SIST-TP CEN/TR/ISO/ASTM 52912:2020
(Main)Additive manufacturing - Design - Functionally graded additive manufacturing (ISO/ASTM/TR 52912:2020)
Additive manufacturing - Design - Functionally graded additive manufacturing (ISO/ASTM/TR 52912:2020)
This will be delivered in the form of a Technical Report. The aim of this document is to
describe the concept of Functionally Graded Additive Manufacturing and to document current
practices. It recognizes that Functionally Graded parts have the potential to support the
development of Next-Generation products, based on the use of specialised materials that
have been optimized for their functional properties. The report also clarifies the definitions of
terms being used today such as 4D Printing (4DP), Smart Memory Polymers (SMP), Stimuli-
Responsive Materials (SRM), Functionally Graded Materials (FGM), Multi-Material Printing
(MMP), Variable Property Rapid Prototyping (VPRP), Self-Assembly and Self-Disassembly.
The report outlines key manufacturing processes and examples of materials that have been
used to produce FGM parts as well as their potential applications. The report will include a
review of capabilities and limitations of existing CAD and Finite Element Method (FEM)
software that can support the production of Functionally Graded Additive Manufactured parts.
It discusses how existing software has been used to simulate FG materials that can have
discrete or continuous variation of mechanical properties such as varying elastic modulus of
the FGM piece. Finally, the report will discuss current limitations and suggests areas for
future work.
Technischer Bericht für die Gestaltung von additiv gefertigten, gradierten Bauteilen (ISO/ASTM/TR 52912:2020)
Fabrication additive - Conception - Fabrication additive à gradient fonctionnel (ISO/ASTM/TR 52912:2020)
L'utilisation de la fabrication additive (FA) permet la fabrication de composants géométriquement complexes en déposant des matériaux avec exactitude et de manière contrôlée. Les progrès technologiques dans le domaine du matériel, des logiciels de FA, ainsi que l'ouverture de nouveaux marchés exigent une plus grande flexibilité et une plus grande efficacité des produits actuels, ce qui encourage la recherche de matériaux nouveaux dotés de capacités à gradient fonctionnel et de hautes performances. Cela a été désigné par la fabrication additive à gradient fonctionnel (FGAM), une technique de fabrication couche par couche qui consiste à faire varier graduellement le rapport de l'organisation du matériau au sein d'un composant pour répondre à une fonction prévue. Comme la recherche dans ce domaine a gagné en intérêt dans le monde entier, les interprétations du concept de FGAM exigent une plus grande clarification. L'objectif du présent document est de présenter une compréhension conceptuelle de la FGAM. L'État de l'Art actuel et les capacités actuelles de la technologie de FGAM seront examinés, ainsi que ses obstacles et limites technologiques. Les formats d'échange de données et certaines applications récentes sont ici évalués, suivis de recommandations sur les stratégies possibles pour surmonter les obstacles et les orientations futures pour le décollage de la FGAM.
Aditivna proizvodnja - Konstruiranje - Proizvodnja delov s funkcijsko porazdeljenimi lastnostmi (ISO/ASTM/TR 52912:2020)
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SLOVENSKI STANDARD
SIST-TP CEN/TR/ISO/ASTM 52912:2020
01-december-2020
Aditivna proizvodnja - Konstruiranje - Proizvodnja delov s funkcijsko
porazdeljenimi lastnostmi (ISO/ASTM/TR 52912:2020)
Additive manufacturing - Design - Functionally graded additive manufacturing
(ISO/ASTM/TR 52912:2020)
Technischer Bericht für die Gestaltung von additiv gefertigten, gradierten Bauteilen
(ISO/ASTM/TR 52912:2020)
Fabrication additive - Conception - Fabrication additive à gradient fonctionnel
(ISO/ASTM/TR 52912:2020)
Ta slovenski standard je istoveten z: CEN/TR/ISO/ASTM 52912:2020
ICS:
25.030 3D-tiskanje Additive manufacturing
SIST-TP CEN/TR/ISO/ASTM 52912:2020 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
CEN/TR/ISO/ASTM
TECHNICAL REPORT
52912
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
October 2020
ICS 25.030
English Version
Additive manufacturing - Design - Functionally graded
additive manufacturing (ISO/ASTM/TR 52912:2020)
Fabrication additive - Conception - Fabrication additive Technischer Bericht für die Gestaltung von additiv
à gradient fonctionnel (ISO/ASTM/TR 52912:2020) gefertigten, gradierten Bauteilen (ISO/ASTM/TR
52912:2020)
This Technical Report was approved by CEN on 31 August 2020. It has been drawn up by the Technical Committee CEN/TC 438.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR/ISO/ASTM 52912:2020 E
worldwide for CEN national Members.
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CEN/TR/ISO/ASTM 52912:2020 (E)
Contents Page
European foreword . 3
2
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
CEN/TR/ISO/ASTM 52912:2020 (E)
European foreword
This document (CEN/TR/ISO/ASTM 52912:2020) has been prepared by Technical Committee ISO/TC
261 "Additive manufacturing" in collaboration with Technical Committee CEN/TC 438 “Additive
Manufacturing” the secretariat of which is held by AFNOR.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Endorsement notice
The text of ISO/ASTM/TR 52912:2020 has been approved by CEN as CEN/TR/ISO/ASTM 52912:2020
without any modification.
3
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
TECHNICAL ISO/ASTM TR
REPORT 52912
First edition
2020-09
Additive manufacturing — Design
— Functionally graded additive
manufacturing
Fabrication additive — Conception — Fabrication additive à gradient
fonctionnel
Reference number
ISO/ASTM TR 52912:2020(E)
©
ISO/ASTM International 2020
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ISO/ASTM TR 52912:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/ASTM International 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may be
reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester. In the United States, such requests should be sent to ASTM International.
