Post on 18-Nov-2014
description
Surface Finish Metrology
© 2000 Taylor Hobson Ltd
Centre of Excellence
Taylor Hobson Ltd
Contents 1. Why do we need to measure Surface Finish?
2. Measurement Methods
3. Measurement Datums
4. Reproducing the Surface
5. Terminology
6. Filters
7. Parameters
8. Bearing Area (Material Ratio)
9. The Rk Parameter
10. Form Measurement
11. Calibration Methods.
12. Conics and Aspherics.
13. 3D (Areal) Measurement.
14. Drawing Indication.
Why do we need to measure Surface
Finish?
Nature of Surfaces
The microstructure of the material
Nature of Surfaces
The microstructure of the material The action of the cutting tool
Nature of Surfaces
The microstructure of the material The action of the cutting tool The instability of the cutting tool on the material
Nature of Surfaces
The microstructure of the material The action of the cutting tool The instability of the cutting tool on the material
Errors in machine tool guideways
Nature of Surfaces
The microstructure of the material The action of the cutting tool The instability of the cutting tool on the material
Errors in machine tool guideways Deformations due to stress patterns in the component
Nature of Surfaces
The microstructure of the material The action of the cutting tool The instability of the cutting tool on the material
Errors in machine tool guideways Deformations due to stress patterns in the component
Unwanted Properties on a Surface
Deep valleys which may be susceptible to crack propagation
Too many peaks which may cause early surface breakdown and wear when in contact with a mating component
Excessive waviness which may cause noise or indicate machining problems
Wanted Properties on a Surface
Sufficient valleys for oil retention when lubrication is an important factor
Sufficient peaks for retention of paint and adhesives
Sufficient distribution of valleys for formability
Smooth surface profiles for reduced, noise, vibration or high reflectance.
Why Do We Need to Measure Surface Finish?
Process Control
Predicting Component Behaviour
Monitoring Component Performance
Why Do We Need to Measure Surface Finish?
The Ideal Situation
Why Do We Need to Measure Surface Finish?
The Reality - Process Control
Why Do We Need to Measure Surface Finish?
Predicting Component Behaviour
Why Do We Need to Measure Surface Finish?
Monitoring Component PerformanceBack to Contents Page
Measurement Methods
Measurement Methods
Contact Type Instruments
Non-Contact Type Instruments
How Do We Measure Surface Finish?
Comparison Plates
Contact Type Instrument
Measurement Methods
Traverse Direction (X)
Stylus Movement (Z)
Data Point Spacing (X)
Inductive Type of Transducer
Stylus
Beam
Knife Edge Pivots
Ferrite Slug (Armature)
Coil
Coil
Measurement Methods
Piezo-Electric Type of Transducer
Stylus
Beam Piezo Element
Measurement Methods
Laser
PhotoDiode
Laser Type of Transducer
Stylus
Beam
Back to Contents Page
Click Here for Further Information
Measurement Methods
Measurement Datums
Skid (surface) Datum
Skid Stylus Movement (Z)
Traverse Direction (X)
Measurement Datums
Benefits of Using a Skid Datum
• Reduces Effects of Vibration• No Surface Levelling Required • Instrument Portability • Robust Design
Measurement Datums
Effect of Skid to Stylus Pitch
Actual Height
H1 H2 Apparent Height
Measurement Datums
Effect of Skid to Stylus Pitch
Resultant Profile P-V = 0µm
P-V = 10µm
Measurement Datums
Independent Datum
Traverse Unit Datum Traverse Direction
Measurement Datums
Independent Datum
Traverse Unit Datum
Datum SkidOptical Flat
Traverse Direction
Measurement Datums
Back to Contents Page
Reproducing the Surface
Stylus Tip Geometry
2µm
Conisphere Stylus Truncated Pyramid Stylus
