Machine makers are expanding what medical manufacturers can do with electrical discharge machining while refining the process itself
“You guys are crazy!”
That’s what Makino EDM product line manager Brian Pfluger was told—loudly—by a medical-industry customer after Pfluger recommended he use coated wire to make a custom housing for cancer treatment machines. Coated wire costs twice as much as uncoated, standard brass wire, so its use in the client’s application would increase manufacturing costs by about $100.
But, as Pfluger demonstrated to the red-faced client, the coated wire used in conjunction with Makino’s (Auburn Hills, MI) high-energy applied technology—or HEAT—would make a 60-hour job into a 34-hour task: A cost-benefit analysis revealed the client would save money, not waste it unnecessarily, because the 26 hours saved on the custom housing job would allow the client to earn $1300–$3900 in machine time for another piece, based on shop-time estimates of $50–$150 per hour.
“What’s more valuable to your operations,” Pfluger asked his client, “saving $100 in manufacturing costs, or gaining 26 additional hours of billable machine time?”
According to Pfluger, the mollified client said: “You know what? I never thought about it that way.”
Pfluger’s anecdote underscores the complexity of medical manufacturing with already-complex wire electric discharge machining. Since the invention of wire EDM in the 1960s, the technology has made difficult-to-machine shapes possible in conductive metals. It’s opened the door to making medical devices such as heart stents, mini-tools for robots that assist during “keyhole” surgery, and implants that replace hips, knees, elbows and shoulders.
Just as wire EDM has made more complex medical devices possible, the machines that make this type of manufacturing possible continue to advance as well.
Makino came out with two new wire EDMs in September: the U3 with X, Y and Z axes travels of 370 × 270 × 220 mm, respectively; and the U6, which increases the machine travels to 650 × 450 × 420 mm.
The worktable on the U-Series is stationary, to improve machining precision and provide greater flexibility for workpiece setup. The U-Series offers a choice of wire guide systems on the machine. Customers now have the ability to choose either a PICO (round) guide system or a Split-V Guide system, depending on their applications or preference.
Pfluger explained that the PICO round wire guide offers a typical guide life of 2000–3000 machining hours. The V Guide, which is patented Makino hardware, is pricier but comes with a guarantee to last 12,000 machining hours, possibly making it a better buy in the long run. The Split-V Guide system also requires less maintenance and offers longer life because the diamond contact area is larger.
Each machine features HyperCut, a fine-finish technology that improves cycle time by producing a surface finish of 3 µm Rz in three passes. A competitive product would require four to five passes to achieve the same quality finish, Pfluger claimed. HyperCut also offers a 20% reduction in cycle time and 14% reduction in wire consumption, compared with previous Makino technology.
The U-Series also has a new CNC system, Hyper-i, which features a 24″ (610-mm), user-friendly touch screen that works like many smartphones or tablets, with pinch, pull and drag operations.
“It looks like a giant iPad,” Pfluger noted, “And that’s the way it works.”
The software includes digital manuals and an on-board training tutorial system for the operator. Also, Hyper-i automatically records and translates production process data into pie and bar charts that make assessing machine utilization time quick and intuitive.
“So this becomes a piece of management software,” said Pfluger.
Virtually No Recast
The need for speed in wire EDM has manufacturers tweaking flushing rates and other variables to eke out any tiny improvement in the time necessary to finish a workpiece.
“That’s actually the holy grail at this point,” said Steve Bond, national sales manager for Methods Machine Tools Inc. (Sudbury, MA).
“In the 1980s and 1990s, the speed chart [showing improvements] was almost vertical,” says Bond. “But it slowed down in the 2000s.
“We’re not able to make those speed leaps anymore. Now we’re looking at what kind of [improvements in] results can we get off the machine.”
Methods, a supplier of precision machine tools, automation and accessories, introduced the Fanuc RoboCut CiA Series, including the C400iA and C600iA wire EDM machines, in February 2013.
In 2012, Fanuc tweaked its part holder to tilt the workpiece to make high angles for multiple-axis cutting, Bond explained: “How you manage that process lets you do things you’ve never done before,” he said.
The latest developments have led to improvements in surface integrity that produce virtually no recast, Bond said.
Recast is a problem in medical manufacturing because the microfractures inherent with it are good places for bacteria to lodge and multiply, which can cause problems with infections in a patient. Micro fractures may also hamper how well bone grows into spine hardware and may cause the body to reject microclips used to clamp off blood vessels in the brain.
To date, manufacturers have recommended coated wire to prevent recast, which is more expensive, or to manipulate the EDM machine’s power supply: the decrease in energy results in reduced fracturing, or recast. But Fanuc’s new software and hardware on the CiA series manipulates its 5F power supply to keep material from resolidifying on the workpiece.
