MQC (Metrology and Quality Control ) • InSem -30 marks • Oral – 25 marks • EndSem- 70 marks
MQC (Metrology and Quality Control )• InSem -30 marks
• Oral – 25 marks
• EndSem- 70 marks
What is Metrology?
A Greek word
Science of precision measurement
For engineer, it is science of measurement of lengths and
angles and all related quantities like width, depth, diameter,
straightness, roundness, etc., with high accuracy.
Who Needs Accurate Measurements?
Pharmaceutical Industry
• Metrology laboratories test weights and volume standards for pharmaceutical companies
• Products include medicines like aspirin, antibiotics, vaccines, insulin, & vitamins
Defense Industry
• Metrology laboratories test standards for many military and defense companies
• These companies make the guidance systems for the Patriot missiles and other things that are
top secret
Space Station, Satellites….
• Metrology laboratories test standards for many companies that provide parts of the space shuttle
• These parts include the metal, heat shield, electronics, fabrics, o-rings, optics, and tires
Retail Measurements
• State metrology laboratories test standards used to test retail scales and meters
• These include gas pumps, produce scales, milk, bread and other packaged items, and price scanning systems
Almost Everybody!
Production Circuit
Research and development
Metrology within research and development
is important to
Avoid defective goods later on
Validate process
Check scientific theories
Construction, adjustment, acceptance test
Within this step metrology checking:
If production machines are located
according to plant layout
If machines components are located
properly
If production moulds and tooling
profile are within tolerance
Single part inspection
A single part- a lot of geometries to be check, it involves:
Shape of the parts
Angularities
Drilling position
Milling outline
Assembly of parts
Metrology helps in assembling parts accurately:
Upto this point everything fits perfectly and
functions smoothly- in theory
However, when assembling parts, inexplicable
gap occurs. Metrology help in avoiding, fingering
out, eliminating these cause
Now, a couple of definitions…
“the science that deals with measurement”
“to determine the dimension, quantity or capacity of
something”
Measure
Metrology
SEVEN BASE UNITS (SI)
Mass Kilogram (kg)
Length Meter (m)
Time Second (s)
Temperature Kelvin (K)
Electric Current Ampere (A)
Amount of Substance Mole (mol)
Luminous Intensity Candela (cd)
Accuracy and Precision
• Accuracy is how close an individual value is to the true or accepted value
• Precision is the consistency of a series of measurements
Gage R&R
• Terms in gage R&R
Gage – a gage is any device that is used to obtain measurement.
Repeatability – is ability of measuring instrument to give the samevalue of reading repetitively over a period of time with the samemeasurement conditions, same instrument and observer, samelocation and same condition of use maintained throughout.
Reproducibility –relates to the closeness of output reading for thesame input when there are changes in the method of measurement,observer, measuring instrument, location, condition of use and time ofmeasurement.
Uncertainty
• Denotes the degree of accuracy with which the measurement has made
• Error = true value – measured value
• Instead of specifying measurement error, it is common practice to denote the range of error.
• This region in which error is estimated to lie is called uncertainty
• Example, 100 ± 1.2
Principle of Measurement
Traceability • Traceability means that a measured result can be related to stated
reference, usually national or international standard through anunbroken chain of comparison, all having stated uncertainties.
• Traceability gives the user confidence that his/her measurementsagree with the national standards within the stated uncertainty.
• It also ensure that the measurements will be equivalent to thosemade using different instruments from different suppliers.
• This is particularly important when importing or exporting goods.
Standards of Measurement
Types of standards
1. Primary standards(reference standard)
2. Secondary standards(calibration standard)
3. Tertiary standards(inspection standard)
4. Working standards(working standard)
Line standard
• Distance measured between two parallel lines or surfaces
• Example – meter tape, vernier
• Distance is measured between the line which matches with zero and the line which matches with the point which is to be measure
Line standard
Meter Yard
Meter
• It is distance between center position of two lines etched on a polished surface of a bar of pure platinum alloy(90%) and iridium alloy (10%).
• 1 meter = 1.09361 yard
Yard
• Yard is bronze bar with squarecross-section.
• The yard is distance between twocentral transverse lines on theplugs when the temperature ofbar is at 62 degree F.
• 1 yard = 0.9144 meter
End standards
• Distance is measured as separation of two parallel surfaces
• Examples – limit gauges, slip gauges
• Accurate and specially used in industries
• Small distance measuring capacity
Wavelength standard
• Sometimes error may occurs due to-
variation in size of gauge
Variation in temperature, pressure, overall environment
• Use of wavelength monochromatic light which isnatural and static unit of length as a workingstandard will reduce errors.
• 1 meter = 1650763.73 X wavelength of radiation
Error
• Error is the difference between a measured value and the “true” value
% error = True value – measured value X 100%
True value
Sources of Error1. Defects in instruments
2. Manual adjustment of instruments
3. Manufacturing error in instruments
4. Environmental effects
5. Human errors
6. Error due to location of the object
7. Measuring force of instrument
8. Error due to object surface finish
Types of Error
1. Alignment Error
2.Environmental Error
• These errors are caused due to surrounding
temperature, pressure, humidity, nuclear radiation,
vibration magnetic field
• To avoid error all metrology laboratories are maintain
at 20 degree Celsius.
3.Contact Error
Improper contact between measuring instrument and work piece
4. Parallax Error
• The position of the observer at thetime of taking reading can createerrors in measurement
5.Random error
These errors are caused due to
• Backlash and friction in the instruments
• Variation in position of setting work piece
• Displacement in joints of instruments
6.Systematic error (controllable error)
These errors includes
• calibration error
• Error due to ambient condition
• Error due to stylus pressure
7.Dirt error
• Presence of dirt in atmosphere may
change the reading by fraction.
