homebrew micro plasma cutter
Posted by
Graham Stabler
on 2004-12-18 17:19:18 UTC
I realize of course this may be a bit of a dream but I would like to
try as I think I will learn a lot from the process. I have
discovered that the power supply aspects of a plasma cutter are
fairly straightforward, essentially a DC supply. I have also learnt
about starting the arc and that using a high voltage pilot arc is
not a good idea in the CNC arena. Likewise the method where the
torch touches the work is not overly suitable.
The best method seems to be that used by Hypertherm, it is described
very well in this patent:
http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=EP0490882&F=0
The patent includes an unusually good drawing and description of
both a machine and hand type cutting head and the mode of
operation. Essentially the electrode is forced into contact with
the nozzle by a spring. In this short circuit condition the nozzle
is connected to the supply. When gas is forced into the cavity that
surrounds the electrode it is lifted as it is shaped as a piston.
As the contact is broken between the electrode and nozzle current
passes between them and a plasma is created and blown out of the end
of the nozzle. This is the pilot plasma. To initiate the cut the
nozzle is brought upto the workpiece and the arc transfers from the
nozzle to the workpiece as the pilot plasma allows current to flow
and the workpiece is a second return path for the supply. At this
point the nozzle is disconnected from the supply return. And away
she cuts. In reality this all happens very quickly and you don't
actually have to bring the cutter to the work with the pilot running.
Another interesting thing is that in this version rather than a
swirl ring being used swirl holes cut tangentially into the cavit
around the electrode are used.
To be realistic I am going to set my goal to be the home production
of a jet of plasma. It may end up being one of those pointless but
fun projects like a plasma ball but who knows.
Graham
try as I think I will learn a lot from the process. I have
discovered that the power supply aspects of a plasma cutter are
fairly straightforward, essentially a DC supply. I have also learnt
about starting the arc and that using a high voltage pilot arc is
not a good idea in the CNC arena. Likewise the method where the
torch touches the work is not overly suitable.
The best method seems to be that used by Hypertherm, it is described
very well in this patent:
http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=EP0490882&F=0
The patent includes an unusually good drawing and description of
both a machine and hand type cutting head and the mode of
operation. Essentially the electrode is forced into contact with
the nozzle by a spring. In this short circuit condition the nozzle
is connected to the supply. When gas is forced into the cavity that
surrounds the electrode it is lifted as it is shaped as a piston.
As the contact is broken between the electrode and nozzle current
passes between them and a plasma is created and blown out of the end
of the nozzle. This is the pilot plasma. To initiate the cut the
nozzle is brought upto the workpiece and the arc transfers from the
nozzle to the workpiece as the pilot plasma allows current to flow
and the workpiece is a second return path for the supply. At this
point the nozzle is disconnected from the supply return. And away
she cuts. In reality this all happens very quickly and you don't
actually have to bring the cutter to the work with the pilot running.
Another interesting thing is that in this version rather than a
swirl ring being used swirl holes cut tangentially into the cavit
around the electrode are used.
To be realistic I am going to set my goal to be the home production
of a jet of plasma. It may end up being one of those pointless but
fun projects like a plasma ball but who knows.
Graham