EDM and Other Great Ideas
Alternative metalcutting technologies continue to improve
By Robert B. Aronson
Miniaturization, harder, more costly materials, and greater automation have interested manufacturers in processes other than conventional machining. EDM has grown over the last few decades from a novelty to a mainstream manufacturing process. At the same time, the "laboratory only" processes are getting more attention. Here's a look at both options.
Methods Machine Tools (Sudbury, MA), the exclusive importer of Fanuc EDM machines, finds that customer requirements for the equipment they sell include more wire EDMs, greater automation, the ability to make ever smaller parts, and a decrease in labor costs. Explains Steve Bond of the company's EDM group, "This is a shift away from the tool-and-die customers who dominated the market not long ago. As to specific product lines, land-based turbines and aerospace, particularly small jet engines, are major customers. Sinker systems for making or remanufacturing turbine blades is also a strong market." To meet the need for greater automation, Bond notes, "Robots are almost a commodity now. Most machines have them."
Greater simplicity for the operator is another goal. As an example, the new Fanuc iD model is designed to make the machine user-friendly. One of the reasons for this machine was the need from the Chinese market to accommodate operators with very low skill levels. "They put more 'smarts' in the 310i control," says Bond. "This simplifies untended operation and setup."
A new area where wire EDM is growing for the company is PCD tool manufacturing and other applications involving the new generation of harder materials. "In this work we are taking over more former grinding projects," says Bond.
Because of the overall interest in near-net-shape parts, there is a renewed emphasis on fine machining as opposed to rough cutting. To meet this need, company designers refined power supplies and minimized vibration.
One of the newer EDM machines offered by Methods Machine Tool is the CT-300, a high-speed CNC holedriller EDM. It has a 21-station automatic electrode/guide changer (AEC/AGC) with no moving parts. For electrodes greater than 0.012" (0.3 mm) in diam, the operator need not change electrodes and wire guides on long-running jobs. These machines drill deep, small holes from 0.004 to 0.256" (0.1–6.5-mm) diam using rotating brass or copper electrodes.
New developments at Agie Charmilles USA (Lincolnshire, IL) are guided by the need to provide both flexibility and automation. Users want to minimize worker training and increase the number of tasks each unit can perform. The most recent machine designed to meet those needs is the 350-S.
For example, EDM finishing of premilled cavities is a major task. In the past, the EDM electrode would follow a preprogrammed orbit cycle without considering the shape that was premilled. With the new design, the operator describes the orbit pattern needed. "This feature can reduce cutting time by up to 30%," says Business Development Manager Gisbert Ledvon. "The machine is a complementary blending of EDM technology with high-speed milling." To increase productivity, the X and Y axes position faster with a maximum acceleration rate of 5 m/sec2.
The machine has a 160-tool or electrode magazine option to handle complex jobs. A chip in each electrode holder indicates the tool's offset, then an integrated scanner reads the information stored on the chip, and the software program factors the offsets into the CNC program so the proper electrode is offset is used for each task.
"A new market is opening for EDM with PCD tools," explains Ledvon. "The B axis on the 350-S gives the EDM greater maneuvering capability to create complex tool geometry.
"A new trend you will see more and more is on-line documentation," says Ledvon. "With it, operators can get instructions, and use key words to get help for certain applications. This means the operator gets maximum performance from a machine quickly, without special training."
On the wire side, Agie Charmilles offers the AC vertex 1F. It uses 0.008" (0.2-mm) diam wire to make high-accuracy, small parts such as stamping dies. Because of the greater accuracy, on both punch and die, the tool life can be increased significantly.
For operations where machining cost is an issue, the company offers the LRC (low running cost), a new wire EDM Technology called DCP—Direct Cut Performance. This innovation produces better results in one cut than in two cuts (rough and finishing).
Makino EDM (Auburn Hills, MI) offers several EDM machines. For microEDM. there is the Edge 2 Fine Hole, a precision hole drilling EDM, and the UP J2, a horizontal wire EDM. This machine features automatic threading down to 0.0008" (0.02-mm) diam wire.
