Where the wired things are

New EDM control systems can that track true machine utilization by breaking down actual machining time, setup time, and idle time. Photo courtesy of Makino.

In electrical discharge machining (EDM), parts are submerged in liquid then cut and machined using the careful application of electrical discharges. A die-sinker EDM uses a solid piece of brass or carbide as an electrode, while a wire cut EDM relies on a wire and dielectric fluid to do its work.

Both high- and low-tech options are available to boost productivity in wire EDM cutting. The high-tech choices include using intuitive machine controls and RFID chips, and the lower-tech options include simply being picky about the type of wire you use.

“Evaluate the use of coated or stratified wire,” advised Brian Pfluger, EDM product manager at the Makino Die/Mold Technology Center. “Most people tend to gravitate towards using a standard brass wire, basically for the sheer economy of operation.”

A pound of coated wire costs about US$11. While more expensive than plain wire, coated wire can boost rough cut speed performance by 20 to 30 per cent, according to Pfluger.

Another option is wire with an enriched zinc/brass alloy outer coating, which is less prone to breakage and offers 25 per cent faster cycle times than basic brass wire.

“You have to make the choice between spending more on a coated wire for maximum rough cut speed, or staying with the standard brass wire, which saves money, but takes longer if you’re only doing a one-cut job,” explained Greg Langenhorst, technical marketing manager for MC Machinery Systems, a division of Mitsubishi. “Most tooling jobs require higher accuracy and better surface finishes than what you get with a high-speed, one-cut, so brass wire is used with additional skim cuts to improve both accuracy and finish.”

Increase Productive Time

Langenhorst also believes that many shops don’t use wire EDMs to their fullest capacity.

“We all know that when a machine is not running, it’s not making money, so [the question becomes] how do we keep that wire spool spinning for more hours a day?” said Langenhorst.

The first step is to examine the type of work being done and set the tooling and fixturing in a way that minimizes setup time.

“In some cases, if you make the blank larger, for example cutting several punches from a single block, the larger block will provide better clamping areas that will speed your setup. A few dollars of extra steel is a minimal cost compared to extra hours trying to fixture a block that could easily be clamped to the machine table. The same holds true when using vises, rails, and other aftermarket tooling to take most of the setup time away from the machine table,” said Langenhorst.

EDM controls can now track the use of consumables and wire, as well as machine usage. Photo courtesy of MC Machinery Systems.

Pfluger agreed about the importance of uptime and pointed to a technical solution.

“Most shops, unless they’re a pure production shop, really do a poor job of monitoring or recording actual machine utilization time,” said Pfluger. “Depending upon the type of work that you’re doing, you typically want to set up your longer-run jobs at night so you gain that unattended machining time. In any EDM operation, the key underlying operational goal is to maximize that unattended machining time because that’s where EDM really shines.”

Control Technology

Advanced controls give shop owners a tool to track productivity. For example, the Hyper-i control system for Makino EDMs has a built-in record function that tracks true machine utilization by breaking down actual machining time, setup time, and idle time.

“This gives shops a metric to measure themselves against, to look at how much they are using the machine,” said Pfluger.

The M800—the latest addition to Mitsubishi’s MV series of wire EDM machines—was also designed with data collection in mind. Scheduled for release in September, the M800 has an enhanced function to track the use of consumables and wire, as well as machine usage.

This raises a truism: If you want to boost wire EDM productivity, make sure your machine controls are up to date and easy to use.

“[Our] control is designed so that you can take a simple 2-D G-code program, load it into the machine, go into your setup page, tell it what type and size wire you’re using, what type and thickness your workpiece material is, what you expect to get as far as accuracy or surface finish for the end product, and it will automatically build your program for you,” said Langenhorst.

New controls operate like a smartphone. The idea behind today’s controls is that everyone in the modern world has a smartphone, so they know how to operate it and are familiar with it. It’s second nature. Makino’s Hyper-i control system, for example, has a 24-in. touchscreen interface and offers simplified programming procedures.

“We looked to reduce the number of keystrokes and entry points required to get the machine to produce the final part. Compared to our previous control system, the Hyper-i system uses 40 per cent fewer button strokes or keystrokes,” said Pfluger.

