Wire EDM Industry | Growth of Wire EDM

EDM continues to evolve

Chalmers, Raymond E

New technical developments and custom applications drive change

11 puns aside, the electrical-discharge machining (EDM) market is hot. Many suppliers of wire-cut and sinker EDM machines describe last year as the best sales year ever, with total sales for the category exceeding $1.5 billion. Analysts predict sales will rise 7% annually through 2004, fueled by advances in machine reliability, productivity, and programming; all this despite EDM still being categorized as "alternative" or "special" machining equipment.

In fact, new bywords for describing EDM processing ought to lead with "productivity, in the literal sense of the word," says Gabriele G. Carinci, president, AGIE Ltd. (Davidson, NC). "One of the biggest myths that needs dispelling is that one man is needed to operate one machine," he says. With such options as multiple parts in one setup, including parts of different heights and materials, EDM processing can certainly help parts manufacturers control high labor costs while keeping prices low and quality high for customers. Doing so, Carinci says, requires "a dual level of integration-the machine being a system integrating with the operational system of the company. The single biggest area where Agie plays a pivotal role is systems thinking. You can't just drop a machine into a shop."

Other suppliers concur. Greg Langenhorst, EDM division product manager for MC Machinery Systems Inc., a Mitsubishi Corporation (Wood Dale, IL), describes the EDM marketplace as "a forum for constant customer education." Because EDM equipment is not cheap-even low-end equipment goes for $125,000-and erosion rates still require overnight jobs and untended operation, manufacturers take machine reliability and operating efficiency as givens. Education plays a role in teaching manufacturers not only to recognize advances in machining speed, but to exploit them to improve total process speed. A variety of options come into play here, including new developments in EDM, as well as a growing array of programming and automation choices.

On the wire side, one advance speeding EDM processing is the antielectrolysis power supply. Formerly an option on Mitsubishi equipment, the patent-pending development is now offered by the manufacturer as standard. In machines lacking this feature, stray voltage leaking off the wire produces rust, which must be removed by polishing. Electrolysis also causes excessive bluing in titanium parts and microcracking in carbide tooling, causing carbide dies or punches to chip during machining or break down more quickly in production.

Version 3 of the company's antielectrolysis power supply, called AE3, uses fine-pulse control circuits to precisely control machining currents in the discharged energy field. This feature minimizes reductions in surface hardness due to electrolytic deterioration or corrosion, helping prevent workpiece chipping even during extended machining. When machining ultrahard alloys, including carbide and other sintered materials, almost no strength reduction occurs because of binder depletion after machining, according to the company. When used on a machine that produces plastic molding dies, the antielectrolysis power supply can greatly reduce grinding and polishing; when used on iron-based materials, it minimizes rust and oxidizing zones.

With its Isopulse generator's surface-integrity feature, Charmilles (Lincolnshire, IL) even guarantees no microcracking when machining carbide, along with a uniform surface finish featuring a recast layer less than 0.000040' (0.0010-mm) thick. Running costs may decrease as well, since with such efficient power supplies, antirust agents may no longer be necessary. Mitsubishi research also indicates a nearly threefold increase in the service life of the ion-exchange resin used in standard submerged machining because of the more efficient power supply.

On the sinker side, adaptive controls using "fuzzy logic" to variably control acceleration and deceleration rates are another hot topic. Understanding why fuzzy logic helps improve EDM operation requires understanding two basic processes in sinker EDM: sludge creation and sludge removal.

Basically, the energy released by the sinker creates a sludge that's usually made up of resolidified workpiece material, electrode material, and tars from the dielectric fluid. Machine builders usually remove sludge by flushing or machine-controlled jump strategies in the discharge area so the discharge remains stable. Balancing sludge creation and sludge removal yields stable machining. Make too much sludge relative to sludge removal and an unstable process results. Too little sludge relative to sludge removal means slow machining. You need adaptive controls to adapt or modify discharge control parameters to keep the system in balance.

Also necessary is a jump strategy that addresses the machine's jump-up, jump-down, and jumpspeed parameters. The jump-up parameter defines the set distance that the electrode retracts for removing sludge particles, either by the retracting action itself or by auxiliary flushing. Applying through-electrode flushing can greatly diminish the need for jump actions during roughing.

The jump-down parameter defines the amount of time electrical discharge pulses can occur. Jump speed is the acceleration and deceleration rate required to attain the jump height and return distance defined by the jump-up parameter. Although typically linear, these rates can be nonlinear. Large electrodes that generate greater hydraulic forces usually mean slower speeds.

