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The application of statistical technology in motor quality management

modern quality management is the science that closely combines management, statistics, mathematics and accounting. The control of product quality is to use statistical methods to study various problems in production and put forward decisions to prevent quality problems. It is also possible to find out the quality problems in time by counting the qualified rate of parts in each process of production and drawing dynamic charts, so as to reduce costs and eliminate waste

in our work practice, we use the questionnaire, cause and effect table and arrangement chart in statistical technology to track and record the quality control activities of products in the production process, collect data, sample inspection and quality analysis, and promote the solution of problems by identifying symptoms, analyzing causes, looking for measures. Aiming at the quality problem of low qualification rate of permanent magnet DC motor, this paper investigates and analyzes the statistical data of test records, so as to provide scientific data for the product quality control activities of the enterprise

1 investigation of unqualified conditions of permanent magnet DC motor

the qualification rate of permanent magnet DC motor in production is low and the repair rate is high. According to the experimental records and statistical data accumulated in the Institute for many years, the investigation is carried out with the motor produced in a certain period, and strive to draw a reasonable conclusion. The investigation of the nonconformity of permanent magnet DC motor is shown in Table 1

among the 25 unqualified motors, 10 motors are qualified after one repair after assembly, and the final number of unqualified motors is 15. The inspection results are shown in Table 2, and the cause distribution of nonconformity is roughly similar to that of the first test

it can be seen from the table that the high rated speed is the main reason for the disqualification, accounting for 40% of the total disqualification in the first test and 40% of the total disqualification after one repair

2 causes

(1) user index requirements are extremely strict. The speed tolerance of rated point is ± 5%. The linearity of rated point, overload point and no-load point is too high, which is difficult to meet the requirements for the manufacture of permanent magnet DC brush motor. It can be seen from the questionnaire that the main reason for the disqualification is the high rated speed, which is because users have requirements not only for load points, but also for overload points. The qualified rate of overload speed can be easily improved when the rated speed is at the upper limit; If the rated speed is at the lower limit, the unqualified rate of overload speed will increase greatly, which will virtually reduce the range of ± 5% of the rated speed, and it is also easy to cause the rated speed to exceed the upper limit, that is, the speed is high, which is the main reason for the high unqualified rate of the motor

(2) the magnetic properties of magnetic steel are unstable and dispersive. This has an impact on the working characteristics of the motor and directly changes the rated working point

(3) the motor structure is square, and the neutral surface of the brush cannot be adjusted. It is impossible to accurately ensure that the exploration constitutes a reasonable and feasible working mechanism for the development of composite material body, which affects the performance parameters of the motor. From the motor principle, it can be seen that the neutral surface position of the brush can adjust the size of the air gap magnetic flux, so as to improve the performance of the motor

(4) processing technology of motor. The elasticity of the spring during heat treatment cannot be accurately guaranteed, and the bending angle is not easy to accurately control, which makes it difficult to control the brush pressure. The elasticity of brush spring, contact reliability and the change of contact resistance are common problems in miniature brush DC motor

3 measures taken

(1) due to the strict requirements of users' technical indicators, the data must be automatically processed during assembly to select the brush holder, stator and rotor. According to the experience of previous repair, it is best to select and match according to the test data while doing the test in the laboratory, which is the most effective measure

(2) magnetic steel purchased by designated manufacturers. This ensures the consistency of magnetic properties and reduces their dispersion

(3) the electric brush holder is changed into an adjustable neutral surface structure. Due to the limited structural space of the motor, the processing technology is more complex and difficult to guarantee, which reduces the qualification rate of semi-finished products. Considering the limitation of regulating the performance of the neutral face motor, it is temporarily processed according to the original design

(4) improve the process rules and try to overcome the errors caused by human factors. Strictly control the quality during brush welding. When the brush holder is sub assembled, ensure that the brush is in a free state and meets the requirements of the drawing. When bending the brush spring, the angle must be ensured to meet the drawing and process requirements

4 arrangement of unqualified conditions of permanent magnet DC motor

the statistical table of unqualified conditions of permanent magnet DC motor according to the first test results is shown in Table 3

draw the arrangement diagram according to the statistical table in Table 3, as shown in Figure 1

the unqualified situation of permanent magnet DC motor is counted according to the test results after the first repair. 4. The table of safety protection pins installed on the main machine of the simply supported beam impact tester is shown in Table 4

according to the above statistical table, draw the arrangement diagram of unqualified motor after the first repair, as shown in Figure 2

it can be seen from the table that the high rated speed is the main cause of disqualification. It accounts for 40% of the total qualified number in the first test and 40% of the total unqualified number after the first repair. The cause and effect diagram of unqualified permanent magnet DC motor is shown in Figure 3

corrective measures: screen magnetic steel, unify the dimensional accuracy of air gap, and strengthen the inspection of winding turns. (end)

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