1、Designation: F2915 11Standard Specification forAdditive Manufacturing File Format (AMF)1This standard is issued under the fixed designation F2915; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This specification describes a framework for an inter-change format to address the current and future needs ofadditive manufacturing technolog
3、y. For the last three decades,the STL file format has been the industry standard for trans-ferring information between design programs and additivemanufacturing equipment. An STL file contains informationonly about a surface mesh and has no provisions for represent-ing color, texture, material, subs
4、tructure, and other propertiesof the fabricated target object. As additive manufacturingtechnology is quickly evolving from producing primarilysingle-material, homogenous shapes to producing multimate-rial geometries in full color with functionally graded materialsand microstructures. There is a gro
5、wing need for a standardinterchange file format that can support these features.1.2 The additive manufacturing file (AMF) may be pre-pared, displayed, and transmitted on paper or electronically,provided the information required by this specification isincluded. When prepared in a structured electron
6、ic format,strict adherence to an extensible markup language (XML)(1)2schema is required to support standards-compliant interoper-ability. The adjunct to this specification contains a W3C XMLschema and Annex A1 contains an implementation guide forsuch representation.1.3 This standard does not purport
7、 to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.4 This standard also does not purport to addres
8、s anycopyright and intellectual property concerns, if any, associatedwith its use. It is the responsibility of the user of this standardto meet any intellectual property regulations on the use ofinformation encoded in this file format.2. Terminology2.1 Definitions Specific to This StandardThis secti
9、on pro-vides definitions of terms specific to this standardthese termsalso include the common terms seen in many documentsrelated to extensible markup language (XML) and additivemanufacturing. See also Annex A1 for definitions of additionalterms specific to this specification.2.1.1 attribute, nchara
10、cteristic of data, representing oneor more aspects, descriptors, or elements of the data.2.1.1.1 DiscussionIn object-oriented systems, attributesare characteristics of objects. In XML, attributes are charac-teristics of elements.2.1.2 comments, nall text comments associated with anydata within the a
11、dditive manufacturing file (AMF) not contain-ing core relevant, technical, or administrative data and notcontaining pointers to references external to the AMF.2.1.3 domain-specific applications, nadditional, optionalsets of AMF data elements specific to such areas as noveladditive manufacturing proc
12、esses, enterprise workflow, andsupply chain management.2.1.3.1 DiscussionData sets for optional AMF domain-specific applications will be developed and balloted separatelyfrom this specification.2.1.4 extensible markup language, XML, nstandard fromthe WorldWideWeb Consortium (W3C) that provides forta
13、gging of information content within documents offering ameans for representation of content in a format that is bothhuman and machine readable.2.1.4.1 DiscussionThrough the use of customizable stylesheets and schemas, information can be represented in auniform way, allowing for interchange of both c
14、ontent (data)and format (metadata).2.1.5 STL (file format), nfile format native to the stereo-lithography computer-aided drafting (CAD) software that issupported by many software packages; it is widely used forrapid prototyping and computer-aided manufacturing.1This specification is under the jurisd
15、iction of ASTM Committee F42 onAdditive Manufacturing Technologies and is the direct responsibility of Subcom-mittee F42.04 on Design.Current edition approved June 1, 2011. Published July 2011. DOI: 10.1520/F2915-11.2The boldface numbers in parentheses refer to the list of references at the end ofth
16、is standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2.1.5.1 DiscussionSTL files describe only the surfacegeometry of a three-dimensional object as a tessellation oftriangles without any representation of color, texture, or ot
17、hercommon CAD model attributes. The STL format specifies boththe American Standard Code for Information Interchange(ASCII) and binary representations.3. Key Considerations3.1 There is a natural a tradeoff between the generality of afile format and its usefulness for a specific purpose. Thus,features
18、 designed to meet the needs of one community mayhinder the usefulness of a file format for other uses. To besuccessful across the field of additive manufacturing, this fileformat is designed to address the following concerns:3.1.1 Technology IndependenceThe file format shall de-scribe an object in a
19、 general way such that any machine canbuild it to the best of its ability. It is resolution and layer-thickness independent and does not contain information spe-cific to any one manufacturing process or technique. This doesnot negate the inclusion of properties that only certain ad-vanced machines s