“At 1000× magnification, you can’t find recast,” says Bond.
The series’ new 31iWB Control adaptive CNC contains high-speed processors that can read power supply data to monitor and adjust the wire EDM’s spark: If sparks are going well, the machine speeds up.
The machines can also operate in EcoMode, which slows down the wire.
Machines in the series constantly monitor and record variables such as voltage, cutting speed, flush pressure, and wire tension for quality control purposes. The recording could potentially be used in root cause analysis in the event of a medical part failure. They also offer remote monitoring and control of up to 24 machines via a hand-held device through Fanuc’s new RoboCut Link i technology.
“So, on an iPad I can run the machine from anywhere in the world and know what part is coming off the machine,” said Bond.
Two in One
GF Machining Solutions’ new offerings include the CUT 2000 S and CUT 3000 S, the next generation of its CUT 2000/3000 line that offers new options, but still can accommodate wires as thin as 0.05 mm in diameter.
“The 3000 is our most sophisticated machine,” said Gisbert Ledvon, director of business development for GF Machining Solutions (Lincolnshire, IL).
Available for the new line is an automatic wire changer that, in conjunction with the 2000 and 3000 machines’ ability to accommodate two wire spools and the open-V guide system, lets the operator use a bigger wire for the rough cut and switch to a smaller wire for skim cutting without having to manually change the wires.
“We know customers who are buying two machines … but with our technology you don’t have to,” said Ledvon.
When the wire does need to be changed, GF Machining Solutions offers its new Threading-Expert, a retractable device, to drive wire from the upper guide to the part’s upper surface start hole or to the lower guide through a tube.
The standard Threading-Expert configuration includes a nozzle to improve threading reliability, whatever the diameter (<0.03 mm), under standard conditions (close to the surface), according to the company’s website. Also available are a nozzle for thin wire (0.03–0.07 mm) and one dedicated to 0.15–0.1-mm wire. Both work close to the surface without breaking through the workpiece.
The IVU Advance—with improvements to GF Machining Solutions’ Intelligent Vision Unit—is like having two additional shop employees, one for quality control and another to reprogram the CNC. The optical-based measurement system works by comparing an image of a part after cutting, but while still on the machine, to print dimensions. If there’s a deviation, the IVU Advance automatically corrects the CNC program for that and subsequent parts.
By making corrections, the IVU Advance keeps the machines running even while untended, and increases shop productivity, Ledvon said.
The Intelligent Power Generator on the Cut 2000 S and 3000 S enables the machines to push to the maximum limits for speed, just up to the point of the wire breaking. As a result, the machines cut 30% faster than previous AgieCharmilles technology.
The IPG works by sending feedback from the spark gap, or cutting zone, about variables, such as contamination from debris or the shape of the spark, to the digital generator by way of the CNC.
“The trick is to get that information back to the CNC,” noted Ledvon. “The CNC decides the spark shape and form to maintain maximum cutting speed.” It can also change the flushing pressure to eliminate problems with contamination from debris.
Back from the Drawing Board
After a less-than-hearty reception to versions No. 1 and 2 of the MD+PRO series wire EDM, which is specifically designed for medical and small parts production, Mitsubishi Corp., which is sold through MC Machinery Systems Inc. (Wood Dale, IL) listened to its customers and headed back to the drawing board.
In addition to a smaller footprint, Mitsubishi focused on areas that cost customers money, including: energy consumption, maintenance time, setup and programming time, part-cutting time, cost of consumables and, in some cases, having to purchase a larger machine for work that was just a little too big for the MD+PRO II.
The X and Y ballscrews in the MD+PRO III have been replaced by a new noncontact cylindrical drive system that uses linear shaft motors with two-millionths glass scales for improved accuracy and zero maintenance. The machine travels are about 2″ (51 mm) greater in both X and Y, with only a minimal increase in the floor-space requirement.
Additional enhancements include a new internal communications system that employs fiber-optics instead of hard wiring to both the servosystem and power supply, which makes the response time four times faster and more energy efficient. Through a combination of energy-saving technological improvements, like a chiller pump that cycles on and off instead of running 24/7, the machine reduces energy consumption 30–35% compared with the previous version. The improved V350-V anti-electrolysis generator and new Digital Matrix Sensor specifically shape each spark to match the cutting conditions, which let the machine take a bigger bite out of the workpiece with less wear on the wire. So the MD+PRO III doesn’t need to run the wire speed as fast and subsequently uses less wire to do its job.
“With multiple passes, it’s using 60% less wire than previously,” noted Greg Langenhorst, technical marketing manager at the company’s Wood Dale, IL, location. “Of all the consumables used in the wire EDM process, wire is the most expensive by far. So, it’s a huge thing when you can reduce your wire consumption by 60%.”
