QUALITY MANAGEMENT ISSUES IN THE MANUFACTURE OF ASYNCHRONOUS MOTORS

O. P. MURAVLEV, Yu. Ya. KOVALEV, A. D. NEMTSEV, O. L. RAPOPORT

(Presented by the scientific seminar of the Departments of Electrical Machines and General Electrical Engineering)

Recently the problem of the quality of industrial products in all countries of the world without exception has increasingly become a problem of paramount importance. The high quality of national products guarantees the effectiveness of social labor and capital investment, stable sales of goods within the country and beyond its borders, and a favorable export structure. But in the modern world the significance of the problem of product quality is not limited to its economic content; it also acquires great political significance. Product quality can, in many respects, influence the course of competition between the socialist and capitalist systems [1].

Product quality is understood as the aggregate of properties that ensure the satisfaction of specific needs [2]. Product quality is, as it were, a lens in which the achievements and shortcomings of an industry are concentrated. It is formed at all stages: in the conduct of scientific research, in design, in preparation for production, and in the production process.

At the present stage of the scientific and technological revolution, improving product quality is an obligatory condition for technological progress and further economic growth. In our country there are all the necessary conditions for the development and introduction into the national economy of systems of state management of product quality, but for this it is necessary to carry out extensive and painstaking work to create quality-management systems for individual products and branches of industry.

The existing system for ensuring quality does not meet modern requirements, and a way out of the situation that has arisen is possible only through an integrated approach to solving the problem of improving quality. It is necessary to create a special product quality management system (PQMS). The principal goal of the PQMS system is to obtain optimal quality (from the point of view of the plant’s customer).

The optimal level of quality is understood as such a level at which the total value of the reduced costs for the production and consumption of the product, under fixed conditions of its use, is minimal. Product quality management is the establishment, assurance, and maintenance of the required level of product quality during its development, production, and operation. We shall consider the issues of ensuring the quality of asynchronous motors during their manufacture.

When developing a quality management system at an electrical-machine-building plant, it is necessary to resolve the following issues:

1. Establishing the existing level of quality and analyzing the enterprise’s capabilities.
2. Developing a scientifically grounded system of tolerances for all parameters of asynchronous motors (dimensions, relative arrangement of surfaces, and technical characteristics).
3. Organizing incoming inspection.
4. Ensuring quality in the production process.
5. Forecasting the quality level.
6. Planning the quality level.
7. The economic efficiency of quality improvement.

Product-quality management should be regarded as a large system, and in developing the QCMI system it is necessary to use the achievements of systems engineering [4], which makes it possible to employ the most modern scientific discoveries for solving complex technical and economic problems.

The systems approach, or systems analysis, deals with problems for which no solution exists by ordinary mathematical methods, since it is impossible to determine precisely the quantities that are to be optimized in the mathematical sense. Under these conditions, systems analysis makes it possible to determine the boundaries of possible solutions (the solution space) or to provide a set of alternatives. It thereby makes it possible to substantiate recommendations for developing a solution much more precisely than the intuition and experience of a manager.

With the aid of systems analysis it is possible to consider tasks of a more or less distant perspective; to take into account highly complex internal properties and external interrelations of the system under study; to study problems under conditions of great uncertainty; and to reveal and describe insufficiently clear goals and properties of systems. Methods of systems analysis, together with methods of operations research, make it possible to establish the parameters of complex systems and to obtain a clearer and, most importantly, comprehensive idea of the paths and consequences of solving the tasks posed.

Let us consider in more detail what work is being carried out on the above-mentioned issues at the Tomsk Polytechnic Institute jointly with the Special Design Bureau of the Sibelektromotor plant.

Analysis of the enterprise’s capabilities is reduced to analysis of the individual technological processes that determine the quality level. As preliminary studies conducted at the Sibelektromotor plant have shown, many technological processes in the machining of parts and assemblies do not ensure the required tolerances, and therefore there is a high probability of producing defective output.