20、upport (for example, color, multiple mate-rials, and so forth), but these are defined in such a way as toavoid exclusivity.3.1.2 SimplicityTheAMF file format is easy to implementand understand. The format can be read and debugged in asimple ASCII text viewer to encourage understanding andadoption. N
21、o identical information is stored in multiple places.3.1.3 ScalabilityThe file format scales well with increasein part complexity and size and with the improving resolutionand accuracy of manufacturing equipment. This includes beingable to handle large arrays of identical objects, complexrepeated in
22、ternal features (for example, meshes), smoothcurved surfaces with fine printing resolution, and multiplecomponents arranged in an optimal packing for printing.3.1.4 PerformanceThe file format should enable reason-able duration (interactive time) for read-and-write operationsand reasonable file sizes
23、 for a typical large object. Detailedperformance data are provided in Appendix X1.3.1.5 Backwards CompatibilityAny existing STL file canbe converted directly into a valid AMF file without any loss ofinformation and without requiring any additional information.AMF files are also easily converted back
24、 to STL for use onlegacy systems, although advanced features will be lost. Thisformat maintains the triangle-mesh geometry representation totake advantage of existing optimized slicing algorithm andcode infrastructure already in existence.3.1.6 Future CompatibilityTo remain useful in a rapidlychangi
25、ng industry, this file format is easily extensible whileremaining compatible with earlier versions and technologies.This allows new features to be added as advances in technol-ogy warrant, while still working flawlessly for simple homog-enous geometries on the oldest hardware.4. Structure of This Sp
26、ecification4.1 Information specified throughout this specification isstored in XML format. XML is an ASCII text file comprisinga list of elements and attributes. Using this widely accepteddata format opens the door to a rich host of tools for creating,viewing, manipulating, parsing, and storingAMF f
27、iles. XML ishuman readable, which makes debugging errors in the filepossible. XML can be compressed or encrypted or both ifdesired in a post-processing step using highly optimizedstandardized routines.4.2 Another significant advantage of XML is its inherentflexibility. Missing or additional paramete
28、rs do not present aproblem for a parser as long as the document conforms to theXML standard. Practically, this allows new features to beadded without needing to update old versions of the parser,such as in legacy software.4.3 PrecisionThis file format is agnostic as to the preci-sion of the represen
29、tation of numeric values. It is the respon-sibility of the generating program to write as many or as fewdigits as are necessary for proper representation of the targetobject. However, a parsing program should read and processreal numbers in double precision (64 bit).4.4 Future Amendments and Additio
30、nsAdditional XMLelements can be added provisionally to any AMF file for anypurpose but will not be considered part of this specification.Anunofficial AMF element can be ignored by any reader and doesnot need to be stored or reproduced on output. An elementbecomes official only when it is formally ac
31、cepted into thisspecification.5. General Structure5.1 The AMF file begins with the XML declaration linespecifying the XML version and encoding, for example:5.2 Blank lines and standard XML comments can be inter-spersed in the file and will be ignored by any interpreter, forexample:5.3 The remainder
32、of the file is enclosed between anopening element and a closing element.These elements are necessary to denote the file type, as well asto fulfill the requirement that all XML files have a single-rootelement. The version of the AMF standard as well as allstandard XML namespace declarations can be us
33、ed, such as thelang attribute designed to identify the human language used.The unit system can also be specified (mm, inch, ft, metres, ormicrometres). In absence of a unit specification, millimetresare assumed.5.4 Within the AMF brackets, there are five top levelelements:5.4.1 The object element de
34、fines a volume orvolumes of material, each of which are associated with amaterial identification (ID) for printing. At least one objectelement shall be present in the file. Additional objects areoptional.5.4.2 The optional material element de-fines one or more materials for printing with an associat
35、edmaterial ID. If no material element is included, a single defaultmaterial is assumed.5.4.3 The optional texture element definesone or more images or textures for color or texture mappingeach with an associated texture ID.F2915 1125.4.4 The optional constellation el-ement hierarchically combines ob
36、jects and other constellationsinto a relative pattern for printing. If no constellation elementsare specified, each object element will be imported with norelative position data. The parsing program can determine therelative positioning of the objects if more than one object isspecified in the file.
