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The Effect of Shell Thickness, Insulation and Casting Temperature on Defects Formation during Investment Casting of Ni-base Turbine Blades
Mälardalen University, School of Innovation, Design and Engineering, Innovation and Product Realisation.ORCID iD: 0000-0003-3086-0901
TPC Componenst AB, Hallstahammar, Sweden .
Mälardalen University, School of Innovation, Design and Engineering, Innovation and Product Realisation.
2015 (English)In: Archives of Foundry Engineering, ISSN 1897-3310, E-ISSN 2299-2944, Vol. 15, no 4, p. 115-123Article in journal (Refereed) Published
Abstract [en]

Turbine blades have complex geometries with free form surface. Blades have different thickness at the trailing and leading edges as well as sharp bends at the chord-tip shroud junction and sharp fins at the tip shroud. In investment casting of blades, shrinkage at the tip-shroud and cord junction is a common casting problem. Because of high temperature applications, grain structure is also critical in these castings in order to avoid creep. The aim of this work is to evaluate the effect of different process parameters, such as, shell thickness, insulation and casting temperature on shrinkage porosity and grain size. The test geometry used in this study was a thin-walled air-foil structure which is representative of a typical hot-gas-path rotating turbine component. It was observed that, in thin sections, increased shell thickness helps to increase the feeding distance and thus avoid interdendritic shrinkage. It was also observed that grain size is not significantly affected by shell thickness in thin sections. Slower cooling rate due to the added insulation and steeper thermal gradient at metal mold interface induced by the thicker shell not only helps to avoid shrinkage porosity but also increases fill-ability in thinner sections.

Place, publisher, year, edition, pages
2015. Vol. 15, no 4, p. 115-123
Keywords [en]
Casting defects, Grain structure, Investment casting, Niyama criterion, Shrinkage porosity, Turbine blades, Crystal microstructure, Grain size and shape, High temperature applications, Insulation, Investments, Nickel, Porosity, Shells (structures), Shrinkage, Thermal insulation, Thin walled structures, Turbine components, Turbines, Casting defect, Casting temperatures, Different thickness, Metal-mold interface, Process parameters, Turbine blade, Turbomachine blades
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-29379DOI: 10.1515/afe-2015-0090ISI: 000215109300022Scopus ID: 2-s2.0-84943736284OAI: oai:DiVA.org:mdh-29379DiVA, id: diva2:862782
Available from: 2015-10-23 Created: 2015-10-23 Last updated: 2018-08-28Bibliographically approved
In thesis
1. Developing Process Design Methodology for Investment Cast Thin-Walled Structures
Open this publication in new window or tab >>Developing Process Design Methodology for Investment Cast Thin-Walled Structures
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Components for engineering systems, such as gas turbines and jet engines operating at high temperature are usually produced in superalloys. The investment casting process is most widely used for manufacturing these components due to the ability of the process to produce parts with complex geometries to close dimensional tolerances. Other processing routes are less advantageous due to high mechanical strength and hardness of these alloys, which make formability and machining difficult even at high temperature. The global requirements for lower fuel consumption and emissions are increasing the demands to lower the weight of cast components in jet engines. The ability to produce components with lower wall thickness will not only help to reduce the cost of production and resource usage but also help to improve the efficiency of engineering systems resulting in lower fuel consumption and reduced emissions of environmentally hazardous gases. However, casting of thin walled components is challenging due to premature solidification in thin sections and long feeding distances often resulting in incomplete filling, cold shuts and shrinkage porosity.

The castability of thin-sections is dependent upon selection of appropriate values of casting parameters to achieve favorable conditions for the mould filling and solidification. In foundry environment, fluctuation in these targeted values of casting parameters is common due to semi-automated nature of process. The effects of casting parameters on mould filling and defect formation have been widely reported in the literature, however effect of fluctuations in targeted values of casting parameters resulting from typical variation in the foundry is not well documented. Moreover, the origin of process variation and how to manage them in foundries, especially in relation to thin-walled casting has not been well documented. 

In this work, the common variations in critical process parameters, originating from foundry practices and equipment are identified. The effect of variations and resulting fluctuation in targeted values of casting parameters on castability of thin-walled castings is evaluated. The casting process is simulated by defining boundary conditions which replicate the foundry conditions and properties of foundry materials in a commercial casting simulation software. The effect of fluctuation of casting parameters on castability of thin-walled castings is established by casting trials as well as simulations and the validity of simulation is evaluated. A methodology to design a casting process is established by proposing methods to minimize the process variation as well as using Design of Experiments (DoE) based simulation work to achieve reliability and repeatability in the process.

It is concluded that the mould temperature, casting temperature and pouring rate are common casting parameters affected by the variation originating from equipment and the casting practices. The variation in these parameters strongly effects the castability of thin-walled sections. The significance of these variations is validated by simulation and it is concluded that the validity of simulation is not only strongly dependent upon the foundry specific material data but also depends upon setting up valid boundary conditions according to the equipment and practices used. It is also concluded that by introducing material data and accurate boundary conditions, simulation can be used as tool to facilitate process development in foundries. A systematic implementation of simulations based on DoE and optimization resulted in significant reduction in process development time.

The result of this work has been further developed into a process design methodology for investment casting foundries working with casting of thin-walled castings for high temperature applications. The term process design in this work is defined as design and evaluation of gating system as well as identifying optimized values of casting parameters to cast components in foundry.

 

Place, publisher, year, edition, pages
Västerås: Mälardalen University, 2018
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 257
National Category
Natural Sciences Other Natural Sciences
Research subject
Innovation and Design
Identifiers
urn:nbn:se:mdh:diva-38767 (URN)978-91-7485-377-3 (ISBN)
Public defence
2018-04-06, Filharmonin, Mälardalens högskola, Eskilstuna, 10:00 (English)
Opponent
Supervisors
Available from: 2018-02-27 Created: 2018-04-12 Last updated: 2018-08-28Bibliographically approved

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