ASTM F2915-11
(Specification)Standard Specification for Additive Manufacturing File Format (AMF)
Standard Specification for Additive Manufacturing File Format (AMF)
ABSTRACT
This specification provides a framework for an interchange format to address the current and future needs of the additive manufacturing technology. The additive manufacturing file (AMF) may be prepared, displayed, and transmitted on paper or electronically, provided the requirements presented in this specification are met. When prepared in a structured electronic format, strict adherence to an extensible markup language (XML) schema is required to support standards-compliant interoperability.
SCOPE
1.1 This specification describes a framework for an interchange format to address the current and future needs of additive manufacturing technology. For the last three decades, the STL file format has been the industry standard for transferring information between design programs and additive manufacturing equipment. An STL file contains information only about a surface mesh and has no provisions for representing color, texture, material, substructure, and other properties of the fabricated target object. As additive manufacturing technology is quickly evolving from producing primarily single-material, homogenous shapes to producing multimaterial geometries in full color with functionally graded materials and microstructures. There is a growing need for a standard interchange file format that can support these features.
1.2 The additive manufacturing file (AMF) may be prepared, displayed, and transmitted on paper or electronically, provided the information required by this specification is included. When prepared in a structured electronic format, strict adherence to an extensible markup language (XML)(1) schema is required to support standards-compliant interoperability. The adjunct to this specification contains a W3C XML schema and Annex A1 contains an implementation guide for such representation.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.4 This standard also does not purport to address any copyright and intellectual property concerns, if any, associated with its use. It is the responsibility of the user of this standard to meet any intellectual property regulations on the use of information encoded in this file format.
General Information
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: F2915 – 11
Standard Specification for
Additive Manufacturing File Format (AMF)
This standard is issued under the fixed designation F2915; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope to meet any intellectual property regulations on the use of
information encoded in this file format.
1.1 This specification describes a framework for an inter-
change format to address the current and future needs of
2. Terminology
additive manufacturing technology. For the last three decades,
2.1 Definitions Specific to This Standard—This section pro-
the STL file format has been the industry standard for trans-
videsdefinitionsoftermsspecifictothisstandard—theseterms
ferring information between design programs and additive
also include the common terms seen in many documents
manufacturing equipment. An STL file contains information
related to extensible markup language (XML) and additive
only about a surface mesh and has no provisions for represent-
manufacturing. See alsoAnnexA1 for definitions of additional
ing color, texture, material, substructure, and other properties
terms specific to this specification.
of the fabricated target object. As additive manufacturing
2.1.1 attribute, n—characteristic of data, representing one
technology is quickly evolving from producing primarily
or more aspects, descriptors, or elements of the data.
single-material, homogenous shapes to producing multimate-
2.1.1.1 Discussion—In object-oriented systems, attributes
rial geometries in full color with functionally graded materials
are characteristics of objects. In XML, attributes are charac-
and microstructures. There is a growing need for a standard
teristics of elements.
interchange file format that can support these features.
2.1.2 comments, n—all text comments associated with any
1.2 The additive manufacturing file (AMF) may be pre-
data within the additive manufacturing file (AMF) not contain-
pared, displayed, and transmitted on paper or electronically,
ing core relevant, technical, or administrative data and not
provided the information required by this specification is
containing pointers to references external to the AMF.
included. When prepared in a structured electronic format,
2.1.3 domain-specific applications, n—additional, optional
strict adherence to an extensible markup language (XML)(1)
sets of AMF data elements specific to such areas as novel
schema is required to support standards-compliant interoper-
additive manufacturing processes, enterprise workflow, and
ability. The adjunct to this specification contains a W3C XML
supply chain management.
schema and Annex A1 contains an implementation guide for
2.1.3.1 Discussion—Data sets for optional AMF domain-
such representation.
specific applications will be developed and balloted separately
1.3 This standard does not purport to address all of the
from this specification.
safety concerns, if any, associated with its use. It is the
2.1.4 extensible markup language, XML, n—standard from
responsibility of the user of this standard to establish appro-
the WorldWideWeb Consortium (W3C) that provides for
priate safety and health practices and determine the applica-
tagging of information content within documents offering a
bility of regulatory limitations prior to use.
means for representation of content in a format that is both
1.4 This standard also does not purport to address any
human and machine readable.
copyright and intellectual property concerns, if any, associated
2.1.4.1 Discussion—Through the use of customizable style
with its use. It is the responsibility of the user of this standard
sheets and schemas, information can be represented in a
uniform way, allowing for interchange of both content (data)
This specification is under the jurisdiction of ASTM Committee F42 on
and format (metadata).
