Additive Manufacturing File Format

Hod LipsonHod.lipson@cornell.edu

Chair, ASTM F42/Design Task Group on File FormatsNovember 10, 2009

With Jonathan Hiller

Join The Discussion

http://groups.google.com/group/stl2 To join the task group visit

Goals

• Identify needs of new file format • Propose new standard• Reach consensus• Catalyze adoption

Outline of presentation

• Summarize survey• Outline proposed standard• Process and timetable for moving forward

Survey

http://www.mae.cornell.edu/lipson/stl2.htm

Distribution Lists

• RPML• SFF• RM• VRAP

• GARPA• CIRP• ASTM• STL2

0

20

40

60

80

100

120

140

160

180

n=162 survey submissions

+90 Rapid Manufacturing De Montfort University Materialise USA surface generation3M Healthcare Delcam plc Met-L-Flo Inc Synthes (USA)3T RPD Ltd. Delcam plc Mettis Aerospace Ltd Technical University of CataloniaA1Technologies Ltd Delft Spline Systems Mydea Technical University of DenmarkA3DM Delphi Diesel Systems Mydea Technologies Texas State University- San MarcosAdditive Manufacturing Research GroupDesign Prototyping TechnologiesNASA Langley The Argen CorporationAdvanced Laser Materials, LLC DeskArtes Oy National Institute of Standards and TechnologyThe MITRE CorporationAeronautics Institute of Technology, BrazilDirect Dimensions, Inc. National R&D Institute for Nonferrous and Rare MetalsTiconaAlign Technology EPFL, Switzerland National Univ. Singapore TranscenData Europe LtdAndong natl. univ. at S. Korea ETH Zürich NAVAIR U.S. NavyAPSOM INFOTEX LTD EXCELTEC netfabb GmbH Univ Texas AustinArizona State University Fab Folk New Balance Shoe Co University of Auckland, New ZealandASERM - AIJU fcubic NextFab Organization University of Duisburg-Essen (GER)Assa Ashuach Studio FIT North Carolina State University University of Erlangen-NurembergAstra Tech AB Ford Motor co Northern Lights, NRRI - UofM, DuluthUniversity of HuddersfieldBarco NV Belgium Freedom of Creation NTUT University of LouisvilleBath University Fundación Prodintec Nuhill Technologies, Inc.. University of ManchesterBathsheba Sculpture LLC Georgia Tech ON DEMAND MANUFACTURINGUniversity of Maribor, Faculty of Mechanical Engineering, SloveniaBerenschot Government (Army) Paramount Industries University of MichiganBiomedical Modeling Inc. GPI Prototype Phonak AG University of minnesota, NRRIBoeing GRZ Software LLC POM Group, Inc. University of Twente, NetherlandsBRP-Powertrain Halpin & Hines Prosthetics industry University of WashingtonC.R.P. Technology Hopkinson Protofacturing Group Inc. University of WolverhamptonCambridge Consultants IET Red Bull Technology US ArmyCardiff University IFW Dresden Renishaw PLC US Army RDECOMCastings Technology InternationalIowa State University Royal Plastic Mfg., Inc. Utah State UniversityCCSL Iowa State University RP Department, CMRDI Institute, EgyptUtah State UniversityCentral Piedmont Community CollegeIQS Self, UPenn, Siemens Industry VG Kunststofftechnik GmbHChrysler, LLC and the 3DSUG ISTI - CNR - Italy Shapeways Victoria UniversityChrysler, LLC and the 3DSUG Laboratory DIPI, ENISE, FranceShapeways VTTcirtes LAFITT S.A. Shapeways Washington State UniversityClemson University Las Palmas de Gran Canaria UniversityShore Design Widgetologyclonenature LEITAT, Tech.Center Solidscape, Inc. Z CorporationCOPROIN LGM and CADspan Status d.o.o Z CorporationCornell University Lockheed Martin Stratasys Zip-Bit, Inc.cstcc Loughborough University StratasysDalgarno Loughborough University Stratasys Inc.

Your interest in RP file format

11%

33%

28%

19%

9%

Chart Title

CAD software developer

Designer/User

Academic/Theoretic

RP Service Provider

RP Equipment manufacturer

n=246

http://www.mae.cornell.edu/lipson/stl2.htm

Prioritized Features

1

1.5

2

2.5

3

3.5

4

4.5

5

n=162. Error bars = 1 Standard Deviation

Prioritized Features

1

1.5

2

2.5

3

3.5

4

4.5

5

n=162. Error bars = Standard Error

Other features

• Main feature: keep it simple! • ISO 9000-ish features like product tracking• Interoperability within different manufacturers• Compatible with FEA applications• Identification of parent CAD program• Restricted number of printings• Support multiple shells• Editable ASCII/Text format

Other features

• Information about build orientation• Stability/robustness• No redundancy• Volume validity• Lock or encrypt the file with a password• Ability to put a permanent 'watermark‘• Supporting geometry in native way• Keep triangle mesh / No triangle mesh

Existing Formats

• 3D PDF– Proprietary, closed

• ISO 14649 (STEP-NC)– Mostly for NC control, G-Code

• STEP / IGES, SAT, Parasolid– Too complex, missing features e.g. no mesostructure

• X3D VRML– Mesh, color, texture, lighting

All: no provision for AM, e.g. materials, internal structure

Existing Formats

• PLY– 3D Scanner data

• 3DS– Limited mesh size

• SLC– Limited information

All: no provision for AM, e.g. materials, internal structure

Reaching consensus, adoption• Non proprietary / open source• Endorsement by major CAD / Manufacturers• Use ASTM / Voting• Backwards compatible (STL)• Expandable, XML• Publish for comments / discussion• Open source software• Conversion tools• Limit the scope: Not a CAD model• Make the format good

