Additive manufacturing — Design — Functionally graded additive manufacturing

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.

Fabrication additive — Conception — Fabrication additive à gradient fonctionnel

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.

General Information

Status
Published
Publication Date
24-Sep-2020
Current Stage
6060 - International Standard published
Start Date
25-Sep-2020
Due Date
05-Jul-2020
Completion Date
25-Sep-2020
Ref Project

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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
---------------------- Page: 1 ----------------------
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
---------------------- Page: 2 ----------------------
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
---------------------- Page: 4 ----------------------
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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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
© ISO/ASTM International 2020 – All rights reserved 1
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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.
2 © ISO/ASTM International 2020 – All rights reserved
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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

© 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 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

[72]

requirements . 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

6 © ISO/ASTM International 2020 – All rights reserved
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ISO/ASTM TR 52912:2020(E)

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 heterogeneous compositions with density variation [Figure 5 e)]

a) Conventional MMAM b) MM FGAM (2 materials) c) MM FGAM
(3 materials)
d) Switched composition e) Varied density heterogeneous
Figure 5 — Various classes of multi-material arrangement

The variation of material within a heterogeneous component can be classed as 1D, 2D and 3D

[48]

gradient . Key parameters include the dimension of the gradient vector, the geometric shape and

the repartition of the equipotential surfaces. Figure 6 shows a diagram that classifies the different

gradients of FGAM parts that can be assigned.
Key
1 one-dimensional gradient
2 two-dimensional gradient
3 three-dimensional gradient
Figure 6 — Representation of classifying FGAM gradients
© ISO/ASTM International 2020 – All rights reserved 7
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ISO/ASTM TR 52912:2020(E)
6 Advances of functionally graded additive manufacturing
6.1 General

AM has provided benefits including design freedom, reduced time to market in product development,

[5]

service and increased R&D efficiency . The emergence of FGAM expands the potential of prototyping

of more efficient engineering structure that restore better function and structural performance with

[61]
no tooling costs .

FGAM presents a new production paradigm in terms of industrial machinery, assembly processes, and

[20]

supply chains . It provides a vast range of opportunities for design, performance, cost and lifecycle

management. For instance, light-weight designs can be achieved by adjusting the lattice structures to

retain the structural strength and to achieve reduction in weight. The material matrix, reinforcement,

volume, shape and location of reinforcement and the fabrication method can all be tailored to achieve a

[18]

particular desired property for a specific application . Ground-breaking innovation can be achieved

through material substitution, especially in the medical implants industry, a
...

RAPPORT ISO/ASTM TR
TECHNIQUE 52912
Première édition
2020-09
Fabrication additive — Conception
— Fabrication additive à gradient
fonctionnel
Additive manufacturing — Design — Functionally graded additive
manufacturing
Numéro de référence
ISO/ASTM TR 52912:2020(F)
ISO/ASTM International 2020
---------------------- Page: 1 ----------------------
ISO/ASTM TR 52912:2020(F)
DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO/ASTM International 2020

Tous droits réservés. Sauf prescription différente ou nécessité dans le contexte de sa mise en œuvre, aucune partie de cette

publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique,

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soit d’un organisme membre de l’ISO dans le pays du demandeur. Aux États-Unis, les demandes doivent être adressées à ASTM

International.
ISO copyright office ASTM International
Case postale 401 • Ch. de Blandonnet 8 100 Barr Harbor Drive, PO Box C700
CH-1214 Vernier, Genève West Conshohocken, PA 19428-2959, USA
Tél.: +41 22 749 01 11 Tél.: +610 832 9634
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Web: www.iso.org Web: www.astm.org
Publié en Suisse
ii © ISO/ASTM International 2020 – Tous droits réservés
---------------------- Page: 2 ----------------------
ISO/ASTM TR 52912:2020(F)
Sommaire Page

Avant-propos ..............................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Domaine d'application ................................................................................................................................................................................... 1

2 Références normatives ................................................................................................................................................................................... 1

3 Termes et définitions ....................................................................................................................................................................................... 1

4 Abréviations .............................................................................................................................................................................................................. 1

5 Concept de la fabrication additive à gradient fonctionnel (FGAM) ..................................................................3

5.1 Généralités .................................................................................................................................................................................................. 3

5.2 Compositions homogènes — FGAM mono-matériau ............................................................................................ 4

5.3 Compositions homogènes — FGAM multi-matériaux ........................................................................................... 4

6 Progrès de la fabrication additive à gradient fonctionnel ........................................................................................ 8

