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Visual Six Sigma: Making Data Analysis Lean by Leo Wright, Mia L. Stephens, Philip J. Ramsey, Marie A. Gaudard, Ian Cox

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8.1. Setting the Scene

For the past 25 years, MoldMat Ltd. has supplied the plastic used by one of its major customers in Italy in making white garden furniture. Over the years, mysterious crises occur during which the flowability of the plastic leads to low yields for both MoldMat and its Italian customer. To date, all efforts to find the root causes of these crises have failed. After the most recent crisis, a new team is formed, led by an engineer named Carl Linton, a black belt with training in Visual Six Sigma.

8.1.1. Manufacturing Process

White garden chairs and furniture command a very good price, but they are difficult to make owing to the impact of whitening agents on plastic flowability. Getting the right balance of whiteness and flow is not easy. As the proportion of additives in the mix increases to make the plastic whiter, the flow of the plastic is impaired.

The process for making white plastic begins with the preparation of a filler mixture, or slurry. The white filler, which is an inert powder, is sourced from a number of quarries in Africa. It is mixed with unpurified river water in a stirred tank in the filler preparation section of the MoldMat polymer plant (Exhibit 8.2). The filler preparation tank is agitated and held at a target concentration. The tank is topped off each day with filler and water. Small amounts of a viscosity modifier are added to the slurry if the viscosity gets too high.

Clear plastic is made by heating and stirring a monomer in a batch ...

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