Ideal applications: The electrical discharge machining is suitable for generating complex profile with tight tolerances for extremely hard electrically conduction materials. Read previous post:Laser Cutting ProcessNormally the Carbon dioxide (CO2 laser is used here for precision cutting of materials. Wire EDM (Electrical Discharge Machining) is a precision metal removal process whereby a wire electrically charged and as it comes near the metal work piece, metal is removed via erosion.  The path of the wire is CNC controlled. Electric discharge machining (EDM), sometimes colloquially also referred to as spark machining, spark eroding, burning, die sinking or wire erosion,[1] is a manufacturing process whereby a desired shape is obtained using electrical discharges (sparks).
When the distance between the two electrodes is reduced, the intensity of the electric field in the volume between the electrodes becomes greater than the strength of the dielectric (at least in some point(s)), which breaks, allowing current to flow between the two electrodes. In 1770, English physicist Joseph Priestley studied the erosive effect of electrical discharges. Additional researchers entered the field and contributed many fundamental characteristics of the machining method we know today.
Electrical discharge machining is a machining method primarily used for hard metals or those that would be very difficult to machine with traditional techniques.
Ideally, EDM can be seen as a series of breakdown and restoration of the liquid dielectric in-between the electrodes. To obtain a specific geometry, the EDM tool is guided along the desired path very close to the work; ideally it should not touch the workpiece, although in reality this may happen due to the performance of the specific motion control in use.
The presence of these small craters on the tool results in the gradual erosion of the electrode. A further strategy consists in using a set of electrodes with different sizes and shapes during the same EDM operation. In any case, the severity of the wear is strictly dependent on the technological parameters used in the operation (for instance: polarity, maximum current, open circuit voltage).
Difficulties have been encountered in the definition of the technological parameters that drive the process.
Two broad categories of generators, also known as power supplies, are in use on EDM machines commercially available: the group based on RC circuits and the group based on transistor controlled pulses.
In the first category, the main parameters to choose from at setup time are the resistance(s) of the resistor(s) and the capacitance(s) of the capacitor(s).
In generators based on transistor control, the user is usually able to deliver a train of pulses of voltage to the electrodes. A framework to define and measure the electrical parameters during an EDM operation directly on inter-electrode volume with an oscilloscope external to the machine has been recently proposed by Ferri et al.[14] These authors conducted their research in the field of ?-EDM, but the same approach can be used in any EDM operation. The first serious attempt of providing a physical explanation of the material removal during electric discharge machining is perhaps that of Van Dijck.[15] Van Dijck presented a thermal model together with a computational simulation to explain the phenomena between the electrodes during electric discharge machining.
Further models of what occurs during electric discharge machining in terms of heat transfer were developed in the late eighties and early nineties, including an investigation at Texas A&M University with the support of AGIE, now Agiecharmilles.
Among these, the model from Singh and Ghosh[19] reconnects the removal of material from the electrode to the presence of an electrical force on the surface of the electrode that could mechanically remove material and create the craters. Sinker EDM, also called cavity type EDM or volume EDM, consists of an electrode and workpiece submerged in an insulating liquid such as, more typically,[21] oil or, less frequently, other dielectric fluids.
These sparks usually strike one at a time[21] because it is very unlikely that different locations in the inter-electrode space have the identical local electrical characteristics which would enable a spark to occur simultaneously in all such locations.
In wire electrical discharge machining (WEDM), also known as wire-cut EDM and wire cutting,[23] a thin single-strand metal wire, usually brass, is fed through the workpiece, submerged in a tank of dielectric fluid, typically deionized water.[21] Wire-cut EDM is typically used to cut plates as thick as 300mm and to make punches, tools, and dies from hard metals that are difficult to machine with other methods. The wire, which is constantly fed from a spool, is held between upper and lower diamond guides. The wire-cut process uses water as its dielectric fluid, controlling its resistivity and other electrical properties with filters and de-ionizer units. Along with tighter tolerances, multiaxis EDM wire-cutting machining center have added features such as multiheads for cutting two parts at the same time, controls for preventing wire breakage, automatic self-threading features in case of wire breakage, and programmable machining strategies to optimize the operation. Wire-cutting EDM is commonly used when low residual stresses are desired, because it does not require high cutting forces for removal of material.
The workpiece may undergo a significant thermal cycle, its severity depending on the technological parameters used. The EDM process is most widely used by the mold-making tool and die industries, but is becoming a common method of making prototype and production parts,[24] especially in the aerospace, automobile and electronics industries in which production quantities are relatively low. For the creation of dies for producing jewelry and badges by the coinage (stamping) process, the positive master may be made from sterling silver, since (with appropriate machine settings) the master is significantly eroded and is used only once.
