8. Case Studies of Six Sigma Improvement Projects
8.2 Non-manufacturing Applications: Development
Korea Heavy Industries & Construction Company (which changed its name to Doosan Heavy Industries Company in 2001) learned Six Sigma management skills from General Electric in 1997, and started Six Sigma to achieve manage- ment innovation. In early 2000, the company published a book called “Six Sigma Best Practices” in which 15 Six Sigma project activities are contained. The long-term vision of the company is to become a “Competitive world-class company of 21st century with the best quality and technology.” To achieve this vision, the company made its own MAP (man- agement action plans), with which CST (critical success themes) were selected for quality and productivity innovation.
This case study presented here is one of the CSTs which is contained in the Six Sigma Best Practices. The Engineering &
Technology Division of this company desired to solve one CST, namely “Reduction of Short Shelf-Life Material (SSLM).” Management formed a project team with a full-time BB and five part-time GBs to tackle this project.
17.00 16.80 16.60 16.40 16.20 16.00 15.80 15.60
0.60[mm]
[mm]
AverageRange
16.54 16.30 16.06
0.44 0.20 0.50
0.40 0.30 0.20 0.10 0.00
(1) Define
There were many materials necessitating storage on a shelf for some period of time to be subsequently used to create var- ious products. Each material had its own specified shelf life- time depending upon whether it was stored in a refrigerator or not. Some frequently used materials and their specifications are listed in Table 8.5. The shelf life-time was counted from the manufactured date.
Table 8.5. Stored materials and their specified shelf
However, due to poor storage conditions and other rea- sons, the shelf life-times became short, and they could not be used in good condition. Such SSLM resulted in some COPQ, environmental pollution and additional testing expenses.
(2) Measure
During the period of July – December, 1999, scrap materi- als were found during the process of manufacturing many products. Table 8.5 shows the scrap materials for the product, stator bar and connecting ring.
Storage in refrigerator Storage in storeroom Material
Shelf life-time Storage
condition Shelf life-time Storage condition Mica paper tape (#77865)
Mica paper tape (#77906) Gl yarn flat tape prepreg Mica M tape (#77921) Modified epoxy varnish Polyester resin–35%
Epoxy impreg fiber cloth (#76579) Pa–polyster sesin
Pb–catalyster Polyester comp
6 months 6 months 1 year 6 months 6 months 1 year 6 months 10 months 10 months
1 year
below 7°C 2–10°C below 5°C
2–10°C below 10°C
2–10°C 2–10°C 2–10°C 2–10°C 2–10°C
3 months 3 months 3 months 2 months 2 months 6 months 1 month 3 months 3 months 3 months
below 23°C 18–32°C 18–32°C 18–32°C 18–32°C 18–32°C 18–32°C 18–32°C 18–32°C 18–32°C
Glass cloth & tape 1 year 2–10°C 3 months below 25°C
Polyester comp
…
1 year 2–10°C 3 months 18–32°C
Table 8.6. Scrap materials in the stator bar & connecting ring
The products/processes that were of particular concern are listed in Table 8.6 along with their current process capabilities.
Table 8.7. Current process capabilities
(3) Analyze
In order to discover the sources of defects and variation, a cause-and-effect diagram was sketched by the team as shown in Figure 8.9.
Product/process Defect Unit Opportunity Total
Opportunity DPU DPO DPMO
Process capability (sigma level) Stator bar &
connecting ring 61 12 50 600 5.083 0.101 101,667 2.77
Stator W’g ass’y 148 13 71 923 11.385 0.160 160,347 2.49
Lower frame A. 31 14 8 112 2.214 0.277 276,786 2.09
Rotor coil A. 4 17 5 85 0.235 0.047 47,059 3.17
Total 244 1,720 0.142 141,860 2.57
Defect: Over shelf life-time of SSLM
Unit: 4 items categorized in the processing using SSLM Opportunity: Quantities of SSLM used in unit Total opportunity = Unit × Opportunity DPU = Defects/Unit
DPO = Defects/Total opportunity DPMO = DPO/1,000,000
Short-term capability = Long-term capability + 1.5
Scrap Cause of scrap
Material Purchase
quantity Quantity Unit Number of times
Change in manufacturing
schedule
Earlier purchase
No control of storage Etc.