The newest EDM, the EDAC 1, is a sinker machine featuring short travel for fine work. Distances in the X, Y, Z axes are 220, 180, and 300 mm. "It's suitable for extremely fine details," explains EDM Product Manager, Jeff Kiszonas. "For example, using a copper-tungsten electrode, the machine can make an internal radius of 0.5µm with a surface finish, of 0.6 µm RY. In tests, we have achieved surface finishes measured in nanometers on the UPJ2."
These machines are intended for the growing microEDM market. Most shops use them for small molds and computer chip lead-frame tooling, as well as aerospace and medical parts. Production ranges from prototype to high volume with the machines using toolchangers and running untended.
"There is no clear answer as to when to machine and when to use EDM," says Kiszonas. "The line between the two continues to blur. With our milling machines now using 0.0010" [0.0254-mm] diam ball mills at 40,000 rpm, milling can take over some operations formerly in the domain of EDM. But if you want a sharp inside corner, you need EDM."
"One problem for most precision EDM machines is part holding," says Kiszonas. "Part holding is behind what the machines can do, and makers of those products are working to catch up."
To meet the needs of the small-lot manufacturer, MC Machinery Systems (Wood Dale, IL) offers the MD+PRO II, a precision machine that has a rotating B axis, that is used during turn-and-burn operations, and gives the ability to machine narrow slots. The footprint measures 67 x 190" (1701 x 4826 mm). "We listened to the production people who want the maximum number of parts from the smallest plant area," says Greg Langenhorst of the MC Machinery EDM division. "But one of the issues with EDM machines is access to the maintenance areas such as the filters. The redesgned filter container reduces floorspace requirements by 20%."
The Mitsubishi PM4 control makes automation from rough-cut to finish-machining possible. The control also has the ability to make parts of different thicknesses without changing the spar-control settings.
There are other issues that control EDM design, Langenhorst points out. "Companies with unions can control how far a worker has to move to operate machines. The distances walked by operators influence their piecework rate, so placement of machines is of great concern to them. Also, OSHA has rules about access to junction boxes. Both these issues strongly influence machine size and placement."
Another trend is grouping EDM and waterjet machines. "Rough-cutting with an EDM is slow and generates a lot of filter-clogging debris," he says. "It's usually more efficient to cut out a part with waterjet and use EDM for the detail cuts."
Some Mitsubishi waterjets are designed to work with an EDM so that the combined machines function as a single manufacturing unit.
A series of waterjet systems is available with from two to five axes. All machines are powered by a 60-hp (45-kW) motor that can deliver water at 60,000 psi (413,700 kPa).
"A few production improvements on a new model doesn't cause much excitement today," explains P. J. Naughton of Sodick Inc. (Schaumburg, IL). "What stops the crowd is new technology that reduces labor cost.
"We answered that need with our new LQG and LNG controls for CNC sinker machines," he says. Typically, an operation needs more than one graphite electrode, particularly when adding small details to a mold cavity or insert, because of electrode wear. With their new machine, Sodick claims to reduce wear to less than 0.1% while increasing machining speed by as much as 25%. In some cases, only one electrode is required. Minimal electrode wear also results in machined parts with sharper detail.
The LNG control is standard on the Sodick AD3L, and the LQG control is standard on the Sodick AQ series sinker EDMs. The improvement in performance is the result of a new control that more efficiently regulates the spark.
"Recent development in advanced materials has required entirely new approaches and metalcutting strategies. One such process is ultrasonic machining. This type of technology may be used instead of EDM when working with nonconductive materials. Ultrasonic machining provides a flexible solution in which the entire material range can be run at a higher material removal rate than conventional grinding or machining. Both soft and hard materials can be machined by quickly changing an ultrasonic tool with a conventional tool or vice versa using the automatic toolchanger.
In the area of laser machining, DMG America (Schaumburg, IL) offers two units. The Lasertec 40 is designed chiefly for fine and filigree-tructured workpieces. It ablates material to a maximum vertical depth of 3 mm. This machine can produce the finished part in one easy step, therefore replacing the time-consuming EDM process of electrode manufacturing followed by the burning process.
