Editing Electrical discharge machining (section)

===Wire EDM===<!-- [[Wire cutting]] redirects here -->
[[File:Robofil-300-WireCut.jpg|thumb|CNC Wire-cut EDM machine]]
[[File:Wire erosion.png|thumb|'''1''' Wire. '''2''' Electrical discharge erosion (Electric arc). '''3''' Electrical potential. '''4''' Workpiece]]

In ''wire electrical discharge machining'' (WEDM), also known as ''wire-cut EDM'' and ''wire cutting'',<ref name="todd">{{cite book |first1=Robert H. |last1=Todd |first2=Dell K. |last2=Allen |first3=Leo |last3=Alting |year=1994 |title=Manufacturing Processes Reference Guide |publisher=Industrial Press Inc. |isbn=0-8311-3049-0 |pages=175–179 |url=https://books.google.com/books?id=6x1smAf_PAcC}}</ref> a thin single-strand metal wire, usually [[brass]], is fed through the workpiece, submerged in a tank of dielectric fluid, typically deionized water.{{sfn|Jameson|2001}} Wire-cut EDM is typically used to cut plates as thick as {{convert|300|mm|in|abbr=on}} 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 which is centered in a water nozzle head. The guides, usually [[CNC]]-controlled, move in the ''x''–''y'' plane. 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). The upper guide can control axis movements in the GCode standard, ''x''–''y''–''u''–''v''–''i''–''j''–''k''–''l''–. This allows the wire-cut EDM to be programmed to cut very intricate and delicate shapes.

The upper and lower diamond guides are usually accurate to {{convert|0.004|mm|mil|abbr=on}}, and can have a cutting path or ''kerf'' as small as {{convert|0.021|mm|mil|abbr=on}} using [[diameter|Ø]] {{convert|0.02|mm|mil|abbr=on}} wire, though the average cutting kerf that achieves the best economic cost and machining time is {{convert|0.335|mm|mil|abbr=on}} using Ø {{convert|0.25|mm|mil|abbr=on}} brass wire. 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.{{sfn|Jameson|2001}} 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). Spools of wire are long — an {{convert|8|kg|lb|abbr=on}} spool of {{convert|0.25|mm|mil|abbr=on}} wire is just over {{convert|19|km|mi}} in length. Wire diameter can be as small as {{convert|20|µm|mil|abbr=on}} and the geometry precision is not far from ± {{convert|1|µm|mil|abbr=on}}.

The wire-cut process uses water as its dielectric fluid, controlling its resistivity and other electrical properties with filters and [[PID controller|PID controlled]] [[ion|de-ionizer]] units. The water flushes the cut debris away from the cutting zone. Flushing is an important factor in determining the maximum feed rate for a given material thickness.

Along with tighter tolerances, multi axis EDM wire-cutting machining centers have added features such as multi heads 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. If the energy per pulse is relatively low (as in finishing operations), little change in the mechanical properties of a material is expected due to these low residual stresses, although material that hasn't been stress-relieved can distort in the machining process.

The work piece may undergo a significant thermal cycle, its severity depending on the technological parameters used. Such thermal cycles may cause formation of a recast layer on the part and residual tensile stresses on the work piece. If machining takes place after heat treatment, dimensional accuracy will not be affected by heat treat distortion.<ref>[http://www.header.com/capabilities/edm.html ELECTRICAL DISCHARGE MACHINING (EDM)]. header.com</ref>