Chapter 27

7 Quality Control ToolsBackground and Its Importance 7 Quality Control Tools

The 7 Quality Control tools are simple statistical tools used for problem solving. These tools were either developed in Japan or introduced to Japan by the Quality Gurus such as Deming and Juran.

Kaoru Ishikawa has stated that these 7 Quality Control Tools can be used to solve 95% of all problems.

The 7 Quality Control Tools is a designation given to a fixed set of graphical techniques identified as being most helpful in troubleshooting issues related to quality. They are used to analyze the production process, identify the major problems, control fluctuations of product quality, and provide solutions to avoid future defects.

Why 7 QC Tools?

The Deming Chain

- Improve Quality- Decrease Costs- Improve Productivity- Decrease Price- Increase Market- Stay in Business- Provide More Jobs- Return on Investment

Quality is a very important feature for successful businesses to uphold.

Quality control focus on improving processes to ensure better quality. It is essential that customers are given products and services that are convenient for them and hence, worth the money they pay. In order to be successful in business, we need to remember that customer satisfaction is always the most important goal.

Customer satisfaction is part of the Six Sigma principles, it’s ensure the best possible products and services are sold to customers at a consistent level, businesses should use the Seven Quality Control tools (7 QC Tools). The efficient and effective use of these 7 QC tools can help maintain the consistency of the products and services being produced. The use of these tools is spread out throughout the different phases of the DMAIC process.

7 QC As Tools

The 7 QC tools is a title given to a fixed set of graphical techniques identified as being most helpful in troubleshooting issues related to quality. The 7 QC tools are fundamental instruments to improve the process and product quality. They are used to examine the production process, identify the key issues, control fluctuations of product quality, and give solutions to avoid future defects.

These are the tools which facilitate the organization to resolve the basic problems. When an organization starts the journey of quality improvements, the organization normally has many low hanging fruits; which should be tackled with these basic 7 QC tools. These 7 QC tools are easy to understand and implement and does not need complex analytical/ statistical competence.

List of 7 Quality Control Tools Are:

The 7 QC tools as defined by the American Society for Quality (ASQ) and accepted throughout the quality engineering community which includes:

1. Cause-and-effect diagram (“fishbone” or Ishikawa diagram)

2. Pareto chart (80/20 Rule)

3. Control Charts

4. Scatter diagram (Shewhart Chart)

5. Histograms

6. Flowcharts

7. Check Sheet (Tally Sheet)

1. Cause-and-effect diagram (“fishbone” or Ishikawa diagram)

History Background

The Fishbone Diagram was invented by Professor Kaoru Ishikawa of Tokyo University, a highly regarded Japanese expert in quality management. He first used it in 1943 to help explain to a group of engineers at Kawasaki Steel Works how a complex set of factors could be related to help understand a problem.

Definition:

A Cause-and-Effect Diagram is a tool that helps identify, sort, and display possible causes of a specific problem or quality characteristic (Viewgraph 1). It graphically illustrates the relationship between a given outcome and all the factors that influence the outcome.

Cause-and-Effect Diagram

Graphical sample diagram of the tool

Benefits of Using Fishbone Diagram

The fishbone diagram was designed by Japanese quality control expert Kaoru Ishikawa. His purpose was to provide a means of identifying underlying causes of problems so that solutions were not misapplied to secondary causes; if underlying causes are missed, larger problems develop. The fishbone diagram is meant to detect root causes of problems through group thinking by asking why each potential cause happens. The fishbone diagram is traditionally worked from right to left with "bones" for each cause branching from the center bone. The complexity of the fishbone lies in the smaller branching bones supporting each potential cause and answering "why".

Advantages

Major advantages to the fishbone diagram accord with the purpose and method of the fishbone.

1. It identifies cause and effect relationships in problems.

2. The method operates through the function of joint brainstorming discussions.

3. Brainstorming allows for broad-ranging thinking, steering teams away from "in a rut" thinking patterns.

4. These diagrams ask "why does this happen" again and again at each stage as each potential cause is identified.

5. Fishbone allows for prioritizing relevant causes so the predominating, underlying root cause is addressed first.

Disadvantages

Some major disadvantages relate to the greatest strengths of the fishbone diagram.

1. Brainstorming produces irrelevant potential causes along with relevant ones, resulting in a time and energy drain.

2. Brainstorming is as often based on opinion as on fact and evidence.

3. A very large space for working out the diagram is needed for complex problems with many branching bones and "why"-bones.

