During the cutting process, the standoff or the torch-to-work distance is adjusted by regulating the arc voltage or the power supply voltage. The plasma power supply provides a steady current when the plasma torch is cutting. Whereas, depending on the distance between the electrode of the torch and the workpiece, the voltage varies. Thus, the voltage goes up when the torch-to-work distance increases and vice versa.
During the plasma cutting process, in order to maintain a constant distance from the workpiece, the THC (torch height control) makes use of the arc voltage. This enables the cutting system to maintain the correct torch height despite variations in the material being cut or the cutting bed flatness. The operator sets the arc voltage which is usually between 100 to 200 VDC.
Once the THC has completed the IHS (initial height sensing) process and the plasma torch has pierced the workpiece, the motion of the plasma cutter is enabled and the plasma torch begins to move. Once the cutting process starts, the THC adjusts the plasma torch upwards or down to retain the target voltage.
Every voltage setting corresponds to a particular height that allows the arc to produce a clean and straight cut. The torch height has the most effect on the bevel angle of the workpiece. If the voltage is too high, more material is removed from the upper portion of the kerf rather than the bottom. This results in a positive bevel and excessive rounding. If the voltage setting is too low, then too much material is removed from the bottom of the workpiece. This results in a negative bevel or undercutting.
Recommendations for THC
- If your THC is broken or not functioning, then ensure that you fix it and if it is very old then upgrade it.
- If your plasma cutting machine does not have a THC, then get one.
- If you are buying a new plasma cutting machine, then invest in one that has a very good THC and to profit from your investment, ensure that your operators are trained to make use of all the THC functions.
These days, THCs available in the market have many capabilities and features. Piercing that is done at the correct height will save you money on the consumables and cutting at the right height will result in precise, good quality cut and minimum rework and finishing. Investing in a good THC is a very good idea as in the long run it will pay for itself.