Tech Front: ECG Expands Precision Applications
The Electrochemical Grinding Process (ECG) is shedding its identity as a "special use" nontraditional machining method. Applications in manufacturing aircraft engines and power turbines continue to grow as more difficult-to-machine materials are used. Many of the newest and most exciting applications are found in the medical device and biomedical engineering fields for precision machining of implants and surgical cutting tools, and manufacturing components for diagnostic devices, chromatography, and test equipment. ECG has gone well beyond the traditional burr-free cutoff of small tubing for hypodermic needles for which it is well known.
According to Tom Travia, general manager of Everite Machine Products Co. (Philadelphia), the hardness of the workpiece isn’t a significant factor in the ECG machining process. In fact, Travia says, ECG generally works best on the materials that are the most difficult to machine by conventional methods. "Metals with high amounts of chrome, nickel and cobalt cut best because they are high in electrochemical reactivity. Stainless steels, cobalt-chrome, Inconel, Nitinol, and carbide are routinely processed by ECG. The cobalt-chrome used in implants is about the toughest material you can cut with carbide tools, but with ECG it cuts like aluminum."
Much like conventional abrasive grinding, ECG is used for form grinding, tube cutoff, notch and slot cutting, and even sharpening of cutting edges, but with the added benefit of eliminating the secondary deburring process. Burr-free, smooth surfaces and sharp cutting edges may seem like a contradiction, but with over 50 years of experience in building ECG machines, Travia says Everite has solved that challenge, as well as achieved tolerances required for today’s precision machining parts.
Everite’s current class of machines are able to hold tolerances of 0.0004" (0.01 mm) or less in many applications. "The ECG process was once thought of as a bit of a black art—hard to control and not very well understood. Advances in machine tools, control systems, sensors, and use of CNC technology have made that idea obsolete. Control of the ECG variables such as DC voltage, electrolyte flow, feed rate, electrolyte filtration, and wheel type have all be improved so that the process has become not only very repeatable, but very accurate as well," Travia explains.
With medical device designers constantly pushing the envelope of smaller parts, tighter tolerances, and more exotic materials, modern manufacturing methods are challenged to produce burr-free parts. Though laser and EDM are considered mostly burr-free, high temperatures generated during the cut can leave a layer of damaged material or recast as it cools. The recast and subsequent heat affected zone (HAZ) can be troublesome on many delicate parts and exotic materials. "The ECG process has the advantage of much higher cutting speed without recast layer or HAZ," says Travia.
ECG machines use specially formulated grinding wheels that fall into one of two separate categories: conventional or superabrasive. The conventional wheels are a mixture of abrasives (aluminum oxide and/or silicon carbide), copper powder, and phenolic resin. These conventional ECG wheels are still widely used in cutoff and surface grinding because they are inexpensive and easy to dress into the desired shape for form grinding. Wheel shaping or truing is usually accomplished by a diamond tool whether single point, block diamond form, or motorized rotary diamond roll. All of these methods have their advantages and disadvantages, but cost and lead time of formed diamond dressing tools continue to be a problem.
One recent breakthrough by Everite is the development of EC/CUT machinable diamond dressing matrix that can be easily machined to shape for quick production of diamond dressing tools with almost any conceivable shape. Form grinding not considered practical before has now become fairly routine. Another impact on the ECG process has been the expanded use of diamond and CBN wheels. The development of very high temperature polymide bonds in conjunction with diamond and CBN wheels has allowed ECG users to take full advantage of the increased metal removal rates offered by ECG without the associated wheel wear or continuous dressing. In addition, ECG wheels are essentially self-cleaning unlike those used in abrasive or creep feed grinding systems, Travia concludes. ME
For more information on Everite Machine Products, go to www.everite.com, or telephone 215-425-3750.
Laser MicroJet Technology
Synova (Ecublens-Lausanne, Switzerland) has entered into an OEM agreement with Makino Milling Machine Co. Ltd. (Tokyo, Japan) to manufacture Laser MicroJet (LMJ) machines based on Synova’s LMJ waterjet-guided laser cutting technology and Makino’s machine building prowess. Target markets for the LMJ machines are high-precision metal and hard-material processing applications, including hard-metal tools as well as consumer electronic goods. The new manufacturing cooperation brings together Synova’s long-standing LMJ process application know-how with Makino’s machine manufacturing expertise.
Synova is a leading provider of laser cutting systems for micromachining and dicing applications. Its proprietary Laser MicroJet technology, has emerged as a cost-effective alternative to conventional laser machining and diamond saw cutting for high-volume production of advanced electronic and micromechanical devices. LMJ applications are found in medical, semiconductor, electronic, automotive, and solar industries for cool laser cutting of devices like stents, semiconductors, wafers, thin films, PCD, and solar photovoltaic cell materials, among others.
