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STATISTICAL QUALITY CONTROL

The metric and English measuring systems are the two measuring systems commonly used throughout the world. The metric system is universally used in most scientific applications, but, for manufacturing in the United States, has been limited to a few specialties, mostly items that are related in some way to products manufactured abroad. | CHAPTER 36__ STATISTICAL QUALITY CONTROL Magd E. Zohdi Department of Industrial Engineering and Manufacturing Louisiana State University Baton Rouge Louisiana 36.1 MEASUREMENTS AND QUALITY CONTROL 1175 36.6 CONTROL CHARTS FOR ATTRIBUTES 36.6.1 The p and np Charts 1180 1182 36.2 DIMENSION AND TOLERANCE 1175 36.6.2 The c and u Charts 1183 36.7 ACCEPTANCE SAMPLING 1183 36.3 QUALITY CONTROL 1175 36.7.1 Double Sampling 1184 36.3.1 X R and r Charts 1175 36.7.2 Multiple and Sequential Sampling 1184 36.4 INTERRELATIONSHIP OF TOLERANCES OF 36.8 DEFENSE DEPARTMENT ASSEMBLED PRODUCTS 1179 ACCEPTANCE SAMPLING BY VARIABLES 1184 36.5 OPERATION CHARACTERISTIC CURVE OC 1180 36.1 MEASUREMENTS AND QUALITY CONTROL The metric and English measuring systems are the two measuring systems commonly used throughout the world. The metric system is universally used in most scientific applications but for manufacturing in the United States has been limited to a few specialties mostly items that are related in some way to products manufactured abroad. 36.2 DIMENSION AND TOLERANCE In dimensioning a drawing the numbers placed in the dimension lines are only approximate and do not represent any degree of accuracy unless so stated by the designer. To specify the degree of accuracy it is necessary to add tolerance figures to the dimension. Tolerance is the amount of variation permitted in the part or the total variation allowed in a given dimension. Dimensions given close tolerances mean that the part must fit properly with some other part. Both must be given tolerances in keeping with the allowance desired the manufacturing processes available and the minimum cost of production and assembly that will maximize profit. Generally speaking the cost of a part goes up as the tolerance is decreased. Allowance which is sometimes confused with tolerance has an altogether different meaning. It is the minimum clearance space intended between mating parts and represents the condition of tightest