PRAGMATIC APPLICATION OF GAUGE-MANPOWER CORRELATION FISHER CONTROLS Alexandria Stewart, Michael Stinn, Justin Thede, Alicia Wieland
Transcript
Slide 1
Slide 2
PRAGMATIC APPLICATION OF GAUGE-MANPOWER CORRELATION FISHER
CONTROLS Alexandria Stewart, Michael Stinn, Justin Thede, Alicia
Wieland
Slide 3
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 Fishers 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