1. Chapter 6: Quality Management
© Holmes Miller 1999

2. Quality Specifications
Design quality: Inherent value of the product in the marketplace
Dimensions include:
Performance
Features
Reliability/Durability
Serviceability
Aesthetics
Perceived Quality.
Conformance quality: Degree to which the product or service design specifications are met 7

3. Importance of Quality Costs & market share Market Gains Reputation
Volume
Price
Improved
Increased
Quality
Profits
Lower Costs
Productivity
Rework/Scrap
Warranty

4. The Concept of Consistency: Who is the Better Target Shooter?
Not just the mean is important, but also the variance
Need to look at the distribution function

5. Funnel Experiment (Deming)
Tampering with a stable system only increases the production of faulty items and mistakes.
Tampering is taking action based on the belief that a common cause is a special cause.
Improvement of a stable system nearly always means reduction of variation.
One necessary qualification of anyone in management is stop asking people to explain ups and downs that come from random variation.

6. Basic Forms of Variation
Example: A poorly trained employee that creates variation in finished product output.
Assignable variation is caused by factors that can be clearly identified and possibly managed
Common variation is inherent in the production process
Example: A molding process that always leaves “burrs” or flaws on a molded item. 3

7. Two Types of Causes for Variation
Common Cause Variation (low level)
Common Cause Variation (high level)
Assignable Cause Variation
Need to measure and reduce common cause variation
Identify assignable cause variation as soon as possible

8. Taguchi’s View of Variation
Traditional view is that quality within the LS and US is good and that the cost of quality outside this range is constant, where Taguchi views costs as increasing as variability increases, so seek to achieve zero defects and that will truly minimize quality costs.
High
Incremental
Cost of
Variability
High
Zero
Lower
Spec
Target
Upper
Taguchi’s View
Incremental
Cost of
Variability
Zero
Lower
Spec
Target
Spec
Upper
Spec
Traditional View 30

9. Internal Failure Costs
Costs of Quality
Appraisal Costs
External Failure
Costs
Prevention Costs
Costs of
Quality
Internal Failure Costs

10. Six Sigma Quality
A philosophy and set of methods companies use to eliminate defects in their products and processes
Seeks to reduce variation in the processes that lead to product defects
The name, “six sigma” refers to the variation that exists within plus or minus six standard deviations of the process outputs

11. The Statistical Meaning of Six Sigma
Process capability measure
Lower
Specification
Limit (LSL)
Upper
Specification
Limit (USL)
Process A
(with st. dev sA)
x Cp P{defect} ppm
1 ,000
2 ,500
3 ,700 4 5
6 x
X-3sA
X-2sA
X-1sA X
X+1sA
X+2s
X+3sA 3
Process B
(with st. dev sB)
X-6sB X
X+6sB
Don’t confuse control limits with specification limits: a process can be in control,
yet be incapable of meeting customer specs

12. Six Sigma Quality (Continued)
Six Sigma allows managers to readily describe process performance using a common metric: Defects Per Million Opportunities (DPMO)

13. Six Sigma Quality (Continued)
Example of Defects Per Million Opportunities (DPMO) calculation. Suppose we observe 200 letters delivered incorrectly to the wrong addresses in a small city during a single day when a total of 200,000 letters were delivered. What is the DPMO in this situation?
So, for every one million letters delivered this city’s postal managers can expect to have 1,000 letters incorrectly sent to the wrong address.
Cost of Quality: What might that DPMO mean in terms of over-time employment to correct the errors? Other costs?

14. Six Sigma Quality: DMAIC Cycle
Define, Measure, Analyze, Improve, and Control (DMAIC)
Developed by General Electric as a means of focusing effort on quality using a methodological approach
Overall focus of the methodology is to understand and achieve what the customer wants
A 6-sigma program seeks to reduce the variation in the processes that lead to these defects
DMAIC consists of five steps….

