A common belief in the moldmaking industry is that a lower quality electrode material can be used to produce superior surface finishes if a high quality EDM machine is used. While the technologies of the newer generation EDM sinkers have allowed the EDMer to become more proficient in the application,

this technology only goes so far when it comes to producing fine surface finishes economically with low quality electrode materials. True, improved EDM sinker technologies have the ability to monitor the condition of the EDM process and make adjustments to run more efficiently. However, these changes are generally limited to optimization in the roughing stage or to eliminate arcing in the EDM cavity. Often, the production of fine surface finishes in the cavity does not come with the technological improvements of the EDM sinker unless an electrode material of higher quality is used.

The current business environment in which we are operating requires shorter cycle times and reduced production costs. For many of the applications in the market today—specifically medical and aerospace—meeting the demands of the business environment is not congruent to trying to save a few dollars on the electrode material.

Since the primary element in producing a quality mold is time, this is the facet of the application that must be considered when determining the profitability of the job. As time increases, profitability is reduced. Therefore, trying to achieve a fine surface finish with a lower quality material is like trying to run a NASCAR race with low octane fuel. It just isn’t a wise choice.

In general, the material characteristics of the electrode play a much larger role in achieving a fine surface finish than one might think. When we think of fine finishes, we may envision something similar to a glossy finish that reflects light very easily.

Conversely, in today’s mold design a fine finish means more than a surface that has been polished. Many of the molds that are currently being produced require a textured finish that must be consistent throughout the cavity. In light of this, any variation of the texture within the cavity stipulates that the finish be retextured through additional EDM processes, acid etching and so forth. These actions require additional time and increased costs—therefore limiting the profitability of the application.

With a high quality electrode material, the surface finish of the cavity is one area where opportunity exists for savings of time and costs while still producing a quality mold. A high quality electrode material can be thought of as a material of small particle size and having a consistent microstructure and uniformity between the particle size and porosity.

As previously stated, the microstructure of the electrode material plays a vital role in the ability to achieve a quality EDM finish in the cavity. As the EDM cavity is a replication of the microstructure of the electrode, the ability to obtain fine surface finishes is limited with materials of inconsistent structures. If a low- to mid-quality electrode material is used in a textured cavity, there is an increased risk that the texture will be uneven. Also, since various components of the mold are often outsourced to different companies, this increases the potential that the textured finish will be mismatched.

If this occurs, the most common means to rectify the situation is to acid etch the cavity. In the etching process, the EDM finish must first be removed; therefore, allowing the etching to take place. This creates another issue in itself as sufficient stock must remain in the cavity for the etching process.

If inadequate amounts of stock remain in the cavity, the etching depth will be limited and may not provide satisfactory results. Therefore, this increases the importance of getting the job done with the right combination of electrode material and machine parameters.