EN ISO/ASTM 52925:2022

Additive manufacturing of polymers - Feedstock materials - Qualification of materials for laser-based powder bed fusion of parts (ISO/ASTM 52925:2022)

This document provides guidance and recommendations for the qualification of polymeric materials intended for laser-based powder bed fusion of polymers (PBF-LB/P). The parameters and recommendations presented in this document relate mainly to the material polyamide 12 (PA12), but references are also made to polyamide 11 (PA11). The parameters and recommendations set forth herein cannot be applicable to other polymeric materials.

Additive Fertigung von Polymeren - Ausgangsmaterialien - Qualifizierung von Materialien für das laserbasierte Pulverbettschmelzen von Teilen (ISO/ASTM 52925:2022)

Dieses Dokument stellt einen Leitfaden und Empfehlungen für die Qualifizierung von Polymerwerkstoffen zur Verfügung, die für die laserbasierte Pulverbettfusion von Polymeren (PBF-LB/P) bestimmt sind. Die in diesem Dokument aufgeführten Parameter und Empfehlungen beziehen sich hauptsächlich auf den Werkstoff Polyamid 12 (PA12), es wird aber auch auf Polyamid 11 (PA11) Bezug genommen. Die hier dargelegten Parameter und Empfehlungen können nicht auf andere Polymerwerkstoffe angewendet werden.

Fabrication additive de polymères - Matières premières - Qualification des matériaux pour la fusion laser de pièces sur lit de poudre (ISO/ASTM 52925:2022)

Le présent document donne des conseils et des recommandations pour la qualification des matériaux polymères destinés à la fusion laser de polymères sur lit de poudre (PBF-LB/P). Les paramètres et recommandations présentés dans le présent document concernent principalement le polyamide 12 (PA12), mais des références sont également faites au polyamide 11 (PA11). Les paramètres et recommandations énoncés ici peuvent ne pas être applicables à d’autres matériaux polymères.

Aditivna proizvodnja polimerov - Surovine - Kvalifikacija materialov za lasersko spajanje prahu v postelji (ISO/ASTM 52925:2022)

Parametri in priporočila, predstavljeni v tem standardu, se v glavnem navezujejo na material poliamid 12 (PA12). Standard se izrecno sklicuje tudi na poliamid 11 (PA11). Obseg, v katerem je mogoče te parametre in priporočila prenesti na druge materiale, je treba preverjati za vsak posamezen primer.

General Information

• Status: Published
• Publication Date: 03-May-2022
• Withdrawal Date: 29-Nov-2022
• ICS: 25.030 - Additive manufacturing
• Technical Committee: CEN/TC 438 - Additive Manufacturing
• Drafting Committee: CEN/TC 438 - Additive Manufacturing
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 04-May-2022
• Completion Date: 04-May-2022
• Ref Project: SIST EN ISO/ASTM 52925:2023 - Additive manufacturing of polymers - Feedstock materials - Qualification of materials for laser-based powder bed fusion of parts (ISO/ASTM 52925:2022)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO/ASTM 52925:2023
01-marec-2023
Aditivna proizvodnja polimerov - Surovine - Kvalifikacija materialov za lasersko
spajanje prahu v postelji (ISO/ASTM 52925:2022)

Additive manufacturing of polymers - Feedstock materials - Qualification of materials for

laser-based powder bed fusion of parts (ISO/ASTM 52925:2022)

Additive Fertigung von Polymeren - Qualifizierungsgrundsätze - Klassifizierung von

Teileigenschaften (ISO/ASTM 52925:2022)

Fabrication additive de polymères - Matières premières - Qualification des matériaux

pour la fusion laser de pièces sur lit de poudre (ISO/ASTM 52925:2022)
Ta slovenski standard je istoveten z: EN ISO/ASTM 52925:2022
ICS:
25.030 3D-tiskanje Additive manufacturing
SIST EN ISO/ASTM 52925:2023 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO/ASTM 52925:2023
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SIST EN ISO/ASTM 52925:2023
EN ISO/ASTM 52925
EUROPEAN STANDARD
NORME EUROPÉENNE
May 2022
EUROPÄISCHE NORM
ICS 25.030
English Version
Additive manufacturing of polymers - Feedstock materials
- Qualification of materials for laser-based powder bed
fusion of parts (ISO/ASTM 52925:2022)
Fabrication additive de polymères - Matières Additive Fertigung von Polymeren

premières - Qualification des matériaux pour la fusion Qualifizierungsgrundsätze - Klassifizierung von

laser de pièces sur lit de poudre (ISO/ASTM Teileigenschaften (ISO/ASTM 52925:2022)

52925:2022)
This European Standard was approved by CEN on 5 April 2022.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

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

© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO/ASTM 52925:2022 E

worldwide for CEN national Members.
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SIST EN ISO/ASTM 52925:2023
EN ISO/ASTM 52925:2022 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO/ASTM 52925:2023
EN ISO/ASTM 52925:2022 (E)
European foreword

This document (EN ISO/ASTM 52925:2022) 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.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by November 2022, and conflicting national standards

shall be withdrawn at the latest by November 2022.

