[richrod]

Hi Guys,

I am having trouble scaling an EDM electrode. Any of you know of a software that can extract the geometry of an electrode and scale it automatically for roughing and finishing?

Or does any one know a rule of thumb i can use to determine the scaling?

By the way I am using Graphite and a ACRA ZNC Sinker EDM,

thanks

[titan99]

In Unigraphics there are two ways to do it.
1. keep the original electrode model, use two set of programs each one for roughing & finishing electrodes. Here you can play with the tool diameters according to the spark gaps.
2. Another method is have roughing & finishing electrodes, and program individually. so you two sets of programs for roughing & finishing electrodes. The original electrode model is just translated(in UG), or scalled in other softwares according to get the required spark gaps.

http://www.titanengg.com.sg

[richrod]

Ok,

The problem we have is that we tried to make an electrode and it came out to big,

Do you have a shrink factor we can apply to our electrode, for roughing and finishing?

.0004% for example?

thanks

[MrWild]

Do it in your CAD software. AutoCAD allows you to scale easily.

[richrod]

I am actually looking for a scale factor that anybody uses as a standard so I can resize my electrodes to make another test run,

thanks

[ToddB3]

Richrod

Electrodes are not "scaled", they are undersized based upon an overcut. This overcut is determined by the power settings and the geometry you are trying to EDM.

If you take a rectange .500" x 1.000" and you had a power setting that had an overcut of .005" per side. You would make your electrode .490" x .990". The feature size doesn't matter, every dimension will change by the overcut amount.

To add more to this, some machines can orbit. You can take that same electrode with the .005"/side undersizing, but only use a power setting that has .001" overcut and orbit .004" per side. Basically you move in a cicular (or square) pattern to achieve the desired size. Using a lower power setting will make the surface smoother and more precise.

If you could scan the power setting section and the geometry that you are trying to cut, I could help you out. Also what software/machinery do you have at your disposal?

[easymike29]

In Autocad:
Draw your part to finish dimensions.
Turn it into a poly line.
Issue the "offset" command (Smaller by the spark gap)
The resultant dimensions will be your electrode sizes.
Gene

[richrod]

Please find power setting table and geometry attached,

any help is appreciated,

thx

[richrod]

We have full VMC capacity 3-axis and use virtual gibbs for programing and have solidworks 2008

[ToddB3]

Rich

Wow, that is a pretty big electrode. I have a few more questions to ask. Does your EDM have an orbiting capability? I looked them up on the web and the brochure doesn't mention one. What material are you burning? Also what type of surface finish are you looking for? And finally, what tolerance are you trying to hold?

I'm asking these questions because everything makes a difference in how you would approach this. The orbit capability (or lack there of) will determine the style of electrodes. If you can orbit, you can make all of the electrodes to the same undersizing. You can then expand your orbit as you decrease your power. This will give you a finer surface finish and you will be able to hold closer tolerances. If you cannot orbit you will need to make electrodes in different sizes to compensate for the different power settings. The material will affect how many electrodes you will need. Carbide will wear electrodes more than steel, and aluminum will wear them even less. The required surface finish and tolerances will also dictate final power settings and even number of electrodes.

[richrod]

To answer your questions:

1. We don have orbiting

2. We are using Graphite to burn 440 stainless steel, hardened.

3. Tolerance is +/- .005"

4. It is for a mold cavity, so we are looking for a good finish, but we know that we have to polish afterwards.

thx

[ToddB3]

Rich

Because you don't have orbiting, you will need to make roughers and finishers. Due to the size of the burn (and assuming you have not roughed anything out) , I would suggest 2 different trodes. For the first trode (rougher), I would go with -.010 per side. The second trode -.0020 per side. I came up with these using the supplied settings.

-Rougher
Current (L.A.) 45, On-time 300, Off-time 1, Voltage 40, Surface Finish 18, Electrode Wear .3%, Speed 270, Fine Gap .320, Rough Gap .460

-Finisher
Current (L.A.) 9, On-time 2, Off-time 1, Voltage 40, Surface Finish 1.8, Electrode Wear 32%, Speed 52, Fine Gap .055, Rough Gap .075

The rough gap shows .460mm toatal which equals .0180". So each side will need .009" undersizing. This will also allow .001" per side for the finisher to take. The finisher has .075mm (.003"). If we use .002" per side it will give you .0005" stock for polishing.

As far as manufacturing the electrodes, Gibbs should have a stock allowance in its 3D toolpaths (I use MasterCam). All you have to do is run one at -.010" and one at -.002" (I would run two at .002"). Keep in mind when you run the rougher to stay short of your depth by about .010" as well.

This should get you pretty close, but without being in front of the machine this is the best I can help.

[jetski]

As you power settings change so goes the overburn. We program on size and then lie to the cutter diameter in the program. For example instead of programing a .375 dia ball mill over an electrode contour that needs .004 overburn. I go with a .375-.008 or .367 dia ball. You have to burn a test piece on your machine at different settings to determine the overburn on the machine at the settings. To do this cut a 1.000" cube and burn a pocket then check the size at that burn setting. Do another setting and take notes. Every machine is just a little different. I have an old Elox 1940-50 vintage and a newer 1990 Roboform Charmille cnc, very different. Up to .04 per side at 128 amps on the Charmille with a golf ball finish in rough with minimal wear, and .0002 at the other end with the finest finish I have ever seen on an edm and max electrode wear. So my overburn on my machine is .04 to .0002 depending on amps or wattage going through the cottage. Have fun it is time for cookies, milk, and story time here.