15. Six Sigma Quality: DMAIC Cycle (Continued)
1. Define (D)
Customers and their priorities
2. Measure (M)
Process and its performance
3. Analyze (A)
Causes of defects
4. Improve (I)
Remove causes of defects
5. Control (C)
Maintain quality

16. Example to illustrate the process…
We are the maker of this cereal. Consumer Reports has just published an article that shows that we frequently have less than 15 ounces of cereal in a box.
Exercise: What should we do?
Define -- What is the critical-to-quality characteristic?
Measure -- How would we measure to evaluate the extent of the problem?
Analyze -- How can we improve the capability of our cereal box filling process?
Improve -- How good is good enough? Motorola’s “Six Sigma”
Control -- Statistical Process Control (SPC)

17. Analytical Tools for Six Sigma and Continuous Improvement: Flow Chart
No, Continue…
Material Received from Supplier
Inspect Material for Defects
Defects found?
Yes
Can be used to find quality problems
Return to Supplier for Credit 4

18. Analytical Tools for Six Sigma and Continuous Improvement: Run Chart
Can be used to identify when equipment or processes are not behaving according to specifications
0.44
0.46
0.48
0.5
0.52
0.54
0.56
0.58 1 2 3 4 5 6 7 8 9 10 11 12
Time (Hours)
Diameter

19. Analytical Tools for Six Sigma and Continuous Improvement: Pareto Analysis
Can be used to find when 80% of the problems may be attributed to 20% of the
causes
80%
Frequency
Design
Assy.
Instruct.
Purch.
Training 12

20. Analytical Tools for Six Sigma and Continuous Improvement: Checksheet
Can be used to keep track of defects or used to make sure people collect data in a correct manner
Monday
Billing Errors
Wrong Account
Wrong Amount
A/R Errors 16

21. Analytical Tools for Six Sigma and Continuous Improvement: Histogram
Can be used to identify the frequency of quality defect occurrence and display quality performance
Number of Lots 1 2 3 4
Defects in lot
Data Ranges 14

22. Analytical Tools: Cause and Effect Diagrams (Fishbone Diagrams)
Materials
Machines
Specifications / information
People
Vise position
set incorrectly
Machine tool coordinates set incorrectly
Vice position shifted during production
Part clamping surfaces corrupted
Part incorrectly positioned in clamp
Clamping force too high or too low
Cutting tool worn
Dimensions incorrectly specified in drawing
Dimension incorrectly coded
In machine tool program
Material too soft
Extrusion stock
undersized
Extrusion die undersized
Extrusion rate too high
Extrusion temperature too high
Error in measuring height
Steer support
height deviates
from specification
Can be used to systematically track backwards to find a possible cause of a quality problem (or effect) 17

23. Types of Statistical Sampling
Attribute (Go or no-go information)
Defectives refers to the acceptability of product across a range of characteristics.
Defects refers to the number of defects per unit which may be higher than the number of defectives.
p-chart application
Variable (Continuous)
Usually measured by the mean and the standard deviation.
X-bar and R chart applications 6

24. Analytical Tools for Six Sigma and Continuous Improvement: Control Charts
Can be used to monitor ongoing production process quality and quality conformance to stated standards of quality
970
980
990
1000
1010
1020 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
LCL
UCL

25. Statistical Process Control (SPC) Charts Normal Behavior
UCL
Normal Behavior
LCL
Samples over time
UCL
Possible problem, investigate
LCL
Samples over time
UCL
Possible problem, investigate
LCL
Samples over time 16

26. Process Capability Process limits Specification limits
How do the limits relate to one another? 28

27. Process Capability Index, Cpk
Capability Index shows how well parts being produced fit into design limit specifications.
As a production process produces items small shifts in equipment or systems can cause differences in production performance from differing samples.
Shifts in Process Mean 29

28. The Cereal Box Example
We are the maker of this cereal. Consumer reports has just published an article that shows that we frequently have less than 15 ounces of cereal in a box. We would like to have 16 ounces in each box.
Let’s assume that the government says that we must be within ± 5 percent of the weight advertised on the box.
Upper Tolerance Limit = (16) = 16.8 ounces
Lower Tolerance Limit = 16 – .05(16) = 15.2 ounces
We go out and buy 1,000 boxes of cereal and find that they weight an average of ounces with a standard deviation of .529 ounces.

29. Cereal Box Process Capability
Specification or Tolerance Limits
Upper Spec = 16.8 oz
Lower Spec = 15.2 oz
Observed Weight
Mean = oz
Std Dev = .529 oz
What does a Cpk of mean? This is a process that will produce a relatively high number of defects. Many companies look for a Cpk of 1.3 or better… 6-Sigma company wants 2.0!

30. Basic Forms of Statistical Sampling for Quality Control
Acceptance Sampling is sampling to accept or reject the immediate lot of product at hand
Statistical Process Control is sampling to determine if the process is within acceptable limits 3