Re: [CAD_CAM_EDM_DRO] Re[1]: wire edm info ( was Safety/Reliability )

Thanks Terry,

There is some useful information here. The biggest problem I have with wire
EDM is understanding how the feedback circuits work and link into the CNC
part of the machine. In a sinker EDM excess current flow through the
electrode or shorting it to the work causes it to back out by simply
reversing the stepper or servo motor until the current falls between the set
limits again, however, in a wire EDM this has to happen in at least 2
dimensions (3 in a machine with a tilting head?). To do this, presumably,
the CNC part of the setup must have a way of remembering the exact cut
direction for the previous few steps so it can back away from the cut in
this same direction without the wire shorting onto the sides of the cut. I
don't think actually making the mechanics of a wire machine is a problem at
all but this sensing and feedack into the CNC is a real stumbling block and
so any insight you could give into this aspect would be a real help.

Ian
--
Ian W. Wright
Sheffield UK
www.iw63.freeserve.co.uk

----- Original Message -----
From: "Terry L. Ridder" <terrylr@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: 05 November 2000 01:09
Subject: [CAD_CAM_EDM_DRO] Re[1]: wire edm info ( was Safety/Reliability )


> hello;
>
> what would you like to know about the wire edm
> machines? there machines are used to cut a2 and
> m2.
>
> i will provide a brief run down on what i know
> from looking at them for possible conversion.
>
> these machines are old, so the information may
> or may not be useful.
>
> 1. the wire used is a hard brass on reels. the wire
> is fed off the reel using a small hard rubber drive
> wheel very similar to how wire on a mig welder to
> driven. once used the wire is clipped about every
> two feet and drops into a bin. the hard brass wire
> comes in several different sizes.
>
> 2. table is x, y, & z. these machines use ball screws.
> the table axis are driven by stepper motors through
> tooth belt reduction. motors look like nema 23
> or nema 32. deionized water is used as the coolant
> and wash. the coolant pump is a positive displacement
> rotary style pump. the coolant tubing places through
> the pump and the small cam shaped rotor presses against
> the clear plastic coolant tubing. it looks like a
> wankle rotary engine except it is a pump. there are
> enough lobes on the cam to prevent pulsation of the
> coolant. the coolant pump is driven by a variable
> speed dc motor. this adjusts the flow rate.
>
> 3. the voltage control, is adjusted by a primative
> dac.
>
> 4. the controller can be programmed to cut multiple
> parts from the same blank by programming a single
> part and using a move and repeat command. the
> controller must be issued pause/dwell commands
> near to where cutting is complete and the any slugs
> would drop. this is to avoid shorting the wire out
> and/or jamming the slug.
>
> 5. resin bed looks like a small water softener.
>
> 6. there are motion sensors and coolant sensors.
> if the motion sensor detect that the wire has stopped
> moving the machine will e-stop. however, the coolant
> pump will continue to run. if the coolant sensors
> detect a stoppage of coolant flow the machine will
> e-stop. a reduction in coolant flow will cause a
> reduction in voltage to the wire.
>
> 7. if you have ever looked at a mig welder that
> is basically how the wire is bothed moved and receives
> the voltage.
>
> 8. slower feed rates produce a cleaner finish whereas
> fast feed rates produce a rather rough finish.
>
> 9. there are current sensors that detect if the wire
> breaks.
>
>
> On Sat, 4 Nov 2000, Ian Wright wrote:
>
> ian>
> ian> Hi Terry,
> ian>
> ian> Would your possible work on the wire EDM machines allow you to
contribute
> ian> anything to the group which may help us design one for home use -
perhaps
> ian> information / circuits from the manuals?
> ian>
> ian> Ian
> ian>
>
> --
> Terry L. Ridder
> Blue Danube Software (Blaue Donau Software)
> "We do not write software, we compose it."
>
> digging deep, i feel my conscience burn
> i need to know who and what i am
> this hunger jolts me from complacency
> rocks me, makes me meet myself
> ----kendall payne---closer to myself---
>
>
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