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PRAGMATIC APPLICATION OF GAUGE-MANPOWER CORRELATION FISHER CONTROLS Alexandria Stewart, Michael Stinn, Justin Thede, Alicia Wieland

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FISHER CONTROLS Fisher Controls is a manufacturer of control valves Headquartered in Marshalltown, IA These valves control elements like pressure, flow, and liquid level They are used in many industries, including nuclear power plants, oil and gas refineries, pulp and paper factories, etc. Due to these applications, having valves that are within engineering specification is important

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PROCESS Fisher’s operators machine parts to specifications set by their engineers After each machining operation, the dimension machined is measured by the operator and verified as acceptable by an inspector When machining is complete, each part undergoes a final inspection process The inspector measures the part, either with a micrometer or a caliper

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PROBLEM Parts are being rejected at ±0.001” out of tolerance Inspectors use their own discretion as to which measurement device is appropriate in a given situation It is suspected that the current procedures are not producing this kind of accuracy The objective of this study is to analyze measurement capability and suggest appropriate changes

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PROCEDURES Gauge R&R Study Three operators measured 10 small parts three times each with a caliper This was repeated using a set of 10 larger parts Three measurements per part were taken using a micrometer on the 10 small parts by the same three operators Figure 1: 1” Stem Measurement Process Chart Figure 2: 8” Ring Measurement Process Chart

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DATA

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ANALYSIS

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Gage Capability Ratio (GCR) GCR < 0.1 wanted for a gage to be considered appropriate GCR < 0.01 is preferred for most applications Micrometer had smallest GCR of either device Item – DeviceGauge Capability Ratio 1” Stem – Caliper0.266 1” Stem – Micrometer0.152 8” Ring – Caliper0.209

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ANALYSIS The micrometer variation is consistently smaller than those of the caliper Caliper variation was consistent Figure 3: Repeatability, Reproducibility, and R&R

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ANALYSIS Micrometer measurements are more precise than the caliper Calibration for accuracy is possible, but imprecision cannot be fixed Figure 4: Range and Distribution of Stem Measurements

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ANALYSIS Comparison of operator consistency between 1” stems and 8” rings Operator 3 consistently lower than 1 and 2 Variation was independent of part size Figure 5: Average measurements of 1” stems with caliper Figure 6: Average measurements of 8” rings with caliper

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ANALYSIS Comparison of measurement devices Variation between operators was larger using the caliper Measurements of each part were consistent regardless of the device Figure 5: Average measurements of 1” stems with caliperFigure 7: Average measurements of 1” stems with micrometer

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ANALYSIS

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RECOMMENDATIONS Create and implement standard protocol for measurement tools For part features with tolerances less than ±0.005”, always use a micrometer With calipers, we are 95% sure that a measurement could be skewed nearly as much as 0.004 inches By using a micrometer, our 95% confident maximum error is less than 0.001”, allowing for a much more accurate measurement Use this data as an awareness tool to further establish the importance of using the appropriate tool for specific situations Conduct a training event for the inspectors and establish standard measurement procedures Standardization across all inspectors on how to hold the device Digital caliper shows value during measurement – can bias recorded measurement if inspector views screen during process

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