When adequate flushing conditions exist, a conventional jump strategy does very well. A new jump strategy that allows a greater retraction distance at a faster acceleration rate can address marginal or no-flush conditions that would severely test a conventional power supply. At IMTS '98, Mitsubishi unveiled its Fuzzy Pro II upgrade, an adaptive control system incorporating this new jump strategy. It uses a variably controlled acceleration and deceleration rate that can retract the electrode from the burn by as much as two inches. The company predicts marked processing-- time improvements for deep rib or cavity burns, small undersize applications, and marginal or no-- flush conditions.

Three things help the Fuzzy Pro draw maximum performance out of a sinker EDM's fine-pulse power supply: a processing-area sensor that automatically recognizes the area being machined; another sensor that detects hydraulic reaction force; and an adapter that recognizes changes in gap stability in microseconds. Fuzzy Pro contains a function that automatically recognizes the electrode's contact area with the workpiece during discharge. Because the previous method of adaptive control made decisions based only upon gap stability, adding measured contact area as a factor means achieving optimum machining depth conditions much faster. Power level increases can only occur after detecting sufficient contact and appropriate gap stability.

Also, since the control can measure electrode geometry and contact area, Fuzzy Pro automatically sets burning conditions during machining of the electrode's leading edge. This automated action reduces what is normally a very complicated set of programming steps to an automatic operation.

Controls and related programming advances of this sort not only speed and sometimes automate machine setup and operation, they give users the possibility of incorporating EDM knowledge and know-how into their systems and equipment.

Also at IMTS, Agie unveiled its Futura V SuperStar control for its Mondo Star die sinking systems. Working in Windows 95, the control has a wizard-based job setup function with EDM and erosion-- specific knowledge built in. Operators can program an elaborate four-cavity mold with complex orbits and measuring cycles in about 10 minutes compared to more than an hour in other systems. An automatic erosion-programming feature allows the programmer to click on an icon for the necessary erosion complexity. After running the calculations, the control recommends erosion settings, number, and best undersizes for electrodes that meet the required part accuracy and finish specifications.

An optional feature, StarView, employs a camera and modem so the control can use the Internet for remote monitoring. With a phone line and Web browser, users can ask Agie support personnel to dial into the system and walk them through any setup or service problems.

Recently, Agie's EDM equipment also received acclaim for its design. Earlier this year at the CeBit show in Hannover, Germany, the Agiecut Classic and Evolution wire EDM systems and the Agietron Innovation diesinking system received Best Products status in the Industry category of the Industrie Forum Design awards program. These were not simply aesthetic awards; they recognized EDM technical advances as well. Screens punched into the machines' doors and sides, for example, are not simply design elements, but also dissipate heat and emissions.

Custom applications drive advances in some areas. Raycon, a TransTec Advanced Machines company (Ann Arbor, MI) recently launched a new EDM four-head drilling machine, capable of precision-drllling microholes in a variety of fuel injectors. Capable of machining holes of 0.1 mm in diam and as deep as 1 mm, the new system can drill as much as 25% faster than previous machines. Part of the speed increase is due to the company's flow measurement technology. The flow system measures the total flow of each nozzle and generates a statistical process control analysis of the last 32 parts measured.

Next, the system generates the deviation of average flow from the specified mean, and uses the software database to keep the system in control, making absolute electrode size less vital than it was. Fuel injectors needing drilling can be mounted on individually programmable stations on the A axis. The A-- axis assembly is in turn mounted on a servo-driven U axis, and EDM electrodes and servoheads on a linear X axis. A resident database helps simplify part programming, and a warning indicator automatically advises when an electrode falls below usable levels.

Where will EDM's continuing evolution lead? More and more often, EDM intelligence will be resident in the equipment. Machining speeds and overall part processing speeds will certainly increase. Given the ability to take advantage of automation and untended operation, EDM systems should continue to help manufacturers meet productivity and part accuracy goals reliably and cost-effectively

Want More Information?

SME's Fundamental Manufacturing Processes video series includes a program on EDM, describing and explaining both ram and wire-cut processes. For information, contact Customer Service toll free at (800) 733-4763, 8 am-6 pm, Eastern Time, Monday through Friday.

For more technical information on EDM systems, use the following numbers on the reader service card.

Company Circle

AGIE Ltd................................400

Charmilles 401

MC Machinery Systems 402

Raycon 403

Raymond E. Chalmers

Special Projects Editor