Plastics moulded parts -- Tolerances and acceptance conditions

This document specifies possible manufacturing tolerances for plastic moulded parts. This document specifies all integral features with general tolerances with surface profile tolerance within a specified datum system. It allows for additional specifications in case of functional needs and requirements using the ISO-GPS-tools for dimensional and geometrical tolerating. This document addresses injection moulding, injection compression moulding, transfer moulding, compression moulding and rotational moulding of non-porous moulded parts made from thermoplastics, thermoplastic elastomers and thermosets of thermoplastics. This document is applicable to other plastic processes if agreed to by the contractual parties. Moulded part surface imperfections such as sink marks, undesired flow structures and roughness, as well as joint lines are not addressed in this document. This document is not intended to supplant, replace or in any way interfere with requirements for tolerances found in product standards.

Moulages plastiques -- Tolérances et conditions de réception

General Information

Status
Published
Publication Date
27-Aug-2018
Technical Committee
Drafting Committee
Current Stage
6060 - International Standard published
Start Date
01-Aug-2018
Completion Date
28-Aug-2018
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ISO 20457:2018 - Plastics moulded parts -- Tolerances and acceptance conditions
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INTERNATIONAL ISO
STANDARD 20457
First edition
2018-09
Plastics moulded parts — Tolerances
and acceptance conditions
Moulages plastiques — Tolérances et conditions de réception
Reference number
ISO 20457:2018(E)
ISO 2018
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ISO 20457:2018(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2018

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Published in Switzerland
ii © ISO 2018 – All rights reserved
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ISO 20457:2018(E)
Contents Page

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

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

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

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

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

4 Symbols and abbreviated terms ........................................................................................................................................................... 2

4.1 General ........................................................................................................................................................................................................... 2

4.2 Symbols ......................................................................................................................................................................................................... 2

4.3 Abbreviated terms ............................................................................................................................................................................... 3

5 Tolerancing of plastic moulded parts ............................................................................................................................................. 3

5.1 General ........................................................................................................................................................................................................... 3

5.2 Intention ....................................................................................................................................................................................................... 4

5.3 General tolerances ............................................................................................................................................................................... 5

5.4 Direct tolerancing (individual tolerancing) ................................................................................................................... 5

5.5 Tolerancing of draft angles ........................................................................................................................................................... 5

5.6 Dimensioning, tolerancing and measuring of radii ................................................................................................. 6

5.7 Specification of freeform surfaces .......................................................................................................................................... 6

6 Moulding compound properties .......................................................................................................................................................... 6

6.1 General ........................................................................................................................................................................................................... 6

6.2 Moulding shrinkage and shrinkage anisotropies ...................................................................................................... 6

6.3 Moulded material stiffness or hardness............................................................................................................................ 8

7 Dimensional and geometrical tolerancing ................................................................................................................................ 8

7.1 Dimensional tolerancing................................................................................................................................................................. 8

7.1.1 Tolerance grades for features of sizes ........................................................................................................... 8

7.1.2 Determination of the tolerance grades ......................................................................................................11

7.2 Geometrical tolerancing ...............................................................................................................................................................14

7.3 Parting line/Tool offset .................................................................................................................................................................16

7.4 Tolerancing of angular dimensions ....................................................................................................................................17

8 Acceptance conditions for moulded part production (ABF) ................................................................................17

Annex A (informative) Dimensional reference levels for application and production of the

moulded parts ......................................................................................................................................................................................................18

Annex B (informative) Causes and influential factors on the moulding shrinkage of non-

porous plastics .....................................................................................................................................................................................................20

Annex C (informative) Evaluation of the production expense ................................................................................................21

Annex D (informative) Validation of machine or process capability ...............................................................................24

Annex E (informative) Main causes for dimension, form and location deviations in moulded

part production ...................................................................................................................................................................................................25

Annex F (informative) Example for determining the D dimension for application of Table 9 ...........26

Annex G (informative) Feasible acceptance parameters ..............................................................................................................27

Bibliography .............................................................................................................................................................................................................................28

© ISO 2018 – All rights reserved iii
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ISO 20457:2018(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 Technical Committee ISO/TC 61, Plastics.

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 2018 – All rights reserved
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ISO 20457:2018(E)
Introduction

In comparison to metal materials, significantly larger deviations with respect to dimension, form and

location are expected when manufacturing moulded parts. Based on particular properties, such as

high deformability and low stiffness, the functional accuracy requirements in order to economically

manufacture moulded parts are much lower for plastics than for metals.

The physical and chemical properties as well as the material modification options of plastics are vastly

different from those of metals. Properties of plastics relevant to dimensional accuracy in the moulding

application and during processing by the original mould method (injection moulding, compression

moulding, rotational moulding) require a different evaluation and quantification of geometrical

tolerances in comparison to metal materials. The tolerance standards applicable for metal parts,

therefore, cannot be adopted for plastic structures or can only be applied to a very limited extent which

led to the development of this document.

