Engineering Measurementsite.iugaza.edu.ps/jalaydi/files/2010/02/Measurement-14.pdf · 1 Importance...

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Dr. Juma Y. Alaydi

Engineering Measurement

Lecture 14Surface Finish

April 12, 2014 Engineering Measurement2

Surface Finish

April 12, 2014 Engineering Measurement

Outline

Importance of Surface Roughness1

3

Surface Texture2

Surface Roughness3

Surface Roughness Measurement4

5

uOne of the first thing one notice is the surfacefinish

uThe nominal surfaces appear as absolutelystraight lines, ideal circles, round holes, and otheredges and surfaces that are geometrically perfect

uActual surfaces of a part are determined by themanufacturing processes used to make it



During machining processes roughness can be found due to:

1.Mechanical vibration in the machine

2.Fixing both of W/P and cutting tool (eccentricity)

3.Metallurgical deficiencies (material defect)

4.Cutting procedure (cutting depth, feed rate….)

Why Surfaces are Important?ØSurfaces affect safetyØ Friction and wear depend on surfaceØ characteristicsØSurfaces affect mechanical and physical

propertiesØAssembly of parts is affected by their surfacesØSmooth surfaces make better electrical contacts


Surface Texture



The topography and geometric features ofthe surface

•When highly magnified, the surface isanything but straight and smooth

•It has roughness, waviness, and flaws•It also possesses a pattern and/or directionresulting from the mechanical process thatproduced it

Four Elements of Surface Texture


1. Roughnesssmall, finely-spaced deviations from nominal

surfaceØDetermined by material characteristics and processes thatformed the surface

2. Wavinessdeviations of much larger spacingØWaviness deviations occur due to work deflection,

vibration, heat treatment, and similar factorsØRoughness is superimposed on waviness


3.Laypredominant direction or pattern of the surface texture

4.Flawsirregularities that occur occasionally on the surfaceØIncludes cracks, scratches, inclusions, and similar defects in the surfaceØAlthough some flaws relate to surface texture, they also affect surface

Evaluation of Surface Roughness



RMS Value, Rq

Rq is the Root Mean Square of the distance of the filtered or unfiltered Roughness Profile from its mean line.


Center Line Average(CLA), Ra

Ra is the Arithmetic Average of the distance of the filtered or unfiltered Roughness profile from its Mean Line

Advantages: Statistically very stable parameter. Easy and cheap to implement into instrumentation. Good for random type surfaces (Processes like grinding)

Disadvantages:


Maximum Peak to valley height, Rt or Rmax

ØRt is the highest Peak to the lowest Valley in the assessmentlength

ØRp is the highest Peak in the assessment lengthØRv is the lowest Valley in the assessment length.


Average peak to valley height, Rz


Surface Roughness Specification

Surface texture symbols in engineering drawings: (a) the symbol,(b) symbol with identification labels.


Surface Finish Process• Grinding• Lapping• Honing• Buffing• Barrel Tumbling• Barrel rolling

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Dr. Juma

April 12, 2014 26Engineering Measurement

Engineering Measurementsite.iugaza.edu.ps/jalaydi/files/2010/02/Measurement-14.pdf · 1 Importance...

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