LECTURE 1 METROLOGY

Question 1

Manufacture:

Answer 1

1. Something made from raw materials by hand or by machinery
2. A productive industry using mechanical power and machinery
3. The act or process of producing something

Question 2

How things are manufactured:

Answer 2

◦ Machine selection
◦ Tool Selection
◦ Optimizing machine, process, tools and time.
◦ Additive vs Subtractive vs Forming Processes

Question 3

Manufacturability

Answer 3

Manufacturability = The ease that something can be
There’s usually more than one way to make
something. Resolving the most efficient processes is
often difficult.

Question 4

Metrology

Answer 4

Metrology: noun me·trol·o·gy - The science of measurement

Question 5

Attributes

Answer 5

Attributes
Good or bad, pass or fail, accept or reject
Typically, with the use of gages, go or no-go

*Qualitative
*Fast and economical
*Pass or fail
*Mostly for standard and less severe
applications (Automobile)
*Useful after process development
*Large production volume
* Not ideal for tight tolerance differences

Question 6

Variables

Answer 6

Variables
Use of measuring tools to determine actual dimensions

What determines if the. Value is acceptable or not? TOLERANCE

*Quantitative
*Slow and expensive
*Exact dimension is needed
*Useful for highly reliable applications
(Aircrafts)
*Needed for development
*Small production volume

Question 7

Allowance – Fits – ANSI

Answer 7

Class 1. Loose fit
Class 2. Free fit
Class 3. Medium Fit
Class 4. Snug Fit
Class 5. Wringing fit
Class 6. Tight fit
Class 7. Medium force fit
Class8. Heavy force and Shrink fits

Question 8

Class 1. Loose fit

Answer 8

large allowance
Accuracy is not essential.

Question 9

Class 2. Free fit:

Answer 9

Class 2. Free fit:
Liberal allowance.
For running fits where speeds are above 600 rpm and pressures are 600 psi ( 4.1 MPa)
or above

Question 10

Class 3. Medium Fit

Answer 10

Class 3. Medium Fit:
Medium allowance.
For running fits below 600 rpm and pressure below 600 psi ( 4.1 MPa) and for
sliding fits.

Question 11

Class 4. Snug Fit:

Answer 11

Class 4. Snug Fit:
Zero allowance.
No movement under load is intended, and no shaking is wanted. This is the tightest fit
that can be assembled by hand

Question 12

Class 5. Wringing fit:

Answer 12

Class 5. Wringing fit: zero to negative allowance. Assemblies are selective and not interchangeable.

Question 13

Class 6. Tight fit:

Answer 13

Class 6. Tight fit:
slight negative allowance.
An interface fit for parts that must not come apart in service and are not to be
disassembled or are to be disassembled only seldom.
Light pressure is required for assembly. Not to be used to with stand
other than very light loads.

Question 14

Class 7. Medium force fit:

Answer 14

Class 7. Medium force fit:

An interference fit requiring considerable pressure to assemble.

Ordinarily assembled by heating the external member or cooling the internal member to provide expansion or shrinkage.

Used for fastening wheels, crank
disks, and the like to shafting. The tightest fit that should be used on cast iron external members.

Question 15

Class8. Heavy force and Shrink fits:

Answer 15

Class8. Heavy force and Shrink fits:

considerable negative allowance.

Used for permanent shrink on steel members.

Question 16

Tolerance – Fits – ISO (Metric)

Answer 16

3 Types:
1. Clearance Fits
2. Transition Fits
3. Interference Fits

Question 17

Factors in selecting inspection equipment

Answer 17

1. Gage Capability
   Rule of 10 – Selected measuring equipment should be 10 times more precise than the tolerance
   of the dimension being measured.
2. Linearity – Calibration accuracy over its working range.
3. Repeat Accuracy – How repeatable the device is
4. Stability
5. Magnification - Amplification of the output portion of the device, bigger dials as the
   dimension gets smaller.
6. Resolution - Sensitivity

Question 18

Destructive testing

Answer 18

Quantitative results
Do not require interpretation
Restricted for costly measurements
High cost equipment
Consistent results

Advantages
1. Provides a direct and reliable measurement of how a material or component will respond to service conditions.
2. Provides quantitative results, useful for design. *
3. Does not require interpretation of results by skilled operators.
4. Usually find agreement as to meaning and significance of test results.