2µm
Traverse Direction
Reproducing the Surface
Click Here for Further Information
Stylus Tip - Effects of Tip Size & Shape
Reproducing the Surface
Stylus Tip - Flanking
Reproducing the Surface
Profile produced by Stylus
Stylus Tip
B
BA
A
Stylus Tip - Flanking Back to Contents Page
Reproducing the Surface
Terminology
Data PointsTerminology
AliasingSampling Interval
True Signal Aliasing Signal
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Terminology
Roughness, Waviness & Form
Sample Surface
Terminology
Roughness, Waviness & Form
Form
Terminology
Roughness, Waviness & Form
Waviness
Terminology
Roughness, Waviness & Form
Roughness
Back to Contents Page
Filters
Terminology
Filtering-Separates Roughness and Waviness
Surface Interaction
Filtering Using Graphical TechniquesSampling Length
Filters
Filters
Form
Sample
Cut-off
Ra,Rq,Rz etc...Roughness Filter
Filters
Form
Sample
Cut-off
Wa,Wq,Wz etc...Waviness Filter
Electronic & Digital Filter Types
• ISO 2CR Filter• 2CR PC•Gaussian
Filters
ISO 2CR Filter
ISO 2CR Filtered Profile
Filters
Unfiltered Profile
Click Here for Further Information
ISO 2CR Filter Effect
Modified Profile Relative
to Filtered Mean Line
Filters
Mean Line Established By Filter
2CR PC Filter2CR PC Filtered Profile
Filters
Unfiltered Profile
ISO 2CR PC Filter
Modified Profile Relative
to Filtered Mean Line
Filters
Mean Line Established By Filter
Gaussian Filter
Unfiltered Profile
Gaussian Filtered Profile
Filters
Gaussian Filter
Profile Filter
Sampling Length
X
Z
Unfiltered Profile
Mean LineCut-off
Filters
Click Here for Further Information
The Effects of Filtering
Unfiltered Profile
Waviness Amplitude = 100µm
Roughness Wavelength = 0.25 mm
Waviness Wavelength = 8.0 mm
Roughness Amplitude = 20µm
Filters
The Effects of 2CR Roughness Filter
8.0 mm Cut-off filter
Waviness Amplitude = 75µm
Roughness Wavelength = 0.25 mm
Waviness Wavelength = 8.0 mm
Roughness Amplitude = 20µm
Filters
2.5 mm Cut-off filter
Waviness Amplitude = 24µm
Roughness Wavelength = 0.25 mm
Waviness Wavelength = 8.0 mm
Roughness Amplitude = 20µm
Filters
The Effects of 2CR Roughness Filter
0.8 mm Cut-off filter
Waviness Amplitude = 2µm
Waviness Wavelength = 8.0 mm
Roughness Amplitude = 20µm Roughness Wavelength
= 0.25 mm
Filters
The Effects of 2CR Roughness Filter
0.25 mm Cut-off filter
Waviness Amplitude = 0µm
Roughness Amplitude = 15µm Roughness Wavelength
= 0.25 mm
Filters
The Effects of 2CR Roughness Filter
0.08 mm Cut-off filter
Waviness Amplitude = 0µmRoughness Amplitude
= 4µm Roughness Wavelength = 0.25 mm
Filters
The Effects of 2CR Roughness Filter
Relationship of Sampling, Assessment & Traverse Length (ISO 2CR)
Sampling Length (Cut-off)
Assessment (Evaluation) Length
Traverse Length
Filters
Run-up Over travel
Filter Types
• ISO 2CR- 1st 2 Cut-offs discarded• 2CR PC- 1st & Last Cut-offs discarded•Gaussian- Half 1st & Half Last Cut-off Discarded
Filters
Cut-off Selection
0.8mm Sampling Length (Cut-off)
Filters
Cut-off Selection
Filters
0.25mm Sampling Length (Cut-off)
Choosing the Correct Cut-off Value
1.25 mm
Traverse Direction
Filters
Cut-off Selection Unless otherwise indicated on a drawingthe table above should be used to
determine the cut-off
Filters
Bandwidth=Ratio of Lc/Ls
Ls
Filters
Back to Contents Page
Lc
Parameters
Parameters
Analysis Types
•Roughness - Prefix R•Waviness - Prefix W•Primary - Prefix P
Parameters
Parameter Types
•Amplitude Parameters defined from Z co-ordinates
Parameters
• Amplitude Parameters defined from Z co-ordinates• Spacing Parameters defined from X co-ordinates
Parameter Types
Parameters
• Amplitude Parameters defined from Z co-ordinates• Spacing Parameters defined from X co-ordinates• Hybrid Parameters X & Z co-ordinates
