In-machine metrology key to accurate micro part production

At EDM Department, an Alicona Infinite Focus optical 3-D measuring machine is linked to a Makino EDAC micro ram EDM in the background. All images courtesy EDM Department.

Accurate and reliable production of microparts requires a stable machining process and consistent measurement capability.

“Process capability is basically the one thing you must have,” said Mark Raleigh, CEO of EDM Department Inc., Bartlett, Ill. “Call it overcapacity or overkill, but you must have a process that is stable to one half your part tolerance,” His company develops advanced flexible-manufacturing systems, with about 30 percent of its business in system R&D, 50 percent in system production and 20 percent in turnkey solutions combining the two. Much of the work is focused on EDMing, with conventional machining and laser ablation used mostly to make EDM electrodes.

The measuring machine has made a 3-D high-resolution scan of the part.

EDM Department and Alicona Imaging GmbH have partnered to develop advanced metrology systems that confirm micromachining process stability, adopting the Nano tooling referencing chuck system from System 3R and the Infinite Focus optical 3-D measuring system from Alicona.

“A 3-D, high-resolution sensor scan is now integrating every transfer of our manufacturing processes,” Raleigh said. “We started statically by taking the part out of the machine on a 3R chuck, putting it down, doing a 3-D scan, then feeding the information back to the machine tool. But as you start to get into the micron world, you sometimes can’t take the part out of the machine and put it back in accurately enough.”

EDM Department and Alicona developed an integrated solution employing on-machine, high-resolution 3-D metrology that can measure the results of a cutting process and evaluate its accuracy without removing the part. “The system can use up to 100 million measurement points in any field of view, from areas as large as 1,000mm² to as a small 1mm².” Raleigh said. “Not only are we measuring form, we can characterize surfaces; with one instrument, we can measure form and roughness.”

The production facility usually employs the system when micron-level precision is required. In chip cutting operations, for example, the 3-D scanning system precisely apportions roughing stock. Instead of setting roughing depth by trial and error, then backing off an arbitrary amount when the DOC is too large, the result of preliminary roughing is scanned and overlaid on a solid model of the part to show excess stock.

“Say we are no closer than 50µm to anywhere on the part; if that is the case, we can bring the roughing cut in 25µm closer. We take the finishing requirements and cut them in half, so the life of finishing cutters goes through the roof,” Raleigh said.

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