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Design and Manufacture 2 > Surface finishes > Flashcards

Surface finishes Flashcards

1
Q

What are the 2 methods of measuring surface finish

A

Contact and Non Contact

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2
Q

What is an example of contact methods

A

Skid & stylus Profilometers

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3
Q

What material is used for the stylus in Profilometers

A

Diamond

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4
Q

How do Profilometers work

A

The rider is dragged across the surface where the stylus measures the surface profile

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5
Q

What are some advantages of Profilometers

A

Acceptable standards
Accuracy using a 20nm tip provides high resolution
Independence- not sensitive to surface contaminants such as colour and reflection

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6
Q

List some methods of smoothing a surface in order of roughness

A

Turning
Rough grinding
Finish Grinding
Lapping

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7
Q

Name an non contact method for measuring surface finish

A

Optical profilomentry

eg. phase shift, interformetry and vertical scanning

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8
Q

What is another name for a phase shift interferometer

A

Laser interferometer

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9
Q

What type of light does a phase shift interferometer use

A

Laser/monochromatic

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10
Q

What are Phase shift interferometers used for

A

very smooth surfaces

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11
Q

Are phase shift interferometers accurate

A

Yes very, can be used to measure light up to a 100th of the wavelength used

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12
Q

What is another name for vertical scanning interferometers

A

Coherence scanning inferometers or scanning white light inferometers

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13
Q

What is vertical scanning suitable for

A

Very rough surfaces

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14
Q

What does vertical scanning use

A

White light

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15
Q

What values of n mean constructive interference and what mean destructive

A

Constructive when n is even

Destructive when n is odd

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16
Q

What is the equation for the difference in distance travelled by the light

A

diff=n*lamda/2

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17
Q

Why are phase shift interferometers so accurate

A

The combine information from multiple phase shifted images of same object by moving position of mirror

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18
Q

How accurate can phase shift interferometers measure

A

Up to lamda/100

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19
Q

Which is more accurate vertical scanning or phase shift interferometers

A

Phase shift

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20
Q

Why wont vertical scanning damage the surface

A

Because it is anon contact method of scanning

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21
Q

For dimensional measurement what are the techniques of measuring

A

Contact and Non-contact

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22
Q

What are the types of contact techniques for dimensional measurement

A

Portable and non-portable

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23
Q

For dimensional measurement what are the types of non-contact measurement

A

Active 3D scanning (uses radiation) and Passive 3D scanning (uses light)

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24
Q

What is are examples of contact dimensional measurement

A

Callipers and micrometres

25
Q

How would a coordinate measuring system be used to measuring dimensions while making contact
for both portable and non portable

A

Portable- hand operated device with contact probe is placed on device and probe is tracked using a tracking system
Non-portable- Object is secured to a fixed bed and a computer controlled robotic arm is used to collect data

26
Q

What are the 3 types of active 3D scanning

A

Time of flight- laser pulse and uses d=vt
Triangulation- how far away an object is effects the position of laser on camera FOV
Structures light pattern- light cast onto a surface and deformation of pattern is used to find position

27
Q

Why is Passive 3D scanning cheaper than active 3D scanning

A

Because they do not emit light they use reflected light

28
Q

Name 2 types of passive 3D scanning

A

Stereoscopic systems

Photometric systems

29
Q

Which type of scanning can be used for reverse engineering

A

Passive 3D scanning

30
Q

What is more precise portable or non-portable contact coordinate measuring systems

A

Non-portable

31
Q

What is faster 3D scanning or Non-portable contact CM

A

3D scanning

32
Q

What is the most accurate a non-contact CMM can be

A

A few nano meters

33
Q

How expensive are portable and non portable contact measuring methods

A

Both can cost 10s of 1000s but non-contact is more expensive

34
Q

To what precision can portable CM systems measure

A

Up to about 20 micro meters

35
Q

How precise can non-contact triangulation methods be

A

Reasonably precise, 10s of microns

36
Q

What is the price for a non-contact triangulation method which measures at a precision of 200 microns

A

About £450

37
Q

What is the advantage of structured light over triangulation

A

Faster as it can scan multiple points at once

38
Q

What is the typical price for a structured lights dimensional measuring system

A

About £2000 with an accuracy of about 60 microns

39
Q

How easy to obtain are Photometric methods of dimensional measurement

A

Very can be purchased as an app on smart phones

40
Q

Name a method used for measuring of a surface’s flatness

A

Optical flats

41
Q

What is an optical flat

A

A clear extremely flat piece of quartz

42
Q

How does an optical flat work

A

Under monochromatic light interference bands are created and the deformation allows the flatness to be calculated. Deformation is formed by a flaw in the surfaces flatness causing the optical flat to be displaced at an angle so the light will take a different path through the flat creating a different pattern.

43
Q

Explain constructive and destructive interference

A

Constructive- 2 waves that are in phase combine to create a wave with greater amplitude
Destructive- 2 waves out of phase with each other combine to produce 0 or a wave of reduced amplitude

44
Q

What causes the dark areas when using an optical flat

A

Destructive interference

45
Q

Surface roughness increases as…..

A

Tolerance range increases

46
Q

What is the importance of surface texture

A

It has an effect of friction, wear and lubrication
It effects the appearance- ability to be painted, coated, bonded or welded
Effects crack propagation
Effects thermal and electrical conductivity

47
Q

What is roughness on a surface

A

Finley spaced surface irregularities resulting from machining operation.

48
Q

What is surface roughness dependant on

A

Speed, material of tool, work piece material and depth of cut

49
Q

What is surface waviness

A

A surface irregularity of greater spacing than roughness caused by tool deflection

50
Q

What causes surface waviness

A

Cutting pressure, Work piece deflection, vibration of part, deposition of built up deflection and tool vibration

51
Q

What is a lay

A

A term used to designate direction of pattern produced by machine process

52
Q

All surfaces are taken……………… to lay direction

A

Normal

53
Q

How do you measure a surfaces flatness

A

Using Optical flats

54
Q

How do you measure a surface dimension

A

Using contact (callipers and micrometers) and non contact (active 3D scanning and passive 3D scanning) methods

55
Q

How do you measure surface finish

A

Using Contact (skid and stylus Profilometers) and non contact (interferometry) including phase shift and vertical

56
Q

What are the 2 methods for measuring surface roughness

A

Centre line average (CLA) Ra

Root Mean Square (RMS) Rq

57
Q

What is centre line average

A

Average height from a mean line for all the coordinates of the surface regardless of sign

58
Q

What is the root mean square value

A

Defined as square of the mean of the square of the coordinates of surface measured from the centre line

Design and Manufacture 2 (5 decks)

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