The Quality Improvement Model Is Process Capable Define

The Quality Improvement Model Is Process Capable ? Define Process Select Measures Collect & Interpret Data Is Process Capable? Purpose: Determine the adequacy of the process with respect to customer /management needs. Is Process Stable ? No Investigate & Fix Special Causes Yes Improve Process Capability No Is Process Capable ? Yes Use SPC to Maintain Current Process 8 -1

Is Process Capable ? Capable Process A stable process that meets customer requirements. Histogram Control Chart UCL CL LCL 2 4 6 8 10 12 14 1618 20 22 24 26 28 3032 Run Order Lower Spec Upper Spec Target Capability assessments for unstable processes, may not be indicative of how the process is actually performing. 8 -2

Assessing Process Capability l Is Process Capable ? Counting Measures The average percent defectives. § The average number of defects. § l Instrument Measures § Comparing both the center of the process and the process variation 8 -3

Capability Assessment for Counting Measures “Order Entry Process” Week # Errors 1 15 2 22 3 18 4 10 5 13 6 9 7 27 8 12 9 24 10 22 11 8 12 8 13 26 14 16 15 20 16 10 17 16 18 9 19 15 20 20 Total 320 Is Process Capable ? Control Chart 35 30 Number of Errors UCL=28. 0 25 20 Avg=16. 0 15 10 5 0 LCL=4. 0 5 10 15 20 Week Is this process adequate as is? Should it be improved? 8 -4

Capability Assessment for Instrument Measures Is Process Capable ? Histogram Control Chart UCL CL LCL 2 4 6 8 10 12 14 1618 20 22 24 26 28 3032 Run Order Lower Spec Upper Spec Target Is this process adequate as is? Should it be improved? 8 -5

Measures of Process Capability Cp = Specification Range = True Process Range USL - LSL 6 sc Is Process Capable ? Cp < 1. 0 ® Process is not capable of meeting specs Cp = 1. 0 ® Process is marginally capable Cp > 1. 0 ® Process is capable of meeting specs Problem: We are assuming the process has a target that is in the center of the specification range, and that the process is in fact centered on that target. Distance from process average = min (USL - x , x - LSL) Cpk = to closest specification limit 1 True Process Range 3 sc 2 Note: a negative result is possible if the process average is outside specifications Cpk < 1. 0 ® Process is not capable of meeting specs Cpk = 1. 0 ® Process is marginally capable Cpk > 1. 0 ® Process is capable of meeting specs Benefits: • Optimal values are attained by running exactly between specs. • Can (must) be used for 1 -sided specifications Warning: Capability assessments for unstable processes, may not be indicative of how the process is actually performing. 8 -6

Is Process Capable ? Process Capability LSL USL How much material is out of spec? § In the short term? § In the long term? 8 -7

Is Process Capable ? Process Capability Ratios LSL USL Voice of The Process Voice of The Customer 8 -8

Process Capability - The Strategy Is Process Capable ? Centering –The Process Is On Target Spread – Reduce The Variation Defects LSL Defects USL 8 -9

Process Capability Ratios Is Process Capable ? 2 Key Metrics for Measuring Capability X- LSL USL- X Cpk Min( , ) 3 3 8 -10

Process Capability Ratios - Concept Cp Is Process Capable ? Total Tolerance Process Spread 8 -11

Process Capability – Example 1 LSL 27 Inches USL 33 Inches Is Process Capable ? u = 30 Inches =1 Cp = _____ Sigma Level = _____ 8 -12

Process Capability – Example 2 LSL 29 Inches USL 31 Inches Is Process Capable ? u = 30 Inches =1 Cp = _____ Sigma Level = _____ 8 -13

Process Capability – Example 3 LSL 28 Inches USL 32 Inches Is Process Capable ? u = 30 Inches =. 333 Cp = _____ Sigma Level = _____ 8 -14

Process Capability – Example 4 LSL 28 Inches USL 32 Inches Is Process Capable ? u = 33 Inches =. 333 Cp = _____ Sigma Level = _____ 8 -15

Process Capability Ratios Is Process Capable ? X- LSL USL- X Cpk Min( , ) 3 3 X- LSL Cp. L 3 USL- X Cp. U 3 A metric to take into account process shift 8 -16

Process Capability – Example 5 LSL 28 Inches USL 32 Inches Is Process Capable ? u = 33 Inches =. 333 Cp. L = ______ Cp. U = ______ Cpk = ______ Recall Cp=2. 0 8 -17

