High density plasma arc cutting such as our 6000 Series CNC Plasma, can effectively cut through thick plate, however the most challenging aspect of the process is the initial piercing of the material. We will now go over a few basic strategies to allow your machine to effectively pierce through inches of metal.
Photographers love rooster tails, as all those sparks make for some eye catching graphics, however for a shop supervisor, this shower of molten metal represents unfortunate but necessary waste. Until the arc penetrates the plate bottom, the molten metal needs somewhere to go. Then there is also the issue of double arcing, which is when the arc path goes from the electrode to the nozzle and then to the workpiece, which causes damage to the consumables There are many ways in which you can try to minimize these problems, such as using edge starts, however this is not always a viable or preferable option as it can cause a lot of scrap. We will now go over several techniques to attain an efficient pierce through thick plate, whether that is carbon or stainless steel, aluminum, or other materials.
Technique #1 – Travel Pierce
To control the flow of that blown back molten metal, a traditional travel can be used. With this technique, the torch is set in motion at a fast gouge speed and then slows to a creep speed as it travels for several inches before penetrating through. This will help control where the molten spatter goes. Lifters can also raise the torch to a specific pierce height and then descend to the cutting height, which helps minimize the creep distance. The drawback to this technique however, is that such lead ins can increase the material scrap, which is an expensive proposition when dealing with thick material.
Technique #2 – Chain Cutting
A chain cutting strategy might make sense if a nest requires OD cutting of numerous small parts. With this technique the torch pierces and then cuts many small profiles in a single path, avoiding the need to pierce more than once.
Technique #3 – At the Nozzle
A more pointed torch tip angle is used by some to combat blowback. With a longer more slender front end of the torch, you may get less slag actually hitting the torch surface. Torches may also have water cooled shield cups. With the shield cups, instead of remaining on the torch, spatter hits the cooled torch and quickly solidified before it has a chance to attach.
Technique # 4 Extreme Piercing
Using an inefficient piercing strategy can lead to a stalled pierce, which is a crucible like molten pool of metal at the bottom of the pierce hole. The plasma energy heats and reheats the soup, but not the unmelted metal underneath. A stationary pierce from a power source with sufficient energy can overcome this, using what is called a double pierce. The plasma arc first pierces the metal thickness partway, then the arc stops leaving a blind hole. Following this, the operator scrapes spatter from the plate surface and then repositions the torch so that the arc will pierce about 0.25 in. away from the pierce hole’s sidewall. With this technique, room is created for gases and molten metal to blow down and up the opposite sidewall of the blind pierce hole, until the arc penetrates the plate bottom.
Now that you have a basic idea of the various techniques, it is up to you or your technician to weigh the various factors to determine the most cost effective piercing strategy. Using the right technique or combination of these techniques can lead to the production of tight tolerance cuts made quickly and effectively. Here at MultiCam Canada we offer a wide range of Plasma solutions, as well as training to ensure you get the most out of your CNC Plasma. Feel free to reach out, so we can help you choose the perfect machine for the application you have in mind.
At our online store – http://cncplasmastore.ca/, you can find a wide range of plasma consumables for your next plasma project.