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AE 224
Metrology and
Computer Aided Inspection [CAI]I
AE 224 Metrology and Computer Aided Inspection
• Syllabus:• Introduction to Metrology • Fundamentals of dimensional Measurement• Length Standards• Application of light Interference for precision measurements• Fits and tolerances• Concepts and practice of gauging• Comparators and their applications• Linear and angular measurements• Thread and gear inspection• Form, flatness, straightness and alignment measurements• Surface metrology• Co-ordinate metrology• Laser applications in metrology; • Vision inspection• Micro and nano metrology.
AE 224 Metrology and Computer Aided Inspection
Text Books:• Reference Books
Jain R.K., Engineering Metrology, Khanna Publishers.
• Busch., Fundamentals of Dimensional Metrology, Delmar Publishers (1998)
• Shotbolt, C.S. and Galyer. J., Metrology for Engineers,
5th ed., Cassell Publ. (1990).
AE 224 Metrology and Computer Aided Inspection
Reference Books:• Graham T. Smith., Industrial Metrology, Surface and
Roundness.• D. J. Whitehouse., Handbook of Surface Metrology.• Bala Muralikrishnan, Jay Raja., Computational Surface
and Roundness Metrology.
Introduction
• What is Metrology?• Quality in Manufacturing.• Why Precision Length Measurements?• Need for reliable Standards.• Standard of Length.• Shop floor standards.• Traceability.
What is Metrology ?Metro - logy
from Greek 'metron' [measure], and –logy
Meaning Measurement Science
In English, the term Metrology is often used for Linear Measurements
Engineering MetrologyIndustrial MetrologyDimensional Metrology
Manufacturing Metrology
Quality in Manufacturing
Changing Concepts on quality and their significanceInspection ProductProcess Control ProcessQuality Assurance DesignTQM People & SystemsStrategic Quality Management Product Life
Quality covers all activities from the concept to thefinal disposal of the product.
Inspection
• Passive - Inspect - Accept - Reject• Active - Inspect - Infer - Act• Dynamic - Inspect – Act
All three modes of inspection are still practiced in industries
Tolerance and Inspection
• Wide tolerances - Passive Inspection• Medium Tolerances - Active Inspection• Close Tolerances - Dynamic Inspection
• Passive Inspection – Sampling• Active inspection – SQC• Dynamic Inspection – In-process measurement
Metrology- Applications
Why Precision Length Measurements?
Majority of manufacturing measurements deal withdimensions which are in linear units.
Though the dimensions are normally given in mms, thetolerances on these dimensions are given inmicrometers and of late even in nanometers.
All measurements are comparisons.Comparison with reference to a standard
Measurement Accuracies
Measurement accuracies should be better thanthe accuracy expected in the measured entity.As a thumb rule, the measurement accuracyshould be an order better than the measuredvalue.
Systematic and Random Errors
• Systematic errors are caused by assignable factors such as setting errors, temperature, humidity, …
• Random errors are caused by unknown sources, including human errors.
Accuracy and Precision
Measurement Accuracies
1
)(1
2
1
n
xx
n
xx
n
ii
n
ii
Average ------Mean Variation ----- Standard deviation
Precision of a Measurement device
Measurement Accuracies
Take an example of a dimension:10mm + 5 mm (tolerance 10 mm)
For checking this we need an accuracy of 1 mm.That instrument is to be calibrated to 0. 1 mmThat in turn has to be calibrated to 0.01mmThat in turn has to be calibrated to 0.001mmAnd so on …………………. …..Where to stop?
Tolerance Trend
Length Standards
• Basic Standards of Length – Meter ; Yard• Auxiliary Standards• Shop floor reference• Slip Gauges and accessories
• 1889 Physical
Meter Standard
• 1960 Wavelength Wavelength of Krypton- 86
was accepted to define the meter.
1 650 763.73 wavelengths in a vacuum of the radiation of krypton-86 is one Meter
(m)
Meter Standard
• 1983 In terms of time. New definition of Meter in Seconds!
Meter is the length travelled by light in
1 / 299 792 458 s.
Meter Standard
Laser Standard
It was also in 1960 that the first laser was constructed and by the mid 1970s lasers were being used as length standards. This is now realized by iodine-stabilized helium-neon lasers.
Line and End Standards
• In line standard, the distance between two lines marked on it, is the specified length.Original meter was a line standard.
• In End standard, the distance between the ends of a bar or a block is the specified distance.
• Line standards need auxiliary set ups to measure.• End stands need only simple accessories for their
applications.
Shop floor measurements
Auxiliary Standards:-Length BarsBlock or Slip Gauges
A box of Slip gauges
Reference (‘00’)Calibration (' 0 ')Inspection (‘ I’ )Workshop (‘II’)
Shop floor measurements
Slip gauge accessories
Shop floor measurements
Auxiliary Standards:-Length Bars
A box of Length Bars
Airy Points
• Definition: The best points for supporting a bar horizontally so that the end slopes become zero. If the bar is of length L and there are n supports, the supports should be separated by distance L/sqrt(n2-1). For two support this is 0.5773 L .
Support points
Traceability
For international trade there is the need toadhere to the standard scrupulously – especiallywith diminishing tolerances.
This means that all linear measurements doneare to be traceable to the standard of length –the meter.
Traceability
It is practically impossible to directly refer to the meterfor all measurements. So it is done by reference tosecondary or auxiliary standards which are calibratedwith reference to the standard meter.
Like wise all other measuring instruments are to becalibrated with secondary standards, ensuringtraceability to the meter.
ISO 9000 recommends this.
Light Interference for Precision Measurements
• Interference of light.• Optical flat.• Simple set-up for interference.• Measurement of length by comparison.• Slip gauge comparison.• Distance measurement using interference.• “Absolute” Measurement of Length. • Laser Interferometer.
Whitworth’s flat surface generation
Production of Master Surfaces and Squares
Light Interference
Principle of Distance Measurement
Surface and Form Measurements
Slip Gauge Interferometer
Laser Interferometer
Tolerancing
Fundamental Deviations
Specifying Fits
Quality of fits
Types of Fits
Hole and Shaft Basis System
Preferred Fit Families
• For hole tolerances, tolerance zones H7, H8, H9 and H11 are used preferably.
• For shaft tolerances, tolerance zones h6, h7, h9 and h11 are used preferably.
• Preferred Fits • Clearance fits: H11/c11, H9/d9, H8/f7, H7/g6, H7/h6,
C11/h11, D9/h9, F8/h7, G7/h6Transition fits: H7/k6, H7/n6, K7/h6, N7/h6Interference fits: H7/p6, H7/s6, H7/u6, P7/h6, S7/h6, U7/h6
Standard Fits• Loose Running H11/ c11• Free Running H9/ d9• Loose Running H11/ c11• Easy Running - Good quality easy to do-H8/ f8• Sliding H7/ g6• Close Clearance - Spigots and locations H8 f7• Location/Clearance H7/ h6• Location- slight interference H7/ k6• Location/Transition H7/ n6• Location/Interference- Press fit which can be separated H7/ p6• Medium Drive H7/s6• Force H7/u6
Gauges
Plug Gauge
Gauges
Gauges
Adjustable Gap Gauge
Ring Gauge
Taylor’s Rules on Gauge Design
Fundamentals of Linear Measurements
• Abbe Principle• Measuring force and Measurement• Environment• Contact and Non-contact measurement• Measurement and Sensing
Abbe Principle
• The scale of a linear measuring system should be co-linear with the spatial dimension or displacement to be measured or else the measurement must be corrected for the associated Abbé error.
Abbe Error