37、5.4.5 The optional metadata elementspecifies additional information about the object(s) and ele-ments contained in the file.5.5 Only a single object element is required for a fullyfunctional AMF file.6. Geometry Specification6.1 The top level element specifies a unique idand contains two child eleme
38、nts: and. The element can optionally specify amaterial.6.2 The required element lists all verticesthat are used in this object. Each vertex is implicitly assigneda 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-dimen
39、sional (3D) space using the, , and elements.6.3 After the vertex information, at least one element shall be included. Each volume encapsulates a closedvolume of the object. Multiple volumes can be specified in asingle object. Volumes may share vertices at interfaces but maynot have any overlapping v
40、olume.6.4 Within each volume, the child element shall be used to define triangles that tessellate the surface of thevolume. Each element will list three verticesfrom the set of indices of the previously defined vertices. Theindices of the three vertices of the triangles are specified usingthe , , an
41、d elements. The order of the verticesshall be according to the right-hand rule such that vertices arelisted in counter-clockwise order as viewed from the outside.Each triangle is implicitly assigned a number in the order inwhich it was declared starting at zero (see Fig. 1).6.5 Smooth Geometry:6.5.1
42、 By default, all triangles are assumed to be flat and alltriangle edges are assumed to be straight lines connecting theirtwo vertices. However, curved triangles and curved edges canoptionally be specified to reduce the number of mesh elementsrequired to describe a curved surface.6.5.2 During read, a
43、 curved triangle patch shall be recur-sively subdivided into four triangles by the parsing program togenerate a temporary set of flat triangles at any desiredresolution for manufacturing or display. The depth of recursionshall be determined by the parsing program, but a minimallevel of four is recom
44、mended (that is, convert a single curvedtriangle into 256 flat triangles).6.5.3 During write, the encoding software shall determineautomatically the minimum number of curved triangles re-quired to specify the target geometry to the desired tolerance,assuming that the parser will perform at least fou
45、r levels ofsubdivision for any curved triangle.6.5.4 To specify curvature, a vertex can optionally contain achild element to specify desired surface normal atthe location of the vertex. The normal should be unit length andpointing outwards. If this normal is specified, all triangle edgesmeeting at t
46、hat vertex should be curved so that they areperpendicular to that normal and in the plane defined by thenormal and the original straight edge.6.5.5 When the curvature of a surface at a vertex isundefined (for example, at a cusp, corner, or edge), an element can be used to specify the curvature of a
47、singlenonlinear edge joining two vertices. The curvature is specifiedusing the tangent direction vectors at the beginning and end ofthat edge. The element will take precedence in case ofa conflict with the curvature implied by a element.6.5.6 Normals shall not be specified for vertices referencedonl
48、y by planar triangles. Edge tangents shall not be specifiedfor linear edges.6.5.7 When interpreting normal and tangents, Hermite in-terpolation will be used. See Annex A3 for formulae forcarrying out this interpolation.6.5.8 The geometry shall not be used to describe supportstructure. Only the final
49、 target structure shall be described.6.6 Restrictions on GeometryAll geometry shall complywith the following restrictions:6.6.1 Every triangle shall have exactly three different verti-ces.6.6.2 Triangles may not intersect or overlap except at theircommon edges or common vertices.6.6.3 Volumes shall enclose a closed space with nonzerovolume.FIG. 1 Basic AMF File Containing Only a List of Vertices andTrianglesThis Structure Is Compatible with the STL StandardF2915 1136.6.4 Volumes may not overlap.6.6.5 Every vertex shall be referenced by at least threetriangles
