Manufacturers of products as diverse as die and mold, aerospace and medical devices are gaining advantage with improved wire and sinker electrical discharge machines (EDM). Machine tool builders continue to tackle EDM improvements by increasing operating speeds, reducing wire consumption, improving auto threading for lights-out operation and improving spark generating power supplies.
At the same time, as more traditional machining processes are advancing their capabilities, EDM, and especially wire EDM, is finding new applications in additive manufacturing by cutting off high-value 3D printed components from their backing plates or in precision hole drilling for aerospace engines. Wire EDM and sinker EDM each have benefited from technologies that lower the cost of manufacturing. Here’s how.
Mike Bystrek, national wire EDM product manager, and Pat Crownhart, national sinker EDM product manager, for MC Machinery Systems Inc., Elk Grove Village, Illinois, describe the challenge to EDM technology to produce the fastest, lowest cost and most accurate ways to manufacture workpieces.
“The steps we’ve taken on the wire side with our MV series have reduced hourly cost significantly by reducing wire electrode consumption. Making that possible is incorporation of fiber optics and the High-Speed Spark Detection System, which optimizes the spark shape to remove more workpiece material while reducing wear on the wire. This allows us to slow the wire speed down without impacting machine performance while reducing wire consumption by over 60 percent over previous models,” said Bystrek.
The two key considerations for cost-effective wire EDM performance are reducing wire consumption and auto threading the wire itself. “Without reliable wire threading the process is pretty much worthless,” said Bystrek. “It’s why we recommend annealing the wire to make it as straight as possible by removing memory from being wound on the spool. It’s the best way to improve reliability and reduce machine downtime.”
By annealing the wire, users can thread (while submerged) almost any size start hole reliably and thread directly through the gap at the break point. This provides two advantages: time savings and maximum unattended time. “In previous generations, when the wire on the EDM broke, it had to be cut and go back to the start point and retrace through the wire kerf to the break point and re-start machining,” said Bystrek. “If the part moved due to stress or other factors, it could be difficult to get back to the break point. In that case you would require operator intervention and lose unattended machining hours. Now the machine threads at the break point.”
The PowerMaster feature on MC Machinery’s MV machine enables automated motion by detecting the spark condition in the gap in real time. “A useful application would be when you’re cutting off additive parts on a growth plate,” he said. “Typically, you are cutting through various steps in material and the faster the machine can adapt and read those conditions, the better the performance will be. Power Master takes the guess work out because the machine automatically adapts to the conditions that it sees.”
According to Crownhart, sinker EDM does better what other processes like milling can’t do as well, particularly machining the hardest materials or the smallest workpieces with the sharpest corners and most accurate detail. “In production applications for sinker EDM there is a definite trend toward multiple use of accurate electrodes that can be used several times before being replaced, reducing cost per part,” he said. Applications for sinker EDM include extremely hard materials with smaller, deeper, difficult geometries, sharp corners and delicate parts where burrs from conventional machining are undesirable.
“Automation is a growing part of our sinker business, especially if the workpiece fits on a 12" [304.8-mm]” square pallet,” said Crownhart. Robots can service multiple machines, for example, taking electrodes from an EDM to a graphite mill or to machining centers. “We have machines with controls that can be set up on the left or right sides, allowing flexible configuration of the robot sitting in between machines,” he added. “A coordinate measuring machine (CMM) can also be included in the cell, receiving electrodes from the robot for qualification prior to setup and accepting finished workpieces for measurement on the CMM.”
AccuteX wire and sinker EDM machines and fast hole-drilling machines from Absolute Machine Tools Inc., Lorain, Ohio, incorporate the latest technology for cost-effective, reliable and low-maintenance operations, particularly in untended operations, according to Technical Director Mark Cicchetti.
“Untended wire EDM processing depends for success on low maintenance and reliable automatic wire threading [AWT],” said Cicchetti. “AccuteX AWT is a dry threading technology that doesn’t use waterjet threading. We rely on annealing to straighten the wire and a patented servo-controlled tension device to shape the tip and create a needle point. That allows us to thread reliably.”
In combination with a good programming system, AccuteX AWT provides the flexibility to write programs specifically for untended operation, ensuring that the right tooling is available to set up jobs accurately and efficiently, he added.
