Power Cylinder Metrology
Stanley Weng
Cylinder Systems Development
• Surface Finish
Outline
– Measurement Instruments
» skidless
» skidded
– Surface Finish components
» Cutoff
» Filters
– Parameters of Surface Finish
– Typical Surface Finish for Cylinder Liner
• Roundness
Outline
– Measurement Instrument
– Harmonic Analysis
• Filtering
– Roundness Analysis
• Reference Circle
• Roundness Parameters
• Cylindricity
– Definition of Cylindricity
– Instrument
– Cylindricity Analysis
Functional Considerations
– Cylinder Liners / Bores
• surface finish, bore distortion
• roundness
– Piston Rings
• circumferential waviness, face surface finish, etc.
– Piston
• circumferential waviness, groove surface finish, etc.
Typical Surfaces
•
•
•
•
•
Cast
Turned / Bored / Milled
Ground / Honed
Plateau Honed
lapped
Typical Roughness Profiles
• Patterned (Turned / Bored / Milled)
• Random (Cast, Ground, Honed, EDM)
• Stratified (Plateau Honed)
Patterned (Turned) Profile
Random (Ground) Profile
Stratified (Plateau Honed) Profile
Typical Instrumentation for
Surface Finish
•
•
•
•
•
•
Stylus Methods (CTC)
Light Scattering
Optical Focusing (Wyco)
Pneumatic
Area Capacitance
Ultrasonic
Stylus Based Measurement
• Skiddless Instruments
– Laboratory Applications
– Can also evaluate Form & Waviness (Wear
Analysis)
– Cost : High
• Skidded Instruments
– “Shop Floor” Applications
– Can not evaluate Form & Waviness and Wear
– Cost : Low
Skiddless Measurement
Skidded Measurement
Skidded Instruments
• Advantages
• Relatively Inexpensive
• Easy setup
• Vibration Isolation
• Disadvantages
• Cannot “see” waviness
• Significant errors over peaks.
Error Caused by Skid
Error Caused by Skid
Aspect Ratio
• Vertical and Horizontal Magnifications are
typically not the same in plotted profiles.
• In other words, the aspect ratio is typically
not 1:1.
Components of a Trace
• Unfiltered Profile (P)
– Form Profile (F)
– Waviness Profile (W)
– Roughness Profile (R)
Unfiltered and
Form Profiles
Piston Ring Groove
Waviness Profile
Form removed from Ring Groove Data
Roughness Profile
Waviness and Form removed
Wavelength Regimes
Roughness
Waviness
Form
Process
Tool Nose Radius
Abrasive Size/Density
Material Properties
Chatter/Vibration
Stiffness
Controls
Guideway Straightness
Alignment
Thermal Effects
Product
Friction
Fluid Retention
Localized Contact
Load Carrying
Conformability or
Bending
(of mating surface)
Wavelength (l)
“Cutoff”
• The Roughness Cutoff (lc) indicates the
wavelength which separates roughness from
waviness.
• The Waviness cutoff (lw) separates
waviness from form.
– Though very functional, this is not often used.
– Most instruments do not accommodate lw.
Cutoff Selection
Unfiltered and Waviness (8.0 mm cutoff)
15
10
µm
5
0
-5
-10
-15
0
5
10
15
mm
20
25
30
20
25
30
Roughness (8.0 mm cutoff)
15
10
µm
5
0
-5
-10
-15
0
5
10
15
mm
lc: 8.0 mm Wt = 3.5 µm Ra = 2.16 µm
Cutoff Selection
Unfiltered and Waviness (2.5 mm cutoff)
15
10
µm
5
0
-5
-10
-15
0
5
10
15
mm
20
25
30
20
25
30
Roughness (2.5 mm cutoff)
15
10
µm
5
0
-5
-10
-15
0
5
10
15
mm
lc: 2.5 mm Wt = 10.4 µm Ra = 0.77 µm
Cutoff Selection
Unfiltered and Waviness (0.8 mm cutoff)
15
10
µm
5
0
-5
-10
-15
0
5
10
15
mm
20
25
30
20
25
30
Roughness (0.8 mm cutoff)
15
10
µm
5
0
-5
-10
-15
0
5
10
15
mm
lc: 0.8 mm Wt = 14.2 µm Ra = 0.42 µm
Filtering for Roughness
• Profile data is filtered to remove waviness
and form error prior to roughness
assessment.
