sdm forms & materials for manufacturable robotics...

1

SDM Forms & Materials forManufacturable Robotics [per D. Koditschek]

Mark Cutkoskyand the SU-RiSE team

Feb 20, 2004

2

Outline

• What is SDM and what does it have todo with parameterizing materials?

• What comes next?

RiSE Materials and Manufacturing3

Issues

(Some) layered manufacturing methods make itpossible to produce parts with varying orheterogenous materials properties– What are the implications for how parts must be

represented in a CAD system? (How do we specify thematerial variations, for example?)

– What are some useful applications of graded materials?– How does the ability to vary materials properties

enlarge the space of possibilities available to designers?– How can we optimize materials properties for a given

design objective?


Traditional manufacturing:a sequential process ofshaping and assembly

From RP and CNC to . . .

2000

1970

1990Shape Deposition Manufacturing ( SDM)

RP CNC


Deposit (part)

Shape

EmbedDeposit (support)

Shape

PartEmbedded Component

Support

Shape Deposition Manufacturing(CMU/SU)


What is the SDM machine?


Computational issues:Process Planning

• Process constraints• Manufacturability• Support structures

• Deposition method• Deposition parameters• Path planning

• Machining method• Tool selection • Machining parameters• Path planning

Decompose Deposit Machine

Decompose Deposit MachineInput


How to make an egg


Cool SDM stuff to date

10 mm10 mm

Embedded componentsCham et al., 1999

Embedded sensorsWuensch., 2001

Multi-materials - Roger, 2000

Fiber-reinforcedjoints

Moto, 2001RiSE foot V4 (2-17-04)


Embedded sensor example:pressure sensor unit for pneumaticactuators

Screen shot from SDM CAD environment:several steps in the “building block”design/fabrication sequence for theembedded pressure sensor package

PC board CAD file forcommercial MEMS pressuretransducer & instrumentation


Embedded sensor example(continued)

Completed pressure sensor unitready for connection to apneumatic actuator.

A batch of four parts during thefinal machining step.Part material is urethane (yellow).Sacrificial support material is wax (red),filling cavities and encasing the circuitleads to protect them.

Fabrication instructions archived at http://cdr.stanford.edu/dml/biomimetics/documents.html


Embedded actuator example

Deposition: part and support materialsare cast in place, aftereach machining stage

Shaping: structures are machined a pallet on a CNC mill


Original Design SDM Re-Design

• Pin Joints Replaced With Flexural Regions to Introduce locally tailored Compliance and Damping• More robust than a pin joint...• More robust than using a single homogeneous material and varying flexure thickness

Graded Materials


Design considerations:

• How much does the ability to vary materialschange the “space” of opportunitiesavailable to a designer?

• How can we optimize materials propertiesfor a particular design?

• Is materials optimization independent ofshape optimization?


Design synthesis: shape optimization

Shape optimizationexample:Find the minimum-weight shelfstructure, bounded by box B,that supports load W without failing.B

W

Space within B is divided into N cells, each of whichcan be filled or empty. Number of unique designs ≈ 2N

(Of course, most of the naive solutions will not befeasible. Still, the search space is large.)


Ability to vary material composition

Support structure

depositionheads

Deposition heads can becontrolled to depositvarying amounts of eachmaterial* as the part isbuilt. Total materialcomposition variesthroughout the part.

Volume fractions always add to unity*

*void, or empty space, is treated as a special case of material


Material composition: product space

Product Space:)!1(!

)!1(

1

1

!

!+=""

#

$%%&

'

!

!+

mr

mr

m

mrC

urethane

glass

void

teflon

m = number of materials (including void)vi = volume fraction of each material

r = deposition mixture resolution

1

1

=!=

m

i

iv

Example: urethane, glass fibers, teflon, and void, controlled to aresolution of 10% volume fraction ⇒ 286 unique mixtures possible.


Design space dimensions with arbitrarygeometry and heterogeneous materials:

(E3 × Rm)Shape + material optimization:Assume m possible materials,(including void) with a mixtureresolution of r.B

W

Space within B is discretized into N cells, each of whichcan be filled with a unique mixture of materials.

Number of unique designs ≈

Example: 10×10×10 cells, 4 materials, 10% mixture resolution⇒ 2861000 designs!

(r + m -1)!

r!(m - 1)!

N


Materials selection and optimizationexample [M. Ashby book]

Consider a flexure orelastic hinge (as in the legsof the Sprawlita robots)

What is the best materialfor the hinge region?

(See Ashby chart on E versus σfail)

Goal: find material that • is strong enough• allows us to minimize Rbend

Ashby, M.F., "Materials Selection in Mechanical Design," 2nd. edition, Butterworth Heinmann, Oxford, 1999.


Graded Materials• Graded interface increases surface area, resulting in increased bonding• Function needs to be applied To discretize the graded regions based upon a

specified tolerance parameter


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 urethanehardness. Processed to minimize

machining on soft surfaces


1 12

43

Support MaterialHard Part MaterialSoft Part Material

1 3

2

4 1

3

2

4

Adjacency Graph Precedence GraphCompliant Joint

Functional considerations:fatigue life determines plan

Soft material should becast into surrounding material


Refined compliant joint

1 12

43

Support MaterialHard Part MaterialSoft Part Material

1 3

2

4 1

3

2

4

Adjacency Graph Precedence Graph

55

5

5

Functional considerations:fatigue life determines plan

Planing producessmooth surface

Why must 4 precede 5?


Psuedo-boundary formation


Catalog of SDM-compatible polymersand their properties

NEW: http://www-cdr.stanford.edu/twiki/bin/view/Main/UrethaneProperties

Older:http://www-cdr.stanford.edu/biomimetics/documents/material/property.htmhttp://www-cdr.stanford.edu/biomimetics/documents/material/consideration.htmhttp://www-cdr.stanford.edu/biomimetics/pdf/detc2000_final.pdf

sdm forms & materials for manufacturable robotics...

Documents