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Tool and die making, the industrial art of manufacturing stamping dies, plastics molds and jigs and fixtures to be used in the mass production of solid objects.
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Metrology and Computer Aided Inspection (MEng 6223) Lecture Measurement, Gauging and Selective Assembly
Standards of Measurement • Human beings have always been innovative and have exploited the natural resources of the earth to manufacture products and devices that satisfy their basic needs and desires. • Thus, quantity with standard? • A standard is an exact quantity that people agree to use for comparison • If different measurements are made using the same standard we can compare them • The international system of unity was developed in 1960 • We now call this the SI system for short
Continuous … • SI is a set of standards that are universally accept and used by Scientists around the world • The SI system is based on multiples of 10 • Prefixes used to show which multiple of 10 is being used In every measurement, a number is followed by a unit. Observe the following examples of measurements: Number and Unit 35 m 0.25 L 225 lb 3.4 hr
Measurement In a measurement • a measuring tool is used to compare some dimension of an object to a standard. • of the thickness of the skin fold at the waist, calipers are used.
Units in the Metric System In the metric and SI systems, one unit is used for each type of measurement: Measurement Metric SI Length meter (m) meter (m) Volume liter (L) cubic meter (m3) Mass gram (g) kilogram (kg) Time second (s) second (s) Temperature Celsius (C) Kelvin (K)
Line and End standard measurements • Line standard Length is expressed as the distance between two lines • End standard Length is expressed as the distance between two flat parallel faces • Wavelength standard Wavelength of monochromatic light is used to measure length
Classification of measuring Instruments According to the functions: • Length measuring instrument/ Linear Measurement • Anglemeasuring instrument/angular Measurement • Instrument for checking deviation from geometrical forms • Instrument for determining the quality of surface finish.
Continue… • Dimensions of the measuring instruments are classified as follows • Low resolution devices (up to 0.25mm) • Medium resolution devices (up to 0.0025mm) • High resolution devices (less than microns) • Low resolution devices • Graduated devices (Steel rule) • Non graduated devices -Calipers • Medium resolution devices • Micrometer, Vernier caliper, Dial gauge • High resolution devices • Gauges such as Slip gauges, Comparators, Optical flats
Linear measuring instruments • Straight edge (Steel rule) • Outside caliper • Inside caliper • Verniercaliper • Outside micrometer • Inside micrometer • Vernierheight gauge • Vernierdepth gauge • Dial gauges Measuring the angle of Taper: Bevel Protractor Tool Makers microscope Sine bar Auto Collimator Sine Centre
Linear Measuring instruments Classification based on the accuracy that can be obtained • Non-precision type instruments : It includes steel rule, caliper, divider; depth gauge, telescopic gauge etc. • Precision type instruments :It includes verniercalliper, vernier height gauge, vernierdepth gauge, micrometer, slip gauges, etc.
Assignment two, 10% • Write the steps to reading a micrometer and venire caliper • Type of error • Sources of Errors • Method of mitigation
Telescopic gauge • Indirect measuring device • Used for measuring internal diameter of holes, slots and grooves, etc • Consists of handle, two telescopic rods and locking screw
Slip gauges • Universally accepted end standard of length in industry. • A rectangular block made up of high grade hardened steel • Independent of any subsequent variation in size or shape • Carefully finished by high grade lapping to a high degree of finish, flatness and accuracy • They can be used to measure tolerances in the range of 0.001 to 0.0005 mm very accurately.
Comparators • A comparator is a precision instrument used to compare the dimension of a given component with a given standard, rather than obtaining an absolute value of measurement.
Comparators Uses • In mass production, where components are to be checked at a very fast rate. • For inspection of working gauges and standards • Attached with some machines, comparators are used as working gauges to maintain required tolerances at all stages of manufacturing. • For grading components depending upon their tolerances
Interchangeability:- When components are mass produced, unless they are interchangeable, the purpose of mass production is not fulfilled. • By interchangeability, we mean that identical components, manufactured by different personnel under different environments, can be assembled and replaced without any further rectification during the assembly stage, without affecting the functioning of the component when assembled.
Comparators Types of Comparators • Mechanical comparators • Optical comparators • Electrical and Electronic comparators • Pneumatic comparators • Fluid displacement comparators
Assignment three, 10% Explain the following methods with help sketches • Reed Comparator • Sigma Comparator • Optical Comparators • Radius gauge • Thread comparator ( Screw thread gauge)
Limit gauges • Gauges are scale-less inspection tool used to check the dimension of parts • They do not determine actual size or dimension of part • Used to check whether the inspected part is within the specified limit or not • If the gauge is an exact copy of mating part of the component to be checked, it is called standard gauges
Continue…. • Widely used for checking the limit of dimensions of part, i.e low limit and high limit. They are known as GO-gauge and NO-GO-gauge • Go gauge’ should pass through or over a part while ‘Not Go gauge 'should not pass through or over the part.
THE TAYLOR PRINCIPLE Taylor’s Principle lays it down: • A GO Gauge will check all the dimensions of the work piece in what is called the maximum metal condition (indicating the presence of the greatest amount of material permitted at a prescribed surface) • That NOT GO Gauges shall check only one dimension of the work piece at a time, for the minimum metal conditions (indicating the presence of the least amount of material permitted at a prescribed surface) size
Assignment four, 5% Explain theoretical background of Taylor principle take into account the limit gauge.
Hole Shaft LIMITS, FITS & TOLERANCE • Terminology:- The terms related to limit system as per Bureau International System (BIS) are as below; • Size:- It is a number expressed in a particular unit in the measurement of length. • Basic Size:- It is the size based on which the dimensional deviations are given. Basic Size • Actual Size:- It is the size of the component by actual measurement after it is manufactured. It should lie between the two limits of size.
Limits of size:- These are the extreme permissible sizes within which the operator is expected to make the component. Maximum limit of size is the greater of the two limit size, whereas the Minimum limit of size is the smaller of the two limit of size.
Upper Deviation Lower Deviation Tolerance • Tolerance:- It is the difference between maximum limit of size and the minimum limit of size. It is always positive and is expressed only as a number without a sign. Hole Max.dia. Min.dia. Shaft • Zero line:- In graphical representation of the above terms, the zero line represents the basic size. This line is also called as the line of zero deviation.
Tolerance... • In mass production, components are manufactured with the tolerance limits, suggested by the designer to facilitate interchangeability. • Various measuring instruments are used to measure the actual dimensions and compared with the standard specified dimensions to decide the acceptability • In mass production, gauges are used to check the compliance of the limits of the part with the permissive tolerance limits, instead of measuring the actual dimensions
Assemble fitting As we observed shaft and hole relation in case • Very Loose • Loose • Tight It is degree of loose or Tightness between two mating parts to perform a definite function • Clearance fit • Transition fit • Interference fit
Hole Shaft • FIT:-It is the relationship that exists between two mating parts, a hole and shaft with respect to their dimensional difference before assembly. Three types of fit are given hereunder; Clearance fit
Continue Systems of Fit: There are two systems by which a fits can be accomplished: • Hole basis system • Shaft basis system
Selective Assembly In selective assembly components produced are classified into groups according to their sizes by automatic gauging. This is done for both Holes and Shafts and then corresponding parts will be matched properly. It reduces chance of defective assembly and also the cost of assembly as parts may be produced in wider tolerances. • Ex: Assembly of piston with cylinder bores.