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.

Any feedback and questions on this document should be directed to the users’ national standards

body/national committee. A complete listing of these bodies can be found on the CEN website.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: 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 the

United Kingdom.
Endorsement notice

The text of ISO/ASTM 52925:2022 has been approved by CEN as EN ISO/ASTM 52925:2022 without

any modification.
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SIST EN ISO/ASTM 52925:2023
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SIST EN ISO/ASTM 52925:2023
INTERNATIONAL ISO/ASTM
STANDARD 52925
First edition
2022-04
Additive manufacturing of polymers —
Feedstock materials — Qualification of
materials for laser-based powder bed
fusion of parts
Fabrication additive de polymères — Matières premières —
Qualification des matériaux pour la fusion laser de pièces sur lit de
poudre
Reference number
ISO/ASTM 52925:2022(E)
© ISO/ASTM International 2022
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SIST EN ISO/ASTM 52925:2023
ISO/ASTM 52925:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/ASTM International 2022

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: [phone] Phone: [phone]
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Website: www.iso.org Website: www.astm.org
Published in Switzerland
© ISO/ASTM International 2022 – All rights reserved
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SIST EN ISO/ASTM 52925:2023
ISO/ASTM 52925:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Symbols and abbreviations ......................................................................................................................................................................1

4.1 Symbols ......................................................................................................................................................................................................... 1

4.2 Abbreviations .......................................................................................................................................................................................... 2

5 Sampling ....................................................................................................................................................................................................................... 2

5.1 General ........................................................................................................................................................................................................... 2

5.2 Characterisation of virgin powder and powder blends ..................................................................................... 2

5.3 Characterisation of used powder ........................................................................................................................................... 2

6 Factory test report ............................................................................................................................................................................................. 3

6.1 General ........................................................................................................................................................................................................... 3

6.2 Particle size distribution ............................................................................................................................................................... 3

6.3 Residual monomer content/extract content ................................................................................................................ 3

6.4 Supplementary data ........................................................................................................................................................................... 3

7 Factors influencing processability ...................................................................................................................................................4

7.1 General ........................................................................................................................................................................................................... 4

7.2 Spreadability of the powder ....................................................................................................................................................... 4

7.3 Relative humidity of the powder (surface moisture) ........................................................................................... 4

7.4 Particle size distribution ............................................................................................................................................................... 5

8 Factors affecting part quality ................................................................................................................................................................ 5

8.1 General ........................................................................................................................................................................................................... 5

8.2 Melting behaviour, melt flow and MVR............................................................................................................................. 6

8.2.1 General ........................................................................................................................................................................................ 6

8.2.2 Laboratory methods ....................................................................................................................................................... 6

8.2.3 Melt volume-flow rate (MVR) ................................................................................................................................. 6

8.3 Melting temperature and recrystallisation temperature ................................................................................ 7

Annex A (informative) Hausner ratio, H ........................................................................................................................................................ 9

Annex B (informative) Determination of the melt volume-flow rate (MVR) .........................................................12

Annex C (informative) Round robin MVR test ........................................................................................................................................15

Bibliography .............................................................................................................................................................................................................................18

iii
© ISO/ASTM International 2022 – All rights reserved
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SIST EN ISO/ASTM 52925:2023
ISO/ASTM 52925:2022(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 of 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

www.iso.org/iso/foreword.html.

This document was prepared by ISO/TC 261, Additive manufacturing, in cooperation with ASTM

Committee F42, 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.
© ISO/ASTM International 2022 – All rights reserved
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SIST EN ISO/ASTM 52925:2023
INTERNATIONAL STANDARD ISO/ASTM 52925:2022(E)
Additive manufacturing of polymers — Feedstock
materials — Qualification of materials for laser-based
powder bed fusion of parts
1 Scope

This document provides guidance and recommendations for the qualification of polymeric

materials intended for laser-based powder bed fusion of polymers (PBF-LB/P). The parameters and

recommendations presented in this document relate mainly to the material polyamide 12 (PA12), but

references are also made to polyamide 11 (PA11). The parameters and recommendations set forth

herein cannot be applicable to other polymeric materials.
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.

