Compliant polishing tools are utilized incomprehensibly as a part of vehicle and aviation businesses to clean complex surfaces and structures. The major advantages of using coated abrasive tools are that they are compliant and their geometry conforms to the surface of the workpiece. Though they have been used for finishing operations for a long time, not much work has been done to understand the effect of compliance on the distribution of forces in the contact area of such tools. Such understanding would help to reduce the trial and error operations involved and thereby reducing rework and cost. The objectives of this study are as follows: 1) Study the effect of tool (rubber pad and abrasive cloth) compliance on contact pressure distribution and material removal of commonly used compliant polishing tools 2) The tool compliance is in turn studied by conducting material characterization; along with the geometry of the workpiece, other machining parameters are the key variables in this study 3) Design and analyze an active complaint finishing tool

1. Seah Kheng Wee, MAE
Presented By
Komanduri Raghava Kumar
School of Mechanical & Aerospace Engineering
5 May, 2017
Study of Pressure Distribution in
Compliant Polishing Tools
1

2. • Introduction
• Project Objective and Scope
• Project Overview
• Literature Review Summary
• Overall Methodology
• Results and Discussions
• Conclusion
• Scope for future work
• Learning Outcomes
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3. • Polishing is usually carried out in the final stage of production
• Manual polishing takes up to 37-50% of total production time
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4. • Coated abrasive tools are used extensively in manufacturing industry
• Tools are replaceable and have conformable geometry
• A backing pad provides additional stiffness
• Not much work has been done to understand the effect of compliance on the
pressures distribution in the contact area of coated abrasive tools.
• An appreciation of the development of pressure distributions using FEM can
help to predict the surface profiles produced after polishing.
4
Controllable compliance
Well controlled surface finishImproved performance

5. Project Objective
•Study the effect of tool (rubber pad and abrasive cloth) compliance on contact pressure distribution
•Conduct material characterization to study the tool compliance
•Design and analyze an active complaint finishing tool
Scope
•This project only deals with the circular form of abrasive discs
•The effect of tool compliance on contact pressure distribution is investigated only under static
conditions
•The finite element analysis only deals with the structural component
•Abrasive grains are not modelled because of the inherent complexity
•The fully developed tool integrated with the robot will be able to provide fine polishing for a wide
range of mechanical components
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6. 6
Tool Simulation
The newly designed active tool is simulated in ABAQUS to analyze the load and pressure
distribution. These results are compared with the experimental results for validation
purposes.
Laboratory Experiments
Several tests like tensile testing, removal of grains, measurements of grains, etc. were carried
out to study material properties. Following this, pressure distribution tests were carried out.
Literature Review
A detailed study on the mechanics of polishing, types of abrasives, current active compliant
tools, difference between hard and compliant tools, weft and warp yarn in a woven fabric, etc.

7. The Polishing Process
•Polishing is the mechanism that gives the final surface characteristics like roughness, geometry,
tolerances and integrity.
•Some advantages of polishing include:
– Gives a natural appearance with a high gloss and sheen
– Produces a relatively durable finish
– Never requires stripping
– Can be applied with a standard low speed weighted floor machine.
•Different types of polishing
Mechanics of Abrasion
Source: University of Toledo, The Polishing Process, Ohio: University of Toledo, 2017 7

8. Types of Abrasives
•Bonded Abrasives
•Coated Abrasives
•Non-woven Abrasives
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Source: Federation of European Producers of Abrasives, "Bonded Abrasives,"
Federation of European Producers of Abrasives.
Source: Federation of European Producers of Abrasives, "Coated Abrasives,"
Federation of European Producers of Abrasives.

9. Current Active Compliant Tools
PushCorp Inc supplies compliance force devices on which the clients can mount their own devices.
These gadgets are pneumatic-headed to provide the axial compliance, like ATI's AC instrument.
Hard and Compliant Tools
9
Hard Tools Compliant Tools
A hard tool, like a grinding wheel, is very
stiff and does not conform to the free-form
surface being polished.
A compliant tool can fit the surface profile
and impose favorable pressure (or force) on
the polishing region of the surface.
Currently, a constant force is maintained
using force control in the robot, and
complex components are polished based on
this technique. But constant force will not
assure constant pressure thereby leading to
uneven material removal.
Using the tool with precise compliance is
required to produce uniform material
removal thereby increasing dimensional
accuracy and reducing rework which would
lead to more time and cost.

