In this article, we will be looking at some piercing strategies that fabricators employ to achieve efficient cuts while plasma cutting.
The conventional creep-in or travel pierce regulates the flow of molten metal that is blown back during the pierce and directs the metal away from the torch. The pierce is started by setting the torch at fast gouge speed and then the speed is slowed down to a creep speed. The plasma torch travels several inches and then penetrates the plate. This process helps to control the direction of the molten spatter.
Travel pierce also lets you ease into the cut slowly and allows the molten material to go in the opposite direction of the pierce. The molten material can be deflected in the direction you want that can be controlled via programming. Modern cutting systems allow you to raise the plasma torch to a certain pierce height and then lower it to the cutting height. This helps to reduce the creep distance.
However, these kinds of lead-ins can increase the metal scrap, which can become quite an expensive thing, especially when cutting thick materials such as stainless steel. This can also result in holes of small diameter.
If you need to cut many small parts from the outer diameter, you can use the chain cutting strategy. In this case, the plasma torch pierces and then cuts several small profiles in the same single path. This means that piercing once is sufficient.
The pre-piercing strategy works well when you want inner diameter cuts of several small profiles. The plasma cutting machine completes all the pierces and then stops so that the operator is able to clean the metal spatter and also switch the consumables if required.
Plasma cutting makes use of constant current. As the plasma torch rises, the plasma arc length also increases and the arc voltage increases to a particular point until the plasma machine’s maximum operating voltage. After this point, when the power supply cannot supply adequate voltage to support the plasma arc, the arc gets extinguished.
The power supply should have sufficient reserve on the arc voltage to resist the increased arc length and standoff distance. The spatter on the torch is minimized when you are at such a great height from the plate.
Today, modern sources of power offer high operating voltages that allow a very high standoff distance between the plasma torch and the plate. Initially, the plasma arc transfers to the workpiece at a pre-set height after which, the lifters raise the plasma torch to a pierce height that is higher. Power supplies can reach higher arc voltages and can keep the arc at the particular pierce height till the pierce is completed. When the pierce is finished, the plasma torch will drop down to the cut height.
A new plasma cutting system with new consumables can penetrate a plate in half the time taken by an older system. As consumables wear out, pierce times also increase. Setting a steady pierce time helps in achieving complete penetration notwithstanding how much consumables have been used.
Using different pierce strategies can help you customize according to the type and thickness of the material being cut in order to achieve greater productivity, efficient cuts and lower downtime.