How to Stop Pitting In EDM Machining

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

You invest hours designing an injection mold core or cavity, days CNC milling and grinding to obtain the size and shape needed. The only thing remaining is the EDM machining of the particulars. You have the Graphite Electrode Scraps made up, which takes a couple more days, and lastly everything is setup in your CNC EDM machine. 

Typically, you might make four cavities, that will create four precisely identical plastics parts when every thing is finally completed. Factor are going well, you have run the first 6 different shaped electrodes via the process, now there is just one more. Only another 16 hours and you will probably be carried out and onto the following project. 

So, you get it all set up to run all night, and you really feel confident that every thing is as it should be, you can sleep peacefully with out waking up in a start, questioning in the event you did this or that before going home. 

The following morning you verify on your job the following morning and inspect it whilst nonetheless within 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. Soon, he comes in and tells you he needs to show you some thing. Certain sufficient, right in the bottom of the deepest part, a rib that's there to make the plastic part stronger, is a pit. An additional name for this pit is a DC arc, or zit, or some expletive that's unprintable. What this indicates is the fact that there's a little hole, or crater at the most inaccessible region of your mold that appears like it was bombed when you view it via a microscope.( Graphitized Petroleum Coke) 

Now you need to obtain creative and fix it, in the event you can. Usually there is some convoluted method to repair it by cutting out the poor component and making an insert to replace the pitted region. Sometimes although, it's just not possible to repair it and also the whole piece should be scrapped! 

Some producers claim that their machines have software program that prevents DC arcing, and to an excellent extent they do. Mainly this really is by retracting the electrode out from the reduce so flushing can occur. Some have a high speed oscillating effect that improves the flushing also. Then there are some which have improved cutting parameters which will adapt when the machine senses a DC arc. 

All of these methods really get down to enhancing flushing. Even higher tech, new EDM machines will pit. I know because I've had to polish numerous surfaces EDM'd by these machines! You will find a nice looking surface that's not so easy to detect until you start removing the very first layer of recast.( Broken Baked Electrode) 

Then you definitely will find many, pits, not large enough to scrap the component, but definitely big enough to create the polishers’ job far more tough and possibly changing the dimensional integrity of the steel.