>> Continued from page 41 << Figure 3: PEMed mould. >>
Examples and Applications Applications exist in essentially every manufacturing market. Some typical examples are fuel injection components in diesel- automotive; artificial heart valves in medical; turbine blade features in aerospace, rotary shaver heads in consumer products; sensor components in energy; and punch and dies in tooling.
The following are specific examples of the PEM capabilities. Machining surface features from tens to hundreds of microns have been accomplished with the PEM process. For example, the mould in figure 3 was machined in 9 minutes using a stainless steel electrode. Surface finish is 0.01 micron Ra with a feature depth of approximately 0.5 mm. Similar results have been obtained machining a texturing die consisting of pyramid geometry. Similarly, a surface micro structure consisting of 70 micron diameter pins, 250 microns high with a center spacing of 200 microns is machined into stainless steel in 12 minutes. The surface finish obtained by PEM machining is primarily determined by the material. A homogenous material with tight grain structure generally produces the best surface finish. If there are voids or eutectics such as carbides, these will affect the surface finish results.
Manufacturing dies and punches with the PEM process has resulted in significant time and cost savings. Punched for small screw heads such as those used in cell phones are machined in the hardened condition using a multi-position tool. The head diameter of these punches is 0.8 mm with an appropriate taper and edge radius. Likewise, the miniature driver for these screws can be machined with a 48 position tool at a machining rate of less than 4 seconds per part.
The coin die features shapes, size and surface textures which have different requirements across the face of the die. The matching
<< Figure 4: Coin die. >>
conditions need to be machined into the electrode with a typical machining gap allowance of 10 microns. A precise electrolyte flow pattern is provided by the tool design to allow the required feature and surface to be machined. The medallion die of figure 4 illustrates the range of detail produced by PEM. A variety of these dies have been produced including one with a hologram feature. The machining time for a die ranges from 8 to 25 minutes depending on size and detail.
42 | commercial micro manufacturing international Vol 6 No.6
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