As mentioned in a previous blog post, the plasma arc is a charged current that is created between the electrode and the piece of material being cut. Since the heat of the plasma is so intense it is able to melt the material and make a successful cut.
The torch never actually touches the material to make the cut. Rather the plasma arc or current reaches from the end of the torch to the material to create the powerful connection. Because of this the problem of arc stretching can occur. Ideally the torch should be right above the part of the material being cut and directing the plasma arc straight down. Arc stretching happens when the plasma arc is stretched either behind the torch, or to either side rather than being directly below it. This can happen after a pierce start when the arc is cutting too slowly and does not match the torch movement. Reasons for arc stretching include improperly programmed cut paths, incorrect lead-ins and lead outs, as well as jobs where the torch is allowed to cut off the edge of the material. It is important to prevent arc stretching not only because it will affect the quality of cut but also is detrimental consumable life. When the arc stretches it becomes angles and can cut into your nozzle with damaging results.
How do you prevent arc stretching from occurring? The following are a few suggestions:
1) Use edge starts instead of pierce starts
2) Make sure the cut file is programmed correctly
3) Ensure that torch angle is correct
4) Use the correct consumables for your machine and cut specifications