Graded Materials Graded Materials Very Common Nature Few

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 3 D 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 3 D geometry • With Graded Materials, Flexure Size Can Be Increased To Increase Strength of Part SDM Re-Design

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

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

• • • 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-90 A (Cast Only, Very Soft) IE-65 D IE-70 DC

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. 5 D/3 D • Ordering • Materials • Tool Size Constraints Example of 2. 5 D/3 D Geometry White Regions (Soft Material) in 2. 5 D Clear Regions (Hard Material) in 3 D 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. 5 D/3 D

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 • • 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 -750 mmpm 1/8” or larger 2. 200 -400 mmpm 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 1 DOF 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

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.