How to Prevent Pitting In EDM Machining

The scene is all as well familiar to anybody connected with EDM machining, aka electrical discharge machining. The situation goes something like this:

You spend hours designing an injection mold core or cavity, days CNC milling and grinding to get the size and shape required. The only factor remaining will be the EDM machining from the details. You have the Graphite Electrode Scraps made up, which requires a couple more days, and lastly every thing is setup in your CNC EDM machine.

Usually, you may make 4 cavities, that will create 4 exactly identical plastics parts when everything is lastly completed. Thing are going well, you've run the very first 6 various shaped electrodes via the process, now there is just one more. Only an additional 16 hours and you will be carried out and onto the following project.

So, you get it all set up to run all night, and you feel confident that everything is as it ought to be, you can sleep peacefully with out waking up in a start, questioning if you did this or that before going home.

The following morning you verify on your job the following morning and inspect it while nonetheless in the machine, it all checks out, so you remove it, clean it up and give it to the mold polisher to make it all shiny and nice. Quickly, he comes in and tells you he needs to show you some thing. Certain enough, correct in the bottom of the deepest component, a rib that's there to make the plastic part stronger, is a pit. An additional name for this pit is really a DC arc, or zit, or some expletive that is unprintable. What this means is that there is a small hole, or crater at the most inaccessible area of your mold that appears like it was bombed when you view it via a microscope.( Graphitized Petroleum Coke)

Now you'll need to get inventive and repair it, if you can. Generally there is some convoluted way to repair it by cutting out the bad component and making an insert to replace the pitted region. Occasionally though, it's just not possible to repair it and the whole piece should be scrapped!

Some manufacturers claim that their machines have software program that prevents DC arcing, and to a great extent they do. Mostly this is by retracting the electrode out of the reduce so flushing can occur. Some possess a higher speed oscillating impact that improves the flushing as well. Then there are some which have improved cutting parameters which will adapt when the machine senses a DC arc.

All of those techniques truly get down to enhancing flushing. Even high tech, new EDM machines will pit. I know because I have had to polish numerous surfaces EDM'd by these machines! You'll find a nice looking surface that is not so simple to detect until you begin removing the very first layer of recast.( Broken Baked Electrode)

Then you will find many, pits, not large enough to scrap the component, but certainly large enough to make the polishers’ job much more difficult and possibly altering the dimensional integrity from the steel.