Wednesday, February 22, 2017

Don’t Read This If You Use Graphite Electrodes For EDM

In electrical discharge machining, graphite electrodes are the most popular for making the complicated components in injection mold making. Even though EDM copper still has a huge market in Europe and Asia, the use of EDM graphite is gaining momentum there as well.

The reason is actually rather simple: EDM graphite is easy to machine, it performs well in the EDM machining process, and is relatively inexpensive. Electrodes that are machined using graphite can be re-dressed over and over again, sharp details can be machined into it, and the wear ratios are very favorable as well.

Graphite Electrodes For EDM
ZK-System.com Graphite Electrode

Manufacturing graphite electrodes for EDM does have one serious drawback: dust. Anyone who has milled, drilled or ground graphite knows how bad this can be.

Enter the graphite dust solutions

I recall machining graphite as an apprentice and having to literally hold my breath during each pass. Soon we added shop-vans to suck up the annoying dust, only to discover that the particle size of Poco 3 was smaller than the filter could manage.

So, the boss added an industrial grade vacuum system and we soon had hoses mounted from each machine to the ductwork. This was a huge improvement, though there was still an amazing amount of dust that escaped.

Graphite machining centers to the rescue

Newer high-speed milling machines arrived in the shop, each equipped with negative pressure chambers that remove nearly all the dust from the work area.This finally solved the problem and made everyone’s life much more pleasant.

Moldmakers in Asia, Europe, and the USA have an ongoing debate as to which material is best for electrical discharge machining: copper or graphite.

Graphite Electrodes For EDM
Wedo Moldmaker Graphite Electrode

EDM Graphite
Really, both choices are excellent, and your unique application and equipment will determine which is best for your needs. Investing in quality EDM supplies only makes sense. Industrial supplies play a key role in mold making, skimping on quality only hurts in the end.

Graphite is by far the most common electrode material used in the United States. EDM technology has advanced so that all new machines have circuitry that adapts to either graphite or copper. Graphite has many outstanding characteristics, here is a partial list:

  • No need to redress grinding wheels; the details remain sharp almost indefinitely.
  • Ability to achieve fine finishes
  • Low wear
  • Very good for roughing operations, less expensive grades can be used

Grades of graphite
There are four primary grades of graphite used in EDM machining .

  • Angstrofine- Less than 1 micron particle size. This is used when an extremely fine finish is required.
  • Ultrafine- Less than 5 micron particle size. Most finishing electrodes are of this type.
  • Superfine- 6-10 micron particle size. This type is generally used for roughing in cavities with larger details.
  • Fine- 11-20 micron particle size. Used for roughing in large cavities

Cost of graphite
Choosing the correct grade of EDM graphite for the job can mean substantial cost savings. For example: using an Ultafine grade for roughing a large cavity is wasting money. A lesser grade of graphite will actually outperform a fine grade in such a case.

Conversely, using a Fine grade instead of an Ultrafine grade to machine fine details will not only waste money, but not produce the desired results.

Good electrode material choices and correct EDM machining parameters can greatly affect the bottom line. It is important as well, to have an organized system of storing your graphite, so precious time is not wasted on using the wrong type by mistake.

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