stylus probe

7/28/2019 Stylus Probe

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IPE 381Chapter:11

Surface Finish

Abdullah-Al-MamunLecturer, Dept. of IPE


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Outline

Importance of Surface Roughness

Surface Texture

Surface Roughness Surface Roughness Measurement


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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


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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


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Surface Technology

Concerned with: Defining the characteristics of a surface

Surface texture

Surface integrity

Relationship between manufacturing processes and

characteristics of resulting surface


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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


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11.2 Meaning and Terminologies

of Surface Texture


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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


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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


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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 asurface

In popular usage, surface finish is often used as a

synonym for surface roughness

Both terms are within the scope of surface texture


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Surface Roughness

Average of vertical deviations from nominalsurface over a specified length surface

gth

Figure : Deviations from nominal surface used in the two definitions

of surface roughness.


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Surface Roughness

Mean line of the Profile: It is the line that divides the effective profilesuch 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.


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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

iiy

1

2

q N

1

R


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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


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Surface Roughness

Specification

Figure : Surface texture symbols in engineering drawings: (a) the

symbol, and (b) symbol with identification labels.


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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


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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


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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


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Stylus Probe Instrument

The Tomlinson Surface Meter:


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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 ofstylus.


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Taylor Hobson Telyserf


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Self Study

11.9 Analysis of Surface TracesWorked out Qustion and Answers (From page 661-663)

Thank You

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