Wire-cut EDM overview and integrated CADCAM programming's importance

Wire-cut EDM employs small diameter wire as the electrode, which is continuously fed through two independently controlled guides - one above, one below the workpiece - following a programmed path. Image: The wire-cut EDM process explained Typical wire diameters range from 0.001 - 0.01 inches (0.025 – 0.250 mm), although some wires have diameters as small as 0.0004 inches (0.01 mm), a tenth of the diameter of an average human hair. The hardness of the workpiece being machined has no effect on the cutting speed, as there is no physical contact between the wire and the part being machined. When the wire, which is charged with electricity, reaches a certain voltage, a spark jumps from the electrode to the workpiece and disintegrates some of the material. Those particles are then cooled and flushed away from the gap by a dielectric fluid (deionised water or oil). This process happens thousands of times per second. With the wire constantly being renewed, as it is fed from a spool, the outcome is an accurate, even, cutting path through workpieces sometimes over 40 inches (200 mm) in depth. Because of its 'non-contact' cutting method, machining using wire EDM eliminates cutting stress and the resultant mechanical distortion associated with conventional contact machining methods. It can also machine exotic materials, such as super alloys, medical grade stainless steel, titanium, tungsten carbide, aluminium alloys, copper and more. Work hardened metals, exceptionally ductile or brittle materials that are difficult to machine by conventional methods, can be shaped effectively and efficiently by wire EDM. The cut material is totally burr-free and the edges are perfectly straight, which means that multiple thin parts can be stacked and cut, without the problems associated with burrs. The extremely fine finish from the wire EDM process often eliminates the need for grinding or other finishing procedures. The cutting operations are grouped into vertical (2-axis, including waste destruction pocketing), land and taper (vertical and angled wire paths typically used for stamping dies), and 4-axis (extrusion dies and medical/production components). Finally, but much less common, some wire EDM machines now incorporate a rotary axis that allows indexing of the billet, allowing machining on different faces without the need for an additional set-up, as well as more complicated turn and burn rotary control. More complex parts, such as helical cutting tools, can now be programmed and machined using wire EDM, allowing for greater precision and a higher degree of finish. Given the very small 'tool diameter' – the wire - highly complex, contoured shapes can be produced in a single piece, rather than several component parts, thereby producing a finished part that is simpler in design, more accurate and which has a better finish than a similar part produced using conventional cutting tools. A major advantage of the wire EDM process is its reliability. Because the programs are computer generated and the electrode is constantly being fed from a spool – meaning the wire electrode is used only once – the last part is identical to the first. As the cutter wear found in conventional machining does not exist, tighter machining tolerances (+/- 0.0002 inches [0.005 micron] is easily achievable) can be maintained, without additional cost. One of the primary uses for wire EDM is for the manufacture of mould tooling from hardened steel. Moulds often require apertures to be cut into the tooling (inserts, core pins, lifters etc) that require sharp corners and tight tolerances that cannot be manufactured with conventional milling techniques, due to the cutting tool diameter and material thickness. To produce the mould, the intricate shapes must be cut using the wire EDM process. Image: A mould core Image: A mould plate A CNC program controls the machine tool movements and, given the high level of geometrical complexity involved in a mould tool, a CADCAM system is nearly always required to produce this. The benefit of an integrated CADCAM system, rather than a CAD-only or CAM-only system is that the part can be designed and the CNC machine code generated for that part from within a single software solution. If the design then needs modification, it can be made in CAD, and the CNC machine program is automatically regenerated by the CAM. Image: Wire-cut EDM programming Image: Wire-cut EDM programming - selecting cutting technology Although extremely accurate and reliable, the wire EDM process is also relatively slow. A single mould plate, depending on its complexity, could require several days of machining to achieve the finished result. One of the most important features of a CADCAM system for wire EDM is the ability to control the cutting order or 'strategy' of programs with multiple apertures. This is because the wire passes right through the workpiece, producing 'drop out' parts that are completely detached from the main billet of material. Take the example of a complex mould tool with multiple apertures that all need to be cut using wire EDM. The wire EDM process is so reliable that the aim is to run the machine without operator intervention for as long as possible. One way of achieving this is to program a small 'tag' on each aperture, in the CAM system, so that the slug does not fall out of the work piece and cause the machine to stop. This is an example of a cutting strategy. To take it one step further, a CAM strategy could be chosen that not only adds a small tag to each aperture, but also adjusts the cutting path to cut every aperture leaving its tag (this could happen unmanned overnight) and then cuts the tags off individually in the morning when the operator is available to keep an eye on proceedings. The importance of a dedicated wire EDM CADCAM solution cannot be over emphasised when dealing with automated, unattended situations like this. Online only article