Takeshi Kawai Parts Manager, 1st Production Section Hamanako Denso (March 1979)
Editor’s introduction: this QC circle is made up primarily of housewives who approach
their circle activities in the spirit of brightening and enlivening their work, an important factor when one must manage both a home and a job. The company is sited near the birthplace of Sakichi Toyoda. In fact, the circle meetings are held in the house where he was born and to pay respect to his dying exhortation to ‘strive to learn and create and stay ahead of the times’. The three lines of their QC circle motto start with the three syllables of his given name:
SAra ni hatten (further development) KItaeyo tagai ni (mutual improvement) CHIe to doryoku de (with wisdom and effort)
The following account of their activities concerns the use of special equipment for winding automobile regular coils. Responding to a zero-defects policy at the company, the entire group set out to reduce the rate of defects from 0.2% to 0.02%. To see this difficult project through to completion, the leader applied the whole range of QC techniques and obtained co-operation from the company staff as well as the full QC circle. Patient data collection and analysis bore fruit and after six months, the target was more than achieved.
The report below covers all the necessary information about reducing defects in a machine processing step but, doubtless due to space limitations, it is less detailed than one would like in describing the housewife-dominated membership of the circle and explaining how the improvements were carried out.
(a) Introduction
Our QC circle is engaged in making one of the important parts of an automobile: we wind regulator coils. Stimulated by the catch-phrase ‘zero major defects/ we decided to tackle the problem of breaks in these V coils.
(b) Process and our circle
Our process consists of machine-winding the coil, wrapping the lead wire around the terminal, soldering it to the terminal, checking the resistance and visual appearance and delivering the coil to the next process (Figure 7.15). I am the only male in this 12- member circle. Nine of the women are housewives. The housewives’ average age is 38 and they have an average of two children each.
Fig. 7.15 Regular coil winding. (Source: Asian
Productivity Organization, 1984.)
The QC circle got off to a difficult start, with only 50% attendance at the weekly after work meetings. The low attendance was discussed during the noon breaks and members gave such reasons as, ‘It makes people late in fixing meals for their families’ and Transportation home afterwards is a problem.’ As a result, we decided to:
1. Hold the meetings on Mondays, so that members could make their dinner preparations the day before (Sunday).
2. Give everybody a lift home afterwards.
We also decided to put craft materials and other diversions in the rest area at the factory and to take other steps to create a pleasant atmosphere, as well as to supply members who could not attend meetings with notepaper on which they could submit their suggestions so that everyone could participate in some way.
(c) Reason for starting the project
The company had begun a zero-defect campaign. Since breaks were the most serious defect in the regulator coils for which we were responsible, we chose this as our project.
(d) Goal setting
We set a target of reducing the break rate from its current (June 1977) value of 0.2% to 0.02% by the end of December.
(e) Understanding the present situation
I looked over 500 defective coils manufactured during June to see where the breaks had occurred and showed 206 of them to the entire circle. Together, we summarized the general results of this study in a Pareto diagram (Figure 7.16).
(f) Study of causes
We decided to focus on breaks at the beginning of the winding and had each member suggest three reasons why breaks might occur there. We then arranged these suggestions in a cause-and-effect diagram (Figure 7.17).
(g) Factorial analysis
1. Individual differences: to see how different workers performed, we had three people wind coils on the same machine (No. 1). These turned out to be no great difference in the rate of defects.
2. Material differences: three gauges of copper wire are used. All of the breaks occurred with the thinnest gauge (diameter 0.14 mm).
3. Machine differences: breaks occurred on all the machines but we found that the rate increased with the tension load.
4. Correlation between tension load and rate of breaks was determined from a study of 3000 coils produced at each workstation (Figure 7.18). I did this analysis myself and presented the results to the circle members.
Our QC circle then made another cause-and-effect diagram to try to find the reason for the variation in tension. We investigated and planned studies of the spring pressure, the felts and rollers A and B (Figure 7.19). A special instrument was needed to measure spring pressure, so we asked the production engineering section to make that measurement.
(h) Actions and results
By putting sealed bearings on both rollers A and B, we got the variation in tension load within the designated limits and the defect rate, which had been 0.2% in June, fell to 0.09% in September (Figure 7.20). But this was still short of our target of 0.02%. Our circle therefore made yet another factorial analysis to search for other causes that might be keeping the defect rate high (Figure 7.21).
In regard to action 3, slackening the lead wire, I showed the members how to put light thumb pressure on the wire when wrapping it around the terminal. As a result, breaks at the beginning of the winding disappeared.
Fig. 7.16 Pareto diagram showing locations of
breaks. (Source: Asian Productivity Organization, 1984.)
Fig. 7.17. Cause-and-effect-diagram for
suggestions why breaks occur. (Source: Asian Productivity Organisation, 1984.)
Fig. 7.18 Correlation between tension load and
rate of breaks. (Source: Asian Productivity Organization, 1984.)
Fig. 7.19 Investigation plan. (Source: Asian
Productivity Organization, 1984.)
(i) Results and institutionalization
By actions 1 to 4, we were able to get the rate of breaks down from 0.2% in June 1977 to the 0.02% target level in November (Figure 7.22).
To institutionalize this result, we had the following four items added to the check sheet and work instructions:
1. Check tension load.
2. Check tension, roller A and roller B. 3. Clean rollers.
4. Handle coils correctly.
(j) Conclusion
Through the co-operation of the QC circle members, the causes of the breaks were found, corrective actions were taken and the target was achieved by the end of the year. There was a time along the way when the circle’s efforts did not seem to be having results and members began to lose heart but, thanks in part to advice from management, we were able to complete our project and enjoy a sense of collective satisfaction.
Fig. 7.20 Results of actions. (Source: Asian
Fig. 7.21 Further factorial analysis and actions.
(Source: Asian Productivity Organisation, 1984.)
Fig. 7.22 Results achieved. (Source: Asian
Productivity Organization, 1984.)
(k) Future plans
1. Having achieved our year-end target of 0.02% break defects, we plan to revise our goal and go for zero.
2. By stimulating QC circle activities and getting everybody to work on the problem, we hope to reduce the break rate in other steps in the production process.