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11:50Am and Saturday 13:00Am - 14:50Pm MENG 436 Class FA Metrology & Quality Control Fall 1433H (2012G) Saturday, Monday & Wednesday 11:00am - 11:50am and Saturday 13:00am - 14:50pm MENG 436 Class FA Dr. Walid A. Aissa Associate Professor, Mech. Engg. Dept. Faculty of Engineering at Rabigh, KAU, KSA Chapter #2 September XX, 2012 Announcements: Dr. Walid’s e-mail and Office Hours [email protected] Office hours for Metrology & Quality Control will be every Sunday and Tuesday from 11:00 – 13:00 am in Dr. Walid’s office (Room 5-109 ). Text book: 1-Metrology for Engineers, J.F.W. Galyer & C. R. Shotbolt, 4th Edition, Cassell Ltd., London, ISBN-0- 304 30612 6, 1980. 2-Essentials of Quality With Cases and Experimental Exercises, Victor E. Sower, John Wiley & Sons Inc., London, ISBN-978-0-470-50959-3, 2011. Chapter 2 DIMENSIONAL METROLOGY Objectives of CH2: To • Recognize concepts of -Dimensional Metrology, - Dimensions Measurement Using Steel Ruler, Vernier Caliper and Micrometer. Chapter 2 2. Dimensional Metrology 2.1. Definition: • Dimensional metrology is that branch of Metrology which deals with measurement of “dimensions“ of a part or workpiece (lengths, angles, etc.) • Dimensional measurements at the required level of accuracy are the essential link between the designers’ intent and a delivered product. Although the huge technological advance in the field of measurements, which enabled the use of precise , complicated and electronic instruments for measurement of dimensions, however simple mechanical devices still considered basic tools for measurement of dimensions in workshops and labs. The most important simple mechanical devices are: 1) Steel ruler 2) Vernier Caliper 3) Micrometer 2.2. Dimensions Measurement Using Steel Ruler: Steel ruler is the most common tool for measurement of dimensions in workshop. Usually, it is made of Steel Which is not affected by variations of temperature, humidity and vibrations in workshop. Steel ruler often has two scales; one (in mm) on one side and one (in inch) on the other side . Conversion rule between the two systems of units is: 1 inch = 25.4 mm The accuracy of some steel rulers is 1 mm. The accuracy of other steel rulers is 0.5 mm. Steel rulers; graded based on British units, are graded in parts of inch: 1/128, 1/64, 1/32, 1/16, 1/8, ¼, ½, 5/8, ¾, 7/8. 2.2.1. Types of Steel Rulers: Steel rulers used in workshop have different lengths; 6 in, 12 in and 18 in. -Steel rulers may have special end to be fixed on one end of workpiece to increase the accuracy of measurement. -Narrow Steel rulers used for measurement of depth of holes. -Small steel rulers with holder for measurement of small dimensions. 2.2.2. Utilizing steel rulers for dimensions measurement: . EXAMPLE 2–1: A =?, B = ?, C = ?, D = ?. A B A = 12 mm. B = 22 mm. C = 31.5 mm. D = 40.5 mm. Examples of dimensions measurement on steel ruler 2.3. Dimensions Measurement Using Vernier Calipers: -During cutting operations of workpiece, operator verifies that the dimensions of workpiece coincides with those specified in process sheets in terms of shape, dimensions and surface finish . -When required quality of workpeice exceeds the accuracy of steel ruler , Vernier Calipers or micrometers should be used for dimensions measurement. -In addition , Vernier Calipers and micrometers should be used for mounting (or maintenance) of machines and cutting tools. -The importance of Vernier Calipers in workshops and machining centers is due to both high capabilities of dimensions measurement and ease of operation. 2.3.1. Uses of Vernier Calipers: a) External Measurements : b) Internal Measurements : c) Depth Measurements : 2.3.2. Parts of Vernier Caliper: -Vernier Caliper consists of two main parts: a) Fixed part : consists of fixed Jaw connected to main scale (usually main scale is graded in “mm” from one side and in “inch” in the other side). Integer numbers are read on main scale. b) Movable part : It slides relative to fixed part. It consists of movable Jaw and vernier scale . Vernier scale is graded in “fraction of mm” representing the accuracy of the instrument. c) Stem for depth measurement. Vernier scale enables the reading of fractions on main scale with high accuracy. This accuracy is usually in 0.1 mm (= 1/10 mm) or 0.05 mm (= 1/20 mm) or 0.02 mm (= 1/50 mm) . Measurement is done by putting the part to be measured between the movable jaw and fixed jaw without pressing by force. 