10. 10
Source: L. Zhang (2001)

11. Importance of Compliance in Polishing
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12. Pressure Distribution due to Compliance
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13. Tensile Testing
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14. Warp and Weft Yarn
Mechanical Modelling of Composites
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15. Cloth Backing Weights
Hyper-elastic Material Models
•Odgens Model
•Polynomial Model
•Yeoh Model
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16. • The effect of tool compliance such as ‘Hard’ and ‘Soft’ on contact pressure
distribution for rubber pad was studied to a very limited extent earlier.
• This project not only aims to provide fine polishing for a wide range of mechanical
components but also explores the scope for future work in this field where simulations
can be fine-tuned to predict the contact pressure more precisely.
• This project primarily focuses on developing the material properties of composite
materials like elastic modulus and poissons ratio which would not only give more
accurate simulation results but also broaden the scope of this project to the usage of
several types of abrasive materials for polishing.
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17. Tensile Testing
Samples of Y grade and T grade (samples in the X direction and samples in the Y
direction) measuring 250mm by 25mm and samples of 3M120 and 3M60 measuring
70mm by 20mm were cut for tensile testing.
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18. 18

19. Abrasive Material Study
The tensile specimens were chemically treated to understand the properties of the
underlying material. Also, the composition of the different fibers in the fabric (called blend
percentage) was found out through certain tests.
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20. Additionally, the pattern of the fibers in the backing material was examined.
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Y T
3M120 3M60

21. To extract only the cloth out of the abrasive roll, the abrasive roll was boiled in 5-8%
solution of caustic soda for 15-20 mins. As time passed, the chemicals and grains
disintegrated giving the bare cloth.
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22. Pressure Distribution Study
The ABAQUS assembly was modelled in such a way that the work coupon was fixed. One
half of the tool head was modelled in an incline of 15 degrees with the work coupon. The
abrasive disc which was modelled as a continuum shell element can be seen attached to the
rubber pad. Reference point 2 can be seen at the center of the shaft where a downward
vertical force of 10N is applied.
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23. The rubber pads were pressed against the titanium work coupons, and the load
displacement curves were captured. The INSTRON machine was programmed in such a
way that the compression would take place till the force reaches 10N. Once the force
reaches 10N, the disc is held against the coupon for 5 seconds. Following this, the disc is
retracted back till the force drops to 0N.
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24. Once the load displacements curves were obtained, the material properties of the hard and
soft rubber pad were determined by using a trial and error method. The hard pad has a
shore hardness of 80+, and the soft pad has a shore hardness of 40+. Thus, the following
figure was used as a reference to determine the material properties.
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25. These data points were keyed into the uniaxial stress-strain material properties in
ABAQUS, and the simulation was run. The load displacement plots obtained were
compared to experimental load displacement plots. The material properties corresponding
to the best fit simulation curve were assumed as the material properties of the hard pad
and soft pad respectively.
However, the matching load displacement plots weren’t enough to conclude the material
properties. It was important for the simulation and experimental pressure distribution
values to match as well.
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Film Type Abbreviation Pressure Range
Extremely Low Pressure 4LW 0.05-0.2 MPa
Ultra-Ultra Low Pressure LLLW 0.2-0.6 MPa
Ultra Low Pressure LLW 0.5-2.5 MPa
Low Pressure LW 2.5-10 MPa

26. 26

27. 27

28. Additional Experiments
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29. Analysis of the Active Compliant Tool Design
Three different design versions were modelled on Solidworks, and their feasibility was
studied accordingly.
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Design 1

30. 30
Design 1

31. 31
Design 1

32. 32
Design 2

33. 33
Design 3

34. Several ABAQUS simulations were done using the final tool design to study the effect of
stiffeners on the contact pressure.
•The young’s modulus of stiffener was given around E=200 MPa
•Load applied was 5N
•The max pressure for retrieved stiffeners was 0.2435 MPa compared with 0.7194 MPa
fully inserted stiffener
•Soft nitrile rubber (Shore A 45 ±5) property was used for the backing pad and tubes.
•For the stiffeners, two different properties were tried.
– HARD NITRILE RUBBER STIFFENER (Shore A 80 ± 5)
– STIFFENER WITH E= 200 MPa
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35. 35

36. Tensile Testing
It can be clearly seen that Y, T, 3M120 and 3M60 have different stresses and strains in
both directions. This phenomenon might be due to different cloth thicknesses.
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37. Abrasive Material Study
The blend percentage test was carried out whose results are as follows.
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Sample T
Sample Y

38. Following this, the fiber patterns in the obtained bare cloths were observed.
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Sample TSample Y Sample 3M60

39. The warp and weft yarn are always perpendicular to each other. It appears that it's at an
angle because of the pattern formed by the particular type of weave. In this case, the
particular type of weave is called TWILL i.e. 2 up/1 down. So the pattern formed by
weaving in the 2/1 configuration makes the yarn look like it is at an angle.
The warp direction is held under high tension during the entire weaving process and hence
the warp yarn is stronger than the weft yarn. Thus, the abrasive rolls Y and T having
different young’s moduli in X and Y directions is justified. In order to ensure that these
results obtained were accurate, tensile testing was done for several samples to ensure
repeatability of results.
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41. 41

42. 42

43. 43
Abrasive Sample Warp Direction
(Higher Stiffness)
Weft Direction
(Lower Stiffness)
Y X direction/0o
direction
Y direction/90o
direction
T X direction/0o
direction
Y direction/90o
direction
3M120 Y direction/0o
direction
X direction/90o
direction
3M60 Y direction/0o
direction
X direction/90o
direction

