Flushing!

One of the major problems of EDMing is that the particles removed from the work piece remain in the spark gap and disturb the sparking process. With the exception of a few state-of-the-art machines that claim to be able to burn electrodes without any flushing system in use, providing a method for the removal of waste particles is crucial. To accomplish this the electrode should be provided with a flushing hole.

Without good flushing during the machining process the best machine control settings can easily be thrown off, slowing down the machining process at the sacrifice of production efficiency and quality.

What size of holes should be in the electrode? When it comes to installing the flushing channels in the electrode, the pattern, location and size of the holes vary with each electrode. I recommend using from 0.020 in. to 0.060 in. micro flush drills, depending on the electrode. Typically I have used .030 in. and found it most effective in 90% of the applications.

I have flushed hundreds and hundreds of electrodes in a variety of shapes and sizes, and have found a little creative thinking to be a big help in correctly positioning flush channels.

When examining an electrode to determine where the flushing channels should be, here are some pointers to follow:

Look for areas on the electrode where debris can be trapped–pockets or grooves that are formed in the electrode or ribs that go deep into the workpiece can trap debris at the bottom of the cavity.

When ever possible angle the flush lines so that during the EDM process the spike created by the flush hole will be burned away as the electrode advances into the workpiece. As well, on multiple electrodes, stagger the position of the flush hole from one electrode to the other, so that when the cavity is finished polishers will not have as much hand work with the little bit of spike remaining.

When working with these micro flush drills ranging form 0.020 in. to 0.040 in. one must use caution to prevent the drill from plugging and wandering off location. Take small pecks with the drill extending it by small amounts as you progress deeper and deeper. Using this method, I have been able to drill 0.020 diameter holes 6.0 in. deep in very thin ribs.

The following is a general guideline for matching electrode rib width with flushing hole diameter:

There are some machine manufactures that now claim that they can burn electrodes with no flushing required, but currently the process needs more development to be effective in all applications.

After all the flushing holes have been installed, using a small amount of air pressure (carefully) one can quickly determine that all the lines are connected together inside the electrode. Then plug off the main distribution channel and you’re ready to go.

For those readers who are moldmakers, think of the flushing system in the electrode similar to the installing of water lines in a mold. Flushing in complex electrodes can present great opportunities to expand your problem solving skills. Just a final reminder: When working with graphite–always deploy an efficient system of dust control over this material as you machine it.

Mark is the chair of manufacturing and transportation at St. Clair College in Windsor, Ont.