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

D ESIGN P ROCESSING F ABRICATION

D ESIGN

Original Design SDM Re-Design Rocker Pin Joints Replaced With Flexural Regions to Introduce Compliance and Damping Benefits of Graded Materials 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

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-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

Material Selection Polyurethane (part): Hardness: Machinable/Cast Only Bond Issues - cure time, shrinkage (#’s) IE-90A IE-70DC IE-65D (Cast Only, Very Soft)

Material Selection Wax (support): Machinability Shrinkage Melting Point Red Wax Blue Wax Green Wax Palette Blocks; Excellent Machinability Castable; Medium Machinability Water Soluble; Poor Machinability

Design Constraints 2.5D/3D Tool Size Constraints Ordering 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

Flexures 2.5D/3D Increased Width Maximize Bond Area Materials Minimize Sharp Edges Plastic Fails in Tension

P ROCESSING & F ABRICATION

Pouring Maintenance & Technique Clean Technique: Clear Division Between Clean and Unclean Objects Attire Dry Gas Under Gloves Outer Gloves Mask Eye Protection Toe-Covering Shoes Lab Coat

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 Wet-Dry Bond Cutting Depths: Roughly Half Tool Diameter Feed Rates: mmpm 1/8” or larger mmpm 1/16”

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 Original DesignSDM Re-Design 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

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

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.