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Six Sigma Machining Case Study
Cycle Time Example
By Joe Barckett
A small family owned machining company, which provides machining services to the aerospace industry, wanted to reduce the cost of manufacturing by reducing the machining cycle time of a specific product. It was their first exposure to Six Sigma and a paradigm shift in operations needed to occur.
The key Project Engineer decided to utilize the Six Sigma DMAIC improvement process to reduce the cycle time. With the help of SAI Global he formed a Six Sigma team that included machine operators and management.
During the DMAIC process the team accomplished the following:
Define Phase: The current cycle time was in excess of 1200 seconds with a standard deviation of 31 seconds. The team agreed on the scope of the project and set a goal of 50% reduction in cycle time without negatively effecting the variation and set a minimum sigma level of 3. Several risks were identified: overtime reduction, less time for inspection, and a faster business pace. An "as is" process map and SIPOC were developed.
Measure Phase: From the three metrics defined as input, process and output, nine key metrics were identified. Operational definitions were written, and a new data collection method was put in place. A Gage R&R was performed on the new measurement system and showed less than 5% study variation. The data that was collected was analyzed for stability and showed no special cause variation present. The Sigma value was calculated for the current process and showed a large negative value.
Analyze Phase: Using the data collected in the measure phase, team member expertise and statistical analysis, four significant "x" factors were validated as root causes for long cycle time. Further data showed a potential for over 40% improvement.
Improve Phase: Solution generation techniques and Lean concepts were used to generate potential solutions. The solutions were then ranked presented to management and then piloted. Statistical validation techniques were used to prove effectiveness of the selected solutions. Control charts showed the new process was stable while descriptive statistics showed a Sigma value in excess of 5 sigma. There was also a 20% reduction in the number of process steps.
Control Phase: New documentation was developed, as well as a new process map, and old documentation was updated. Training plans were developed and implemented as part of the solution implementation. Potential problems were identified in 3 categories: Methods, Human factors and Environment. Control plans were put in place to manage the risks. Finally, lessons learned were outlined and results calculated.
The Results of Applying the Six Sigma DMAIC Process:
Table 1 shows the results of the project:
Over a 46% improvement in average cycle time
Over an 80% reduction in variation
Figure 1 shows the results graphically:
| |
Original |
New |
| Average Cycle Time |
1245 seconds |
670 seconds |
| Standard Deviation |
31 seconds |
5.5 seconds |
| Percentage Improvement |
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> 46% |
Table 1
Figure 1
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