In this blog, we’ll look at EDM machines and in particular, one type of manufacturing process – wire EDM – in order to find out how everything works and what sort of problems can arise. We’ll also discover why measuring workpieces in-situ plays an important role in ensuring that the desired manufacturing outcomes are achieved.
To understand what we’re talking about let’s start with the basics. EDM stands for Electrical Discharge Machining and an EDM machine is a precision manufacturing tool that uses electrical discharges (in simple terms, sparks) to remove material from a conductive workpiece. It’s become increasingly popular because of its suitability to produce complex shapes and fine details working with hard materials that can be difficult to work with using more conventional methods of cutting.
EDM Machining: a short primer
There are two main types of EDM. The first, Sinker EDM (the name refers to die-sinking) uses a shaped electrode that is submerged in dielectric fluid and then moved towards a workpiece to create a desired form of cavity. It’s frequently used to create complex cavities (and other shapes), often in Mold-making.
It’s the second type that we’ll focus on in this blog, Wire EDM (also known as WEDM). Wire EDM machines deploy a continuously fed wire as the electrode (typically made of brass or copper). Here, the wire moves along a programmed path and discharges electrical sparks that erode the workpiece material. The most common applications of WEDM are cutting intricate shapes, contours, and small features, for example in dies, Molds, and other parts requiring high precision and fine surface finishes.
How it works
Now that we know the basics, how do EDM machines work? In both cases, the machines generate rapid, controlled, electrical discharges between the electrode (wire or, in sinker, shaped) and the workpiece. The discharges create intense heat and this melts or vaporizes small amounts of material from the workpiece, as required. Both the electrode and the workpiece are usually submerged in dielectric fluid which cools the work surface and flushes away removed particles.
Incidentally, EDM is an example of an approach to manufacturing called non-contact machining because the electrode and the workpiece don’t make physical contact. The plus here is the elimination of mechanical stress, which contributes to EDM’s suitability for high-precision work.
As well as offering precision and accuracy, and suitability for cutting complex shapes, EDM has other advantages. Among these, it’s particularly suitable for working in hard materials like tool steel, titanium, and exotic alloys that can be hard to work using traditional cutting approaches. Also, since there’s no physical contact (see above), not only is there minimal stress but there’s also no tool wear. An electrode wears out far more slowly than the cutting tools used in traditional forms of machining. All of this makes EDM the approach of choice in several specific applications. Foremost among these are:
- Tool and die making – dies, Molds, and intricate shapes are commonplace
- Aerospace – where high precision and high standard surface finishes are required
- Medical devices – where small, precise parts for instruments and implants are necessary
- Automotive – where precision engine and transmission components are needed
- Electronics – where micro-components and connectors need to be finely detailed
To summarize, for the reasons above (and others) EDM machines have become indispensable in many high-precision industries.
So, what could possibly go wrong?
Like any other machining process, EDM machines are nevertheless subject to specific issues which means that they must be constantly maintained, one aspect of which is through measurement. The most common problems they experience include:
- Broken wire
There are many reasons for this including poor discharge state, issues with the flushing gate, worn conductive blocks, dirty wire guide mechanisms, too much tension in the wire, and others all of which can cause the EDM wire to break. - Processing speed problems
Again, many issues can cause these ranging from the input of incorrect processing parameters to unstable discharges to unconducive water and others. - Surface line issues
These have causes ranging from problems with the quality of the electrode wire to the type of workpiece material (does it contain impurities?) to over high temperatures of the working fluid. - Edge finding
Wears often break when finding an edge, particularly if the wire tension in the machine configuration isn’t correct or wire alignment is imperfect. - Workpiece shape
If the workpiece is even slightly concave or convex, the cutting and trimming processes will be compromised.
There are many other common problems, too, for instance the surface of the workpiece not being polished, errors in cutting shapes, taper errors in the workpiece, and feed line and ARC connection issues.
All will, if left unchecked, lead to imperfect outcomes from the machining process which must, of course, be eliminated. The point is this: while EDM machining is extremely effective, the machines themselves must be maintained in perfect condition to avoid problems in manufacturing and to ensure that the workpiece is finished to the required specification.
Camera based workpiece measurement
One solution to the challenges above is to use the specifically designed measurement tool for wire EDM machines. A leading example of this is the CU2 Track Wire EDM tool from Conoptica. It enables workpiece quality and integrity to be both verified and improved while the workpiece is still in the machine by measuring geometry, so that production can be tuned in real-time.
We’ve seen (above) that to produce the desired results, EDM machines must be tuned constantly to address the common problems we’ve identified and Conoptica’s CU2 streamlines and perfects how to do this by enabling a cut-adjust-recut approach. With the tool, measuring geometries, z measurement, or giving form deviation are all possible inline either by automation or manually by using the visual interface as an aid. The advantages are easy to enumerate, including:
- Measurement of a variety of geometries (edges, holes, cylinder, arcs)
- The ability to quickly identify form deviations
- Generation of measurement reports
Also, because it’s integrated into the machine, CU2’s backlit illumination allows the machine itself to measure cuts with the precision of a high end CMM.
In conclusion, Wire EDM is an extremely effective approach to manufacturing, but one which requires care and accuracy in the machine to deliver results. Conoptica’s CU2 Track Wire EDM tool should be an integral part of achieving successful outcomes.
About Conoptica
To summarize, in maintaining Wire EDM machines measurement systems should play a vital role. Conoptica has been providing high tech camera-based measurement solutions for the metal working industry since 1993.
We make sure that the metal working industry has access to key quantitative data about their products and tools. Conoptica is the market leader for measurement equipment in the wire & cable industry.