“It allows us to set up parts quickly and accurately, as well as manage the slug that has to be removed if users need to skim out the hole accurately or simply want to complete the cut. To minimize downtime and maximize uptime, AccuteX EDMs use full digital AC power supplies which are naturally electrolysis-free, minimizing the oxidation of parts in long, untended operations,” Cicchetti said.
Absolute Machine Tools offers two levels of sinker EDM machines. “The ZNC sinker EDM represents good value capability, particularly for a shop just getting into EDM that has been outsourcing,” Cicchetti said. “The ZNC EDM enables them to get started economically while gaining a lot of capability—including a fully integrated orbiting head that is included on 70 percent of the ZNC sinkers. The orbiting head allows them to minimize their electrode manufacturing and improves surface finish and accuracy.”
The second level of Absolute’s sinker product line comprises the large machines, 1 m and above with power supplies from 90-480 A. “Currently, the largest machine we have installed in the North American market is a 3-m machine,” he said. “Applications with our large machines involve using smaller electrodes to put in precise features that can’t be milled efficiently. Large EDMs are primarily used for aerospace parts made of tough materials that are difficult to machine and in moldmaking in which detail and surface finish are extremely important.”
Cicchetti considers Absolute’s EDM drilling machines as unmatched tool room grade machines. “They are capable of handling maximum 770 lb [349 kg] workpiece weight even on the small models,” he said. “We also offer a full complement of options, including guide changing and Windows-based controls to import DXF files and program parts automatically. We can drill holes from 0.100 mm in diameter up to 6 mm.”
As a supplier of consumables, Absolute’s main focus is on being a single-source, full-service supplier of products that have been thoroughly tested in its machines. In addition, Absolute supports its product line with over $10 million of inventory in spare parts at its Lorain and Mason, Ohio facilities.
At the EMO show in Hannover, Germany, in September, GF Machining Solutions exhibited, among other innovations, technologies for spark control and monitoring in wire EDMing, human machine interface (HMI) concepts, automation and a new horizontal wire EDM designed to complement metal additive manufacturing (AM) systems.
New Spark Track technology, with an Intelligent Spark Protection System (ISPS), is designed to provide valuable information about spark distribution on the wire, according to GFMS, which has U.S. headquarters in Lincolnshire, Illinois. Spark Track allows users to completely avoid wire breakage, regardless of machining conditions, as well as reduce part defects and simplify machine operation, according to GFMS. Spark Track technology resolves common problems like wire oscillation, varied heights and tapered surfaces by keeping discharges along the wire as uniform as possible.
The AgieCharmilles CUT 2000 X wire EDM was shown featuring new onboard Spark Track technology and an Integrated Vision Unit (IVU) for streamlined production management. The CUT 2000 X’s Vision 5 software interface allows manufacturers to optimize production, achieve flexible job management and improve quality and productivity. The Vision 5 interface simplifies last-minute machining sequence modifications and allows for special actions to be introduced directly inside the job to ramp up quality and productivity.
Open guides on GF Machining Solutions’ automatic wire changer (AWC) allow manufacturers to use a combination of different wire diameters between roughing and finishing, thereby reducing machining time for small and complex geometries —resulting in up to 32 percent greater productivity. Additionally, two 25-kg wire spools are available that eliminate the need to modify the wire circuit when switching wires, which increases flexibility.
GFMS introduced its AgieCharmilles CUT AM 500, a new horizontal wire EDM designed to complement metal additive manufacturing (AM). The AgieCharmilles CUT AM 500 makes it easier than ever to quickly separate additively manufactured metal parts from the build plate while maintaining geometrical accuracy and ensuring assembly readiness, according to the company. The universal AgieCharmilles CUT AM 500 is an automation-ready alternative to the use of standard EDM equipment or a band saw to separate AM parts from build plates.
Manufacturers in every industry are looking for improved productivity, which advanced wire and sinker EDM technology is delivering through improved wire usage and better control of power supplies, according to Alicia Smith, regional sales manager, Belmont Equipment and Technologies, Madison Heights, Mich.
“Everyone is looking for cost reduction and faster throughput with emphasis on how many quality parts can be consistently produced at the end of the day,” said Smith. “The challenge for shops is to be more efficient and cost effective in using their resources of equipment and people. Belmont’s focus is to save shops money by providing solutions based on new ideas, technologies and materials to achieve higher productivity and reduced downtime.”