4. The complex interrelationships of multiple factors are difficult to show on a fishbone

2. Pareto charts

Historical Background

The theory behind the Pareto Chart originated in 1897 when an Italian economist named Vilfredo Pareto created a formula representing the uneven distribution of wealth - what later came to be known as the 80-20 rule. ... However, this Pareto Chart is constructed from one dimension only - defect frequency.

What does a Pareto chart tell you?

A Pareto Chart is a graph that indicates the frequency of defects, as well as their cumulative impact. Pareto Charts are useful to find the defects to prioritize in order to observe the greatest overall improvement

Definition:

The Pareto principle (also known as the 80/20 rule, the law of the vital few, or the principle of factor sparsity) states that, for many events, roughly 80% of the effects come from 20% of the causes. ... Pareto developed both concepts in the context of the distribution of income and wealth among the population.

Pareto Chart

Graphical sample diagram of the tool

Benefits of a Pareto Chart

1. Drawing a Pareto chart is easy.

2. It helps you segregate the problems and their causes.

3. It helps you focus on solving the few causes generating the most problems.

4. It shows you the problems to focus on to get a significant improvement.

5. It helps you visualize problems quickly, so it is an excellent visual communication tool.

Limitations of a Pareto Chart

The following are a few limitations of Pareto chart

1. The Pareto principle is a rule of thumb that you cannot apply in all cases.

2. It does not help you find the root cause of the problem, so you will need another tool such as root cause analysis.

3. If there are many problems, you may need more sub-Pareto charts to segregate, which sometimes may be cumbersome.

4. It shows the frequency of a problem, not the severity.

5. It focuses on past data which might not be significant to current or future scenarios.

Conclusion

A Pareto Chart consists of vertical bars and a line graph. The bars represent the individual values of the problem in descending order from left to right; the line shows the cumulative sum. This chart helps project managers find the minor causes that are affecting the project significantly. It helps prioritize tasks and activities. Being a variant of a bar chart, it is simple to draw, use, and communicate problems to stakeholders. - Disadvantages (if any)

3. Control Charts

Historical Background

Control charts, also known as Shewhart charts (after Walter A. Shewhart) or process-behavior charts, are a statistical process control tool used to determine if a manufacturing or business process is in a state of control. It is more appropriate to say that the control charts are the graphical device for Statistical Process Monitoring (SPM). Traditional control charts are mostly designed to monitor process parameters when underlying form of the process distributions are known. However, more advanced techniques are available in the 21st century where incoming data streaming can-be monitored even without any knowledge of the underlying process distributions. Distribution-free control charts are becoming increasingly popular.

The control chart is a graph used to study how a process changes over time. Data are plotted in time order. A control chart always has a central line for the average, an upper line for the upper control limit, and a lower line for the lower control limit. These lines are determined from historical data.

Definition:

The control chart is a graph used to study how a process changes over time. Data are plotted in time order. A control chart always has a central line for the average, an upper line for the upper control limit, and a lower line for the lower control limit. These lines are determined from historical data.

Control chart

Graphical sample diagram of the tool

The benefits of control charts

Improve process control to give less variation in the output, lower the unit cost and increase the process capacity. Provide a common language for all staff to discuss and improve processes. Control charts are not a substitute for action.

What is the purpose of control chart?

A control chart is used to monitor a process variable over time. ... That process variable can be plotted on a control chart over time. The objective of the control chart is to find any "special" causes of variation as well as to reflect the process improvements that have been made.

- Disadvantages (if any)

4. Scatter diagrams

Historical Background of Scatter Diagram

Scatter plots are glorious. Of all the major chart types, they are by far the most powerful. They allow us to quickly understand relationships that would be nearly impossible to recognize in a table or a different type of chart. (Take this visualization of the relationship of country religiosity and wealth, for example.) Michael Friendly and Daniel Denis, psychologists and historians of graphics, call the scatter plot the most “generally useful invention in the history of statistical graphics.”

The origins of this invaluable invention, however, are not entirely clear.

Behold! Originally called scatter diagrams, scatter plots typically plot points on the cartesian coordinate system developed by René Descartes in the 17th century, with perpendicular lines representing the two axes. We call the

horizontal one the x-axis and vertical one the y-axis—the use of those letters stems from their role in algebra. Descartes developed his coordinate system to demonstrate the link between geometry and algebra, and he likely did not imagine it would be used plot the relationship between real-world things.