• Two aspects of the filter must be defined :
– Filter type
– Filter cutoff wavelength
Fourier Analysis
• Can be used to determine predominant
wavelengths in a data set.
• Fast Fourier Transforms (FFT’s) have been
historically used in the analysis of
roundness data.
– The same techniques can be useful in roughness
analysis.
Cutoff Selection via
Fourier Analysis
Unfiltered Profile
2
µm
1
0
-1
-2
0
1
2
3
4
mm
5
6
7
8
0.8 mm Waviness
0.8 mm Waviness Profile
2
µm
1
0
-1
-2
0
1
2
3
4
5
6
7
8
mm
0.8 mm Waviness Transmission
0.5
Amplitude (µm)
0.4
0.3
0.2
0.1
0
0.01
0.1
1
Wavelength (m m )
10
0.25 mm Waviness
0.25 mm Waviness Profile
2
µm
1
0
-1
-2
0
1
2
3
4
5
6
7
8
mm
0.25 mm Waviness Transmission
0.5
Amplitude (µm)
0.4
0.3
0.2
0.1
0
0.01
0.1
1
Wavelength (m m )
10
0.08 mm Waviness
0.08 mm Waviness Profile
2
µm
1
0
-1
-2
0
1
2
3
4
5
6
7
8
mm
0.08 mm Waviness Transmission
0.5
Amplitude (µm)
0.4
0.3
0.2
0.1
0
0.01
0.1
1
Wavelength (m m )
10
Filter Types
•
•
•
•
•
2CR : Electronic Filters
PC - 2CR : Phase Corrected 2CR
Gaussian : Most recent filter.
M1 : Triangular approximation to Gaussian.
Rk (Valley Suppression) : Used for
stratified (plateaued) surfaces.
2CR Filters
• Resistor-capacitor network used in original
instruments.
• 75% transmission at cutoff
– phase lagging.
• Can be implemented in software.
• Some instruments refer to as (ISO).
– Based on older ISO standards.
2CR Waviness Circuit
2CR - Phase Corrected (PC)
• A digital (software) filter which reproduces
the transmission of the 2CR filter without
phase distortion.
• First introduced by Rank Taylor Hobson.
Known as the ‘PC’ filter.
• 75% transmission at the cutoff.
Gaussian Filters
• Named based on Gaussian weighting
function used to determine waviness.
• Recently introduced in ISO.
• ‘Symmetric’ filter in that waviness can be
directly subtracted from form to get
roughness.
Gaussian Filters
• 50% transmission at the cutoff.
• ‘Sharper’ in the frequency domain than
2CR.
• Can be computationally expensive.
– Various ‘fast’ implementations are in use. The
most common being the triangle or ‘M1’ filter.
Gaussian vs. 2CR Filters
2CR
Gaussian
Gaussian vs. 2CR Filters
Gaussian & 2CR Roughness Filters (0.8 mm)
Transmission
1
0.8
2CR
0.6
Gaussian
0.4
0.2
0
0.01
0.1
1
Wavelength (m m )
10
Valley Suppression Filtering
(DIN 4776)
• Filtering methodology used to remove
“valley influences” from waviness profile.
• Reduces “push-ups” on sides of valleys.
Valley Suppression Filtering
(DIN 4776)
• Data is filtered and waviness profile is used
to “clip” the valleys.
Valley Suppression Filtering
(DIN 4776)
• Resulting (clipped) profile is filtered and
valleys are re-inserted.
Stylus Tip Radius Implications
Band Pass Roughness
0.8 mm (300:1)
Transmission
Band Pass Roughness (0.8 mm - 300:1)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.0001
2 µm tip
lc
ls
0.001
0.01
0.1
Wavelength (m m )
1
10
Sampling Implications Aliasing
300:1 Bandwidth Implications
• 0.8 mm cutoff (lc )
– 2.5 µm short wavelength cutoff (ls)
– 2.0 µm stylus tip radius
– 0.5 µm data point spacing
300:1 Bandwidth Implications
• 2.5 mm cutoff (lc )
– 8.0 µm short wavelength cutoff (ls)
– 5.0 µm stylus tip radius
– 1.5 µm data point spacing
Parameterizing
the Profile
Parameterizing
the Profile
• Currently there are nearly 300 parameters
that have been defined/published for the
analysis of surface profiles.
