PM0010 : Describe the following quality control tools: a. Ishikawa diagram b. Flow chart c. Pareto chart d. Scatter diagram
Posted February 27, 2012on:
PM0010 : Describe the following quality control tools:
a. Ishikawa diagram
b. Flow chart
c. Pareto chart
d. Scatter diagram
- Ishikawa Diagram – also known as the Fishbone Diagram or the Cause-and-Effect Diagram, is a tool used for systematically identifying and presenting all the possible causes of a particular problem in graphical format. The possible causes are presented at various levels of detail in connected branches, with the level of detail increasing as the branch goes outward, i.e., an outer branch is a cause of the inner branch it is attached to. Thus, the outermost branches usually indicate the root causes of the problem. The Ishikawa Diagram resembles a fishbone (hence the alternative name “Fishbone Diagram”) – it has a box (the ‘fish head’) that contains the statement of the problem at one end of the diagram. From this box originates the main branch (the ‘fish spine’) of the diagram. Sticking out of this main branch are major branches that categorize the causes according to their nature. In semiconductor manufacturing, 4 major branches are often used by beginners, referred to as the ‘4 M’s’, corresponding to ‘Man’, ‘Machine’, ‘Materials’, and ‘Methods’. Sometimes 5 branches are used (‘5 M’s’), with the fifth branch standing for ‘Measurement’, or even ‘M-ironmen.’ These ‘M’s’ or problem cause categories are used to classify each cause identified for easier analysis of data. Of course, one is not constrained to use these categories in fishbone diagram. Experienced users of the diagram add more branches and/or use different categories, depending on what would be more effective in dealing with the problem.
- Flow chart: – A typical definition of “Flow Chart” usually reads something like …A flow chart is a graphical or symbolic representation of a process. Each step anthem process is represented by a different symbol and contains a short description of the process step. The flow chart symbols are linked together with arrows showing the process flow direction.
- Pareto Chart: – A Pareto Chart is “a series of bars whose heights reflect the frequency or impact of problems. The bars are arranged in descending order of height from left to right. This means the categories represented by the tall bars on the left are relatively more significant than those on the right” .The chart gets its name from the Pareto Principle, which postulates that 80 percent of the trouble comes from 20 percent of the problems.
- Scatter diagram: – A scatter diagram is a tool for analyzing relationships between two variables. One variable is plotted on the horizontal axis and the other is plotted on the vertical axis. The pattern of their intersecting points can graphically show relationship patterns. Most often scatter diagram is used to prove or disprove cause-and-effect relationships. While the diagram shows relationships, it does not by itself prove that one variable causes the other. In addition to showing possible because and-effect relationships, a scatter diagram can show that two variables are from common cause that is unknown or that one variable can be used as a surrogate for the other.