Additive Manufacturing File Format Hod Lipson Chair, ASTM F42/Design Task Group on File Formats November 10, 2009 With Jonathan Hiller

Join The Discussion 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

Distribution Lists RPML SFF RM VRAP GARPA CIRP ASTM STL2

n=162 survey submissions

Your interest in RP file format n=246

Prioritized Features n=162. Error bars = 1 Standard Deviation

Prioritized Features 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 (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 – ABS – Tango Black – Nylon 1234 By physical property – 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 PATCH PLANNAR 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

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

Watermark / Copyright 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

Process 1.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

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Bibliography Extensible Markup Language (XML) 1.0 (Fifth Edition), W3C Recommendation 26 November 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 , Austin, TX, USA.STL 2.0: A Proposal for a Universal Multi- Material Additive Manufacturing File Format GILMAN, C. R. & ROCK, S. J. (1995) The use of STEP to integrate design and solid freeform fabrication. Solid Freeform Fabrication Symposium. Austin, TX.