practice 1: metrology · 2021. 1. 4. · laboratorio de procesos de fabricación 1 school of...

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Laboratorio de Procesos de Fabricación 1

School of Engineering

Department of Mechanic Engineering

Laboratory of Fabrication Process

Practice 1: Metrology

Theoretical Framework1

Magnitude (measurable) Attribute of a phenomenon, body or substance, which it is susceptible of being

distinguished qualitatively and determined quantitatively.

NOTE: 1) The word “magnitude” may refer to a magnitude in general way or in a

particular way. EXAMPLE:

a) Magnitude in general way: length, time, mass, temperature, electric resistance,

concentration in a substance;

b) Magnitude in particular way: length of a determined stick, electric resistance in

a determined tread, concentration of ethanol in a solution of wine.

2) The magnitudes that can be classified each other in order, are called magnitudes of

the same nature.

3) Magnitudes of the same nature are in the next groups: work, heat, energy, thickness,

circumference, and wavelength.

4) Symbols of the magnitudes are defined in ISO 31 standard.

Basic Magnitude Any of the magnitudes which, in a magnitude system, are accepted by agreement as functionally independent from one another EXAMPLE: Magnitude of length, mass and time are generally used as basic magnitudes in the mechanics area.

NOTE: the basic magnitudes from the System International of units (SI) are in the table of the note 1.12.

1 Source: Centro Español de Metrología (CEM) Alfar, 2, 28760 - Tres Cantos – Madrid Telephone:

+34 91 807 47 00 http://www.cem.es/cem/es_ES/metrologia/metrologia.jsp?op=glosario

http://www.cem.es/cem/es_ES/metrologia/metrologia.jsp?op=glosario

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Dimension of a Magnitude Expression which represents one magnitude in a magnitude system as the product of the power factor, which represent the basic magnitude in that system. EXAMPLES:

a) If we have a system with basic units of length, mass and time, represented as L, M,

T each one, the force dimension is LMT-2

b) In this same system of magnitudes, ML-3 is the dimension of mass concentration, and the mass density

NOTE: 1) The factor representing a basic magnitude is called the dimension from that basic

magnitude.

2) For the dimension’s algebra peculiarity review ISO 31-0.

Unit (measure) A particular, defined and accepted by agreement magnitude, which is compared with other magnitudes from the same nature, so they can be expressed quantitatively taking this magnitude into account. NOTE:

1) Units of measurement have their names and symbols assigned by agreement.

2) Units of magnitudes with same dimension can have the same name and symbol, even if they are not from the same nature.

International System of Units, SI Unit System adopted and recommended for the General Conference of Weight and Measure (CGPM). NOTE:

The SI nowadays is based on seven basic units:

Magnitude Name Symbol Magnitude Name Symbol

Length Meter M Thermodynamic Temperature

Kelvin K

Mass Kilogram Kg Quantity of substance

Mol mol

Time Second S Luminous Intensity

Candle cd

Electric current Ampere A

Measure Set of operations which seeks to determine the value of a magnitude.

NOTE: The operation development can be automatic.

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Metrology

Science of measure or dimension.

NOTE: Metrology includes every aspect, theoretical and practical, which refers to the

measurements, whatever are their nature and uncertainty, and in whatever scientific and

technological fields they take place.

Measurement Uncertainty

Parameter associated with the final result, which characterizes the dispersion of values

that may be attributed to the measure. 2

NOTE:

1) The parameter can be, for example, a standard deviation or semi amplitude from it with

a determined trust level.

2) The measurement uncertainty includes some components that can be evaluated from

the statistical distribution of some measures, which can be characterized with the

experimental standard deviation. The other components, which also can be

characterized by standard deviation, are evaluated with the prediction based on

experience or any other information.

3) We understand that the result from the measure is the best estimation from the

measure value and with the uncertainty components, even the ones that come from

systematic effects, like corrections and patterns of reference, add in the dispersion of

the standard deviation.

Tools / Equipment of measure

Gadget, which purpose is to take measurements, it can be used alone or with some other

tools.

Transducer of measure

Device that receive a signal and show a measure according with the law used in that moment.

EXAMPLE:

a) thermocouple

b) current transformer

c) strain gauge

d) pH electrode

2 This definition comes from the Guía para la Expresión de la Incertidumbre de Medida where you can find

more detail information (watch 2.2.4 and the annex D [10]).

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Visual display measing instrument

Measuring instrument, which shows a value.

