Did you know that following the correct piercing techniques can help to improve productivity and reduce operational costs? Well, that’s absolutely correct. The main cause of components of a plasma torch failing prematurely is following the wrong piercing technique. In this article, we will be discussing proper techniques of piercing.
The Pierce Process
When the plasma torch is fired, a pilot arc is produced when the DC voltage combines with a high-voltage electric spark. The white-blue pilot arc is emitted from one end of the plasma torch in a steady stream. An electric circuit is formed by the pilot arc from the electrode to the conductive metal that is being cut. The arc then transfers to the metal and starts to pierce it. If the plasma torch is at a position that is higher than its greatest pierce height, then the pilot arc is formed in the air. However, if it is at a lower height, the pilot arc transfers onto the workpiece and begins piercing.
Steps of a Pierce
The arc that is transferred, heats the workpiece where it reaches the melting point and the molten metal starts to blow away. At the start of the piece operation, the molten material begins to spray over the plate’s top, directly from the point of the pierce. The molten spray is usually seen as a burst of sparks.
A hole with a round bottom forms as the jet of plasma pierces into the metal. This hole causes the molten spray to blow directly towards the torch.
As the arc completely passes through the plate, the molten material and the sparks are blown out through the hole that has been pierced. As the piercing is finished and the plasma arc is now at its fullest strength, the cutting machine starts moving and the plasma torch begins to cut. If the plasma torch moves too quickly, the arc will not pierce the material fully and if the plasma torch is too slow, the material from the workpiece will keep getting removed and the hole will keep getting enlarged until the arc is extinguished.
Tips and Techniques for Piercing
Piercing High and Cutting Low
As a rule, piercing should be done at one and a half to two times the cut height or at the greatest transfer distance. Piercing at a height helps to prevent problems such as snuffing, double arcing and bridging.
Using the Creeping Pierce Technique
If your CNC cutting system has the capability, it is recommended that you make use of the creeping pierce technique. In this technique, the torch is slowly moved during the entire pierce operation that causes the molten material blowing out in the form of a “rooster tail” to avoid touching the front portion of the plasma torch.
Don’t Estimate the Pierce Height Manually
It is not recommended that you use manual piercing, instead use the IHS or initial height sensing option if available on your plasma cutting system. Even operators with considerable experience do not have a precisely calibrated eye.
Never Pierce Beyond the System’s Capabilities
Never push the plasma cutter beyond the limits that it is capable of piercing at. Typically, the pierce rate is around half that of the cutting rate.
Try and use edge-starting or chain cutting whenever possible and try to moderate the number of piercings being used.
We have looked at the various steps followed during the process of piercing and by following the correct methods of piercing, you can not only improve the cutting speeds and hence productivity but also achieve significant cost savings.