Six-sigma16 - Six Sigma Control Statistical Process Control...

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1 Six Sigma Control Statistical Process Control Advanced statistical process control Lean tool for control Measurement system re-analysis
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2 Statistical Process Control Objectives and benefits Selection of variables Rational subgrouping Selection and application of control charts Analysis of control charts Pre-control
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3 Objectives and Benefits Statistical process control (SPC) is a technique for applying statistical analysis to measure, monitor, and control processes. The major component of SPC is the use of control charting methods . The basic assumption made in SPC is that all processes are subject to variation. This variation may be classified as one of two types, random or chance cause variation and assignable cause variation. Benefits of statistical process control include the ability to monitor a stable process and identify if changes occur that are due to factors other than random variation. When assignable cause variation does occur, the statistical analysis facilitates identification of the source so that it may be eliminated. The objectives of statistical process control are to determine process capability, monitor processes and identify whether the process is operating as expected or whether the process has changed and corrective action is required.
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4 Example 13 X-bar and R Chart At an heavy truck engine assembly plant, one of the parts, a camshaft, must be 600 mm + 2 mm long to meet engineering specifications. There has been a chronic problem with camshaft length being out of specification, which causes poor-fitting assemblies, resulting in high scrap and rework rates. Your supervisor wants to run X and R charts to monitor this characteristic, so for a month, you collect a total of 100 observations (20 samples of 5 camshafts each) from all the camshafts used at the plant to establish an X-bar and R chart.
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5 Length 601.6 600.4 598.4 600 596.8 602.8 600.8 603.6 604.2 602.4 598.4 599.6 603.4 600.6 598.4 598.2 602 599.4 599.4 600.8 600.8 598.6 600 600.4 600.8 600.8 597.2 600.4 599.8 Sample Sample Mean 20 18 16 14 12 10 8 6 4 2 602 600 598 _ _ X=600.23 UCL=602.474 LCL=597.986 Sample Sample Range 20 18 16 14 12 10 8 6 4 2 8 6 4 2 0 _ R=3.890 UCL=8.225 LCL=0 1 1 Xbar-R Chart of Length
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6 Control Chart 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 UCL LCL Sample number Mean Out of control Normal variation due to chance Abnormal variation due to assignable sources Abnormal variation due to assignable sources
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7 Statistical Process Control • Variations and Control Common cause variation or random variation : Natural variations in the output of a process, created by countless minor factors. Random variation is usually left alone. Special cause or nonrandom variation
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Six-sigma16 - Six Sigma Control Statistical Process Control...

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