2.3.3. Method of Dimension Measurement Using Vernier Caliper: Measurement of dimension using Vernier Caliper is done on two basic steps: a) Look at Vernier scale; and precisely, at zero position, read the number left to it on the main scale in integer “mm”; “A”. Main scale ruler Vernier scale Do not read from edge of Vernier scale Measurement reading at best Reading of main scale on left coincidence of vernier scale of vernier scale zero zero and main scale. b) Look at Vernier scale; and precisely, at zero position, read the number left to it on the main scale in integer “mm”. Multiply this number by “Accuracy of Vernier”. The resulting number is called: Vernier reading; “B”. c) The sum of “A” and “B” is “Vernier Caliper reading of the measured dimension”. d) “Accuracy of Vernier ” is obtained from specification list of the instrument. Usually, it is registered on the “Vernier Caliper”. e) If “for any reason”, You could not obtain the “Accuracy of Vernier” from instrument specification list of the instrument or You could not read it on the “Vernier Caliper”; You can simply specify it as follows; Keeping in mind that the “Total Vernier scale = 1 mm”, “Number of divisions of Vernier scale = N”. Hence, “Accuracy of Vernier = 1/N ”. e.g., if “ N =10”. Hence, “Accuracy of Vernier = 1/10 = 0.1 mm” , if “ N = 20”. Hence, “Accuracy of Vernier = 1/20 = 0.05 mm”& if “N = 50”. Hence, “Accuracy of Vernier = 1/50 = 0.02 mm”. EXAMPLE 2–2: What is the Caliper reading? Solution: A = 3.6 cm = 36 mm. N = 20, Accuracy = 1/N = 1/20 = 0.05 mm. B = 13 × 0.05 mm = 0.65 mm . Hence, Vernier Caliper reading of the measured dimension = 36 mm + 0.65 mm = 36.65 mm= 3.665 cm. EXAMPLE 2–3: What is the Caliper reading? Solution: A = 2.4 cm = 24 mm. N = 50, Accuracy = 1/N = 1/50 = 0.02 mm. B = 31 × 0.02 mm = 0.62 mm . Hence, Vernier Caliper reading of the measured dimension = 24 mm + 0.62 mm = 24.62 mm= 2.462 cm. 2.3.4. Types of Calipers: a) Vernier Caliper: Vernier Caliper used for measurement of external diameter of a cylinder b) Digital Caliper: Digital Caliper used for measurement of external diameter of cylinder; Reading is 36.34 mm. c) Dial Caliper: Dial Caliper used for measurement of external dimension of workpiece. d) Depth Caliper: used for measurement of depth of longitudinal grooves and length of holes and grooves. There are three types of depth calipers; namely: 1- Vernier Caliper for depth measurement: Vernier Caliper for depth measurement. 2- Electronic Caliper for depth measurement: Electronic Caliper for depth measurement. 3- Dial Caliper for depth measurement: Dial Caliper for depth measurement. e) Height Caliper: This caliper is used for measurement of workpiece height and for making marks on it. Height Caliper 2.4. Dimensions Measurement Using Micromters: Micrometer is one of the most precise dimension measuring instruments in the workshops and labs. Its accuracy might reach 0.01 mm. In some instruments, it might reach 0.001 mm. Micrometers are characterized by simplicity and ease of operation. Knowledge of correct method of use of micrometer is essential for any technician or engineer supervising the machining or inspection of workpieces. 2.4.1. Parts of Micrometer: External micrometer contains of two main parts: a) Fixed part: consists of frame ; U shape, for holding remaining parts ;fixed and movable. The frame holds the anvil and spindle (measuring rod), which are used to fix the workpiece to be measured. The frame also holds the sleeve with main scale. The sleeve is graded in mm upward and in 0.5 mm downward. b) Movable part: The main movable part is the sleeve ; which when turned using Ratchet Knob, the spindle (measuring rod) advances to hold the part to be measured. Usually, the perimeter of the sleeve is divided into 50 divisions. When the sleeve is turned one complete turn, the measuring rod advances by 0.5 mm. Hence, it could be concluded that the accuracy of the device is 0.5 mm/50 = 0.01 mm. 2.4.2. Correct Method of Reading of Micrometer Measurement: Micrometer is very sensitive. So, it is used for accurate measurement . Specifying Micrometer reading goes through the following steps: 1) Main Micrometer reading: -Look at the edge of Sleeve with main scale. Read the value marked on cylindrical main scale. Register it; call it A. -Look whether there is 0.5 grade (or not) at the edge of cylindrical main scale after the value of A. In the case of existing of this grade, add B = 0.5 mm to the measure. In the case of non existence of this grade, add B = 0.0 mm to the measure. 2) Reading of the measure on sleeve: -Define the coincidence of sleeve scale and main line on cylindrical main scale. Multiply, the value registered on sleeve by the value of the accuracy of the device. Call the result of multiplication; C. 3) Specifying Micrometer Reading of Measured Dimension: -Hence, Micrometer Reading of Measured Dimension = A + B + C. EXAMPLE 2–4: What is the Micrometer reading? Solution: A = 7.0 mm, B = 0.0 mm, C = 38 ×××0×000....01010101mm=mm= 0.38 mm, Hence, Micrometer Reading of Measured Dimension = A + B + C = 7.0 mm+ 0.0 mm+ 0.38 mm = 7.38 mm EXAMPLE 2–5: What is the Micrometer reading? Solution: A = 7.0 mm, B = 0.5 mm, C = 22 ×××000...010101 mm= 0.22 mm, Hence, Micrometer Reading of Measured Dimension = A + B + C = 7.0 mm+ 0.5 mm+ 0.22 mm = 7.72 mm 2.4.3.
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