01 Introduction to Metrology

Metrology & Quality Assurance (MEL 311) Text Books Title

Engineering Metrology

Author

 I. C. Gupta

Publisher 

 Dhanpat Rai Publications

Title Author

Engineering Metrology and Measurements  Raghavendra and and Krishnamurthy

Publisher 

Oxford 

Title

Statistical Quality Control

Author

 M. Mahajan

Publisher 

 DhanpatRai

Assessment Course

Sessional – I : 15%, Sessional – II : 15%,

Assessment

Teachers Assessment Assessme nt : 10%, End Exam : 60%

Concept of Metrology  Metrology

concerns measurements.

itself

with

the

study

of

 Measurement

is an act of assigning an accurate and precise value to a physical variable.

 Meaningful

measurements require common and defined measurement standards.

 Measurements

provide a basis to judge the process information, informa tion, quality assurance and process control.

Accuracy and Precision Accuracy:  It is the degree of agreement of the measured dimension with its true magnitude. Precision: It is the degree of agreement of the repeated measurements of a quantity made by using the same method, under similar conditions. Repeatability is random in nature and, by itself, does not assure accuracy, though it is a desirable characteristic. Accuracy and Precision are desirable characteristics for any measuring instrument.

Accuracy and Precision

Precise but not not Accurate

Accurate but not Precise

Precise and Accurate

Not Precise and not Accurate

Accuracy:  It is the degree of agreement of the measured dimension with its true magnitude. Precision:  It is the degree of agreement of the repeated measurements of a quantity made by using the same method, under similar conditions.

Inspection 

Inspection is defined as a procedure in which a part or product characteristic is examined to determine whether it conforms to the design specification.



Basically inspection is carried out to evaluate a specific design or quality attribute of a component or product.



In inspection, the part either passes or fails. Inspection become a very important aspect of quality control.



Inspection is essential to accomplish interchangeability of manufactured components or spare parts.

Some Terminology Calibration Calibration is a comparison of two instruments, one of known uncertainty (standard) and one of unknown uncertainty (your instrument). Sensitivity Sensitivity is the smallest variation in input, which can be detected as an output. Good resolution is a prerequisite in order to detect sensitivity. Stability and Drift Stability is an error that is a function of time, whereas Drift is a function of temperature (of the measurement electronics). Tolerance The maximum allowable deviation on the dimensional or geometrical characteristics from a specified value.

Dimensional Features

Linear Measurements

Dial Gauge or Indicators



Used to check the variation in tolerance  during the inspection process of a machined part, measure the deflection  of a beam or ring under laboratory conditions



Dial indicators typically measure ranges from 0.25mm to 300mm, with graduations of 0.001 mm to 0.01mm

Slip Gauges

Supporting Elements

Angle Plate

Surface Plate

V-Block

Limits, Fits and Tolerances

Comparators 

A comparator compares the unknown dimensions of a part with some standard setting which represents the basic size.



Dimensional variations from the standard setting are amplified and measured.

Inspection for limits is generally done by using Limit Gauges

a

Production Drawing is basis for Inspection

Geometrical Features

Radial and Axial Run-out Run-out is a surface control and It controls the surfaces that are constructed (i) Around a datum axis (Radial run-out). (ii) Perpendicular to a datum axis (Axial run-out).

Car wheel

Measurement of Axial Run-out

Roundness/Cylindricity

Squareness Measurement

Autocollimator for Flatness and Straightness Measurement

Surface Roughness (Ra) Measurement

Screw Thread Measurement

Tool Makers Microscope •

•

•

Tool maker microscope is a precision Optical Microscope which magnifies the object under observation. A high precision micrometric X-Y stage and the Z axis travel is used to measure the dimensions. Measurement on parts of complex form e.g. - profile of external thread, tools, gauges, etc.

Profile Projector •

•

•

Profile projector is an optical instrument utilized for linear measurements. It is a valuable instrument in manufacturing line for the quality control assessment . The projector magnifies the profile of the specimen, and shows this on the built-in projection screen.

Machine Vision Systems

Profile mapping using coordinate measuring machine (CMM)

Most of the geometrical features can be measured using CMM

Next Topic:

Standards of Measurement