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Gmoccapy Plasma - the plasma version of Gmoccapy

upload:gmoccapy_plasma.png

As with the main GUI, the plasma screen is designed to be used with a touch screen and is thus optimized for touch
It can however be used with keyboard and mouse


1. Requirements
2. Some background on Plasma operations
3. THC - Torch Height Control
3.1. What is THC
3.2. How does it work


1. Requirements

Please refer to the Gmoccapy page for detailed requirements. [gmoccapy wiki page]

The plasma screen has been included in the latest master branch. It can be found under the sim directory. You will be required to copy all the relevant files to your config. More on this later.

2. Some background on Plasma operations

Plasma operations on CNC machines is a bit of an orphan process. When cutting metal with a flame, the uneven heating up of the metarial will cause the sheet to bend and buckle. To start with, most sheets of metal does not come out of the mill or press in a very even or flat state. Thick sheets (30mm plus) can be out of plane as much as 50mm to 100mm. Most CNC gcode programs will start from a know reference or a piece of stock that has a know size and shape. Gcode is written to rough the excess of and finally cut the finished part.
With plasma the unknown state of the sheet makes it impossible to generate gcode that will cater for these variances in the material.For this reason the THC ( Torch Height Control ) concept was designed. More detail on THC later in the document.
The purpose of the THC function is to make sure that the torch remains at a certain height above the work piece. Not having gcode to do this, one has to interject somewhere in the control loop to get the Z axis to track the material height. By nature of this statement it is clear that plasma and THC does not adhere to the rules for normal CNC and has to be treated with caution.

Suffice to say that it is almost impossible to do decent production plasma cutting without a proper THC system implemented.

3. THC - Torch Height Control

3.1. What is THC

THC is a method devised to control the height of a plasma torch while cutting sheet metal under full control of a cnc system. Due to the fact that the metal constantly changes it shape while being cut, it is necessary to track the surface of the metal in order to get the best possible cut results.

3.2. How does it work

Several things has to happen in order for a THC system to have all the required information, input and output, to make things happen correctly. The plasma torch is lifted as high as possible and still make a good arc when we pierce. This is called pierce gap. Then the torch is dropped to a pre-set height in order to give the best possible cut results for the given material. This will save the consumables as there is a lot of molten metal that comes off the top of the material when piercing. Once this arc is established, the cutting can commence and at this point the normal cnc procedures take over. The process is as follows:


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Edited December 28, 2013 1:35 am by Mariusl (diff)
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