06/08/2022 at 21:36 •
In the last few days, I did some cutting tests using a 1.6mm electrode from a TIG welder.
Here is the design that I used so far:
1.6mm tungsten electrode with 4mm T fitting, a piece 4mm tube at the back, and a 4mm brass tube at the front.
On the Wikipedia Page about ECM, they write that the removal rate in mm/minute is proportional to the amps per square mm - So for fast machining I would need a high amps per square mm value.
I tried out different things and noticed that there are some challenges to overcome:
First, it seems like machining takes place wherever the stream of water hits the workpiece (around the electrode). The closer to the electrode, the more material is removed.
I also noticed that if the stream diameter gets larger, the conducting surface gets also larger and with it, the cutting path diameter increases and the resistance decreases - like if you use a cable with a larger diameter.
If everything would stay the same during cutting this would not be a problem like you set your stream diameter and it always stays the same so that you always get the same cutting path size.
The problem with that is that after some time, dirt from cutting builds up on the electrode, which alters the steam and while doing so leads to a changing cutting path size and also slower machining because with a larger water stream the machine is removing more material. It also messes with the distance keeping because if the distance threshold was set to eg. 3.15A in the beginning, with a larger stream diameter and reduced resistance, the machine reaches a reading of 3.15A at a position further away from the workpiece than intended.
So this is a problem that needs to be solved.
Here you can see a picture of the stream before and after cleaning off the cutting dirt from the electrode. You can also see the cutting path that increased its diameter over time because of the dirt.
I think I will first try to find a way to prevent dirt from building up on the electrode to get a consistent cutting path quality and after that, I will focus my work on getting higher amps per square mm / cutting speed.Maybe something like this could work to wipe off the dirt:
06/05/2022 at 19:34 •
Over the last few days, I built a new "waterproof" Wire ECM setup to reach the goals that I could not reach with my wire EDM setup.
I haven't finished the wiring, yet, but I'm already able to cut 5mm aluminum and 3mm steel with it by moving the axes by hand.
The advantages of ECM over EDM are:
- There is no electrode wear $
- No need for a DI filter $
- Electrolyte can be mixed by using just tap water, salt and citric acid $
- Less risk of a wire break because if everything works as it should there is no wear on the wire.
- It's quiter than EDM.
The speed of both machine setups is around the same.
A disadvantage of ECM (for now) is that it's less precise, so that a small electrode is cutting a large cutting path.
I hope I can improve this in the future with more precise control of the gap between electrode and workpiece and by optimizing the water jet inline with the wire.
Next, I will finish the wiring and try to cut some metal.