EXAMPLE:

a) Voltmeter with analog indication. b) Digital frequency meter.

Registrer measuring instrument

Instrument of measure that register a rate. EXAMPLE:

a) barograph b) thermoluminescent dosimeter c) Recording spectrometer

NOTE: 1) The record (display) can be analogic (continuous line or discontinuous) or

digital. 2) The values of different magnitudes can be register at the same

time. 3) A register instrument also can display information.

General Notes

1) In general, as you raise the hierarchy of the measure, there’s more demand in details

about the way in which the measure and its uncertainty is obtained. However, at any level,

from the commercial activities and rules of market, through the industrial engineering, to

the primary national laboratories and the “Buro Internacional de Pesos y Medidad” (BIPM),

all the information required to re-evaluate the measuring process must be available to the

one who might need it.

2) Every day a lot of measures are made in the industry as in commerce, without explaining

the uncertainties of measures. So many measures are made with instruments that need

periodical calibration or legal inspection. If those instruments are update with the

calibrations or any other document that required, you are able to get the necessary

information in order to know the doubt rate of the tools from those documents.

3) When you say the final measure and the doubt rate, you should give more information than

the required. So as an advise you can do:

a) Describe clearly the used method in order to get the final average and the doubt rate,

starting with the experimental observations and the input data.

b) Make a list of all the components of the doubt rate, and record the way you evaluate

those components.

c) Show the resultant analyze methodology in a way you can follow easily it step by step,

and in case you need it you will be able to repeat that step, getting the same answer.

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d) Give all the information, adjustments and constant data used at the experiment with all

the sources.

4) Always is important to make yourself the next question: Have you gave enough and clear

information, so in the future the experiment can be review and refresh if there appears new

information or data?

TOLERANCE AND SIZING

The basic purpose of any manufacturing process is to produce pieces in a determined size and

shape. All the required information including size and shape in order to get a good and quality

product is in the technical drawing from the part.

However, is impossible to get a measure equal in all the made pieces. Any process no matter

how simply it is will have differences. When you have together all these size differences plus

the doubt of the own measure in order to get a good design and performance in the product, is

necessarily consider a gap in the nominal dimension specified in the drawing. This gap

consider in the design of the drawing is called Tolerance.

In general, you can suppose that with a small tolerance you probable will have a good

performance in the piece. However, you can also suppose that with bigger tolerances the piece

will be cheaper and easier to fabricate. That’s why the Design engineer is responsible of

defining an acceptable tolerance for each dimension in a part, component or assembly and

every dimension must have a small tolerance enough to get a proper performance of the

product and wide enough so that the fabrication process will be competitive in the market.

INSTRUMENT IN THE LABORATORY

Scale

This is the most basic instrument of measure. The scale is use to take measures alone or it

can be combined with a compass, with precision of 1/64” (≈0.015” o 1.4mm).

The appropriate use of the scale combined with other measure instruments like inside or

outside compass, inside gauge, flex meter, together they are the basis of the dimensional

measure.

The correct use of the scale must be learned with practice.

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Compass

Before instruments like Vernier were discovered, people use compasses and rules to take

measures (inside, outside, dividers, hermaphrodite). For example to take a measure of an

outside diameter, you first use the compass to take the dimension, put the piece between the

ends of the compass and then put the compass over the rule to read the measure. Another

way to proceed with the compass is using the rule and put the tips of the compass in a specific

dimension and then you can start roughing, when the compass get a cross the piece it has the

measure you want.

Compasses for measure

Vernier Nowadays this is one of the most mechanical instruments used to take measures in the

industry. Today are analogue and digital version. It is a lineal instrument; you can take inside,

outside measure or deepness. The precision of the Vernier have to be with the graduation of

scales, the design of the guides to move it, and the parallelism and perpendicularity of the

jaws. All these details also have to be with the quality and stability from the material and the

process of fabrication. And finally the most important factor to determine the precision is the

ability of the operator that will take the measure.

Analogic Vernier Digital Vernier

Micrometer The micrometer is also a measure tool very convenient and it is used to measure objects with high precision, using data with hundredths of millimeters (0.01mm) or thousands of inches (0.001”).

