Metrology NOTE

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Metrology, Engineering


<ul><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p>DMM 2412 </p><p>METROLOGY </p></li><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p> Table o f Contents </p><p> CHAPTER 1 Fundamentals Of Metrology </p><p>1.1 WHAT IS METROLOGY 2.1 NEEDS AND FUNCTIONS OF INSPECTION 3.1 OBJECTIVES OF METROLOGY 4.1 PRINCIPLES OF METROLOGY </p><p> CHAPTER 2 Basic Inspection and Procedures </p><p>2.1 INTRODUCTION 2.2 TESTING AND ITS PROCEDURES 2.3 TYPES OF MEASUREMENTS 2.4 FACTORS IN SELECTING TESTING INSTRUMENT 2.5 CALIBRATION 2.6 CARE OF MEASURING INSTRUMENTS </p><p> CHAPTER 3 Measurement Errors </p><p>3.1 INTRODUCTION 3.2 FACTORS AFFECTING THE ACCURACY OF A MEASURING SYSTEM 3.3 TYPES OF ERRORS 3.4 SOURCES OF MEASUREMENT ERRORS </p><p> CHAPTER 4 Vernier Caliper </p><p>4.1 INTRODUCTION 4.2 PARTS OF A VERNIER CALIPER 4.3 MEASURING ACCURACY 4.4 READING THE SCALE 4.5 DIAL CALIPER 4.6 DIGITAL CALIPER 4.7 DEPTH VERNIER CALIPER 4.8 APPLICATIONS OF VERNIER CALIPER </p><p> CHAPTER 5 Micrometer </p><p>5.1 INTRODUCTION 5.2 EXTERNAL MICROMETER 5.3 DEPTH MICROMETER 5.4 INTERNAL MICROMETER 5.5 SPECIAL TYPES OF MICROMETERS </p><p> CHAPTER 6 Mechanical Dial Indicator </p><p>6.1 INTRODUCTION 6.2 PRINCIPLE OF A DIAL INDICATOR (PLUNGER TYPE) 6.3 PARTS OF A DIAL INDICATOR 6.4 HOW DOES A DIAL INDICATOR WORK 6.5 MEASURING ACCURACY 6.6 READING THE SCALE 6.7 GUIDELINES WHEN USING DIAL INDICATOR 6.8 SOURCES OF ERRORS 6.9 APPLICATIONS OF DIAL INDICATOR </p></li><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p>CHAPTER 7 Gauge Block </p><p>7.1 INTRODUCTION 7.2 TYPES AND GRADES 7.3 STANDARD SET OF GAUGE BLOCKS 7.4 TO DETERMINE THE GAUGE BLOCKS COMBINATION 7.5 CHECKING SURFACE FLATNESS OF GAUGE BLOCKS 7.6 GAUGE BLOCK APPLICATIONS 7.7 MAINTENANCE AND CARE OF GAUGE BLOCKS </p><p> CHAPTER 8 Surface Plate Inspection </p><p>8.1 INTRODUCTION 8.2 WHAT IS A SURFACE PLATE 8.3 ADVANTAGES OF GRANITE SURFACE PLATE 8.4 CARE OF SURFACE PLATE 8.5 SOURCES OF ERRORS 8.6 SURFACE PLATE ACCESSORIES OR HOLDING DEVICES 8.7 PRINCIPLES OF SURFACE PLATE INSPECTION 8.8 EXAMPLES OF HOLDING DEVICES USED IN CONJUNCTION WITH A SURFACE PLATE </p><p> CHAPTER 9 Instruments for Testing Angles </p><p> 9.1 INTRODUCTION 9.2 TESTING ANGLES </p><p>9.3 EXAMPLES OF APPLICATION 9.4 CALCULATION METHOD </p><p> CHAPTER 10 Gauges </p><p>10.1 INTRODUCTION 10.2 ADVANTAGES OF GAUGES 10.3 DISADVANTAGES OF GAUGES 10.4 FACTORS IN SELECTING MATERIALS FOR GAUGES 10.5 MATERIALS FOR GAUGES 10.6 TYPES OF GAUGES </p><p> CHAPTER 11 Profile Projector </p><p>11.1 INTRODUCTION 11.2 APPLICATION 11.3 TEST PROCEDURES 11.4 DIFFERENT STANDARD OVERLAY CHARTS 11.5 TYPES OF MEASUREMENT 11.6 MAINTENANCE OF OPTICAL COMPONENTS </p><p> CHAPTER 12 Surface Roughness Measurement </p><p>12.1 INTRODUCTION 12.2 SURFACE TEXTURE MEASUREMENT 12.3 DEFINITIONS OF SURFACE ROUGHNESS TERMS 12.4 WAVE LENGTH LIMIT C 12.5 BASIC TERMS OF SURFACE TEXTURE 12.6 EFFECTS OF VARIOUS CUT-OFF VALUES 12.7 DEFINITION OF SURFACE PARAMETERS 12.8 ADDITIONS TO THE SURFACE SYMBOL </p></li><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p>12.9 CHOICE OF THE WAVELENGTH LIMIT C 12.10 INSTRUMENTS FOR TESTING ROUGHNESS </p></li><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p> FUNDAMENTALS OF METROLOGY </p><p>CHAPTER 1 </p></li><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p>1.1 WHAT IS METROLOGY Metrology is the science of measurement. However, we have to go one step ahead and must also deal with the correctness of measurement. We have to observe whether the measuring result is given with the sufficient correctness and accuracy for the particular need or not. Thus, in industrial terms metrology is primarily concerned with methods and techniques of measurement based on agreed units and standards. The practice of metrology involves precise measurement, which requires the use of apparatus and equipment to permit the degree of accuracy required to be obtained. In a broader sense, metrology is not limited to length measurement. It is also concerned with the industrial inspection and its various techniques from the raw material to the finished product or even assembled parts. </p><p>1.2 NEEDS AND FUNCTIONS OF INSPECTION </p><p>a. To determine good or bad parts Our five senses are basically instruments, which are used to inspect certain objects based on observation, curiosity or enjoyment. We can use our nose to smell (i.e. to check) whether there is a gas leak. We can use our tongue to taste whether the food is good or bad. In industrial terms, inspection basically is defined as the function of comparing or determining the conformance of a product to specifications or requirements. In other words, the function of inspection is to inspect a product in order to determine whether it is good or bad, and whether it can be accepted or whether it has to be rejected. More specifically, inspection refers to the measurement, visual assessment or testing of a product, process or the act of making a product. </p><p> b. To achieve interchangeability Nowadays many new