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Adjusting Voltage on Plasmacam

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DCMW
Posts: 13
Joined: Mon Jul 10, 2017 7:47 am

Adjusting Voltage on Plasmacam

Postby DCMW » Wed Oct 18, 2017 9:09 am

I am still a newbie with my table. I see in my Hypertherm cut charts that it has specific voltages to be set at when cutting different material. Im not sure how to adjust the Arc Voltage for my cutter and my table. I have the Advanced Height Control as well.

jimcolt
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Re: Adjusting Voltage on Plasmacam

Postby jimcolt » Wed Oct 18, 2017 5:16 pm

Plasmacam uses voltage sampling (if you have advanced height). This technology has been used on expensive industrial plasma cutters for a few decades, and in my opinion is the most foolproof way to accurately maintain correct cut height.

Arc voltage and torch height are somewhat proportional. Put a DC voltmeter on the negative electrode and the positive plate connections for a plasma cutter and during steady state cutting (constant speed and constant height) you will see a fairly steady DC voltage between about 75 and as much as 200 Volts. Do another identical cut and physically raise the torch a bit.....when you do that the Plasma arc gets longer and you will see a higher voltage on the voltmeter, lower the torch and the voltage will go down.

Typical arc voltage based height controls have an operator setting for voltage.....and the Hypertherm cut charts supply a known voltage that (with a new set of consumables) will produce the correct cut height......assuming you have everything else (speed, amperage, material thickness, gas pressure/flow) exactly as the cut chart suggests. The important thing to remember is that the physical distance between the end of the torch and the plate (also listed in the cut chart) is maintained for consistent cut quality. So.....when you set the voltage on most cnc machines....you basically are setting the height. Higher voltage, higher height. You really do not know exactly what the height is because changes in speed, changes in air pressure, electrode wear will all affect the resistance of the plasma arc....which will change the height. So setting an accurate voltage is a good way to control height...but is not perfect.

The Plasmacam height control has no voltage setting....just a height setting. The operator sets the physical cut height. On the first cut the torch indexes to the plate and ohmically senses the surface (quite accurate). Second, the torch retracts an accurate distance to the pierce height and fires the torch , piercing through the plate. Third, once the pierce is complete, the torch indexes down to the physical cut height. Fourth, as soon as the x and y axis accelerate to close to the programmed cut speed...the plasma arc voltage is quickly sampled and the voltage for the correct physical height is automatically set. This process works well and compensates automatically for electrode wear, for speed changes, etc.....and makes cut quality more consistent. Industrial machines have been using this voltage sampling technology for many years...hopefully more of the light industrial cnc machines will adopt it as well! Jim Colt Hypertherm


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