61st Technical Conference & Equipment Expo Program
WEDNESDAY, OCTOBER 8, 2014, CONTINUED 9:15 a.m. - 9:45 a.m.
Paper No. 17
The Effect of Shell Thickness and Insulation on Defect Formation in Investment Cast Ni-base Alloys Mohsin Raza / Björn Fagerström, Mälardalen Högskola Mark Irwin, TPC Components AB, Sweden Turbine blades have complex geometries with free form surfaces. Manufacturing of such a complex geometries in Ni-based superalloys is typically done by the investment casting process. Blades have different thickness at the trailing and leading edges as well as sharp bends at the chord-tip shroud junction and sharp fi ns at the tip shroud. Shrinkage at the tip-shroud and cord junction is a common problem in casting of turbine blades, especially when produced in alloys with large freezing range. In this work, the effect of shell thickness on shrinkage porosity is evaluated.
The test geometry used in this study is a thin-walled air-foil structure which is representative of a typical hot-gas-path rotating turbine component. The alloy used in study is a Ni-base super alloy with large solidifi cation interval. Casting trials were performed to develop a relation between the mechanism driving formation of shrinkage and shell thickness. It was observed that shell thickness is signifi cant to achieve a steeper thermal gradient which is essential in order to minimize the width of the mushy zone. It was also observed that a slower cooling rate along with a steeper thermal gradient at the metal- mold interface not only helps to avoid shrinkage porosity but also increases fi ll-ability in thinner sections.
9:45 a.m. - 10:00 a.m. 10:00 a.m. - 10:30 a.m.
Coffee Break sponsored by Ceradyne, Inc., a 3M Company Nalco
Paper No. 18
An Evaluation of Autoclave Performance of Thin Wall Printed Investment Casting Patterns and Minimum Shell Thickness Necessary to Avoid Shell Cracking in the Autoclave Thomas Mueller, Voxeljet Investment casting patterns created using an additive manufacturing or 3D printing process have become very popular and are now used by nearly all industrial investment foundries.
The most common
cause of failure remains shell cracking in the autoclave as the result of thermal expansion of the pattern.
Thin-wall castings have
been particularly troublesome and have been very diffi cult for most foundries to process. Foundries often resort to skipping the autoclave step altogether and go right to burnout which introduces other issues. This study attempted to compare the autoclave performance of thin- wall patterns for leading additive manufacturing technologies. Thin- wall patterns were created in four different wall thicknesses by three different additive manufacturing technologies.
The patterns were
assembled onto sprues, and the assemblies were then shelled and autoclaved. The shells were then examined for cracks. In addition, the study attempted to determine the minimum shell thickness required to survive the autoclave cycle. Patterns were created by the same three additive manufacturing technologies and a number of identical assemblies built.
The assemblies were all shelled but
with decreasing number of layers. All assemblies were autoclaved together and then examined for failure. The results of this investigation will allow foundries to better evaluate the choice of pattern for thin wall applications and to understand how strong their shell must be to survive the autoclave cycle.
28 ❘ October 2014 ®
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