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INTRODUCTION TO METROLOGY MODULE 1 BY Prof. Avinash MECH_INT CLASSES 5 TH SEM MECHANICAL

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INTRODUCTION TO

METROLOGY

MODULE 1

BY Prof. Avinash

MECH_INT CLASSES

5TH SEM MECHANICAL

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

Categories of metrology

Industrial metrology

Scientific metrology

Legal metrology

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

Universal bevel protractor

Sine bar

Angle gauges

Clinometers

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

Pitch Errors

Progressive error

Periodic error

Drunken error

Erratic or irregular errors

Measurement of major diameter

Measurement of Minor Diameter

Measurement of effective Dia.(2

wire method)

Thread gauge micrometer

Principle of floating carriage Dial

micrometer

Contd.

Next lec

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

Errors in gears

Backlash

Runout

Composite

Testing techniques

Measurement of surface finish

Machine tool testing

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

Profilometer

Tomlinson surface meter

Taylor Hobson

M/c tool testing

Next lec…