CP & CPK Measure Short-term Capability Is Process Capable ? Is The Process In Control ? Is It Producing Defects ? A Short-term Capability study covers a relatively short period of time (days, weeks) generally consisting of 30 to 50 data points. The actual number depends on the subject under study. 8 -18

Long Term Performance Is The Process In Control ? Is Process Capable ? Short term Capability Is It Producing Defects ? A long-term capability study covers a relatively long period of time (weeks, months) generally consisting of 100 -200 data points. Again, the actual amount depends on the subject under study. 8 -19

A Further Look at Capability Is Process Capable ? Compare the estimates of the process deviations from the short-term and long-term data Descriptive Statistics Variable N Mean Std. Dev short term 30. 6 2. 23 long term 180 33. 8 4. 44 What is the difference between the short-term and the long-term data? What implication does this have in doing capability studies? 8 -20

The Dynamic Process LSL Is Process Capable ? USL Short-Term Capability Long-Term Capability Over time, a process tends to shift by approximately 1. 5 8 -21

Measures of Process Performance P p = Specification Range = USL - LSL 6 ss True Process Range Is Process Capable ? P p < 1. 0 ® Process Performance is not meeting specs P p = 1. 0 ® Process Performance is marginally meeting specs P p > 1. 0 ® Process Performance is meeting specs Problem: We are assuming the process has a target that is in the center of the specification range, and that the process is in fact centered on that target. Distance from process average to closest specification limit min (USL - x , x - LSL) P pk = = 1 3 ss True Process Range 2 Note: a negative result is possible if the process average is outside specifications Ppk < 1. 0 ® Process Performance is not meeting specs Ppk = 1. 0 ® Process Performance is marginally meeting specs Ppk > 1. 0 ® Process Performance is meeting specs Benefits: • Optimal values are attained by running exactly between specs. • Can (must) be used for 1 -sided specifications 8 -22

Performance vs. Capability Is Process Capable ? DSO Days Sales Outstanding for 55 Days These data show that the process, if well controlled can perform much better than it currently is 8 -23

Is Process Capable ? Capability vs. Performance DSO Days Sales Outstanding for 55 Days Capability: Only random or short term variability Process Performance: Total Variation including shifts and drifts (Cp & Cpk) (Pp & Ppk) 8 -24

Process Performance Ratios Is Process Capable ? X- LSL USL- X P pk Min( , ) 3 3 The P-family of indices are computationally the same as the C-family of ‘capability’ indices, but use the observed long-term standard deviation. 8 -25

How Does Process Capability Relate to Six Sigma? A goal of Six Sigma is to have: Is Process Capable ? Cp = 2. 0 Cpk = 1. 5 Cpk is 1. 5 to allow for a 1. 5 sigma shift from target. If the six-sigma goal is achieved, the 1. 5 drift can occur with a low risk of producing material out of specification. Example: The target viscosity for a plastic is 0. 76. sc from the process is 0. 01. The lower and upper spec from the process are 0. 70 and 0. 82, respectively. LSL USL 0. 70 0. 71 0. 72 0. 73 0. 74 0. 75 0. 76 0. 77 0. 78 0. 79 0. 80 0. 81 0. 82 T-1. 5 sc T+1. 5 sc T 8 -26

Six Sigma Goals (Defect Level) Is Process Capable ? The Quality goal of six sigma corresponds to 3. 4 ppm defect level. For attributes data, the ppm level is calculated by: For variables data, the ppm level is calculated using the normal table. 8 -27

Minitab: Process Capability Analysis Is Process Capable ? Is it in control ? Is it Normal ? How does the process variation compare to the spec limits ? 8 -28

WARNING!!! Is Process Capable ? Statistical Assumptions Made In Capability Studies 1. Data Comes From a Stable Process If not, work towards getting the process in control § Don’t despair, you can still make some assumptions about your process in the mean time § 2. Data are Normally Distributed § If not, transform it (ask the instructor) If Items #1 and #2 aren’t met, results will be misleading 8 -29

Minitab: Process Capability Analysis l Is Process Capable ? Minitab has many tools that will help you in this area. We will find Process Capability under: Stat>Quality Tools> Capability Sixpack> Normal Open Line 1. MTW in the Mintab Datasets Folder and go to the Capability Sixpack 8 -30