Additive Manufacturing Technologies and is the direct responsibility of Subcom-
2.1.5 STL (file format), n—file format native to the stereo-
mittee F42.04 on Design.
lithography computer-aided drafting (CAD) software that is
Current edition approved June 1, 2011. Published July 2011. DOI: 10.1520/
F2915-11. supported by many software packages; it is widely used for
The boldface numbers in parentheses refer to the list of references at the end of
rapid prototyping and computer-aided manufacturing.
this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F2915 – 11
2.1.5.1 Discussion—STL files describe only the surface human readable, which makes debugging errors in the file
geometry of a three-dimensional object as a tessellation of possible. XML can be compressed or encrypted or both if
triangles without any representation of color, texture, or other desired in a post-processing step using highly optimized
common CAD model attributes.The STLformat specifies both standardized routines.
the American Standard Code for Information Interchange 4.2 Another significant advantage of XML is its inherent
(ASCII) and binary representations. flexibility. Missing or additional parameters do not present a
problem for a parser as long as the document conforms to the
3. Key Considerations
XML standard. Practically, this allows new features to be
3.1 There is a natural a tradeoff between the generality of a
added without needing to update old versions of the parser,
file format and its usefulness for a specific purpose. Thus,
such as in legacy software.
features designed to meet the needs of one community may
4.3 Precision—This file format is agnostic as to the preci-
hinder the usefulness of a file format for other uses. To be
sion of the representation of numeric values. It is the respon-
successful across the field of additive manufacturing, this file
sibility of the generating program to write as many or as few
format is designed to address the following concerns:
digits as are necessary for proper representation of the target
3.1.1 Technology Independence—The file format shall de-
object. However, a parsing program should read and process
scribe an object in a general way such that any machine can
real numbers in double precision (64 bit).
build it to the best of its ability. It is resolution and layer-
4.4 Future Amendments and Additions—Additional XML
thickness independent and does not contain information spe-
elements can be added provisionally to any AMF file for any
cific to any one manufacturing process or technique. This does
purposebutwillnotbeconsideredpartofthisspecification.An
not negate the inclusion of properties that only certain ad-
unofficialAMF element can be ignored by any reader and does
vanced machines support (for example, color, multiple mate-
not need to be stored or reproduced on output. An element
rials, and so forth), but these are defined in such a way as to
becomes official only when it is formally accepted into this
avoid exclusivity.
specification.
3.1.2 Simplicity—TheAMFfileformatiseasytoimplement
and understand. The format can be read and debugged in a
5. General Structure
simple ASCII text viewer to encourage understanding and
5.1 The AMF file begins with the XML declaration line
adoption. No identical information is stored in multiple places.
specifying the XML version and encoding, for example:
3.1.3 Scalability—The file format scales well with increase
in part complexity and size and with the improving resolution
5.2 Blank lines and standard XML comments can be inter-
and accuracy of manufacturing equipment.This includes being
spersed in the file and will be ignored by any interpreter, for
able to handle large arrays of identical objects, complex
example:
repeated internal features (for example, meshes), smooth
curved surfaces with fine printing resolution, and multiple
components arranged in an optimal packing for printing.
5.3 The remainder of the file is enclosed between an
3.1.4 Performance—The file format should enable reason-
opening element and a closing element.
able duration (interactive time) for read-and-write operations
These elements are necessary to denote the file type, as well as
and reasonable file sizes for a typical large object. Detailed
to fulfill the requirement that all XML files have a single-root
performance data are provided in Appendix X1.
element. The version of the AMF standard as well as all
3.1.5 Backwards Compatibility—Any existing STL file can
standardXMLnamespacedeclarationscanbeused,suchasthe
be converted directly into a validAMF file without any loss of
lang attribute designed to identify the human language used.
information and without requiring any additional information.