• For greater accuracy, electronic
precipitators should be incorporated in
the lab.
Slip gauges• They are rectangular blocks of steel with
cross-section of 30x10 mm
• They can be used as reference standard, transferring dimension, for calibration and for direct measurement.
• They are supplied in set of 112 pieces to 32 pieces.
• Their faces are flat, parallel, has high degree of surface finish and accurately manufactured.
• Slip gauges are attached to each other by wringing process
Wringing
• Wringing is property of measuring faces of gauge block of adhering by sliding or pressing against each other.
Slip gauge set
• Principle – minimum slips
• Eg. 52.375mm
1.005+1.37+50=52.375
Exercise -73.975 mm
Linear measurement
1. Engineering steel rule
2. Calipers
3. Vernier caliper and its type
4. Micrometer and its type
1.Engineering steel rule
• Principle – comparison of unknown length with previously calibrated length
• Construction – strip of hardened steel with line graduations engraved at an interval of faction of standard unit of length.
• Accuracy – 0.5 mm
• Length of scale- 150,300,600,1000 mm
2.Calipers
• Principle- legs of the calipers are set against work piece, the distance between legs is transfer to scale.
Spring Caliper
3. Vernier caliper
• Principle – it uses two scales one fixed and other movable, then the difference these two scales can be utilized, to enhance the accuracy of measurement.
How to take reading?
• Total reading = main scale reading + (no. of division coinciding on vernierscale) X least count
• Least count = 𝑠𝑚𝑎𝑙𝑙𝑒𝑠𝑡 𝑑𝑖𝑣𝑖𝑠𝑖𝑜𝑛 𝑜𝑛 𝑚𝑎𝑖𝑛 𝑠𝑐𝑎𝑙𝑒
𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑖𝑣𝑖𝑠𝑖𝑜𝑛𝑠 𝑜𝑛 𝑣𝑒𝑟𝑛𝑖𝑒𝑟 𝑠𝑐𝑎𝑙𝑒
• Total reading = 12 + 8 x 0.02 = 12.16 mm
Applications of vernier caliper
4.Vernier height gauge• Principle – it works on
same principle of verniercaliper
5.Vernier depth gauge• Principle – it works on same principle as that of
vernier caliper
6.Micrometer
• Principle – it works on the principle of movement of a nut and a screw
How to take reading?
7.Screw thread micrometer
• Principle – similar to simple micrometer
8.Inside micrometer
9.Depth micrometer
• Used for measurement of depth of holes, slots
Angular measurement
1. Sine bars
2. Sine center
3. Angle gauges
4. Auto-collimator
5. Angle dekkor
1.Sine bars
• Construction-
Working of sine bars
h L
Angle measurement for heavy components
Sine center
Advantages
• Accurate and precise
• Easily available
• Cheap
Disadvantage
• Application is limited
• Accurate upto 45 degree
• Difficult to hold in position
2.Angle gauge
• Angle gauges are the wedge shaped block and are used for angle measurement.
• These are 13 pieces, divided into 3 types
The first series angles are 1°,3°,9°,27°,41°
The second series angles are 1’,3’,9’,27’
The third series angles are 3”,6”,18”,30”
The angle gauges can be used for large number of combination by adding or subtraction of these gauges from each other
Addition of angle Subtraction of angle
For example, to measure 43°24’12”_______?
Applications of angle gauges
• Use of angle gauge (greater than 90°)
• Use of angle gauge (less than 90°)
3.Auto-collimator
• This is an optical instrument which is used for measuring small angular deviation.
• Working principle of auto-collimator
Collimating lens
Working of auto-collimator
4.Angle dekkor
Roundness
• Roundness is a condition of surface of revolution such as cylinder,cone or sphere where all points on surface intersected by any planeperpendicular to common axis or passing through a common centerare equidistant from the axis.
• Circularity is only in one plane, whereas roundness even includesthree dimensions such as in balls of ball bearing
The error of circularity at a cross section can be of following type
• Ovality – this errors occurs when there is a difference between the diameters.
• Error = maximum diameter – minimum diameter
• Lobbing –in this case, the diameter measured at any two position remains constant. Say D1 but still it is not exactly equal to the original diameter D.
• Irregularities of specific form- in this case, the variation in the diameter occurs due to irregular surface profile
Roundness measurement by polar graph
Error =𝑒𝑟𝑟𝑜𝑟 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑓𝑟𝑜𝑚 𝑡ℎ𝑒 𝑝𝑜𝑙𝑎𝑟 𝑔𝑟𝑎𝑝ℎ
𝑟
where r is the constant whose value depends on shape and work piece and angle of block
Calibration
• Calibration is the process of checking the accuracy ofmeasurement of an instrument or gauge by comparing it withthe measurement with similar instrument that has been certifiedas a standard of known accuracy.
• Calibrations directly links customer’s measuring instruments tonational or international standards.
• Calibrations means to find out weather the instrument givescorrect reading or not.
Standard procedure for calibration
1. Cleaning of instruments
2. Determination of error
3. Check for tolerable limits
4. Minor changes
5. Allotment of calibration set-up
6. Next calibration date
Example
1.Vernier caliper
Zero error
Flatness of measuring jaw
Parallelism of measuring jaw
Error in reading
Width of spherical inside measuring jaws
Example
2.Micrometer
Zero error
Flatness of measuring surface
Parallelism of measuring surface
Error in reading
Relative movement of moving parts
General appearance
Traceability • Traceability means that a measured result can be related to stated
reference, usually national or international standard through anunbroken chain of comparison, all having stated uncertainties.
• Traceability gives the user confidence that his/her measurementsagree with the national standards within the stated uncertainty.
• It also ensure that the measurements will be equivalent to thosemade using different instruments from different suppliers.
• This is particularly important when importing or exporting goods.