Electrical Discharge Machining (EDM), also known as spark machining, spark eroding, die sinking, wire burning or wire erosion, is a metal fabrication process where a desired shape is obtained by using electrical discharges (sparks). This type of machining causes the material to be removed from the workpiece by a series of rapidly recurring electrical discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. One of the electrodes is referred to as the tool-electrode, or simply the tool or electrode, while the other is called the workpiece-electrode, or the workpiece. The process depends on the tool and workpiece not making actual physical contact. As the voltage between the two electrodes is increased, the intensity of the electric field in the volume between the electrodes becomes greater than the strength of the dielectric (at least in some places), which breaks down, allowing current to flow between the two electrodes. This phenomenon is the same as the breakdown of a capacitor (condenser). As a result, material is removed from the electrodes. Once the current flow stops (or it is stopped - depending on the type of generator), new liquid dielectric is usually conveyed into the inter-electrode volume, enabling the solid particles (debris) to be carried away and the insulating proprieties of the dielectric to be restored. Adding new liquid dielectric in the inter-electrode volume is commonly referred to as flushing. Also, after a current flow, the difference of potential between the electrodes is restored to what it was before the breakdown, so that a new liquid dielectric breakdown can occur and a new spark can be created.
Wire EDM Cutter
The method of Electrical Discharge Machining (EDM), also known as Spark Machining or Spark Erosion, is a manufacturing process that involves the use of electrical discharge (spark) to produce desired parts from sheet metal. There are three types of EDM:
- EDM,
- Wire-cut EDM,
- Fast hole drilling EDM.
EDM wire, also known as WEDM, involves the use of a thin single-strand conductive metal wire (such as brass) and deionized water, which allows the use of wire derived from EDM.
How does wire EDM work?
In wire electrode machining, material is removed from the workpiece by a series of rapidly repeating electrical discharges between the wire or electrode and the workpiece, separated by a dielectric fluid. Wire EDM can easily cut hard conductive materials and produce complex parts with high precision. Dielectrics are used to prevent short circuits in spark processes and waste disposal.
What is wire EDM used for?
Wire EDM is a metalworking process that proves to be an excellent choice for the production of small precision parts. It can also be used in many other applications, including in the automotive, aviation, electronics, and other industries, such as:
– creating molds,
– complex equipment and tools,
– rapid prototyping and full production,
– applications requiring low residual stress levels,
– small and detailed parts,
– drilling small holes,
– metal decay repair,
– circular production.
EDM Wire
Wire Electrical Discharge Machining (WEDM), also known as Wire EDM, a thin single-strand metal wire (usually brass) is fed into a bath of a dielectric fluid artifact (usually deionized water). The EDM wire makes the electroerosion process used for cutting sheets up to 300 mm thick, as well as for making punches, tools, and dies from hard metal, which would otherwise be difficult to machine. The wire, which is constantly fed from a reel, is held between the upper and lower diamond guide, located in the middle of the water jet nozzle head. The guide, usually CNC-controlled, moves along the x-y plane axis. On most machines, the upper slide can also move independently along the z-u-v axis, allowing for the cutting of cones and transitions (e.g., circles at the bottom, squares at the top). The upper slide can control the axis movement in the G-Code standard, x-y-u-v-i-j-k-l. This allows for programming wire cutters to cut very complex and delicate shapes. The accuracy of the upper and lower diamond guide is usually 0.004 mm (0.16 mils) and can have a cutting path or clearance as small as 0.021 mm (0.83 mils) using a 0.02 mm (0.79 mils) wire, despite the provided average cut. The best cost and machining time using a 0.25 mm brass wire is 0.335 mm.
Prototype Production
The EDM process is most commonly used in the molding, tooling, and die industry, but it is becoming a common method of prototype production and part manufacturing, especially in the relatively low-volume aerospace, automotive, and electronics industries. In the EDM rod, graphite, tungsten copper, or pure copper electrodes are machined to the desired (negative) shape and introduced into the workpiece at the end of a vertical slider.
Coin Die Production
For the production of jewelry dies and badges or for punching and perforating (using pancake dies) during coin minting (stamping), the obverse pattern can be made of 925 sterling silver, as (with the appropriate machine settings) the pattern is heavily eroded and is used only once. The resulting negative form is then hardened and used in drop hammers for the production of embossed flat steel from chunks of bronze, silver, or low-resistance gold alloys. In the case of badges, these flat surfaces can be further shaped into curved surfaces using another form. This type of EDM is usually performed in oil-based immersion dielectrics. The finished product can be further refined with hard enamel (glass) or soft (paint), or galvanized with pure gold, or nickel. Softer materials, such as silver, can be hand-carved as an enhancement.
Drilling small holes
Drilling with the use of electrical discharge machining is used for many things. In a wire EDM machine, small hole drilling is used to drill a through hole in the workpiece, through which the wire must pass to perform the wire EDM operation. A separate EDM head specifically designed for drilling small holes is mounted on the wire EDM, allowing etching of finished parts of large hardened plates on demand without the need for pre-drilling. Small hole EDM is used for drilling leading and trailing edges of turbine blades used in jet engines. The airflow through these small holes allows the engine to operate at higher temperatures than otherwise. The high-temperature, very hard monocrystalline alloys used in these blades make routine machining of these high aspect ratio holes extremely difficult, sometimes even impossible. Small hole electrical erosion can also be used to create micro-holes for fuel system components, spinning nozzles for synthetic fibers, such as artificial silk, and many other applications.
There are also standalone EDM machines for drilling small holes in the x-y axis, also known as super drills or drills, which can machine blind or through holes. EDM uses a long brass or copper tube electrode, which rotates in a holder with a constant flow of distilled or deionized water through the electrode as a flushing agent and dielectric. The electrode tube behaves like a wire in wire EDM, with a spark gap and wear rate. Some small hole EDM machines can drill 100 mm of soft or hardened steel in less than 10 seconds with an average wear rate ranging from 50% to 80%. This drilling operation can produce holes from 0.3 mm to 6.1 mm. Brass electrodes are easier to machine, but are not recommended for wire cutting operations, as corrosion caused by brass particles can cause "brass on brass" wire cracking, therefore the use of copper is recommended.
Advantages and disadvantages of EDM
EDM ensures the maintenance of appropriate precision of machining and the ability to process complex parts. This process is often compared to electrochemical machining. The advantages of EDM include:
- the ability to process complex shapes, which would otherwise be difficult to produce using conventional cutting tools;
- ability to machine very hard materials with very narrow tolerances;
- capability of machining very small parts, while conventional cutting tools may cause damage to the parts due to excessive pressure of the cutting tool;
- lack of direct contact between the tool and the workpiece. As a result, delicate parts and delicate materials can be handled without noticeable deformation;
- provides a good surface finish, which can be achieved through unnecessary finishing paths.
- ability to achieve very fine holes;
- making conical holes;
- internal profile and internal corners of pipes or vessels to 0.001 inch.
Disadvantages of EDM include:
- difficulty in finding professional operators,
- slow material removal;
- potential fire hazards associated with the use of dielectrics based on fuel oil;
- additional time and costs associated with creating EDM sinking/erosion electrodes;
- due to electrode wear, it complicates the reproduction of sharp corners on the machined object;
- specific power consumption, which is very high;
- high energy consumption;
- execution of "cutting";
- excessive tool wear during machining;
- Non-conductive materials can only be processed using specific process configurations.
EDM makes the need for machining elements much more precise. The possibility of using electrical discharge machining depends on having the appropriate equipment and operator.