This past July GF Machining Solutions (GFMS) introduced the AgieCharmilles CUT P series of wire EDMs. These machines feature the AC CUT HMI 2, designed to streamline file management and enhance operator efficiency. The HMI 2 has a 19-in. touchscreen and is Windows® 7-based.

During measurement, wire feed can be slowed to reduce energy and wire consumption. Photo courtesy of MC Machinery Systems.

CUT P series wire EDMs also have an eConnectivity feature to link the machines to an IoT network. In an IoT network, all computers, machine tools, machine controls, and equipment in a plant are connected electronically to gather data and monitor performance. Such data can be used for predictive maintenance and to gauge part process consistency—key components for maintaining productivity.

“There are some people that are focused on maintenance. This machine tells them when it’s almost time to change the filters. Other people are looking more for consistency. They want to know that the process is being done correctly. The machine collects data [and] can predict when this part is going to reach the final stages,” said Eric Ostini, senior product manager at GFMS.

Other CUT P optional features include e-connect, e-control, and e-supervision. The e-connect feature sends out emails or texts if problems occur while the machine is running unattended. Using the e-control and e-supervision functions, operators can control these EDMs remotely.

Wire EDMs from Mitsubishi also have an Internet-based monitoring system that allows operators to check how production is going from a phone or tablet. Makino has an EDM Mail option that can send distress messages, while EDM Viewer lets operators remotely view the machine control from a desktop or smart device.

Boosting Productivity

“Typically with any wire or sinker EDM, the faster you machine, the less accuracy you achieve,” said Pfluger.

Technology now exists to reduce this gap. Makino’s HyperCut machining technology is one example.

Operators using HyperCut can achieve a 3-µm Ra surface finish and 1-µm (0.00004-in.) straightness in only three passes, according to the company. This three-pass process, as Pfluger calls it, can reduce cycle time by 20 per cent and wire consumption by 14 per cent.

Another way to increase productivity is to reduce downtime caused by wire re-threading.

“Machines with reliable auto-threading systems that can insert a submerged part rather than draining the tank for each insert will save several minutes per thread. Choosing a machine that has built-in wire breakage sensing that reduces the risk of breaking wire during a rough cut keeps the machine running and not trying to recover from a broken wire,” said Langenhorst. “We have seen that the annealing of the wire in the auto-threader is a key factor in successful threading.”

The length of annealed wire, the straightness of the wire, and the cut point at the tip are all key factors in a system. A self-cleaning wire transport system helps reduce maintenance of the auto-threading unit, which is critical to many hours of successful operation.

CUT P wire EDMs have automatic slug management (ASM) and automatic slug welding (ASW) systems. The former reduces the need to manually extract slugs (a time-consuming process), and the latter reduces the need for additional manual intervention while cutting processing time. These EDMs also come equipped with RFID chips that track wire characteristics and the amount of wire left on the spool, said Ostini.

When operators have a better sense of how much wire remains, they’re less likely to change spools unnecessarily for fear of running out of wire in the middle of a job.

Another helpful new feature on wire EDMs sold by GFMS lets operators slow down the wire feed rate to 1 m per minute during the measuring cycle. According to Ostini, a normal measuring cycle uses wire at about 8 m per minute.

Wire speed on the MV series from Mitsubishi also can be slowed by almost 60 per cent, reducing wire consumption and energy use.

Keep It Clean

The last, and simplest, piece of advice for boosting wire EDM productivity is to clean the machine.

“A clean machine is a happy machine, and this starts with the use of proper filtration. Wire EDM creates loads of very fine particulate waste, which needs to be filtered out to maintain proper DI [deionized] water conductivity,” said Langenhorst.

Cheap filters allow dirt to pass through, which then gets into the DI resin system and shortens its life. It also negatively affects the operating conductivity range. Cutting technology is developed for a set range, exceeding it creates poor spark transfer from the wire to the workpiece, resulting in slow cutting speeds, poor surface finish, and increased risk of wire breakage.

“Clean water is crucial to most of the systems of a wire EDM, so letting your filters go to the point of passing dirt through the system is only going to cost you more in downtime cleaning of all the plumbing to regain the machines reliability,” said Langenhorst.