Problem of Roughness output of Electric Discharge Machine

Discussion in 'General Electronics Chat' started by Abdel_Rahman, Sep 12, 2016.

  1. Abdel_Rahman

    Thread Starter Member

    Jul 19, 2016
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    We have an Electric Discharge Machine "ONA I-360 Die sinking EDM machine"
    Its driver has been defected and lost program, we have built a new driver for it using micro-controller (arduino). it is now working . Its movement and TON and Toff of the sparks now can be controlled.
    But the problem is about its roughness, output work piece is rough, and electrode is wearing fast even decreasing TON.
    We need help how to decrease electrode wearing, also how to increasing smoothness of the outputted work-piece.
    thanks in advance.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What do you mean by the 'driver'?
    You have obviously not replicated the spark control as per original, these are world wide distributed machines so you should be able to obtain all the schematics and parts required to restore to original design
    You didn't by any chance reverse the polarity of the electrodes.
    Max.
     
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    As someone who ran an EDM in industry and is trying to build one for myself, roughness of the burn/cut is usually a product of the spark amperage. Higher amperage = rougher finish. Did your "rebuild" of the machine remove the control of the amperage? I'm not familiar with that brand so I don't know if amperage is controlled with toggle switches or if it uses software for digital amp control. Do you have a wiring diagram of the power side of the circuit?
     
  4. Abdel_Rahman

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    Jul 19, 2016
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    I mean the by the driver controller (processor)
    also polarity has not been reversed
     
  5. MaxHeadRoom

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    Ona are are large sophisticated EDM company since the '50's so I would anticipate the control is state of the art, but will depend on the age of the machine.
    Is there a reason you did not repair with original components?
    Max.
     
  6. Abdel_Rahman

    Thread Starter Member

    Jul 19, 2016
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    Yes I did, as it has a noisy signal while trying make use of it.
    Can we use a gap voltage as a feed back instead of amperage??
     
  7. Abdel_Rahman

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    Jul 19, 2016
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    It was 1987 model, so we try to make a new controller which we can connect to computer and communicate with later.
    When I check it, its batteries of microcontrollers had a zero voltage, it
     
  8. MaxHeadRoom

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    Gap voltage/collapse method was often used on older machines and can be effective.
    The age of the machine is just over support what Ona claim is up 25yrs, But I would have thought it might have got some results if contacting the service support.
    How much of the original control are you using?
    Max.
     
  9. Abdel_Rahman

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    Jul 19, 2016
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    I have totally cancelled the controller, I am using all of its power components (rectifier, mosfets, hydraulic RAM ....), I think ONA - if supporting - would sell us the old driver, but we want to build a more recent and more cheap driver which we can easily communicate with..
    we have tried contact them for schematics and they offer a costly price for it.
     
  10. MaxHeadRoom

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    There is also a EDMhomebuilders news group on Yahoo Groups that also might offers some insight, I havn't been there for a while so I don't know how far they have progressed.
    It sounds as though your spark gap monitoring could be one of the problems, as well as degree of charge, if capacitive bank style.
    Max.
     
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  11. shortbus

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    Gap voltage is the normal way of getting control feedback. Amperage is the actual cutting force in the gap, and is usually controlled by using different values of capacitors being switched in or out of the discharge circuit. The caps being charged during the spark"off" time and discharged into the gap during the "on" time.

    People claim to be doing this control using a homemade micro controller circuit, but when pressed for the actual circuit, they won't share it, or show the machine actually running. There needs to be much isolation from the discharge gap for one to work, the gap is basically acting as one of the early forms of "spark transmission radios".
     
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  12. Abdel_Rahman

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    Jul 19, 2016
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    that may be the main cause of high noise affecting our machine control cicruit
     
  13. MaxHeadRoom

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    The old style Elox I used to maintain used a a selectable capacitor bank and hydraulic servo to advance the die until the die touched the work and the spark occurred and the voltage collapsed, it then sensed no voltage and backed off to allow recharge, this defectively maintained a small gap where the servo maintained the small oscillations necessary to maintain the charge/spark & collapse when the spark occurred.
    This requires a system of maintaining the cap charge together with fine servo action.
    Max.
     
  14. Abdel_Rahman

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    Jul 19, 2016
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    is touching work piece is necessary for the spark or only maintaining a very small gap and detecting voltage falling??
     
  15. MaxHeadRoom

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    On the Elox spark usually occurs as the electrode touches the work, I believe.
    Some operate on the ionization of the electrolyte when a small gap is presented.
    Here is a couple of PDF, one of the old Elox M/C.
    One is a self build book by Ben Fleming but is too large to upload, if you think you can use it email me an address.
    Max.
     
    Last edited: Sep 12, 2016
  16. shortbus

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    Touching the electrode to the work is not necessary or even wanted in EDM. Even in an Elox machine. There needs to be a certain amount of gap between the two, set by the "open circuit voltage" of the machine. Unless the machine is equipped to reverse direction at certain set time intervals(not all are). When the burn is happening if the machine is set correctly and with proper flushing, the machine should never have to retract until the set depth is reached.

    The servo is controlled with a window type comparator, above a certain voltage it advances toward the work. Below a certain voltage it retracts. Between the two voltages it does not move. This makes the gap stay active and sparks to form and remove metal. Touching the electrode to the work would be a short circuit and the electrode would retract.
     
  17. MaxHeadRoom

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    The Elox states approx 5 thou spacing is the gap maintained between electrode and work piece.
    Max.
     
  18. ronv

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    Nov 12, 2008
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    I understand it is a large schematic, but it would be useful if you could post it.
    Does it show any symptoms when running like a lot of move in or out.
    What does the window circuit look like. What voltages and capacitor sizes are you using.
    How do you decide to move in or out?
    It is quite possible it is noise.
     
  19. shortbus

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    The old ones I ran had a gap closer to 0.001 or 0.0015 inch.
     
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