Control

Logigramme

The old standard ISO 8402 (now cancelled) gave the following definition of it:

"Control: activities such as measuring to examine, test or pass to the gauge one or more characteristics of an entity and to compare the results with the requirements specified in order to determine if conformity is obtained for each characteristic "( ISO8402:1994, § 2.15.).

Control is a technical act making it possible to determine the conformity of a product. To carry out a control on a product, it is necessary as a preliminary to determine the characteristics and to choose of them the limits (the engineers would say "the tolerances") inside whose the product is in conformity.

It is necessary that these limits are known by the "controller" who will carry out control. It also implies that with resulting from the technical act of control, a decision is made with regard to conformity:

•  Does your product conform?

•  Products not-in conformity which have to be rejected?

•  Products not in conformity being able to be improved?

•  Product not in conformity being able to be accepted in exemption.

Characteristics of a control

A control is defined by a certain number of parameters:

•  The frequency of control: systematic, by taking away

•  The characteristics of the product which must be controlled.

•  The type of control: non-destructive, destructive (sometimes called "test").

•  Control method: by measurement, comparison, appreciation (visual monitoring for example).

•  methods of control to use: measuring apparatus, reference frame

•  The entity which carries out control: personnel of manufacture (auto-control [3 ]), specialized, staff personnel supervisory, machine (automation of control).

To choose the characteristics of a control, it is necessary to take into account the technical constraints (criticality of the characteristic to be controlled, the precision necessary of the measuring apparatus, qualification of the personnel carrying out control etc.) but also of the economic constraints.

The economic aspects exploiting the nature of control, is the means to engage and the characteristics to be controlled.

It is necessary to choose in priority, the characteristics having an influence on safety, the functionality of the product.

The risk associated with non-detection must be taken into account. The client can limit this choice by forcing a certain number of characteristics to be controlled and/or controls to be carried out.

The frequency of control

If a control is carried out in a systematic way on totality (100%) of the parts, it makes it possible to carry out a sorting and to eliminate nonconformities directly. It is an often long and expensive method which cannot be systematically selected.

Control by removing random products from the production process enables a swift detection of defects in the manufacturing process. The methods can be empirical.

To do this we choose a rate of recurrence of taking away of the type "X parts every hour", "of all the manufacturing batches" etc.

The methods can be of statistical type by using methods MSP where standards specific to this type of control.

Type of control

Certain controls can be carried out without destroying the part or the unit which must be controlled: measurements dimensional, electric, of colors, etc.

Same certain non-destructive control methods called (ultrasonics inspection, dye penetrant inspection etc.) allow us to control certain characteristics like "health issues".

In certain cases, it is not possible to control a characteristic without destroying the product to be controlled. It is thus impossible to control all the parts.

The destructive control of a limited number of products validates a batch. In this case, control is accompanied, or even sometimes, is replaced by a control of the parameters of manufacture (temperature, pressure, amperage etc.) having an influence on obtaining the characteristic being able to be measured only by one destructive process.

E-mail: dossier.controle@quali-fiable.com