Taking into account that, in manufacturing asynchronous motors, a large number of random factors are at work, for assessing the quality level it is expedient to take as the criterion the probability that, in the assembled motor, all parts and assemblies satisfy the technical specifications:

\[ P_T = \prod_{j=1}^{m} P\left[X^{(j)}\right], \tag{1} \]

where

\[ P\left[X^{(j)}\right] \]

is the probability that all parameters of the \(j\)-th assembly or part satisfy the technical specifications.

\[ P\left[X^{(j)}\right] = \prod_{i=j}^{n} P\left[x_i^{(j)}\right], \tag{2} \]

where

\[ P\left[X_i^{(j)}\right] \]

is the probability that the \(i\)-th parameter of the \(j\)-th assembly or part satisfies the technical specifications.

The criterion of the quality level in this form has a physical meaning: \(P_{\text{г}}\) is the probability that, in the motor, all parameters satisfy the requirements of the technical specifications.

With the aid of the proposed quality criterion, a wide range of practical problems can be solved: it is possible to compare the quality of electric machines of the same type manufactured by different enterprises in the country; to evaluate the effectiveness of using new materials and technological processes; to assess the technology and stability of product quality over time when certifying products for the “Quality Mark.” When calculating the probabilities \(P[x_i^{(j)}]\), the limiting parameters are identified, i.e., the “bottlenecks” in quality assurance, and these data can be used to improve technological processes. This criterion makes it possible to evaluate jointly the capabilities of the enterprise’s technological processes and the effectiveness of existing inspection. We have successfully applied it to evaluate the quality level in the manufacture of stator windings and parts produced by machining as applied to asynchronous motors.

The quality level for any product shows steady growth. This growth occurs, on the one hand, as a result of technical and scientific progress and, on the other, because, as people come to know objects and phenomena ever more deeply and discover new properties, they make fuller use of them to satisfy needs. Asynchronous motors are no exception, and their quality level rises periodically. But the improvement of quality is not systemic in nature; only isolated measures are carried out. In order to establish the quality level of asynchronous motors manufactured at a plant, it is necessary to determine the capabilities of the existing technological processes and to evaluate the effectiveness of inspection. This can be done using methods of mathematical statistics.

At present, the establishment of tolerances is carried out either by directive or experimentally. In this case, stricter tolerances are usually assigned, which leads to an increase in the cost of electric machines without any substantial improvement in their quality and reliability. The task of assigning tolerances is deeply interconnected with the calculation, design, manufacture, and operation of electric machines. It is necessary to ensure complete interchangeability not only in geometric dimensions, but also in operating, starting, and energy characteristics, and in reliability and durability.

For the creation of a scientifically grounded system of tolerances for all parameters of asynchronous motors, the necessary prerequisites are available: at the department a method has been developed for calculating tolerances for technical characteristics [5—7]; intensive work is being conducted on the calculation of tolerances affecting the eccentricity of the rotor relative to the stator, on parts obtained by machining, and on the slotting of cores. Methods are being developed for optimizing tolerances by cost. The quality of materials and purchased components used in the manufacture of products depends on the organization of incoming inspection at the enterprise. Therefore, incoming inspection is one of the effective ways to improve reliability and durability. The basic principle in introducing this inspection should be that the costs of introducing and carrying it out should not exceed the amount of prevented production losses (due to poor-quality purchased materials, semi-finished products, and defects). The first version of incoming inspection for wire insulation was developed by us jointly with the reliability department of the Special Design Bureau of the “Sibelektromotor” plant and is presented in the methodology “A System for Inspecting Stator Windings of Asynchronous Motors Ensuring the Specified Reliability.” This methodology makes it possible to evaluate also the economic efficiency of introducing such inspection.

Quality assurance in the production process includes a broad range of issues which, in most cases, are solved with the aid of methods of mathematical statistics. From the standpoint of application, two principal types of statistical quality control are distinguished:

1) statistical quality regulation—current control of the production process by methods of mathematical statistics;

2) acceptance inspection, which is applied during incoming, in-process, and final inspection of finished products.

If statistical quality regulation is used to prevent defects in production through direct intervention in the technological process, sampling methods do not have a direct influence on the manufacture of products. They serve to inspect finished products and to identify the amount of defects and the sources of their occurrence in the technological process.

To carry out statistical quality regulation, control charts are used; they make it possible to represent visually the course of the technological process on a graph, to detect violations of the technology, and to ensure current control and defect prevention through timely intervention in the technological process.

Methods of acceptance inspection are applied at enterprises chiefly in conducting incoming, intermediate, or final inspection in order to verify compliance with technical requirements for product quality.

