Editing Electrical discharge machining (section)

==Generalities==
[[File:EDM scheme.png|thumb|upright=1.4|'''1''' Pulse generator (DC). '''2''' Workpiece. '''3''' Fixture. '''4''' dielectric fluid. '''5''' Pump. '''6''' Filter. '''7''' Tool holder. '''8''' Spark. '''9''' Tool.]]
Electrical discharge machining is a machining method primarily used for hard metals or those that would be very difficult to machine with traditional techniques. EDM typically works with materials that are electrically conductive, although methods have also been proposed for using EDM to machine insulating [[ceramic materials|ceramics]].<ref>{{cite journal |title=Assisting Electrode Method for Machining Insulating Ceramics |journal=CIRP Annals - Manufacturing Technology |volume=45 |pages=201–204 |year=1996 |last1=Mohri |first1=N. |last2=Fukuzawa |first2=Y. |last3=Tani |first3=T. |last4=Saito |first4=N. |last5=Furutani |first5=K. |doi=10.1016/S0007-8506(07)63047-9}}</ref><ref>{{cite journal |title=Effect of technological parameter on the process performance for electric discharge milling of insulating Al2O3 ceramic |journal=Journal of Materials Processing Technology |volume=208 |pages=245–250 |year=2008 |vauthors=Liu YH, Li XP, Ji RJ, Yu LL, Zhang HF, Li QY |issue=1–3 |doi=10.1016/j.jmatprotec.2007.12.143}}</ref> EDM can cut intricate contours or cavities in pre-hardened [[steel]] without the need for heat treatment to soften and re-harden them. This method can be used with any other metal or metal alloy such as [[titanium]], [[Haynes International|Hastelloy]], [[kovar]], and [[inconel]]. Also, applications of this process to shape [[polycrystalline diamond]] tools have been reported.<ref>{{cite journal |title=Micro machining glass with polycrystalline diamond tools shaped by micro electro discharge machining |journal=Journal of Micromechanics and Microengineering |volume=14 |issue=12 |pages=1687 |year=2004 |last1=Morgan |first1=C. J. |last2=Vallance |first2=R. R. |last3=Marsh |first3=E. R. |bibcode=2004JMiMi..14.1687M |s2cid=250921623 |doi=10.1088/0960-1317/14/12/013}}</ref>

EDM is often included in the "non-traditional" or "non-conventional" group of [[machining]] methods together with processes such as [[electrochemical machining]] (ECM), [[water jet cutting]] (WJ, AWJ), [[laser cutting]], and opposite to the "conventional" group ([[turning]], [[milling machine|milling]], [[grinding (abrasive cutting)|grinding]], [[drilling]], and any other process whose material removal mechanism is essentially based on mechanical forces).<ref>McCarthy, Willard J. and McGeough, Joseph A. [https://www.britannica.com/technology/machine-tool "Machine tool"]. ''Encyclopædia Britannica''</ref>

Ideally, EDM can be seen as a series of breakdown and restoration of the liquid dielectric in-between the electrodes. However, caution should be exerted{{by whom?|date=January 2025}} in considering such a statement because it is an idealized model of the process, introduced to describe the fundamental ideas underlying the process. Yet, any practical application involves many aspects that may also need to be considered. For instance, the removal of the debris from the inter-electrode volume is likely to be always partial. Thus the electrical properties of the dielectric in the inter-electrodes volume can be different from their nominal values and can even vary with time. The inter-electrode distance, often also referred to as spark-gap, is the result of the control algorithms of the specific machine used. The control of such a distance appears logically to be central to this process. 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. The control system of the electrode may fail to react quickly enough to prevent the two electrodes (tool and workpiece) from coming into contact, with a consequent short circuit. This is unwanted because a short circuit contributes to material removal differently from the ideal case. 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. Ultimately, a description of this process in a suitable way for the specific purpose at hand is what makes the EDM area such a rich field for further investigation and research.{{unbalanced opinion|title=I say that "a description of this process in a suitable way for the specific purpose at hand" not only doesn't make it a "rich field", but that the sentence holds almost no meaning.|date=January 2025}}{{tone inline|reason=This entire paragraph reads like the overwritten type of report one might do for a school assignment when one hasn't bothered reading very much material and decides to use lots of non straightforward language and joining clauses to make it appear well thought out... it doesn't match the tone of the rest of the article at all...  I'm suspicious it was copied from somewhere else in its entirety originally, and it seems to have been deleted for copyvio several times, but search engines suck so much now thanks to ML and so many http-only sites have died off since it was added that it's extremely difficult to find an original...  the entire paragraph could be effectively summarized as "A one sentence simplified description of the process does not describe all aspects considered in practice"|date=January 2025}}<ref name="descoeudres">Descoeudres, Antoine (2006). [https://infoscience.epfl.ch/record/84931/files/EPFL_TH3542.pdf Characterization of electrical discharge machining plasmas]. ''Thèse EPFL'', no 3542.</ref>