Definition:

The scatter diagram graphs pairs of numerical data, with one variable on each axis, to look for a relationship between them. If the variables are correlated, the points will fall along a line or curve. The better the correlation, the tighter the points will hug the line.

Graphical sample diagram of the tool

Benefits of a Scatter Diagram

It shows the relationship between two variables. It is the best method to show you a non-linear pattern. The range of data flow, i.e. maximum and minimum value, can be determined. Observation and reading are straightforward.

Scatter plots can also be a perfect opportunity to prove or disprove the relationship between two variables, as well. According to most experts, there are three main types of scatter plots to concern yourself with:

1. Those with absolutely no correlation to speak of.

2. Those with what you might call a “moderate” correlation.

3. Those with a very strong correlation.

Provided that the quality of the data that you’re using to build your scatter plot is as high as it can be, you can finally settle old arguments and determine whether Variable X actually has the impact on Variable Y that certain people seem to think it does.

5. Histograms

Historical Background

Histogram was first introduced by Karl Pearson in 1891. Pearson coined the word “histogram” by using the following two words: “historical diagram” which is the function of a histogram. It is a graph figure which is used to display past data.

Where did the name histogram come from?

The word histogram comes from the Greek histos, meaning pole or mast, and gram, which means chart or graph. Hence, the direct definition of “histogram” is “pole chart.” Perhaps this word was chosen because a histogram looks like several poles standing side-by-side.

Definition:

A histogram is a plot that lets you discover, and show, the underlying frequency distribution (shape) of a set of continuous data. This allows the inspection of the data for its underlying distribution (e.g., normal distribution), outliers, skewness, etc.

Histogram

Graphical sample diagram of the tool

Benefits of the Histogram

1. Using the histogram helps us to make the decision making process a lot more easy to handle by viewing the data that was collected or will be collected to measure pass performance of any given company.

2. A histogram offers a way to display the frequency of occurrences of data along an interval.

3. When you Use the data presented in the histogram, you can regulate statistical information.

4. The Histograms track helps determine trend. For instance, if you have divided the horizontal line into 12 segments representing January through December and the vertical line is divided into temperatures, you can see the trend of temperatures during the year.

5. You can use histogram calculations to make your picture clearer to read and to categorize your data into many diverse classes.

Conclusion

In conclusion, when one uses histogram for calculations of frequency and other necessary actions like decision making and so on, it is the area of the bar that shows the frequency of incidences for each bin. Therefore, this shows that the height of the bar does not really show how many incidences of scores there were within each specific bin. The histogram is the produce of height multiplied by the width of the bin that shows the frequency of incidences within that bin.

6. Flowcharts

Historical Background

The first structured method for documenting process flow, the "flow process chart", was introduced by Frank and Lillian Gilbreth in the presentation "Process Charts: First Steps in Finding the One Best Way to do Work", to members of the American Society of Mechanical Engineers (ASME) in 1921.

A flowchart is a type of diagram that represents a workflow or process. A flowchart can also be defined as a diagrammatic representation of an algorithm, a step-by-step approach to solving a task.

The flowchart shows the steps as boxes of various kinds, and their order by connecting the boxes with arrows. This diagrammatic representation illustrates a solution model to a given problem. Flowcharts are used in analyzing, designing, documenting or managing a process or program in various fields.

Flowcharts are used in designing and documenting simple processes or programs. Like other types of diagrams, they help visualize what is going on and thereby help understand a process, and perhaps also find less-obvious features within the process, like flaws and bottlenecks. There are different types of flowcharts: each type has its own set of boxes and notations. The two most common types of boxes in a flowchart are:

- a processing step, usually called activity, and denoted as a rectangular box.

- a decision, usually denoted as a diamond.

A flowchart is described as "cross-functional" when the chart is divided into different vertical or horizontal parts, to describe the control of different organizational units. A symbol appearing in a particular part is within the control of that organizational unit. A cross-functional flowchart allows the author to correctly locate the responsibility for performing an action or making a decision, and to show the responsibility of each organizational unit for different parts of a single process.

Flowcharts depict certain aspects of processes and are usually complemented by other types of diagram. For instance, Kaoru Ishikawa defined the flowchart as one of the seven basic tools of quality control, next to the histogram, Pareto chart, check sheet, control chart, cause-and-effect diagram, and the scatter diagram. Similarly, in UML, a standard concept-modeling notation used in software development, the activity diagram, which is a type of flowchart, is just one of many different diagram types.

