When you are using an automatic plasma cutting system for your cutting purposes, the THC or automatic torch height control is the most important element of the cutter. However, most often than not, it is the THC that is usually the non-functional, misused or missing part in the plasma cutting machine. In several fabrication units, you will notice that the plasma torch is moved up and down manually by the operator. The operator either is not trained to use the THC or the THC is not working properly. By not making use of the THC facility, the fabrication shop is not getting the maximum benefit out of its plasma cutting operation.
There are many different types of THCs or standoff controls available in the market that have a variety of features and functions. However, all of them use the same elements to control the plasma torch’s position with respect to the material being cut. The standoff or the torch-to-work distance is key to the consumable’s life as well as cut quality.
Various Elements of the Torch Height Control
This is a motor-driven device. When it receives signals from the control console, it moves the torch upwards or down. It comprises a rack and pinion, screw drive and belt driven mechanisms that cause the movements.
The control console is the brain of the plasma cutting machine. The input commands are received from the remote control and it sends the commands for output to the motor-driven torch positioner. It also monitors voltage signals and position feedback.
This essentially comprises a voltage divider card that is located inside the power supply unit. During the cutting process, the voltage divider card checks the voltage of the power supply. The interface splits the voltage signal and directs a smaller voltage to the control console.
This unit is the HMI or human-machine interface. The operator uses the remote control to set the two key cutting parameters – arc voltage and initial height. The remote control may be located within the CNC control or in a separate box.
It is very important to understand the concept of IHS or Initial Height Sensing. This is an adjustable factor and determines the height at which the plasma torch will start the arc and begin to cut through the workpiece. To set the initial height, the THC must locate the position of the workpiece first. There are many ways to do this. However, for a precise and high-quality cut, it is very crucial that the plasma torch must find the workpiece and retract to the correct piercing height.
Torch Height Control is very important when it comes to the plasma cutting process as the position of the torch and the pierce determines the success of the cutting process. If the plasma torch pierces very low, then the torch, as well as the consumables, will be damaged and if the pierce is too high, then the plasma arc will not transfer to the workpiece.