ISO copyright office ASTM International
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Published in Switzerland
ii © ISO/ASTM International 2020 – All rights reserved
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ISO/ASTM TR 52912:2020(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abreviations . 1
5 Concept of Functionally Graded Additive Manufacturing (FGAM) .3
5.1 General . 3
5.2 Homogeneous compositions — Single Material FGAM. 3
5.3 Heterogeneous compositions — Multi-material FGAM . 4
6 Advances of functionally graded additive manufacturing . 8
6.1 General . 8
6.2 AM and FGAM process . 8
6.3 Material extrusion . 9
6.4 Powder bed fusion .12
6.5 Directed energy deposition .13
6.6 Sheet lamination .14
7 Current limitations of FGAM .16
7.1 General .16
7.2 Material limitations . .16
7.2.1 General.16
7.2.2 Defining the optimum material property distribution .17
7.2.3 Predicting the material properties of manufactured components .17
7.2.4 Material selection .17
7.2.5 Understanding differences and defining tolerances .17
7.3 Limitations of current additive manufacturing technologies .17
7.4 CAD Software limitations .18
7.4.1 General.18
7.4.2 Data exchange formats .19
8 Potential applications of FGAM .20
8.1 General .20
8.2 Biomedical applications .21
8.3 Aerospace applications .21
8.4 Consumer markets.21
9 Summary .22
Bibliography .23
© ISO/ASTM International 2020 – All rights reserved iii
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ISO/ASTM TR 52912:2020(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by ISO/TC 261, Additive manufacturing, in cooperation with ASTM F 42,
Additive manufacturing technologies, on the basis of a partnership agreement between ISO and ASTM
International with the aim to create a common set of ISO/ASTM standards on additive manufacturing
and in collaboration with the European Committee for Standardization (CEN) Technical Committee
CEN/TC 438, Additive manufacturing, in accordance with the agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO/ASTM International 2020 – All rights reserved
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ISO/ASTM TR 52912:2020(E)
Introduction
Functionally Graded Materials (FGMs) were developed in 1984 for a space plane project to sustain high
thermal barriers to overcome the shortcomings of traditional composite materials (AZO Materials, 2002).
Traditional composites [Figure 1 a)] are homogeneous mixtures, therefore involving a compromise
between the desirable properties of the component materials. Functionally Graded Materials (FGMs)
are a class of advanced materials with spatially varying composition over a changing dimension, with
[56]
corresponding changes in material properties built-in . FGMs attain their multifunctional status by
mapping performance requirements to strategies of material structuring and allocation [Figure 1 b)].
The manufacturing processes of conventional FGMs include shot peening, ion implantation, thermal
spraying, electrophoretic deposition and chemical vapour deposition. Since additive manufacturing
processes builds parts by successive addition of material, they provide the possibility to produce
products with Functionally Graded properties, thereby introducing the concept often known as
Functionally Graded Additive Manufacturing (FGAM). As this area of work is new, driven by academic
research, and lacks available standardisation, there have been multiple different names proposed by
different researchers in different publications as terms for this area, for example, functionally graded
[56] [57]
rapid prototyping (FGRP) , varied property rapid prototyping (VPRP) and site-specific properties
[72]
additive manufacturing . However, even if there clearly is a great need for clarification of key terms
associated with FGAM, this document does not include any attempts of alignment in terminology.
This document is an overview of state of the art and the possibilities for FGAM enabled by present AM
process technology and thus a purely informative document. Since this overview is based on available
publications, and in order to facilitate cross referencing from these publications, this document has
used the terms concerning FGAM as they are used in the original publications.
a) Traditional composite b) FGM composite
Figure 1 — Allocation of materials in a traditional composite and an FGM composite
© ISO/ASTM International 2020 – All rights reserved v
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
TECHNICAL REPORT ISO/ASTM TR 52912:2020(E)
Additive manufacturing — Design — Functionally graded
additive manufacturing
1 Scope
The use of Additive Manufacturing (AM) enables the fabrication of geometrically complex components
by accurately depositing materials in a controlled way. Technological progress in AM hardware,
software, as well as the opening of new markets demand for higher flexibility and greater efficiency
in today’s products, encouraging research into novel materials with functionally graded and high-
performance capabilities. This has been termed as Functionally Graded Additive Manufacturing
(FGAM), a layer-by-layer fabrication technique that involves gradationally varying the ratio of the
material organization within a component to meet an intended function. As research in this field has
gained worldwide interest, the interpretations of the FGAM concept requires greater clarification.
The objective of this document is to present a conceptual understanding of FGAM. The current-state of
art and capabilities of FGAM technology will be reviewed alongside with its challenging technological
obstacles and limitations. Here, data exchange formats and some of the recent application is evaluated,
followed with recommendations on possible strategies in overcoming barriers and future directions
for FGAM to take off.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Abreviations
AM Additive Manufacturing (see ISO/ASTM 52900)
AMF Additive Manufacturing Format, see 8.4.2.1 (see ISO/ASTM 52900)
[48]
CAD Computer Aided Design
[14]
CAE Computer Aided Engineering
DED Directed Energy Deposition, see Clause 6 (see ISO/ASTM 52900)
DMLS Direct Metal Laser Sintering, the name for laser-based metal powder bed fusion process
[40]
by EOS Gmbh
EBM Electron Beam Melting, the name for electron beam based metal powder bed fusion
[40]
process by Arcam AB
[19]
FAV Fabricatable Voxel, see 8.4.2.2
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ISO/ASTM TR 52912:2020(E)
[48]
FEA Finite Element Analysis
FEF Freeze-form Extrusion Fabrication, a material extrusion process based on the extrusion
of feedstock in the form of pastes and application of freeze drying to form a green body
which can be consolidated to the desired material properties by sintering. Presently
[34]
only used for research and development projects.
[18]
FEM Finite Element Method
[39]
FDM Fused Deposition Modelling, name for material extrusion processes by Stratasys Ltd.
[61]
FGAM Functionally Graded Additive Manufacturing
[61]
FGMs Functionally Graded Materials
FGRP Functionally Graded Rapid Prototyping, name for FGAM used by Neri Oxman in some
[56]
publications.
LMD Laser Metal Deposition, a common name for directed energy deposition processes that
uses laser as the source of energy to melt and fuse metallic materials as they are being
[21]
deposited, see Clause 6.
LOM Laminated Object Manufacturing, name of sheet lamination processes originally
[42]
developed by Helisys Inc.
MMAM Multi-Material Additive Manufacturing, name used for AM when using more than one
[61]
material in the same process.
MM FGAM Multi-Material Functionally Graded Additive Manufacturing, name for FGAM when the
functional grading is based on building parts using more than one material in the same
process, and the composition of the different material components is controlled by the
[43]
computer program.
PBF Powder Bed Fusion (ISO/ASTM 52900)
SHS Selective Heat Sintering, name of a powder bed fusion process that fuse polymer
powder by means of a thermal printhead instead of the more common laser. The
process was originally developed by Blueprinter but has been withdrawn from the
[40]
market following the bankruptcy of this company.
SLM Selective Laser Melting, name for laser-based metal powder bed fusion process orig-
inally developed in collaboration between F&S Stereolithographietechnik GmbH (Fock-
ele & Schwarze) and Fraunhofer Institute for Laser Technology. This name is a regis-
[40]
tered trademark of SLM Solutions Group AG and Realizer GmbH.
SLS Selective Laser Sintering, name for powder bed fusion process originally developed by
DTM Corp, but which has been assumed by 3D Systems by the acquisition of this com-
pany. Since this was the first powder bed fusion process to be commercialized, it has
[40]
sometimes been used synonymously for all powder bed fusion processes.
STL Stereolithography, name for a digital file format for three dimensional solid models
originally developed for the Stereolithography process by 3D Systems, hence the name.
