SURFACE FINISH
• is the nature of a surface as defined by the 3
characteristics of lay ,surface roughness,
and waviness.
• It comprises the small local deviations of a surface
from the perfectly flat ideal
• control friction and transfer layer formation during
sliding
• Surface textures can be isotropic or anisotropic
• The latter process may
be grinding, polishing, lapping, abrasive
blasting, honing, electrical discharge
machining(EDM), milling, lithography, industrial
etching/chemical milling, laser texturing, or other
processes.
Characteristics
Lay
the direction of the predominant surface pattern
ordinarily determined by the production method
used.
Surface roughness
measure of the finely spaced surface irregularities
Related to the friction and wear properties of a surface
Affects the productivity of wind generation farms
Waviness
measure of surface irregularities with a spacing
greater than that of surface roughness
occur due to warping, vibrations, or deflection
during machining
occur from machine or work deflections,
chatter, residual stress, vibrations, or heat treatment
Application of waviness
In bearing balls and bearing races is one of the
reasons for vibrations and noise in ball bearings
In flat milled sealing surfaces, "orange peel" on
painted surfaces, and chatter on round shaft surfaces
Terminology
1. Roughness :
Roughness consists of surface irregularities which result
from the various machining process. These irregularities
combine to form surface texture.
2. Roughness Height :
It is the height of the irregularities with respect to a
reference line. It is measured in millimeters or microns or
micro inches. It is also known as the height of unevenness.
3. Roughness Width :
The roughness width is the distance parallel to the
nominal surface between successive peaks or ridges which
constitute the predominate pattern of the roughness. It is
measured in millimeters
4. Roughness Width Cut Off :
Roughness width cut off is the greatest spacing of respective
surface irregularities to be included in the measurement of the
average roughness height. It should always be greater than the
roughness width in order to obtain the total roughness height
rating.
5. Lay :
Lay represents the direction of predominant surface pattern
produced and it reflects the machining operation used to
produce it.
6. Waviness :
This refers to the irregularities which are outside the roughness
width cut off values. Waviness is the widely spaced component
of the surface texture. This may be the result of work piece or
tool deflection during machining, vibrations or tool run out.
7. Waviness Width :
Waviness height is the peak to valley distance of the
surface profile, measured in millimeters.
Factors Affecting the Surface Finish
A) The machining variables which include
a) cutting speed
b) feed, and
c) depth of cut.
B) The tool geometry
a) nose radius
b) rake angle
c) side cutting edge angle, and
d) cutting edge.
C) Work piece and tool material combination
and their mechanical properties
D) Quality and type of the machine tool used,
E) Auxiliary tooling, and lubricant used, and
F) Vibrations between the work piece, machine
tool and cutting tool.
G)Temperature
Thank you
