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• Importance of Surface Roughness
• Surface Texture
• Surface Roughness
• Surface Roughness Measurement
Surfaces
• The nominal surfaces appear as absolutely straight
lines, ideal circles, round holes, and other edges and
surfaces that are geometrically perfect
• Actual surfaces of a part are determined by the
manufacturing processes used to make it
– Variety of processes result in wide variations in
surface characteristics
Why Surfaces are Important
• Aesthetic reasons
• Surfaces affect safety
• Friction and wear depend on surface
characteristics
• Surfaces affect mechanical and physical
properties
• Assembly of parts is affected by their surfaces
• Smooth surfaces make better electrical contacts
Surface Technology
• Concerned with: – Defining the characteristics of a surface
– Surface texture
– Surface integrity
– Relationship between manufacturing processes and
characteristics of resulting surface
Surface Texture
The topography and geometric features of
the surface
• When highly magnified, the surface is
anything but straight and smooth– It has roughness, waviness, and flaws
• It also possesses a pattern and/or
direction resulting from the mechanical
process that produced it
Elements of Surface Texture
1. Roughness - small, finely-spaced
deviations from nominal surface – Determined by material characteristics and
processes that formed the surface
2. Waviness - deviations of much larger
spacing – Waviness deviations occur due to work deflection,
vibration, heat treatment, and similar factors
– Roughness is superimposed on waviness
Four Elements of Surface
Texture3. Lay - predominant direction or
pattern of the surface texture
4. Flaws - irregularities that occur
occasionally on the surface
– Includes cracks, scratches,
inclusions, and similar
defects in the surface
– Although some flaws relate
to surface texture, they
also affect surface integrity
Surface Roughness and
Surface Finish• Surface roughness - a measurable
characteristic based on roughness deviations
• Surface finish - a more subjective term
denoting smoothness and general quality of a
surface
– In popular usage, surface finish is often used as a
synonym for surface roughness
– Both terms are within the scope of surface texture
Surface Roughness
Average of vertical deviations from nominal
surface over a specified length surface
gth
Figure : Deviations from nominal surface used in the two definitions
of surface roughness.
Surface RoughnessMean line of the Profile: It is the line that divides the effective profile
such that, within sampling length the sum of squares of distances
(y1, y2, ….yn) between effective points and mean line is minimum.
Center line of the Profile: It is the line for which the area embraced
by the profile above or below the line is equal.
Surface Roughness
• Center Line Average (CLA), Ra is the Arithmetic Average of the
distance of the filtered or unfiltered Roughness profile from its Mean
Line.
• Maximum Peak to valley height, Rt or Rmax.
• RMS Value, Rq is the Root Mean Square of the distance of the
filtered or unfiltered Roughness Profile from its mean line.
Ni
i
y1
ia ||N
1R
Ni
i
iy1
2q
N
1R
Surface Roughness
• Ten Point height of Irregularities, Rz is numerically the average
height difference between the five highest peaks and the five lowest
valleys within the assessment length.
• Rz is also known as the ISO 10 point
height parameter.
5
)YYYY(Y)YYYYY((ISO)R
v5v4v3v2v1p5p4p3p2p1
z
Surface Roughness
Specification
Figure : Surface texture symbols in engineering drawings: (a) the
symbol, and (b) symbol with identification labels.
Surface Texture Symbols
0.030
^
0.015
cut-off
Lay
Max
Roughness
Spacing
0.002.-263
32
Max Waviness Width
Max Waviness
Height
Max
Ra
Min Ra
11.5. Methods of Measuring
Surface Roughness• Touch Inspection
• Visual Inspection
• Scratch Inspection
• Microscope Inspection
• Surface Photographs
• Micro Interferometer
• Wallace Surface Dynamometer
• Reflected Light Intensity
11.6. Direct Instrument
Measurement• Stylus Probe Instrument
– A skid or shoe is drawn slowly over the surface.
– A stylus move over the surface with the skid.
– An amplifying device for magnifying the stylus movement and
indicator.
– A recording device to produce trace of the surface profile.
– A mean of analyzing the trace
Stylus Probe Instrument
• The Taylor-Hobson Talysurf
– As the probe moves, Armature
pivots around a E shaped
stampings.
– Any movement on the stylus
causes the air gap to vary.
– Amplitude of a.c. current is
modulated.
– Signal is demodulated to get
the vertical displacement of
stylus.