Home Grown Wire EDM


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    Default Home Grown Wire EDM

    I have wanted to make my self a precision 4 axis WEDM for about 12 years now (ever since I heard of them), now I think I am ready mentally to attack the project. I have questions about them and hope the plethora of collective knowledge demonstrated by this forum can help me in my terrible quest!

    So to start off!

    I know that the key to a good EDM is the power supply, in your experience what makes the perfect setup? Will a quick discharge like a capacitor discharge suffice? Or would it require a constant arcing that which can be found with a current controlled square wave?

    Is there more to an EDM power supply then frequency control, voltage control, and current control?

    I was thinking of making a power supply that can go to 100 KHz PWM voltage control and capacitive current control. I would like to use a variety of wire but preferred .003" I am not sure about the optimum power but would build it to 1000 watts, is this enough?

    a diagram of the power supply:

    220V filtered DC
    |
    V
    Switch <--- Square Wave generator 0 - 100Khz PWM V control
    |
    V
    Switched Capacitor Bank <---- Digital Bank control for power of spark
    |
    V
    Wire Cutter

    Any help would be great! Thanks!

    Cheers!

    Similar Threads:


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    Member vladdy's Avatar
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    I had built one about 10 years back, real basic unit that I used to remove broken taps and such...
    No longer have it, but I found a surplus power supply that was relatively high voltage [I think over 200v], and used manual feed with a current meter for monitoring, don't remember current draw anymore.
    For a wash fluid I used plain diesel fuel, low pressure with relatively large volume to carry away the dust..not real safe, but was real handy and worked well enough..
    I do remember that indicated current [and resulting arc size] would make quite a difference on the actual diameter of the cut, mine wasn't a wire style, just plain ground to shape carbon electrodes [arc-air rods]..

    enjoy...



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    If I were going to do a WEDM, I'd want a square wav power supply that would allow you to set on and off times. This ability smooths out the cuts and allows you to machine at a faster pace.



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    Registered the4thseal's Avatar
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    camtronics has plans......maybe you might look at them . i am intersested but it is the unknown...........if it could work i am in.



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    Wink For years..

    I've been putting it off for years.
    New years resolution! Time for me to have a go too.

    Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. THREE ways to fix things: The RIGHT way, the OTHER way, and maybe YOUR way, which is possibly a FASTER WRONG WAY!


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    Hi,
    Happy new year to all.
    I'm working on an small homemade EDM switched mode pulse generator. I'm aiming for 0-15A (maybe more), 0 - 150V and 0 - 100kHz pulses (isofrequent and isoenergetic). The unit should be able to work at will in a pulse or relaxation mode). The electronic project is already in an advanced fase, but for the moment I'm lacking expensive measuring equipment for making good relevent load measurements, snubber adjustment and calibration of current limiters/controllers. The whole thing will be controlled with a microcontroller to set all kind of parameters for finishing result and speed optimizations. And above all it should be affordable for a simple student as me. The primary objective is to use it for a zinc EDM, but later on I plan another version for wire EDM.



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    1000W is way more than enough for .003 wire. Our big machines only have a 60 amp power supply and i havent ever seen it maxed out on .01 wire and i have cut things 15 inches in height before. I would think that you would want to Square wave to be able to control the cut more. A big factor in EDM is being about to control the curf of the cut(the with of the cut overburn ect) so you should be able to control that a little better.



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    Quote Originally Posted by the4thseal View Post
    camtronics has plans......maybe you might look at them ..
    are those the ones with the draw slides? struck me as a joke, i might be wrong but i'd want to hear of someone's success with it before i purchased draw slide plans. jim glass @ the chaski forum has built a wire edm and there's some good content on this site on the challenges of doing so.

    I've want to make one as well, cost of the brass wire is the current excuse



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    I am still doing allot of research right now as to determine the operational requirements for the power supply. Yea 1000W is allot, and I still am not sure on the power range that I am looking for. I am fixing to make a test circuit with a TIP121 transistor as a switch, it will do about 6A at 70V (I think) still trying to figure a scheme to measure discharge voltage to determine gap width. The microcontroller I am using is the 18F1220 running at 40Mhz or 10 million instructions per second. I should be able to capture the voltage and current with its AD converter but if it will not work for this app. I will use a 18F4431 a bit of an overkill but it should work. it should also serve as a controller for the switching power supply.

    I have been reading allot of specks on machines and put there current rating to about 20A this is max current to the work right? That should not be a problem to achieve for my circuit topology.

    I could find no info on frequency or pulse width and timing though… not yet anyway!



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    Question Switch mode?

    Have a look at the UC3842/3/4/5 switchmode driver family.
    Very simple to use, quite flexible.
    Drive power devices directly.
    Current limiting cycle by cycle.
    Built in oscilator and 5v reference.
    Easy to use opto isolator in feed back loop, cycle by cycle.
    If they use them set top boxes, they don't cost much.

    Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. THREE ways to fix things: The RIGHT way, the OTHER way, and maybe YOUR way, which is possibly a FASTER WRONG WAY!