Belmont provides capital equipment, including wire, sinker and drilling EDMs, supplies and accessories, services for design and/or build of custom EDM electrodes, and ancillary products like tooling, wire, filtration systems and graphite blanks.
Both wire and sinker EDMing are well-suited for applications where traditional machining processes like hard milling still can’t do the job as well, for example when cutting extremely hard materials where fine and delicate details, sharp corners or burr free parts are required. “Wire EDM, for example, has become more cost-effective by slowing down wire feed, which is made possible by new generator settings and wire coating technology to reduce wire consumption,” she said. “This approach can be applied to conventional wire EDM applications as well as newer opportunities for separating AM parts from build plates,” Smith said.
“Onboard technology, improved power supplies, and settings on our newest machines are controlling the spark better for sinker EDMing. The technology senses the spark for better arc control in the gap. These improvements in power supply control give the manufacturing engineer confidence in a long burn cycle for consistent parts, increased speed and improved finishing results,” said Smith.
Automation continues to play an important role in both wire EDM and sinker EDM productivity, especially with increased reliance on cellular manufacturing configuration. “EDM automation with a robot handles production applications where the part repeats over and over again or for short-run part production of different parts where the robot moves the pallet in and out of the EDM work envelope. For sinker EDMing, automation also involves moving the electrode in and out of the milling side to machine the electrode and into the tank for EDM processing,” said Smith.
From a manufacturing cost perspective, the largest expense in operating a wire EDM is the cost of the consumed wire, according to Brian Pfluger, EDM product line manager, Makino Inc., Mason, Ohio. “Contrary to conventional thinking, the wire consumption rate—how fast the wire spool turns—has nothing to do with machining speed,” he said. “The wire unspool speed only needs to be at a rate where the wire is stable and not going to break during machining. Many machines have their default wire unspool rates set far above this minimum threshold.”
Makino has introduced 0.016" (0.40-mm) diameter wire that can apply more power without fear of breakage. Available on Makino’s U6 H.E.A.T. Extreme wire EDM, the larger diameter wire produces machining speeds two or three times faster than traditional 0.010" (0.25-mm) diameter wire while maintaining the same hourly wire consumption, according to Pfluger.
“It’s a disruptive move and a big game changer, especially for roughing speeds where we can apply more power. We’re seeing a dramatic improvement in machining time with the same hourly wire consumption,” he said. The generator, with a booster unit on the U6, has doubled power supply from 30-60 A to accommodate the larger wire’s power capability.
Makino has developed its entire Machining Condition library settings from the ground up for low wire consumption, which includes all material types, thicknesses and wire sizes. “The key to low wire consumption settings is adjusting for wire electrode wear to maintain proper accuracy,” said Pfluger. Makino accomplishes this by mechanically compensating for wire electrode wear with a small movement in the U and V axes, which purposely places the wire at small angles to counteract accuracy issues caused by wire electrode wear. “This is all accomplished automatically and the compensation values change as the workpiece thickness increases,” he said.
Proper and consistent control of wire tension and the automatic wire threading (AWT) system on any wire EDM machine are two critical considerations for untended operation with minimal or no wire breakage. Wire tension is also directly responsible for part accuracy and straightness and can also affect surface finish.
Makino has upgraded its wire drive unit to a new system called HyperDrive that provides a larger range of wire tension with improved tension accuracy consistency throughout the entire range. The new tension system is also utilized in a new dynamic adaptive corner control technology that improves the size and straightness accuracy of small radii features. The Corner Control system automatically adjusts wire tension, machining power and flushing pressure to produce the most accurate geometry.
Pfluger explained why the AWT system on any wire EDM is the single most important automated mechanism on the machine for untended operation. Most AWT systems utilize a small pressured waterjet column of water to feed and guide the wire during automatic threading, as this helps to feed and insert the wire through the workpiece and into the machine’s wire guides. AWT units also cut the wire so the machine can position to different parts or features. The cutting process must produce a clean wire tip to aid in wire threading. Many wire EDM manufacturers have developed AWT capabilities of threading in the gap, rethreading the wire at the break points and also waterjet-less threading. “But there is little point to this if the process isn’t reliable or the AWT unit is excessively complex to maintain,” said Pfluger. “It’s why we have focused on stability and ease of maintenance for the AWT system design, including both jet-less and thread-at-break-point capabilities.”