High-Definition Plasma Cutting

The evolution of automated plasma cutting systems

Plasma cutting, a thermal cutting process that has been around since the late 1950s, has benefited from some technological advancements in recent years that make the process much more accurate, productive and cost-effective on the shop floor. These benefits, both from the actual plasma process side and from the Computer Numerical Control (CNC) operator control panel side, have proven to make specifying the correct cutting process for a particular application a much easier task for the welding distributor sales force.

The high temperature metal cutting process was always known for its ability to cut steel, stainless and aluminum with extremely high cutting speeds, but had a reputation as a finicky process with less than perfect cut part accuracy, along with unpredictable operating and maintenance costs. While the speed advantage of plasma cutting always had a place on many production shop floors, the issues with cut part accuracy and high operating costs have steered many end-users to other processes such as oxy-fuel cutting, laser cutting and abrasive water jet cutting over the last couple of decades.

Application Challenges
Expert Operators Required — CNC plasma cutting machines have been in use for over 40 years. The brain of the CNC machine has always been the computer or microprocessor-based control that converts digital data into the motion control that cuts complex parts out of metal plate. The CNC control also controls all of the components of a cutting machine in terms of when to fire the plasma torch, when to activate torch height control systems, as well as many other functions that were part of the automation process. Even with a microprocessor-based control on the machine, an operator had to spend 15 to 20 minutes before cutting each plate to load the part files into the control, align the plate to the cutting bed and set as many as 20 parameters related to gas pressures, gas flows, plasma cutting current, arc voltage and machine motion delays. The CNC control on older technology machines often looked like something out of a science fiction movie with as many as a hundred buttons used for setting up the cutting process. The CNC plasma machine operator had to be well trained in order to get this machine to consistently cut accurate parts. One incorrect setting would affect cut quality and consumable life, and could waste an afternoon of cutting by providing less than perfect parts.

Plasma Cutting

With the right equipment, it is now possible to create bolt-ready holes with a plasma system.

Plasma Cutting Costs — The major cost components involved with plasma cutting of metal parts have always been related to the costs of capital equipment, plasma torch consumables, secondary operations such as grinding and rework on cut parts and gases used in the cutting process, typically oxygen and nitrogen. If the plasma cutting process had not been as fast—typically six times faster than oxy fuel cutting of steel—then the process would never have become a major player in the plate cutting business. The sheer speed of plasma tends to reduce the cost per foot of cut as compared to other, slower processes.

Plasma Cut Quality — The first automated plasma cutting applications I first experienced in the late 1970s produced steel parts quite rapidly, but I remember that virtually every part needed some form of secondary operations, such as grinding of the dross that adhered to the bottom of every cut, reworking of plasma cut holes that had a sever taper and out of roundness or grinding edges that were hardened by the nitriding effect of the nitrogen-based cutting process. Once again, the advantage of the plasma process even with these costly, required secondary operations was the sheer speed of the process.

Technology Enhancements Address Challenges
Over the last 10 to 12 years, there has been a rapid change in plasma cutting technology that affects virtually every aspect of the mechanized plasma cutting process issues named above. These enhancements are actually rather surprising to a technology that has been around for over 40 years. While laser and abrasive water jet technology have advanced and created cut quality niches in the field of metal technology, manufacturers of plasma cutting systems and the associated CNC machines on which the plasma torches are mounted have made dramatic improvements in process cut quality, ease of operation and cutting costs, while at the same time further increasing plasma’s cutting speed advantage on most materials.

Windows PC-Based CNC Controls — Virtually anyone can operate even the most complex, large, multi-torch CNC plasma machine manufactured today. A Windows-based computer has touch screen controls, generally just a few required buttons. It controls 100 percent of the setup parameters for the plasma, the height control and the motion control system. All parameters required for cutting virtually any thickness of metal at any power level are embedded into the memory of the control, so the operator’s primary functions are to load the correct plate type and thickness on the cutting bed of the machine (prompted by the screen on the monitor), check to ensure the plasma cutting torch has the correct consumables (prompted and instructed again by the monitor), move the torch into the starting position and hit the start button. The CNC controls every function that an expert operator was required to do in the past, thus eliminating errors and dramatically improving process consistency.

AS ArcGlide

Automation of the plasma cutting process ensures consistent results, no matter who is at the controls.

The computer-assisted manufacturing (CAM) software, also known as nesting software (for accurately nesting multiple parts on a large sheet of material, ensuring best plate utilization), works closely with the PC-based CNC control to ensure that plasma parameters are set correctly for the parts and material being cut. More advanced CAM software also has the ability to recognize complex part profiles and automatically insert special machine codes that will modify lead-ins, lead-outs, cut speeds and cutting gas mixtures to optimize cut quality, especially on holes and small features. This capability virtually eliminates many secondary operations that were necessary with older technology and less sophisticated systems.

More Accurate, High-Def Systems — While high-definition plasma cutting systems were first introduced in the early 1990s, they were known as a finicky process that also required an expert machine operator to “tweak” the controls for best performance, often resulting in less than perfect conditions. The latest developments with high-definition class plasmas have all of the parameters that control the high-temperature physics in the plasma torch out of the operator’s hands, automating these parameters in conjunction with CAM software and the PC-based control. Electrical interfaces that used to be hardwired, highly complex and prone to failure on the shop floor are now as simple as a single Ethernet-based interface between the CNC control, the plasma, the gas flow control system and the torch height control system. Internal diagnostics allow for instant troubleshooting feedback and can also allow for direct to factory connections for online troubleshooting if needed with the experts.

These new plasma system technologies have addressed cut quality issues, and, through advanced power supply and gas flow control technology, have increased plasma consumable parts life dramatically, in some cases up to six to ten times the life of past plasma systems parts life.

Bottom Line
Automated plasma cutting, while internally far more complex than plasma systems of the past, has proven to be much easier in terms of operator use, cut quality, consistency and consumable life, which  lowers cost per foot of cut with the plasma cutting process. As such, today’s systems are easy to justify on the shop floor when the end-user’s bottom line will be improved.

Gases and Welding Distributors Association
Jim Colt Meet the Author
Jim Colt is strategic account manager at Hypertherm, located in Hanover, New Hampshire, and at www.Hypertherm.com.