Since this conversion to this format has been commonly available in several CAD
programs this file format has until present times effectively been functioning as a
de-facto standard for AM processes. (see ISO/ASTM 52900)
UAM Ultrasonic Additive Manufacturing, name for a metal sheet lamination process by
Fabrisonic LLC. The process fuses thin sheets (or ribbons) of metal by ultrasonic vibra-
[43]
tions.
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ISO/ASTM TR 52912:2020(E)
[8]
VDM Vague Discrete Modelling
VPRP Variable Property Rapid Prototyping, name for FGAM used by Neri Oxman in some
[57]
publications.
3MF 3D Manufacturing Format, a digital file format for three dimensional solid models in
[3]
additive manufacturing, developed by the 3MF consortium, see 8.4.2.3.
5 Concept of Functionally Graded Additive Manufacturing (FGAM)
5.1 General
Additive Manufacturing (AM) is the process of joining materials to make parts from 3D model data,
usually layer upon layer, as opposed to subtractive manufacturing and formative manufacturing
methodologies (ISO/ASTM 52900). AM enables the direct fabrication of fine detailed bespoke
components by accurately placing material(s) at set positions within a design domain as a single
[76]
unit . The use of AM has given opportunity to produce parts using FGM, through a process known as
Functionally Graded Additive Manufacturing (FGAM). AM technologies suitable for the fabrication of
[43]
FGMs include Material Extrusion, Direct-Energy Deposition, Powder Bed Fusion, Sheet Lamination
and PolyJet technology.
Functionally Graded Additive Manufacturing (FGAM) is a layer-by-layer fabrication technique that
intentionally modify process parameters and gradationally varies the spatial of material(s) organization
within one component to meet intended function.
FGAM offers a streamlined path from idea to reality. The emergence of FGAM has the potential to
achieve more efficiently engineered structures. The aim of using FGAM is to fabricate performance-
based freeform components driven by their graduated material(s) behaviour. In contrast to conventional
single-material and multi-material AM which focuses mainly on shape-centric prototyping, FGAM is
a material-centric fabrication process that signifies a shift from contour modelling to performance
modelling. Having the performance-driven functionality built-in directly into the material is a
fundamental advantage and a significant improvement to AM technologies. An example includes highly
customizable internal features with integrated functionalities that would be impossible to produce
[5]
using conventional manufacturing . The amount, volume, shape and location of the reinforcement
in the material matrix can be precisely controlled to achieve the desired mechanical properties for a
[18]
specific application .
Reference [57] describes the concept of FGAM as a Variable Property Rapid Prototyping (VPRP) method
with the ability to strategically control the density and directionality of material substance in a complex
3D distribution to produce a high level of seamless integration of monolithic structure using the same
machine. The material characteristics and properties are altered by changing the composition, phase
or microstructure with a pre-determined location. The potential material composition achievable by
FGAM can be characterised into 3 types:
a) variable densification within a homogeneous composition;
b) heterogeneous composition through simultaneously combining two or more materials through
gradual transition;
c) using a combination of variable densification within a heterogeneous composition.
These three types of characteristics are described in 5.2 and 5.3.
5.2 Homogeneous compositions — Single Material FGAM
FGAM can produce efficiently engineered structures by strategically modulating the spatial position (e.g.
[43]
density and porosity) and morphology of lattice structures across the volume of the bulk material .
We term this as varied densification FGAM (also known as porosity-graded FGAM). Reference [56]
proposed this as a biological-inspired rapid fabrication that occurs in nature such as the radial density
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
ISO/ASTM TR 52912:2020(E)
gradients in palm trees, spongy trabecular structure of bone and tissue variation in muscle which is
heterogeneous in elasticity and stiffness. The directionality, magnitude and density concentration of
material substance in a monolithic anisotropic composite structure contribute to functional deviations
[54]
to modulate the physical properties, and to create functional shapes through structural hierarchy .
[27]
Man-made structures such as concrete pillars are typically volumetrically homogeneous . Varied
densification single-material FGAM was demonstrated through Steven Keating’s work on functionally
graded concrete being fabricated by a MakerBot machine with a modified material extruder. The
concrete piece showed a functional gradient of density to mimic the cellular structures of a palm tree,
from a solid exterior to a porous core. The porosity gradient was achieved by varying the powder
particle sizes that were assigned in different locations during the gradation process or by varying the
[43]
production process parameters . For Reference [27], the density was controlled by aggregating the
water ratio of the concrete at a given position, which led to excellent strength-to-weight ratio, making it
lighter and yet more efficient and stronger than a solid piece of concrete.
5.3 Heterogeneous compositions — Multi-material FGAM
Multiple-material Additive Manufacturing (MMAM) is achievable using conventional 3D printers
[77]
with multiple nozzles to deliver different materials to the platform . In powder bed fusion, MMAM
can be realized by utilizing a conventional delivery device in combination with a suction module to
[7]
remove powder after the solidifying process-step . As sharp interfaces exist in most conventional
[72]
MMAM composites where two materials meet and interact, this creates a brittle phase . Failure is
commonly initiated between discrete change of materials properties, such as delamination or cracks
[17]
caused by the surface tension between two materials . Multi-material (MM) FGAM seeks to improve
the interfacial bond by removing the distinct boundaries between dissimilar or incompatible materials.
The mechanical stress concentrations and thermal stress caused by different expansion coefficients
[72]
will be largely reduced . Figures 2, a) and b) explain the approach of voxellization of Multi-material
Additive Manufacturing according to Reference [7].
4 © ISO/ASTM International 2020 – All rights reserved
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ISO/ASTM TR 52912:2020(E)
a) Conceptual diagram showing voxels arranged in 3D form (Fraunhofer IGCV and
Reference [7])
b) Illustration of MMAM (Fraunhofer IGCV and Reference [7])
Key
1 building direction
2 mono-material
3 2D hybrid
4 2D multi-material
5 3D multi-material
6 substrate
Figure 2 — Voxellization of multi-material additive manufacturing
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
ISO/ASTM TR 52912:2020(E)
a) Multi-material AM b) Functionally
...
