• Document: Qualifying Capacitive Sensing Hole Measurement System Technology for Performing Gage R&R Studies
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08AMT-0050 Qualifying Capacitive Sensing Hole Measurement System Technology for Performing Gage R&R Studies Robert Magee Capacitec, Inc. Copyright © 2008 SAE International ABSTRACT CHP probe to look at the superiority of the measurement device for this type of application. Most notably the time The Capacitec CMS3 Reader, coupled with the CHP 48 savings in hole profiling going through multiple structure sensor probe, achieves +/-3µm accuracy by mapping 24 times at the same time, which is an advantage using the diameters in high tolerance drill holes for the 48 imbedded capacitive sensor probe. manufacture of composite or metal aircraft components. Gage repeatability and reproducibility (gage R&R) MAIN SECTION studies presented will show better than +/-0.0001 inches (2.5µm) for this measurement technique. Using non- CAPACITANCE MEASUREMENT OVER CONTACT contact inspection for quality control is a way to perform MEASUREMENT this inspection more efficiently than traditional contact measuring instruments, while reducing sampling time Capacitive Sensing Hole Measurement System compared to other methods. Gage repeatability is Technology for quality control has many advantages improved using non-contact methods because capacitive over conventional split ball gages and calipers for hole sensing at short distances has a linear and predictable dimensional inspection of precision holes. Capacitive correlation to displacement. Gage reproducibility is also technology allows for micro-inch accuracy in dimensional better because different users introduce a different touch checks and utilizing a non-contact method the inspector using bore gages and other contact measuring devices. can’t influence the indicator reading. This allows for In conclusion, using a probe that profiles 24 diameters at better in-process trend analysis of products with many the click of a button using non-contact capacitance holes to inspect. Further with the CMS3 Measuring technology not only saves time but is a significant system, 24 diameters are instantly recorded, profiling the improvement to overall gage R&R. hole in question compared to the single diameter which has to be physically moved to record more than one point. INTRODUCTION The CMS3 originally was designed as a system to measure aircraft fastener holes, but the concept should Gage R&R, repeatability and reproducibility can be very make it a valid process to measure all types of holes helpful when making a decision to choose bore gages or that also require tight tolerance. Typical flaws the CMS3 using the non-contact methods such as capacitive is designed to detect which affect cylindrical fastener sensing like the CMS3 and CHP sensor probes to holes are barreling, bell-mouthing and ovality as shown measure high precision hole diameters in aerospace in Figure 1. Even with the best of technique by the components. High tolerance and precise holes are technician, using split ball gages and other contact required for rivet and bolt holes on aircraft components measurement methods, reproducibility is difficult to to minimize ultimate fatigue and failure of components maintain between users. With capacitance non-contact and structures. With aluminum and composite methods, the operator will get repeatable data and less components making up most of the structures, many influence of variance between users because 1000’s of holes are drilled which require 100% capacitance is independent of placement in hole. inspection. A gage R&R study can show variability of the measurements obtained by a single operator using the same ring gage standard (repeatability) while also taking into account the variability of the measurement system caused by different operator behavior (reproducibility). A study was performed on the CMS3/ The advantage of the CMS3 (figure 3) is it’s superiority over other measuring methods for inspecting holes in aircraft assemblies because of the time savings and Fasteners Proper Fit and Typic

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