6.1 Généralités .................................................................................................................................................................................................. 8

6.2 Procédé de FA et de FGAM ............................................................................................................................................................ 8

6.3 Extrusion de matière ......................................................................................................................................................................10

6.4 Fusion sur lit de poudre ...............................................................................................................................................................12

6.5 Dépôt de matière sous énergie concentrée .................................................................................................................14

6.6 Stratification de couches .............................................................................................................................................................15

7 Limitations actuelles de la FGAM .....................................................................................................................................................17

7.1 Généralités ...............................................................................................................................................................................................17

7.2 Limitations du matériau ..............................................................................................................................................................17

7.2.1 Généralités .........................................................................................................................................................................17

7.2.2 Définition de la distribution optimale des propriétés du matériau..................................18

7.2.3 Prédiction des propriétés matérielles des composants fabriqués .....................................18

7.2.4 Sélection du matériau ...............................................................................................................................................18

7.2.5 Compréhension des différences et définition des tolérances ................................................18

7.3 Limitations des technologies actuelles de fabrication additive .................................................................19

7.4 Limitations des logiciels de CAO ...........................................................................................................................................19

7.4.1 Généralités .........................................................................................................................................................................19

7.4.2 Formats d’échange de données ........................................................................................................................20

8 Applications potentielles de la FGAM ..........................................................................................................................................22

8.1 Généralités ...............................................................................................................................................................................................22

8.2 Applications biomédicales .........................................................................................................................................................23

8.3 Applications aérospatiales .........................................................................................................................................................23

8.4 Marchés grand public .....................................................................................................................................................................23

9 Résumé ........................................................................................................................................................................................................................24

Bibliographie ...........................................................................................................................................................................................................................25

© ISO/ASTM International 2020 – Tous droits réservés iii
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ISO/ASTM TR 52912:2020(F)
Avant-propos

L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes

nationaux de normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est

en général confiée aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude

a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,

gouvernementales et non gouvernementales, en liaison avec l'ISO participent également aux travaux.

L'ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui

concerne la normalisation électrotechnique.

Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont

décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier de prendre note des différents

critères d'approbation requis pour les différents types de documents ISO. Le présent document a

été rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir

https:// www .iso .org/ fr/ directives -and -policies .html).

L'attention est attirée sur le fait que certains des éléments du présent document peuvent faire l'objet de

droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour responsable

de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant

les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de

l’élaboration du document sont indiqués dans l’Introduction et/ou dans la liste des déclarations de

brevets reçues par l’ISO (voir https:// www .iso .org/ fr/ iso -standards -and -patents .html).

Les appellations commerciales éventuellement mentionnées dans le présent document sont données

pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un

engagement.

Pour une explication de la nature volontaire des normes, la signification des termes et expressions

spécifiques de l’ISO liés à l’évaluation de la conformité, ou pour toute information au sujet de l’adhésion

de l’ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles

techniques au commerce (OTC), voir le lien suivant: https:// www .iso .org/ fr/ foreword -supplementary

-information .html.

Le présent document a été élaboré par l’ISO/TC 261, Fabrication additive, en coopération avec

l’ASTM F 42, Technologies de fabrication additive, dans le cadre d’un accord de partenariat entre l’ISO et

ASTM International dans le but de créer un ensemble commun de normes ISO/ASTM sur la fabrication

additive et en collaboration avec le Comité Européen de Normalisation (CEN), Comité technique CEN/

TC 438, Fabrication additive, conformément à l’Accord de coopération technique entre l’ISO et le CEN

(Accord de Vienne).

Il convient que tout retour d’information ou questions sur le présent document soit adressé à l'organisme

national de normalisation de l'utilisateur. Une liste complète de ces organismes peut être consultée à

l'adresse www .iso .org/ members .html.
iv © ISO/ASTM International 2020 – Tous droits réservés
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ISO/ASTM TR 52912:2020(F)
Introduction

Les matériaux à gradient fonctionnel (FGMs) ont été développés en 1984 pour un projet d'avion spatial

pour soutenir les barrières thermiques élevées pour surmonter les défauts des matériaux composites

traditionnels (matériaux AZO, 2002). Les composites traditionnels [Figure 1 a)] sont des mélanges

homogènes, impliquant par conséquent un compromis entre les propriétés souhaitables des matériaux

constitutifs. Les matériaux à gradient fonctionnel (FGMs) sont une classe de matériaux avancés dont la

composition varie dans l'espace sur une dimension changeante, avec des changements correspondants

[56]

dans les propriétés des matériaux incorporés . Les FGMs atteignent leur statut multifonctionnel en

associant les exigences de performance à des stratégies de structuration et d'allocation du matériau

[Figure 1 b)].