production techniques have been developed and products are being manufactured in large scale due to low-cost methods of mass production. It is very essential that products must be fit and mate if any product is chosen at random for interchangeability purposes. Thus, to achieve interchangeability of products, inspection has to be performed sufficiently and this can be done either by measuring or gauging. The gauging method is very economical for mass production. </p><p> c. To improve and develop precision measuring instruments Inspection also led to the development of precision measuring instruments and improvements of inspection methods due to demands of high accuracy and precision works or products. Inspection has also created a spirit of competition and led to the production of quality products on a large scale basis by eliminating variations, thus improving processing techniques. </p><p> d. To support the manufacturing department Inspection also supports the manufacturing department by designing and maintaining a system that assesses the quality levels of the work that is done, and the products that are made, according to objectified standards of measurement criteria. </p></li><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p>1.3 OBJECTIVES OF METROLOGY a. To ensure the products designed are within the process and measuring instrument </p><p>capabilities available in the plant. b. To determine the process capabilities and ensure that these are better than the </p><p>relevant parts tolerances. c. To determine the measuring instrument capabilities and ensure that these are </p><p>adequate for their respective measurements. d. To minimize the cost of inspection by effective and efficient use of available </p><p>facilities, and to reduce the cost of rejects and rework through application of Statistical Process Control Techniques. </p><p>e. Standardization of measuring methods: This is achieved by laying down the inspection methods for any product right at the time when the production technology is prepared. </p><p>f. Maintenance of the accuracy of measurement: This is achieved by periodical calibration of all measuring instruments used in the plant. </p><p>1.4 PRINCIPLES OF METROLOGY </p><p>a. Fundamental Units and Standards To determine whether the parts meet the requirements or specifications, we need to perform measurement to collect the data or information. Of course, we need both measuring unit and measuring instrument according to standards before we can start to take any measurement. Units are defined and expressed in standards. Units are the language of measurement and must be constant. The measuring unit of length is Meter. Originally, in 1889 a meter is defined as the distance between two lines on a specific bar which is made of platinum-iridium rod to represent the length of a meter. Thirty of these bars are manufactured. One was kept at the International Bureau of Weights and Measures in Paris as the international standard. The others were sent to laboratories around the world. However, this standard bar has its limitation. It is not stable and constant due to the effect of temperature and environmental factors. Thus, in 1960 a Meter was redefined as 1,650,763.73 wavelengths of a particular orange light emitted by the gas krypton 86. Again, in 1983 the meter was redefined in terms of speed of light. The new definition says: The meter is defined as the length of path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. </p><p> b. Units used in Metrology The units used are laid down in the International Units System (S.l = System International) as shown in the table in the following page. </p><p>Quantity Units SymbolsLength meter m Mass kilogram kg Time second s </p><p>Thermodynamic Temperature Kelvin K Electric Current Ampere A </p><p>Table 1.1 List of Basic SI Quantities, Units and Symbols </p></li><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p>Prefixes Symbol Multiplier Meaning Giga G 1000000000 109 billion Mega M 1000000 106 million kilo k 1000 103 thousand </p><p>Hekta H 100 102 hundred Deka Da 10 101 ten deci d 0.1 10-1 tenth centi c 0.01 10-2 hundredth milli m 0.001 10-3 thousandth micro 0.000001 10-6 millionth </p><p>Table 1.2 List of Prefixes c. Derived Units and Conversions The units derived from the basic unit of meter are kilometer, decimeter, centimeter, millimeter, micrometer, and nanometer. </p><p> 1 km = 1000 m 1 m = 10 dm = 100 cm = 1000 mm 1 dm = 10 cm = 100 mm 1 cm = 10 mm 1 mm = 1000 m </p><p> Convert the following for length into values in mm. 0.05m = 0.05 x 1000 = 50 mm 0.88 dm = 0.88 x 100 = 88 mm 300 = 300 x 0.001 = 0.3 mm </p></li><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p>CHAPTER 2 </p><p> BASIC INSPECTION AND </p><p>PROCEDURES </p></li><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p>Measuring </p><p>VERNIER CALIPER </p><p>2.1 INTRODUCTION In the machine shop work, every piece must be made accurately to size and shape specified by the designer. Accurate workmanship also depends primarily on accurate inspection or measurement and layout work. To ensure the