In EDM machining, the choice of electrode material can make a huge difference in the outcome of the job. Finding the right material can be a costly process of trial and error, or you can do a little research to save time and money.
Fortunately, there are basically only two main choices for most moldmaking applications. Of course, there are other materials in use, but they are mostly for special situations.Copper or graphite?
Moldmakers in Asia, Europe, and the USA have an ongoing debate as to which material is best for EDM machining, copper or graphite. Really, both choices are excellent, and your unique application and equipment will determine which is best for your needs.
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:
- >Easy to machine
- 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 sinker EDM.
- 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 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.