Surface finish Flashcards
1
Q
why is surface finish important
A
- aesthetic reasons
- safety
- to reduce friction and wear
- to improve mechanical and physical properties
- to assemble
2
Q
components of the section of a machined metallic part
A
- substrate, not influenced by the cut
- altered layer: modified by temperature and stresses during the cut
- surface texture: profile of the real surface
3
Q
Elements of the surface texture
A
- roughness
- small wavelength deviations from the ideal surface
- determined mostly by the process - waviness
- larger wavelength deviations
- due to deflection, vibration
- roughness is superimposed to waviness - lay
- predominant pattern of the surface texture - flaws
- occasional irregularities on the surface
4
Q
different surfaces definitions
A
- ideal surface: surface as designed by the designer
- real surface: surface limiting the body, generated by the manufacturing process
- primary surface: surface probed by measuring systems, that “filter” the real surface
- reference surface: surface which the the primary surface is referred to
- mean surface: surface obtained from a least squares fitting
5
Q
definitions of surface roughness
A
- vertical deviations yi from the mean surface
- average roughness:
Ra = 1/n * sum(i=1,n) |yi| - squared roughness
Rq = sqrt(1/N * sum(i=1,N) yi^2) - peak to peak roughness
Rt = Rp + Rv
Ra approximated by Rt / 4
6
Q
methods to measure surface roughness
A
- comparison with standard test surfaces
- electronic measurement
- optical techniques
7
Q
electronic measurement
A
- stylus head moves above the surface
- vertical stylus measure the surface profile
- at first, a low pass filtering of the surface is obtained due to the tip of the stylus
- them, a high pass filtering of the obtained signal should be done to remove waviness component.
- to this end, the cutoff length parameter has to be chosen, and influnces the result
- a high pass filtering with cutoff smaller than waviness eliminates the waviness
