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RE-EVALUATING CORE DIMENSIONAL CHANGES


R. Showman, M. Nocera and J. Madigan Ashland Performance Materials, Dublin, OH, USA


G. Baltz, T. Hajduk and J. Wohleber Ford Motor Company, Cleveland, OH, USA


Copyright © 2010 American Foundry Society Abstract


Ford Motor Company’s Cleveland Casting Plant experienced unexpected dimensional changes on gray iron cylinder block castings as measured at the engine plant. The casting plant formed a Statistical Weapons and Tactics (SWAT) team to address the issue. The team generated volumes of background data but failed to fully identify the root causes. Measurements of the waterjacket core showed that dimensions decreased or shrank over time and with different processing changes. While the amount of shrinkage was very small compared to the overall dimensions of the block, the mechanism was not well understood and hereto had not been factored into tooling dimensions. A project was initiated with Ashland Casting Solutions, their binder


Casting Plant Problem and Investigations


The cylinder block casting produced at the casting plant features a tolerance of +/- 0.8 mm (0.031 in.) and measures 19.685 in. (500 mm) long and 11.811 in. (300 mm) tall. This requires constant monitoring of all casting datums to insure casting locators are correctly transferred to the machining- locator datums. The cylinder block casting is made from 11 separate sand cores which must be held to close tolerances as individual cores can create stack-up dimensional issues across the core package assembly. The 11 separate cores may be produced on 19 different core machines utilizing various sets of corebox tooling. Cores are used the same day and/or enter production storage buffers during the manufacturing process, where they may remain for additional periods. In addition, the production facility has no special controls over environmental conditions.


Many casting locator datums on the core package are de- signed to be accessible at the machining line but are not easily accessible on the sand core package, thus making it extremely difficult to gauge prior to making an actual casting. Special gauges and fixtures were used to measure the cores’ positions before placing them into the mold. The casting plant monitors its in-house processes by au- diting final casting dimensions daily using a unique gaug- ing fixture.


International Journal of Metalcasting/Summer 10


supplier, to compare the effects of different materials and process variables on coldbox core shrinkage. Measurement methods were analyzed and Design of Experiments (DOEs) were conducted to measure the shrinkage of cores produced with different materials under various conditions. Additional testing was conducted to investigate the effects of post- coremaking operations like coating, drying, and storage under varying conditions. These results were included with those from other investigations to modify core tooling and resolve the issue at the casting plant.


Keywords: core shrinkage, coldbox, dimensional accuracy, waterjacket core, DMAIC


Blocks are 100% gauged at the engine plant prior to ma- chining. The first operation includes mounting the casting on the locators, checking critical characteristics, and then making the engine block machining locators in reference to the casting locators. All dimensions are checked prior to accepting the block casting into the machining line, and dimensional data is stored at the line for each casting. The casting plant follows line trends to ensure casting dimen- sional compliance.


A lengthy investigation was launched at the casting plant when trend line data indicated a shift of 0.4 mm or 30% of the tolerance in the waterjacket length mean over time. The mean shift was causing an increase in block rejects at the engine plant. Both the left and right waterjacket dimen- sions displayed the same trend, indicating the cores were moving in the same direction. Historically, process fluctua- tions showed shifts in waterjacket lengths independent of each other.


A casting SWAT team was assembled to determine the cause for the shift in the waterjacket core length dimen- sion. The team followed the Six Sigma® (Trademark of Motorola) Define, Measure, Analyze, Implement, Control (DMAIC) process for problem solving. The team began by verifying the measurement systems used at the engine plant and correlated it to the casting plant’s coordinate measur-


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