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ISO DIS 22514-8

2013 Edition, September 19, 2013

Complete Document

STATISTICAL METHODS IN PROCESS MANAGEMENT - CAPABILITY AND PERFORMANCE - PART 8: MACHINE PERFORMANCE OF A MULTI-STATE PRODUCTION PROCESS



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Superseded By: ISO 22514-8

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NOW A PUBLISHED STD * SEE ISO 22514-8
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Description / Abstract:

The aim of this document is to define the evaluation method to quantify the short-term capability of a production process (capacity of the production tool, widely termed 'capability'), ie the machine performance index, to ensure compliance on a toleranced measurable product characteristic, when said process does not feature any kind of sorting system.

If the production process integrates a sorting system, then this one (clearing away non-conform parts) should be analyzed independently.

This standard does not aim to define evaluation methods the capability of a production process that is gauged through long-term observation (capability process or performance process indexes).

This standard defines:

— the principles guiding the development of indicators for quantifying capability, and

— the statistical methods to be employed.

The characteristics used to evaluate production process capability have statistical distributions, and it is presumed, a priori, that at least one of these distributions is multi-modal. A distribution is presumed to be multimodal if it results from the marked effect of at least one cause inducing a significant difference between the produced items.

This standard applies, for example, to characteristics generated by processes such as:

— multi-cavity casting: simultaneously producing several identical parts from a mould featuring several cavities;

Since each cavity has its own geometry and its own position in the mould architecture, it may create a systemic difference on the output result.

— multi-fixture machining: a part produced at the same time, but the produced parts are positioned in relation to the production tool by different fixture systems;

Since each fixture has its own geometry, mount clamps, etc., it may create a systemic difference on the output result.

— batch load treatments: heat treatment applied at the same time on a set of identical parts (the batch load), distributed within a pre-defined space of furnace. The position of an item of the batch relative to the furnace can influence the output result.

Each cavity, fixture, or position in the batch load corresponds to a different state. The multi-states process can be understood as the result of the combination of different states within the same process (e.g. cavity, fixture, position in the batch load).

NOTE It needs to be assured that such systematic differences, if any, constitute only a very small proportion of permissible error so that their impact is harmless and do not affect the capabilities of the process
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