Why is the analog current control so important?
The cutting current must be controllable to automatically lower amperage whenever the cutting speed slows down. If it is not, a bigger quantity of material will be melted and removed from the actual point than necessary to achieve an optimal cut. At the same time, a minimum Plasma density should be maintained, for the arc to stay alive and the cutting process active. The whole system must be balanced to avoid time consuming and consumables damaging interruptions. CNC control over the source current is also indispensable for Pulse Piercing to be feasible.
What is Pulse Piercing?
The cutting energy is controlled by being delivered in high-and-low-current pulses, enabling the reduction of the volume of metal melted. This way we avoid risking molten metal spattering over the nozzle and sensors and destroying them. Pulse piercing is an important tell-tale trial for CNC suitability for High Definition Plasma cutting.
What is Torch Height Control (Arc Control) and why is it of such importance?
Cut quality depends to a high degree on the distance between the torch tip (nozzle) and the surface of the sheet we work on. The Plasma Arc is not cylindrical, it gets narrower in its upper and lower edges; consequently, when we cut too high the cut is performed by its lower edge and vice versa. In both cases the “sides” of the cut are not square. It is only when the cut is performed by the middle section of the Arc that we achieve optimal cuts. Here the presence of a digital Arc Control system interconnected to the CNC is absolutely important. It must be able to interact with the CNC for the ideal Torch Height to be maintained regardless the torch velocity changes and eventual holes in the job.
I have seen cutting machines equipped with all automations required, even top quality ones, nevertheless with obviously inferior cut quality results: What could the reason be for it?
All electronic subsystems and the relevant software should be absolutely matched and fine-adjusted to one another to achieve the best results possible. Here we are talking about intercommunication and response times in the order of less than one thousand of a second! Subsystem co-ordination on such a level is achieved only by adjustments to the minutest detail and is only possible for manufacturers having a vertical manufacturing Know-How of the Plasma High Definition and Laser Cutting Systems. Lack of this Know-How cannot be remedied by outsourcing, regardless the quality of the parts acquired this way, as it makes fine adjustment impossible to achieve, resulting in incompatibilities and wrong configuration; results inferior to the ones theoretically expected are a direct consequence of such minor programming inconsistencies.
What is Oxy-Fuel Cutting?
Oxy-fuel cutting is a chemical reaction between pure oxygen and steel to form iron oxide. It can be described as rapid, controlled rusting.
How does Oxyfuel Cutting work?
Preheat flames are used to heat up the surface of the steel to approximately 1000°C (1800°F - bright red color) but below the metal's melting point. A jet of pure oxygen is then directed toward the heated area in a fine, high pressure stream. A vigorous exothermic chemical reaction takes place between the oxygen and metal forming an aluminium or iron oxide or rust. The pressure of the jet of oxygen blows away the slag or oxide forming a cavity. The preheat and oxygen stream are moved at constant speed to form a continuous cut.
Can oxy-fuel method be used to cut any metal?
The answer is that it cannot! This depends on the melting point of the individual metal's oxides. Only metals whose oxides have a lower melting point than the base metal itself (low carbon steel and some low alloys) can be cut with this process. Otherwise as soon as the metal oxidizes it terminates the oxidation by forming a protective layer. In other words Oxyfuel cuts by burning, or oxidizing, the metal it is severing. It is therefore limited to steel and other ferrous metals which support the oxidizing process. Metals like aluminium and stainless steel form an oxide that inhibits further oxidization, making conventional oxyfuel cutting impossible.
How can I tell whether Oxy-Fuel Cutting is of top quality?
It takes some experience to be able to distinguish between a top and an inferior quality cut. Main points to judge from are:
There must be clean smooth cut surfaces with vertical drag lines.
Little to no dross (slag) on bottom edge (easily removed).
Cut surface flat from top to bottom without undercut.
Squareness of the top corners, that is the eventual arc must be of a minimum radius.
Cut face square with respect to top surface.
Which are the main elements of Oxy-Fuel Cutting?
The Main Terminology relevant to Oxy-Fuel Cutting is the following: Preheat Flame
Torch and Cutting Nozzle
Material Being Cut