ISO/ASTM 52900, Additive manufacturing — General principles — Fundamentals and vocabulary

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO/ASTM 52900, apply.

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 https:// www .electropedia .org/
4 Symbols and abbreviations
4.1 Symbols
The following symbols are used throughout this document:
Symbols Designation Unit
D 10 % quantile of particle size based on the sample volume µm
V10
D 50 % quantile of particle size based on the sample volume µm
V50
D 90 % quantile of particle size based on the sample volume µm
V90
H Hausner ratio —
s standard deviation of repeatability —
s standard deviation of reproducibility —
T processing temperature range °C
T initial crystallisation temperature °C
T initial melting temperature °C
V bulk volume mL
tapped volume mL
© ISO/ASTM International 2022 – All rights reserved
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SIST EN ISO/ASTM 52925:2023
ISO/ASTM 52925:2022(E)
Symbols Designation Unit
η relative viscosity —
rel
bulk density g/mL
ρ tapped density g/mL
4.2 Abbreviations
The following abbreviations are used throughout this document:
DSC differential scanning calorimetry
GPC gel permeation chromatography
MFI melt flow index
MFR melt mass flow rate
MVR melt volume flow rate
PA11 polyamide 11
PA12 polyamide 12
RoHS restriction of the use of certain hazardous substances
5 Sampling
5.1 General

When analysing a small powder sample to determine its quality and suitability for PBF-LB/P, it shall be

ensured that this sample is representative of the powder as a whole.
5.2 Characterisation of virgin powder and powder blends

Each new batch of virgin powder shall be tested and also each powder blend comprising used and

virgin powder should be tested in accordance with the measurement methods listed in this document.

Test of powder blend is recommended for series serial production to ensure consistent part quality.

To minimise the scope of testing and ensure a high level of powder homogeneity, batch size of blended

powder should be as large as possible.
5.3 Characterisation of used powder

Since different temperature histories within the used powder of a part cake can lead to significant

differences in material quality, the total quantity of powder shall be homogenised to obtain a

representative powder sample.

In practice this can be achieved by thoroughly blending the powder in a mixer, for example. Once

blended, the sample can be taken from any part of the powder. If a sufficiently large mixer is not

available, several samples (at least five, each with a mass of at least 20 g) may be taken from different

areas and blended together. Samples for analysis may then be taken from this blend.

IMPORTANT — Ideally, the total volume of powder should be homogenised rather than individual

samples. Ideally, the blending method should be validated.
© ISO/ASTM International 2022 – All rights reserved
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SIST EN ISO/ASTM 52925:2023
ISO/ASTM 52925:2022(E)
6 Factory test report
6.1 General

The factory test report should contain batch-specific measurements of powder parameters

(characteristic values) that can have a critical impact on the manufacturing process.

Each factory test report should include the data according to 6.2 to 6.4.
6.2 Particle size distribution

The particle size distribution has a significant influence on spreadability and bulk density and thus

contributes to the processability and part characteristics. Typical data are the D , D and D

V10 V50 V90

values. These correspond to the particle size at which 10 %, 50 % or 90 % of the volume fraction of

the powder is smaller than this value. A volume- or mass-related analysis is preferable to a numerical

analysis since small particles account for only a small mass or volume fraction, even when they are

present in large numbers.

A large number of large particles impairs the surface quality and fine detailing (detail resolution) of the

part. The D value can be used to indicate the coarse fraction; i.e. 10 % of the volume fraction of the

V90
powder is larger than this particle size.

A high proportion of fine particles produces more fine particulate matter which can contaminate the

AM machine and its surroundings. The smaller the particles, the larger the surface-to-volume ratio and

the stronger the surface forces and electrostatic charge are. This impairs spreadability and can cause

powder deposits to accumulate on the powder spreading device, for example. The D value serves as a

V10

measure of the fine fraction; i.e. 10 % of the volume fraction of the powder is smaller than this particle

size.

The median particle size (D value) provides a good indication of the resulting surface roughness of

V50

parts since this is largely determined by particles adhering to the parts or partially fused particles.

Powder supplier and user have to agree on the method to measure the values and the tolerances. D ,

V10

D and D are mandatory and depending on the PSD (e.g. bimodal) there should be more data in the

V50 V90
report or the total analysis (graph and data) of the PSD.

