MoldMaking Technology

NOV 2018

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EDM/Additive Manufacturing 14 MoldMaking Technology —— NOVEMBER 2018 By Evan Syverson and Tully Mijatovic Some additive machines can print directly onto traditional fixtures for multiple operations. Rethinking EDM for Additive Applications A s manufacturers accept and implement new technolo- gies into their operations, downstream processes often need to be adjusted to accommodate the type of work that then comes down the pipeline. One example is additive manufacturing or D printing. While many of the •irst commercial D parts were for specialty aerospace and medical applications, the technology slowly but surely has crept into much broader manufacturing settings, including the mold and die industries. Because of the unprecedented nature of D printing, these adjustments touch all areas of machining processes. This arti- cle examines the impact of D printing on EDM and speci•i- cally the impact on wire EDM workholding, cutting conditions and machine-tool speci•ications. Workholding One of the most basic considerations before a technician prints a D part is how subsequent processes are affected by early workholding decisions. One factor that complicates these decisions is the great variance in D printers. Some additive machine manufacturers come from the machine-tool world and have quickly leveraged that experience to provide easy solutions just as they would with a traditional CNC machine. Conversely, those that have led innovation speci•ically in D printing often have less experience with questions pertaining to workholding and so may require more ingenuity to strat- egize secondary operations. Naturally, one trend that is taking root quickly is for tra- ditional tooling suppliers to partner with original equipment manufacturers (OEMs) for machines to provide integrated solutions. With validated systems at the OEM level, it is pos- sible for tooling manufacturers to make the secondary opera- tions just a little less laborious. Alternatively, for machinery without an established tooling solution, it may be possible to produce tombstones or other custom •ixtures to expedite the setup process, though these would be less transferable from one operation to the next. For example, a part that requires both wire EDM removal and sinker EDM •inishing likely would not be able to use a tombstone for both. Moreover, operators should be aware that because D print- ing is not a perfectly accurate process, virtually all applications would still bene•it from the inclusion of reference or datum surfaces for more accurate pickups. Cutting Conditions As anyone who has wire-cut into a D-printed part would attest, special care is necessary to avoid wire breaks, which typically result from a combination of hollow spaces designed into D parts and loose powder that has not been sintered, which often coats and •ills these parts. While flushing is important in all EDM applications, it is especially important for additive parts. Inside a typical kerf, flushing jets are con- •ined, which makes it possible for fluid to laminate the EDM wire and to clear swarf ef•iciently and neatly. As the distance from the flushing nozzle increases, this stream becomes more turbulent and less effective. Also, upon hitting an open or hollow cavity within a part, the flushing stream experiences a drop in pressure, expanding the flushing path and creating even more turbulence to disrupt flushing. 3D printing impacts wire EDM workholding, cutting conditions and machine-tool specifications. Images courtesy of Sodick Inc.

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