9.3.3 Types of product quality control

Ensuring and improving the quality of products - one of the main tasks of production. In solving this problem, an important role is assigned to quality control at all stages of production in order to verify the compliance of quality indicators with the established requirements. The variety of types of quality control makes it necessary to systematize and classify them according to a number of signs. Classification of types of product quality control is presented in Fig. 8.6 (GOST 16504-81).

Depending on the possibility of using controlled products, there are destructive and non-destructive testing.

Destructive control makes products unsuitable for further use and, as a rule, is associated with significant costs; Its results are characterized by a certain degree of uncertainty. For these reasons, non-destructive testing is more preferable, based on the results of indirect observations, as well as on the use of X-ray and infrared technology, electronics, etc. At the same time, there are situations when only destructive control is used, namely: firstly, when it is difficult during non-destructive testing, it is impossible to take into account a large number of individual quality indicators, the function of which is the generalized quality indicator to be controlled; secondly, it is sometimes more economically feasible to control to destroy a certain number of units of products instead of the costs of implementing non-destructive testing that considerably exceed their cost.

Depending on the volume of the material being monitored, there is a continuous control, in which all units of production are controlled, and selective control, in which a relatively small number of units of production from the aggregate to which it belongs are controlled. The decision ^* on the quality of products of the entire population, called a batch, is made on the basis of the results of a sample control from the batch, specified limited number of units of production.

Products of the same name, size or type, manufactured according to the same technology, under the same conditions and for a certain period of time, are characterized by quality indicators, the distribution of which is subject to the laws of mathematical statistics. The sampling control, procedures and rules of which are based on the laws of mathematical statistics, is called statistical control of product quality. Due to low costs and a high degree of reliability of results, statistical control is an effective means of ensuring product quality. Selective control, not based on the laws of mathematical statistics, can lead to erroneous conclusions.

Figure 8.6. Classification of types of product quality control

Continuous control is used in single and small-scale production, sampling control - in other cases.

The purpose of the control is to distinguish the quality control of products to determine its validity and acceptance - acceptance control (not necessarily finished products) and product quality control to assess the state of technological processes and decisions about the need for their adjustment. The latter type of control, as a rule, is statistical and is called statistical regulation of technological processes.

Depending on the place of product quality control in the process of its manufacture, there are distinguished input control, operational control, control of finished products, sometimes called finishing, control of transportation and storage of products in an enterprise, etc.

Input control is not mandatory, but in some cases it is very useful and even necessary. For example, product quality indicators during transportation and storage may vary. Before launching into production such products must be tested in the conditions of the enterprise. Input control is necessary in those industries where the quality of the finished product significantly depends on the quality of the raw materials, for example, in microelectronics.

Operational control is important. Timely detection of marriage ^* on operations allows you to exclude the pass to the consumer, improve production efficiency by reducing unproductive losses due to the late detection of marriage.

By the nature of the control distinguish inspection and volatile control. Inspection control is the control of already controlled products, from which the detected defect is excluded. It is carried out when it is necessary to check the quality of work of the Quality Control Department or the control automaton. In special cases, inspection control is carried out by representatives of the customer to increase the reliability of the results of monitoring important types of products.

Flying control is also inspection. Due to the fact that it is carried out suddenly, at random points in time, its results can be more reliable.

Depending on the nature of the decisions made, there are active and passive controls. With active control, decisions are made to improve the quality of products, and with passive control only the defect is fixed.

Depending on the monitored parameter, control is distinguished by a quantitative trait, a qualitative trait, and an alternative trait.

Product quality control, in the course of which the values ​​of one or several parameters are determined, and the subsequent decision on the controlled population is taken depending on these values ​​(for example, on their comparison with the control standards), is called a quantitative control .

Product quality control, in the course of which each unit tested is assigned to a specific group, and the subsequent decision on the controlled population is made depending on the ratio of the number of its units in different groups, called quality-based control .

Control on an alternative basis is a special case when the totality of products consists of two groups: suitable and defective products. The decision on the controlled population is made depending on the number of detected defective units or the number of defects falling on a certain number of units of production.

Control by quantitative trait gives more information than control by qualitative and alternative traits. However, the cost of control on a quantitative basis is greater than the cost of the other two types of control. Therefore, when planning and developing control operations technology, control over an alternative feature is often preferred.

Depending on the controls used, visual, organoleptic and instrumental controls are distinguished.

By the nature of the receipt of products for control, there are continuous monitoring, for example, on a conveyor belt or in a flow, and control of production batches.

Marriage - products unsuitable to meet the needs in accordance with the purpose. The reject criterion is the unacceptable deviation of the properties (parameters) of the product from the requirements of the regulatory documentation. Rejected products have no use value or value, i.e. cannot be a commodity. For society, this is an irrecoverable loss of living and materialized labor, for an enterprise it means a decrease in the efficiency of production, income, and profit.

The reason for marriage is above all unfair labor. Marriage arises as a result of violations of regulatory requirements, mistakes of designers and technologists, incompetent decisions of administrators, violations of technological and production discipline, poor performance of control operations. Poor-quality work of one worker can make useless the work of entire groups, destroy the results of their work. Hence, the main means of preventing marriage is to increase the culture of production, qualifications and personal responsibility of performers for the results of their work.

Marriage is products that, due to defects, i.e. individual deviations from the established requirements, does not meet the technical conditions for its manufacture. Defects can be identified in the manufacture of products, final quality control, at the testing stage and in operation. By nature, defects can be repairable and incorrigible. The correction of defects leads to a rise in the cost of all manufactured products or its individual batches. An incorrigible marriage turns out to be an enterprise for direct economic damage, loss of labor and material and technical resources. The appearance of defects at any stage requires the immediate determination of the place and the reasons for their occurrence in order to promptly resolve the issue of suspending the release of defective products, determining the way to compensate for losses from a marriage and eliminate its cause.