All About Wire EDM Machining: Definition, Application, and Materials
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.
What Is 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.
Who Is the Pioneer of Wire Electrical Discharge Machining?
The person who pioneered the concept behind wire EDM was Joseph Priestley. He was the first to observe – in 1770, no less – that electrical discharges on metal surfaces left damage at the spark points. Priestly was a prolific natural scientist and observer/experimenter who is also credited as the first to isolate oxygen, among other discoveries. In 1943, B. R. Lazarenko and N. I. Lazarenko, two Soviet researchers, stumbled upon the notion of machining intractable materials using spark erosion. Their concept resulted in the development of the first EDM machines.
What Is Wire EDM Used For?
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.
Which Wire Is 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.
What Kind of Materials Can Wire EDM 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.
What Is the Cutting Method Used by Wire EDM?
Electrical discharge as a machining process uses a discharge (spark) between a tool electrode and a material billet to be cut. The spark energy is dissipated as heat at a microscopic point, reaching as high as 12,000°C and vaporizing both parts. However, since the point of contact is so small, the part does not absorb much of that heat. Wire EDM preserves the electrode by moving the wire through the cut area so the cut is always facing fresh wire. The wire is moved across the workpiece – usually in the X-Y plane – following a CNC-controlled path that is programmed in G-code.
How Does Wire-Cut EDM Work?
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.
How Accurate Is Wire EDM?
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.
Who Manufactures Wire EDM Machines?
CNC equipment manufacturers of both specialist and budget varieties make a range of wire EDM machines. The leading manufacturers are: Agie Charmilles, FANUC, Cincinnati Milacron, Hitachi, Xact Wire EDM Corp, KentUSA, and many other first-tier brands. There is also a very competitive market for less well-known but highly capable machine brands. Research the company and specific machines carefully before choosing one.
What Are the 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. |
What Are the 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.
What Are the Best Wire EDM Machines?
The best wire EDM machine manufacturers are:
- Agie: Agie units are known for their reliability, accuracy, capability, and operator friendliness.
- Makino: Makino has a reputation for huge innovation and lower per-part costs than other market leaders.
- Brother EDM: Brother EDM makes simple, reliable machines that are practical for smaller workshops with lower throughput and budgets. Their precision is lower than the market leaders, but still quite impressive.
Is It Possible To Wire EDM Stainless Steel?
Yes, it is possible to cut stainless steel using wire EDM. Austenitic grades of stainless steel are particularly well suited because they are heavily work-hardened to start with.
What Is the Difference 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.
Is Wire EDM Machining Available at Xometry?
Yes, wire EDM machining is available at Xometry. Xometry has access to the full range of EDM machining services.
Summary
This article presented the wire EDM machining, explained what it is, and discussed its different properties and factors to consider when using it. To learn more about wire EDM machining, contact a Xometry representative.
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