Graded Materials

1
Graded Materials

• Graded Materials Very Common Nature

• Few Examples of Functionally Graded Materials in
  Man-Made Assemblies

2
Graded Materials

• SDM Allows Variability in Compliance and Damping
  throughout a Candidate Design

3
Shape Deposition Manufacturing

• Cycle of Material Deposition and Removal
• Complex 3D Geometry, Multi-materials

Deposit (part)
Shape
4
DESIGN
PROCESSING
FABRICATION
5
DESIGN
6
Benefits of Graded Materials

• Rocker Pin Joints Replaced With Flexural Regions
  to Introduce Compliance and Damping

SDM Re-Design
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

7
Graded Materials

• Un-Actuated Five-Bar Leg Mechanism Illustrates
  Benefits of Heterogeneous Material Properties
• Flexure Joints Replace Pin-Joints to Add
  Compliance and Damping

8
Graded Materials

• 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

9
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

10
Bonding

• Wet-Wet Bonds
• Excellent Bond
• Difficult To Control
• Avoid Over-mixing

• 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
Wet-Wet Bond
11
Material Selection

• Polyurethane (part)
• Hardness Machinable/Cast Only
• Bond Issues - cure time, shrinkage (s)

IE-90A
(Cast Only, Very Soft)
Harder
IE-65D
IE-70DC
12
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
13
Design Constraints

• 2.5D/3D

• Ordering

• Tool Size Constraints

• Materials

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
14
Flexures
Minimize Sharp Edges
Plastic Fails in Tension
Increased Width
Materials
Maximize Bond Area
2.5D/3D
15
PROCESSING FABRICATION
16
Pouring Maintenance Technique

• Clean Technique
• Clear Division Between Clean and Unclean Objects
• Attire
• Dry Gas

Eye Protection
Mask
Lab Coat
Under Gloves
Outer Gloves
Toe-Covering Shoes
17
Good Cures

• Aesthetic and Practical Importance
• Pre-vacuum
• Over Pour
• Cure Times

18
Tolerance Issues

• Over Pour/Under Machine
• Excess Material Part Deformation and HAAS
  Tolerance

19
Processing

• Combine Differing Grades of Material Roughly in
  Order of Hardness
• Bond Surfaces Should be Freshly Machined

20
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
21
Application of Graded Materials

• Berkeley 1 DOF Walking Machine
• Four-Bar Linkages Represent Practical Application
  Well Suited to Use of Graded Materials

22
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
23
Compliance for 1DOF Machine

• 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

24
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.