Kaoru Ishikawa developed 7 basic tools of quality management. This tools help average person analyze and interpret the data. These quality tools are used worldwide by managers and employees for inspection and quality management.
This page describes 7 quality control tools. The control chart, cause and effect diagram, flowchart, pareto chart, histogram, run chart and scatter diagram are used as tools to control quality.
Control charts are the way of visualizing how processes are doing over time. These charts are used to determine whether a process will produce a product or service with consistent measurable properties.
EXAMPLE: To count number of defective products or services OR to count number of defects in a given product or service.
Following steps are followed in developing process control chart.
➤Find out operations which are critical in the process where the inspection is required/needed.
➤Identify critical product features.
➤Determine whether the critical product feature/characteristic is a variable or an attribute.
➤Select appropriate process control chart.
➤Establish control limits and use the chart to monitor and improve.
➤Update the limits.
This diagram is referred as Fishbone diagram or Ishikawa diagram. This tool is used to discover all the possible causes for a particular effect. The major purpose of the cause and effect diagram is to find list of possible causes. This is the first step in problem solving.
EXAMPLE: This quality tool is used to detect problem of incorrect deliveries. When a production team is about to launch a new product, the factors that will affect the final product must be recognized. This is done using this diagram.
Following steps are used for constructing a cause and effect diagram.
➤First identify and define the problem or effect for which causes must be identified. Place the problem/effect at the right or head of the diagram.
➤Identify all broad areas of the problem.
➤Write all detailed possible causes in each of these broad areas.
➤Each cause identified should be looked upon for further more specific causes.
➤View the diagram and evaluate main causes.
➤Set goals and take action on the main causes.
A flowchart is basically a pictorial representation which shows all required steps needed for the process. EXAMPLE: The process followed should be considered for making of the product.
➤First familiarize and determine the participants with the flow chart symbols.
➤Draw the process flow chart and fill it out in detail about each element.
➤Analyze the flow chart and determine which steps add value and which don't in the process of simplifying the work.
Pareto charts are used to identify and prioritize problems to be resolved immediately. These charts are based on the idea that large number of problems are caused by small number of causes. They are basically histograms aided by 80/20 rule adopted by Joseph Juran. In 80/20 means 80% of the problems are created by approx. 20% of the causes.
EXAMPLE: Pareto Charts are used when products are suffering from different defects but the defects are occurring at a different frequency. In these situation, manufacturing or development company will concentrate reducing defects having major chunk or eliminate defects which cause financial loss. The figure depicts typical pareto chart.
Following are the steps for constructing pareto chart:
➤Information must be selected based on types or classifications of the defects which occur as a result of the completed process.
➤These data is collected and classified into different categories.
➤Then histogram or frequency chart is constucted which shows number of occurrences.
The diagram called as histogram is basically a bar graph which shows the frequency of the data. It provides easiest way to evaluate distribution of the data.
EXAMPLE: Histograms are used to determine distribution of sales. Other application is to compare revenue results of the company.
Following are the steps involved to create the histogram.
➤ Collect the data and sort them into categories.
➤ Then label the data as dependent set or independent set.
➤ Each mark on either axis (X or Y) should be in equal increments.
➤ For each category, find the related frequency and make the horizontal marks to show that frequency.
Run charts are used to analyze the processes according to time or order.
EXAMPLE of run chart: The company's intention to have their product deliver to their customers on time.
Operations or processes needed to collect data for analysis/measurement.
Data must be divided into two sets of values X and Y. X values represent time and values of Y represent the measurements taken from the manufacturing process or operation.
Plot the Y values versus the X values.
Interpret the data and draw any conclusions that will be beneficial to the process or operation.
Scatter Diagrams are used to study and identify the possible relationship between the changes observed in two different sets of variables.
EXAMPLE: To determine relationship between the production speed of an operation and the number of defective parts made.
Following steps are followed for the construction of a scatter diagram.
➤First, collect two pieces of data and create a summary table of the data.
➤Draw a diagram labeling the horizontal and vertical axes.
It is common that the "cause" variable be labeled on the X axis and the "effect" variable be labeled on the Y axis.
➤Plot pairs of data on the scatter diagram.
➤Interpret the scatter diagram for direction and strength.
These Quality control tools are vary useful in Quality Management.