Les procédés de fabrication des FGMs conventionnels comprennent le grenaillage de précontrainte,

l'implantation ionique, la projection thermique, le dépôt électrophorétique et le dépôt chimique

en phase vapeur. Comme les procédés de fabrication additive construisent des pièces par ajouts

successifs de matériaux, ils offrent la possibilité de réaliser des produits ayant des propriétés à

gradient fonctionnel, introduisant ainsi le concept souvent connu sous le nom de fabrication additive

à gradient fonctionnel (FGAM). Comme ce domaine de travail est nouveau, conduit par la recherche

universitaire et qu'il manque de normalisation disponible, plusieurs noms différents ont été proposés

par différents chercheurs dans différentes publications comme termes pour ce domaine, par exemple,

[56]

prototypage rapide à gradient fonctionnel (FGRP) , prototypage rapide à propriétés variées (VPRP)

[57] [72]

et fabrication additive à propriétés spécifiques au site . Toutefois, même s'il existe clairement un

besoin important de clarification des termes clés associés à la FGAM, le présent document ne contient

aucune tentative d'alignement terminologique. Le présent document est une présentation générale de

l'État de l'Art et des possibilités offertes à la FGAM par la technologie actuelle du procédé de FA, et

constitue donc un document purement informatif. Du fait que cette présentation générale s’appuie sur

les publications disponibles, et afin de faciliter les références croisées à partir de ces publications, le

présent document a utilisé les termes concernant la FGAM tels qu'ils sont utilisés dans les publications

originales.
a) Composite traditionnel b) Composite FGM

Figure 1 — Allocation de matériaux dans un composite traditionnel et un composite FGM

© ISO/ASTM International 2020 – Tous droits réservés v
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RAPPORT TECHNIQUE ISO/ASTM TR 52912:2020(F)
Fabrication additive — Conception — Fabrication additive
à gradient fonctionnel
1 Domaine d'application

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.

2 Références normatives
Le présent document ne contient aucune référence normative.
3 Termes et définitions
Aucun terme n'est défini dans le présent document.

L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en

normalisation, consultables aux adresses suivantes:

— ISO Online browsing platform: disponible à l’adresse https:// www .iso .org/ obp

— IEC Electropedia: disponible à l’adresse http:// www .electropedia .org/
4 Abréviations
FA Fabrication Additive (voir l’ISO/ASTM 52900)
AMF Format de fabrication additive (Additive Manufacturing Format), voir 8.4.2.1
(voir l’ISO/ASTM 52900)
[48]
CAO Conception Assistée par Ordinateur
[14]
IAO Ingénierie Assistée par Ordinateur

DED Dépôt de matière sous énergie concentrée (Directed Energy Deposition), voir Article 6

(voir l’ISO/ASTM 52900)

DMLS Frittage laser direct de métal (Direct Metal Laser Sintering), le nom du procédé de fusion

[40]
laser sur lit de poudre métallique par EOS Gmbh
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ISO/ASTM TR 52912:2020(F)

EBM Fusion par faisceau d'électrons (Electron Beam Melting), le nom du procédé de fusion par

[40]
faisceau d'électrons sur lit de poudre métallique par Arcam AB
[19]
FAV Voxel travaillable (Fabricatable Voxel), voir 8.4.2.2
[48]
FEA Analyse par éléments finis (Finite Element Analysis)

FEF Fabrication par extrusion sous forme lyophilisée (Freeze-form Extrusion Fabrication), un

procédé d'extrusion de matière basé sur l'extrusion de matières premières sous forme de

pâtes et l'application de la lyophilisation pour former une ébauche qui peut être consolidée

aux propriétés souhaitées du matériau par frittage. Actuellement utilisée uniquement pour

[34]
des projets de recherche et de développement .
[18]
FEM Méthode par éléments finis (Finite Element Method)

FDM Modélisation par dépôt fondu (Fused Deposition Modelling), nom donné aux procédés

[39]
d'extrusion de matière par Stratasys Ltd .
[61]

FGAM Fabrication additive à gradient fonctionnel (Functionally Graded Additive Manufacturing) .

[61]
FGMs Matériaux à gradient fonctionnel (Functionally Graded Materials) .

FGRP Prototypage rapide à gradient fonctionnel (Functionally Graded Rapid Prototyping), nom

[56]
de la FGAM utilisé par Neri Oxman dans certaines publications .

