Computer modeling leads topics.

Solidification modeling and gauge measurement control were among the paramount topics in the engineering technical sessions, proving again that using the newest technology and upgrading the old ones are vital to the ongoing health of the foundry industry.

And based on the large attendance of the individual sessions, it seems that much of the industry is taking a hard look at new methods and technologies.

One of the newest techniques being adopted is tracking gauge R&R. Two types of errors associated with the control and analysis of measurement systems can cause the rejection of materials that are good and the acceptance of materials that are poor, reported D. Lively of Indianapolis Coke in his presentation on gauge repeatability and reproducibility.

In stressing the importance of a gauge control program, he said it was necessary to identify all foundry measurement devices, to calibrate and control them as dictated by their workload, to determine how critical the measurement quantity is to the process and to decide the harshness of the environment in which the devices are used.

Accuracy and precision, however, are prone to error. Lively described accuracy as the extent to which the average measurement agrees with the true value of the manufactured part. Precision is the ability of the gauging device to reproduce its own measurements. Variances can be ascribed to operator, materials, test equipment, procedure and sampling frequency variables, but there are methods to quantify each, according to Lively.

G. Upadhya, Metalworking Technology, Inc., Johnstown, Pennsylvania, gave a presentation on 3-D computer modeling of heat transfer, fluid flow and solidification kinetics.

The model ties heat transfer and fluid flow during mold filling and solidification to microscopic solidification models using the latent heat method for the eutectics of gray, white and ductile irons, he said.

Effective use of this tool can identify potential problem regions in a casting and appropriately modify its design. The tool's main advantage is its ability to predict microstructural information such as grain size.

P. Kumar, Tata Iron & Steel Co., India, also presented an example of computer modeling of heat flow and microstructure fineness for chilled aluminum alloy LM 24. After extensive research modeling using copper, cast iron and die steel chills of different thicknesses, it was concluded that within the range of chills used in the investigation, higher heat transfer rates were obtained with thinner chills than with thicker ones.

Kumar also said microstructure fineness is a function of chill thickness. Micro-examination of the casting specimens close to the interface showed that when chill thickness is decreased, grain structure becomes finer.

W. Kapturkiewicz, the Academy of Mines, Krakow, Poland, reported on his experimental work on modeling to describe the solidification kinetics of castings--particularly as it relates to thermal curves and cooling rates for hypoeutectic and eutectic cast iron.

His model showed that segregation of C, P and Si appear to be related to the thermal curves and predicted microstructures. The model also demonstrated that heat-generated fluxes are increasingly higher as the mold wall is approached.

His model proposes to enable the simulation of the solidification kinetics at the macro and microscale levels and allows the following to be determined: dendritic and eutectic grain distribution, solute segregation during grain solidification, volumetric solidification rates and the growth rate of eutectic grains.

The model also defines the cooling rates at various locations within the melt and the volumetric heat fluxes generated, accumulated and dissipated at different locations in the melt.

L. Kallien, MAGMA Foundry Technologies, Inc., Arlington Heights, Illinois, described how computer modeling determines critical solidification times in ductile iron castings.

As examples, he cited a container used for storing nuclear waste and a brake cylinder, both of which were used in numerical simulations and shown in color graphics depicting temperature, gradient, cooling rate or solidification time distribution on the casting surface or in various sections of a casting.