44. 44
Abrasive Type Area of cross-section
Y Width = 25mm, Thickness = 0.8mm, Area
= 20mm2
T Width = 25mm, Thickness = 0.5mm, Area
= 12.5mm2
3M120 Width = 20mm, Thickness = 0.9mm, Area
= 18mm2
3M60 Width = 20mm, Thickness = 1 mm, Area
= 20mm2

45. 45
Abrasive Roll E1(in MPa) E2(in MPa)
Y 1250 800
T 1100 312.5
3M120 1429 1000
3M60 2778 2500

46. The values of these six material parameters namely E1, E2, v12, G12, G13 and G23 were
keyed into ABAQUS’s composite layout manager for simulation purposes.
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Abrasive Roll G12 G13 G23
Y 370.37 370.37 296.29
T 217.14 217.14 115.74
3M120 442.743 442.743 370.37
3M60 976.05 976.05 925.92

47. Pressure Distribution Study
The material property curves HT3 for hard pad and ST1 for soft pad gave similar
simulation and experimental load displacement curves. Thus, the stress-strain values
corresponding to the curve HT3 and ST1 were assumed as the uniaxial material properties
of the hard pad and soft pad respectively.
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48. 48

49. Contact Area and Contact Pressure comparison for experiment and simulation – Hard Pad
Contact Area and Contact Pressure comparison for experiment and simulation – Soft Pad
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Type Contact Length (X) Contact Length (Y) Contact
Pressure
Experiment 43.75mm 17.5mm 0.6Mpa
Simulation 59.21mm 20mm 0.096Mpa
Type Contact Length (X) Contact Length (Y) Max. Contact
Pressure
Experiment 43.75mm 13.125mm 0.4Mpa
Simulation 47mm 14mm 0.324Mpa

50. 50

51. 51

52. 52

53. From the above chart, the effect of the backing pad on pressure distribution can be clearly
seen. The pressure distribution results in case of soft pad seem to be better compared to
the pressure distribution results in case of hard pad. As expected, the hard pad gives higher
maximum contact pressure values as compared to soft pad in all the four cases i.e. when
combined with all the different types of abrasive materials.
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54. • It was understood that the overall stiffness of the abrasive materials varies as
3M60 > 3M120 > Y > T
• In the case of combination with a hard pad, the experimental and simulation load
displacement curves for the different types of abrasive materials varied significantly.
The trends observed in the maximum contact pressure values were
𝑴𝒂𝒙. 𝑪𝑷 (𝒀)>𝑴𝒂𝒙.𝑪𝑷(𝑻)
𝑴𝒂𝒙.𝑪𝑷(𝟑𝑴𝟔𝟎)>𝑴𝒂𝒙.𝑪𝑷(𝟑𝑴𝟏𝟐𝟎)
• In the case of combination with soft pad, the variation between the experimental and
simulation load displacement curves was very less. The experimental load displacement
curves in this case almost seemed to trace the simulation load displacement curves.
The trends observed in maximum contact pressure values were
𝑴𝒂𝒙.𝑪𝑷(𝒀)>𝑴𝒂𝒙.𝑪𝑷(𝑻)
𝑴𝒂𝒙. 𝑪𝑷 (𝟑𝑴𝟔𝟎)>𝑴𝒂𝒙.𝑪𝑷(𝟑𝑴𝟏𝟐𝟎)
54

55. • The rubber backing pad played a vital role in determining the contact pressure values
which in turn affect the material removal rate. The soft pad gave very good results due
to its flexible nature.
• One reason why the results with hard pad were not matching was the bent structure of
the discs. However, this problem did not affect the soft pad results. The soft pad could
conform to the structure of the abrasive discs and thus contribute decently to the
pressure distribution plots.
• The different designs modelled were assessed based on their contact pressure values.
The initial designs were scrapped due to poor control over contact pressure variation.
Another challenge that was posed was the selection of a bearing that could allow both
rotational and translation motion at high RPM (2500rev/min).
• The latest design V3 has been developed keeping in mind the above challenges. At the
same time, several tool simulation results as shown above make this a viable design for
development, printing and industrial use.
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56. • The best way to minimize the current deviations of the experimental results from the
simulation results would be performing several experimental trials by ensuring that the
abrasive discs are not bent.
• Furthermore, the touch down study was limited to static conditions. Future research
can include repeating a set of experiments in dynamic conditions with a particular rpm.
• The experiments can be repeated on concave and convex surfaces to study the change
in compliance, contact pressure and contact area due to an increase or decrease in
force. The pressure distribution results can be compared with material removal
profiles.
• Pressure distribution simulations (similar to the simulations done in this project) with
the Fujifilm pressure films can be performed for the current active compliant tool
design.
• Consequently, the design can be improved to refine the deviations from experimental
results. Following this, the tool design can be patented and integrated with the robot
for testing, validation, product development and deployment.
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57. • Solidworks Modelling
• ABAQUS Finite Element Analysis
• Tensile Testing
• Strain Gauge Application
• Pressure Film Application
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