Parameter Types
Parameters
Amplitude Parameters - Ra Ra
Parameters
Amplitude Parameters - Limitations of Ra Ra
Ra
Ra
Ra
Parameters
Amplitude Parameters Rq (RMS) lr=Sampling Length
Parameters
Amplitude Parameters Rt
ln=Assessment Length lr=Sampling Length
Parameters
Amplitude Parameters Rp Sampling Length
Parameters
Amplitude Parameters Rv Sampling Length
Parameters
Amplitude Parameters Rz
Rz1
Rz2
Rz3 Rz4 Rz5
Rz = Maximum peak to valley in each sample length divided by n sampling lengths
Parameters
Amplitude Parameters Rz1max, Rp1max & Rv1max
Rz1max
Rp1max
Rv1max
Parameters
Spacing Parameters HSC (High Spot Count) lr=Sampling Length (Cut-off) ln=Assessment
Length
A=Slice level B= Mean Line
Parameters
Spacing Parameters HSC (High Spot Count)
Tall narrow peaks Tall narrow peaks tend to work hardentend to work harden
Hardened peaks will eventually Hardened peaks will eventually breakbreakoff and the surface will breakdownoff and the surface will breakdown
Parameters
Spacing Parameters Rpc (Peak Count)
A=Selectable Bandwidth B= Mean Line
Parameters
Spacing Parameters Rpc (Peak Count)
Orange Peel Effect Due to Peaks on Sheet Steel Base Peel Effect Due to Peaks on Sheet Steel Base SurfaceSurface
Base Sheet Steel
Painted Surface
Parameters
Spacing Parameters Sm (Mean Spacing) lr=Sampling Length (Cut-off)
Mean Line
Parameters
Hybrid Parameters- Rdq (Pdq, Wdq) (Rms Slope)
θ
θθ θ
Parameters
Hybrid Parameters- Rdq (Pdq, Wdq) (Rms Slope)
Effects of Surface Slopes on vibration & noise
No Vibration/Quiet Low Frequency Rumble
High Frequency Scream
Parameters
With low surface slopes more light is reflected into the eye and hence has a good appearance
With high surface slopes less light is reflected into the eye and hence has a poor appearance
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Hybrid Parameters- Rdq (Pdq, Wdq) (Rms Slope)
Bearing Area (Material Ratio)
Bearing Area (Material Ratio)
Hybrid Parameters - Rmr
Upper surface defines run-in characteristics
Valleys define lubrication characteristics
Body of surface defines wear/life characteristics
Hybrid Parameters - Rmr
Lapping Plate
Bearing Line
ln=Assessment Length
Rmr= a+b+c+d+e x100 ln
Bearing Area (Material Ratio)
Material Ratio Curve (Rmr) 0 100 %tp(%)
Level p Tp (%) at level p
Bearing Area (Material Ratio)
0 100 %tp(%)
Level p Tp (%) at level p
Material Ratio Curve (Rmr)
Bearing Area (Material Ratio)
Material Ratio Curve (Rmr) 0
Level p Tp (%) at level p
tp(%) 100 %
Bearing Area (Material Ratio)
Amplitude Distribution Curve 0
Level p
Number of Peaks
Bearing Area (Material Ratio)
Click Here for Further Information
Associated MR Curve Parameters-Rsk (Skew)
Surface with Random Amplitude Distribution- Zero SkewSurface with Random Amplitude
Distribution- Zero Skew
Bearing Area (Material Ratio)
Associated MR Curve Parameters-Rsk (Skew)
Surface with dominant peaks-Positive Skew
Bearing Area (Material Ratio)
Associated MR Curve Parameters-Rsk (Skew)
Surface with dominant valleys-negative Skew
Bearing Area (Material Ratio)
Associated MR Curve Parameters-Rku(Kurtosis)
Rku<3
Rku=3
Rku>3
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Bearing Area (Material Ratio)
The Rk Parameter
Parameters
Rk Parameter
Surface Interaction
Material Ratio Curve (Rmr) 0 100 %tp(%)
Bearing Area (Material Ratio)
Material Ratio curveTilted Profile
Parameters
Mean Line
Unfiltered Real Profile
Rk Parameter
Parameters
Mean Line
Unfiltered Real Profile after valley suppression
Valleys removed & kept in memory
Rk Parameter
Parameters
Final Filtered Roughness Profile
Rk Parameter
Parameters
100 %0 tp(%)
40 %
Rdc
