Electrochemical Machining for Medical, Aerospace and More
Workpieces with complex contours often feature sections that are not easy to machine because they are difficult to access. Usually, undercuts, pockets and internals, as well as overlapping bores, do not present major challenges to mechanical machining operations unless such sections need to be deburred. Even those sections of a workpiece that are difficult to access call for burrs to be removed cleanly and without negative impact on the material.
With the mechanical, thermal, electrical discharge and water jet-based technologies used currently, intended output rates, economic viability and repeatability often can not be guaranteed. Medium size and large batch production, in particular, attach great importance to the best possible component quality, and internal burrs and lugs can badly affect component function. In practice, conventional machining presents another problem: the secondary burr.
When burrs are removed using standard machining processes, a secondary or “turned down” burr can form and require further, undefined finish-machining work to be done. These are some of the reasons why Emag has focused its development efforts into the electrochemical deburring process.
Remove the Burr
Unlike electrical discharge machining, electrochemical machining (ECM) is a gentle, electrochemical metal removal process that does not involve spark formations or a recast layer. An electrode is connected to a DC or pulse source to act as a cathode (tool), while the workpiece represents the other electrode and is poled as an anode. The charge in the electrode gap between cathode and anode flows in a watery electrolyte solution—usually sodium nitrate or sodium chlorite—and dissolves metal ions on the workpiece surface. The material removed can later be filtered out from the electrolyte solution as metal hydroxide. The contour of the cathode (tool) is made to fit the machining requirement. This design ensures that deburring takes place only at the point of the workpiece where necessary to remove material (and without causing mechanical or thermal stresses). The pinpoint machining process allows for the most delicate components to be deburred with accuracy and repeatability.
Electrochemical machining takes many forms, but all involve the electrolytic dissolving of metal substrates. This technique is often used in applications involving hard-to-machine materials such as Inconel, high-nickel alloys, titanium, and so on. Because ECM is a non-contact machining process with no heat input involved, the process is not subject to the variances inherent in conventional machining, such as tool wear, mechanical stress and microcracking caused by heat transfer, as well as surface oxidation and the recast layer present with EDM. By contrast, the ECM process is characterized by stress-free stock removal and smooth and precise transitions in machining contours with burr-free surfaces. End products from turbine blisks to dental implants and many automotive industry products are ideal uses for this technology, according to Tobias Trautmann, product manager for ECM/PECM Products at Emag ECM.
Addressing the Need
Emag ECM and PECM technologies for the end user are engineered for low tool wear on the cathode, which is ideal for batch production. They can provide surface finishes to Ra 0.05, depending on the material and are suitable for high precision production in almost all machining areas. Cutting depth is reproducible to <20 microns. Because basic material properties are unaffected, hardness, magnetic and other performance properties are unchanged. Nano and extremely thin-walled section contours are possible to meet the critical requirements of aero and medical applications. Other features include high repeatability, owing to the consistency of the mechanical components and predictability of the machining conditions; minimal secondary operations; and roughing, finishing and polishing in one machine. The process allows users to employ multiple fixtures and run the process simultaneously, facilitating a significant reduction in per-part cycle times.
Standard features offered on the Emag ECM Basic Series machines are a Siemens S7 controller with full graphics display, current relay and voltage monitor, pH control and conductance monitor, temperature control module, machining area of 1,150 mm by 950 mm (45.27 inches by 37.40 inches) and two-handed operator safety controls. Emag also provides ancillary equipment interfacing for work cell setups, including pre- and post-op cleaning stations and multiple machining units, as well as robotic workpiece handling.
Precise electrochemical machining systems operate on the same basic principle of electrolytic dissolution, but include a mechanical oscillation mechanism for more intricate 2D and 3D microstructures. All standard machines include Emag scalable generator technology to as much as 30,000 amps, pulse frequencies to 100 kHz, and a machine base of Mineralit or granite. The high precision of these machines derives directly from the efficient pulsed current source and the machine’s rigidity.
The Premium Series further offers precision imaging, surface finishes to Ra 0.05 (relative to the material) and a high degree of precision in lower speed ranges, essential for micromachining.
Complementing this new machine series is the Emag test laboratory. Users can examine a variety of test cut scenarios to determine the optimum conditions for machining, fixturing, process performance and materials specification, matching the requirements to the most productive machines and systems available.