Sapel Blog
Types of EDM (Spark Erosion) Machining
First of all, if you’re not sure what EDM is, our article What Is EDM? is for you. Electrical discharge machining (EDM) is divided into three main methods, depending on the type of tool electrode, how it is guided and the industrial need:
1. Sinker (Die-Sinking) EDM
This method, also known as cavity-type EDM or ram EDM, is the most traditional form of the technology. In this technique, the tool electrode (usually made of graphite, copper or copper-tungsten) is machined into the exact reverse, or negative, shape of the cavity required. The electrode is then lowered vertically towards the workpiece and, as it approaches it while immersed in dielectric oil, produces repeated sparks.
These sparks form a plasma channel and precisely melt the material, so the workpiece takes on the shape of the tool. Since there is no physical contact in the process, no mechanical stress is put on the workpiece. This method is an unbeatable choice for making plastic injection molds, industrial punches and dies, and deep, complex 3D cavities with sharp internal corners.
2. Wire EDM
Wire EDM, or wire cutting, works like an ultra-advanced fretsaw that never touches the part. Instead of a rigid, shaped electrode, it uses a very thin single-strand metal wire (usually brass, copper or zinc-coated wire) as the electrode. To keep it from snapping as the sparks constantly erode it, the wire runs continuously from one spool to another.
Cutting usually takes place in a tank of deionized water. Here, the computer control system (CNC) precisely guides the wire’s diamond guides in different planes, allowing the tool to cut very complex 2D geometries and even tapered cuts in thick metal plates with exceptionally high accuracy (down to ±1 micrometer). Because no physical cutting forces are applied to the workpiece, this method produces parts with minimal residual stress.
3. EDM Hole Drilling
This specialized method, also known as “super drill” or “hole popper”, is designed to drill deep, extremely small holes in very hard metals quickly. The tool used is a rotating hollow tube (usually brass or copper), with dielectric fluid (deionized water) forced at very high pressure through its center to flush eroded particles quickly out of the depth of the hole.
The sparks produced as the tube rotates and approaches the surface of the part create precise, small-diameter holes. The method is widely used in aerospace, for example to create cooling holes in jet engine turbine blades, which are made of very hard superalloys that conventional drilling cannot handle. It is also a key tool for drilling the start holes that the wire passes through in wire EDM machines.
Key Applications Across Industries
Aerospace and Avionics
The aerospace and aviation industries rely heavily on electrical discharge machining to produce critical parts with complex geometries, very tight tolerances and a high-quality surface finish. The method is used to machine very hard, heat-resistant alloys such as titanium and nickel-based superalloys.
One of its best-known applications is EDM hole drilling to create rows of cooling holes along the leading and trailing edges of turbine blades in jet engines. These holes let gas flow through and make it possible for the engine to run at very high temperatures. Because the blades are made of very hard, single-crystal superalloys and the holes have high aspect ratios, drilling them with conventional methods is practically impossible. Wire EDM is also used in the industry to produce extremely delicate, thin-walled, lightweight parts with minimal mechanical residual stress.
Mold and Tool Making
Sinker EDM, the most traditional form of the technology, is one of the cornerstones of the mold-making and toolmaking industries. In this method, the tool electrode is lowered onto the workpiece to burn its negative shape into it without any mechanical contact. This makes it extremely useful for accurately producing plastic injection molds, industrial punches and dies, and die-casting molds with complex geometries and sharp internal corners. It is also used to make coining dies for jewelry and badges, and blanking dies. Wire EDM, in turn, is widely used to cut and make high-precision dies and tools from hardened industrial steels (without having to anneal and re-harden them).
Medical and Electronics Industries
In medical device manufacturing, micron-level accuracy and preserving the integrity of conductive, biocompatible materials are vital. EDM is a key process for making fine surgical instruments, minimally invasive surgical tools and implants of all kinds from titanium and stainless steel. It can create very small geometric features and grooves on implants that greatly improve how well the implant integrates with the surrounding bone tissue. In the electronics industry, the technology is used to produce microstructures and connectors and for electrical discharge machining on printed circuit boards (PCBs). Wire EDM’s ability to make very narrow cuts and extremely small internal radii (down to 0.025 mm) makes it possible to mass-produce sensitive electronic parts without putting mechanical stress on them.
Salvaging Damaged Parts
One specialized and very valuable use of EDM in repairing and salvaging damaged, expensive parts is metal disintegration machining (MDM). In this process, EDM machines are used to remove broken drills, taps and bolts from engine blocks and other expensive metal castings. Since conventional drilling cannot work on a broken, hardened tool stuck inside a part, a portable EDM tool targets the exact center of the broken piece and melts and disintegrates the drill or bolt without the slightest damage to the threads or the inside wall of the hole, so the part can go back into production. The process is even used to repair and rebuild damaged parts by removing the damaged layer and restoring the original dimensions.