quality of a product has been achieved, the inspections or measurements must be taken to see if the design and manufacturing standards have been achieved. </p><p>2.2 TESTING AND ITS PROCEDURES The main purpose of testing or inspection is to determine whether the products conform to the specification. For example; length, angle, surface quality, shape, and color. Testing can be carried out by two methods: </p><p>a. Measuring b. Gauging </p><p> a. Measuring It is a method of inspection by means of comparing the length or angle with the scale of a measuring instrument. It is done with suitable measuring instruments such as venire caliper, micrometer, dial gauge, etc. The measured value is read off directly from these instruments. Measuring instruments are graduated calibrated instruments, which are used to determine the actual dimensions of the part for comparison with the desired size. These instruments provide actual size information and this can be useful in spotting the needs for adjustments. But generally, it takes more time and is more expensive than the gauge inspection. </p></li><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p>SNAP GAUGE </p><p>Gauging </p><p> b. Gauging It is a method of inspection by means of comparing a part against a gauge such as plug gauge, to determine whether or not the part is within the specified limits. In gauging method, suitable gauges are used to determine if the work piece has a good or bad result without providing the actual dimensions. One of the widely used gauges is the plug gauge. Generally, it consists of 'Go' member and 'No Go' member. Gauges are used for quick verification, but it will not tell you how good or bad a part is. </p><p>Table 2.1 </p><p> 2.3 TYPES OF MEASUREMENT a. Direct Measurement: </p><p>The length of the work piece is compared directly against the line of measuring instrument such as vernier caliper of micrometer. </p><p>Measuring Characteristics Gauging </p><p>more information less </p><p>difficult ease of use easy </p><p>slow time fast </p><p>expensive cost/process cheap </p><p>high skill required worker less skill required </p><p>Depth Vernier CaliperWork piece </p></li><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p>b. Indirect Measurement: The measuring value is obtained by using an intermediary (transfer) measuring device such as caliper, then comparing the measurement obtained against a scale of measuring instrument such as steel ruler. </p><p>c. Comparative measurement: It is comparison between the standard such as gauge blocks and the work piece. The gauge blocks are first set to nominal size of the work piece. Then the measuring value is obtained from the dial gauge which shows the difference between the gauge blocks and the work piece. This method is the best and very accurate measurement can be achieved. </p><p>Measurement is taken by means of caliper. </p><p>Then, it is transferred and compared with a scale of </p><p>measuring instrument.</p><p>Dial Gauge Dial Gauge </p><p>Gauge Blocks Workpiece </p></li><li><p>UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING </p><p>2.4 FACTORS IN SELECTING TESTING INSTRUMENT In general, several factors should be considered when selecting the measuring instrument so that variation in the product can be minimized at lower cost. </p><p> a. The rule of 10 : The measuring instrument should be 10 times or percent more </p><p>precise than the tolerance to be measured. The application of the rule greatly reduces the chances of rejecting good parts or accepting bad parts and performing additional work on them. </p><p>b. Repeat accuracy : How repeatable is the instrument in taking the same reading over and over again on a given standard. </p><p>c. Stability : How well does this instrument retain its calibration over a period of time. As the instrument become more accurate, they often lose stability and become more sensitive to small changes in temperature and humidity. </p><p>d. Magnification : The amplification of the output portion of the instrument over the actual input dimension. The accurate the instrument, the greatest must be its magnification factor, so that the required measurement can be read out clearly compare with the desire standard. </p><p>e. Resolution : This is sometimes called sensitivity and refers to the smallest unit of scale or dimensional input that the instrument can detect. The greater the resolution of the instrument, the smaller will be the things it can resolve and the greater will be the magnification required to expand these measurements up to the point where they can be observed the naked eye. </p><p>f. Inspection cost : This is included cost of instruments used, cost of maintaining and installing the instruments. Always select the measuring instruments and methods of inspection at minimum cost. </p><p>2.5 CALIBRATION A measuring instrument may lose its accuracy (or precision) during use or after a period of time. To maintain its accuracy, it requires a continuing system of calibration control, and this can only be carried out by trained staff in a calibration...</p></li></ul>