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Chapter 2: Introduction to Metrology & Instrumentation

What we will learn?

• CO1

Determine manufacturing processes and technology for various manufacturing products. [PO1,LO1, SS1]{C4}.

• CO2

Evaluate quality of manufacturing products using appropriate techniques and methods. [PO2,LO3,SS1]{C4}.

• CO3

Select suitable manufacturing processes and technologies for particular products.[PO4,LO3,SS1]{C4}.

• CO4

Share knowledge and observation on manufacturing processes and technologies through group presentation in a professional manner. [PO9, LO4, SS2]{A3}.

Metrology

Science of Measurement Why we need to have Metrology?

Why is it so important?

Mars Climate Orbiter (MCO) was launched on 11 December 1998 on a mission to orbit Mars as the first interplanetary weather satellite and to provide a communications relay

for another spacecraft, the Mars Polar Lander. MCO was lost on 23 September 1999 when it failed to enter an orbit around Mars, instead crashing into the planet, destroying the

$125 million craft, part of a $328 million mission.

SI Units

Materials application in Metrology

2.2 Linear Measurement (Direct)

Calipers

2.2 Linear Measurement (Direct)

Micrometer

2.2 Linear Measurement (Indirect)

Dial Gauges/ Indicator

• Instrument used for measuring comparative lengths

• Amplify and measure variations or deviations in the distance between two or more surfaces

• Three uses of dial indicators: a. Roundness

b. Depth

c. Multiple-dimension

Refer S. Kalpakjian page 1010

2.2 Linear Measurement (Indirect)

Dial Gauges/ Indicator

Question 1:

Question 2:

• What type of application?

2.3 Angular Measurement

Bevel Protactor

Sine Bar

Surface Plates

Question 3:

2.3 Comparative Length Measurement

Figure 35.4 Three uses of dial indicators: (a) roundess, (b) depth, and (c) multiple-dimension gaging of a part.

2.3 Measuring Geometric Features

2.3.1 Straightness

Figure 35.6 Measuring straightness manually with (a) a knife-edge rule and

(b) a dial indicator. Source: F. T. Farago.

2.3 Measuring Geometric Features

2.3.1 Straightness

2.3 Measuring Geometric Features

2.3.2 Measuring Roundness

Figure 35.7 (a) Schematic illustration of out-of-roundness (exaggerated). Measuring roundness using (b) a V-block and dial indicator, (c) a round part supported on centers and rotated, and (d) circular tracing. Source: After F. T. Farago.

2.4 Optical Contour Projector

2.4.1 Contour Projector

Profile Projector

• An optical instrument that

can be used for measuring.

• The projector magnifies the

profile of the specimen, and

displays this on the built-in

projection screen.

2.5 Gages

2.5.1 Gage Block

2.5.2 Fixed gages

2.5 Gages

2.5.3 Air gage

Question 4:

• Assume that a steel rule expands by 0.07% due to an increase of environmental temperature. What will be the indicated diameter of a shaft with a diameter 50mm at room temperature.

Question 5:

• Same problem as Question 4, but what happen if the part is made from thermoplastic?

2.6 Modern Measuring Instrument

Figure 35.15 (a) Schematic illustration of a coordinate-measuring machine. (b) A touch signal probe. (c) Examples of laser probes. (d) A coordinate-measuring machine with a complex part being measured. Source: (b) through (d) Courtesy of Mitutoyo Corp.

(b) (c) (d)

Coordinate-Measuring Machine for Car Bodies

Figure 35.16 A large coordinate-measuring machine with two heads measuring various dimensions on a car body. Source: Courtesy of Mitutoyo Corp.

2.6 Modern Measuring Instrument

2.7 General Characteristics

Accuracy: The degree of agreement of the measured dimension with its true magnitude Amplification: Also called magnification. The ratio of instrument output to the input dimension. Calibration: The adjustment or setting of an instrument. Drift: Stability. The instrument capability to maintain its calibration over time. Linearity: The accuracy of reading over its full work time. Precision: Degree to which an instrument gives repeated measurement of the same standard. Resolution: Smallest dimension that can be read on an instrument. Rule of 10: An instrument or gage should be 10 times more accurate than the dimensional tolerances of the part being measured.

2.8 Tolerance, Limits and Fits

When parts are assembled together, engineers

have to decide how they will fit together

How they will fit together?

– Clearance fit

– Transition fit

– Interference fit

Standards BS4500 ANSI B4.1

2.8 Tolerance, Limits and Fits

Tolerancing • Definition: “Allowance for a specific variation in the size and geometry of part.” • Why is it needed: No one or thing is perfect ! • Hence, engineers have come up with a way to make things close to perfect by specifying Tolerances ! – Since variation from the drawing is inevitable the acceptable degree of variation must be specified. – Large variation may affect the functionality of the part – Small variation will effect the cost of the part • requires precise manufacturing. • requires inspection and the rejection of parts.

Cost generally increases with smaller tolerance – Small tolerances cause an exponential increase in cost – Therefore your duty as an engineer have to consider : Do you need Φ1.0001in or is 1.01in good enough? • Parts with small tolerances often require special methods of manufacturing. • Parts with small tolerances often require greater inspection and call for the rejection of parts of a Greater Quality Inspection of a Greater cost. • Do not specify a smaller tolerance than is necessary!

2.8 Tolerance, Limits and Fits

2.8 Tolerance, Limits and Fits

• Tolerance is the difference between the maximum limit of size and the minimum limit of size.

• Fit expresses the relationship between a mating parts with respect to the amount of clearance or interference which exists when they are assembled together.

Standards are needed ... to make it possible to manufacture parts at different times and in different places that still assemble properly. establish dimensional limits for parts that are to be interchangeable. Standard agencies The two most common standards agencies are; American National Standards Institute (ANSI) International Standards Organization (ISO)

2.8 Tolerance, Limits and Fits

Question 6:

When tolerance is used?

2.8 Tolerance, Limits and Fits

2.8 Tolerance, Limits and Fits

Allowance and Clearance

ALLOWANCE • Allowance is defined as an intentional difference between the maximum material limits of mating parts. Allowance is the minimum clearance (positive allowance), or maximum interference (negative allowance) between mating parts. The calculation formula for allowance is: ALLOWANCE = MMC HOLE – MMC SHAFT • CLEARANCE • Clearance is defined as the loosest fit or maximum intended difference between mating parts. • The calculation formula for clearance is: CLEARANCE = LMC HOLE – LMC SHAFT

2.8 Tolerance, Limits and Fits

Tolerance Control

Figure 35.17 Basic size, deviation, and tolerance on a shaft, according to the ISO system.

2.8 Tolerance, Limits and Fits

Geometric Dimensioning & Tolerance

• Why have coordinate measuring machines become important instruments?

• What is meant by comparative length measurement?

• Explain the difference between accuracy and precision?

References

1. Mikell P. Groover, Principles of Modern Manufacturing. 5th edition, John Wiley & Sons Singapore Pte. Ltd. 2013. 2. Kalpakjian Schmid, Manufacturing Engineering and Technology. 7th edition, Pearson Education South Asia Pte. Ltd. 2014.

Class Information

Muhd Faiz Bin Mat @ Muhammad

03-5543 2843 / 019-7902186

T1-A14-10C muhdfaiz@hotmail.fr