IMPORTANT — D , D and D values shall be indicated as a minimum. It is advantageous to

V10 V50 V90
indicate the particle size distribution in full.
Determine the particle size distribution according to 7.4.
6.3 Residual monomer content/extract content

The residual monomer content/extract content of a PBF-LB/P powder should be kept to a minimum

level to minimise the release of gases from the powder. These monomeric gas releases can condense on

colder areas of the additive manufacturing machine and soil the system as a result. Optical elements

soiled in this way absorb laser radiation, leading to a reduction in the laser power delivered to the build

field. This can have a detrimental effect on the mechanical properties and the part density. Soiling of

mechanically stressed components can accelerate ageing or in extreme cases, cause them to fail.

6.4 Supplementary data

Normally, the powder formulation is confidential and is not disclosed. However, the purchaser can

generally assume that the material supplier keeps to his formulation and that the content of fillers and

additives remains constant from one batch to another and is monitored during production. No change

to the formulation or to the additives is acceptable without prior agreement from the customer. It is

unusual to explicitly specify the formulation in the factory test report, as is also the case with plastic

pellets for injection moulding applications. It is recommended that powder be certified to specification

[16]

call-out such as ASTM D6779 . Appropriate certificates (e.g. Safety Data Sheet, “Globally Harmonized

© ISO/ASTM International 2022 – All rights reserved
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SIST EN ISO/ASTM 52925:2023
ISO/ASTM 52925:2022(E)

System of Classification and Labelling of Chemicals”, EU Directive 2011/65/EU) are issued to confirm

that the formulation contains no harmful substances. Important components and their effect on part

characteristics are listed below:

— stabilisers: these prevent thermal degradation within the polymer and also influence the mechanical

characteristics of the resulting part,

— flow agents: these enable less restricted movement of particles relative to one another,

— fillers (e.g. glass beads, fibres, ceramic particles, impact modifiers): fillers in the polymer influence

the mechanical characteristics of the part,
— flame retardants: these influence the flammability of the parts,

— additives: certain additives can be contractually excluded, depending on subsequent use.

IMPORTANT — The supplementary information is recommended to be agreed between the

contractual partners, depending on the desired area of application.
7 Factors influencing processability
7.1 General

Many characteristics of the polymer powder ultimately determine whether or not a part produced by

PBF-LB/P conforms to requirements. However, the tolerance limits of many of these characteristics

largely depend on the AM machine and/or the processing parameters used. For this reason, this

subclause deals only with those factors which make processing fundamentally unfeasible; in other

words, the measurements described below can be used to exclude unsuitable material.

7.2 Spreadability of the powder

The spreadability and flow characteristics of the powder determine the quality of the powder for the

powder spreading device of a PBF-LB/P system.

If a powder is not free-flowing because the particle shape and/or distribution is unfavourable or its

electrostatic charge is too strong, neither the powder feed to the process chamber nor the application of

a thin powder layer in the AM machine can be guaranteed.
Any powder with poor flow characteristics shall be detected and excluded.

There are various possibilities to determine the flowability of powders and their use for PBF-LB/P

powders is under investigation. One possibility that has shown good results in a round robin test

(see Annex A) is the determination of the Hausner ratio H . This is based on determination of pourability

as per ISO 6186 and determination of bulk density as per ISO 60.

Whilst the last two methods are defined very precisely in the corresponding standards, determination

of the Hausner ratio has yet to be standardised. Annex A of this document describes in detail the

definition of the Hausner ratio H , its determination by measurement and its significance.

NOTE The Hausner Ratio is recommended, since there is a good relation to spreadability of powders in PBF-

LB/P.
7.3 Relative humidity of the powder (surface moisture)

When grains of powder are in motion, the surfaces of individual particles come into contact with one

another and then separate again, leading to charge separation which causes the powder to develop

electrostatic charge. Since a polymer is an insulator (non-conductive material), no charge equalisation

can occur within the individual particles. Discharge takes place across the surface moisture of the

particle, as well as via the ambient air. The electrical conductivity of the powder generated by the

surface moisture is therefore critical for breaking down electrostatic charges inside the powder volume.

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SIST EN ISO/ASTM 52925:2023
ISO/ASTM 52925:2022(E)

Since it depends on the moisture at the particle surface, measurement of the moisture using moisture

scales is not informative. With this method, the moisture loss of a sample is measured by increasing

the temperature. However, in the case of polyamides, the polymer itself also absorbs water and this

moisture also escapes on heating. Thus, it is not possible to distinguish whether the water played an

active role in discharge at the particle surface or was trapped inside the particles.

