Different techniques are often employed to produce a part prototype. Choosing the best solution to meet customer requirements can sometimes seem confusing. Makino’s application engineers created the following process comparison to demonstrate several approaches that might be considered for a cell phone mold application.

To decide which of the three methods to use, time constraints, surface finish, material, and accuracy are evaluated. For instance, is time of the essence when producing the part? Does the process call for EDM texturing? Does the customer need to “feel” the part? Is there fine detail involved? Each of these issues comes into play when choosing a solution.

DIRECT MACHINING
As shown below, high-speed direct machining is clearly the fastest way to complete the project. Using a Makino V33 machining center, direct machining takes 4 hours, 52 minutes, and the total process time is 15 hours, 52 minutes. This method produces a cell phone cavity with a good surface finish. If EDM texturing is required, however, a secondary operation will need to be performed using chemicals to etch the surface.

If achieving the correct surface finish and detail is more of a concern with the part, EDM should be used. This is also true if a customer wants to be able to feel the part prototype to get an idea of what the finished product will look like. Either way, producing a copper or graphite electrode is a better approach for these kinds of requirements.

EDM/COPPER
Using the EDM process with a copper electrode brings a more uniform surface finish to the cell phone part than direct machining. Using an electrode also helps in obtaining design approvals because the electrode part can be examined much like the finished product. This

EDM process, which also uses a V33 machining center, has an electrode manufacturing time of 2 hours, 23 minutes and a total process time of 25 hours, 51 minutes. While it takes longer to produce the part than direct machining, a better surface finish is achieved, and a secondary operation to obtain EDM texture is not necessary.

EDM/GRAPHITE
In this application, EDMing with a graphite electrode will achieve better accuracy than using copper, especially with the fine detail on the corner radii of the cell phone buttons. While the process takes longer than direct machining, electrode manufacturing is faster than with copper at 1 hour, 56 minutes, with a total process time of 19 hours, 29 minutes. Again, better surface finish is achieved than with direct machining. In this case, a Makino SNC64G/S graphite milling machine was used.

The key to choosing the appropriate solution for an application is to evaluate each on a case-by-case basis. Consider the cycle times needed, surface finish, material and accuracy when choosing a machining center to support the application’s requirements.