October 2009 / Volume 61 / Issue 10|
By Daniel McCann
Courtesy of Gf AgieCharmilles Ability to machine intricate geometries and hard materials drives growing use of wire EDM prototyping.
Roger Spice, president of Mercatech Inc., estimates that about 25 percent of his business is devoted to EDM prototyping—and the figure is growing.
“I do everything from airplane parts to artwork; and the type of jobs I 'm getting, with sharp corners and radiuses to contend with, can’t be machined in conventional ways,” he said. “In most cases, the design itself determines that the job be done by EDM prototyping.”
As parts get smaller, geometries more intricate and materials harder, EDM increasingly is the prototyping method of choice.
Improvements in EDM technology also have been key—and continual. Whereas EDM cutting speeds 10 years ago averaged about 28 sq. in. per hour, today that figure stands at about 42 sq. in. per hour, said Gisbert Ledvon, business development manager for GF AgieCharmilles, Lincolnshire, Ill.
The higher cutting speed is primarily due to improved generator technology that more efficiently manipulates sparks for removing material. Gisbert added that contemporary EDMs can impart finishes of 0.1μm Ra or better (vs. 0.3μm Ra a decade ago) and accuracies of ±1μm.
At Xact Wire EDM Corp., Waukesha, Wis., the technology’s capabilities and customers’ growing awareness of those benefits have helped increase its EDM prototyping business during the past 5 years, said Project Manager Diane Stamm. “EDM is ideally suited for prototypes because typically no special tooling is required,” she said. “The first part can be made fast and changes can be made fast.” In addition, “more people are becoming aware of the process. It’s been around for quite a while, but there are still many people who are not familiar with EDM.”
Wire EDM vaporizes material via a series of rapid electrical discharges delivered by a thin wire, usually brass. The procedure often is performed under water and the path of the wire is controlled by computer, which permits the sculpting of intricate geometries. While EDM can only work with conductive materials, it is especially effective machining hard metals.Advantages
Prime among the benefits of EDM prototyping are its flexibility and cost savings. Xact’s Stamm cited the example of EDM prototyping a component profile for an aluminum extrusion. “With an aluminum extrusion, tooling can sometimes be very expensive if you aren 't quite sure what the final design is going to be,” Stamm said. “We can wire EDM a shorter version (up to 16 " tall) of the aluminum profile, make it as detailed as the customer needs and then see if that 's what they want.”
Using CAD/CAM software, adjustments can be made to the part geometry to achieve the needed profile before clients invest in tooling for production. While extrusion tooling can cost tens of thousands of dollars, Xact Wire can produce a test piece for just hundreds of dollars.
Courtesy of Xact Wire EDM
Equipped with 40 GF AgieCharmilles and Sodick EDMs, Xact Wire EDM serves the medical, aerospace, electronics, energy and packaging industries. And the company finds wide applications for EDM prototyping. “For parts that are getting smaller and smaller, especially for medical or aerospace, the machining choice moves closer to EDM,” said Stamm, adding that because EDM exerts no cutting force, it does not stress fragile and micro parts.Endo Rings
The prototype components portrayed on this page are 17-4 PH stainless steel rings used in the fabrication of endoscopes. The ring on the left measures about ⅜ " in diameter and the other about ½ " in diameter. To wire EDM the parts, Xact input the client’s designs into a GF AgieCharmilles 300 machine. Xact also selected PEPS software for its CAD/CAM system to generate the CNC code for the EDM.
Using 0.008 " stratified wire, “we started with sheet stock and cut the ID and OD,” Stamm said. “As soon as you separate [a stainless steel part] from its parent material, it’s going to spring because stainless loves to move around.
“The wire releases any kind of stresses already in the material; usually it moves parallel to the surface about a couple thousandths of an inch.”
Courtesy of Mercatech
Workers plan for the steel’s movement by leaving enough stock on the part to allow them to take two or three finish passes to attain the needed tolerances and geometries. Stamm estimated the smaller ring required about a half hour to EDM and the larger one about 45 minutes.
“Metals that tend to workharden or are very gummy are good candidates for EDM,” she continued. “Also, since you can EDM already-hardened metals, you don’t have to deal with heat treat distortion after [rough] machining.”
EDM’s prototyping versatility extends beyond fabricating small components. Xact Wire also EDMs large parts “to save expensive material,” said Stamm. “Rather than have the excess material turn into chips, we can return the piece of leftover material for later use by the customer.”
