metrology ppt
DESCRIPTION
syll covered upto 2day lecTRANSCRIPT
CONTENTS
Metrology basics
Standards and comparators
Limits, fits, tolerances and gauges
Angular measurement
METROLOGY BASICS
Definition of metrology
Scientific metrology, Industrial metrology, Legal
metrology
Need of inspection
Definition of metrology
It is a science of measurement
It is divided upon the quantity under consideration
Need of inspection
To ensure that the part conforms to established
standard
To meet interchangeability of manufacture
To maintain customer relations
To find shortcomings in manufacture
Helps to purchase good quality of raw materials
Helps co-ordination of different departments
To take decision on defective parts
Standards and comparators
Types of material standards
Slip gauge and its accessories
Need for Comparators
Working principle of comparators
Types of comparators
Types of Material Standards
A material standard is an ultimate reference for unit
quantities
Types of material standards:
1. Line standards
2. End standards
3. Wavelength standards
Angular measurements
Angle: opening between two intersecting lines
Instruments used:
1. Universal bevel protractor
2. Sine bar
3. Angle gauges
4. Clinometer
5. Angle dekkor
6. Auto colliminator
Screw measurements
ISO grade and fits of thread(SS)
Errors in threads
1. Major diameter
2. Minor diameter
3. Effective diameter
4. Pitch
5. Flank angles
6. Profile at crest and root
Gear measurement and testing
Analytical and functional inspection
Rolling test
Measurement of tooth thickness(constant chord
method)
Gear tooth vernier
Errors in gears(Backlash, run-out, composite)
Analytical inspection
It consists of determining the following teeth elements in which
manufacturing errors may be present
1. Runout(Tester with dial indicator gives the error)
2. Pitch(comparator and direct angular measurement)
3. Profile(optical projection, involute mm, tooth disp. method)
4. Lead (lead checking instrument)
5. Backlash(locking and measuring)(tooth space-tooth thickness )
6. Tooth thickness(constant chord method)
7. Concentricity
8. Alignment
9. Composite errors(rolling test)
Rolling test (Parkinson’s test)
Master gear rotated with test gear
Test gear mounted on varying platform
Dial indicator to give the errors
Electronic recorder to give variation
Measurement of tooth thickness
Constant chord method
1.Constant chord is the chord joining those points on
opposite faces of the tooth which make contact with
mating teeth when the centre line of the tooth lies
on the line of gear centers.
2. The value of CC can be mathematically calculated
and verified by the instrument
3. advantage: it can be applied for all no. of teeth of
same module as the value of constant chord is same
Gear tooth vernier
It has two arms:
1. For measuring tooth thickness
2. For measuring addendum
The measured value compared with calculated
Measurement of surface finish
1. Factors affecting surface roughness
2. Order of geometrical irregularities (Primary and
secondary texture)
3. Lay (with direction)
4. Sampling length
5. Evaluation of surface finish (CLA, Ra, RMS, Rz)
6. Symbol for representing surface finish
7. Various techniques of qualitative analysis
Factors affecting surface roughness
Vibrations
Material of W/P
Type of machining
Rigidity of m/c system
Sharpness and form of cutting tool
Cutting conditions
Type of coolant used
Order of geometrical irregularities
Primary texture
1. Surface roughness of small WL are called primary
texture
2. Caused by direct action of cutting tool
factors(speed, feed, depth of cut, friction)
3. Lr/Hr<50 (microerrors)
Contd.
Secondary texture
1. Surface irregularities of considerable WL of a
periodic character are called secondary texture
2. Lw/hw>50
Lay (with direction)
It is the direction of predominant surface pattern
produced by tool marks or scratches
It is dependent on the method of production used
Evaluation of surface finish
Peak to valley height method
Average surface roughness method
Form factor or bearing curve method
The average roughness method
CLA(centre line average) method
1. It is the average of the values of ordinates(heights)
from the mean line, regardless of the sign of
ordinates.
2. CLA value = (h1+h2+…hn)/n
= (A1+A2+…An)/L
Area values can be easily measured by planimeter
Contd.
RMS value method:
1. It is the square root of the arithmatic mean of the
values of the squares of the ordinates of the
surface measure from mean line.
Ten point height method
In this method , the average difference between the
five highest peaks and five lowest valleys of the
surface texture.
Conventional method for designing
surface finish
1. Roughness value in Ra (μm)
2. Machining value in mm
3. Sampling length in mm
4. Machining or production method
5. Direction of lay
Inspection techniques:
Inspection by comparison
1. Visual inspection
2. Touch inspection
3. Scratch inspection
4. Microscopic inspection
5. Surface photographs
6. Micro-interferometer
7. Wallace surface dynamometer
8. Reflected light intensity
Contd.
Direct instrument:
1. If a finely pointed probe be moved over the surface of a W/P, the vertical movement of the stylus caused due to irregularities in the surface texture can be used to access the surface finish of the W/P.
Methods:
1. Profilometer
2. Taylor hobson talysurf
3. Sigma microtest
4. Rubert indicator