LMD Dépôt de métal par laser (Laser Metal Deposition), un nom commun pour les procédés de

dépôt de matière sous énergie concentrée qui utilisent le laser comme source d'énergie

pour faire fondre et fusionner les matériaux métalliques au moment de leur dépôt, voir

[21]
l’Article 6 .

LOM Fabrication d’objet stratifié (Laminated Object Manufacturing), nom des procédés de

[42]
stratification de couches développés à l'origine par Helisys Inc.

MMAM Fabrication additive multi-matériaux (Multi-Material Additive Manufacturing), nom utilisé

[61]
pour la FA lorsque plusieurs matériaux sont utilisés dans le même procédé .

MM FGAM Fabrication additive à gradient fonctionnel multi-matériaux (Multi-Material Functionally

Graded Additive Manufacturing), nom de la FGAM lorsque le gradient fonctionnel est basé

sur des pièces de construction utilisant plus d'un matériau dans le même procédé, et que

la composition des différents composants matériels est commandée par le programme

[43]
informatique .
PBF Fusion sur lit de poudre (Powder Bed Fusion) (ISO/ASTM 52900)

SHS Frittage thermique sélectif (Selective Heat Sintering), nom d'un procédé de fusion sur lit de

poudre qui permet de faire fondre une poudre de polymère au moyen d'une tête d'impres-

sion thermique au lieu du laser, plus courant. Le procédé a été développé à l'origine par

[40]
Blueprinter mais a été retiré du marché suite à la faillite de cette société .

SLM Fusion sélective au laser (Selective Laser Melting), nom du procédé de fusion sur lit de

poudre métallique par laser, développé à l'origine en collaboration par F&S Stereolitho-

graphietechnik GmbH (Fockele & Schwarze) et Fraunhofer Institute pour la technologie

laser. Ce nom est actuellement une marque déposée de SLM Solutions Group AG et Realizer

[40]
GmbH .
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ISO/ASTM TR 52912:2020(F)

SLS Frittage laser sélectif (Selective Laser Sintering), nom du procédé de fusion sur lit de poudre

développé à l'origine par DTM Corp, mais qui a été repris par 3D Systems par l'acquisition

de cette société. Comme il s'agit du premier procédé de fusion sur lit de poudre à être

commercialisé, il a parfois été utilisé comme synonyme de tous les procédés de fusion

[40]
sur lit de poudre .

STL Stéréolithographie, nom d'un format de fichier numérique pour les modèles solides tridi-

mensionnels développé à l'origine pour le procédé de stéréolithographie par 3D Systems,

d'où le nom. Depuis que cette conversion vers ce format a été couramment disponible

dans plusieurs programmes de CAO, ce format de fichier a jusqu'à présent fonctionné

efficacement comme une norme de facto pour les procédés de FA. (voir l’ISO/ASTM 52900)

UAM Fabrication additive par ultrasons (Ultrasonic Additive Manufacturing), nom d'un procédé

de stratification de couches de métal par Fabrisonic LLC. Ce procédé consiste à fusionner

[43]
de fines feuilles (ou rubans) de métal par des vibrations ultrasoniques .
[8]
VDM Modélisation discrète vague (Vague Discrete Modelling)

VPRP Prototypage rapide à propriétés variables (Variable Property Rapid Prototyping), nom

[57]
de la FGAM utilisé par Neri Oxman dans certaines publications .

3MF Format de fabrication 3D, un format de fichier numérique pour les modèles solides tridi-

[3]

mensionnels dans la fabrication additive, développé par le consortium 3MF, voir 8.4.2.3 .

5 Concept de la fabrication additive à gradient fonctionnel (FGAM)
5.1 Généralités

La fabrication additive (FA) est un procédé d'adhésion de matières pour fabriquer des pièces à partir de

données de modèles 3D, généralement couche après couche, par opposition à la fabrication soustractive

et aux méthodes de fabrication par mise en forme (ISO/ASTM 52900). La FA permet la fabrication

directe de composants sur mesure très détaillés en plaçant avec exactitude le ou les matériaux à des

[76]

positions définies au sein d’un domaine de conception sous la forme d’une unité unique . L'utilisation

de la FA a donné la possibilité de produire des pièces en utilisant des FGM par le biais d’un procédé connu

sous le nom de fabrication additive à gradient fonctionnel (FGAM). Les technologies de FA adaptées à la

fabrication des FGM comprennent l'extrusion de matière, le dépôt de matière sous énergie concentrée,

[43]

la fusion sur lit de poudre, la stratification de couches et la technologie PolyJet.