SLOVENSKI STANDARD
SIST-TP CEN/TR/ISO/ASTM 52912:2020
01-december-2020
Aditivna proizvodnja - Snovanje - Funkcijsko razvrščena aditivna proizvodnja
(ISO/ASTM/TR 52912:2020)
Additive manufacturing - Design - Functionally graded additive manufacturing
(ISO/ASTM/TR 52912:2020)
Technischer Bericht für die Gestaltung von additiv gefertigten, gradierten Bauteilen
(ISO/ASTM/TR 52912:2020)
Fabrication additive - Conception - Fabrication additive à gradient fonctionnel
(ISO/ASTM/TR 52912:2020)
Ta slovenski standard je istoveten z: CEN/TR/ISO/ASTM 52912:2020
ICS:
25.030 3D-tiskanje Additive manufacturing
SIST-TP CEN/TR/ISO/ASTM 52912:2020 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
CEN/TR/ISO/ASTM
TECHNICAL REPORT
52912
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
October 2020
ICS 25.030
English Version
Additive manufacturing - Design - Functionally graded
additive manufacturing (ISO/ASTM/TR 52912:2020)
Fabrication additive - Conception - Fabrication additive Technischer Bericht für die Gestaltung von additiv
à gradient fonctionnel (ISO/ASTM/TR 52912:2020) gefertigten, gradierten Bauteilen (ISO/ASTM/TR
52912:2020)
This Technical Report was approved by CEN on 31 August 2020. It has been drawn up by the Technical Committee CEN/TC 438.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR/ISO/ASTM 52912:2020 E
worldwide for CEN national Members.
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
CEN/TR/ISO/ASTM 52912:2020 (E)
Contents Page
European foreword . 3
2
---------------------- Page: 4 ----------------------
SIST-TP CEN/TR/ISO/ASTM 52912:2020
CEN/TR/ISO/ASTM 52912:2020 (E)
European foreword
This document (CEN/TR/ISO/ASTM 52912:2020) has been prepared by Technical Committee ISO/TC
261 "Additive manufacturing" in collaboration with Technical Committee CEN/TC 438 “Additive
Manufacturing” the secretariat of which is held by AFNOR.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Endorsement notice
The text of ISO/ASTM/TR 52912:2020 has been approved by CEN as CEN/TR/ISO/ASTM 52912:2020
without any modification.
3
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
TECHNICAL ISO/ASTM TR
REPORT 52912
First edition
2020-09
Additive manufacturing — Design
— Functionally graded additive
manufacturing
Fabrication additive — Conception — Fabrication additive à gradient
fonctionnel
Reference number
ISO/ASTM TR 52912:2020(E)
©
ISO/ASTM International 2020
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SIST-TP CEN/TR/ISO/ASTM 52912:2020
ISO/ASTM TR 52912:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/ASTM International 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may be
reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester. In the United States, such requests should be sent to ASTM International.
ISO copyright office ASTM International
CP 401 • Ch. de Blandonnet 8 100 Barr Harbor Drive, PO Box C700
CH-1214 Vernier, Geneva West Conshohocken, PA 19428-2959, USA
Phone: +41 22 749 01 11 Phone: +610 832 9634
Fax: +610 832 9635
Email: copyright@iso.org Email: khooper@astm.org
Website: www.iso.org Website: www.astm.org
Published in Switzerland
ii © ISO/ASTM International 2020 – All rights reserved
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Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abreviations . 1
5 Concept of Functionally Graded Additive Manufacturing (FGAM) .3
5.1 General . 3
5.2 Homogeneous compositions — Single Material FGAM. 3
5.3 Heterogeneous compositions — Multi-material FGAM . 4
6 Advances of functionally graded additive manufacturing . 8
6.1 General . 8
6.2 AM and FGAM process . 8
6.3 Material extrusion . 9
6.4 Powder bed fusion .12
6.5 Directed energy deposition .13
6.6 Sheet lamination .14
7 Current limitations of FGAM .16
7.1 General .16
7.2 Material limitations . .16
7.2.1 General.16
7.2.2 Defining the optimum material property distribution .17
7.2.3 Predicting the material properties of manufactured components .17
7.2.4 Material selection .17
7.2.5 Understanding differences and defining tolerances .17
7.3 Limitations of current additive manufacturing technologies .17
7.4 CAD Software limitations .18
7.4.1 General.18
7.4.2 Data exchange formats .19
8 Potential applications of FGAM .20
8.1 General .20
8.2 Biomedical applications .21
8.3 Aerospace applications .21
8.4 Consumer markets.21
9 Summary .22
Bibliography .23
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ISO/ASTM TR 52912:2020(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by ISO/TC 261, Additive manufacturing, in cooperation with ASTM F 42,
Additive manufacturing technologies, on the basis of a partnership agreement between ISO and ASTM
International with the aim to create a common set of ISO/ASTM standards on additive manufacturing
and in collaboration with the European Committee for Standardization (CEN) Technical Committee
CEN/TC 438, Additive manufacturing, in accordance with the agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO/ASTM International 2020 – All rights reserved
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Introduction
Functionally Graded Materials (FGMs) were developed in 1984 for a space plane project to sustain high
thermal barriers to overcome the shortcomings of traditional composite materials (AZO Materials, 2002).
Traditional composites [Figure 1 a)] are homogeneous mixtures, therefore involving a compromise
between the desirable properties of the component materials. Functionally Graded Materials (FGMs)
are a class of advanced materials with spatially varying composition over a changing dimension, with
[56]
corresponding changes in material properties built-in . FGMs attain their multifunctional status by
mapping performance requirements to strategies of material structuring and allocation [Figure 1 b)].
The manufacturing processes of conventional FGMs include shot peening, ion implantation, thermal
spraying, electrophoretic deposition and chemical vapour deposition. Since additive manufacturing
processes builds parts by successive addition of material, they provide the possibility to produce
products with Functionally Graded properties, thereby introducing the concept often known as
Functionally Graded Additive Manufacturing (FGAM). As this area of work is new, driven by academic
research, and lacks available standardisation, there have been multiple different names proposed by
different researchers in different publications as terms for this area, for example, functionally graded
[56] [57]
rapid prototyping (FGRP) , varied property rapid prototyping (VPRP) and site-specific properties
[72]
additive manufacturing . However, even if there clearly is a great need for clarification of key terms
associated with FGAM, this document does not include any attempts of alignment in terminology.
This document is an overview of state of the art and the possibilities for FGAM enabled by present AM
process technology and thus a purely informative document. Since this overview is based on available
publications, and in order to facilitate cross referencing from these publications, this document has
used the terms concerning FGAM as they are used in the original publications.
a) Traditional composite b) FGM composite
Figure 1 — Allocation of materials in a traditional composite and an FGM composite
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TECHNICAL REPORT ISO/ASTM TR 52912:2020(E)
Additive manufacturing — Design — Functionally graded
additive manufacturing
1 Scope
The use of Additive Manufacturing (AM) enables the fabrication of geometrically complex components
by accurately depositing materials in a controlled way. Technological progress in AM hardware,
software, as well as the opening of new markets demand for higher flexibility and greater efficiency
in today’s products, encouraging research into novel materials with functionally graded and high-
performance capabilities. This has been termed as Functionally Graded Additive Manufacturing
(FGAM), a layer-by-layer fabrication technique that involves gradationally varying the ratio of the
material organization within a component to meet an intended function. As research in this field has
gained worldwide interest, the interpretations of the FGAM concept requires greater clarification.
