Exploring niches with new EDM technologies

A shop specializing in wire EDM for large mould components now offers EDM “turning” of small, intricate parts. Despite the potential risks involved in early adoption of new technologies, the shop believes this practice gives it a leg-up on the competition and lets it gain experience with alternative machining techniques before offering them to customers. Extreme Wire EDM, located in Grandville, Michigan, is a machine shop that has advanced turning capabilities. However, you won’t find conventional lathes in its clean, Midwestern facility.

The opened its doors in 1998 and soon after, set its sights on wire EDM work for big mould and die components. Brothers and shop co-owners Karl and Brian Bernt realise that this type of work is likely to remain in the United States, and continue to purchase large-capacity wire machines for those industry segments. In fact, Extreme Wire EDM is the first U.S. shop to install a Robofil 640CC, a wire machine manufactured by AgieCharmilles that accommodates workpieces as heavy as 6,614 pounds and as large as 1,300 × 1,000 × 510 mm. A second such machine is currently on order because the first one is so busy.

That said, the brothers don’t have tunnel vision; they continually look for other potential machining niches that the latest EDM technologies might allow them to pursue. Lately, the shop has been winning complex turning jobs using spindle technologies developed specifically for wire EDM. While some of that work complements the hefty mould components that pass through the shop - hardened core and ejector pins, for example - the ability to turn parts of virtually any hardness to 4.8mm in diameter and the tooling pressure and heat associated with lathe turning has opened up new opportunities in new markets.

What’s impressive is that the shop added EDM turning capabilities while the technologies were fresh and despite the fact that it had no worked immediately lined up for the equipment. Adding leading machining technologies in such a proactive way takes a measure of discipline and a certain level of belief. That’s because the initial investment necessary to implement a new machining technology is generally high. The cost often decreases as additional shops begin accepting and adopting the technology. In addition, there’s the chance that the pricey new equipment might sit idle for a while before making money because customers are unfamiliar with the alternate technology and its potential for their particular applications.

Extreme Wire EDM is able to justify this. By integrating new technology without having work in queue for it, the shop can become familiar with its capabilities, nuances and limitations. This "practice" time allows the shop to get a head start on the learning curve and refine the process before offering the capability to its customers.

High speed EDM turning
The shop currently offers two EDM turning processes - turning via continuous workpiece rotation and AgieCharmilles’ "turn-while-burn" technique, which synchronizes workpiece indexing with wire feed. Both are suitable for workpieces of virtually any hardness.

While conventional lathe-turning operations require multiple tool passes to remove material, EDM turning erodes all material that must be cut with each rough and finish pass. Typically, the shop will take one roughing pass and one or more finishing passes, depending on desired surface finish. This is different from typical wire EDM operations in which slugs of solid material are carved from a workpiece. Once the turned profile is completed, the wire cuts the part from the stock, and the part gently sinks to the bottom of the machine’s dielectric-filled tank. The shop performs all turning operations fully submerged to ensure effective flushing.

Mike Wysocki is the shop’s wire EDM technician who performed much of the initial experimenting with the high speed spindle. Mr. Wysocki suggests that optimising EDM turning operations is similar to determining the best combination of spindle speeds and feed rates for a conventional CNC lathe. For instance, faster spindle speeds are required for small-diameter work. The shop is using the latest PEPS programming software from Vero Software to outline the part profile and generate the part program from a customer’s drawing.

The Bernt brothers admit that it is sometimes challenging to get customers to understand the benefits of this alternate type of turning. Some fixture shops, for instance, believe they can create hardened components faster and more affordably in-house, despite the fact that multiple steps are required. They generally have to turn stock on a lathe, send it out for heat treating (which can distort the machined part), and then perform additional machining or grinding operations to bring the component to final size. Wire EDM can accurately turn hardened stock in one fixturing setup, which not only reduces the number of times a shop must touch a part, but also reduces overall manufacturing cost.

Wire EDM turning is also effective for Porcerax II, a porous metal that allows gases to permeate through the material to enable targeted venting of difficult-to-access mould areas. Conventional machining or grinding tends to push material into the pores, reducing the venting capability. This doesn’t occur with EDM.

Simultaneous turning & burning
Soon after purchasing a Hirschmann high speed spindle, the shop invested in an AgieCharmilles Robofil 240 EDM unit equipped with the optional "turn-while-burn" feature. The spindle used for these operations provides a servo-controlled, clockwise and/or counter clockwise indexing rotation that is synchronized with X- and Y-axis wire feed. This allows the machine to produce helical geometries and other complex shapes. The machine and the indexing spindle are purchased as a package because special servos and related components are needed to allow the machine to produce its carefully choreographed movements.

Extreme Wire EDM have opened up a communication channel with Vero, who have developed turn-while-burn operations within the PEPS CAM package with the first test cut of the cam part using a PEPS-generated part program running in August 2008.

Original case study source provided by MMS online

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