The unique properties of plastics mean that three different dimensional reference levels defined in

Annex A and characterized in respect to the main influential factors are taken into consideration.

The following is the preferred sequence of steps to ensure effective cooperation in the effective design

and development of moulded parts.

a) The part designer specifies the functionally required tolerances based on the application

requirements including, part functionality, use environment, and any assembly requirements.

b) The moulded part manufacturer confirms that the functionally required tolerance is greater

than or equal to the tolerance capability of the manufacturing technology to be used. This is to

avoid impractical tolerances which cannot be achieved without incurring adverse economic or

productivity effects. The functionally required tolerances should always be defined in the design

documentation.

c) The functionally required tolerances should always be defined in the design documentation in

order to establish the basis for determining the moulding shrinkage. This is to prevent situations

in which the functionally required tolerances cannot be achieved, if at all, without excessive

scrap generation and excessive cost. After order placement, calculated values with respect to

the moulding shrinkage should be agreed between the part manufacturer and toolmaker or tool

designer, with consultation with the material supplier as necessary.

Dimensional control of the moulded part is primarily affected by the material specified, the part design

and tool layout, and the processing conditions.

In addition to the factors affecting dimensional control, there are other factors which influence

dimensions, part integrity and mechanical properties. These factors include anisotropic behaviour,

warpage and distortion due to non-uniform thicknesses and resulting non-uniform cooling rates, and

fill profiles. These factors and the basic complexity of polymer systems make standardization much

more difficult in comparison to conventional materials such as metals.

Because of the unavoidable process-induced factors, deviations are therefore expected in the moulded

part. The procedure in case of deviations depends on the function of the moulded part and is subject to

mandatory contractual agreement.

— eliminate deviation by design measures (strengthening ribs, optimized material thickness,

optimized fill profiles, etc.);

— correct deviation by specified retention in the tool, i.e. extended cooling cycles;

— acceptance of non-conformance.
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ISO 20457:2018(E)

The acceptance of non-conformance requires appropriate documentations including drawing

corrections, production deviation documentations or updated reference parts.

NOTE 1 Process-induced deviations can be reduced both by effective design of the moulded part and by

optimization of the production process.

NOTE 2 The conventional tolerance chain calculation presupposes rigid bodies and is therefore primarily

unsuitable for plastic parts.
vi © ISO 2018 – All rights reserved
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INTERNATIONAL STANDARD ISO 20457:2018(E)
Plastics moulded parts — Tolerances and acceptance
conditions
1 Scope

This document specifies possible manufacturing tolerances for plastic moulded parts.

This document specifies all integral features with general tolerances with surface profile tolerance

within a specified datum system. It allows for additional specifications in case of functional needs and

requirements using the ISO-GPS-tools for dimensional and geometrical tolerating.

This document addresses injection moulding, injection compression moulding, transfer moulding,

compression moulding and rotational moulding of non-porous moulded parts made from thermoplastics,

thermoplastic elastomers and thermosets of thermoplastics. This document is applicable to other

plastic processes if agreed to by the contractual parties.

Moulded part surface imperfections such as sink marks, undesired flow structures and roughness, as

well as joint lines are not addressed in this document.

This document is not intended to supplant, replace or in any way interfere with requirements for

tolerances found in product standards.
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 286-1, Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes —

Part 1: Basis of tolerances, deviations and fits

ISO 286-2, Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes —

Part 2: Tables of standard tolerance classes and limit deviations for holes and shafts

ISO 291:2008, Plastics — Standard atmospheres for conditioning and testing

ISO 294-4, Plastics — Injection moulding of test specimens of thermoplastic materials — Part 4:

Determination of moulding shrinkage

ISO 2577, Plastics — Thermosetting moulding materials — Determination of shrinkage

ISO 8015, Geometrical product specifications (GPS) — Fundamentals — Concepts, principles and rules

ISO 10135, Geometrical product specifications (GPS) — Drawing indications for moulded parts in technical

product documentation (TPD)

ISO 14405-1, Geometrical product specifications (GPS) — Dimensional tolerancing — Part 1: Linear sizes

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 8015 and the following 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
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ISO 20457:2018(E)
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
design documentation

documents and data necessary for complete structural description of components, assemblies or

machines and devices

Note 1 to entry: These are initially 3D data records and drawings as well as part lists. They might be supplemented

by measuring and test specifications. 3D data records or drawings alone only fully describe plastic moulded

parts in rare exceptional cases.

Note 2 to entry: For further information, see ISO 17450-1, ISO 17450-2 and ISO 17450-3.

