Eight Tips for Avoiding Common Plasma Cutting Mistakes

Even experienced operators make mistakes that can impact cut quality and consumable life. Many of the most common plasma-cutting and consumable issues can be avoided altogether by following the eight tips outlined in this article.

AWS Publications | October 8, 2021 | Processes
Welding Digest ►  Eight Tips for Avoiding Common Plasma Cutting Mistakes

Even experienced operators make mistakes that can impact cut quality and consumable life. Many of the most common plasma-cutting and consumable issues can be avoided altogether by following the eight tips outlined in this article.

 

Tip 1: Make Sure Gas Flow and/or Pressure Are Correctly Set

Whether too high or too low, the wrong gas pressure will cause a host of cut-quality problems. If the gas pressure is too low, the arc will never cleanly cut through metal because it will be too weak. If the gas pressure is set too high, you’ll wind up with an unstable arc. In addition to making sure the gas flow is correct, you should check the gas levels every day to be sure the correct amount of gas is actually reaching the plasma torch.

 

Tip 2: Confirm the CNC Machine Has the Correct Torch Height and Arc Voltage Settings

You should consider both pierce height and cut height on the computer numerical control (CNC) settings. If the pierce height is too low, the torch will be too close to the plate and will almost certainly get splashed with molten metal. If the pierce height is too high, the torch will be too far from the plate. This will cause the arc to not transfer, resulting in a misfire and consumable damage. Cut height is also critical. If the torch is too high, only the very tip of the arc will reach the plate, which will cause top-edge rounding and a positive bevel. If it’s too low, the arc will remove too much metal from the bottom of the plate, leading to a negative bevel. Additionally, the operator should compensate for consumable wear. As the pit depth in the electrode gets deeper, the torch needs to move closer to the plate.

Fig.1-Oct-08-2021-05-48-22-40-PMIf the CNC machine doesn’t have the appropriate torch height and arc voltage settings, consumable damage can occur.

 

Tip 3: Match the Cut Speed in the Operator’s Manual to the Process Being Used

Incorrect CNC settings can lead to many issues. If the cut speed is too slow, cut pieces will develop low-speed dross, a large bubbly accumulation of dross along the bottom edge. Slow speeds may also cause a widening of the kerf and a lot of top spatter. If the speed is too fast, the arc will lag, causing a beveled edge, a narrow kerf, and a small, hard bead of dross along the bottom edge of the cut piece. The correct cutting speed will produce minimal dross, giving you a clean edge that needs little rework.

Fig.2 CroppedIncorrect CNC settings are a common cause of cut-quality issues. It’s important to confirm that the CNC settings match those found in the owner’s manual.

 

Tip 4: Verify the Correct Amperage Is Being Used for the Material and Thickness

The operator’s manual should be double-checked to ensure the correct amperage for the material and thickness being cut is used. This is because amperage is highly dependent on the material and thickness. Though the correct setting can be found in the operator’s manual that came with the system, operators don’t always follow the specifications as closely as they should. This can lead to shortened parts life and reduced cut quality.

 

Tip 5: Regularly Inspect the Torch and Consumables

You should regularly inspect everything and choose the right consumables for the job at hand. The general recommendation is to inspect the torch and consumables at least once a shift. Additionally, the shield and outer retaining cap should be cleaned with a Scotch-Brite™ pad or very fine (400 grit or greater) sandpaper. Do not use anything containing metal, such as a metallic brush or metal scrub pad, because it will scratch the torch and consumables.

When inspecting the swirl ring, do not excessively lubricate it. Too much lubricant on the swirl ring’s o-ring will cause clogging and contamination. Too little lubricant will make it difficult — if not impossible — to get the swirl ring back into the torch without breaking it. When applying lubricant, use just enough to put a shine on the ring. If you can see a physical buildup, you have used too much. With careful use and clean hands, a swirl ring can last for 50 electrode/nozzle changes. If spatter is periodically removed from the face, the outer retaining cap will last for more than 100 electrode/nozzle changeouts.

 

Tip 6: Assemble the Torch so Parts Are Aligned Correctly and Fit Snugly Together

Operators will sometimes install consumables in the wrong order or inadvertently tighten the consumable stackup too much or too little. This can prevent good electrical contact from occurring and impact the flow of gas and coolant through the torch. Contamination should also be avoided. Dirt and grease will shorten consumable life and cause poor cut quality. When installing parts, wash your hands and keep consumables on a clean shop rag. Even better, take your torch and consumables into another clean room before touching anything.

 

Tip 7: Keep a Record of How Long Consumables Last

It’s a good idea to keep a record of how long consumables last; you can either use the number of starts or the arc-on time. From there, guidelines can be developed for expected parts life based on the amperage, material, and thickness being cut. Once the average life is established, you can better plan consumable changeouts.

 

Tip 8: Ensure the Number on Consumable Parts Matches That in the Operator’s Manual

You should check that the part number laser etched on each consumable part matches the part number found in the operator’s manual. Consumable selection depends on the material and thickness being cut, the amperage, and the plasma gas, as well as other cutting parameters. Though the correct consumables for a given job are always listed in the operator’s manual, operators sometimes reference the wrong cut chart or accidentally grab the wrong consumable.

 

Conclusion

The next time you encounter poor plasma-cut quality or consumable life, remember to start your troubleshooting with the CNC machine and consumables. If you do not see improvement after running through these tips, then it might be time to contact the original equipment manufacturer or the table manufacturer. Sometimes plasma-cutting issues have nothing to do with the plasma itself and instead originate with the table (e.g., the table may have motion-quality issues that need to be addressed). However, beginning your troubleshooting with the eight tips listed in this article will help you get to the root of the problem.

 

This article was written by Michelle Avila (communications manager, Hypertherm Inc.) for the American Welding Society.