IPE 381

Chapter:11

Surface Finish

Abdullah-Al-Mamun

Lecturer, Dept. of IPE

Outline

• 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

11.2 Meaning and Terminologies

of Surface Texture

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 Tomlinson Surface Meter:

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.

Taylor Hobson Telyserf

Self Study11.9 Analysis of Surface Traces

Worked out Qustion and Answers (From page 661-663)

Thank You