The objective of this document is to present a conceptual understanding of FGAM. The current-state of
art and capabilities of FGAM technology will be reviewed alongside with its challenging technological
obstacles and limitations. Here, data exchange formats and some of the recent application is evaluated,
followed with recommendations on possible strategies in overcoming barriers and future directions
for FGAM to take off.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Abreviations
AM Additive Manufacturing (see ISO/ASTM 52900)
AMF Additive Manufacturing Format, see 8.4.2.1 (see ISO/ASTM 52900)
[48]
CAD Computer Aided Design
[14]
CAE Computer Aided Engineering
DED Directed Energy Deposition, see Clause 6 (see ISO/ASTM 52900)
DMLS Direct Metal Laser Sintering, the name for laser-based metal powder bed fusion process
[40]
by EOS Gmbh
EBM Electron Beam Melting, the name for electron beam based metal powder bed fusion
[40]
process by Arcam AB
[19]
FAV Fabricatable Voxel, see 8.4.2.2
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[48]
FEA Finite Element Analysis
FEF Freeze-form Extrusion Fabrication, a material extrusion process based on the extrusion
of feedstock in the form of pastes and application of freeze drying to form a green body
which can be consolidated to the desired material properties by sintering. Presently
[34]
only used for research and development projects.
[18]
FEM Finite Element Method
[39]
FDM Fused Deposition Modelling, name for material extrusion processes by Stratasys Ltd.
[61]
FGAM Functionally Graded Additive Manufacturing
[61]
FGMs Functionally Graded Materials
FGRP Functionally Graded Rapid Prototyping, name for FGAM used by Neri Oxman in some
[56]
publications.
LMD Laser Metal Deposition, a common name for directed energy deposition processes that
uses laser as the source of energy to melt and fuse metallic materials as they are being
[21]
deposited, see Clause 6.
LOM Laminated Object Manufacturing, name of sheet lamination processes originally
[42]
developed by Helisys Inc.
MMAM Multi-Material Additive Manufacturing, name used for AM when using more than one
[61]
material in the same process.
MM FGAM Multi-Material Functionally Graded Additive Manufacturing, name for FGAM when the
functional grading is based on building parts using more than one material in the same
process, and the composition of the different material components is controlled by the
[43]
computer program.
PBF Powder Bed Fusion (ISO/ASTM 52900)
SHS Selective Heat Sintering, name of a powder bed fusion process that fuse polymer
powder by means of a thermal printhead instead of the more common laser. The
process was originally developed by Blueprinter but has been withdrawn from the
[40]
market following the bankruptcy of this company.
SLM Selective Laser Melting, name for laser-based metal powder bed fusion process orig-
inally developed in collaboration between F&S Stereolithographietechnik GmbH (Fock-
ele & Schwarze) and Fraunhofer Institute for Laser Technology. This name is a regis-
[40]
tered trademark of SLM Solutions Group AG and Realizer GmbH.
SLS Selective Laser Sintering, name for powder bed fusion process originally developed by
DTM Corp, but which has been assumed by 3D Systems by the acquisition of this com-
pany. Since this was the first powder bed fusion process to be commercialized, it has
[40]
sometimes been used synonymously for all powder bed fusion processes.
STL Stereolithography, name for a digital file format for three dimensional solid models
originally developed for the Stereolithography process by 3D Systems, hence the name.
Since this conversion to this format has been commonly available in several CAD
programs this file format has until present times effectively been functioning as a
de-facto standard for AM processes. (see ISO/ASTM 52900)
UAM Ultrasonic Additive Manufacturing, name for a metal sheet lamination process by
Fabrisonic LLC. The process fuses thin sheets (or ribbons) of metal by ultrasonic vibra-
[43]
tions.
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[8]
VDM Vague Discrete Modelling
VPRP Variable Property Rapid Prototyping, name for FGAM used by Neri Oxman in some
[57]
publications.
3MF 3D Manufacturing Format, a digital file format for three dimensional solid models in
[3]
additive manufacturing, developed by the 3MF consortium, see 8.4.2.3.
5 Concept of Functionally Graded Additive Manufacturing (FGAM)
5.1 General
Additive Manufacturing (AM) is the process of joining materials to make parts from 3D model data,
usually layer upon layer, as opposed to subtractive manufacturing and formative manufacturing
methodologies (ISO/ASTM 52900). AM enables the direct fabrication of fine detailed bespoke
components by accurately placing material(s) at set positions within a design domain as a single
[76]
unit . The use of AM has given opportunity to produce parts using FGM, through a process known as
Functionally Graded Additive Manufacturing (FGAM). AM technologies suitable for the fabrication of
[43]
FGMs include Material Extrusion, Direct-Energy Deposition, Powder Bed Fusion, Sheet Lamination
and PolyJet technology.
Functionally Graded Additive Manufacturing (FGAM) is a layer-by-layer fabrication technique that
intentionally modify process parameters and gradationally varies the spatial of material(s) organization
within one component to meet intended function.
FGAM offers a streamlined path from idea to reality. The emergence of FGAM has the potential to
achieve more efficiently engineered structures. The aim of using FGAM is to fabricate performance-
based freeform components driven by their graduated material(s) behaviour. In contrast to conventional
single-material and multi-material AM which focuses mainly on shape-centric prototyping, FGAM is
a material-centric fabrication process that signifies a shift from contour modelling to performance
modelling. Having the performance-driven functionality built-in directly into the material is a
fundamental advantage and a significant improvement to AM technologies. An example includes highly
customizable internal features with integrated functionalities that would be impossible to produce
[5]
using conventional manufacturing . The amount, volume, shape and location of the reinforcement
in the material matrix can be precisely controlled to achieve the desired mechanical properties for a
[18]
specific application .
Reference [57] describes the concept of FGAM as a Variable Property Rapid Prototyping (VPRP) method
with the ability to strategically control the density and directionality of material substance in a complex
3D distribution to produce a high level of seamless integration of monolithic structure using the same
machine. The material characteristics and properties are altered by changing the composition, phase
or microstructure with a pre-determined location. The potential material composition achievable by
FGAM can be characterised into 3 types:
a) variable densification within a homogeneous composition;
b) heterogeneous composition through simultaneously combining two or more materials through
gradual transition;
c) using a combination of variable densification within a heterogeneous composition.
These three types of characteristics are described in 5.2 and 5.3.
5.2 Homogeneous compositions — Single Material FGAM
FGAM can produce efficiently engineered structures by strategically modulating the spatial position (e.g.
[43]
density and porosity) and morphology of lattice structures across the volume of the bulk material .