Modified epoxy varnish Epoxy impeg fiber cloth Glass cloth & tape Transposition filler
……
92 7,890 958 4,118
31 120 84 55
GL SH RL LB
2 2 5 1
1 2
1 1
2 1 1
1
Figure 8.9. Cause-and-effect diagram for SSLM
In the past six-month period, the total defect count on the materials was 244, and the Pareto diagram for the types of defects is shown in Figure 8.10.
Figure 8.10. Pattern of defects
Defect Pattern
Lack of control of stock materials
Change in manufacturing
schedule
Strict storage condition
Too many/
small storage materials
Others
Count 103 97 15 14 15
Percent 42.2 39.8 6.1 5.7 6.2
Cum. % 42.2 82.0 88.1 93.8 100.0
Count 250 200 150 100 50 0
Percent 100 80 60 40 20 0
Material Men
Defects
Control Purchase
Too many/small materials (3)
Strict storage condition (3)
Short shelf life time-limit (2)
Lack of information (1)
Lack of concern with SSLM (1)
Not accessible electrically (4) Change in manu.
schedule (3) No observation of
first-in, first-out (1) Lack of control of stock materials (1)
No confirmation of Stock material (1)
Early purchase (1)
Inaccuracy of required data (1)
Figure 8.10 shows that insufficient control of SSLM in the storehouse accounted for 42.2% of the total and the unex- pected changes in the manufacturing schedule were responsi- ble for 39.8% of the total defects.
(4) Redesign
In order to reduce the defects of SSLM, the computerized inventory control system was redesigned to increase the con- trol efficiency of SSLM. The current process after the redesign looks as follows.
In this current process, there is no tool for checking and monitoring SSLM, and no one is assigned for checking the defects. The redesigned and improved process (Figure 8.11) makes cross-checking of the manufacturing schedule in advance possible. Also, the related departments can monitor and control SSLMs through an on-line system.
Figure 8.11. Redesigned process for SSLMs
Reconfirm shop load
Manufacturing
process schedule Concurrently related departments exchange information on
manufacturing schedule BOM
MRP
P/O
Store SSLM in refrigerator
Cross checking of actual manufacturing schedule
Control of SSLMs through data warehouse Manufacturing
process schedule BOM MRP P/O Store SSLM
in refrigerator
Inventory control by documentation
(5) Improve
By practicing the improved process, they could obtain the following data for the first three months after the start of its use for SSLMs.
We can compare the quality performances of the old and newly improved processes as follows, clearly showing the impact of the Six Sigma team activities:
(6) Control
In order to maintain the benefits, the team decided to fol- low the following control procedures:
• Update the SSLM instruction manual, and check the manual every six months.
• Educate the workers on SSLM information every month.
• Monitor related data through the on-line computer sys- tem every other month.
Before improvement After improvement DPMO
Sigma level COPQ
141,860 2.57
$190,000/year
11,510 3.77
$15,400/year (estimated) Product/
process Stator bar &
connecting ring Stator wiring assembly Lower frame A.
Rotor coil A.
Unit
13 7 6 10
Opportunity
24 45 3 5
DPU
0.308 0.429 0.167 0 Total
Defect
4 3 1 0 8
Total opportunity
312 315 18 50 695
DPO
0.01282 0.06667 0.05556
0 0.01151
DPMO
12,820 66,670 55,560 0 11,510
Process capability (sigma level)
3.73 3.00 3.09 6.00 (estimated)
3.77
8.3 R&D Applications: Design Optimization of Inner Shield