Transcript Graded Materials - Center for Design Research

Graded Materials
• Graded Materials Very
Common Nature
• Few Examples of
Functionally Graded
Materials in Man-Made
Assemblies
Graded Materials
• SDM Allows Variability in
Compliance and Damping
throughout a Candidate
Design
Shape Deposition Manufacturing
• Cycle of Material Deposition and Removal
• Complex 3D Geometry, Multi-materials
Part
Support
Deposit (part)
Shape
DESIGN
PROCESSING
FABRICATION
DESIGN
Benefits of Graded Materials
•Rocker Pin Joints Replaced With Flexural Regions to Introduce
Compliance and Damping
Original Design
•SDM with Graded Materials Allow
Control of Material Location and
Properties in 3D geometry
•With Graded Materials, Flexure
Size Can Be Increased To Increase
Strength of Part
SDM Re-Design
Graded Materials
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Un-Actuated Five-Bar Leg Mechanism Illustrates
Benefits of Heterogeneous Material Properties
Flexure Joints Replace Pin-Joints to Add Compliance
and Damping
Graded Materials
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Desired Performance of Structural and Flexural
Regions Very Different
Fabricating With Single Material Would Result In
Compliant Structural Regions or Brittle, Failure Prone
Flexures
Ideal Solution Requires Varying Material Properties
Between Different Regions of the Part
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Graded Materials
Graded Interface Increases Surface Area, Resulting in
Increased Bonding
Mixing in Arbitrary Ratios Not Possible
Function Needs to Be Applied To Discretize the
Graded Regions Based Upon a Specified Tolerance
Parameter
Bonding
Wet-Wet Bonds:
•Excellent Bond
•Difficult To Control
•Avoid Over-mixing
Wet-Wet Bond
Wet-Dry Bonds:
•Excellent Control of
Surface
•Increase Surface Area
•Roughen Surface
•Keep Clean - machine as
last step before new pour if
possible
Wet-Dry Bond
Material Selection
Polyurethane (part):
•Hardness: Machinable/Cast Only
•Bond Issues - cure time, shrinkage (#’s)
IE-90A
(Cast Only, Very Soft)
IE-65D
IE-70DC
Material Selection
Wax (support):
•Machinability
•Shrinkage
•Melting Point
Blue Wax
Palette Blocks; Excellent Machinability
Red Wax
Castable; Medium Machinability
Green Wax
Water Soluble; Poor Machinability
Design Constraints
• 2.5D/3D
• Ordering
• Materials
• Tool Size Constraints
Example of 2.5D/3D Geometry
White Regions (Soft Material) in 2.5D
Clear Regions (Hard Material) in 3D
Ordering Defined By Urethane
Hardness. Processed to Minimize
Machining on Soft Surfaces
Flexures
Minimize Sharp
Edges
Plastic Fails in
Tension
Materials
Increased Width
Maximize Bond
Area
2.5D/3D
PROCESSING & FABRICATION
Pouring Maintenance & Technique
• Clean Technique:
• Clear Division Between Clean and Unclean
Objects
• Attire
Eye Protection
• Dry Gas
Mask
Lab Coat
Under Gloves
Outer Gloves
Toe-Covering Shoes
Good Cures
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Aesthetic and Practical Importance
Pre-vacuum
Over Pour
Cure Times
Tolerance Issues
• Over Pour/Under Machine
• Excess Material: Part Deformation and HAAS
Tolerance
Processing
• Combine Differing
Grades of Material
Roughly in Order
of Hardness
• Bond Surfaces
Should be Freshly
Machined
Ideal Machining Parameters
• Please be Conservative (tool speeds very
approximate)
• Cooling: always provide direct cooling from
compressed air
• Cutting Depths:
Roughly Half Tool
Diameter
• Feed Rates:
1. 500-750mmpm 1/8” or
larger
2. 200-400mmpm 1/16”
Wet-Dry Bond
Application of Graded Materials
• Berkeley 1 DOF Walking Machine
• Four-Bar Linkages Represent Practical Application
Well Suited to Use of Graded Materials
Compliance for 1 DOF Machine
• Reduce Assembly Complexity, Increase Robustness
• Four-Bar Mechanism Utilizes Two Rotary Joints and Two Rocker
Joints
•Rocker Pin Joints Replaced With Flexural Regions to Introduce
Compliance and Damping
Original Design
SDM Re-Design
Compliance for 1DOF Machine
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New Design Features
With SDM
Geometry: Constant
Ground Contact
Replaced Pin Joints
With Flexural Region:
Introduced Compliance
& Damping
Leg Preflexes Defines
by Build Orientation
Future Analysis and
Experiments to Tune
Compliance to
Locomotion
Acknowledgements
Thanks to Prof. Mark Cutkosky, Prof. Fritz Prinz, Sanjay Rajagopalan,
Jorge Cham, Yanjie Sun, Jianpeng Dong and Sangkyun Kang and the other
students and staff of RPL and CDR for their help in generating the results
described in this presentation and Dr. Noe Lozano and the SURF program
for supporting this research.