We term this as varied densification FGAM (also known as porosity-graded FGAM). Reference [56]
proposed this as a biological-inspired rapid fabrication that occurs in nature such as the radial density
© ISO/ASTM International 2020 – All rights reserved 3
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ISO/ASTM TR 52912:2020(E)
gradients in palm trees, spongy trabecular structure of bone and tissue variation in muscle which is
heterogeneous in elasticity and stiffness. The directionality, magnitude and density concentration of
material substance in a monolithic anisotropic composite structure contribute to functional deviations
[54]
to modulate the physical properties, and to create functional shapes through structural hierarchy .
[27]
Man-made structures such as concrete pillars are typically volumetrically homogeneous . Varied
densification single-material FGAM was demonstrated through Steven Keating’s work on functionally
graded concrete being fabricated by a MakerBot machine with a modified material extruder. The
concrete piece showed a functional gradient of density to mimic the cellular structures of a palm tree,
from a solid exterior to a porous core. The porosity gradient was achieved by varying the powder
particle sizes that were assigned in different locations during the gradation process or by varying the
[43]
production process parameters . For Reference [27], the density was controlled by aggregating the
water ratio of the concrete at a given position, which led to excellent strength-to-weight ratio, making it
lighter and yet more efficient and stronger than a solid piece of concrete.
5.3 Heterogeneous compositions — Multi-material FGAM
Multiple-material Additive Manufacturing (MMAM) is achievable using conventional 3D printers
[77]
with multiple nozzles to deliver different materials to the platform . In powder bed fusion, MMAM
can be realized by utilizing a conventional delivery device in combination with a suction module to
[7]
remove powder after the solidifying process-step . As sharp interfaces exist in most conventional
[72]
MMAM composites where two materials meet and interact, this creates a brittle phase . Failure is
commonly initiated between discrete change of materials properties, such as delamination or cracks
[17]
caused by the surface tension between two materials . Multi-material (MM) FGAM seeks to improve
the interfacial bond by removing the distinct boundaries between dissimilar or incompatible materials.
The mechanical stress concentrations and thermal stress caused by different expansion coefficients
[72]
will be largely reduced . Figures 2, a) and b) explain the approach of voxellization of Multi-material
Additive Manufacturing according to Reference [7].
4 © ISO/ASTM International 2020 – All rights reserved
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ISO/ASTM TR 52912:2020(E)
a) Conceptual diagram showing voxels arranged in 3D form (Fraunhofer IGCV and
Reference [7])
b) Illustration of MMAM (Fraunhofer IGCV and Reference [7])
Key
1 building direction
2 mono-material
3 2D hybrid
4 2D multi-material
5 3D multi-material
6 substrate
Figure 2 — Voxellization of multi-material additive manufacturing
© ISO/ASTM International 2020 – All rights reserved 5
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ISO/ASTM TR 52912:2020(E)
a) Multi-material AM b) Functionally graded AM
Key
1 dis
...
SLOVENSKI STANDARD
kSIST-TP FprCEN/ISO/ASTM/TR 52912:2020
01-julij-2020
Aditivna proizvodnja - Snovanje - Funkcijsko razvrščena aditivna proizvodnja
(ISO/ASTM PRF TR 52912:2020)
Additive manufacturing - Design - Functionally graded additive manufacturing
(ISO/ASTM PRF TR 52912:2020)
Technischer Bericht für die Gestaltung von additiv gefertigten, gradierten Bauteilen
(ISO/ASTM PRF TR 52912:2020)
Fabrication additive - Conception - Fabrication additive à gradient fonctionnel
(ISO/ASTM PRF TR 52912:2020)
Ta slovenski standard je istoveten z: FprCEN/ISO/ASTM/TR 52912
ICS:
25.030 3D-tiskanje Additive manufacturing
kSIST-TP FprCEN/ISO/ASTM/TR en,fr,de
52912:2020
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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kSIST-TP FprCEN/ISO/ASTM/TR 52912:2020
TECHNICAL ISO/ASTM TR
REPORT 52912
First edition
Additive manufacturing — Design
— Functionally graded additive
manufacturing
Fabrication additive — Conception — Fabrication additive à gradient
fonctionnel
PROOF/ÉPREUVE
Reference number
ISO/ASTM TR 52912:2020(E)
©
ISO/ASTM International 2020
---------------------- Page: 3 ----------------------
kSIST-TP FprCEN/ISO/ASTM/TR 52912:2020
ISO/ASTM TR 52912:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/ASTM International 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may be
reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester. In the United States, such requests should be sent to ASTM International.
ISO copyright office ASTM International
CP 401 • Ch. de Blandonnet 8 100 Barr Harbor Drive, PO Box C700
CH-1214 Vernier, Geneva West Conshohocken, PA 19428-2959, USA
Phone: +41 22 749 01 11 Phone: +610 832 9634
Fax: +41 22 749 09 47 Fax: +610 832 9635
Email: copyright@iso.org Email: khooper@astm.org
Website: www.iso.org Website: www.astm.org
Published in Switzerland
ii PROOF/ÉPREUVE© ISO/ASTM International 2020 – All rights reserved
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ISO/ASTM TR 52912:2020(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abreviations . 1
4 The concept of Functionally Graded Additive Manufacturing (FGAM) .3
4.1 General . 3
4.2 Homogeneous compositions — Single Material FGAM. 4
4.3 Heterogeneous compositions — Multi-material FGAM . 4
5 Advances of functionally graded additive manufacturing . 8
5.1 General . 8
5.2 The AM and FGAM process . 8
5.3 Material extrusion . 9
5.4 Powder bed fusion .12
6 Directed energy deposition .13
7 Sheet lamination .14
8 Current limitations of FGAM .16
8.1 General .16
8.2 Material limitations . .16
8.2.1 General.16
8.2.2 Defining the optimum material property distribution .17
8.2.3 Predicting the material properties of manufactured components .17
8.2.4 Material selection .17
8.2.5 Understanding differences and defining tolerances .17
8.3 Limitations of current additive manufacturing technologies .17
8.4 CAD Software limitations .18
8.4.1 General.18
8.4.2 Data exchange formats .19
9 Potential applications of FGAM .20
9.1 General .20
9.2 Biomedical applications .21
9.3 Aerospace applications .21
9.4 Consumer markets.21
10 Summary .22
Bibliography .23
© ISO/ASTM International 2020 – All rights reserved PROOF/ÉPREUVE iii
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ISO/ASTM TR 52912:2020(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by ISO/TC 261, Additive manufacturing, in cooperation with ASTM F 42,
Additive manufacturing technologies, on the basis of a partnership agreement between ISO and ASTM
International with the aim to create a common set of ISO/ASTM standards on additive manufacturing
and in collaboration with the European Committee for Standardization (CEN) Technical Committee
CEN/TC 438, Additive manufacturing, in accordance with the agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv PROOF/ÉPREUVE© ISO/ASTM International 2020 – All rights reserved
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ISO/ASTM TR 52912:2020(E)
Introduction
Functionally Graded Materials (FGMs) were developed in 1984 for a space plane project to sustain high
thermal barriers to overcome the shortcomings of traditional composite materials (AZO Materials, 2002).