A moisture meter with probe is therefore a suitable alternative. This measurement method determines

the relative humidity of the air. The probe can be inserted in the powder since the relative humidity of

the air is an indirect indication of the surface moisture of the powder. The higher the measured relative

humidity, the higher the surface moisture of the powder. To obtain reproducible measurements,

the probe should be inserted to the same depth in the powder bed each time. The depth should be a

minimum of 200 mm. For PA12 and PA11, relative humidities of 40 % to 60 % measured in this way

have proved ideal for processing the powder.
7.4 Particle size distribution

As already described in 6.2, particle size distribution has an influence on processability and/or part

quality and for this reason it should also be monitored in powder blends comprising used and virgin

powder. Problems with processability can occur if the coarse fraction is too high. These large particles

can cause defects during powder spreading (e.g. stripes or scratches) or even displace small parts in

extreme cases. The coarse fraction also has an influence on the surface quality and detail resolution of

the part. The coarse fraction is characterised by the D value.
V90

The fine fraction also causes defects during coating due to interparticle interactions, electrostatic

charging and resulting poor spreadability. The fine fraction is characterised by the D value.

V10

Various measurement methods are available to determine the coarse and fine fraction by means of

analysis.

One method is laser diffraction pursuant to ISO 13320. Here the powder, dispersed in compressed air

(dry measurement) or in a liquid dispersant (wet measurement) is placed in the path of a laser beam and

the particle size distribution is calculated u
...

SLOVENSKI STANDARD
oSIST prEN ISO/ASTM 52925:2020
01-junij-2020

Procesi aditivne proizvodnje - Lasersko sintranje polimernih delov/laserska fuzija

plasti polimernih delov - Kvalifikacija materialov (ISO/ASTM/DIS 52925:2020)

Additive manufacturing processes - Laser sintering of polymer parts/laser-based powder

bed fusion of polymer parts - Qualification of materials (ISO/ASTM/DIS 52925:2020)

Additive Fertigung - Lasersintern von Polymerteilen/laserbasiertes pulverbettbasiertes

Schmelzen von Polymerteilen - Qualifizierung von Materialien (ISO/ASTM/DIS
52925:2020)

Procédés de fabrication additive - Frittage laser de pièces polymères / fusion laser sur lit

de poudre de pièces polymères - Qualification des matériaux (ISO/ASTM/DIS
52925:2020)
Ta slovenski standard je istoveten z: prEN ISO/ASTM 52925
ICS:
25.030 3D-tiskanje Additive manufacturing
oSIST prEN ISO/ASTM 52925:2020 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO/ASTM 52925:2020
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oSIST prEN ISO/ASTM 52925:2020
DRAFT INTERNATIONAL STANDARD
ISO/ASTM DIS 52925
ISO/TC 261 Secretariat: DIN
Voting begins on: Voting terminates on:
2020-04-10 2020-07-03
Additive manufacturing processes — Laser sintering of
polymer parts/laser-based powder bed fusion of polymer
parts — Qualification of materials
ICS: 25.030
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/ASTM DIS 52925:2020(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. ISO 2020
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oSIST prEN ISO/ASTM 52925:2020
ISO/ASTM DIS 52925:2020(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
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Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols and abbreviations ....................................................................................................................................................................... 1

4.1 Symbols ......................................................................................................................................................................................................... 1

4.2 Abbreviations ........................................................................................................................................................................................... 2

5 Sampling ........................................................................................................................................................................................................................ 2

5.1 General ........................................................................................................................................................................................................... 2

5.2 Characterisation of new (virgin) powder and powder mixes ........................................................................ 2

5.3 Characterisation of used powder ............................................................................................................................................ 2

6 Factory test certificate .................................................................................................................................................................................... 3

6.1 General ........................................................................................................................................................................................................... 3

6.2 Particle size distribution ................................................................................................................................................................ 3

6.3 Residual monomer content/extract content ................................................................................................................. 3

6.4 Supplementary data ........................................................................................................................................................................... 3

7 Factors influencing processability ..................................................................................................................................................... 4

7.1 General ........................................................................................................................................................................................................... 4

7.2 Flowability of the powder ............................................................................................................................................................. 4

7.3 Relative humidity of the powder (surface moisture) ............................................................................................ 4

7.4 Particle size distribution ................................................................................................................................................................ 5

8 Factors affecting part quality .................................................................................................................................................................. 5

8.1 General ........................................................................................................................................................................................................... 5

8.2 Melting behaviour, melt flow and MVR .............................................................................................................................. 6

8.2.1 General...................................................................................................................................................................................... 6

8.2.2 Laboratory methods ..................................................................................................................................................... 6

8.2.3 Melt volume-flow rate (MVR) ............................................................................................................................... 6

8.3 Melting temperature and recrystallisation temperature ................................................................................... 7

Annex A (informative) Hausner ratio (H ) ..................................................................................................................................................... 9

Annex B (informative) Determination of the melt volume-flow rate (MVR) ............................................................12

Annex C (informative) Round robin MVR test ..........................................................................................................................................15

Bibliography .............................................................................................................................................................................................................................18

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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 of 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 www .iso .org/

iso/ foreword .html.

