Using Computer Numerical Control (CNC) plasma cutting to automate the machining process is a smart…
Plasma cutters are an essential manufacturing tool. In comparison to oxyacetylene cutting or saws, cutoff wheels, shears and snips, plasma cutters offer many advantages, including portability, minimal heat-affected-zones (HAZs) and smaller kerfs — not to mention a wide range of cutting applications (gouging, piercing, beveling, etc.).
Despite the ubiquitous use of the plasma cutter, many workers still make basic mistakes while handling the dangerous tool. Even those with decades of welding and cutting experience could benefit from reviewing some safety procedures and proper cutting techniques.
Here are 10 steps for proper plasma cutting:
1. Read the owner’s manual
While it does take patience to wade through many pages of technical writing, most of us just underestimate the importance of doing so. Safety precautions should be memorized, and you should consult the manual with any question you have, no matter how small.
A plasma torch is just about one of the most dangerous tools a worker could operate. The Department of Labor Weekly Fatality/Catastrophe Report indicates that plasma cutter accidents happen at an alarmingly high frequency.
2. Button your shirt cuffs, pockets, and collar
While you know to wear proper safety gear like gloves, jacket and flame-resistant clothing, you might forget to button your cuffs, pockets and collar. No matter how flame-resistant your clothing is, if a stray fiber or strand on an unbuttoned cuff is exposed and catches a spark, it could lead to serious injury or death.
3. Shield your eyes with proper shade lenses
While this step should be in the owner’s manual, it’s especially crucial to your safety, so we’re repeating it here. It’s also important to make sure you aren’t using a shade lens unsuited to the plasma cutter you intend to use. It can be hard to remember to switch to the proper shade lens when we switch machinery. Although you might not notice the difference, your eyes will, and your vision will degenerate over time.
4. Use ordinary compressed air
Contractors often choose bottled nitrogen because it costs less than bottled air. When cutting stainless steel, some also think nitrogen is better because it causes less oxidation.
The truth is that most plasma cutters use a hafnium electrode that functions best in an oxygen-rich environment. Hafnium electrodes will eventually evaporate, which causes plasma cutters to start misfiring and leave behind more dross until they can’t cut at all. It’s in every cutter’s best interest to have hafnium electrodes last as long as possible — which means that compressed air is, in fact, better than nitrogen.
5. Brace your cutting hand
It’s time to start cutting. The best way to trigger the pilot arc is by supporting your cutting hand with your off-hand, like so:
This gives you a great pivot for 180-degree movement, and also maintains a constant 1/16th to 1/8th inch standoff for cutting.
6. Trace your path (without pulling the trigger)
Tracing the cutting path before pulling the trigger is an underrated technique that is very reliable when it comes to plasma cutting, especially for longer cuts. It can create a smooth, continuous cut, rather than more unappealing start-and-stop cuts. One of the worst things you can do in the middle of a cut is stop and think about where you have to go next.
7. Make a sample cut
To make sure all of your settings are correct, make a sample cut on a metal of the same quality and thickness.
8. Know your thickness
For thin metals, a plasma cutter’s pilot arc will punch right through to the other side. This means that you can start your cut with the electrode at 90 degrees to the metal.
For thicker metals, the plasma cutter will need some more space between the material; it’s best to approach thicker metals at a 45 degree angle, which helps avoid the backlash of sparks. Once everything’s under control, roll the torch to 90 degrees.
9. Watch the sparks
As you’re cutting, you should watch the sparks from time to time. If sparks are shooting along the top of the metal, you’re going too fast and need to slow down. At the proper speed, sparks should fly at 15 to 25 degrees opposite the direction of movement of the plasma cutter.
10. Mind the edge
Lastly, pay close attention to the edge of a metal when you’re near the end of the cut, especially when using thicker metals. Just as you started your cut with a roll 45-to-90 degree roll, so you should end it that way, too. You’ll want to roll the torch towards the final edge and pause to make sure you cleanly sever the metal at the end of the cut.