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Chapter 21D. Quality Tools and TechniquesDefine and use various problem-solving andcontinuous improvement tools, including theseven quality control tools, plan–do–check–act (PDCA)/plan–do–study–act (PDSA),Six Sigma DMAIC, root cause analysis, etc.(Application)Body of Knowledge IV.DPart IV.DUnderstanding of basic problem-solving and continuous improvement tools andtechniques is critical for a quality inspector to be effective and to function withinthe larger quality community. It has been said many times that as many as 85percent of the problems encountered in production or service delivery operationscan be solved with these basic tools and techniques. We will begin our discussionwith the seven quality control tools, proceed with a discussion of PDCA/PDSA, and conclude with a discussion of the DMAIC and root cause analysistechniques.SEVEN BASIC QUALITY CONTROL TOOLSThis seven basic quality control tools (plus two variants) consist of the following:1. Histogram2. Stem-and-leaf diagram3. Scatter diagram4. Run chart (also, known as line graph or time series graph)5. Check sheet6. Pareto chart7. Cause-and-effect diagram (also known as fishbone orIshikawa diagram)314
Chapter 21: D. Quality Tools and Techniques 3158. Defect concentration diagram9. Control charts*These basic tools form a simple but very powerful structure for quality improvement.Once inspectors, technicians, and operators/service delivery personnelbecome fully familiar with these tools, management must get involved to sustaintheir use in an ongoing quality improvement process. Management must createan environment where these tools become part of day-to-day production or serviceprocesses. Implementation of these tools without management’s commitmentportends the impending failure of continuous improvement efforts. Thus, besidesdiscussing these tools we will also explore here some of the questions that arisewhile implementing the tools.Every job, whether in a manufacturing company or in a service company,involves a process. As described, each process consists of a certain number of steps.No matter how well the process is planned, designed, and executed there is alwayssome potential for variability. In some cases this variability may be very littlewhile in other cases it may be very high. If the variability is very little then it isusually caused by common causes, which are unavoidable and can’t be controlled.If the variability is very high then we expect that besides the common causes thereare some other causes, usually known as assignable causes, present in the process.Any process working under only common causes or chance causes is consideredto be in statistical control. If a process is working under both common and assignablecauses then the process is considered unstable, or not in statistical control.PLAN–DO–CHECK–ACT (PDCA)/PLAN–DO–STUDY–ACT(PDSA) CYCLEThe PDCA and the PDSA cycles are very common in use and in the language ofthe quality profession. Accordingly, we begin our discussion of these two cycleswith a clarification. That clarification is that these two cycles were not created bythe same person, the two cycles are not structurally the same, and that the twocycles have different philosophical intents. As has been documented by McKinley(2006), the original creators of the cycles were as follows:• Walter Shewhart—Shewhart cycle—PDCA. Development date: late1930s. It should be noted that Shewhart is credited with the “Shewhartcycle.” However, Shewhart did not label the steps of his cycle asPDCA, but rather used the terms specification, production, andinspection.• W. Edwards Deming—Deming cycle—PDSA. Development date: late1950s. Structurally, these cycles differ on the “check” step advocatedby Shewhart as compared to the “study” step advocated by Deming.Part IV.D* A detailed discussion of the basic quality control tools has been presented in Chapters 18and 19 of this book; so the discussion will not be repeated here to avoid duplication.
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Chapter 21: D. Quality Tools and Techniques 315
8. Defect concentration diagram
9. Control charts*
These basic tools form a simple but very powerful structure for quality improvement.
Once inspectors, technicians, and operators/service delivery personnel
become fully familiar with these tools, management must get involved to sustain
their use in an ongoing quality improvement process. Management must create
an environment where these tools become part of day-to-day production or service
processes. Implementation of these tools without management’s commitment
portends the impending failure of continuous improvement efforts. Thus, besides
discussing these tools we will also explore here some of the questions that arise
while implementing the tools.
Every job, whether in a manufacturing company or in a service company,
involves a process. As described, each process consists of a certain number of steps.
No matter how well the process is planned, designed, and executed there is always
some potential for variability. In some cases this variability may be very little
while in other cases it may be very high. If the variability is very little then it is
usually caused by common causes, which are unavoidable and can’t be controlled.
If the variability is very high then we expect that besides the common causes there
are some other causes, usually known as assignable causes, present in the process.
Any process working under only common causes or chance causes is considered
to be in statistical control. If a process is working under both common and assignable
causes then the process is considered unstable, or not in statistical control.
PLAN–DO–CHECK–ACT (PDCA)/PLAN–DO–STUDY–ACT
(PDSA) CYCLE
The PDCA and the PDSA cycles are very common in use and in the language of
the quality profession. Accordingly, we begin our discussion of these two cycles
with a clarification. That clarification is that these two cycles were not created by
the same person, the two cycles are not structurally the same, and that the two
cycles have different philosophical intents. As has been documented by McKinley
(2006), the original creators of the cycles were as follows:
• Walter Shewhart—Shewhart cycle—PDCA. Development date: late
1930s. It should be noted that Shewhart is credited with the “Shewhart
cycle.” However, Shewhart did not label the steps of his cycle as
PDCA, but rather used the terms specification, production, and
inspection.
• W. Edwards Deming—Deming cycle—PDSA. Development date: late
1950s. Structurally, these cycles differ on the “check” step advocated
by Shewhart as compared to the “study” step advocated by Deming.
Part IV.D
* A detailed discussion of the basic quality control tools has been presented in Chapters 18
and 19 of this book; so the discussion will not be repeated here to avoid duplication.