surface Topography Flashcards
what is surface finish and how it is defined?
surface finish / surface texture / surface topography tells about the nature of the surface. Depending on three characteristics Lay, surface roughness and waviness
why is surface finish important?
surface finish affects the friction which in turn affects the wear.
It also predicts performance as irregularities in surface are nucleation sites for formation of cracks.
define surface roughness, lay and waviness?
surface roughness is the measure of finely spaced surface irregularities.
Lay is the direction of predominant surface pattern.
Waviness is measure of surface irregularities with spacing greater than surface roughness.
what are the parameters that define surface roughness?
Ra & Rq / Sa & Sq commonly used R for profile (line) and S for surface (area) and subscript indicate the formula used.
Ra = arithmetic mean, Rq/Rrms = rms, Rv = max valley depth, Rp = max peak height, Rt/Ry = max height of profile, Rsk = skewness, Rku = kurtosis,….
what is the expected range of surface finish in laser cut parts?
6.3 µm to 0.8 µm Ra is common rarely acheived till 0.2 µm
which direction surface finish to be measured?
it can be isotropic or anisotropic. so it is better to measure in both directions.
how does focus variation method work?
several photos were taken with low dof is taken either by moving object or camera and then finding the pixels in focus and the distance moved a 3d map of the surface is generated.
how auto focus works?
two types
using beam splitter 2 images are taken and these are compared if same it is in focus used in DSLR normal mode.
changing the focus and measuring the intensity of light in pixel to be focussed when focussed the intensity is more. used in live mode of DSLR, point and shoot and mirror less. slow.
