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16.6 Control Phase

The Control phase involves mistake proofing the improvements and/or innovations discovered in the Six Sigma project; establishing a risk management plan to minimize the risk of failure of product, service, or process; documenting the improvement and/or innovation in ISO 9000 documentation; and preparing a control plan for the process owners who will inherit the improved or innovated product, service, or process; turning the process over to the process owner; and disbanding the team and celebrating their success.

Team members identified and prioritized two problems while mistake proofing the process improvements discovered in the improve phase. They are: (1) Purchasing agents do not specify "with ridges" on a purchase order and (2) purchasing agents do not consider that the choice of vendor depends on the size of the MSDs being requested on the purchase order. Team members created solutions that make both errors impossible. They are: (1) The purchase-order entry system does not process an order unless "with ridges" is specified on the purchase order and (2) the purchase-order entry system does not process an order unless Office Optimum is the selected vendor for small MSDs and Ibix is the selected vendor for large MSDs.

Team members use risk management to identify two risk elements. They are: (1) failing to train new purchasing agents in the revised purchasing process shown in Figure 16.28 on page 532 and (2) Office Optimum and Ibix are out of MSDs with ridges. Team members assigned risk ratings to both risk elements, as shown in Table 16.24.

Table 16.24. Risk Elements for Purchasing Process

Risk elements

Risk category

Likelihood of occurrence

Impact of occurrence

Risk element score


Failing to train new purchasing agents






Vendor out of MSDs with ridges






Scale: 1–5, with 5 being the highest.

Both risk elements must be dealt with in risk abatement plans. The risk abatement plan for "failing to train new purchasing agents" is to document the revised purchasing process in training manuals. The risk abatement plan for "vendor out of MSDs with ridges" is for POI to request that both Office Optimum and Ibix manufacture only MSDs with ridges, due to their superior durability. This is a reasonable and acceptable suggestion to POI, Office Optimum, and Ibix because the cost structures for manufacturing MSDs with and without ridges are equal, and neither Office Optimum nor Ibix has other customers requesting MSDs without ridges. Office Optimum and Ibix agree to produce only MSDs with ridges after a 6-month trial period in which they check incoming purchase orders for requests for MSDs without ridges. If the trial period reveals no requests for MSDs without ridges, the POI Purchasing Department will revise Figure 16.28 and the appropriate ISO 9000 documentation to reflect the possibility of purchasing only MSDs with ridges. Additionally, Office Optimum and Ibix thanked POI for pointing out to them that average durability is higher for MSDs with ridges than for MSDs without ridges. Both vendors claim that they are going to experiment with possible different ridge patterns to increase durability and decrease costs. Both vendors stated that they anticipate decreased costs from producing only MSDs with ridges because of the lower amortized costs of having only one production line.

Team members prepare ISO 9000 documentation for the revisions to the training manual for the purchasing process from Figure 16.28.

Team members develop a control plan for the PSD that requires a monthly sampling of the boxes of MSDs in inventory. The purpose of the sampling plan is to check whether the boxes of MSDs being purchased are either small Office Optimum MSDs with ridges or large Ibix MSDs with ridges. The percentage of nonconforming boxes of MSDs will be plotted on a p-chart. PSD management will use the p-chart to highlight violations of the new and improved purchasing process shown in Figure 16.28. The p-chart will be the basis for continuously turning the Plan-Do-Study-Act (PDSA) cycle for the revised purchasing process.

Team members check the business indicator from the PSD and determine that production costs in the PSD decreased, probably due to the MSD Six Sigma project (see Figure 16.32). The MSD project took effect in month 73 of Figure 16.32.

16fig32.jpgFigure 16.32 Individuals and Moving Range Chart Obtained from Minitab of Production Costs in the PSD Before and After the MSD Six Sigma Project


This chapter presented a Six Sigma case study. It is time for the champion and black belt to disband the project team, turn the improved process over to the Purchasing Department for continuing turns of the PDSA cycle, and celebrate the project's success with team members.

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