The committee responsible for this document is ISO/TC 261, Additive manufacturing, in cooperation

with ASTM Committee F42, 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.
This is the first edition of this document.
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DRAFT INTERNATIONAL STANDARD ISO/ASTM DIS 52925:2020(E)
Additive manufacturing processes — Laser sintering of
polymer parts/laser-based powder bed fusion of polymer
parts — Qualification of materials
1 Scope

This document establishes specific parameters and recommendations for the qualification of

polymeric materials intended for laser sintering. The parameters and recommendations presented

in this document relate mainly to the material polyamide 12 (PA12), but references are also made to

polyamide 11 (PA11). The parameters and recommendations set forth herein may not be applicable to

other polymeric materials.
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.

ISO ASTM 52900, Additive manufacturing — General principles — Terminology

ASTM D6779Standard Classification System for and Basis of Specification for Polyamide Molding and

Extrusion Materials (PA)
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO/ASTM 52900, apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
4 Symbols and abbreviations
4.1 Symbols
The following symbols are used throughout this standard:
Symbols Designation Unit
D 10% quantile of particle size based on the sample volume µm
v10
D 50% quantile of particle size based on the sample volume µm
v50
D 90% quantile of particle size based on the sample volume µm
v90
H Hausner ratio —
s standard deviation of repeatability —
s standard deviation of reproducibility —
T processing temperature range °C
T initial crystallisation temperature °C
T initial melting temperature °C
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Symbols Designation Unit
V bulk volume mL
tapped volume mL
η relative viscosity –
rel
bulk density g/mL
ρ tapped density g/mL
4.2 Abbreviations
The following abbreviations are used throughout this standard:
AM additive manufacturing
DSC dynamic scanning calorimetry
GPC gel permeation chromatography
MFI melt flow index
MFR melt mass flow rate
MVR melt volume flow rate
PA11 polyamide 11
PA12 polyamide 12
RoHS restriction of the use of certain hazardous substances
5 Sampling
5.1 General

When analysing a small powder sample to determine its quality and suitability for laser sintering, it

must be ensured, that this sample is representative of the powder as a whole.
5.2 Characterisation of new (virgin) powder and powder mixes

Each new batch of virgin powder shall be tested and also each powder mix comprising used and virgin

powder should be tested in accordance with the measurement methods listed in this standard. Test of

powder mix is recommended for series serial production to ensure consistent part quality. To minimise

the scope of testing and ensure a high level of powder homogeneity, batch size of mixed powder should

be as large as possible.
5.3 Characterisation of used powder

Since different temperature histories within the used powder of a part cake can lead to significant

differences in material quality, the total quantity of powder shall be homogenised to obtain a

representative powder sample.

In practice this can be achieved by thoroughly mixing the powder in a mixer, for example. Once mixed,

the sample can be taken from any part of the powder. If a sufficiently large mixer is not available, several

samples (up to five, each weighing 20 g) may be taken from different areas and mixed together. Samples

for analysis may then be taken from this mix.
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IMPORTANT — Ideally, the total volume of powder should be homogenised rather than individual

samples.
6 Factory test certificate
6.1 General

The factory test certificate should contain batch-specific measurements of powder parameters

(characteristic values) that can have a critical impact on the manufacturing process.

Each factory test certificate shall include the data according 6.2 to 6.4.
6.2 Particle size distribution

The particle size distribution has a significant influence on flowability and bulk density and thus

contributes to the processability and part characteristics. Typical data are the D , D and D

v10 v50 v90

values. These correspond to the particle size at which 10 %, 50 % or 90 % of the volume fraction of

the powder is smaller than this value. A volume- or mass-related analysis is preferable to a numerical

analysis since small particles account for only a small mass or volume fraction, even when they are

present in large numbers.

A large number of large particles impairs the surface quality and fine detailing (detail resolution) of the

part. The D value can be used to indicate the coarse fraction; i.e. 10 % of the volume fraction of the

v90
powder is larger than this particle size.