Recommendations on the application of various methods of sampling inspection in the manufacture of parts and assemblies for asynchronous motors are being developed at Tomsk Polytechnic Institute jointly with the Special Design Bureau of the “Sibelektromotor” plant. Some of them are given in article [8].

Ensuring the stability of the quality of asynchronous motors in their production is the most important condition for providing high reliability and durability. The stability of product quality is mandatory for certification for the “Quality Mark,” and ensuring it is a very complex task that must be solved when creating a quality-management system.

To improve product quality, provision must be made in the UKAP system for scientific forecasting. A forecast is a probable statement about the future with a relatively high degree of reliability. The accelerated rates of development of science and technology make it necessary to predict scientifically the ways of improving electrical machines and the possibilities for the emergence of new directions in research.

There are many different approaches and methods for forecasting the development of technology. Using the classification of E. Jantsch [9], it may be noted that the most appropriate for analysis in mechanical engineering will be an integrated approach, including both normative forecasting, based on the study of needs for a given quality, and exploratory forecasting, which determines the possibilities for improving quality. In this form, the problem of forecasting the quality of asynchronous motors is being solved by Tomsk Polytechnic Institute jointly with the Special Design Bureau of the “Sibelektromotor” plant.

The correctness of the forecast is of great importance in drawing up plans for the development of electrical-machine building and related branches, since improving the quality of electrical machines requires the creation of better electrical steel and insulating materials and wire with the required properties, the development of new technological processes, and an increase in the precision of equipment.

Planning the level of quality must be structured in such a way that the quality level is optimal. For this it is necessary to have

assess the level of quality, to have a forecast of the possible improvement of quality, and a method for calculating economic efficiency.

The main task of the economics of quality is the selection of the quality level to which the manufactured product must correspond. This level must be neither too high nor too low. The solution of this problem depends on two factors, which are functions of the quality level—profit and cost.

The introduction of the QMSP system is impossible without improving the qualifications of enterprise personnel, beginning with the direct operators and ending with enterprise managers, since additional knowledge is required. It should be remembered that quality cannot be obtained by inspection alone—it must be created, and everyone must be responsible for quality.

The system of training personnel for the electrical-engineering industry requires the creation of programs and manuals, as is done in many countries, for example in Czechoslovakia, Poland, Sweden, Japan, and others. The effectiveness of expenditures on upgrading qualifications is significantly greater than that of capital investments.

Economic calculations occupy a special place in the quality-management system. Without an assessment of economic efficiency, it makes no sense to introduce any measures for improving quality.

Thus, a fundamental improvement in quality is one of the urgent problems of the electrical-engineering industry. To solve this problem it is necessary to move from the concept of quality inspection to the concept of quality management. The creation of a quality-management system requires solving a large number of questions, the principal ones of which have been considered in the present work.

Quality management in the manufacture of electrical machines is a complex techno-economic problem, and it should be solved first of all by specialists in electrical machines, who know better than others the factors influencing quality, design, production, and operating requirements.

REFERENCES

1. Quality management of products. Standards and Quality, No. 4, 1969.
2. M. P. Babin, A. V. Glichev, A. V. Derbishev. On the mechanization of product quality management. In Standards and Quality, 1969, No. 3.
3. S. A. Fedorov. Elements of the general theory of quality. Standards and Quality, 1969, No. 12.
4. Handbook of Systems Engineering, edited by R. Makola. “Sovetskoe radio,” Moscow, 1970.
5. O. P. Muravlev. Investigation of the influence of the precision characteristics of the technological process on the quality and reliability of asynchronous motors. Dissertation. Tomsk, 1966.
6. O. P. Muravlev, E. K. Strelbitsky. Calculation of tolerances for the parameters of asynchronous motors. In Elektrotekhnika, 1968, No. 11.
7. B. I. Burshtein, O. P. Muravlev, E. K. Strelbitsky. Calculation of tolerances for the output parameters of asynchronous micromotors. In the collection Asynchronous Micromachines. Publishing House of the Kaunas Polytechnic Institute, Kaunas, 1969.
8. O. P. Muravlev, A. D. Nemtsev. Application of statistical methods of quality control in the manufacture of mechanical parts of asynchronous motors. Present collection.
9. E. Yanch. Forecasting Scientific and Technical Progress. “Progress,” Moscow, 1970.