Grizzly Discharges or Super Drill

In this article I want to talk about electric discharges that can gnaw various metals and steels. It will be mainly about electrical discharge machining.

I will assume that most of you are familiar with electric arc welding and the operating principles of this process. A similar principle underlies the EDM created by an electric discharge passing into an arc between two electrodes. If during welding the arc should burn continuously to obtain the most high-quality and even seam, then during erosion treatment this arc is interrupted with a certain frequency. At the initial moment of each breakdown, a part of the metal is pulled out from the surface of the processed material. The process is the destruction of a metal or other conductive material as a result of local exposure to short-term electrical discharges between two electrodes, one of which is a workpiece, and the other is an electrode-tool.Under the influence of high temperatures, heating, melting, and partial evaporation of the metal occur in the discharge zone. The intensity of gnawing depends on the power of the pulses embedded in the discharges, which in turn depend on the characteristics of the power source, the pulse width and the pause, during which the discharge must be able to decay.



It should also be noted such an important parameter as: interelectrode distance, which varies within a few micrometers. During long-term processing, the interelectrode distance must be kept constant, and the coordinate positioning system (in relation to cnc machines) is responsible for this. The discharge is ignited on its own with sufficient clearance and voltage (pulse amplitude). This gap cannot be reduced to zero, as this is fraught with a short circuit and the processing process will be suspended or delayed in time.



All processes of electro-erosion occur in a liquid medium. Most often, ordinary tap water or kerosene is used for the most critical parts. The liquid used mainly serves to remove heat and sludge from the zone of influence of the pulses, therefore it is additionally driven through a series of filters, cleaning the reaction products, such as oxides of the metal being treated and the electrode - the tool, since the latter is also destroyed.

There are a number of varieties of EDM: wire cutting, copying, milling, flashing holes, alloying. Electroerosive processing is used in the manufacture of a large number of classes of parts: dies, die cavities and molds, die parts of machines, carbide shaped cutters and others.

Now let's move on to the practical part.

I’m not myself if I hadn’t tried to make a prototype pulse generator myself, at least in a simple version.

The generator itself is useless, since it must be part of any technological machine for erosion treatment. In this regard, it was decided to make a semblance of an erosive piercing machine, since from one of the previous projects I still had the mechanical part, which is a base with a vertically moving cantilever traverse.

The only thing I changed in it was to change the drive to a stepper motor with an encoder and connect the motor shaft to the belt gear screw.



Stepper motor control is carried out through the Chinese program (WireCut) to control the erosion cutting machine. This program is mainly put by the Chinese on their EDM machines; in Russia, too, many people install it as a modernization of old machines. It comes with the AutoCut expansion board. I don’t really want to dwell on this, since this can greatly inflate the article. In addition, the programmer is so-so, but you can work with it.

The basis of the pulse source was a DC power supply 90V 20A. Then you need to translate this voltage into pulses. From the simplest thing that occurred to me is to take an arduino and pick up the lower or upper key driver with a power transistor to it. Of course, you can use a special PWM chip, but since I was thinking of expanding the functionality in the future, I still settled on the microcontroller.

So, what kind of impulses do we need? And we need pulses in the form of a meander with a constant frequency of up to 30 kHz and with the ability to change the pulse width.



To change the pulse width, I hooked up a 10 kΩ resistor to the controller, which changes the duty cycle from 0 to 50%, set the frequency to static, started at 20 kHz.



Additionally, I displayed the main data, that is, the pulse width in microseconds and the duty cycle as a percentage. He spread a small scarf and made it on his small cnc machine. I have little experience in these matters, but it turned out pretty well.

After desoldering the board, it was the turn to put everything together:



To control the current, I built an ammeter in the circuit, I will use it to monitor the current consumption during processing.

I connected the plus wire to the working electrode, as which I used a piece of copper wire with a diameter of 1.5 mm, that is, we will flash the hole.

I connected the negative wire from the power supply through the generator board and attached it to the sacrificial metal part, which is to be perforated.

The part is a flange made of steel grade 40X 5 mm thick.
Of course, this technology is better to use for processing more durable metal.

The flange was placed in a sealed plastic container filled with 1 liter tap water. Water during the work did not circulate and in no way was purified.



After all the connections, it’s time to turn everything on and check the operation. First, I turned on the generator and set the PWM level to 0%. Then he turned on the power supply unit and slowly began to add duty cycle. Small oxygen bubbles began to stand out on the working electrode. In manual mode, he brought the electrode to the part until the first spark appeared, after which he started the automatic lowering of the electrode at a speed of 1 μm / s with a pulse width of 1.5 μs. This gave weak impulses and quickly led to a short circuit. In further attempts, he began to increase the width of the pulses until, when the electrode was automatically lowered, there was no constant sparking without “plugs”.

He stopped at a pulse width of 5 μs at a frequency of 20 kHz. A further increase in the pulse width leads to more powerful pulses and an increase in current, which overheats my ballast resistor and power transistors.



Reducing the frequency gave better results due to the increase in the width of the pause. This made it possible to increase the lowering speed of the electrode to 5 μm / s, the discharges became stable, and the current increased to 6A. He made several through holes, “drilling” lasted an average of min 15, depending on the “plugs” at the beginning of processing and at the exit from the hole.


Summing up, we can say that this simplified construction (prototype) of the pulse generator works. The generator circuit is far from ideal and it is planned to improve it in parallel with the addition of new pulse generation modes.

This article does not claim to be true of all of the above, since there are many nuances that may not be disclosed in it.

We are all artists and see in different ways.

Thank you for the attention!