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

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