Lasers used are pulsed lasers with pulse durations in the micro or nano-second range, operating at 1064 nm (IR), 532 nm (Green), or 355 nm (UV). Because the jet is virtually hair thin, the level of water consumption is extremely low—on the order of 5 L/hr at 300 bars. Pure de-ionized and filtered water at low pressure is used. The nozzles range in diameter from 30 to 120 µm and are made out of sapphire or diamond, materials with hardness that allows generation of a long stable waterjet.
A first prototype of the Synova/Makino LMJ machine has been built and a Beta prototype is being put into test. The new machine is being sold under the Synova brand. ME
For more information on Synova, go to www.synova.ch,
or telephone 510-396-5664.
3D Desktop Personal Printer
The UP! 3D desktop personal printer is designed for design houses, prototypers, and hobbyists and is capable of printing 3D objects and 3D parts directly from a computer program using ABS or PLA plastic in various colors, which is delivered as a filament. Priced under $3000, the UP! 3D printer is ready to be set up and used in 15 minutes out of the box.
The printer works from an industry-standard 3D file in .STL format. Designs can be created using 3D CAD programs like Solidworks, Autodesk Inventor, or TinkerCAD. Scans of existing objects using a 3D scanner can be saved to .STL or downloaded as shared models directly from the web. Any .STL file can be imported into the UP! software environment, and there is USB internal memory SD flash storage on board. Jobs can run independently of source computer once files are loaded.
Once scaled, rotated, and positioned, the model can be prepared for printing models which are built up layer by layer on a heated build platform. Build volume is 5.5 × 5.5 × 5.25" (140 × 140 × 135 mm). Z resolution settings range from 0.2 to 0.4 mm. The new optional stepper-driven filament feeder design ensures that head filament is consistently fed through the guide tube to the extruder assembly meaning less stress on the extruder feeder for precise regulated flow of plastic to the part. The heated metal build platform keeps parts thermally stable throughout the build cycle. Newest platform design comes with threaded screw-down receivers that the work with the UP!’s new optional perf-board build platform.
A heat windshield protects users from accidentally brushing up against the UP!’s hot end. The windshield redirects air to cool the hot thread as it is being extruded ensuring a perfect finish. Finished parts are solid and durable enough to be working models and can be sanded, machined, and painted. Unit weight is 5 kg; shipping weight 10 kg. Powered filament feeder is included with UP! Start Plus v1.1 model. ME
For more information on UP! 3D Personal Printer,
go to www.up3Dusa.com
Custom Cover for Tilt Table
The tilt table of a new design six-axis DeVlieg horizontal boring mill posed a special problem because of a minimal amount of space available for the retracted cover. The new machine is capable of machining complex aviation gearboxes using its 36" (914-mm) diam rotary table with tilt-up mounting and 3000-rpm, 5" (127-mm) spindle bar. Bourn & Koch Inc. (Rockford, IL) needed a moveable protection covering for their latest design tilt table on the six-axis Jigmill machining center, which was to be used in a heavy-duty machining environment. Because the cover had to protect a very large area while still retracting into a very small space, a traditional "clam shell" metal telescopic-style cover couldn’t be used. Soft fabric covers and bellows lacked the mechanical strength to operate in the confined space and also weren’t feasible.
The solution was found in Gorframe construction, which combines a ridged metal framework with a heavy-duty engineered fabric material. Bourn & Koch engineers provided the design team from A & A Manufacturing (New Berlin, WI) with CAD drawings of the cover’s operating area, complete with matching mounting flanges, rounded corners, and tapered convolutions. The specifications also defined how the framework of the cover was to move within a specified channel. The engineers designed a three-sided Gorframe wire-frame bellows using a ballistic nylon material constructed to open in a fanning motion. A & A sewed the ballistic nylon material around the wires to ensure that each convolution would open evenly. In addition, nylon wear caps were installed on the ends of the wires so that they would move smoothly in the machine’s guide channels.
Once the cover was manufactured, A & A representatives were on hand for a test fit and final installation. The results have been highly successful. The cover has proven to be extremely robust in a harsh environment and complements the machine’s aesthetics while it covers a large area, yet retracts into a very tight space. ME
For more information on A & A Manufacturing,
go to www.aaman.com, or telephone 262-786-1500.
This article was first published in the June 2012 edition of Manufacturing Engineering magazine. Click here for PDF.