lecture4metrology

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PowerpointPowerpoint lectures MECH 213, 2007 edition.lectures MECH 213, 2007 edition.

The contents of this lecture are the sole copyright of J. Jeswiet,Professor of Mechanical Engineering.

Powerpoint format lecture © J. Jeswiet 2007

Unlicensed use of the contents of this lecture outside MECH 213 Unlicensed use of the contents of this lecture outside MECH 213 is illegal is illegal ..

Inquiries should be addressed to: J. Jeswiet, Mechanical Engineering, McLaughlin Hall, Queen’sUniversity, Kingston, ON, Canada K7L 3N6

Fax: [email protected]

The fine printThe fine print

Lecture 4

Queen’s University, Mechanical Engineering

© J. Jeswiet

G G ’ ’ day day mate.mate.

Topic : Met ro logy; measurementsTopic : Met ro logy; measurement s

MANUFACTURING ENGINEERING MANUFACTURING ENGINEERING

MECH 213

pp 1085- Kalpakjian & Schmidt 5th ed; see p 1101 for dimensioning & tolerancing

This lecture is related directly to laboratory 201This lecture is related directly to laboratory 201 -- metrologymetrology



MachineryMachinery’’s Handbooks Handbook

Geometr ic To lerancesGeometr ic To lerances

• Shape Deviat i ons

• cylindricity• circularity• flatness• concentricity• parallelism• perpendicularity• symmetry• etc...

See p 1106 5See p 1106 5thth

eded

Geometric tolerancing is amethod of constraining thedeviation in shape to what isfunctionally allowable for a part.



METROLOGYMETROLOGY

Defin i t ion: Science of physical measurement,

applied to variables such as dimension , surface finish,

and mechanical and electrical properties.

• The centre of the curve is the mean ( ),

and it’s proximity to the true value is accuracy.

x

1−=∑n

x

x

accuracy

precision

• Measurements requireMeasurements require precisionprecision andand accuracyaccuracy.

• A group of measurements when plotted will usuallyfollow a normal distribution or bell curve.

• The repeatability of thismean value is the precision.

StandardStandard

Devia t ion:Devia t ion:

( )

1

2

−

−

=

∑n

x x

σ

Standard deviation (σ) is common measure ofprecision.

± σ, covers 68% of measurements

± 2σ covers 95% of measurements

± 3σ covers 99.73% of measurements

The Industry standard once was,27 in 10,000 parts can be defective;

this is not acceptable anymore.this is not acceptable anymore.

Sigma 6 is now claimed by many industries

- this translates to 2 defects per billion parts made.



Measurement Ins t rumentsMeasurement Ins t ruments

Attributes of Measuring InstrumentsAttributes of Measuring Instruments•• SensitivitySensitivity or ResolutionResolution, must be fine*.

Rough rule of thumb: instrument sensitivity must be 10 times theprecision of the measurement.

• Linearity

•• RepeatabilityRepeatability: the instrument must be capable of repeating readingsto the same accuracy to which it can be read.

•• StabilityStability, is the resistance to drift after calibration.• Speed of Response• Feasibility of Automation

* Fine: capable of delicate perception; perceptible only with difficulty

GaugesGauges•• Gauge BlocksGauge Blocks: blocks are manufactured to standard lengths

and tolerances, for use in calibration.

– Available in several grades: 3 (production) +0.15, to .05 μm; 2

(inspection) +0.10, to 0.05 μm; 1 (laboratory) +0.05, to 0.05 μm; 0.5

(reference) +0.03, to 0.03 μm

•• Angle BlocksAngle Blocks: same principal as above except for angles

•• Plug and Ring GaugesPlug and Ring Gauges: for measurement of diameters,

usually of the go, no go type.



Graduated Measur ing Devic esGraduated Measur ing Devices

• Line-Graduated Rules and Tapes• Vernier Calipers• Diffraction Gratings: by counting interference fringes

a sensitivity of 5 μm or 0.0002 in can be achieved• Linear Digital Transducers: photoelectric, magnetic,

pulses are measured, and provide resolution of 4 μm• Numerical Encoding Discs• Solid-State Photodetector diodes and CCharge-CCoupled

DDevices provide resolution of 3 μm• Toolmaker’s Microscopes equipped with micrometer

driven cross slide stages.

Vernier calipers

micrometer

Standard measurement devices found in any manufacturing facility:Standard measurement devices found in any manufacturing facility:

See p 1088See p 1088



The sine barThe sine bar



Measuring “straightness”Measuring “straightness”

some precision measurements must be made.

• either an intermediate stage,

• or at the end of the machining process

• or for reverse engineering

A CMMCMM, coordinate measurement machine is oftenused to do this.

Point: At some stage of manufacturing,



Measuring the accuracy is a time consumingoperation.

Increased accuracy, at high rates,can now be achieved with CMM’s

CMM’s: coordinate measurement machines

MME CMMRenishaw probe

CMM systems comein many varieties

Probes can be very long

Probes can measure holeroundness & location



Measurement of a thrustercone for the Arianne rocket

Measurement ofroundness of a ring

CMM’s are often used tomeasure large structures

Applying some of the stuff we have seen to information given onApplying some of the stuff we have seen to information given on drawings:drawings:

Recall these symbolsRecall these symbols

and what do we do with them?and what do we do with them?

See p 1106See p 1106



Geometric callGeometric call

out notationout notation

formatformat



Thank you for your attentionThank you for your attention



Probe tips come in different

shapes and sizes



t e l e m e

t r y

Probes can now be mounted in millingmachines with telemetry systems.

G r i n d i n g

C N C l at he

Measuring a

part on a latheafter machining



CMM probes can be used to measurecutting tool position & configuration.

Cutting insert

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