16process_ctrl - Outline 1 Optimization 2 Statistical...

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Unformatted text preview: Outline 1. Optimization 2. Statistical Process Control 3. In-Process Control 2.008 - Spring 2004 2 2.008 - Spring 2004 2.008 Process Control 1 What is quality? 2.008 - Spring 2004 3 Variation: Common and Special Causes Pieces vary from each other: Size Size Size Size But they form a pattern that, if stable, is called a distribution: Size Size Size 2.008 - Spring 2004 4 Common and Special Causes (cont’d) Distributions can differ in… Location Spread Shape Size Size Size …or any combination of these 2.008 - Spring 2004 5 Common and Special Causes (cont’d) If only common causes of variation are present, the output of a process forms a distribution that is stable over time and is predictable: T im e i i Pred ct on Size 2.008 - Spring 2004 6 1 i 7 T im e i ion 2.008 - Spr ng 2004 Size Pred ct Common and Special Causes (cont’d) If i i 8 Variation: Run Chart 0 spec al causes of variation are present, the process output is not stable over time and is not predictable: 2.008 - Spr ng 2004 0.4880 0.4885 0.4890 0.4895 0.4900 0.4905 0.4910 0.4915 1 2 3 4 5 Run number Diameter of part Specified diameter = 0.490” +/-0.001” Process change i 9 Process Control l ( i T im e l ( i imi ) 2.008 - Spr ng 2004 Size Out of Contro Spec al causes present) In Contro Spec al causes el nated i 10 ) i 11 • • i i 12 Shewhart Control Chart 0 ) Di it 2.008 - Spr ng 2004 1. Detect disturbances (special causes 2. Take corrective actions Statistical Process Control 2.008 - Spr ng 2004 Central Limit Theorem A large number of independent events have a continuous probability density function that is normal in shape. Averag ng more samples increases the precision of the estimate of the average. 2.008 - Spr ng 2004 0.990 0.995 1.000 1.005 1.010 10 20 30 40 50 60 70 80 90 100 Run number Average (of 10 samples ameter Upper control limit Lower control lim 2 i Sampling and Histogram Creation 1 2 3 4 5 6 7 8 9 10 i i l lti ld l 0 2 4 6 8 10 12 14 16 18 20 1 2 3 4 5 6 7 8 9 i ∞ random l lti ld l 1 2 3 4 5 6 7 8 9 2.008 - Spr ng 2004 Wheel of Fortune: Equal...
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16process_ctrl - Outline 1 Optimization 2 Statistical...

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