3.2
size

dimensional parameter considered variable for a feature of size that can be defined on a nominal

feature or on an associated feature

Note 1 to entry: In this document, the size is linear, e.g. the diameter of a cylinder or the distance between two

parallel opposite planes, two opposing lines, and two concentric circles. Depending on the type of linear feature

of size, the terms “diameter”, “width”, and “thickness” are synonyms for size.

Note 2 to entry: A size is angular (e.g. angle of a cone) or linear (e.g. diameter of a cylinder). This document only

deals with linear size.
Note 3 to entry: For further information on linear size, see ISO 17450.

[SOURCE: ISO 17450-1:2011, 3.4, modified — References to ISO 14405 have been replaced with “this

document” and a Note 3 to entry has been added.]
3.3
general tolerance

tolerance on geometrical elements used as default, if the element has no direct tolerance (individual

tolerance)
4 Symbols and abbreviated terms
4.1 General

The symbols and abbreviated terms according to ISO 1043, ISO 18064 and the following symbols and

abbreviated terms apply for the application of this document.
4.2 Symbols
C tolerance mean dimension
C tolerance mean dimension for moulded part application
C tolerance mean dimension for moulded part production
C tolerance mean dimension for tool contour production

D furthest distance in the space between the element to be toleranced and the origin of the

datum system used for this positional tolerancing
L moulded part dimension
L tool contour dimension
N nominal dimension for moulded part drawings
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ISO 20457:2018(E)
P total number of points
P point evaluation of the individual influences
T tolerance
t form and location tolerance
T moulded part application tolerance
T moulded part production tolerance
T tool contour production tolerance
VS moulding shrinkage
moulding shrinkage transverse to the melt flow direction
VS moulding shrinkage parallel to the melt flow direction
VS maximum moulding shrinkage
max
VS minimum moulding shrinkage
min
VS average calculated value for the moulding shrinkage
∆L dimensional shift
∆L application-induced dimensional shift
∆L moulding-induced dimensional shift
∆S distribution of the moulding shrinkage
∆VS
difference between VS and VS
4.3 Abbreviated terms
ABF acceptance conditions for moulded part production
ABW acceptance conditions for tool production
GA maximum permissible deviation
IRHD International Rubber Hardness Degree
IT standard tolerance
NW non-tool-specific dimensions
TG tolerance grade
W tool-specific dimensions
5 Tolerancing of plastic moulded parts
5.1 General

The independency principle according to ISO 8015 applies when using this document.

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ISO 20457:2018(E)

Change of the default specification operator for size shall be indicated on the drawing in or near the

title block according to ISO 14405-1, e.g. “Linear size ISO 14405 E” for the envelope principle.

Moulded part drawings or CAD data records correspond to the nominal geometry. The tolerances are

symmetrical to the nominal geometry.

The procedure for the verification of tolerances shall be unambiguously defined and shall be a part

of the contract. It is recommended to separate between ISIR (Initial Sample Inspection Report) and

running production report (requalification). This may include or exclude the individual tolerances and

general tolerances or specified functional tests (e.g. tightness, dielectric strength). If nothing has been

stated in the contract, only individually indicated tolerances are subject for verification.

Unless otherwise defined or by agreement, plastic moulded parts, in which the general tolerances are

not met, do not have to be automatically rejected if the functionality of the part is not compromised.

Certain parts, when removed from their manufacturing environment, can deform significantly from

their defined limits owing to their weight, flexibility or the release of internal stresses resulting from

the manufacturing processes.

Functionally reasonable references with adequate form stiffness have to be specified.

In the case of non-rigid parts, the measuring concept is of special importance (functional orientation,

datum system and overdetermination, gravitational influence, pretension, etc.). See also ISO 10579.

For the orientation of the part, datum target points or small datum target areas have to be used instead

of datum features (e.g. complete planes).

NOTE The datum system reflects the orientation of the part in the assembly. It is important that the datum

system is stable.

In the case of parts moulded from dissimilar materials (e.g. over-moulding) or assemblies using multiple

component parts moulded from different materials, a separate tolerance grade shall be specified for

each material used.

A standard atmosphere in the plastic range is 23 °C ± 2 K and 50 % ± 10 % relative air humidity as

defined in ISO 291.
5.2 Intention

This document has two intentions. One intention is to give the part designer a guideline for producible

tolerances. The other is to serve as a standard for general tolerances for all geometrical features as well

as for direct tolerances (individual tolerances).

Figure 1 gives an overview about the intentions and about the composition of tolerance.

