ARC Voltage ModeThere are applications where it is advantageous using arc voltage as a reference for the cutting height, e.g. when testing new cutting parameters or for scrap metal cutting. High quality clearance control systems offer both operator modes (cutting height mode and arc voltage mode).
CornerWhenever a cutting machine reduces its cutting speed relative to its preset speed, e.g. cutting a corner or very small circles, the arc voltage changes. The height control system tries to adapt to the change and drives down. In the worst case it can collide with the work piece. To avoid any changes in the height during these actions, all modern CNC control systems have an integrated corner function. During slow speed and abrupt changes of the arc control the control is switched off.
Cutbus®Higher productivity and repeatability of cuts are achieved by the CNC control transferring the cutting data directly to the plasma source, gas console and clearance control system. The interface is called CUTBUS®, an open interface between the CNC control, clearance control, plasma source and gas console.
Cutting Height ModeThe cutting height mode, often called the „IHT mode“, is the better choice over the arc voltage mode, because the clearance distance between work-piece and nozzle needs to be fixed in mm or inches. The clearance of the arc voltage is automatically adapted. While the nozzle wears out the clearance is continually adjusted. Therefore, the clearance of all cuts is identical and the cutting quality is optimized.
Elevation HeightWhen piercing thick plates lots of material (slag) splashes up. To protect the nozzle and therefore the consumables, the torch can be lifted to a predicted elevation height, above the pierce height.
Gas pre flowThe productivity is mainly determined by the cutting speed but also by the time between two cuts, e.g. the waiting period for flushing the gas pipes in the torch. IHT clearance control systems for plasma cutting offer the function ‘gas pre flow’ designed to shorten this period. With the signal ‘start initial position finding’ the flushing of the gas pipe is initiated.
KerfIn addition to the corner function, the kerfs sensing system is not available with most current cutting systems. However, the IHT kerfs recognition control system is an important feature of the torch protection and quality of the cut. When the torch travels across a kerf, thereby sensing a metal loss the arc voltage and height sensing would react immediately increasing arc voltage and driving down the torch and in the worst case the torch would collide with the work piece. The IHT controller is preventing such a rapid voltage increase and cutting height reduction by sensing and switching off the controller during kerf crossing.
Retract positionAt the end of a cut the clearance control system does not drive back to the upper end position but to an individually chosen retract position to reach the correct position for the next cut without colliding with the metal sheet.
Tactile Initial Position FindungThis method is essential to determine the metal surface below the nozzle for an accurate cutting height. A confident method is to touch the metal surface with the nozzle. The tactile initial position finding is the standard method used by IHT Automation for plasma cutting. Here, the metal surface is identified by softly touching the surface. The weight for touching the surface is adjustable. Contrary to the ohmic method this also works with rusty or coated metal plates.
Touchless Initial Position FindungPlasma cutting of thin sheet metal is a very challenging task, since the plates are often deformed or wavy. Tension in the plate can lead to uncontrolled swinging. The repeatability of the entire process is missing and cutting quality differs from cut to cut. The Contact Sensor will provide the best possible initial position finding by finding the plate surface with minimal touching.