Traditional composites [Figure 1 a)] are homogeneous mixtures, therefore involving a compromise
between the desirable properties of the component materials. Functionally Graded Materials (FGMs)
are a class of advanced materials with spatially varying composition over a changing dimension, with
[56]
corresponding changes in material properties built-in . FGMs attain their multifunctional status by
mapping performance requirements to strategies of material structuring and allocation [Figure 1 b)].
The manufacturing processes of conventional FGMs include shot peening, ion implantation, thermal
spraying, electrophoretic deposition and chemical vapour deposition. Since additive manufacturing
processes builds parts by successive addition of material, they provide the possibility to produce
products with Functionally Graded properties, thereby introducing the concept often known as
Functionally Graded Additive Manufacturing (FGAM). As this area of work is new, driven by academic
research, and lacks available standardisation, there have been multiple different names proposed by
different researchers in different publications as terms for this area, for example, functionally graded
[56] [57]
rapid prototyping (FGRP) , varied property rapid prototyping (VPRP) and site-specific properties
[72]
additive manufacturing . However, even if there clearly is a great need for clarification of key terms
associated with FGAM, this document does not include any attempts of alignment in terminology.
This document is an overview of state of the art and the possibilities for FGAM enabled by present AM
process technology and thus a purely informative document. Since this overview is based on available
publications, and in order to facilitate cross referencing from these publications, this document has
used the terms concerning FGAM as they are used in the original publications.
a) Traditional composite b) FGM composite
Figure 1 — Allocation of materials in a traditional composite and an FGM composite
© ISO/ASTM International 2020 – All rights reserved PROOF/ÉPREUVE v
---------------------- Page: 7 ----------------------
kSIST-TP FprCEN/ISO/ASTM/TR 52912:2020
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kSIST-TP FprCEN/ISO/ASTM/TR 52912:2020
TECHNICAL REPORT ISO/ASTM TR 52912:2020(E)
Additive manufacturing — Design — Functionally graded
additive manufacturing
1 Scope
The use of Additive Manufacturing (AM) enables the fabrication of geometrically complex components
by accurately depositing materials in a controlled way. Technological progress in AM hardware,
software, as well as the opening of new markets demand for higher flexibility and greater efficiency
in today’s products, encouraging research into novel materials with functionally graded and high-
performance capabilities. This has been termed as Functionally Graded Additive Manufacturing
(FGAM), a layer-by-layer fabrication technique that involves gradationally varying the ratio of the
material organization within a component to meet an intended function. As research in this field has
gained worldwide interest, the interpretations of the FGAM concept requires greater clarification.
The objective of this document is to present a conceptual understanding of FGAM. The current-state of
art and capabilities of FGAM technology will be reviewed alongside with its challenging technological
obstacles and limitations. Here, data exchange formats and some of the recent application is evaluated,
followed with recommendations on possible strategies in overcoming barriers and future directions
for FGAM to take off.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Abreviations
AM Additive Manufacturing (see ISO/ASTM 52900)
AMF Additive Manufacturing Format, see 8.4.2.1 (see ISO/ASTM 52900)
[48]
CAD Computer Aided Design
[14]
CAE Computer Aided Engineering
DED Directed Energy Deposition, see Clause 6 (see ISO/ASTM 52900)
DMLS Direct Metal Laser Sintering, the name for laser-based metal powder bed fusion process
[40]
by EOS Gmbh
© ISO/ASTM International 2020 – All rights reserved PROOF/ÉPREUVE 1
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EBM Electron Beam Melting, the name for electron beam based metal powder bed fusion
[40]
process by Arcam AB
[19]
FAV Fabricatable Voxel, see 8.4.2.2
[48]
FEA Finite Element Analysis
FEF Freeze-form Extrusion Fabrication, a material extrusion process based on the extrusion
of feedstock in the form of pastes and application of freeze drying to form a green body
which can be consolidated to the desired material properties by sintering. Presently
[34]
only used for research and development projects.
[18]
FEM Finite Element Method
[39]
FDM Fused Deposition Modelling, name for material extrusion processes by Stratasys Ltd.
[61]
FGAM Functionally Graded Additive Manufacturing
[61]
FGMs Functionally Graded Materials
FGRP Functionally Graded Rapid Prototyping, name for FGAM used by Neri Oxman in some
[56]
publications.
LMD Laser Metal Deposition, a common name for directed energy deposition processes that
uses laser as the source of energy to melt and fuse metallic materials as they are being
[21]
deposited, see Clause 6.
LOM Laminated Object Manufacturing, name of sheet lamination processes originally
[42]
developed by Helisys Inc.
MMAM Multi-Material Additive Manufacturing, name used for AM when using more than one
[61]
material in the same process.
MM FGAM Multi-Material Functionally Graded Additive Manufacturing, name for FGAM when the
functional grading is based on building parts using more than one material in the same
process, and the composition of the different material components is controlled by the
[43]
computer program.
PBF Powder Bed Fusion (ISO/ASTM 52900)
SHS Selective Heat Sintering, name of a powder bed fusion process that fuse polymer
powder by means of a thermal printhead instead of the more common laser. The
process was originally developed by Blueprinter but has been withdrawn from the
[40]
market following the bankruptcy of this company.
SLM Selective Laser Melting, name for laser-based metal powder bed fusion process orig-
inally developed in collaboration between Realizer Gmbh and Fraunhofer Institute
for Laser Technology. This name is currently a registered trademark of SLM Solutions
[40]
Group AG but is also used by several other companies by license agreement.
SLS Selective Laser Sintering, name for powder bed fusion process originally developed by
DTM Corp, but which has been assumed by 3D Systems by the acquisition of this com-
pany. Since this was the first powder bed fusion process to be commercialized, it has
[40]
sometimes been used synonymously for all powder bed fusion processes.
STL Stereolithography, name for a digital file format for three dimensional solid models
originally developed for the Stereolithography process by 3D Systems, hence the name.
Since this conversion to this format has been commonly available in several CAD
programs this file format has until present times effectively been functioning as a
de-facto standard for AM processes. (see ISO/ASTM 52900)
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UAM Ultrasonic Additive Manufacturing, name for a metal sheet lamination process by
Fabrisonic LLC. The process fuses thin sheets (or ribbons) of metal by ultrasonic vibra-
[43]
tions.
[8]
VDM Vague Discrete Modelling
VPRP Variable Property Rapid Prototyping, name for FGAM used by Neri Oxman in some
[57]
publications.