Definition:

A flowchart is a type of diagram that represents a workflow or process. A flowchart can also be defined as a diagrammatic representation of an algorithm, a step-by-step approach to solving a task. ... Flowcharts are used in analyzing, designing, documenting or managing a process or program in various fields.

Flowchart

Graphical sample diagram of the tool

Benefits of Flowchart

a. Visual Clarity: One of the biggest benefits of a flowchart is the tool's ability to visualize multiple progresses and their sequence into a single document. Stakeholders throughout an organization can easily understand the workflow while finding out which step is unnecessary and which progress should be improved.

b. Instant Communication: Teams can use flowcharts to replace meetings. Simply clarifying progresses offers an easy, visual method to help team members instantly understand what they should do step by step.

c. Effective Coordination: For project managers and resource schedulers, the benefits of a flowchart include the ability to sequence events and reduce the potential for overburdening team members. Eliminating the unnecessary steps help to save time and resources.

d. Efficiency Increase: Efficiency increases are a significant benefit of flowcharts. The flowchart lists each step necessary to perform a process. The flowchart helps a designer remove unnecessary steps in a process, as well as

errors. The flowchart should only include the steps that are requirements to reach the endpoint of the process.

e. Effective Analysis: With the help of flowchart, problem can be analyzed in more effective way. It specifically shows what type of action each step in a process requires. Generally, a rectangle with rounded edges defines the beginning or end of the process, a diamond shape shows the point at which a decision is required, and a square block shows an action taken during the process. A flowchart may also include symbols that show the type of media in which data is stored, such as a rectangle with a curved bottom to show a paper document or a cylinder to symbolize a computer hard drive.

f. Problem Solving: Flowcharts break a problem up into easily definable parts. The defined process displayed by the flowchart demonstrates the method of solving a complex problem. A flowchart reduces the chance that a necessary step for solving a problem will be left out because it appears obvious. In this way, it reduces cost and wastage of time.

g. Proper Documentation: Digital flowcharts serve as a good paperless documentation, which is needed for various purposes, making things more efficient.

7. Check Sheets

Historical Background

The check sheet is one of the seven basic tools of quality control made popular by Dr. Kaoru Ishikawa. The Check Sheet is a simple document that is used for collecting data in real time and at the location where the data is generated.

Definition:

The check sheet is a form (document) used to collect data in real time at the location where the data is generated. The data it captures can be quantitative or qualitative. When the information is quantitative, the check sheet is sometimes called a tally sheet.

Kaoru Ishikawa identified five uses for check sheets in quality control:

- To check the shape of the probability distribution of a process

- To quantify defects by type

- To quantify defects by location

- To quantify defects by cause (machine, worker)

-To keep track of the completion of steps in a multistep procedure

Check Sheet

- Graphical sample diagram of the tool

Benefits of Check Sheet

Graphical sample diagram of the tool

They enable faster capturing and compiling of data, allow the data to be recorded in a consistent manner, and enable capturing essential contextual and descriptive information that otherwise may be overlooked or forgotten.

Check sheets are often used for collecting failure information at specific process steps.

When to use the 7 QC Tools?

Collectively, these tools are commonly referred to as the 7 QC tools. In the Define phase of the DMAIC process, Flowcharts are very important. In the Measure phase, the first three of the 7 QC tools are relevant: Fishbone Diagram, Pareto Chart, and Control Charts. In the Analyze phase, the Scatter Diagram, Histogram, and Checklist are relevant. The Control Chart is also relevant in the Improve phase.

Three key insights regarding the 7 QC Tools

Kaoru Ishikawa, in the year 1985, is credited with making the following statement with respect to these tools:

“As much as 95 percent of all quality-related problems in the factory can be solved with seven fundamental quantitative tools.”

Ishikawa’s statement provides three key insights into these tools, namely that these seven tools are:

1. Applicable in problem-solving situations most commonly encountered by Quality Engineers

2. Quantitative in nature and rely on with the exception of Flowcharts and Cause-and- Effect diagrams, on numerical data

3. Most commonly used in quality control to assist in Tracking, Monitoring and analyzing data

The 7 QC tools are great ways to visualize information relating to problem-solving to improve the quality of processes, products, and services. These tools can be used throughout the DMAIC cycle and also provides evidence of how well the Six Sigma project has been executed according to its data-driven principles.