Calculation of Quality Assurance Costs in the Manufacture of Asynchronous Motors
Abstract Generated abstract
This article addresses the economic assessment of quality assurance in the mass production of asynchronous motors, where quality improvements must be justified by their effect on total production and use costs. It proposes a classification of quality assurance expenditures into costs for eliminating defects, assessing product quality, and preventing defects, and applies this framework to production data for 10,000 third-frame-size A02 series motors. The analysis indicates that quality assurance costs amount to about 2.76 percent of total production costs, with the largest share associated with stator winding quality, followed by mechanical parts, while costs related to technical characteristics are comparatively small. The authors argue that such cost accounting is necessary for developing a mathematical model and broader system of quality management in asynchronous motor manufacturing.
Full Text
CALCULATION OF QUALITY ASSURANCE COSTS IN THE MANUFACTURE OF ASYNCHRONOUS MOTORS
A. G. Verezsh, O. P. Muravlev
(Presented by the scientific seminar of the Departments of Electrical Machines and General Electrical Engineering)
The problem of improving the quality of industrial products is one of the principal problems in all countries of the world. A scientific approach to solving this problem requires a well-founded choice of indicators for assessing the level of quality and determining the economically expedient limits of its improvement. Improvement of product quality must pursue economically justified objectives; otherwise, losses to the national economy inevitably arise.
Asynchronous motors are industrial products of mass consumption, and no special requirements are imposed on their quality level, such as, for example, those imposed on rocket or aviation equipment, where, in order to ensure the required level of quality, economic considerations are sometimes neglected. The quality level of asynchronous motors must be economically optimal. This condition is fulfilled when the total amount of reduced costs for the production and consumption of the product, under fixed conditions of its use, is minimal.
To determine the reduced costs, it is necessary to know the costs of ensuring and improving quality in the production process and the economic benefit to the national economy from improving product quality. The present article gives a classification of the costs of ensuring the quality of asynchronous motors and an analysis of these costs for the 3rd frame size of asynchronous motors of the A02 series.
At present, costs of quality assurance are calculated very rarely. In addition, under existing methods for calculating the costs of manufacturing products, a large part of the expenses for quality assurance is assigned to other items [1].
The costs of ensuring the quality of asynchronous motors, taking into account the existing terminology [1], may be divided into three groups:
1) costs of eliminating defects and rejects;
2) costs of assessing product quality;
3) costs of preventing the occurrence of defects and rejects.
The costs of eliminating rejects and defects are the cost of rejects; the costs of scrapping and correcting production defects; the costs of reworking and remaking defects caused by designers and technologists. The cost of rejects is determined by the amount of final (irreparable) rejects. In the manufacture of asynchronous motors, final rejects consist of the presence of blowholes and cracks in mechanical de-
in steels, poor potting of the short-circuited rotor winding, breakage of the rotor winding bars; defective parts whose dimensions exceed the lower tolerance limit, etc.
Assessment of product quality has the following cost components, directed toward
2.1. incoming inspection of purchased materials and semifinished products (winding wire, insulating materials, electrical steel, bearings, etc.);
2.2. remuneration of inspection personnel;
2.3. tests carried out in the shops;
2.4. inspection equipment and instruments;
2.5. testing of finished products;
2.6. maintenance and verification of inspection-and-testing apparatus.
Measures aimed at preventing the occurrence of defects and rejects include expenditures on
3.1. planning of quality work (development and application of new, more effective inspection methods);
3.2. study, analysis, and control of production processes from the standpoint of ensuring the required product quality;
3.3. design and development of inspection-measuring and testing apparatus;
3.4. training of personnel in methods and means of quality control;
3.5. upgrading the qualifications of Quality Control Department workers.
At present the level of development of electrical machine building is very high, and the introduction of individual measures to improve quality cannot solve the problem as a whole—it is necessary to create a quality-management system in the manufacture of asynchronous motors [2]. Determining the costs of ensuring and improving quality is a necessary part of the work in developing this system. The costs associated with the quality of asynchronous motors should expediently be divided into three parts:
1) costs of ensuring the quality of mechanical parts;
2) costs of ensuring the quality of the winding;
3) costs of ensuring technical characteristics.
On the basis of the above classification of quality-assurance costs, let us analyze the costs in the manufacture of asynchronous motors. The table gives approximate values of the costs of production and of assuring the quality of 10,000 motors of the third frame size.
The costs of rejects were obtained on the basis of reject reports, which indicate the costs associated with eliminating the defect or the cost of final rejects. It should be taken into account that the data are presented for existing production, when by no means all parts and assemblies of asynchronous motors conform to drawings and technical specifications [3]. Analysis of quality-assurance costs shows that the principal share of them falls on expenditures associated with achieving the required quality of the winding and of mechanical parts. These two components differ by almost a factor of two. This is explained by the fact that the cost component for ensuring winding quality also includes the expenses of maintaining the reliability laboratory, which is mainly concerned with questions of winding reliability. Expenditures on ensuring the quality of the technical characteristics, which are established by the state standard and determine the applicability of asynchronous motors in operation, are insignificant.
In the total costs of manufacturing motors, expenditures on quality assurance are small: only about three percent. Such a situation
Table 1
| No. | Cost item | Costs, rub. | % of the total quality-assurance costs | % of the total cost amount |
|---|---|---|---|---|
| 1 | Costs of rejects and elimination of rejects in mechanical parts | 1047 | 10.9 | 0.30 |
| 2 | Costs of rejects and elimination of rejects in the stator winding | 965 | 10.0 | 0.28 |
| 3 | Costs of rejects and elimination of rejects in the rotor | 125 | 1.3 | 0.04 |
| 4 | Total costs of quality assurance for mechanical parts | 2889 | 30.1 | 0.83 |
| 5 | Total costs of quality assurance for the stator winding | 5702 | 59.2 | 1.64 |
| 6 | Total costs of assurance of the quality of technical parameters | 1031 | 10.7 | 0.29 |
| 7 | Sum of quality-assurance costs for asynchronous motors | 9622 | 100.0 | 2.76 |
| 8 | Cost of materials | 190000 | — | 54.60 |
| 9 | Wages of principal production workers | 26600 | — | 7.64 |
| 10 | Shop expenses | 16000 | — | 4.60 |
| 11 | Equipment maintenance | 75100 | — | 21.58 |
| 12 | Plant-wide expenses | 30678 | — | 8.82 |
| 13 | Sum of production costs for motors, excluding nonproduction expenses | 348000 | — | 100.0 |
| 14 | Factory cost | 34.8 | — | — |
This can be explained by the fact that at electrical-machine-building plants no special attention is paid to quality assurance: motors are produced with parts that deviate from the requirements of drawings and technical specifications; the inspection system is not improved; and work to prevent rejects is not carried out.
Conclusions
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A classification of quality-assurance costs in the manufacture of asynchronous motors has been developed, which it is expedient to use in constructing a mathematical model of the quality-management system.
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At the existing level of quality of the asynchronous motors produced, quality-assurance costs are small; more than half of them are attributable to the winding, and only a small part to ensuring technical characteristics.
Literature
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N. S. Brosalov et al. Modern Methods of Organizing Product Quality Control Abroad. Series “Technology and Organization of Production.” Moscow, Institute “Elektronika,” 1968.
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O. P. Muravlev, Yu. Ya. Kovalev, A. D. Nemtsev, O. L. Rapoport. Questions of quality management in the manufacture of asynchronous motors. In the present collection.
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O. P. Muravlev, A. D. Nemtsev. Application of statistical methods of quality control in the manufacture of mechanical parts of asynchronous motors. In the present collection.