La fabrication additive à gradient fonctionnel (FGAM) est une technique de fabrication couche par couche

qui modifie intentionnellement les paramètres du procédé et fait varier graduellement l’organisation

spatiale du ou des matériaux au sein d'un composant en vue de répondre à la fonction prévue.

La FGAM offre une voie simplifiée pour passer de l'idée à la réalité. L'émergence de la FGAM offre

le potentiel d’accomplir des structures élaborées plus efficacement. L'objectif de l'utilisation de

la FGAM est de fabriquer des composants à forme libre basés sur les performances et pilotés par le

comportement de leur ou leurs matériaux à gradient. Contrairement à la FA conventionnelle mono

et multi-matériaux, qui se concentre principalement sur le prototypage centré sur la forme, la FGAM

est un procédé de fabrication centré sur le matériau qui signifie un passage de la modélisation des

contours à la modélisation des performances. L'intégration directe de la fonctionnalité pilotée par

les performances dans le matériau est un avantage fondamental et une amélioration significative

par rapport aux technologies de FA. Un exemple comprend des caractéristiques internes hautement

personnalisables avec des fonctionnalités intégrées qu'il serait impossible de produire en utilisant

[5]

la fabrication conventionnelle . La quantité, le volume, la forme et l'emplacement du renfort dans la

matrice du matériau peuvent être commandés avec précision afin d'obtenir les propriétés mécaniques

[18]
souhaitées pour une application spécifique .

La Référence [57] décrit le concept de FGAM comme une méthode de prototypage rapide à

propriétés variables (VPRP) qui est capable de commander stratégiquement la masse volumique et la

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ISO/ASTM TR 52912:2020(F)

caractéristique directionnelle de la substance d'un matériau dans une distribution 3D complexe afin

de produire un niveau élevé d'intégration continue de la structure monolithique en utilisant la même

machine. Les caractéristiques et les propriétés du matériau sont modifiées en changeant la composition,

la phase ou la microstructure avec un emplacement prédéterminé. La composition potentielle des

matériaux réalisables par la FGAM peut être caractérisée en 3 types:
a) densification variable au sein d'une composition homogène;

b) composition hétérogène par la combinaison simultanée de deux matériaux ou plus par le biais d’une

transition progressive;

c) utilisation d’une combinaison de densification variable au sein d'une composition hétérogène.

Ces trois types de caractéristiques sont décrits en 5.2 et 5.3.
5.2 Compositions homogènes — FGAM mono-matériau

La FGAM peut produire des structures conçues efficacement en modulant stratégiquement la position

spatiale (par exemple, la masse volumique et la porosité) et la morphologie des structures en treillis

[43]

à travers le volume du matériau en vrac . Nous appelons cela la FGAM à densification variée

(également connue sous le nom de FGAM à gradient de porosité). La Référence [56] a proposé celle-ci

sous la forme d’une fabrication rapide d'inspiration biologique qui se produit dans la nature, comme les

gradients de masse volumique radiale des palmiers, la structure trabéculaire spongieuse de l'os et la

variation tissulaire du muscle qui est hétérogène en élasticité et en rigidité. La directivité, l'amplitude

et la concentration de masse volumique de la substance du matériau dans une structure composite

monolithique anisotrope contribuent à des déviations fonctionnelles en vue de moduler les propriétés

[54]

physiques et de créer des formes fonctionnelles par le biais de la hiérarchie structurelle .

Les structures artificielles telles que les piliers en béton sont généralement homogènes sur le plan

[27]

volumétrique . La FGAM mono-matériau à densification variée a été démontrée par le biais des

travaux de Steven Keating sur du béton à gradient fonctionnel fabriqué par une machine MakerBot

avec une extrudeuse de matière modifiée. La pièce en béton présentait un gradient fonctionnel de

masse volumique pour imiter les structures cellulaires d'un palmier, depuis un extérieur solide jusqu'à

un noyau poreux. Le gradient de porosité a été obtenu en faisant varier les tailles des particules de

poudre qui ont été attribuées à différents endroits au cours du procédé de gradation ou en faisant

[43]

varier les paramètres du procédé de production . Pour la Référence [27], la masse volumique a été

commandée en agrégeant le taux d'eau du béton à un endroit donné, ce qui a conduit à un excellent

rapport résistance/poids, le rendant plus léger et pourtant plus efficace et plus résistant qu'une pièce

en béton plein.
5.3 Compositions homogènes — FGAM multi-matériaux

La fabrication additive multi-matériaux (MMAM) peut être réalisée à l'aide d'imprimantes 3D

[77]

conventionnelles dotées de plusieurs buses afin de délivrer différents matériaux à la plate-forme .