Rk Parameter
Parameters
100 %0 tp(%)
Rdc
40 %
AB
D
E
F
C
Rk Parameter
Parameters
C
100 %0 tp(%)
Rdc
40 %
AB
D
E
F
Rk
D1
Mr2Mr1
Rk Parameter
Parameters
tp(%)
C
100 %0
Rdc
40 %
AB
D
E
F
Rk
D1
Mr2Mr1
Area 1
ECRpk
Area 2
E
D
Rvk
Rk Parameter
Parameters
100 %0 tp(%)
40 %
Rk
Mr2Mr1
Rpk
Rvk
Rk Parameter
Parameters
Rk Associated Parameters
• Rk-Core Roughness Depth• Rpk-Reduced Peak Height• Rvk-Reduced Valley Depth
• Mr1-Material Component Relative to Peaks• Mr2-Material Component Relative to Valleys• A1-Material Filled Profile Peak Area• A2-Lubricant Filled Profile Valley Area
Back to Contents Page
Form Measurement
Least Squares Line
Form Measurement
Form Measurement
Straightness (LS Line)
Form Measurement
Straightness (MZ Line)
Form Measurement
Least Squares Arc
R=Calculated LS Radius r-r=LS Arc
r r
Form Measurement
Least Squares Arc - Radius Measurement
t=34.501656mm
r=110mm
l=80mm
l= Measurement Length/2
t= Chordal Heightr= Least Squares Radius
r-t
Form Measurement
Least Squares Arc - Radius Measurement
t=1.833462mm
r=110mm
l=20mm
l= Measurement Length/2
t= Chordal Heightr= Least Squares Radius
r-t
Form Measurement
Least Squares Arc - Radius Measurement
t=1.833962mm
r=109.9705mm
l=20mm
l= Measurement Length/2
t= Chordal Heightr= Least Squares Radius
Back to Contents Page
Calibration Methods
Calibration Methods
Ball Standard
Traverse Direction
Software Corrections
Arcuate Errors
dZ
dX
Traverse Direction
Software Corrections
Stylus Tip Errors
Traverse Direction
Path of Stylus Tip Centre
Calibration Methods
Ra & Rz Roughness Standards
Calibration Methods
Ra & Rz Roughness Standards
Calibration Methods Traverse Direction
2.5µm Step Height
3 Line (Step Height) Standard
Calibration Methods
3 Line (Step Height) Standard
A=Mean Line
B=Calibration Height
Calibration Methods
3 Line (Step Height) Standard
A=Level Surface
B=Pt Value
C=Unlevelled Surface
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Click Here for Further Information
Conics & Aspherics
Conics and Aspherics
Conic Sections
Conic Constants
Ellipse: K< 0 Sphere: K= 0 Oblate Ellipse: K>0
Conics and Aspherics
Z2 + X2 = 1
R22 R12 Z2 + X2 = 1
R2 R2 Z2 + X2 = 1
R22 R12
Conic Constants
Hyperbola: K< -1 Parabola: K= -1
Conics and Aspherics
Z2 + X2 = 1
R22 R12
Z = (Ax)2
What is an Aspheric?
Conventional Spherical Lens
Conics and Aspherics
What is an Aspheric?
Aspheric Lens
Conics and Aspherics
Reasons for using an Aspheric
• Reduces Spherical Aberration• Ability to Produce Vari-focal Lenses • Reduction in Lens Size and Weight • Greater Design Freedom
Conics and Aspherics
How is an Asphere constructed?
Basic Conic Section (Sphere)
Z Axis
X Axis
Conics and Aspherics
Z2 + X2 = 1R2 R2
How is an Asphere constructed?
Aspheric Polynomial Curve
Z=a8|x|8
Basic Conic Section (Sphere)
Z Axis
X Axis
Conics and Aspherics
How is an Asphere constructed?
Aspheric Profile
Aspheric Polynomial Curve
Basic Conic Section (Sphere)
Z Axis
X Axis A
B C
Conics and Aspherics
How is an Asphere constructed?
Aspheric Profile
Aspheric Polynomial Curve
Basic Conic Section (Sphere)
Z Axis
X Axis
A
B
C Aspheric Profile
Aspheric Polynomial Curves
Basic Conic Section
Conics and Aspherics
Standard Equation for An Aspheric Surface
cx2+a1|x| +a2| x|2 + a3| x|3 … +a20 | x|20Z(x)=
1+ 1-(K+1) c2x2
Where: X is the Radial distance from the Aspheric Axis Z is the corresponding vertical distance
a is the indexed Polynomial Coefficient C is the reciprocal of the Base Radius K is the Conic Constant of the Surface
Conics and Aspherics
Base Radius of Curvature
Conics and Aspherics
How Do We Measure an Aspheric Surface?
Optical Flat
Aspheric Axis
Conics and Aspherics
How Do We Analyse an Aspheric Surface?
