Wire EDM has forever changed the way injection molds are made

Wire EDM has become such an integral part of plastic moldmaking that it is hard to imagine how things were done before. When it was first introduced in the 1980’s as a useful machine tool, the common use was in die-making. Over time though, this dramatically changed.

This new process was regarded as almost useless for moldmaking at first because molds have “blind” cavities, unlike stamping dies, which have “through” holes. Wire EDM, or WEDM, by necessity, requires a through hole to operate.

It didn’t take long, however, before WEDM began dominating many aspects of moldmaking.

How WEDM has become so useful in moldmaking

  • Electrodes for sinker EDM
  • Inserts
  • Insert pockets
  • Core pins
  • Mold bases
  • Ejector and core pin holes
  • Contoured parting lines
  • To reduce polishing

Not bad, for a machine once thought of as useless for moldmaking! From a moldmakers viewpoint, WEDM is priceless as a tool. The labor savings from grinding complex core pins, highly detailed inserts with compound angles, and contoured parting lines is truly significant. Not to mention the stress and headaches!


With a little creativity, many electrodes can be cut on the wire EDM. Generally, copper cuts much faster than graphite, and has the advantage of finer finishes and ability to EDM fine details. Premium grade graphite can be used, but is slower to cut.


Many inserts can be WEDM’d, then EDM’d in the sinker EDM. This marriage of technologies is one of the best examples of ingenuity using WEDM. Only minor grinding is required after EDMing to remove the tabs left from WEDM. Many of the tedious grinding operations of the past are now a distant memory, not many people miss them either!

Insert pockets

The pockets that are home to the inserts which were wired, now fit precisely. Nearly all of the pockets that are in difficult to reach locations are now routinely WEDM’d. The hassles of tapered sidewalls, fitting corners, as well as size and location are also now a thing of the past.

Core pins

Complex geometry that was previously milled or ground can be machined more accurately and quickly on a WEDM. Angles, sizes and complex radii are all commonly machined on using wire.

Mold bases

The pockets that hold cores and cavities, plus the holes and pockets that hold interlocks and other details can accurately be cut on a wire machine. An added benefit is that the slug from the pocket is no longer a pile of oily chips! It can be used for other components. An additional savings is in end mills and machine time, since most WEDM is unattended.

Ejector and core pin holes

Usually starter holes are drilled in the cores during CNC machining. Later, after heat-treat, the details are hand polished. Then the holes can be finished in the WEDM. This has many advantages: no bell-mouthing of holes, easier polishing, more accurate hole location and size, and better surface finish.

Contoured parting lines

Many shut-off surfaces and molding surfaces can be finish milled, but others lend themselves to wiring. This greatly increases the accuracy of the complex shapes.

Reduced polishing

Of all the operations to produce a high quality injection mold, polishing is the most vexing. There is often just no way around the fact that a highly skilled moldmaker must polish the mold, at great expense. This often causes a bottleneck in the scheduling and delivery. Using WEDM where applicable greatly helps to reduce the time spent polishing.

All in all, wire edm has had a dramatic and very positive impact on moldmaking. It is hard to imagine a modern shop without a WEDM, or access to a custom wire shop. Accuracy, speed, superior fit and finish are all the direct result of wire EDM.