Thin walls, tight internal radii, tapers, deep blind pockets in hard materials. Sometimes it seems designers are just trying to find the limits of what manufacturing can do. It’s as if they’re hoping manufacturing will say, “Can’t be done.”
The thing is, if manufacturing only has access to conventional machining processes they’re probably right. Some of these features can’t be produced without making a lot of scrap. Others are just impossible. The designer has no choice but to compromise the original design intent in the interests of manufacturability.
But what if there was a process capable of making every feature the “perfect” product needs? Imagine competitors looking at your product and wondering how it was made. Is that fantasy?
No, it’s the application of EDM. EDM produces features not possible by conventional processes. Here’s an explanation.
EDM, (electro-discharge machining), uses micro-arcs of electricity to remove material. A conductive tool or electrode is brought close to the also-conductive workpiece. Fluid fills the gap between them and a huge voltage creates tiny sparks that vaporize workpiece material.
EDM is performed in two ways: sinker/RAM EDM and wire EDM. In sinking the electrode is machined to the mirror image of the part required, then brought close to the workpiece. Material is removed at the closest point and carried away by the fluid. The electrode is inched closer and the workpiece erodes until it takes on the required form. Sinker/RAM EDM enables production of complex geometries, organic shapes and deep blind pockets.
Wire EDM works more like a bandsaw. A vertically-oriented, electrically-conductive wire moves continuously and is brought to the workpiece. Again, fluid fills the gap and voltage creates arcs that erode material. This time though, the wire cuts a thin path. Moving the workpiece in X and Y it’s possible to cut intricate, jigsaw-like shapes.
But wire EDM has another trick up its sleeve. Modern wire EDM machines can incline the wire from vertical, giving a fourth axis. With this capability it’s possible to put tapers on parts like shafts, punches and dies.
Unlike conventional machining processes, sinker and wire EDM don’t touch the workpiece. With no forces applied there’s no distortion. That improves accuracy and also allows remarkably thin walls. Imagine machining honeycomb structures in stainless steel for fluid flow applications.
Conventional material removal processes leave traces on the surface. Machining lines impart, likely affecting in-service performance. Even slow and expensive processes like grinding result in a “lay.”
EDM is different. There’s zero directionality to the finished surface, and with precise optimization of feed, voltage and frequency, uniformly smooth surfaces are possible. For parts designed to slide over one another, that can have a huge impact on friction and performance.
EDM is a specialized process, and achieving quality results takes both skill and experience. For many manufacturers relying on a specialist makes more sense than investing in the capabilities. All that’s required to leave designers wondering how a part was made is to understand the application of EDM. Let it be your secret weapon.