The Lasertec 80 does fine cutting and precision boring. It can penetrate to depths of up to 8 mm in most materials, and can cut diameters of less than 1 mm.
Lasers perform two types of machining: conventional 3-D shapes that might be cut with a milling machine or EDM system, and 3-D trimming. At present, there is a limit to the depth a laser can be controlled for complex 3-D shapes, and the trimming operations are limited to simple cuts on thin flat plate.
Mitsubishi offers lasers capable of trimming in 3-D. This usually involves work around the edges of a flat piece, such as chamfering. Two units available for this work are the VZ1, which can cut 3/8" (9.5 mm) vertically and 1/8" (3 mm) at an angle, and the VZ2, which in mild steel cuts 3/4" (19-mm) thick plates vertically and 1/2" (13-mm) thick plates at an angle.
The company's laser-system design doesn't have separate bottles of carbon dioxide, helium, and nitrogen for the gas mixture, as is common on other designs. Instead, the machine uses a cross-flow system that premixes the gases, eliminating the need for a mixer system and reducing annual gas expense. Their system uses about 3L of laser gas per hr. This is important because of the increasing cost of helium.
"The CO2 laser has progressed nicely," says Jeff Hahn, Laser Div. product manager. "We use the CO2 laser on our 4-kW machines that can cut 1" [25-mm] thick mild steel and 3/4" [19-mm] stainless. YAG lasers have the disadvantage of requiring an enclosure because of the eye hazards."
"There is a power race in the laser industry with 6-kW units available," notes Hahn. "But Mitsubishi has elected to stay with power levels around 4 kW, chiefly because of cost considerations. We are not just talking about initial cost, but the overall cost of the more powerful lasers, which goes up dramatically when you consider the total cost of ownership. There is greater consumable and power use, along with increased maintenance frequency."
Typical part tolerances have been shrinking and SPC has become commonplace in manufacturing. To increase precision and improve process control, Sunnen Products Co. (St. Louis) instituted a major redesign of its high-production machine product line. "Precision component manufacturers require improved bore geometry, and critical surface finish parameters. Honing is a process that provides this solution," says Phil Hanna, machine product manager. "We set out to create a series of machines that provided improved process control with a focus on greater reliability, ease of operation, and automation."
In a multiyear program, Sunnen set out to meet these goals. According to Hanna, "We were particularly interested in reducing the number of parts in the stroking system. In the old design, an elaborate mechanical linkage converted rotary motion from an ac motor to reciprocating motion for the hone. The new design, which reduced the number of parts by 80%, uses a concept Sunnen calls servo-ballscrew control in which electronic controls play a major part."
Coupled with a new load-sensing feed system, this design allows true vertical stroke, can dwell in any part of the bore, and can selectively remove stock to produce optimum bore geometry. In addition, cycle time can be minimized. With the boreprofile display the operator can monitor bore geometry. Optional air gaging with closed-loop feedback simplifies operation further.
Another important change was a move away from custom-built controllers because of the speed of obsolescence and limited capabiliites that plague this type of machine control. "We now use a Windows-based, Xycom Automation Inc. [Boise, ID] industrial computer," he explains. "This protects against rapid obsolescence, and offers greater programming variety and ease of automation."
Comco Inc., (Burbank, CA), makes very precise miniature sandblasting equipment that cleans and finishes parts. "They operate like a waterjet without the water," says Comco's Pat Byrne.
The MicroBlasting machines use 17.5–25 µ abrasive that cuts a very thin layer from a product's surface. An operator controls cutting action by adjusting the air pressure and the amount of media going into the nozzle.
The company offers two models that deliver abrasive at pressures from 40 to 185 psi (280–1298 kPa). "The Comco system's key benefits are the ability to reach inside parts with complex shapes with repeatability and consistency," states Byrne.
Operation can be manual or automated, with the nozzles mounted on CNC-controlled frames that can have as many as four axes. This type of operation depends on part size and complexity, as well as production volume. Microabrasive blasting does not cause changes to the dimensional integrity of the part.
This article was first published in the October 2007 edition of Manufacturing Engineering magazine.