Dans la fusion sur lit de poudre, la MMAM peut être réalisée en utilisant un dispositif de distribution

classique en combinaison avec un module d'aspiration pour retirer la poudre après l'étape de

[7]

solidification . Comme il existe des interfaces nettes dans la majorité des composites MMAM

[72]

conventionnels où deux matériaux se rencontrent et interagissent, cela crée une phase cassante . La

défaillance est généralement provoquée entre des modifications discrètes des propriétés des matériaux,

[17]

comme le délaminage ou les fissures causées par la tension superficielle entre deux matériaux .

La FGAM multi-matériaux (MM) vise à améliorer la liaison interfaciale en supprimant les frontières

distinctes entre des matériaux dissemblables ou incompatibles. Les concentrations de contraintes

mécaniques et les contraintes thermiques causées par les différents coefficients de dilatation seront

[72]

largement réduites . Les Figures 2, a) et b) expliquent l'approche de voxellisation de la fabrication

additive multi-matériaux selon la Référence [7].
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ISO/ASTM TR 52912:2020(F)

a) Schéma conceptuel illustrant les voxels disposés sous forme 3D (Fraunhofer IGCV et

Référence [7])
b) Illustration de la MMAM (Fraunhofer IGCV et Référence [7])
Légende
1 direction de fabrication
2 mono-matériau
3 2D hybride
4 2D multi-matériaux
5 3D multi-matériaux
6 substrat
Figure 2 — Voxellisation de la fabrication additive multi-matériaux
© ISO/ASTM International 2020 – Tous droits réservés 5
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ISO/ASTM TR 52912:2020(F)
a) FA multi-matériaux b) FA à gradient fonctionnel
Légende

1 modification discrète des propriétés des matériaux 3 pilier pour renforcer la forme

2 matériau dur pour le renfort 4 variation en douceur du changement de matériau
[ ]
Figure 3 — Exemple d’une pièce multi-matériaux 73

La Référence [10] traite de l'effet de couplage des matériaux par des configurations en sandwich en

vue d’obtenir une combinaison optimale des propriétés des composants telles que le poids, la dureté de

surface, la résistance à l'usure, la résistance aux chocs ou la ténacité; ou pour produire des gradients

de matériaux afin
...

INTERNATIONAL ISO/ASTM
STANDARD 52912
First edition
Additive manufacturing — Design
— Functionally graded additive
manufacturing
Fabrication additive — Conception — Fabrication additive à gradient
fonctionnel
PROOF/ÉPREUVE
Reference number
ISO/ASTM 52912:2020(E)
ISO/ASTM International 2020
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ISO/ASTM 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 PROOF/ÉPREUVE© ISO/ASTM International 2020 – All rights reserved
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ISO/ASTM 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 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.
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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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INTERNATIONAL STANDARD ISO/ASTM 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
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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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ISO/ASTM 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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ISO/ASTM 52912:2020(E)
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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ISO/ASTM 52912:2020(E)

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 heterogeneous compositions with density variation [Figure 5 e)]

a) Conventional MMAM b) MM FGAM (2 materials) c) MM FGAM
(3 materials)
d) Switched composition e) Varied density heterogeneous
Figure 5 — Various classes of multi-material arrangement

The variation of material within a heterogeneous component can be classed as 1D, 2D and 3D

[48]

gradient . Key parameters include the dimension of the gradient vector, the geometric shape and

the repartition of the equipotential surfaces. Figure 6 shows a diagram that classifies the different

gradients of FGAM parts that can be assigned.
Key
1 one-dimensional gradient
2 two-dimensional gradient
3 three-dimensional gradient
Figure 6 — Representation of classifying FGAM gradients
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ISO/ASTM 52912:2020(E)
5 Advances of functionally graded additive manufacturing
5.1 General

AM has provided benefits including design freedom, reduced time to market in product development,

[5]

service and increased R&D efficiency . The emergence of FGAM expands the potential of prototyping

of more efficient engineering structure that restore better function and structural performance with

[61]
no tooling costs .

FGAM presents a new production paradigm in terms of industrial machinery, assembly processes, and

[20]

supply chains . It provides a vast range of opportunities for design, performance, cost and lifecycle

management. For instance, l
...

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