A high proportion of fine particles produces more fine particulate matter which can contaminate the AM

machine and its surroundings. The smaller the particles, the larger the surface-to-volume ratio and the

stronger the surface forces and electrostatic charge are. This impairs flowability and can cause powder

deposits to accumulate on the recoating system, for example. The D value serves as a measure of the

v10

fine fraction; i.e. 10 % of the volume fraction of the powder is smaller than this particle size.

The median particle size (D value) provides a good indication of the resulting surface roughness of

v50

parts since this is largely determined by particles adhering to the parts or partially fused particles.

IMPORTANT — D , D and D values shall be indicated as a minimum. It is advantageous to

v10 v50 v90
indicate the particle size distribution in full.
7.4 explains how to determine the particle size distribution.
6.3 Residual monomer content/extract content

The residual monomer content/extract content of a laser sinter powder should be kept to a minimum

level to minimise the release of gases from the powder. These monomeric gas releases can condense on

colder areas of the additive manufacturing machine and soil the system as a result. Optical elements

soiled in this way absorb laser radiation, leading to a reduction in the laser power delivered to the build

field. This can have a detrimental effect on the mechanical properties and the part density. Soiling of

mechanically stressed components can accelerate ageing or in extreme cases, cause them to fail.

IMPORTANT — The residual monomer content is indicated as percentage mass and should be

below 0,5 % for polyamide 11 and polyamide 12 powders.
6.4 Supplementary data

Normally, the powder formulation is confidential and is not disclosed. However, the purchaser can

generally assume that the material supplier keeps to his formulation and that the content of fillers and

additives remains constant from one batch to another and is monitored during production. No change

to the formulation or to the additives is acceptable without prior agreement from the customer It is

unusual to explicitly specify the formulation in the factory test certificate, as is also the case with

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plastic pellets for injection moulding applications. Powder shall be certified to specification call-out

such as ASTM D6779. Appropriate certificates (e.g. Safety Data Sheet, “Globally Harmonized System

of Classification and Labelling of Chemicals”, EU Directive 2011/65/EU) are issued to confirm that

the formulation contains no harmful substances. Important components and their effect on part

characteristics are listed below:

— stabilisers: these prevent thermal degradation within the polymer and also influence the mechanical

characteristics of the resulting part.

— fillers (e.g. glass beads): fillers in the polymer influence the mechanical characteristics of the part.

— flame retardants: these influence the flammability of the parts.

— additives: certain additives can be contractually excluded, depending on subsequent use.

IMPORTANT — The supplementary information shall be agreed between the contractual

partners, depending on the desired area of application.
7 Factors influencing processability
7.1 General

Many characteristics of the polymer powder ultimately determine whether or not a part produced by

laser sintering conforms to requirements. However, the tolerance limits of many of these characteristics

largely depend on the AM machine and/or the processing parameters used. For this reason, this section

deals only with those factors which make processing fundamentally unfeasible; in other words, the

measurements described below can be used to exclude unsuitable material.
7.2 Flowability of the powder

The flowability and flow characteristics of the powder determine the quality of the powder recoating.

If a powder is not free-flowing because the particle shape and/or distribution is unfavourable or its

electrostatic charge is too strong, neither the powder feed to the process chamber nor the application of

a thin powder layer in the AM machine can be guaranteed. Any powder with poor flow characteristics

shall be detected and excluded. . There are various possibilities to determine the flowability of powders

and their use for laser sintering powders is under investigation. One possibility that has shown good

results in a round robin test (Annex A) is the determination of the Hausner ratio H . This is based on

determination of flowability as per ISO 6186 and determination of bulk density as per ISO 60. Whilst

the last two methods are defined very precisely in the corresponding standards, determination of the

Hausner ratio has yet to be standardised. Annex A of this standard describes in detail the definition of

the Hausner ratio H , its determination by measurement and its significance.
7.3 Relative humidity of the powder (surface moisture)

When grains of powder are in motion, the surfaces of individual particles come into contact with one

another and then separate again, leading to charge separation which causes the powder to develop

electrostatic charge. Since a polymer is an insulator (non-conductive material), no charge equalisation

can occur within the individual particles. Discharge takes place across the surface moisture of the

particle, as well as via the ambient air. The electrical conductivity of the powder generated by the

surface moisture is therefore critical for breaking down electrostatic charges inside the powder volume.

Since it depends on the moisture at the particle surface, measurement of the moisture using moisture

scales is not informative. With this method, the moisture loss of a sample is measured by increasing

the temperature. However, in the case of polyamides, the polymer itself also absorbs water and this

moisture also escapes on heating. Thus it is not possible to distinguish whether the water played an

active role in discharge at the particle surface or was trapped inside the particles.

