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Figure 1. Fishbone diagram.


ing machine (CMM) and plant floor gauge used to measure the waterjacket core position. Historical waterjacket core length data was reviewed, and process changes were plot- ted against the historical data in an attempt to correlate the mean shift to a known change in the process. The team’s investigation included a look into all production areas: coremaking, molding, melting and cleaning. A drill down tree, a technique used to identify key inputs, was developed to examine all of the processes and identify possible critical characteristics. Some of the factors the team investigated included: coremaking, core transfers, core wash dipping, core temperature affect (old vs. new cores), core placement into the drag mold, the affect of new vs. old pattern and corebox equipment, iron chemistry, iron flow, inoculation, and the affect of shot blast cleaning on the casting dimen- sions. The team used statistical tools to analyze the data collected. Some of the tools utilized included fishbone, analysis of variance (ANOVA), 2-Sample T-test, test for equal variances, regression, multi-vari testing, main effects plots, 23 (two cubed) full factorial DOE, box plots and his- tograms. Examples of the tools are shown in Figures 1-4.


The data collected indicated that a new cope pattern made a 0.0039-in. (0.1-mm) improvement in waterjacket length using a new cope pattern in production. This improvement was confirmed through subsequent trials and analyses of


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Figure 2. Box plot of right waterjacket core dimension vs. cope pattern.


larger sample sizes. Many of the tests conducted during the SWAT investigation showed an initial improvement in waterjacket core length, but when the trials were re- peated to confirm the findings, the results were not repeat- able. This was due to an underlying lurking variable or an interaction between several factors. Some of the factors that appeared to have some impact but were unrepeatable included: inoculation, inoculant type, hot vs. cold cores, and core transfer.


International Journal of Metalcasting/Summer 10


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