel built into the center of the plasma cutter, along with a fan that automatically blows air through the tunnel to cool internal components. Critical components are located on the outside of the tunnel where there is little opportunity for contaminants to collect.

With the aid of Fan-On-Demand, aluminum heat sinks positioned inside the tunnel dissipate the heat generated by the system's electronics. Meanwhile, variable resistors sense component temperatures. When temperatures reach a preset level, a central circuit activates the fan. When temperatures drop, the fan automatically shuts off to minimize the volume of airborne contaminants pulled inside the machine and to conserve energy.

Cutter versatility makes gouging a natural
While the plasma cutter is gaining popularity as a portable and reliable cutting tool, many users miss out on one of its handiest features — its gouging capability.

The traditional gouging method is carbon arc gouging, which uses a power source, a hollow carbon rod, and a compressed air source. A welding machine operates with low voltage and high current, but a high output power source is needed to provide the adequate voltage for quality gouging. A plasma cutter, on the other hand, provides a much higher output, making it a practical gouging tool.

Additionally, the plasma arc process itself is effective because it uses an extremely concentrated high arc-stream velocity. When gouging, a special tip reduces the plasma arc constriction. Less constriction, in turn, produces a lower arc-stream velocity. At the same time, the tip's wider-diameter orifice transforms the narrow cutting arc into a relatively wide and highly effective gouging arc.

To gouge, the operator simply holds the torch approximately 40° to the workpiece and presses the trigger. Unlike the carbon arc process, there is no need to "push" the carbon rod into the workpiece to gouge. There is also no need for the operator to adjust the distance of his hand to the workpiece as the carbon rod is consumed or to stop work to replace the rods. Instead, operators continue gouging by maintaining the necessary distance between the arc and the workpiece and adjusting for travel speed.

Other advancements add to the appeal
Some of the other technological improvements made to plasma arc cutters may seem minor, but they have a significant impact. Torch-shield drag technology and the elimination of high-frequency (HF) starts are just two examples.

Besides its high arc-stream velocity, a plasma arc produces temperatures as high as 72,032° F. These properties are why plasma cutters sever metal so quickly and easily. If an operator cuts or pierces a material too quickly, however, the plasma arc can blow back and damage the cutting tip.

To minimize the potential for tip damage, Miller provides electrically insulated copper drag shields to isolate the tip from the workpiece. This significantly increases tip life and lets the operator drag the torch across a workpiece, which increases productivity.

While increasing torch tip life is important, eliminating high-frequency starts can be critical. Many plasma cutters use a high-frequency start to initiate a plasma arc. However, high frequencies can interfere with nearby electronically controlled equipment or computers. To avoid the problem, most Miller plasma arc cutters employ a contact start that allows the machine to start without high frequency, yet deliver the same performance.

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