101129_Measurement_and_NDT

101129_Measurement_and_NDT - Chapter 10: Measurement and...

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Unformatted text preview: Chapter 10: Measurement and Inspection and Testing DeGarmos Materials and Processes in Manufacturing 10.1 Introduction Measurement Act of measuring or being measured Fundamental activity of testing and inspection Inspection Ensures what is being manufactured will meet specifications Testing Evaluates product quality or performance Manufacturing Principles Products are manufactured to standard sizes and shapes Interchangeable parts became common in the early 1900s Design engineer may have to design or alter specifications to ease manufacturing, assembly, and inspection or lower costs These changes should not sacrifice functionality, product reliability, or performance Attributes vs. Variables Inspection of a product can be done in two main ways Attributes (Gaging) Uses gages Reported as YES/NO, GO/NO GO Variables (Measurements) Uses calibrated instruments Reported in actual dimensions 10.2 Standards of Measurement Fundamental measures Length, time, mass, temperature Candela, ampere All other measurements can be made using a combination of the fundamental measures Linear standards International meter is the standard Inch is based off of the meter standard as .0254m 41,929.399 wavelengths of orange-red light from krypton-86 The US is officially committed to convert to the International System (SI), the English system of feet and inches is still used by many manufacturing plants Metric to English Conversions Table 10-2 lists common metric to English conversions Care should be taken when converting measurements to ensure that standard conversions have been used Standard sizes in the English system may not have a perfectly matching corresponding size in the metric system Length Standards in Industry Gage blocks Provide industry with linear standards of high accuracy Small, rectangular, square, or round in cross section Made with steel or carbide Two flat and parallel surfaces calibrated with light-beam interferometry By combining blocks, any desired dimension can be obtained Figure 10-5 Wrung-together gage blocks in a special holder, used with a dial gage to form an accurate comparator. (Courtesy of DoALL Company.) Gage Blocks Figure 10-3 Standard set of rectangular gage blocks with 0.000050-in. accuracy; three individual blocks are shown. Standard Measuring Temperature Many metal instruments are used for measuring Metals are affected dimensionally by temperature Standard measuring temperature of 68 F (20 C) for precision measuring Gage blocks, gages, and other precision- measuring instruments are calibrated at this temperature Accuracy Versus Precision in Processes Accuracy- ability to hit what is aimed at Precision- repeatability of the process Measuring devices must be both precise and accurate Skill of the operator may also have to be taken into account for measurements Figure 10-6 Accuracy versus precision. Dots in targets Accuracy versus precision....
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101129_Measurement_and_NDT - Chapter 10: Measurement and...

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