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ISO 20457:2018(E)
Figure 1 — Determination of tolerances for plastic moulded parts

Tolerances of features with functional requirements shall be directly specified. General tolerances

apply to non-functional features (e.g. surface profiles, line profiles) and can be as large as practically

possible.
5.3 General tolerances

Only series 1 (simple production) according to Table 8 applies for general tolerances. General tolerances

shall be indicated in or near the title block.
EXAMPLE General tolerances ISO 20457:JJJJ – TG6.

General tolerances for size apply only on explicitly drawn dimensions on the drawing indicated without

direct tolerances (individual tolerances). General tolerances for positions apply to features of sizes with

respect to the master datum system only.

Profile tolerances of a surface shall be applied as general tolerances, specified in detail in the drawing,

restricting all 6 degrees of freedom.

General tolerances for features of linear size apply only on explicitly drawn nominal dimensions in the

drawing.
5.4 Direct tolerancing (individual tolerancing)

Tolerances (dimensional or geometrical) for functional elements/dimensions shall be explicitly

specified.

The dimensional tolerance shall be indicated directly by dimensions for moulded parts with justifiably

high dimensional stability requirements. When doing so, it shall be noted that the dimensional boundary

lines or points represent inspection dimensions (reference dimensions, acceptance dimensions). The

number of directly toleranced functional elements/dimensions per moulded part shall be kept as low as

possible for economic reasons.
5.5 Tolerancing of draft angles

Drafts (also draft angles) are production-induced inclinations on the moulded part in the demoulding

orientation of moving tool parts (e.g. punches, gate valves, jaws), which are specified as an integral

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ISO 20457:2018(E)

component of the moulded part drawings or the CAD data records of the moulded part manufacturer

for tool design and tool making as well as parts production. Inclination dimension differences specified

in terms of design are not a component of dimensional tolerances or form and location deviations.

Measuring points shall be defined at suitable areas for functional dimensions in the specification in

order to allow for comparable measuring results.
5.6 Dimensioning, tolerancing and measuring of radii

Minimum 90° of the circle segment shall be provided as a measurable contour for the specification of radii.

NOTE Radii can alternatively be toleranced by profile forms.
5.7 Specification of freeform surfaces

Functional free form surfaces shall be specified with a surface profile tolerance. The verification shall

be fixed in the contract between producer and costumer.
6 Moulding compound properties
6.1 General

This document does not contain any type lists for moulding compounds or their assignment to

attainable production accuracies. Accuracy-relevant properties shall be considered in order to indicate

a general assignment scheme for the large number and variety of moulding compounds.

6.2 Moulding shrinkage and shrinkage anisotropies

The moulding shrinkage (VS) is the relative difference between the tool contour dimension L at

23 °C ± 2 K and the corresponding moulded part dimensions L 16 h to 24 h after production, stored

until measurement and measured according to ISO 291:2008, Table 1, unless otherwise specified by

contract or the relevant ISO-material specification. It is calculated according to Formula (1).

 
VS =−1 ×100% (1)
 
 W 
where
L is the moulded part dimension;
L is the tool contour dimension.

The relative moulding shrinkage for thermoplastics and thermoplastic elastomers is determined

(e.g. test panels) according to ISO 294-4 and for thermosets according to ISO 2577 on standard test

specimens. Physical causes of the moulding shrinkage and the effect of influencing factors are indicated

in Annex B and Annex E.
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ISO 20457:2018(E)

Shrinkage anisotropy is quantified by the absolute difference ∆VS from moulding shrinkage transverse

to the melt flow direction VS and the moulding shrinkage parallel to the melt flow direction VS . See

Formula (2).
DVS =−IV��SVSI (2)
⊥ II
Primary causes for anisotropicity include:

— moulding impediments as a result of different thermal contraction by solidified boundary layers,

material concentrations and locally different tool contour temperatures as well as by the effect of

the moulded part design;
— shrinkage differences due to over-moulded parts for example metal inserts;

— orientation of fillers and reinforcements, and molecular orientation as a result of shear and elongation

flows. In particular, particle shape and aspect ratio (length-thickness ratio or side-thickness ratio)

of the fillers and reinforcements affect the anisotropy characteristics.

It can be derived from the variety of influences on the moulding shrinkage and shrinkage anisotropy that

numerical values are only realistic as range data. The resultant distribution of the moulding shrinkage

∆S is derived from the extreme values VS and VS It is calculated according to Formula (3).

max min
DSV=−SVS (3)
maxmin

The degree and uniformity of the shrinkage distribution can be affected by many factors including

production conditions (process optimization), batch-relevant moulding compound differences, moulded

part shape and sprue technology.

Average calculated values of the moulding shrinkage VS are specifications for tool design, construction

and sampling of the tools. It is calculated according to Formula (4).
VS =+05, VS VS (4)
Rmax min

This calculated value, which is a basis for the tool design, is primarily expected from the moulded part

man
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