Out of these two main categories of scrap, the damaged or defective coils constituted nearly 77 per cent for the total value (Rs 7.22 lakh) and hence the team decided to focus the attention on that area. Based on this finding, the team formulated the mission statement as follows:
Mission statement:
Reduce the cost of rejection due to defective or damaged coils from Rs 7.72 lakh to Rs 3.35 lakh (50 per cent) in eight months.
Diagnostic journey:
In order to understand the problem, the team decided to collect more detailed and authentic data. A format was designed for data collection. The possible defects identified were as follows:
· Damage due to blending at the expansion stage
· Damage to the mouth of the copper tube at the expansion stage
· Leakage in the internal length of coil
· Leakage near tube sheet joint
Testing of theories
Theory 1: Use of wrong punches while making the tube sheets cause coil leakages
This study was conducted by using the technique of study of current operations, Pareto analysis of available data and process dissection by stream. Pareto diagram of three months data revealed that five types of coils constitute 78.4 per cent by value of the total rejection. Process dissection by stream was done and it was found that four out of five coils use tube sheets made on Amada punch press using a single punch. The different types of tube sheets in the coil shop are manufactured on Amada punch press or conventional press using dedicated dies. In a dedicated die there are various punches depending on the number of holes on the tube sheet whereas, in Amada punch press there is a single punch irrespective of the number of holes required on the tube sheet. The diameter of the punch used was 9.97 mm. The team decided to increase the diameter to 10.13 mm and accordingly new punches were ordered and tried out. The results were encouraging as the leakages near the tube sheet joint were totally eliminated during the trial period of one week.
The theory was proved valid.
Theory 2: Brazers damage the coil while brazing
This theory involved the study of operators and hence in camera detailed study of their activities was conducted to identify their positive or negative knacks. This study was conducted under the pretext of establishing the norms for brazing rod consumption per joint. For the above study, two brazers with higher skills and two with lower skills were identified based on the experience of the team members. Their performances were observed from the beginning of the shift to the end of the shift. Consumption of brazing rod was noted along with other details necessary for the teams observation. As the number of reading was less than 40, the data collected was analyzed by using the box plot.
As expected, the brazers with lower skills proved to be consuming more brazing rods compared to those with higher skills. The wrong brazing practices used by brazer D resulted in three coils rejected out of 40 coils brazed by him. These three coils had to be reworked.
The theory was proved valid.
Remedial journey:
From the first theory it was concluded that smaller sized punches were causing leaks and were replaced by higher size punches. From the second theory it was proved that brazers were responsible for damaging the coils by using wrong practices.
Holding the gains:
The smaller sized punches were destroyed to make the remedy irreversible. The process sheet was accordingly modified and frequent audits were done to ensure that the brazers religiously use the stickers.
Intangible benefits:
The achievement has instilled in a new level of confidence among the team members, who are now more enthusiastic to take up such challenging projects. The results have boosted the overall morale of the workers in the coil shop.
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