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A moisture meter with probe is therefore a suitable alternative. This measurement method determines

the relative humidity of the air. The probe can be inserted in the powder since the relative humidity of

the air is an indirect indication of the surface moisture of the powder. The higher the measured relative

humidity, the higher the surface moisture of the powder. To obtain reproducible measurements,

the probe should be inserted to the same depth in the powder bed each time. The depth should be a

minimum of 200 mm. For PA12 and PA11, relative humidities of 40 % to 60 % measured in this way

have proved ideal for processing the powder.
7.4 Particle size distribution

As already described in 6.2, particle size distribution has an influence on processability and/or part

quality and for this reason it should also be monitored in powder mixes comprising used and virgin

powder. Problems with processability can occur if the coarse fraction is too high. These large particles

can cause defects during recoating (e.g. stripes or scratches) or even displace small parts in extreme

cases. The coarse fraction also has an influence on the surface quality and detail resolution of the part.

The coarse fraction is characterised by the D value.
v90

The fine fraction also causes defects during coating due to interparticle interactions, electrostatic

charging and resulting poor flowability. The fine fraction is characterised by the D value.

v10

Various measurement methods are available to determine the coarse and fine fraction by means of

analysis.

The best-known is laser diffraction pursuant to ISO 13320. Here the powder, dispersed in compressed

air (dry measurement) or in a liquid dispersant (wet measurement) is placed in the path of a laser beam

and the particle size distribution is calculated using detectors which measure the light scattering

pattern.

Optical image analysis is another method. A distinction is made between static image analysis for

resting particles (ISO 13322-1) and dynamic image analysis for particles in motion, dispersed in air or

liquid (ISO 13322-2). Both versions are based on the analysis of 2D projected images of powder particles,

which provide information about particle size distribution and particle shape (including sphericity).

Sieving analysis (ASTM D1921 or ISO 3310) is a robust method of analysing powders. Here a powder

sample is poured into a tower containing several sieves. The top sieve has the largest mesh width and

each lower sieve has a smaller mesh width than the one above. By weighing the individual fractions

retained in each sieve it is possible to determine the particle size distribution of the powder by weight

of the single fractions.

For powder monitoring purposes, a simplified version comprising just one coarse sieve could be used

to determine purely the coarse fraction and establish an internal threshold for coarse material. The

mesh width of the coarse sieve should correlate with the layer thickness subsequently required (the

thinner the layers, the finer the sieve). Mesh widths from 120 µm to 200 µm shall be used. The coarse

fraction retained on the sieve should not exceed 5 %. No contaminants or extremely large particles/

agglomerates should be visible. This method is a very reliable means of detecting insufficiently sieved

powder or a sieve damage during powder processing.
8 Factors affecting part quality
8.1 General

A range of factors have an impact on part quality. Material characteristics which have an influence on

the finished part and can be measured using analytical methods are described in the following sections.

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8.2 Melting behaviour, melt flow and MVR
8.2.1 General

The flow characteristics of a polymer melt are largely determined by the molecular weight distribution

and the temperature, pressure and shear rate of the melt. The higher the melt temperature, the lower

the viscosity. This effect is even more pronounced with laser sintering than with conventional polymer

processing methods, since shear and pressure are not involved. In this case, temperature, molecular

shape and chain length determine whether the powder forms an adequate melt film, how many pores

remain in the part and how well the layer bonds to the previous layer. The flow characteristics of the

melt thus give an indication of the part mechanics and the layer-to-layer bonding.

The process parameters (e.g. laser power and scan speed) are normally selected to produce a homogenous

melt layer. Too low melt flow leads to the formation of pores in the component or poor layer bonding.

Both outcomes can have an adverse effect on part mechanics. Thus it is extremely important to control

the melt viscosity of both virgin powders and powder mixes in order to produce high-quality parts.

8.2.2 Laboratory methods

The viscosity is determined at molecular level via the molecular structure and molecular mass

distribution. GPC (gel permeation chromatography) can be used to obtain information about the

molecular chain length and the static distribution of chain lengths in the material. However, since the

method is extremely time-consuming and costly, it is recommended only for detailed analyses.

Determination of the solution viscosity also provides information about the average chain length and

molecular mass. This is done using polymers in varying concentrations dissolved in specific solvents.

Typical solvents include m-cresol, tetrachloroethane and concentrated sulphuric acid. Polyamides are

measured in a capillary viscometer in accordance with ISO 307. The relative viscosity (η ) is calculated

rel
...