Many of the prototyping projects Mercatech takes on must be EDMed due to extremely tight tolerances and accuracies. “We also get a lot of jobs that will have one shape on the top of the U, V axis and another shape on the bottom of the X, Y axis,” Spice said. “This again requires the use of wire EDM, since the upper and lower heads can move independently of each other.” One job (below, left) called for machining a series of 2 "-long × ⅛ "-wide slots in a stainless steel aerospace component. “If you tried to machine that with an endmill, you would have radiuses in the corners and the client needed sharp corners,” Spice said.
After loading the part design into his EDM’s Esprit CAD/CAM software, Spice carefully inspected the component. “You have to check the part material for any deformities to make sure it’s flat when you put it into the machine—that’s critical,” he said. “If the customer wants the profile to match the squareness of the face plate you’re cutting the part from, it has to be flat. Then you line it up and clamp it down.” Spice used 3R rail clamping to secure the material.
He loaded 0.0010 " wire into his EDM’s headers. “On parts that are ground or machined flat, you want your heads as close to the part as possible,” he said. “If you have a lot of gap in there between the upper head and the top of the part surface, the flushing doesn’t work very well and it’s going to slow down the cutting process. We made that part in one cut, within ±0.001 ".”Hard Metals
Another factor driving EDMing for prototypes has been the growing use of harder metals. “There’s been a trend during the last year or so, in aerospace in particular, where companies are [prototyping] new special alloys for jet engines and other components,” said GF AgieCharmilles’ Ledvon. “These materials are lighter, more wear resistant, tougher to break and very difficult to machine conventionally.”
Shops that did invest in expensive cutting tools for such jobs, he continued, often saw their tools wear due to material hardness after a pass or two. But because hardness is no obstacle for an EDM, the process has proven to be the more economical and effective solution for these emerging special alloys.
Courtesy of Xact Wire
“The biggest advantage of EDM prototyping is the consistency of the part,” Ledvon continued. “If you program a 3-D model and generate an ISO code for your wire EDM to cut a part today, and then 6 months from now that customer wants another part with the exact dimensions, finish and accuracy, you just bring the program back into the wire EDM and you will get the very same part.”EDM Challenges
Despite EDM’s technological gains, fixturing remains a common challenge, especially for small, intricate parts. Numerical Precision Inc., Wheeling, Ill., a manufacturer of aerospace components, has developed a workholding solution that’s proven effective for many EDM prototype jobs. “One of the ways we’ve addressed [fixturing] is by using EDM tooling traditionally used for holding small electrodes,” said Karl Dahlstrom, vice president of manufacturing and engineering. “Instead of holding the electrodes with the tooling, we hold parts with it and we 're able to get repeatability.”
The other big challenge to EDM prototyping is the human factor. It’s important to work closely with the customer’s engineering and design staff to ensure that they’re “taking into account the limitations of their designs and how they can affect costs,” Dahlstrom said. “If you can lend a manufacturing perspective to the design process up front, it saves money for everyone and makes producing both prototypes and the production parts that much more achievable.”
While EDM technological improvements in recent years have helped widen the technology’s applications and usefulness, EDM makers and users alike are anticipating further advances in versatility and effectiveness.
GF AgieCharmilles’ Ledvon, for example, foresees a greater emphasis on combining EDM with other operations. “In other words, people might use high-speed, 5-axis milling to a certain degree on a particular part, and then switch over to wire EDM, or vice versa,” he said. “I do see a trend of people buying the latest and greatest technology and trying to combine it more. Also, the materials will continue to get harder and smaller.” CTEAbout the Author: Daniel McCann is senior editor of Cutting Tool Engineering. He can be reached at email@example.com or (847) 714-0177.
Bright EDM forecast
of EDM prototyping is only one aspect of the wider application of the technology. According to a 2006 EDM market study conducted by the consulting and analysis firm Frost & Sullivan, San Antonio, EDM manufacturing, in general, promises continued growth. "EDMs can do a far more precise job [compared to conventional machining] in lesser time due to their contactless machining process, making them the preferred option with many end-user industries,” according to Frost & Sullivan. “Moreover, EDMs use the spark erosion technology that enables the machining to be carried out with ease and eliminates the need for a further finishing process.”
Frost & Sullivan forecasts a compound annual growth rate of 6.9 percent for sales of EDMs through 2012. The technology’s top three market drivers are:
The top two market restraints for EDM technology are:
The consulting firm also suggested that to solidify further demand for EDMing, end users must continually be educated about advances in the technology. “Vendors need to promote the benefits of the latest EDM technologies that include the ability to machine nano parts, download CAD files directly and convert them into machine codes and drill fine holes. As customers realize the advantages of these technologically superior machines that can perform multiple functions, EDMs are expected to witness greater demand.”
GF AgieCharmilles LLC
Numerical Precision Inc.
Xact Wire EDM Corp.
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