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Chapter: Mechanical : Total Quality Management (TQM) : TQM Tools & Techniques

The seven traditional tools of quality

I - Pareto chart: II - Flowchart: III - Cause-and-Effect Diagrams IV - Check Sheet V- Histograms VII - Control Charts VI - Scatter Diagrams

The seven traditional tools of quality


I - Pareto chart: Italian economist Vilfredo Pareto Shows on a bar graph which factors are more significant. This method helps to find the vital few contributing maximum impact.


Purpose: The purpose of the Pareto chart is to prioritize problems No company has enough resources to tackle every problem, so they must prioritize.


Pareto Principle: The Pareto concept was developed by the describing the frequency distribution of any given characteristic of a population. Also called the 20-80 rule, he determined that a small percentage of any given group (20%) account for a high amount of a certain characteristic (80%).


Conclusion: The most important thing in improving quality is to start somewhere, doing something. As you begin using the Pareto chart to decide where your problems are, you will discover many things about your processes and will come because you will know where to improve.


II - Flowchart: A technique that separates data gathered from a variety of sources so that patterns can be seen (some lists replace "stratification" with or "run chart").


Purpose: Flow Charts provide a visual illustration of the sequence of operations required to complete a task.


A picture of the steps the process undergoes to complete it's task. Every process will require input(s) to complete it's task, and will provide output(s) when the task is completed. Flow charts can be drawn in many styles. Flow charts can be used to describe a single process, parts of a process, or a set of processes. There is no right or wrong way to draw a flow chart. The true test of a flow chart is how well those who create and use it can understand it. Input ---------------------Process----------------Output


III - Cause-and-Effect Diagrams - 1943 by Mr. Kaoru Ishikawa at the University of Tokyo


Purpose: One important part of process improvement is continuously striving to obtain more information about the process and it's output. Cause-and-effect diagrams allow us to do not just that, but also can lead us to the root cause, or causes, of problems.



Constructing the Cause-and-Effect Diagram:


Step 1: Select the team members and a leader. Team members knowledgeable about the quality. Team members focus on the problem under investigation.


Step 2: Write the problem statement on the right hand side of the page, and draw a box around it with an arrow running to it. This quality concern is now the effect.


Step 3: Brain-storming. The team members generate ideas as to what is causing the effect.


Step 4: This step could be combined with step 3. Identify, for each main cause, its related sub-causes that might affect our quality concern or problem (our Effect). Always check to see if all the factors contributing to the problem have been identified. Start by asking why the problem exists.


Step 5: Focus on one or two causes for which an improvement action(s) can be developed using other quality tools such as Pareto charts, check sheets, and other gathering and analysis tools. Conclusion: Improvement requires knowledge. The more information we have about our processes the better we are at improving them. Cause-and-effect diagrams are one quality tool that is simple yet very powerful in helping us better understand our processes.


IV - Check Sheet

Purpose: Check sheets allow the user to collect data from a process in an easy, systematic, and organized manner.


Data Collection: Before we can talk about check sheets we need to understand what we mean by data collection. This collected data needs to be accurate and relevant to the quality problem. The first is to establish a purpose for collecting this data. Second, we need to define the type of data that is going to be collected. Measurable data such as length, size, weight, time,...etc., and countable data such as the number of defects. The third step is to determine who is going to collect that data and when it should be collected.


V- Histograms


Purpose: To determine the spread or variation of a set of data points in a graphical form. It is always a desire to produce things that are equal to their design values.


Histograms: A histogram is a tool for summarizing, analyzing, and displaying data. It provides the user with a graphical representation of the amount of variation found in a set of data.


Constructing a Histogram: The following are the steps followed in the construction of a histogram:


Data collection: To ensure good results, a minimum of 50 data points, or samples, need to be collected


Calculate the range of the sample data: The range is the difference between the largest and smallest data points. Range = Largest point - smallest point.


Calculate the size of the class interval. The class interval is the width of each class on the X axis. It is calculated by the following formula:

Class interval = Range / Number of classes.


Calculate the number of data points (frequency) that are in each class. A tally sheet is usually used to find the frequency of data points in each interval.


Conclusion: Histogram is simple tools that allow the user to identify and interpret the variation found in a set of data points. It is important to remember that histograms do not give solutions to problems.


VI - Scatter Diagrams


Purpose: To identify correlations that might exist between a quality characteristic and a factor that might be driving it.


Scatter Diagrams: A scatter diagram is a nonmathematical or graphical approach for identifying relationships between a performance measure and factors that might be driving it. This graphical approach is quick, easy to communicate to others, and generally easy to interpret.


Interpreting the Results: Once all the data points have been plotted onto the scatter diagram, you are ready to determine whether their exists a relation between the two selected items or not. When a strong relationship is present, the change in one item will automatically cause a change in the other. If no relationship can be detected, the change in one item will not effect the other item. Their are three basic types of relationships that can be detected to on a scatter diagram: 1. Positive relationship 2. Negative relationship 3. No relationship


Conclusion: Scatter diagrams allow the user to graphically identify correlations that could exist between a quality characteristic and a factor that might be driving it. It is a quality tool that is simple, easy to communicate to others, and generally easy to interpret


VII - Control Charts


Purpose: Process is in control and to monitor process variation on a continuous basis. Identifying the tolerance level in the variations. Control charts is one SPC tool that enables us to monitor and control process variation. Types of variation Common and Special Cause Variation


Control charts: Developed in the mid 1920's by Walter Shewhart of Bell labs. There are two basic types of control charts, the average and range control charts. The first deals with how close the process is to the nominal design value, while the range chart indicates the amount of spread or variability around the nominal design value. A control chart has basically three line: the upper control limit UCL, the center line CL, and the lower control limit LCL. A minimum of 25 points is required for a control chart to be accurate.

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