A Brief History of Plasma Cutting
The Plasma Trail
By Jeff Walters Sr., V.P. Plasma, American Torch Tip
Plasma cutting has evolved, in the last few decades, into a reliable productive technology with ever growing potential.
Manufacturers of plasma cutting equipment have made rapid advances in the technology in the past 20 years or so, but it hasn’t been an easy road. The systems of today produce accurate cuts with low distortion and clean edges, but this was the hard-won result of intense technical development and careful real-world testing.
Trial-and-error methods and repeated equipment adjustments were typical for mechanized plasma cutting in the 1980s. Even with the system properly adjusted and optimized, the low cutting speeds and heat produced in the plasma cutting process allowed the metal to distort and warp. Consumable life was relatively short and the amount of smoke and noise created during the cutting process was immense.
Some Assembly Required
The rough-edged quality of parts cut with plasma prior to the 1990s required a lot of rework and preparation before they were usable. Secondary operations – grinding and filing to remove the dross/spatter from parts, reaming and cleaning holes, machining edges –increased the cost of every part cut on early plasma equipment.
The DC output of early plasma cutting system power supplies had voltage fluctuations that caused output current to vary. The results would sometimes lead to a very rough cut and short consumable life. When cutting tables are down for consumable changeout, valuable production time is lost.
The need to increase productivity became the driving force behind the development of better and more efficient plasma cutting systems.
Time For A Cool Change
Developing cooler, longer lasting electrodes has been an area of much product development and testing with variations in electrode shape and style, electrode materials and cathode materials.
Plasma cutting became a viable solution for many more applications when the switch was made during the late 1980s from the tungsten electrode to the modern-style cathode with hafnium electrode insert. Hafnium electrodes can operate with nitrogen, oxygen, air or blends of these gases, while the tungsten electrodes used in the earlier cutting torches needed nitrogen gas. This meant newer plasma cutting systems could cut various metal types by switching to the appropriate gas.
In 1995 American Torch Tip Co., a manufacturer of plasma torches and consumables, secured a patent on a long-life electrode that averaged 200 pierces, almost doubling the previous pierce life. The design includes an electrode retained in a post with an extended exterior surface promoting superior heat transfer to the coolant and extending electrode life.
The 90s also brought changes to power supply control systems. Microprocessors were used to control ramping gas pressures and amperage which increased consumable life, improved part quality and further reduced production costs for manufacturers. Ramping the gas pressure and power amperage smoothly up and down at the beginning and end of cuts greatly improves accuracy and finish.
Nesting software has improved the ‘intelligence’ of the plasma cutting system. Critical to a precise cut is the ability to have the correct lead-in cut parameters and pierce times and to change speed or output based on where the cut is in the part shape.
The modern plasma cutting equipment has made the machine operator’s job much less complex because the need to tweak manual control settings has been greatly reduced. All of the programming, nesting, determining tool-path, ramping the gas and amperage during different parts of the cut, continually varying the cutting speeds, and even decisions about optimum pierce point locations, is done during the pre-cutting programming by the software.
Currently, it is not uncommon to average 1,000 pierces per electrode, and occasionally an electrode will last more than 3,000 pierces.
Latest and Greatest
• Modern-day systems can pilot using nitrogen gas, limiting the pilot energy, and then switch to a second gas for cutting. This reduces the electrode deterioration that occurs at start up as the system transfers the plasma arc to the work surface.
• Automated torch lifters respond to plate height and warpage by continually adjusting the torch height and amperage, thus maintaining the optimum distance to the work surface. The advancement of software intelligence and torch lifter technology has minimized distortion.
• The availability of precision plasma consumables, has allowed fabricators to produce steel parts with minimal heat-affected zones. .0125″ steel cut at speeds over 250 inches per minute is cool to the touch a few seconds after being cut.
• Plasma “marking” is also possible. Power supplies with refined low amperage capabilities have the ability to engrave layout lines, part numbers, inscriptions, installation and orientation details.
New life-extending refractory materials are being developed for electrode use and there is on-going experimentation with various nozzle vent configurations and advanced gas mixing technologies.
New power supply designs with multiple in-line choppers and innovative inverter configurations will allow the smooth delivery of power with very little fluctuation and smoother more accurate ramp-up and ramp-down.
This ongoing evolution of plasma cutting systems, computer microprocessors and software will allow more precise, complex and cleaner cuts and lead to higher productivity and profit for those businesses that take advantage of the changing technology.