Minitab: Process Capability Analysis Is Process Capable ? Enter the information shown below and select OK 8 -31

Minitab: Process Capability Analysis Is Process Capable ? Your output should look like this: 8 -32

Example - Capability Study Results l Notice that both Cp / Cpk and Pp / Ppk values are given l The data shows that the Capability of the process (Cpk) is 1. 32 and the Entitlement (Cp) is 1. 35 § l This shows that the process is on target. Why? The data also shows the Performance of the process (Ppk) is reasonably capable with a value of 1. 26 § l Is Process Capable ? This indicates the process is in control. Why? But how good should a process get… Next Slide? 8 -33

Process Performance and Capability l Is Process Capable ? The Ppk can closely approach the Cp when Ppk Cp The Customer specifications truly reflect customer requirements § The process in under statistical control § The data approximate the normal distribution § The process average is very close to target. § l The Cp is like a benchmark or entitlement Cp § l Sigma capability is driven primarily by random error (Common Cause Sources of Variation) We would like Ppk to be very close to a Cpk of 1. 5 Ppk § This would be a process that is performing at a Six-Sigma level 8 -34

Test Method Capability Variation Types Variation can be broken down into two types, process and test. These two types are listed and described below: Variation Type Process Test Component(s) The variation due to the: • process itself • raw materials • Sampling ? All other types of variation, including: • Sampling ? • Sample preparation • Between analysts • Within analysts • Test Equipment • Environment • Any other variation not part of the process NOTE: Test variation may not be just variation due only to test, it encompasses all sources other than process. Is Process Capable ? 8 -35

Total Variability Components Where: Is Process Capable ? (Assumes process is stable) (For Unstable Processes) Can be estimated three ways: 1) Standard Reference Material – Repeated Sampling 2) Half-Blind Technique 3) Gauge R&R (Estimated by subtracting test from total variability) 8 -36

Repeated Sampling (SRM) Technique Is Process Capable ? Advantages Long-term estimate of test variability Easy to administrate Can be used to assess accuracy (known value) Can be used to test experimental bias (known value) Can be used as a SPC monitor Disadvantages Only one level of the process is studied People get used to what value "should be" 8 -37

Half-Blind Technique Is Process Capable ? Advantage Long-term estimate of test variability Multiple levels of the process are represented by using different samples Disadvantage Hard to administrate Cannot be used to test accuracy 8 -38

Gauge R&R Technique Is Process Capable ? Advantages Quick initial estimate of test variability Can be used to assess accuracy (known value) Can be used to test experimental bias (known value) Analyst portion can be estimated Multiple process levels studied Disadvantages Hard to administrate Short-term estimate of test variability Detailed experimental plan needed. Analysis more difficult 8 -39

Measures of Test Method Capability Is Process Capable ? Eastman has traditionally used: Percent of variation due to test method Six Sigma uses the following measures: Percent Gauge R&R Precision to Tolerance Ratio 8 -40

How Good is Good? … The Debate is On Is Process Capable ? Eastman has traditionally used: Percent Test Variability: Goal is 20 to 30% Six Sigma uses the following measures: Percent Gauge R&R: Less Than 30% P/T Rate: Best Case 10%, Acceptable 30% Problem: 30% Gauge R&R translates to 9% Percent Test Variability (Unrealistic for a lot of tests in Chemical Industry) Note: Initial analysis is showing that processes can be monitored with SPC techniques even when the percent test variability is as high as 50%! 8 -41

Resources Allocation? Is Process Capable ? 8 -42

Review • Indices to measure processes capability §Cp – Goal is 2, Short Term Sigma used in Estimate Is Process Capable ? §Cpk – Goal is 1. 5, Short Term Sigma used in Estimate §Pp – Approach Cp, Long Term Sigma used in Estimate §Ppk – Approach Cpk, Long Term Sigma used in Estimate ØNote: All of the above are equal for stable processes on target • Indices to measure test method capability §Percent Test Variation – Goal is 20 to 30% §Percent Gauge R&R – Less than 30% (Percent Test < 9%) § 50% may be more reasonable §P/T Ratio – Best Case 10%, Acceptable at 30% 8 -43

Exercise Is Process Capable ? 1. ) Your Catapult Team should complete page 11 of the “Catapult Process” handout. Limit yourselves to 30 minutes for this exercise. 8 -44