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    neilw20, never used that one before, but I have used the MAXIM version of a SMPS, it worked very well, I might use something like this, I dunno. It depends on how ambitious I am. Thanks for the suggestion.



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    Default first sketch of the power supply

    Here is my sketch of the power supply.

    In this setup I have a transistor (Q1) connecting the wire tool to ground through an inductor (L1) and a current sense resistor (R1). The current is fed to an accumulating filter which "averages" the current reading to make it more suitable for my A to D in the microcontroller. this is where I will at least chop the current to the wire but hope to do a pwm current control, (L1) will add reactance to the circuit an allow a smooth current control. As you can see the power for the spark is supplied by a buck SMPS of a standard implementation and is also controlled by the uC, the uC also turns the high voltage on with the relays. I don’t have some of the circuitry modeled in this sketch, such as the clock circuit for the uC, and the idle resistor on the load side of the buck converter. You might notice that for the voltage references and dividers, there are additional capacitors, well that is because the AD converter in the uC likes a low impedance source, the caps help provide it, and also they help smooth irregularities so the program does not chase its tale. They also reduce the parts count by a huge amount as they are replacing opamp buffing circuits.

    This is what I am thinking now anyway. But I think I may need to start with the machine or I will have no way to test the Power supply

    Also can anyone tell me what (I'm with stupid) is supposed to mean? It has been driving me nuts for a while.

    Attached Thumbnails Attached Thumbnails Home Grown Wire EDM-edmpssketch-jpg  


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    Talking Stupi?

    He's my cousin.

    Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. THREE ways to fix things: The RIGHT way, the OTHER way, and maybe YOUR way, which is possibly a FASTER WRONG WAY!


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    Hi
    I have a Chinese Pc driven WEDM machine this thing is 15 years old and I have been doing all its repairs for a long time. So I know a little bit about wire cutting machines. I cannot speak for the new machines many of them now use Ac current for the spark. My machine the maximum current you can use is 3 amps and that cut 120mm of steel I normally cut around 40mm steel and then I use around 1.5 amps at 25volts the transformer is rated at 90volts. The cutting current is not the problem the problem is with the software. One needs to reverse the motors if the voltage goes below 5volts and again when the voltage is up. You should first speak to some one like EMC and see if they have a solution for that problem. I would not recommend you go for 4 axis I do all my cutting in 2 axis its faster. My machine use a 0.2 steel wire on a drum that changes direction, it would be possible to fit something like that to a CNC mill.



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    Quote Originally Posted by gombault View Post
    The cutting current is not the problem the problem is with the software. One needs to reverse the motors if the voltage goes below 5volts and again when the voltage is up. .
    that's the reason i tout the newall encoders for this project, not because I have aspirations of machining to a few millionths but because of the resolution it would give on the distance the wire travels toward or away from the work....I speculate that a lower frequency, lower wattage diy WEDM would benefit from a very fine control this distance.



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    Talking Drama!

    Quote Originally Posted by gombault View Post
    Hi
    The cutting current is not the problem the problem is with the software. One needs to reverse the motors if the voltage goes below 5volts and again when the voltage is up.

    Ahh, the challenges! Actually where I am at right now is trying to come up with an elegant circuit to measure the breakdown voltage of the gap, I am thinking about using a capacitor that will add reactance without significantly changing the properties of the cut. That way the gap breakdown voltage is a function of time and can be measure that way. This can be used to add a feedback loop to the control circuitry, which I think I am going to build a dedicated uC unit for that and interpret the G-code directly. I am also going to add AC capability to minimize electrolysis.

    I like the Idea of a 4-Axis but I must admit I don’t know much about it. I know that x,y are the cartisan movements and the u,v are the offsets, however are these absolute measurements? or are they based on a virtual plane at the top and bottom of the parts? If so that means I have to calculate the real points in real time off of the G-code representing virtual points! Oh the drama!

    And about the 5th axis! is this just the x,y plane moving in the z axis or is it both x,y and u,v moving at the same time.

    I want to add a b axis but that is trivial compared to the others



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    Baby steps. Start with two axis and go for more in round two. This would keep the learning curve to something with possibilities of success.



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    MrWild, you are right, baby steps are best, however if I eventually wanted a 4-axis as apposed to a 2-axis, the structure would be vastly different so if I don’t want to build two machines of this magnitude I will need to bite the bullet and go for the 4-axis. I will not likely build another WEDM after this one (too many other projects on the list).

    Besides it will be a 2-axis until I figure out the programming to make it a 4-axis.

    Cheers!



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    llilrex, curious if you developed an opinion on what frequency would be most practical.

    On four axis, if i owned a job shop and bought a WEDM, yup I'd want it. but as a home shop guy I'm not coming up with a lot reasons to...isn't the most common use for four axis WEDM to create draft angles on stamping dies? so far at home haven't need that, but maybe i'm stuck thinking inside the box. adds a lot of complexity.



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    what!!!!!!!! are you not feeling well?????? if i had a 4 axes i would sit up thinking of things to do. even it was just to cut the morning butter for toast!!!!!!:-)



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