The unit system can also be specified (mm, inch, ft, metres, or
AMF files are also easily converted back to STL for use on
micrometres). In absence of a unit specification, millimetres
legacy systems, although advanced features will be lost. This
are assumed.
format maintains the triangle-mesh geometry representation to
take advantage of existing optimized slicing algorithm and
5.4 Within the AMF brackets, there are five top level
code infrastructure already in existence.
elements:
3.1.6 Future Compatibility—To remain useful in a rapidly
5.4.1 —The object element defines a volume or
changing industry, this file format is easily extensible while
volumes of material, each of which are associated with a
remaining compatible with earlier versions and technologies.
material identification (ID) for printing. At least one object
This allows new features to be added as advances in technol-
element shall be present in the file. Additional objects are
ogy warrant, while still working flawlessly for simple homog-
optional.
enous geometries on the oldest hardware.
5.4.2 —The optional material element de-
4. Structure of This Specification
fines one or more materials for printing with an associated
4.1 Information specified throughout this specification is material ID. If no material element is included, a single default
material is assumed.
stored in XML format. XML is an ASCII text file comprising
a list of elements and attributes. Using this widely accepted 5.4.3 —The optional texture element defines
data format opens the door to a rich host of tools for creating, one or more images or textures for color or texture mapping
viewing,manipulating,parsing,andstoringAMFfiles.XMLis each with an associated texture ID.
F2915 – 11
5.4.4 —The optional constellation el-
ement hierarchically combines objects and other constellations
into a relative pattern for printing. If no constellation elements
are specified, each object element will be imported with no
relative position data. The parsing program can determine the
relative positioning of the objects if more than one object is
specified in the file.
5.4.5 —The optional metadata element
specifies additional information about the object(s) and ele-
ments contained in the file.
5.5 Only a single object element is required for a fully
functional AMF file.
6. Geometry Specification
6.1 The top level element specifies a uniqueid
and contains two child elements: and
. The element can optionally specify a
material.
6.2 The required element lists all vertices
that are used in this object. Each vertex is implicitly assigned
a number in the order in which it was declared starting at zero.
The required child element gives the posi-
tion of the point in three-dimensional (3D) space using the
, , and elements.
6.3 After the vertex information, at least one
element shall be included. Each volume encapsulates a closed
volume of the object. Multiple volumes can be specified in a
singleobject.Volumesmayshareverticesatinterfacesbutmay
FIG. 1 Basic AMF File Containing Only a List of Vertices and
not have any overlapping volume.
Triangles—This Structure Is Compatible with the STL Standard
6.4 Within each volume, the child element
shallbeusedtodefinetrianglesthattessellatethesurfaceofthe
volume. Each element will list three vertices thelocationofthevertex.Thenormalshouldbeunitlengthand
from the set of indices of the previously defined vertices. The pointing outwards. If this normal is specified, all triangle edges
indices of the three vertices of the triangles are specified using meeting at that vertex should be curved so that they are
the,,andelements.Theorderofthevertices perpendicular to that normal and in the plane defined by the
shall be according to the right-hand rule such that vertices are normal and the original straight edge.
listed in counter-clockwise order as viewed from the outside. 6.5.5 When the curvature of a surface at a vertex is
Each triangle is implicitly assigned a number in the order in undefined(forexample,atacusp,corner,oredge),an
which it was declared starting at zero (see Fig. 1). element can be used to specify the curvature of a single
6.5 Smooth Geometry: nonlinear edge joining two vertices. The curvature is specified
6.5.1 By default, all triangles are assumed to be flat and all using the tangent direction vectors at the beginning and end of
triangle edges are assumed to be straight lines connecting their thatedge.Theelementwilltakeprecedenceincaseof
a conflict with the curvature implied by a element.
two vertices. However, curved triangles and curved edges can
optionally be specified to reduce the number of mesh elements 6.5.6 Normals shall not be specified for vertices referenced
only by planar triangles. Edge tangents shall not be specified
required to describe a curved surface.
6.5.2 During read, a curved triangle patch shall be recur- for linear edges.
sively subdivided into four triangles by the parsing program to 6.5.7 When interpreting normal and tangents, Hermite in-
generate a temporary set of flat triangles at any desired terpolation will be used. See Annex A3 for formulae for
resolution for manufacturing or display.The depth of recursion carrying out this interpolation.
shall be determined by the parsing program, but a minimal 6.5.8 The geometry shall not be used to describe support
level of four is recommended (that is, convert a single curved structure. Only the final target structure shall be described.
triangle into 256 flat triangles). 6.6 Restrictions on Geometry—All geometry shall comply
6.5.3 During write, the encoding software shall determine with t
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