Disadvantages
1. Applied only to a sample; must show that the sample is representative of the group.
2. Tested parts are destroyed during testing.
3. Usually cannot repeat a test on the same item or use the same specimen for multiple tests.
4. May be restricted for costly or few-in-number parts.
5. Hard to predict cumulative effect of service usage.
6. Difficult to apply to parts in use; if done, testing terminates their useful life.
7. Extensive machining or preparation of test specimens is often required.
8. Capital equipment and labor costsareoftenhigh.

Question 19

NDT

Answer 19

Qualitative results
Skilled interpretation of results
Low material cost
Low cost equipment
More subjective results

Advantages
1. Can be performed directly on production items without regard to cost or quantity available.
2. Can be performed on 100% of production lot (when high variability is observed) or a representative sample (if sufficient similarity is noted).
3. Different tests can be applied to the same item, and a test can be repeated on the same specimen.
4. Can be performed on parts that are in service; the cumulative effects of service life can be monitored on a single part.
5. Little or no specimen preparation is required.
6. The test equipment is often portable.
7. Labor costs are usually low.

Disadvantages
1. Results often require interpretation by skilled operators.
2. Different observers may interpret the test results differently.
3. Properties are measured indirectly and results are often qualitative or comparative.
4. Some test equipment requires a large capital investment.

Question 20

NDT Visual Inspection

Answer 20

Principle:
Illuminate the test specimen and observe the surface.
Use of optical aids or assists permitted.
most inspection is by human eye, video cameras and computer-vision systems.

Advantages: Simple, easy to use, relatively inexpensive.

Limitations: Depend on skill and knowledge of inspector. Limited to detection of surface flaws.

Material limitations: None.

Geometrical limitations: Any size or shape providing viewing accessibility of surfaces to be inspected.

Permanent record: Photographs or videotapes are possible or Inspectors’ reports.

Remarks: Should always be the initial and primary means of inspection and is the responsibility of everyone associated with partsmanufacture.

Question 21

NDT Magnetic Particle Inspection

Answer 21

Principle:
When magnetized ferromagnetic materials will have a distorted magnetic field in the vicinity of flaws and defects.
Magnetic particles will be strongly attracted to regions where the magnetic flux breaks the surface.

Advantages:
Relatively simple, fast, easy-to-interpret
portable units exist
can reveal:
surface
subsurface flaws and inclusions (as much as or 6 mm deep)
small, tight cracks.

Limitations:
Parts must be relatively clean

alignment of the flaw and the field affects the sensitivity so multiple inspections with different magnetizations may be required

can only detect defects at or near surfaces

must demagnetize part after test

high current source is required

some surface processes can mask defects

post cleaning may be required.

Material limitations:
Must be ferromagnetic

Geometrical limitations:
Size and shape are almost unlimited
most restrictions relate to the ability to induce uniform magnetic fields within the piece.

Hard to use on rough surfaces.

Permanent record:
Photographs, videotapes, and inspectors’ reports are most common. The defect pattern can be preserved on the specimen by an application of transparent lacquer, or transferred to a piece of transparent tape that has been applied to the specimen and peeled off.

Question 22

NDT Ultrasonic Inspection

Answer 22

Principle: High-frequency sound waves are propagated through a test specimen and the transmitted or reflected signal is monitored and interpreted.

Advantage:
Can reveal internal defects
high sensitivity to most cracks and flaws
high-speed test with immediate results
can be automated and recorded, portable
high penetration in most important materials (up to 60 ft in steel)
indicates flaw size and location
access to only one side is required

Limitations:
Difficult to use with complex shapes;
external surfaces and defect orientation can affect the test
a couplant is required
the area of coverage is small
trained, experienced, and motivated technicians may be required.

Material limitations: Few-can be used on metals, plastics, ceramies, glass, rubber, graphite, and concrete, as well as joints and interfaces between materials.

Geometric limitations: Small, thin, or complex shaped parts or parts with rough surfaces and nonhomogeneous structure pose the greatest difficulty.

Permanent record: Ultrasonic signals can be recorded for subsequent playback and analysis. Strip charts can also be used.