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TECHNICAL PAPERS

Investigation of Interface Agent for Investment Casting With Ice Patterns

[+] Author and Article Information
Qingbin Liu, Ming C. Leu

Department of Mechanical and Aerospace Engineering, University of Missouri—Rolla, Rolla, MO 65409

J. Manuf. Sci. Eng 128(2), 554-562 (Oct 03, 2005) (9 pages) doi:10.1115/1.2162902 History: Received June 05, 2004; Revised October 03, 2005

Investment casting with ice patterns is similar to that with wax patterns but with significant process differences. A major difference in our developed method is that an interface agent needs to be coated around the ice pattern to protect it from damage during the process. We have studied the criteria for choosing the interface agent and discovered that the most important factor is the cohesion parameter. The thickness of the interface agent affects the dimensional accuracy of the generated metal casting. To compensate for this, mathematical models have been constructed to predict the thickness of the interface agent for a large cylindrical part and for a small part. The interface layer thickness and the temperature distribution within the ice part and the solidifying interface agent have been investigated. For solid ice cylinders, both the immersion time and the cylinder diameter affect the interface layer thickness. For small parts, the interface thickness is mainly dependent upon the ratio between the volume and surface area of the ice part and to a lesser extent upon the physical properties of the materials. Superheat has little influence on the interface layer thickness. Based on the analysis, the dimensional accuracy of the metal castings for small parts can be much improved by compensating the interface layer thickness. The analytical results agree well with experimental observations.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Principle of rapid freeze prototyping

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Figure 2

Experimental RFP system

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Figure 3

Investment casting process

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Figure 4

Some fabricated metal castings from ice patterns

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Figure 5

Triangular graph showing the location of water, alcohol, and interface agent. The solid and dotted circle in the graph refer to the schematic solubility window of water and alcohol, respectively.

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Figure 6

Surface finish of molds made by different interface agents: (a) mixture of silicone oil and kerosene and (b) the chosen interface agent

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Figure 7

The temperature distribution within the ice pattern, solidified interface agent, and liquid interface agent during solidification

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Figure 8

Analogous temperature distributions in (a) solidifying interface agent, and (b) a semi-infinite solidified interface agent (see Ref. 13)

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Figure 9

Predicted temperature distribution within a semi-infinite ice part for different immersion times. The times in the legend refer to immersion times.

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Figure 10

Predicted temperature distribution within the solidifying interface agent for different immersion times. The times in the legend refer to immersion times.

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Figure 11

Predicted interface layer thickness versus time for various ice cylinder diameters. The dimensions in the legend refer to ice cylinder diameters.

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Figure 12

Predicted interface layer thickness versus cylinder diameter for different immersion times. The times in the legend refer to immersion times and the temperatures in the legend refer to initial temperatures of interface agent.

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Figure 13

Comparison of interface thickness between the predicted results and the experimental results. The measured result is based on the average of three data.

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Figure 14

Predicted interface thickness for different V∕A ratios for a small ice part. The temperatures in the legend refer to initial temperatures of interface agent.

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