graded materials graded materials very common nature few examples of functionally graded materials...
Post on 01-Jan-2016
237 Views
Preview:
TRANSCRIPT
Graded Materials
• Graded Materials Very Common Nature
• Few Examples of Functionally Graded Materials in Man-Made Assemblies
Shape Deposition Manufacturing
• Cycle of Material Deposition and Removal• Complex 3D Geometry, Multi-materials
Part
Support
Deposit (part)
Shape
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
BondingWet-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 BondWet-Wet Bond
Material SelectionPolyurethane (part):•Hardness: Machinable/Cast Only•Bond Issues - cure time, shrinkage (#’s)
IE-90A
IE-70DC
IE-65D
(Cast Only, Very Soft)
Material SelectionWax (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 GeometryWhite Regions (Soft Material) in 2.5DClear 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
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
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:
1. 500-750mmpm 1/8” or larger
2. 200-400mmpm 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 Design SDM 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.
top related