Tips for Getting the Most Out of Wire EDM

Quick take: Wire EDM performs best when shops treat setup, wire condition, flushing, and machine discipline as one system instead of chasing only parameter tweaks. This page is most useful when it is read with copper-EDM and EDM-surface references.

Related references: EDM Conquers Copper: Settings and Electrode Guide, Understanding EDMed Surfaces, and Shop math: Practice makes perfect.

Wire EDMing requires a range of equipment and complex operations, which can lead to a variety of problems. But the capability and flexibility of the electrical adaptive control technologies that monitor the EDM process—such as flushing, wire tension, automatic wire threading, wire consumption levels, geometry control, surface quality, water resistivity level and water chiller/thermal stability—have greatly improved over the past 10 years.

Adaptive control enables the EDM to adapt to changing conditions by adjusting its internal parameters. Adaptive control can also help prevent wire breakage and automatically fine-tune the process for maximum speed and efficiency.

Courtesy of GF AgieCharmilles

Wire EDMs that use an oil-based dielectric machine carbide workpieces without cobalt depletion. This GF AgieCharmilles machine also features an automatic wire changer.

“The wire EDM process is [inherently] unstable,” said Brian Pfluger, EDM team leader for Mason, Ohio-headquartered Makino Inc., who is based in Auburn Hills, Mich. “So the electrical adaptive control tries to continuously self-optimize. If it detects a problem, such as a change in material thickness or a step-down, it will back off a little from the settings or use more aggressive settings to create a stable burn condition to maintain the best efficiency and accuracy.

“The control is always trying to cut as fast as it can while maintaining a stable machining condition,” Pfluger continued. “Even if you tell it to cut faster, the control will use settings that are stable. You can change your target parameters, but you want overall consistency. There is a productive limit to how hard you can push the EDM. If you push too hard, your wire breaks. Adaptive control is there to prevent that.”

The continued development of adaptive control has allowed previous accuracy and surface finish problems to become mostly a thing of the past. The control allows much better regulation and focus of the discharge spark to get repeatable results. This helps improve part quality and metallurgical integrity.

Of particular concern are recast layer and the heat-affected zone. Because EDM- ing is a thermal process, recast layer and HAZ will always be a reality, but newer adaptive controls have virtually eliminated these layers and concerns.

“The adaptive control allows the operator to fine-tune the wire EDM process to prevent recast,” said Pete Intihar, vice president of AccuteX EDM, Mason, Ohio. “The recast layer used to be from 0.001 ” to 0.005 ” deep, but with the new technology, it is only 0.0002 ” deep or less, depending on the material,” he noted. “You can’t get away from it 100 percent, but it is practically eliminated.”

Courtesy of Makino

This Ti6Al4V medical part was machined on Makino’s DUO43 wire EDM in 5 minutes, 30 seconds (3 hours, 40 minutes for 40 parts). It took four passes to produce a 30 µin. Ra surface finish with 0.004 “-dia. brass wire.

One of the most important adaptive control features for wire EDMing is the ability to “tune” it for specific materials, such as titanium and Inconel. However, the machines are not capable of knowing which type of steel is being machined, according to Dave Kari, wire EDM director of Top Tool Co., Minneapolis. “All the EDMs are set up for D-2 tool steel, so for a piece of A-2 tool steel, for example, the settings require some changing,” he said. “A-2 requires 20 percent less power and more off time and somewhat higher voltages to help with the flushing and burning characteristics of the steel. Not everyone knows this.” Top Tool is a metal stamping manufacturer. The company is trending toward making microtooling but manufactures large parts as well.

Another surface finish problem is rust on steel parts. Most new wire EDMs have an anti-electrolysis system as part of the adaptive control that protects the cutting zone.

Another method to help prevent or control rust is to add chemical rust inhibitors to the water dielectric. While the chemical inhibitors are effective, they do require some maintenance and monitoring.

“The inhibitors can shorten the life of the resin system, which affects the water conductivity level,” Makino’s Pfluger said. (Resin is added to dielectric to maintain conductivity). “As you replenish water to make sure that rust preventative is effective, you have to closely monitor its concentration level.” Pfluger noted chemical rust inhibitors are not necessary when using Makino’s system.

The rust problem increases when using burn time, according to Kari. “With a bigger part, you still get a certain amount of rust. We had a part that took 115 hours, and we had to use rust inhibitor,” he said.

Benefits of Oil

Wire EDMs that use an oil-based dielectric instead of water “are really starting to come into play,” said Ken Baeszler, a product manager at GF AgieCharmilles, Lincolnshire, Ill. “Because water is inherently corrosive, it will corrode carbide and other materials susceptible to cobalt depletion if they are left in the work tank too long. With oil, carbide is not subject to that level of cobalt depletion, so we can put long campaigns, say, 100 hours’ worth of carbide work, in the tank and not worry about [corroding the cobalt]. This is great for unattended production.”

In addition to carbide tooling, such as stamping dies, oil-based dielectric EDMs work well with wire 0.003 ” in diameter and below and for smaller parts.

Courtesy of Makino

These pieces of 8.0 “×6.0 “×2.0 ” P-20 tool steel were tested on Makino’s DUO64 wire EDM. Both samples were submerged in water at a 15 microsiemens per centimeter conductivity level for a consecutive 24-hour period. The block on the right was tested without the rust prevention circuit being active, and the block on the left was tested with the rust prevention circuit being active. The left sample demonstrates the effectiveness of the anti-rust circuit, which prevents rust formation using a special cathode plate that electrically protects the entire machine working area, including the cutting zone.

“The oil contains the spark, making it less aggressive,” said Dave Thomas, president of Sodick Inc., Schaumburg, Ill. “The conductivity of water is much higher than oil so in water dielectric each spark is more violent. EDMing in oil can also, in some cases, allow the use of larger diameter wire because of the smaller spark gap compared to water dielectric.”

Until recently, it was commonly accepted that the disadvantage of using oil dielectric was cutting speed. “Precision tools could be machined without carbide depletion but cutting times could be 30 percent slower,” Thomas said. “Sodick’s Eco-cut technology reverses this speed comparison with water dielectric and now offers faster machining times.”

Another benefit is that, because oil maintains a specific conductivity, it doesn’t require deionizing. “So you don’t need a resin with an oil-based system,” Baeszler said. “A lot of people don’t realize that.”

Prevent Wire Breakage

One of the easiest ways to increase cutting speeds is to use coated wire instead of plain brass. However, this requires balancing cost vs. results because the coated wire costs about twice as much.

“Most shops run with brass wire based on its economy,” said Makino’s Pfluger. “Running coated wire can make the EDM run 30 percent faster, but it’s double the price.”

Courtesy of Sodick

EDMs that use an oil-based dielectric instead of water work well with fine wire and carbide workpieces.