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Micrometer is an instrument that works with two end points, which get closer through a

millimeter screw of high precision. Nowadays there is a version analogic and another

digital. It is use for outside measures; there are versions of flat faces (cylinders), tips (thin

measures), plates (to get the measure between gear theet) and some other special

versions. The maximum length that the micrometer give us is limited not like the Vernier,

but it also give you a higher precision. Usually the length of a micrometer is of 25 mm, the

smallest are from 0 to 25 mm, the next one is from 25 to 50 mm and so on.

Telescopic gauges A telescopic gauge is an indirect measure instrument. You must introduce the top of the gauge (closed) inside a circumference or any space and then you open the top of the gauge and the tips will touch the inside walls from the figure you are measuring. Then you just take out the gauge and then you can use a Vernier or a micrometer to measure the space of the gauge head that will be equal to the inside space in the figure. You must lock the top of the gauge before you take it out from the space you are measuring, in order to have a good measure.

Appropriated use of the telescopic gauges.

Telescopic gauge

✓ First you choose the correct gauge according with the diameter of the piece you want to measure. You close the top of the gauge, until the tips of the head are completely inside and then you lock the top of the gauge spinning a screw until it is fit enough to hold the tips in the top contracted.

✓ The gauge is opened loosing slowly the adjusting screw, always avoiding a sudden shock between the walls of the piece and the gauge.

Digital micrometer from

3” to 4”.

Analogic micrometer from

0” to 25”.

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✓ Put the gauge in the center of the piece, holding the opposite side, they you open the gauge until it touch both walls, always being careful of putting the gauge in the middle of the piece.

✓ Adjust the screw so the top of the gauge will keep the size measured and then take it out the piece without modifying that size.

✓ Use a Vernier or a micrometer in order to measure the size took with the gauge.

COORDINATE MEASURING MACHINE There is a huge variety of coordinate measuring machines (CMM) around the world. There are too many machines of general use, but there are also other machines made to achieve specific works in special components or for defined industries. These kinds of machines are common in the automotive, aerospace, molds, tools, die industries, etc.

Every CMM has a settle table with a mobile structure which holds a tip. The tip is a device of contact that forms part of the measure tool and it is made of a precision globe (or even with a pointed tapered shape), it is overlap in a handle connected mechanically with a position sensor, able to detect coordinates with precision in the space.

An essential piece of the CMM is the tip because through this one the surface that will be measure is touched, in order to measure a dimension in a flat surface, the tip must touch the surface. These tip or contact detectors are known as TTPs (Touch Trigger Probes). These are located in an assembly of springs with three poles and three pairs of balls. The three pairs of balls and the three rollers, that at the same time are connected to make an electrical circuit, can be easily take out of balance with any move at the tip. As is shown in the next image, if you need to measure X, then the tip is move until it is touching the face A. So then the CMM determine the 3D position of that point. After that you need to move the sensor to the point B and touch it, so the dimension of X will be the difference between the two points and also with the diameter of the tip. There are so many kinds of tips shapes that can be use in order to make easy measure parts hard to achieve.

The precision of this kind of measures depend on factors like the kind of tip, the CMM, the controller and the software that process the information, also the quality of the measure made. The precision of this kind of machines is of 0.01 mm (≈0.0005”) and the repeatability of these machines are from 0.02 mm (≈0.001”).

Besides that this machines are easy to handle, this measure tools can be operate quickly.

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Goals 1) The student will understand the security rules relevant for this practice. 2) The student will recognize the way that the measure must be done, and the

conventional measures tools. 3) The student will know most frequently measure tools used and conventional in

factories. 4) The student will distinguish how to understand the measures and the doubt

associated with it. 5) The student will use the conventional measure tools (scale, Vernier, Micrometer) in

order to get the dimensions of a simple piece.

6) The student will learn abilities, and limitations of measures instruments like the optical comparator and the CMM.

SECURITY To use the basic measure tools is necessary to practice the next advises.

WARNING! REASON

Do not apply excessive force in the measure tools This can make a permanent deformation in the tool.

Do not take out any measure tool from the metrology area. This area has controlled temperature and taking out

the instrument from this environment can make wrong measures because of thermal dilatation.

Clean the piece and the contact area between the piece and the measure tool.

Get a right measure.

Keep always a clean measure tool. Do not get the tool out of calibration and then do

not lose precision.

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To operate the coordinate machine you must follow beside the last warnings, the next advises.

WARNING! REASON

Use an air pressure of 3 bar (Check out the manometer behind the machine).

To achieve stability and make precision measures.

Do not hit the tip of the CMM. The tips are made of beautiful materials (jewels like ruby) and they are delicate, brittle and expensive.

