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Peter Loetzner CEO


EMAG LLC (North America) www.emag.com


ViewPoints N


ew material substrates and an increasing number of compact designs in aerospace engines, automotive transmissions, medical devices and elsewhere have had the dual effect of stimulating more creative approaches to machining, plus a review of the many tech- niques long classified as nontraditional. Specifically, the expanding use of nickel-based alloys such as Waspaloy and Inconel, along with new polymer composites, derivative titanium alu- minides and cobalt chrome materials call for a new approach. Traditional processes are limited in their ability to machine these new materials. The geometries of today’s blisks, defusers, compact transmission gear assemblies and the always nonlinear world of medical machining initially drove a trend toward more five-axis machining. However, that scenario car- ries high capital investment, substantial tooling costs and other burdens for the production department. The appeal and profitability of such work is substantial, but so are the investments needed.


Thus, nontraditional, alternative technologies should certainly be considered for such work, including laser, EDM and the rapidly advancing methods of electrochemical machining or ECM. These non-chipcutting technologies have decided advantages in the production of very contoured surfaces, where the finish is critical for maintaining end effects such as heat dissipation on the blisks in a compact jet engine or transmission gears in close proximity, free flow in fuel injectors and, of course, the stability, comfort and functionality of a knee joint in the human body. ECM is essentially electrolysis for a metal surface. The workpiece is the positive anode and the tool is the negative cathode. A current flows between the two and an electrolyte removes metal ions from the surface of the workpiece.


ECM, a technology pioneered early in the 20th century and used as a production technique for a short time in the middle of the last century, fell dormant in most sectors due to toxic waste considerations, owing to the chemical composition of the electrolytes used and the corresponding dis- posal methods. With the evolution of high-tech filtration systems, however, the environmental impact of the process is no longer of concern. Accuracies in the application of ECM technology have likewise progressed to a point where the achievement of single-digit micron


112 ManufacturingEngineeringMedia.com | November 2014


A Closer Look at Alternative Machining


tolerances is now possible in many cases. Coupled with the low tool wear, high-strength alloy machining possibilities, repeatability and even the “traditional” ECM role of deburring leading and sharp edges, this technology is on the march forward in many markets today. One significant emerging market for this method is the highly compact world of consumer mobile electronics.


Despite the decidedly different machining envelope and mechanics of ECM machines, they are quite suitable for end-of-line applications in a traditional mill or turn machine sequence with auto-loading or robotic part articulation. As an example, a firearms manufacturer could use this tech- nology as a noncontact process to create virtually any rifling profile with top finish and accuracy quality. With no cathode wear, thousands of barrels can be produced with the same tool and the chemical process creates no heat affected zone.


These non-chipcutting technologies have advantages in the production of contoured surfaces, where the finish is critical.


Likewise, in the expansion of near-net piece part production, ECM can perform the final machining operations with precision to bypass an ad- ditional grinding process.


Pre-machined cathodes and the abundance of current chemistries available for the electrolyte solutions combine with the quickly trainable skill levels required to run the machines and also the lights-out capabili- ties of ECM on long runs such as power gen turbine blade assemblies, all of which produce a most attractive cost-to-benefit scenario. As more complex geometries and materials that present significant challenges to traditional chipcutting techniques emerge on the market, such alternative machining methods as ECM will merit a closer look by forward-thinking manufacturers and job shops alike. When low tool wear, noncontact machining and high-precision contour surfacing to Rz


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0.05 converge in a practical production solution, it is an exciting moment for those of us in the machine tool world. Let’s look at those alternatives. ME


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