All About Wire EDM Machining
Learn more about this technology and how it is used in manufacturing.
The use of electrical discharges as a machining method originated from the work of two engineers in the Soviet Union in 1943. They developed a simple electric discharge machine that could precisely erode hard-to-work materials like tungsten, using discharges from a simple resistor-capacitor network. Their machine development sparked a series of innovations over the next 20+ years.
Around the same time in the US, a spark-erosion machine was also being developed for removing broken bolts and taps from aluminum castings. That initial machine could arc at the rate of 60 discharges per second. Later versions using vacuum tube pulse generation were able to make several thousand arcs per second, resulting in a practical machining rate.
The subsequent development of spark machining using a steadily fed wire as the source electrode resulted in the process we now call wire EDM. After considerable experimentation with the conversion of punch-card-driven mills as wire eroders, a successful wire EDM machine was developed in the Soviet Union in 1967. By the 1980s, electrical discharge machining (EDM) could functionally run at 64 mm2/min, resulting in a viable alternative machining method for otherwise hard-to-work materials like pre-hardened steels, tungsten, stainless steel, and titanium. This article will further discuss wire EDM machining, its definition, applications, and materials.
An Introduction to Wire Electrical Discharge Machining
Wire electrical discharge machining (wire EDM) is a process that works by continuously feeding a wire electrode under tension on a vertical axis. Discharge voltage is applied through the wire, crosses via a dielectric liquid, and strikes the grounded workpiece. The workpiece is moved in an X-Y plane to trace a cut pattern through the material. This erosion can commence from the outside edges of the workpiece or by drilling a hole first. EDM is capable of eroding a hole through the billet to be used as a starting point for a contained cut path.
The process is sometimes complicated by the specific pattern to be cut and the need to clear eroded material from the surface. The process takes place in an electrolyte bath of paraffin or deionized water. This bath acts primarily as a coolant and a semiconductor that enables tightly controlled arcing, but it also makes for a convenient way to flush out debris. Wire EDM machines started as a type of arc bandsaw or EDM cutter, built to cut complex 2D shapes. However, they have continuously evolved to the point that modern 5-axis wire EDM machines can perform remarkably complex operations. For more information, see our guide on the Types of Machining Processes.
Other names for wire electrical discharge machining (wire EDM) are spark erosion, spark eroding, wire erosion, wire burning, wire cutting, and die sinking.
How Wire EDM is Used
Wire EDM is used for the direct, single-stage processing of hard materials from basic billet form to a finished state. Its single-stage nature reduces costs and improves toolmaking precision for a range of industries, including extruder, punch, and die tooling, aerospace, medical equipment, automotive, and electronics.
This benefit arises from the process’ ability to directly work with pre-hardened tool steels. The hardening process can introduce serious internal stresses and distortion/inaccuracy in machined parts. The ability to cut pre-hardened materials removes this issue almost entirely. The introduction of 5-axis CNC wire EDM machines has increased the breadth of tasks that the technology can undertake. The additional degrees of freedom in part design make complex three-dimensional products much more feasible.
The Wire Used in an EDM Machine
The wire used in an EDM machine comes in various grades and purposes. Among the choices are: copper, brass, tungsten, molybdenum, coated (zinc-coated and diffusion-annealed), and steel-core wires. The wire acts as the EDM device’s cutting tool. Each type of wire affects the machining process in different ways.
Whatever the wire type, it can only be used once and has only scrap value after use. The material breaks down during the electrical discharge process. EDM wire is sold by weight and classification. Its handling makes the difference between an optimized setup and one that is disrupted by breakages, poor precision, or other production interruptions.
Materials Wire EDM Can Cut
Wire EDM can cut all metals. In particular, it is used for cutting pre-hardened die steels, titanium, austenitic stainless steels, tungsten, and molybdenum. Though functional, it is generally not cost-effective to cut soft materials such as copper, bronze, brass, and non-hardened steel, all of which can be easily machined by cheaper conventional means. However, if the part must be manufactured in a single stage or with no added heat, EDM is the only practical option.
How Wire-Cut EDM Works
Arc-eroded material from both the work (the equivalent of cuttings or swarf) and the electrode is flushed out of the cut area by the dielectric liquid. As the arc erodes the workpiece, the table advances the work along a preprogrammed path. This process results in the most precise and fine cutting available from any CNC equipment. The machining process aims to maintain a very small spark gap, across which the arc forms. At no time should the electrode wire actually touch the workpiece.
Wire EDM Accuracy
Typical high-end machines maintain a wire positional accuracy of 40 millionths of an inch (0.000004”). Special high-precision machines can maintain 0.000001” accuracy. It is common for cut parts to maintain tolerances of 0.0001”, or one ten-thousandth of an inch.
Advantages of Wire EDM
Wire EDM has several remarkable properties that set it apart as a metal processing method. The advantages are listed in Table 1 below:
| Characteristics | Description |
|---|---|
Characteristics Production efficiency | Description High overall manufacturing efficiency, since few follow-on processes, is needed and extreme surface finish quality is directly achievable. |
Characteristics All metals capability | Description Unlimited ability to process conductive materials of any hardness or brittleness. |
Characteristics High precision | Description Extreme tolerances, with feature accuracies approaching 10 millionths of an inch and general tolerances of 40 millionths of an inch being common. |
Characteristics Low distortion | Description Zero-distortion processing— there is no bulk heating, no tearing or fracture, and no impact, so internal stresses and distortion resulting from processing can be kept close to zero. |
Characteristics Very fine features | Description Unlimited feature complexity in 2D parts (and limited 3D complexity in 5-axis wire EDM production) as the wire is infinitely maneuverable and cannot misapply force. |
Characteristics Safe operation | Description Wire EDM is safe, despite high voltages, so unsupervised processing is the norm, reducing costs without increasing risks. |
Disadvantages of Wire EDM
Wire EDM is not suited to all tasks. The disadvantages are listed below:
- Wire EDM is not suitable for plastics, composites, and natural materials. It only functions on conductive materials.
- Cuts relatively slowly. This slow process makes per-part costs higher than other machining processes (when comparing like for like).
- Consumable costs are high, as the wire cannot be reused.
Differences Between EDM and Wire Cut EDM
EDM uses a shaped electrode made of copper or carbon to cut intricate partial 3D cavities. The electrodes themselves are machined by conventional processes. Spark electrodes are then used in a pulsating height mode that allows cooling and full flushing of the work face. EDM is only as precise as the electrode machining but allows significant complexity in the shape of the eroded surface. This method is used for complex and precise shapes within molds and die-casting tools. It can operate on pre-hardened material, reducing overall costs and allowing more extreme hardening without tool distortion. Wire EDM, on the other hand, uses a continuously fed wire electrode for essentially 2D cutting. This process is ideal for complex 2D profiles for extrusion tools, punch/die sets, etc., as well as extreme precision processing of hard materials for aerospace and military applications.
How Xometry Can Help
Wire EDM machining is available at Xometry. Xometry offers the full range of EDM machining services.
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