But where version No. 3 really shines is in its intelligent automatic threader, Langenhorst said. It’s been redesigned to anneal up to 14″ (356 mm) of wire and reduces wire curl for working on tall parts as well as submerged threading and rethreading through the gap if the wire breaks.
“There isn’t anybody out there who can say, ‘We’ve got a better automatic threader,’” says Langenhorst. “We’ve got that covered.”
New EDM Cuts Turbine Fir Tree Challenges Down to Size
The AgieCharmilles CUT 200 Dedicated, at first glance, appears the same as any other wire-EDM system from GF Machining Solutions. However, the company has transformed it into one specifically for larger, heavier aerospace applications—in particular, machining the fir tree patterns on jet engine turbine parts.
As the aerospace industry implements tougher materials, the new AgieCharmilles CUT 200 Dedicated gives manufacturers an alternative to conventional machining processes, such as broaching, when it comes to generating fir trees geometries. In fact, preliminary analyses shows that the cost of the wire-EDM process is approximately 40% less compared to broaching while maintaining similar productivity levels.
Broaching shears material and in the process can harden part surfaces. These hardened surfaces, in turn, cause the broach to wear and dull. So instead of one broach imparting about 100 tree patterns, it might last for only 20, and the tools are expensive to replace. EDM, on the other hand, is cost effective and cuts any shape in challenging materials.
Plus, EDM provides the versatility to quickly changeover to cut new shape geometries, whereas broaching requires, in most instances, between nine months and a year to develop a completely new tool. Since several EDMs replace one broaching system, manufacturers also gain increased production reliability. They avoid operations coming to a halt because a broaching machine is down. Additionally, having multiple EDMs as opposed to one or two broaching systems gives manufacturers the option to spread production capacity to different global locations if needed.
The key design changes and features of the AgieCharmilles Dedicated line of machining solutions include a new innovative A/B rotary table, in-process probing and the company’s e-Tracking software as well as other software functionality. The new table system not only enhances the process of EDMing large, heavy aerospace parts, it allows the machine to be easily automated.
In the development of the new machine, workpiece weight was a main factor, and one the company overcame with its special nonconventional, nontrunnion-style table. It is a rotary table with B-axis rotation and +25/−25º A-axis tilt, both of which ride in a horizontally orientated crescent-shaped axis that provides a swaying motion to the right and left.
The table allows the CUT 200 Dedicated to handle much heavier loads—up to 551.16 lb (250 kg)—without the risk of flexing. What differentiates the GF Machining Solutions design and gives it strength is that the table is actually built down into the machine itself.
In the past, machine tool OEMs would locate A/B tables on top of a machine’s existing standard table. Unfortunately, workpieces would then sit too high, which required extremely tall Z-axis travels. And, with workpieces so high, the machine’s lower flush nozzles were further away from the work zone—making for poor flushing conditions and diminished cutting speed and accuracy.
GF Machining Solutions removed the table of its standard AgieCharmilles CUT 200 wire EDM, bored out a cavity underneath the machine’s casting and installed the new style table. Doing so eliminates issues with part weight and its affect on the table. Plus, the design is one that locates the tilt motion directly under the worktable clamping surface for even more load support and accurate table motion.
Since all GF Machining Solutions machine bases are polymer granite, the AgieCharmilles CUT 200’s existing base provides more than enough strength, stability and rigidity for the new table design. Workpieces also sit lower in the machine, so the machine’s lower wire guide head is very close to the work zone to deliver excellent flushing conditions, which in turn allows for increased cutting speed and accuracy.
With large aerospace jet engine parts, automation on wire EDMs with standard A/B tables has always been extremely difficult, if not impossible. Standard tilt tables take up a lot of a machine’s work envelope and restrict a robot’s maneuverability to load and unload parts.
The table design of the AgieCharmilles CUT 200 Dedicated allows for easy automation. For that same reason, GF Machining Solutions removed all the power cables from the machine and rerouted them at the back of the work envelope to further clear the workspace and eliminate any interference. Additionally, the upper and lower guide heads move out of the way to let a robot enter for loading and unloading.
All the generator functionality on the AgieCharmilles CUT 200 Dedicated is geared toward tough aerospace materials such as titanium and Inconel. The machine’s advanced generator technology—developed and tested through years of research with aerospace OEMs, universities and other academic institutions—ensures surface integrity in both those materials while it eliminates any visible recast layers or micro cracks after four trim cuts.
While the AgieCharmilles CUT 200 Dedicated’s intent was aerospace turbine applications, it is also well suited for components in the energy and power generation industry sectors.