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Chapter: Mechanical - Manufacturing Technology - Theory Of Metal Cutting

Surface finish

The machining processes generate a wide variety of surface textures. Surface texture consists of the repetitive and/or random deviations from the ideal smooth surface.


Surface finish

 

The machining processes generate a wide variety of surface textures. Surface texture consists of the repetitive and/or random deviations from the ideal smooth surface. These deviations are

 

Roughness: small, finely spaced surface irregularities (micro irregularities)

 

Waviness: surface irregularities of grater spacing (macro irregularities)

 

Lay: predominant direction of surface texture

 

Three main factors make the surface roughness the most important of these parameters:

 

Fatigue life: the service life of a component under cyclic stress (fatigue life) is much shorter if the surface roughness is high

 

Bearing properties: a perfectly smooth surface is not a good bearing because it cannot maintain a lubricating film.

Wear: high surface roughness will result in more intensive surface wear in friction.

 

Surface finish is evaluated quantitatively by the average roughness height, Ra

 

Roughness control

 

Factors, influencing surface roughness in machining are

 

Tool geometry (major cutting edge angle and tool corner radius),

 

Cutting conditions (cutting velocity and feed), and

 

Work material properties (hardness).

 

The influence of the other process parameters is outlined below:

 

Increasing the tool rake angle generally improves surface finish

 

Higher work material hardness results in better surface finish

 

Tool material has minor effect on surface finish.

 

Cutting fluids affect the surface finish changing cutting temperature and as a result the built-up edge formation.

 

 

 


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