3MF 3D Manufacturing Format, a digital file format for three dimensional solid models in
[3]
additive manufacturing, developed by the 3MF consortium, see 8.4.2.3.
4 The concept of Functionally Graded Additive Manufacturing (FGAM)
4.1 General
Additive Manufacturing (AM) is the process of joining materials to make parts from 3D model data,
usually layer upon layer, as opposed to subtractive manufacturing and formative manufacturing
methodologies (ISO/ASTM 52900). AM enables the direct fabrication of fine detailed bespoke
components by accurately placing material(s) at set positions within a design domain as a single
[76]
unit . The use of AM has given opportunity to produce parts using FGM, through a process known as
Functionally Graded Additive Manufacturing (FGAM). AM technologies suitable for the fabrication of
[43]
FGMs include Material Extrusion, Direct-Energy Deposition, Powder Bed Fusion, Sheet Lamination
and PolyJet technology.
Functionally Graded Additive Manufacturing (FGAM) is a layer-by-layer fabrication technique that
intentionally modify process parameters and gradationally varies the spatial of material(s) organization
within one component to meet intended function.
FGAM offers a streamlined path from idea to reality. The emergence of FGAM has the potential to
achieve more efficiently engineered structures. The aim of using FGAM is to fabricate performance-
based freeform components driven by their graduated material(s) behaviour. In contrast to conventional
single-material and multi-material AM which focuses mainly on shape-centric prototyping, FGAM is
a material-centric fabrication process that signifies a shift from contour modelling to performance
modelling. Having the performance-driven functionality built-in directly into the material is a
fundamental advantage and a significant improvement to AM technologies. An example includes highly
customizable internal features with integrated functionalities that would be impossible to produce
[5]
using conventional manufacturing . The amount, volume, shape and location of the reinforcement
in the material matrix can be precisely controlled to achieve the desired mechanical properties for a
[18]
specific application .
Reference [57] describes the concept of FGAM as a Variable Property Rapid Prototyping (VPRP) method
with the ability to strategically control the density and directionality of material substance in a complex
3D distribution to produce a high level of seamless integration of monolithic structure using the same
machine. The material characteristics and properties are altered by changing the composition, phase
or microstructure with a pre-determined location. The potential material composition achievable by
FGAM can be characterised into 3 types:
a) variable densification within a homogeneous composition;
b) heterogeneous composition through simultaneously combining two or more materials through
gradual transition;
c) using a combination of variable densification within a heterogeneous composition.
These three types of characteristics are described in 4.2 and 4.3.
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4.2 Homogeneous compositions — Single Material FGAM
FGAM can produce efficiently engineered structures by strategically modulating the spatial position (e.g.
[43]
density and porosity) and morphology of lattice structures across the volume of the bulk material .
We term this as varied densification FGAM (also known as porosity-graded FGAM). Reference [56]
proposed this as a biological-inspired rapid fabrication that occurs in nature such as the radial density
gradients in palm trees, spongy trabecular structure of bone and tissue variation in muscle which is
heterogeneous in elasticity and stiffness. The directionality, magnitude and density concentration of
material substance in a monolithic anisotropic composite structure contribute to functional deviations
[54]
to modulate the physical properties, and to create functional shapes through structural hierarchy .
[27]
Man-made structures such as concrete pillars are typically volumetrically homogeneous . Varied
densification single-material FGAM was demonstrated through Steven Keating’s work on functionally
graded concrete being fabricated by a MakerBot machine with a modified material extruder. The
concrete piece showed a functional gradient of density to mimic the cellular structures of a palm tree,
from a solid exterior to a porous core. The porosity gradient was achieved by varying the powder
particle sizes that were assigned in different locations during the gradation process or by varying the
[43]
production process parameters . For Reference [27], the density was controlled by aggregating the
water ratio of the concrete at a given position, which led to excellent strength-to-weight ratio, making it
lighter and yet more efficient and stronger than a solid piece of concrete.
4.3 Heterogeneous compositions — Multi-material FGAM
Multiple-material Additive Manufacturing (MMAM) is achievable using conventional 3D printers
[77]
with multiple nozzles to deliver different materials to the platform . In powder bed fusion, MMAM
can be realized by utilizing a conventional delivery device in combination with a suction module to
[7]
remove powder after the solidifying process-step . As sharp interfaces exist in most conventional
[72]
MMAM composites where two materials meet and interact, this creates a brittle phase . Failure is
commonly initiated between discrete change of materials properties, such as delamination or cracks
[17]
caused by the surface tension between two materials . Multi-material (MM) FGAM seeks to improve
the interfacial bond by removing the distinct boundaries between dissimilar or incompatible materials.
The mechanical stress concentrations and thermal stress caused by different expansion coefficients
[72]
will be largely reduced . Figures 2, a) and b) explain the approach of voxellization of Multi-material
Additive Manufacturing according to Reference [7].
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a) Conceptual diagram showing voxels arranged in 3D form (Fraunhofer IGCV and
Reference [7])
b) Illustration of MMAM (Fraunhofer IGCV and Reference [7])
Key
1 building direction
2 mono-material
3 2D hybrid
4 2D multi-material
5 3D multi-material
6 substrate
Figure 2 — Voxellization of multi-material additive manufacturing
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a) Multi-material AM b) Functionally graded AM
Key
1 discrete change of material properties 3 pillar to reinforce shape
2 hard material for reinforcement 4 smooth variation in material change
[ ]
Figure 3 — Example of a part with multi-materials 73
Reference [10] addressed the coupling effect of materials through sandwich configurations to
achieve an optimum combination of component properties such as weight, surface hardness, wear
resistance, impact resistance or toughness; or to produce material gradients to change the physical,
[22][28]
chemical, biochemical or mechanical properties through complex morphology . As the geometric
arrangement of the two phases influences the overall material properties, the accuracy of the AM process
is properly managed to ensure that the final component fulfils the expected functional requirements
[72]
. The difference between a Multi-material AM and a Functionally Graded AM part is illustrated in
Figure 3 by Reference [73], Figure 4 further describes the continuous graded microstructure of FGAM
using 2 materials.
Key
1 phase 1 (particles with phase 2 as matrix)
2 transition phase
3 phase 2 (particles with phase 1 as matrix)
Figure 4 — Continuous graded microstructure of FGAM — 2 materials
The continuous variation within the 3D space can be produced by controlling the ratios in which two
[43]
or more materials that are mixed prior to the deposition and curing of the substances . According to
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Reference [75], the compositional variation is controlled by the computer program to be considered
as FGAM. Raw materials that are pre-mixed or composed prior to deposition or solidification are not
considered to be FGAM. FGAM multi-layer composites can be divided into 4 types: transition between
2 materials [Figure 5 b)], 3 materials or above [Figure 5 c)], switched composition between different
locations [Figure 5 d)] and
...
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