Seattle Concrete Case

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Summary Seattle Concrete Company (SCC) produces bags of concrete mix for its customers. These bags have a stated weight of 40 pounds per bag. Given the steep penalties for under filling bags, SCC sets a target of 41 pounds per bag to ensure under filling due to natural variations still remain above the 40 pound threshold. Historically, they have operated with a single production shift, but have recently added a second shift to meet their growing demand. Management is interested in a full analysis of their process to ensure that the control limits and capabilities are within reason, and to ensure that the addition of a second shift isn’t causing issues to their process. To accomplish this, a data set was constructed. Ten bags were…show more content…
The remainder of the paper will tackle the details behind the various analysis and our findings, along with any recommendations for management. Statistical Process Control Methods: (X ) ̅& R Control Charts Given that SCC Management would like to observe statistical process control performed for each of the shifts with 3σ standards, we have developed X ̅ and R Charts for each shift. The R-Control chart demonstrates that process variability during both shifts is in control as observed in figures 1 and 2; none of the sample ranges fall outside of the control limits. However, there is a difference in patterns for the R-chart between these two shifts. The first shift shows a normal pattern in which case no action should be necessary. This should not be surprising since this is the normal operation of the company and management has been supervising this shift for quite some time. Although the control limit has not been exceeded for the second shift, the chart shows a very slight upward trend. Each first hour of everyday the range value is at its lowest and each last hour (8th hour) of everyday, the range value is at its highest. This can be explained by the shift in supervisors between the first and last shift and the buildup of mix. Once the buildup of mix in the chute becomes excessive, the end result could show a lot of variability. The first
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