Aspheric DataRadius=40.0mm
K= -1A4= 5.3188e-007A6=5.5231e-009A8=-1.6774e-011A10=-6.3352e-
014
Conics and Aspherics
Aspheric Form FitX Axis
Z Axis
AB
Aspheric Axis
Conics and Aspherics
Residual Error after Aspheric Form Removal
+Z Axis
-Z Axis
-X Axis
+X Axis
A
Aspheric Axis
Aspheric Axis
Conics and Aspherics
How Do We Analyse an Aspheric Surface?
Conics and Aspherics
Aspheric Parameters
Conics and Aspherics
Aspherics-Further Analysis
Convex Component-Concave Residual Form Error-Increase Base Radius
Conics and Aspherics
Convex Component-Convex Residual Form Error-Decrease Base Radius
Conics and Aspherics
Aspherics-Further Analysis
Smallest Rt Value Achieved-True Shape & Base Radius
Conics and Aspherics
Back to Contents PageAspherics-Further Analysis
3D (Areal) Measurement
3D Measurement
Advantages of 3D (Areal) over 2D
• Good Visualisation of the Surface• More Statistically Stable
• Better at Detecting & Analysing Defects • Many Methods of Representing the Data
3D Measurement
Disadvantages of 3D (Areal)
• Longer measurement cycles• Measurement Produces Large Data Files• Mainly Restricted to R & D • Sometimes Visually Subjective
3D Measurement
Contact Measurement Method
Y Axis Incremental MovementTraverse Direction
3D Measurement
Non-Contact Measurement Method
Y Axis Incremental Movement
Measurement Axis (X)
Laser CCD Detector
3D Measurement
Critical Dimensions for 3D Measurement
Profile 1
Profile 2
Z1
Z2
ΔXΔZ
ΔY
3D Measurement
Data Analysis
3D Measurement
Levelling the Data
3D Measurement
Form Removal Cylinder Liner- No Form Removed Cylinder Liner- Form Removed
3D Measurement
Viewing 3D Data Meshed Axonometric View
3D Measurement
Viewing 3D Data Photo Simulation View
Pseudo- Colour View
3D Measurement
Viewing 3D Data Continuous Axonometric View
Contour View
3D Measurement
3D Filtering
0.8mm
0.8mm
• 0.8mm Gaussian Filter
• ½ Cut-off Lost Top, Bottom Left & Right
Sampling Area
3D Measurement
3D Parameter Types
• Amplitude• Spatial• Hybrid • Functional
3D Measurement
3D Amplitude Parameters- Prefix: S
Sa =arithmetic mean of the deviations from the mean plane
Sq =RMS of the mean of the deviations from the mean plane
St =total peak to valley over the sample area
Sp =height of the highest peak to mean plane
Sv =depth of the deepest valley to mean plane
3D Measurement
3D Spatial Parameters
SPc =peak count between two selectable planes
Sds =density of summits contained in a sampling area
Std =texture direction of the surface
3D Measurement
3D Hybrid Parameters
SΔq =RMS slope of the surface
Ssc =mean summit curvature of the surface
Sdr =developed interfacial area ratio of the surface
3D Measurement
3D Functional Parameters
Stp=surface bearing area ratio
Sbi =surface bearing index
Sci =core fluid retention index
Svi =valley fluid retention index
3D Measurement
Volume/Defect Analysis
3D Measurement
Step Height Analysis
Drawing Indication
Drawing Indication
Conventional Surface Texture Symbol
Graphical Symbols for Surface Texture
6.8
Requirement for Surface Texture
1
Requirement for Surface Texture, Material Removal Required
2
Requirement for Surface Texture, Material Removal Not Permitted
3
Graphical Symbols for Surface Texture
Drawing Indication
Graphical Symbols for Surface Texture
Drawing Indication
(d) (e) 3
(c) Turned(a) 0.0025-0.8/Rz
6.8(b) 0.0025-0.8/Ra 2.2
Click Here for Further Information
Graphical Symbols for Surface Texture
Drawing Indication Fe/Ni 15p cr 0.0025-0.8/Rz 6.8
Drawing Indication
Bi-Lateral Tolerancing
Graphical Symbols for Surface Texture
U Ra 0.9L Ra 0.3
Drawing Indication
The 16% Rule (Default Rule)
• No more than 16% of the measured values for an upper limit should exceed the specified value
• No more than 16% of the measured values for a lower limit should be less than the specified value
Drawing Indication
The MAX Rule
RzMAX 0.9
End
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