On wire-cut EDM machines, small hole drilling EDM is used to make a through hole in a workpiece in through which to thread the wire for the wire-cut EDM operation. Small hole EDM is used to drill rows of holes into the leading and trailing edges of turbine blades used in jet engines. Small hole EDM is also used to create microscopic orifices for fuel system components, spinnerets for synthetic fibers such as rayon, and other applications.
There are also stand-alone small hole drilling EDM machines with an x–y axis also known as a super drill or hole popper that can machine blind or through holes. Several manufacturers produce EDM machines for the specific purpose of removing broken tools (drill bits or taps) from work pieces. Very small work pieces where conventional cutting tools may damage the part from excess cutting tool pressure. Photo chemical machining — Photochemical machining (PCM) is a method of fabricating metal components using reactive etchants to corrosively oxidize selected areas of metal. Electro chemical machining — ECM is a method of removing metal by an electrochemical process.


Typically, the tool (either a wire or a probe) consists of one electrode and the work piece is another electrode.  The work piece is sometimes immersed into the non-conducting dielectric liquid to increase the potential difference between the two electrodes. He has worked in various design projects in automobile, power plant and heavy earth moving equipment domain since 2005. Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. This phenomenon is the same as the breakdown of a capacitor (condenser) (see also breakdown voltage). Furthering Priestley's research, the EDM process was invented by two Russian scientists, Dr. EDM typically works with materials that are electrically conductive, although methods for machining insulating ceramics[5][6] with EDM have also been proposed. However, caution should be exerted in considering such a statement because it is an idealized model of the process, introduced to describe the fundamental ideas underlying the process. In this way, a large number of current discharges (colloquially also called sparks) happen, each contributing to the removal of material from both tool and workpiece, where small craters are formed. This is often referred to as multiple electrode strategy, and is most common when the tool electrode replicates in negative the wanted shape and is advanced towards the blank along a single direction, usually the vertical direction (i.e. For example, in micro-EDM, also known as ?-EDM, these parameters are usually set at values which generates severe wear. In one approach, a digital generator, controllable within milliseconds, reverses polarity as electro-erosion takes place. In an ideal condition these quantities would affect the maximum current delivered in a discharge which is expected to be associated with the charge accumulated on the capacitors at a certain moment in time. Because other sorts of generators may also be used by different machine builders, the parameters that may actually be set on a particular machine will depend on the generator manufacturer. This would enable the user to estimate directly the electrical parameter that affect their operations without relying upon machine manufacturer's claims. However, as Van Dijck himself admitted in his study, the number of assumptions made to overcome the lack of experimental data at that time was quite significant.
However, for small discharge energies the models are inadequate to explain the experimental data. This would be possible because the material on the surface has altered mechanical properties due to an increased temperature caused by the passage of electric current. These sparks happen in huge numbers at seemingly random locations between the electrode and the workpiece.
Hence, a longer on time produces a deeper cavity for that spark and all subsequent sparks for that cycle, creating a rougher finish on the workpiece. The reason that the cutting width is greater than the width of the wire is because sparking occurs from the sides of the wire to the work piece, causing erosion.[21] This "overcut" is necessary, for many applications it is adequately predictable and therefore can be compensated for (for instance in micro-EDM this is not often the case). Such thermal cycles may cause formation of a recast layer on the part and residual tensile stresses on the workpiece. In Sinker EDM, a graphite, copper tungsten or pure copper electrode is machined into the desired (negative) shape and fed into the workpiece on the end of a vertical ram. The resultant negative die is then hardened and used in a drop hammer to produce stamped flats from cutout sheet blanks of bronze, silver, or low proof gold alloy.
A separate EDM head specifically for small hole drilling is mounted on a wire-cut machine and allows large hardened plates to have finished parts eroded from them as needed and without pre-drilling. Gas flow through these small holes allows the engines to use higher temperatures than otherwise possible. EDM drills bore holes with a long brass or copper tube electrode that rotates in a chuck with a constant flow of distilled or deionized water flowing through the electrode as a flushing agent and dielectric. It is used for working extremely hard materials or materials that are difficult to machine using conventional methods. Metalworking is the process of working with metals to create individual parts, assemblies, or large scale structures. Doug is fluent in G-code and spends much of his day programming custom tool needs on Lyn-Tron's Fanuc Wire EDM. The gap between the electrodes are maintained such that electric discharge can happen after certain voltage and by the process work piece gets eroded locally to generate the cut.
One of the electrodes is called the tool-electrode, or simply the ‘tool’ or ‘electrode’, while the other is called the workpiece-electrode, or ‘workpiece’.
EDM can cut intricate contours or cavities in pre-hardened steel without the need for heat treatment to soften and re-harden them.
