Statistical Quality Control

• Dr. Walter Shewhart - he introduced the concept of “controlling the quality” rather than inspecting it into the product
• Chance or common - inevitable or unavoidable, usually large in number and random in nature
• Assignable - nonrandom, can be identified and eliminated
• Control charts - it is used to monitor quality by the application of statistical methods in all stages of the production
• Descriptive statistics - is the monitoring of quality by the application of statistical methods in all stages of production
• Acceptance sampling inspection - it consists of proper sampling, determining quality variation of the sample, and making inferences to the entire batch under investigation
• Statistical process control - it makes use of control charts, a tool which may influence decisions related to the functions of specification, production or inspection
• Variable Chart - is a chart using actual records of numerical measurement on a full continuous scale such as meter, grams, and liter; examples are the X (mean) and R (range) charts
• Attribute Chart "go or no-go chart" - is a chart, which makes use of discrete data classifying the number of items conforming and the number of items failing to conform to any specified requirements; an example of an attribute chart is the control chart for fraction defective known as P chart; and C chart which shows the number of defects per unit
• Variable Charts - measurements of parts may vary in length, diameter, tensile strength and so on
• Mean Chart - the first chart designed for variable with the purpose that is to portray the fluctuation in the sample means
• Range Chart - shows variation in the ranges of the samples
• Percent Defective Chart "P-chart or “p bar chart” - this chart shows graphically the proportion of the production that is not acceptable
• C Bar Chart - c chart portrays the number of defects per unit, this is to show graphically how many defects appear in a unit of a production