Do not make any sudden movement with the axis of the CMM.

Hitting and excessive force in the machine will take out of balance the machine.

WARNING! REASON

Work with the machine only with regulated electrical power supply.

Avoid any oscillation of voltage and any possible electric shock because may damage the transducer in

the machine.

Keep fresh environment while the machine is working. The machine has electronic devices highly sensitives to

heat.

The user SHOULD NOT lean on any part of the CMM. Beside, SHOULD NOT get up the table or the machine

any other piece than the one that will be measured, write on the marble, or any other action like these.

Any mechanical deformation will take out the calibration of the machine.

MATERIAL, TOOLS AND EQUIPMENT

1) Material

a) Pieces for manual measures

b) Pieces for coordinate measures.

2) Tools

a) Scale, inside and outside compass

b) Vernier

c) Micrometer

3) Equipment

d) CMM Poli with tip and centering sphere.

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PROCEDURE

1) Before you get into the laboratory Print and read all the practice. Make the Pre-

report.

2) Be five minutes before the class hour with comfy clothes, shoes, no jewels or chains, the pre-report and practice printed and stapled (Page 12 – 16).

3) Pick up material, tools and accessories required for the practice in the warehouse.

4) The teacher will apply a quiz before the practice to review the theoretical framework which also will be the attendance for the class.

5) The teacher will explain how works the measure tools and the CMM.

6) Each student will get a piece in order to measure it. The dimensions to be measured in the piece will be in the draw.

7) After the explanation will measure the piece provided by the teacher. The professor will explain the coordinates systems (general and local) from the machine, the correct alignment of the piece on the marble (CMM table) and the right use of the control.

8) Each student will have a chance to measure characteristics of the piece (the

characteristics will be in the draw as A1, A2, A3, P1, P2 and R1) and everyone will be responsible of taking their own notes from the geometric characteristics measured in the attached draw.

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Department of Mechanical Engineering

Laboratory of Manufacturing Process

PRE-PRACTICE REPORT 1) Research how must be read an analogic measure tools (scale, Vernier,

Micrometer), and solve the next measures shown in the following tables. Note: In order to get a better image of the measures took with the different tools, is recommended to download a PDF, so you will be able to make a zoom in the different pictures.

Measures made with different analogic Vernier.

1

mm

2

”

3

”

4

”

5

mm

6

mm 7

”

8

mm

Practice 1

Metrology

Student

ID

Group

Instructor

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Measures made with different analogic Micrometers.

1

mm

2

mm

3

mm

4

mm

5

mm

6

mm

7

mm

8

mm

9

”

10

” 11

”

12

” 13

”

Bibliographic reference used to learn about analogic measures:

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2) Investigate the methodology used in the CMM to change measure data of absolute coordinate (the own machine) in to a local coordinate in the piece (Zero of piece), and then write it down.

3) The clear description of work piece geometry is pretty much important in order to get quality, interchangeability and a consistent production. Give a short description from at least four elements required to give a clear description:

Bibliographic reference used to learn about required elements from geometric characteristic in a work piece:

Bibliographic reference used to learn about how CMM change from global coordinate to local coordinate:

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Department of Mechanical Engineering

Laboratory of Manufacturing Process

PRACTICE REPORT A ball bearing of Deep track will be measure like shown

in the image. Characteristics dimensions will be

measured are outside, inside diameter and width.

Measure with compass and scale.

Characteristic Dimension (units)

Outside diameter: ” Inside diameter: ” Width: ”

Practice 1

Metrology

Student

ID

Group

Instructor

Basic measure of a bearing

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Measure with Vernier.

Measure with micrometer.





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Measure with CMM.

The piece which will be measure with CMM is a training work piece, showing next. Get the dimensions pointed in the draw according with the views.

Coordinate Point X Y Dimension

A1

A2 A3

Table #1 Circumference A1, A2 y A3

Point Dimension

P1 P2 R1

Table # 2 Angles P1, P2 y Distance R1

DELIVER PRACTICE PRE-REPORT AND REPORT Make sure that the pre-report and report data in the ID chart and that every element is

answer before the delivery. Then go to the warehouse and give back material, tools and

accessories. Leave a cleaned and ordered working area.

SIDE VIEW

TOP VIEW

practice 1: metrology · 2021. 1. 4. · laboratorio de procesos de fabricación 1 school of...

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