Re: [CAD_CAM_EDM_DRO] Re: Software for wire EDM control?

Hi Zafar,

Thanks for the excellent descriptions! I take it the tapers it can do
are somewhat limited. If watching an ampere meter is enough to get the
feed right, that could simplify a hobby WEDM design. A "feed rate
override" might suffice in this case.

Three axis calculations are done (3D)? Then are the UV moves just
calculated from the taper information and the XY tool path? I suppose
what kind of parts are being made. This may be all that's needed for
mold relief.

And yes, a pix would be welcome!

Alan KM6VV
SherlineCNC

Zafar Salam wrote:

>
> Hi everybody,
>
> I've been following this thread with great interest because I own a chinese
> wire edm for the last eight years. The chinese machines mostly run on
> molybdenum wires of dia .15 to .20 mm. We normally tie a 200 m piece of wire
> on it's drum which moves back and forth between two hardened v-section
> pulleys. This length of wire lasts about 24 hours after which it weekens and
> breaks up. Typical cutting speeds are 25 mm per hour in a 25 mm thick steel.
> For thicker or thinner sections speeds vary proportionally. Speeds on
> Aluminium are the fastest and carbides cut the slowest. Surface finish
> improves a little with lower currents. The 0.18 mm wire, which is most
> widely used, can withstand a current upto 2.5 amperes in contineous
> operation.
>
> It uses 3B code. I've seen newer models of this machine which use G codes
> too. It is a 4 axis machine. Work is clamped on the table which moves in X-Y
> direction. Lower end of the wire passes through a pulley which is
> stationary. Upper end's pulley is attached to another small two axis drive
> U-V. Taper is controlled through the movement of both X-Y and U-V. The 3B
> code doesn't have options for 4 axes. We can only put the amount of taper
> required in the machine with the height of the workpiece and the controller
> figures out which axis to move. With newer machines running on G-code, top
> and bottom different shapes machining is also possible.
>
> It doesn't trace back automatically when a short circuit between wire and
> work piece happens. It just halts there. There is a button on the controller
> which manually backs the table on the cutting path. So if the short circuit
> persists then we have to press that button to clear it. Normally short
> circuit doesn't happen if we have set the machine parameters correctly. Ther
> is a knob on the controller which control the stability of cut. What this
> knob does is control the speed of the steppers. If we set it to a higher
> speed than the material removal rate then a short circuit happens. Slower
> speeds result in an unstable current on the ammeter.
>
> I am a mechanical engineer, so can't explain all this in the ee terms. Also
> excuse me for using the metric units. We are taught to use metric units from
> elementary school. It's hard to even think in imperial units :).
>
> I hope all the geniuses out there can figure out a simple plan for building
> and controlling a wedm at home. I would sure like to give it a try myself.
>
> Regards,
> Zafar
>
> P.S. I can post videos of my machine's operation if anyone is interested.
>
> ----- Original Message -----
> From: "RichD" <cmsteam@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Wednesday, July 30, 2003 11:08 AM
> Subject: Re: [CAD_CAM_EDM_DRO] Re: Software for wire EDM control?
>
> > Alan & Jon,
> > I have used the Hitachi WEDM (1994 model) many times at school. It is old
> > and does not have all the bells & whistles that the new ones have
> (thankyou!).
> > We use a plain g-code prog (no g0, z, or tool calls). Only coordinate
> positioning.
> > It is 4 axis, but we have not learned how to use the U-V as yet.
> > It does auto backup when a problem with the cut is sensed to retry for a
> good
> > cut. This happens sometimes at the end of a cut when the scrap drops and
> fouls the wire.
> > Auto tracing to retract or retrace/restart a cut is a feature.
> > It cuts thru any metallic or conductive material. The fastest I have seen
> is about
> > .2"/min. thru steel. We use plain tap water flush as Atlanta water is
> almost
> > mineral free. Cuts are very smooth and predictable.
> > Wire is hard brass .010" dia. fed continuously thru tensioning rollers and
> saffire guides.
> > Power is applied to the wire via graphite rubbing blocks.
> > If anyone would like info or pics to help design a home built, just ask.
> > There is no internal documentation available, but a user manual 4" thick!
> > We have been repairing it ourselves, so know a little of the guts of it.
> > RichD