• For the most part, these parameters can be
grouped into 4 major categories...
Surface Texture Parameters
• Averaging / Statistical
– Ra, Rq, Rsk
• Peak to Valley
– Rp, Rv, Rt, Rpm, Rtm (RzDIN)
Parameters (cont.)
• Bearing Ratio
– tp, Rk, Rpk, Rvk, Mr1, Mr2
– Rpq, Rvq, Rmq (Cummins/ISO)
• Spacing / Slope
– Sm, Delq
Average Roughness
(Ra)
• The average distance from an individual
data point to the mean line.
Zi
RMS Roughness
(Rq)
• The standard deviation (RMS) of
profile heights.
Zi
Rq  
Skewness
(Rsk)
Peak to Valley Parameters
Rp
Rt
Rv
Average Peak to Valley
Parameters
• Rpm : Average Peak Height
• Rvm : Average Valley Depth
• Rtm (RzDIN) : Average Peak to Valley
Bearing Ratio Curve
• A graphical representation of the amount (%) material “cut”
at a given depth.
0
tp%
100%
Cummins’ Probability Analysis
• Rpq : Plateau RMS Roughness.
• Rvq : Valley RMS Roughness.
• Rmq : Transition Bearing Ratio
Rpq
Rvq
Rmq (%)
Typical Waviness Parameters
• Wt : Rt equivalent for waviness profile
• Wa : Ra equivalent for waviness profile
• Wc : Average peak to valley, using all
waviness peaks and all valleys.
• Waviness profile has relatively few peaks and valleys
US Standard Symbology
(ASME Y36 - 1996)
b
c/f
a
a
b
c
d
e
f
maximum Ra (µm)
e
production method
roughness cutoff, lc, (mm)
direction of lay
minimum material removal (mm)
parameter other than Ra (µm)
d
Cylinder Liner Plateau Surface
Finish Parameters
• Rpq
– Plateau RMS Roughness - Oil Consumption and break-in Related
• Rvq
– Valley RMS Roughness - Durability and scuffing resistance Related
(Wear and Scuffing)
• Rmq
– Percent bearing Area at which the plateau and valley probability lines
intersect.
• Rz
– Maximum peak-to-valley height in the sampling length
• Vc
– Number of valleys at a prescribed depth relative to the roughness profile
mean line
Wyko Images of the Tested Bore
Topographies
series
fine plateau
laser pockets spiral glide
series rough
Stylus Traces of the Tested
Bore Topographies
series
fine plateau
laser
pockets
5 µm
5 mm
spiral glide
series
rough
Traces From a Typical
Cylinder Liner
Piston Ring Groove Analysis
(2.5 mm)
Raw Data & Form Error (2.5 mm)
2
1.5
1
µm
0.5
0
-0.5
-1
-1.5
-2
0
1
2
3
mm
4
5
Piston Ring Groove Analysis
(0.25 - 2.5 mm)
Form Removed & Band Pass Waviness (2.5 - 0.25 mm)
2
1.5
1
µm
0.5
0
-0.5
-1
-1.5
-2
0
1
2
3
mm
4
5
Piston Ring Groove Analysis
Raw Data & Band Pass Waviness (0.25 - 2.5 mm)
0.7
Amplitude (µm)
0.6
0.5
0.4
0.3
0.2
0.1
0
0.01
0.1
1
Wavelength (m m )
10
Piston Pin Bore Surface Finish
Analysis
Piston Pin Bore
8
6
µm
4
2
0
-2
-4
0
5
10
15
20
mm
25
30
Piston Pin Bore Analysis
Magn
Filter
Corporate
Metrology
Roundness
Why Measure Roundness?