The size of the craters is a function of the technological parameters set for the specific job at hand. Strategies are needed to counteract the detrimental effect of the wear on the geometry of the workpiece. That produces an effect similar to electroplating that continuously deposits the eroded graphite back on the electrode. Little control, however, is expected over the time duration of the discharge, which is likely to depend on the actual spark-gap conditions (size and pollution) at the moment of the discharge. In particular, the time between two consecutive pulses and the duration of each pulse can be set. The details of the generators and control systems on their machines are not always easily available to their user. All these models hinge on a number of assumptions from such disparate research areas as submarine explosions, discharges in gases, and failure of transformers, so it is not surprising that alternative models have been proposed more recently in the literature trying to explain the EDM process.


As the base metal is eroded, and the spark gap subsequently increased, the electrode is lowered automatically by the machine so that the process can continue uninterrupted. On most machines, the upper guide can also move independently in the z–u–v axis, giving rise to the ability to cut tapered and transitioning shapes (circle on the bottom square at the top for example). Flushing is an important factor in determining the maximum feed rate for a given material thickness.
The high-temperature, very hard, single crystal alloys employed in these blades makes conventional machining of these holes with high aspect ratio extremely difficult, if not impossible. The electrode tubes operate like the wire in wire-cut EDM machines, having a spark gap and wear rate.
A new method for machining electrically nonconductive workpieces using electric discharge machining technique. 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. This method can be used with any other metal or metal alloy such as titanium, hastelloy, kovar, and inconel.
For instance, the removal of the debris from the inter-electrode volume is likely to be always partial. They can be with typical dimensions ranging from the nanoscale (in micro-EDM operations) to some hundreds of micrometers in roughing conditions. One possibility is that of continuously replacing the tool-electrode during a machining operation. This resembles the sink of the tool into the dielectric liquid in which the workpiece is immersed, so, not surprisingly, it is often referred to as die-sinking EDM (also called conventional EDM and ram EDM). This is a barrier to describing unequivocally the technological parameters of the EDM process.
As the electrode approaches the workpiece, dielectric breakdown occurs in the fluid, forming a plasma channel,[9][16][17][18] and a small spark jumps.
Several hundred thousand sparks occur per second, with the actual duty cycle carefully controlled by the setup parameters. Some small-hole drilling EDMs are able to drill through 100 mm of soft or through hardened steel in less than 10 seconds, averaging 50% to 80% wear rate. Adding new liquid dielectric in the inter-electrode volume is commonly referred to as flushing. Thus the electrical proprieties of the dielectric in the inter-electrodes volume can be different from their nominal values and can even vary with time. Thus, the maximum duration of discharge is equal to the duration of a pulse of voltage in the train.
Moreover, the parameters affecting the phenomena occurring between tool and electrode are also related to the controller of the motion of the electrodes.
A longer off time, for example, allows the flushing of dielectric fluid through a nozzle to clean out the eroded debris, thereby avoiding a short circuit. Also, after a current flow, a difference of potential between the two electrodes is restored to what it was before the breakdown, so that a new liquid dielectric breakdown can occur. The inter-electrode distance, often also referred to as spark-gap, is the end result of the control algorithms of the specific machine used. Two pulses of current are then expected not to occur for a duration equal or larger than the time interval between two consecutive pulses of voltage. Brass electrodes are easier to machine but are not recommended for wire-cut operations due to eroded brass particles causing "brass on brass" wire breakage, therefore copper is recommended.
The tool-electrode can also be used in such a way that only a small portion of it is actually engaged in the machining process and this portion is changed on a regular basis.
The typical part geometry is a complex 3D shape,[21] often with small or odd shaped angles.
Also, not all of the current between the dielectric is of the ideal type described above: the spark-gap can be short-circuited by the debris.
Vertical, orbital, vectorial, directional, helical, conical, rotational, spin and indexing machining cycles are also used. In their efforts to exploit the destructive effects of an electrical discharge, they developed a controlled process for machining of metals. The control system of the electrode may fail to react quickly enough to prevent the two electrodes (tool and workpiece) to get in contact, with a consequent short circuit.
Their initial process used a spark machining process, named after the succession of sparks (electrical discharges) that took place between two electrical conductors immersed in a dielectric fluid. This is unwanted because a short circuit contributes to the removal differently from the ideal case. The discharge generator effect used by this machine, known as the Lazarenko circuit, was used for many years in the construction of generators for electrical discharge. The flushing action can be inadequate to restore the insulating properties of the dielectric so that the current always happens in the point of the inter-electrode volume (this is referred to as arcing), with a consequent unwanted change of shape (damage) of the tool-electrode and workpiece.



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