Surface finishes

Question 1

What are the 2 methods of measuring surface finish

Answer 1

Contact and Non Contact

Question 2

What is an example of contact methods

Answer 2

Skid & stylus Profilometers

Question 3

What material is used for the stylus in Profilometers

Answer 3

Diamond

Question 4

How do Profilometers work

Answer 4

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

Question 5

What are some advantages of Profilometers

Answer 5

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

Question 6

List some methods of smoothing a surface in order of roughness

Answer 6

Turning
Rough grinding
Finish Grinding
Lapping

Question 7

Name an non contact method for measuring surface finish

Answer 7

Optical profilomentry

eg. phase shift, interformetry and vertical scanning

Question 8

What is another name for a phase shift interferometer

Answer 8

Laser interferometer

Question 9

What type of light does a phase shift interferometer use

Answer 9

Laser/monochromatic

Question 10

What are Phase shift interferometers used for

Answer 10

very smooth surfaces

Question 11

Are phase shift interferometers accurate

Answer 11

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

Question 12

What is another name for vertical scanning interferometers

Answer 12

Coherence scanning inferometers or scanning white light inferometers

Question 13

What is vertical scanning suitable for

Answer 13

Very rough surfaces

Question 14

What does vertical scanning use

Answer 14

White light

Question 15

What values of n mean constructive interference and what mean destructive

Answer 15

Constructive when n is even

Destructive when n is odd

Question 16

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

Answer 16

diff=n*lamda/2

Question 17

Why are phase shift interferometers so accurate

Answer 17

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

Question 18

How accurate can phase shift interferometers measure

Answer 18

Up to lamda/100

Question 19

Which is more accurate vertical scanning or phase shift interferometers

Answer 19

Phase shift

Question 20

Why wont vertical scanning damage the surface

Answer 20

Because it is anon contact method of scanning

Question 21

For dimensional measurement what are the techniques of measuring

Answer 21

Contact and Non-contact

Question 22

What are the types of contact techniques for dimensional measurement

Answer 22

Portable and non-portable

Question 23

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

Answer 23

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

Question 24

What is are examples of contact dimensional measurement

Answer 24

Callipers and micrometres

Question 25

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

Answer 25

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

Question 26

What are the 3 types of active 3D scanning

Answer 26

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

Question 27

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

Answer 27

Because they do not emit light they use reflected light

Question 28

Name 2 types of passive 3D scanning

Answer 28

Stereoscopic systems | Photometric systems

Question 29

Which type of scanning can be used for reverse engineering

Answer 29

Passive 3D scanning

Question 30

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

Answer 30

Non-portable

Question 31

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

Answer 31

3D scanning

Question 32

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

Answer 32

A few nano meters

Question 33

How expensive are portable and non portable contact measuring methods

Answer 33

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

Question 34

To what precision can portable CM systems measure

Answer 34

Up to about 20 micro meters

Question 35

How precise can non-contact triangulation methods be

Answer 35

Reasonably precise, 10s of microns

Question 36

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

Answer 36

About £450

Question 37

What is the advantage of structured light over triangulation

Answer 37

Faster as it can scan multiple points at once

Question 38

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

Answer 38

About £2000 with an accuracy of about 60 microns

Question 39

How easy to obtain are Photometric methods of dimensional measurement

Answer 39

Very can be purchased as an app on smart phones

Question 40

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

Answer 40

Optical flats

Question 41

What is an optical flat

Answer 41

A clear extremely flat piece of quartz

Question 42

How does an optical flat work

Answer 42

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.

Question 43

Explain constructive and destructive interference

Answer 43

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

Question 44

What causes the dark areas when using an optical flat

Answer 44

Destructive interference

Question 45

Surface roughness increases as.....

Answer 45

Tolerance range increases

Question 46

What is the importance of surface texture

Answer 46

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

Question 47

What is roughness on a surface

Answer 47

Finley spaced surface irregularities resulting from machining operation.

Question 48

What is surface roughness dependant on

Answer 48

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

Question 49

What is surface waviness

Answer 49

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

Question 50

What causes surface waviness

Answer 50

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

Question 51

What is a lay

Answer 51

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

Question 52

All surfaces are taken.................. to lay direction

Answer 52

Normal

Question 53

How do you measure a surfaces flatness

Answer 53

Using Optical flats

Question 54

How do you measure a surface dimension

Answer 54

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

Question 55

How do you measure surface finish

Answer 55

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

Question 56

What are the 2 methods for measuring surface roughness

Answer 56

Centre line average (CLA) Ra | Root Mean Square (RMS) Rq

Question 57

What is centre line average

Answer 57

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

Question 58

What is the root mean square value

Answer 58

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