Proposed Format

Current STL

Name

• AMF– Additive Manufacturing Format– Additive Manufacturing File

New format needed

• Tailor to AM community needs– No content constraints

• Retain Community Control– Not Proprietary

• Neutral– Avoids association with existing companies

XML

• Meta-format: Format of formats– Text based– Easy to read/write/parse– Existing editing tools– Extensible– Highly compressible

• Mentioned by a number of constituents– E.g. Materialise– Based on work by J. Hiller (Cornell)

Addresses needs: Editable / Extensible / Readable / Open / Non proprietary

General Concept• Part (objects) defined by regions and materials

– Regions defined by triangular mesh – Materials defined by properties/names

• Mesh properties can be specified– Color– Tolerance– Texture

• Materials can be combined– Graded materials– Microstructure

Basic Structure

Addresses needs: Simple / Watertight / Backward Compatible (STL)

Compressibility

Addresses needs: Small / Compressible

Need to look at dependency on # of digits

Multiple Materials

Addresses needs: Multiple Materials, No leaks between regions (shared vertices)

Graded Materials

Microstructure

Addresses needs: Periodic meso/microstructure

Material properties

• By manufacturer’s name– <Name> ABS </Name>– <Name>Tango Black </Name>– <Name>Nylon 1234 </Name>

• By physical property– </Property Type=“Elastic Modulus” Value=“4E9”>– </Property Type=“Poisson Ratio” Value=“1.2”>

• External reference (URL)

Addresses needs: Material specifications/libraries

Color and Graphics

• By volumetric region– Solid color

• By vertex– Specify Vertex color– Specify Vertex coordinate in a bitmap

Addresses needs: Color graphics

Color and Graphics

Tolerances

• By volumetric region– Nominal tolerance– Allowed variation from original volume

• By vertex– Specify point tolerance (?)– Point to point

Addresses needs: Tolerance

Non-meshed geometry?• Other representations are

not mutually exclusive• Voxel maps

– For digital/inkjet microstructure

• NURBS– Add slope vectors to some

triangle mesh edges– Other STEP types?

• Functional Representations– implicit equations, e.g:

NURBS PATCHPLANNAR PATCH

NURBS PATCHPLANNAR PATCH

Optionally add slope vectors to some triangle mesh edges to allow for very accurate geometry. Perfect sphere can be made with ~20 patches

Print Constellation

• Print orientation• Duplicated objects• Sets of different

objects• Efficient nesting• Hierarchical

Metadata

<Metadata><Datum ID=“Author” Data=“John Doe”></Datum><Datum ID=“Company” Data=“…”></Datum><Datum ID=“Description” Data=“…”></Datum><Datum ID=“Originating CAD System” Data=“…”></Datum><Datum ID=“Originating CAD File” Data=“…”></Datum><Datum ID=“Comment” Data=“…”></Datum>

</Metadata>

Encryption

<Metadata><Datum ID=“Author” Data=“John Doe”></Datum><Datum ID=“Company” Data=“…”></Datum><Datum ID=“Description” Data=“…”></Datum><Datum ID=“Comment” Data=“…”></Datum><Datum ID=“Encryption” Data=“Prompt”></Datum>

</Metadata>

Key garbles vertex coordinates (e.g. using XOR); need key to un-garble

Watermark / Copyright

<Metadata><Datum ID=“Author” Data=“John Doe”></Datum><Datum ID=“Company” Data=“…”></Datum><Datum ID=“Description” Data=“…”></Datum><Datum ID=“Comment” Data=“…”></Datum><Datum ID=“Copyright” Data=“Owner”></Datum>

</Metadata>

Copyright name garbles vertex coordinates (e.g. using XOR); copyright must be present to un-garble

Other features

• URL can be used in lieu of material data to allow for external libraries

• Validation checksums– E.g. Original vs. actual part/region volumes

• Automatic error checking– Readers/writers must check for intact topology,

e.g.• All nodes referenced by at least 3 triangles• All edges referenced exactly twice per region

Next steps

Process1. Initial basic format

– Triangle mesh– Materials– Colors– Metadata

2. Experiment with new tags independently– Mesostructure– Tolerances– F-rep

3. Add new tags formally when mature– Once a year– With open source imlementation

Process

• Open source code– Slicer– Viewer– Bidirectional STL Converter

• Any future feature– Requires open source implementation– BSD-Type license that allows free commercialization

• Consensus– Identify liaison persons representing all major

equipment manufacturers and CAD systems

Optional Certification

• Certified AMF readers/writers must support small set of mandatory tags– All mesh and region tags

• Support of color, materials, etc not mandatory• Small suite of test cases to be validates

Schedule

• Draft for comments– April 1

• Draft for voting– July 1

Join The Discussion

http://groups.google.com/group/stl2 To join the task group visit

Bibliography• Extensible Markup Language (XML) 1.0 (Fifth Edition), W3C

Recommendation 26 November 2008 http://www.w3.org/TR/REC-xml/• Hiller, J., Lipson, H. (2009) "STL 2.0: A Proposal for a Universal Multi-

Material Additive Manufacturing File Format" Solid Freeform Fabrication Symposium (SFF'09), Aug 3-5 2009, Austin, TX, USA.

• GILMAN, C. R. & ROCK, S. J. (1995) The use of STEP to integrate design and solid freeform fabrication. Solid Freeform Fabrication Symposium. Austin, TX.