ISO 16337:2021

INTERNATIONAL ISO
STANDARD 16337
First edition
2021-04
Application of statistical and related
methods to new technology and
product development process —
Robust tolerance design (RTD)
Application des méthodes statistiques et des méthodes liées aux
nouvelles technologies et de développement de produit — Plans
d'expériences robustes
Reference number
©
ISO 2021
© ISO 2021
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ii © ISO 2021 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Robust tolerance design . 2
4.1 General . 2
4.2 RTD experimentation . 4
4.2.1 Data generation . . 4
4.2.2 Experimental design for data collection . 4
4.2.3 Analysis of variance . 7
4.3 Tolerance determination .10
4.3.1 Estimating total variance if tolerance is changed .10
4.3.2 Deciding tolerance .11
5 RTD case study (1) — Stabilizing a circuit by using theoretical formula .12
5.1 Experimentation .12
5.1.1 Objective . .12
5.1.2 Experimental design for data collection and analysis of variance .13
5.2 Tolerance determination .16
6 RTD case study (2) — Stabilizing the piston by using a simulation experiment .18
6.1 Experimentation .18
6.1.1 Objective . .18
6.1.2 Experimental design for data collection and analysis of variance .18
6.2 Tolerance determination .21
Bibliography .26
Foreword
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This document was prepared by Technical Committee ISO/TC 69, Applications of statistical methods,
Subcommittee SC 8, Application of statistical and related methodology for new technology and product
development.
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iv © ISO 2021 – All rights reserved

Introduction
The designer of a product typically decides the specifications of the product and passes them on to the
manufacturing section for use in manufacturing the product. The specifications include the designed
nominal values and tolerances for the parts and/or elements of the product. The optimum nominal
values of the design parameters are determined by robust parameter design (RPD), and the optimum
tolerances are determined by robust tolerance design (RTD).
RPD, as described in ISO 16336, is applied to the product prior to RTD. In RPD, the major noise factors are
used to evaluate robustness as measured by the signal-to-noise ratio, which represents the variability
of product output. It is a measure for comparing robustness between levels of control factors. RPD
identifies the combination of the values of the design parameters as an optimum RPD condition for
minimizing the variability, that is, maximizing the robustness.
RTD, as described in this document, is a method for selecting the degree of errors of the parts or
elements of the product from the viewpoint of variability under the optimum RPD condition, that is,
the combination of optimum nominal values of the design parameters. If a manufactured product has
errors from the designed nominal values, the product output will deviate from the designed value. The
error in a design parameter should be smaller than the designed error limit to keep the product output
within the designed variability. This is why the design parameters need a tolerance.
The design of a product can be finalized by setting the optimum error limits of the design parameters
by using RTD. The expected variance in output of a product manufactured with errored parts or
elements can be estimated using RTD. After RPD is used to identify a set of optimum values for the
design parameters, RTD is used to check whether the estimated variance is smaller than the target
variance under the optimum RPD condition.
RPD can be used to set the optimum nominal values of the design parameters without increasing
manufacturing cost while RTD is closely related to the manufacturing cost. Smaller tolerances, meaning
higher-grade parts or elements, result in higher costs, while larger tolerances, meaning lower-grade
parts or elements, result in lower costs. To finalize the product design, the cost of manufacturing the
product is considered. The loss function in the Taguchi methods is used to transform the benefits of an
improvement in quality into a monetary amount, the same as a cost.
The cost of the improvement and the benefits of the improvement in quality should be balanced in
deciding the tolerances. RPD and RTD together provide a cost-effective way of optimizing product design.
If RPD cannot achieve the product variability smaller than the target variability, the tolerances of the
design parameters are reduced to improve the variability, but smaller tolerances result in higher costs.
On the other hand, if RPD can achieve the product variability much smaller than the target variability,
the tolerances of the design parameters are increased to reduce manufacturing cost, so larger tolerances
result in lower costs.
Products manufactured with optimum nominal values and tolerances of design parameters are robust
to noise situations under usage conditions after shipment. Robust products minimize users’ quality
losses due to defects, failures, and quality problems.
INTERNATIONAL STANDARD ISO 16337:2021(E)
Application of statistical and related methods to new
technology and product development process — Robust
tolerance design (RTD)
1 Scope
This document specifies guidelines for applying the robust tolerance design (RTD) provided by the
Taguchi methods to a product in order to finalize the design of the product.
NOTE 1 RTD is applied to the target product to set the optimum tolerances of the design parameters around
the nominal values. RTD identifies the effects of errors in the controllable design parameters on product output
and estimates the total variance of the product output if the tolerances are changed. Hence, RTD achieves the
target variance of the output from the viewpoints of robustness, performance, and cost.
NOTE 2 The tolerance expresses a maximum allowable error in the value of a design parameter in the
manufacturing process. In a perfect world, the parts or elements of every product have the designed nominal
values of the design parameters. However, actual manufacturing does not reproduce the exact designed nominal
values of the design parameters for all products. The actual products have errors in the values of their parts or
elements. These errors are supposed to be within the designed tolerances.
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 16336, Applications of statistical and related methods to new technology and product development
process — Robust parameter design (RPD)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 16336 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 http:// www .electropedia .org/
3.1
tolerance
difference between the upper specification limits and lower specification limits
3.2
robust tolerance design
RTD
method of setting optimum tolerances from the viewpoints of robustness, performance, and cost
4 Robust tolerance design
4.1 General
A company’s product design section normally gives the specifications of a product, that is, the nominal
values and tolerances of the design parameters, to the manufacturing section. The manufacturing
section uses the designed specifications in manufacturing the product. When specifications specify the
limits of a design parameter as m±Δ , the parameter value x in the manufacturing process should
satisfy the following restriction:
mx−≤ΔΔ≤+m , (1)
where m and Δ denote a nominal value and its permissible difference, respectively. Only the symmetric
(±Δ ) case is discus
...