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Short Run SPC ASQ Portland Section 0607

Short Run SPC ASQ Portland Section 0607. By Ed Landauer, C.Q.E., P.E. November 13, 2012. Short Run SPC. What it is What it isn’t SPC is not intended to be a substitute for inspection and testing Programs such as JIT make Short Run SPC more common. What Constitutes a Short Run?.

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Short Run SPC ASQ Portland Section 0607

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  1. Short Run SPCASQ Portland Section 0607 By Ed Landauer, C.Q.E., P.E. November 13, 2012

  2. Short Run SPC • What it is • What it isn’t • SPC is not intended to be a substitute for inspection and testing • Programs such as JIT make Short Run SPC more common

  3. What Constitutes a Short Run? • A run of 25 parts? • A run of 100 parts? • A run of 1000 parts? • A run of 50,000 parts? • A single part?

  4. General Categories of Short Runs • Not enough parts in a single production run to develop or maintain control limits on the process • Process cycles are so short that production runs are over before sufficient data can be gathered • Many different parts are made for many different customers • Examples

  5. Example: CNC Machine • Extremely complex machine • Has dozens of different tools • That produce hundreds of different parts • With thousands of characteristics

  6. Example: CNC Machine- Generic Operations • Select a tool • Position a tool • Rotate a tool • Move the part • Remove the metal

  7. Example: CNC Machine • Nearly all problems encountered after the initial set-up involve the ability of the machine to position the tool precisely • For example, the location of a single hole provides information on the location of the tool in both the x and y directions

  8. Sample Set of Data • Twelve subgroups- 3 observations per subgroup 5.0037 5.0009 4.9973 5.9974 6.0021 5.9981 5.0015 5.0023 5.0029 5.9990 5.9983 6.0018 4.9989 4.9981 4.9985 6.0015 5.9977 6.0023 7.0014 6.9991 7.0003 6.0031 5.9987 5.9987 7.0009 6.9979 6.9975 5.9985 6.0011 6.0021 6.9979 6.9995 7.0021 6.0017 6.0021 6.0001

  9. Method 1: Target Average and Range Charts • Subtract nominal (or target) value from the actual measurements x* = x - nominal • Can plot several parts from a given process on a single chart • Can plot several features from a single part on a single chart

  10. Method 1: Restrictions • Nominal (or target) values must be close to each other with the same tolerance • Or the most restrictive tolerance must be used for all

  11. Method 1: Control Limits • Calculate averages and ranges of the deviations from target • Control limit formulas are the same as for traditional control charts

  12. Method 2: Standardized Variables Control Charts • Good for recurring families of parts • They are independent of the unit of measure • They are scaled so that different characteristics can be plotted on the same chart • They are “true” process control charts

  13. Method 2: Calculations • Use the normalizing transformations • Need to use historical averages from previous data in the calculations

  14. Method 2: Control Limits • X-bar Chart -A2 andA2 • R chart D3 and D4

  15. Short Run Attribute Chart- c-chart • Job shop welding process • Produces small quantities of single order only parts • Operation always involves joining parts of similar material and size • Can plot chart of weld imperfections per 100 inches of weld

  16. Short Run Attribute Chart- p-chart • Job shop welding process • Similar operation to previous slide • Plot chart of the number of weld imperfections per total welds per 100 inches of weld

  17. Summary • Only minor change in mechanics to move from traditional SPC to Short Run SPC • The biggest difference in the perception of Statistical Process Control rather than Statistical Product Control

  18. Questions?

  19. Thank You! EDL22@comcast.net

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