•
•
•
•
•
Fit
Sliding
Sealing
Rolling
Lubrication
Magn
Filter
Corporate
Metrology
Measurement Approaches
•
•
•
•
•
Two Point Diameters
V-Block
Run-out over Centers
Polar Instruments
Coordinate Measuring Machines
Roundness Instrument
Work
Piece
Probe
Column
Spindle
Work Table
Roundness Instrument
Components
•
•
•
•
•
•
Base
Tilting and Centering Table
Spindle
Column
Probe / Transducer
Stylus / Ball
Roundness Instrument
Schematic Diagram of a Roundness Instrument
Surface
Stylus
Tip
Traced
Profile
Transducer
Drive
Spindle
Bearing
External
Disturbances
Rotary
Encoder
Reference
Profile
Amplifier
ADC
Total
Profile
Filter
Roundness
Profile
Analysis
Tip Radius Effects
• Mechanical Filtering
Tip Radius Effects
• Convolution over Surface Features
Stylus
Traced Profile
Surface
Harmonic Analysis
• Any Roundness Profile can be expressed as a combination
of different undulations per revolutions (harmonics) of
various amplitudes.
• Fourier Transform is used to decompose roundness profile
into different harmonics.
Harmonic Analysis
5 UPR
2 UPR
+
=
Total Roundness
Profile
12 UPR
18 UPR
Harmonic Analysis
• Why ?
– To identify lobing characteristics.
– To identify presence of structured repetitive noise due to
instrument or environment.
– To do chatter analysis.
Filters
•
•
•
•
2CR
Phase Corrected
Gaussian
Triangular Approximation
Filtering
Why Filter ?
– To isolate the undulations (UPRs) of interest.
– To smooth the data.
– The filter value depends on the function of the feature.
Effects of Filtering
Filter : 1-500
Roundness : 3.1µm
Filter : 1-50
Roundness : 2.1µm
Filter : 1-150
Roundness : 2.8µm
Filter : 1-15
Roundness : 1.7µm
Roundness Analysis
• The roundness analysis requires establishment of a center
based on a reference circle. The reference circle can be
specified according to
–
–
–
–
Least Square Method
Minimum Zone Method
Maximum Inscribed Circle Method
Minimum Circumscribed Circle Method
Reference Circles
r
R
R
r
OOR = R - r
Least Square Circle
(LSC)
Minimum Radial Zone
(MRZ, MRS)
Reference Circles
R
R
r
r
OOR = R - r
Maximum
Inscribed Circle
(MIC)
Minimum
Circumscribed Circle
(MCC)
Roundness Parameters
• Total Roundness (Ot) :
– It is defined as the difference between the radii of two concentric
circles which envelopes the roundness profile. The circles are
constructed from the center established by the reference circle.
This is a peak to valley measurement.
It is defined for all reference circles.
Roundness Parameters
• Maximum Peak (Op) :
– It is the distance of maximum peak from the Least Square Circle.
• Maximum Valley (Ov) :
– It is the distance of deepest valley from the Least Square Circle.
These parameters are defined for only LSC.
Roundness Parameters
Op
Ov
Ot
Roundness Parameters
• Eccentricity (E & ):
– It is the position of the center of the profile relative to some datum
point. It is expressed in terms of a magnitude (E) and an angle (
• Concentricity (C):
– It is the diameter of the circle with center at the datum point and
passing through the center of the profile. It is twice the magnitude
of eccentricity.
Roundness Parameters
Roundness Parameters
• Runout ( ) :
90°
– It is a measure of total distance a
indicator placed on the surface
will travel when the part is
rotated about the datum axis.
Runout
Profile
Center
0°
180°
Datum Point
270°
Roundness Parameters
• dr/d
– It is the maximum deviation
from peak to valley in any
window of given angle  in a
roundness profile
d
dr
Typical Ring Cir-cumferential
Waviness
Print Specification
0.002
MRZ
50
0.01
Tip Radius
Filter
Reference Circle
Roundness Specification
GD&T Symbol for Roundness
Note : There is no datum required to inspect
roundness.
Cylindricity
• It is defined as the radial separation of 2
co-axial cylinders enveloping the total
surface such that their radial difference
is minimum.
• GD&T Symbol -
Cylindricity
• It combines the characteristics of axial form, radial form
and overall variation of size.
• Thus, cylindricity is a composite of :
Radial Form Error
Axial Form Error
Size (Taper) Error
Cylindricity
• It can be analyzed using reference cylinder
based on similar methods as roundness :
–
–
–
–
Least Square Method
Minimum Zone Method
Maximum Inscribed Cylinder Method
Minimum Circumscribed Cylinder Method
Cylindricity
Harmonics
Roundness at different Z
Straightness