14.1 The History of PAC
Karl Fulton
The Development of PAC
Originally developed for cutting stainless steel, Plasma arc cutting (PAC) started in the 1950s. Tungsten inert gas welding had already been developed to weld exotic metals. Bob Gage constricted the arc and increased the flow of gas. This gave the arc enough heat and momentum to cut through metals. A patent was awarded to Bob Gage in 1957 for Plasma arc cutting (PAC) (Giles, 2022). In the beginning the PAC systems were not reliable and did not produce high quality cuts. Stainless steel is only a small section of the market also. If plasma arc cutting wanted to compete it would need to be an option for carbon steel and produce high quality cuts. In the late 60s companies were researching this and because of the advantage in cut speeds compared to oxy fuel cutting. Other improvements that needed to be made were cut consistency and the increase of consumable life. Speed and quality of cuts were increased on carbon steel by using compressed oxygen but this reduced consumable life. There were major advancements in the 80s with hand held torches, the utilization of compressed air and removing the need for high frequency starting. This has greatly reduced the overall weight of the PAC system. In the last ten years companies continue to improve cut quality, consumable life and versatility.
Basics of the Process
Similar to the arc welding processes you will have a power source, torch, shielding gas and ground. The electric arc and shielding gasses are constricted through an orifice creating a plasma that can range from 18,000 degrees F to 40,000 degrees F. This flow of gasses will shape the arc/plasma and blow the molten metal away leaving a clean cut edge with minimum dross.
This is highly effective at cutting any electrically conductive metals. The most common being carbon steel, stainless steels and aluminum. Plasma Arc Cutting is one of the fastest ways to cut materials between ¼” and 2“ thick. A lower end plasma cutter will cut up to 11/16” the higher end models can cut up to 2”. Industrial high amperage machines have the ability to cut upward of 6” material.
A plasma arc cutter is also capable of piercing, gouging and beveling pipe or plate.
Advantages of PAC include:
- High cut speeds and good cut quality
- Little to no prep work
- No preheat required start
- Low heat affected zone and reduced distortion
- Ability to cut any conductive metal Carbon steel, Stainless steel, Aluminum, copper
- Very little secondary work (post cut grinding)
- Minimal maintenance required.
Disadvantages of PAC:
- Initial cost is more expensive than Oxy-Fuel
- Must have and electrical source
- Must have air compressor or compressed gasses
- Fumes from material being cut may be hazardous
What is plasma?
Plasma can not be characterized as a solid, liquid or gas. Typically as you increase the energy in the matter, it will change states. When you heat ice it will turn to water and as you continue to heat the water it will turn to steam. (Turning from solid, to liquid, to gas.) But where does plasma fit?
Think about lighting. It can’t be a solid with no melting point and doesn’t hold a shape. It has no surface tension and no boiling point so it is not a liquid. It is not a gas because you can’t capture a sample of plasma and put it in a cylinder.
Plasma molecules are breaking down, they are heated to a point beyond being a gas. The typical characteristics of plasma are bright emitting light energy and very high radiating thermal energy. This makes plasma the fourth state of matter.
Some common places you can see plasma are in fluorescent bulbs, neon lights, and plasma TVs
A star is a giant ball of plasma held together by its own gravity.
Another example of plasma is Auroras or the northern lights are solar winds from the sun iterating with the magnetic field of the earth and impacting gas molecules in the atmosphere
You will also see plasma during any arc welding process. The arc you see is plasma. The difference with plasma arc cutting is the arc/plasma is constricted. Electrons flow from the hafnium electrode and collide with neutral gas molecules. These collisions free more electrons and create positively charged molecules or ions. This creates a cascading column of collisions radiating heat and bright light. The swirling gas in the torch centers the plasma on the electrode and pushes it out the nozzle to be used to cut, gouge or shape metal.
Uses of PAC In Industry Today
There are a wide variety of industries that use Plasma arc cutting (PAC) these should be separated into two categories: Handheld plasma and mechanized plasma.
These are some examples of how ar handheld plasma system would be used in industry:
- General fabrication, food processing equipment, tank fabrication
- Facility maintenance, railway and sawmill maintenance
- Shipbuilding and shipyards
- Container fabrication and repair
- Vehicle repair and restoration, removing floor panels and exhaust and bracket removal.
- Agricultural equipment repair.
- Ornamental fabrication(artwork)
Mechanized Plasma arc
It’s important to note that mechanized plasma systems will have a wider range of material thickness. These machines can range from less than 45 to over 400 amps. The other advantage of mechanization is to produce repeatable parts with a very close tolerance. This is normally done on a table with an XY axis, on a pipe beveler, or robotic arm.
These are some examples where a mechanized plasma system would be used in industry:
- Job shops/fabrications shops
- Heavy equipment manufacturing for agriculture or construction
- Vehicle fabrication
- Ship or submarine building
- Production shop that just fills orders on cut parts.
Attributions
- Figure 14.3: image released under the Pexels License
- Figure 14.4: OPEN by makou0629 is released under CC BY 2.0
- Figure 14.5: C3-class Solar Flare Erupts on Sept. 8, 2010 [Full Disk] by NASA Goddard Space Flight Center in the Public Domain; United States government work
- Figure 14.6: TorchCuttingCloseup by Hypertherm in the Public Domain; Public Domain dedication, not CC0
- Figure 14.7: Pumpkin by Karl Fulton, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 14.8: Parts Cut on CNC Plasma Table by Karl Fulton, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 14.9: Robotworx-plasma-cutting-robot by Robotworx is released under CC BY 3.0
- Figure 14.10: Retro Systems CNC Pipe Combo System by Steve Brown Photography is released under CC BY 3.0
- Figure 14.11: Plasmaschneidanlage-im-Einsatz by Kjellberg Finsterwalde is released under CC BY 3.0
A gas heated by an arc to at least partially inonized condition, enabling it to conductan electric curent. Ref AWS A3.0M/A3.0:2020. Standard Welding Terms and Definitions
Unwanted byproduct of molten metal, this material can stick to the bottom the metal being cut.