There are several different types of machines and industrial applications that use the EDM process for high precision machining of metals. Listed below is a brief description of EDM and some of the most widely used and not-so-well- known EDM systems.

Electrical Discharge Machining (EDM)

EDM is a high precision metal removal process that uses thermal energy from a fine, accurately controlled electrical discharge (spark) to erode (vaporize) metals. The scope of the EDM process ranges from the drilling of micro-holes that are smaller than a human hair to machining 100,000 pound automotive dies. In EDM, the workpiece must be electrically conductive and the machining gap submerged in a dielectric fluid. In the EDM sinking process, the inverted image of the tool electrode is gradually impressed in the workpiece.

Although each machine type is significantly different in design and application, they all use thermal energy produced by pulsed spark discharges for metal removal. The two primary types of EDM systems are "Die-Sinking" and "Wire" EDM. Die-Sinking machines are also called Sinker, Ram-Type, Conventional, Plunge or Vertical EDM.

Wire Electrical Discharge Machining (WEDM)

This widely used EDM process removes material using electrical discharge erosion action with a wire electrode traveling longitudinally through the workpiece. The relative moving passage between the wire electrode and workpiece is controlled by a CNC system according to a preprogrammed CNC program to cut the workpiece into desired shapes. WEDM is widely used to cut punches and dies, shaped pockets and many other industrial applications.

Electrical Discharge Milling

This newer EDM process uses standard cylindrical rotating electrodes to perform electrical discharge erosion in the form of milling. A mold cavity is formed by successive passes of the electrode down to the desired depth. Material removal rates are similar to die-sinking machines. In EDM Milling, the use of standard cylindrical electrodes significantly reduces the cost of making expensive, complex electrode shapes.

Electrical Discharge Grinding (EDG)

This EDM process (also known as Rotary EDM and EDM Grinding) uses a rotating electrically conductive wheel (similar in size to a standard abrasive grinding wheel) as the tool electrode to perform electrical discharge erosion similar to creep-feed grinding. This process is used as an elective alternative for sharpening carbide and diamond tipped cutting tools, thus reducing the high cost of using diamond grinding wheels. EDG machines are more commonly used throughout the European countries than in the U.S.

Electrical Discharge Dressing (EDD)

This EDM system uses the electrical discharge erosion effect to dress grinding wheels in real-time when mechanically grinding tough materials. In this process, the grinding wheel must be electrically conductive. A metal bonded diamond grinding wheel is usually dressed by this method. A pulsed electrical voltage is applied between the electrode and grinding wheel in which the generated electrical discharge removes the built-up edges on the grinding wheel. This process can also be used to produce a specially formed grinding wheel.

Ultrasonic Aided EDM (UEDM)

This is a thermal material removal process in which material is removed by electrical discharge erosion with a tool electrode that is vibrating at ultrasonic frequency. The ultrasonic vibration improves the machining stability and substantially increases machining rates when drilling small or micro holes.

Abrasive Electrical Discharge Grinding (AEDG)

This is a hybrid process in which material is removed by the combination action of the electrical discharge erosion and mechanical grinding for machining advanced ultra-hard materials. This process is particularly useful for machining polycrystalline diamond (PCD) materials. Electrical discharges help to increase the material removal rate and the mechanical grinding generates a fine surface finish.

Micro Electrical Discharge Machining (MEDM)

Micro EDM is defined here as a miniature sinker type machine which normally utilizes a diamond V-groove to rotate the tool electrode to 10,000 rpm. Electrode diameters down to 5 micron are possible which are used for producing micro holes or other shapes in thin electrically conductive materials. The electrodes are made by a reverse polarity method using another specialty EDM process known as "Wire Electrical Discharge Grinding" (WEDG). The most common size range for Micro EDM is from 20µm to 250µm. One of the major manufacturer's of Micro EDM equipment offers a machine with .1 µm resolution using a CNC system for controlling the X-Y-Z axes. It will routinely drill 10µm to 200µm with an accuracy of ±1-2µm. Due to the very small nature of this work, MEDM is accomplished with the aid of a microscope.

Micro Wire EDM (MWEDM)

This EDM process uses a tungsten wire electrode with a diameter as small as 10µm. Micro Wire EDM systems focus mainly on the machining of 0.1 to 1mm size parts, which, due to material, thickness, etc., are impossible to form using the semiconductor process. These machines utilize a specially developed wire travel system, spark generator and MWEDM monitoring system capable of analyzing and controlling extremely small energy levels.

Mole EDM

This highly specialized EDM process has the ability to machine a curved path or tunnel through the workpiece. This process is referred to by its originally developers as "Mole EDM" because it is like a mole digging a tunnel into the ground. The Mole EDM machine's shape is similar to a bar which can be bent and a shape memory alloy is used as an actuator. An ultrasonic wave is used to detect the form of tunnels machined by this process. It was originally developed by Tokyo University Engineering Department and Mitsubishi Electric Corporation in Japan.

Double Rotating Electrodes EDM

This method uses rotating electrodes to erode a rotating workpiece, which can produce various workpiece shapes by combining the relative positions and angular velocities of electrode and workpiece. By keeping angular velocities of the two axes identical, its developers report that high precision spirals can be generated with a diameter error less than .004 mm, circular error less than .002 mm and surface roughness of Ra .063µm.

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Article from our friends at EDM Technology Transfer