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aerospace methology


Display monitor shows holes to be inspected on Paradigm Precision’s VisionGauge 700 Series Digital Optical Comparator.


uct until we obtain a large enough sample to introduce a sampling plan. And even with the plan, we must meet strict requirements including dimensional tolerances which can be as small as ±0.0063 mm,” said Min Tong, quality control supervisor at Paradigm.


“Falling short of these exacting standards on one or two holes may not make an engine fail, but missing the mark even slightly has other consequences” said Hellwig. “Penalties can be assessed if 100% inspection criteria are not success- fully met, which can affect us fi nancially, not to mention our company’s reputation in the industry.” One of Paradigm’s families of precision-machined prod-


ucts are heat shields. Up to 160 different operations, includ- ing turning, milling and EDM drilling, are involved with manu- facturing 16 different shield sizes. The heat shields are made of Single Crystal Superalloy materials that provide maximum strength and tolerance in the high-heat environment of turbine engines. Paradigm uses EDM drilling machines to drill the heat shield cooling holes, ranging in size from 0.4 to 1.9-mm diameter and in quantities from over 50 to nearly 400 holes, at different locations and angles into the assorted heat shields. The cooling holes must line-up precisely where the OEM specifi es via CAD fi les and prints. “We were using a CMM to perform part inspection to


ensure the holes were in the right location per the OEM’s re- quirements,” said Tong. “However, because the holes are so small, we could not use the CMM to directly probe the holes. The CMM is unable to validate hole sizes below 0.76 mm. Instead, inspectors had to insert gage pins into the holes. Complicating the process, the pin size needed to be as close to the hole size as possible in order to make a tight fi t. Then the probe needed to be rotated at a right angle to measure the pin and project the position of the hole.” Tong reported several limitations and challenges when using the CMM to inspect the small holes. For one, gage pins range in size from 0.28 to 6.35 mm, in 0.001" (0.0254 mm) increments, to accommodate the smaller holes. But if the pin is not perfectly positioned, the CMM probe can defl ect off the pin, adding errors to the inspection process. Tong said, “Add to this the overall problem the varying hole locations and angles present for the probe to properly adjust. The heat shields have holes located with less than 2° of separation and with different angles. The angle of the CMM’s probe only offers resolution every 7.5°, so it was very diffi cult to achieve the accuracy our customers required.” To minimize errors at that time, Tong said, their only op- tion was to try to fi nd the best probe possible for measuring at angles.


The CMM inspection process was taking Paradigm inspectors up to six hours to fully inspect 365 holes on one part. To reduce inspection time, they were measuring just two holes per side and then using Mylars to determine if the checked cooling holes fell in an acceptable range. Tong said, “This was not accurate enough to meet our customers’ requirements, and if requested, we were not able to perform any SPC studies.” Paradigm Precision determined that this inspection process was not acceptable, so they researched inspection options that didn’t include contact probing.


Test & Measurement Effi ciency


Paradigm selected VisionGauge Digital Optical Compara- tor 700 Series, featuring fi ve-axis inspection to effi ciently view the heat shield holes from all sides and angles and solve their inspection challenges. VisionGauge Digital Optical Comparators are made by VISIONx Inc. (Pointe-Claire, Que- bec Canada) and exclusively distributed in North America by Methods Machine Tools Inc. (Sudbury, MA). The fi ve axes of motion (X, Y, Z, Rotary, Tilt) enable quick, accurate inspection of all sides and angles on complex parts, such as in the aerospace and industrial gas turbine industries. Extremely powerful “adaptive” software locates features of interest on different surfaces with varying refl ectiv-


136 — Aerospace & Defense Manufacturing 2015


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