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. 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. The size of the craters is a function of the technological parameters set for the specific job at hand. They can be with typical dimensions ranging from the nanoscale (in [[micro-EDM]] operations) to some hundreds of micrometers in roughing conditions.{{tone inline |reason=Ideally, I shouldn't be seeing the word "ideally" this much.  Also to summarize again, "Different uses of a tool cause different tool lifetimes", which could be applied to any tool used for any varying set of purposes.  Saying a lot without really saying anything here.|date=January 2025}}

The presence of these small craters on the tool results in the gradual erosion of the electrode. This erosion of the tool-electrode is also referred to as wear. Strategies are needed to counteract the detrimental effect of the wear on the geometry of the workpiece. One possibility is that of continuously replacing the tool-electrode during a machining operation. This is what happens if a continuously replaced wire is used as electrode. In this case, the correspondent EDM process is also called wire EDM. 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. This is, for instance, the case when using a rotating disk as a tool-electrode. The corresponding process is often also referred to as EDM grinding.<ref>{{cite journal |title=Fabrication of micro-electrodes by multi-EDM grinding process |journal=Journal of Materials Processing Technology |volume=140 |pages=332–334 |year=2003 |last1=Weng |first1=F. T. |last2=Shyu |first2=R. F. |last3=Hsu |first3=C. S. |issue=1–3 |doi=10.1016/S0924-0136(03)00748-9}}</ref>

A further strategy consists in using a set of electrodes with different sizes and shapes during the same EDM operation. 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. z-axis). This resembles the sink of the tool into the dielectric liquid in which the workpiece is immersed, so it is often referred to as die-sinking EDM (also called conventional EDM and ram EDM). The corresponding machines are often called sinker EDM. Usually, the electrodes of this type have quite complex forms. If the final geometry is obtained using a usually simple-shaped electrode which is moved along several directions and is possibly also subject to rotations, often the term EDM milling is used.<ref>{{cite journal |title=Tool Wear Compensation and Path Generation in Micro and Macro EDM |journal=Journal of Manufacturing Processes |volume=7 |pages=75–82 |year=2005 |last1=Narasimhan |first1=J. |last2=Yu |first2=Z. |last3=Rajurkar |first3=K. P. |doi=10.1016/S1526-6125(05)70084-0}}</ref>

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). For example, in micro-EDM, also known as μ-EDM, these parameters are usually set at values which generates severe wear. Therefore, wear is a major problem in that area.{{tone inline |title=Wear is a problem in an area that is set up to produce severe wear?  This has to have been done as a last minute report...  Anyway at least there's no "ideally" here, but wasn't all of this said in roughly one sentence 2 paragraphs up beginning with "To obtain a specific geometry"?|date=January 2025}}

The problem of wear to graphite electrodes is being addressed. In one approach, a digital generator, controllable within milliseconds, reverses polarity as electro-erosion takes place. That produces an effect similar to electroplating that continuously deposits the eroded graphite back on the electrode. In another method, a so-called "Zero Wear" circuit reduces how often the discharge starts and stops, keeping it on for as long a time as possible.<ref>Koelsch, James (October 2009). "EDM: A Changing Competitive Calculus", ''Manufacturing Engineering'', Society of Manufacturing Engineers</ref>