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Effects of Process Related Variations on Fillablity Simulation of Thin-Walled IN718 Structures
Mälardalen University, School of Innovation, Design and Engineering, Innovation and Product Realisation.ORCID iD: 0000-0003-3086-0901
Swerea SWECAST AB, Jönköping, Sweden.
TPC Components AB, Hallstahammar, Sweden.
Mälardalen University, School of Innovation, Design and Engineering, Innovation and Product Realisation.ORCID iD: 0000-0002-7816-1213
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2017 (English)In: International Journal of metalcasting, ISSN 1939-5981, E-ISSN 2163-3193, Vol. 12, no 42, p. 1-11Article in journal (Refereed) Published
Abstract [en]

Due to the ability to produce net shape parts that maintain tight dimensional tolerances, investment casting has been widely used to manufacture components used in the hot gas path in gas turbines since 1950’s.1 In the power generation and aerospace industries, the overall weight reduction of engineering systems is much sought after, especially for turbines. Weight reduction of an engineering system can be achieved by using integrated multifunction components or by reducing component weight either by improving component design or using lightweight materials. Increased demands have been put on investment casting foundries by the turbine industry to produce complex thin-walled components.2 Weight reduction of components is essential to lower fuel consumption and reduce environmental impact.3 Casting of thin-sections is challenging due to premature solidification in thin-walled sections and long feeding distances often resulting in incomplete filling, cold shuts and shrinkage porosity.4 A number of studies have been performed to investigate important aspects of investment casting of thin-walled geometries. Flemings5 demonstrated that superheat and metal head had greater effect on fluidity than melt viscosity and surface tension for thicker sections. Flemings5 also concluded that for thin sections surface tension became important, limiting mold filling. For the nickel base superalloys (IN100 alloy), Chandraseckariah and Seshan6 concluded that the pouring temperature and mold temperature had greater effect on fluidity than other casting variables, such as, vacuum level and shell thickness. In an attempt to address the additional challenges imposed by thin-walled castings, Campbell and Oliff7 established mould filling criteria for thin walled castings. It was shown that at low heat content in a vertical mould set-up fluidity was limited by solidification which they termed flowability, a dynamic aspect, whereas at high heat content of a vertical mould system, fluidity was limited by surface tension which they termed as fillabillity, a static aspect. Campbell8 also performed investigations on the effect of capillary repulsion in thin-section moulds and surface tension on the filling pattern in the mould cavity. It was suggested that the surface oxide films formed during filling were pinned to the mould wall blocking the melt flow, resulting in decreased fluidity. These films also caused cold shuts and other internal defects in castings. Campbell9 established gating design requirements for thin-walled castings by investigating the effect of different gating methods and their effect on fillability in thin-walled castings. Bottom-gating was concluded superior to top-gated systems and bottom-gating reduced the filling instabilities. The prediction by simulation has become a vital step in the development of efficient manufacturing processes. The reliability of simulation is significantly dependent upon material properties, metallurgical models as well as accuracy in defining boundary condition.10 The boundary conditions are influenced by equipment and operation related variations arising from mould handling and melt pouring.11 Other parameters such as the mould filling sequence in casting of multi-cavity moulds are related to cluster design and equipment related limitation in process control tolerances. The degree of variation in critical process parameters is also highly dependent on the degree of automation. The relative importance of these process uncertainties on casting quality is not well understood. Although the physical principles governing fill and solidification are well established,12 it is difficult to account for uncertainties in process parameters when defining boundary conditions for simulations. As concluded in a related study,13 there is a lack of literature available that addresses the effect of variation in process parameters on the accuracy of simulation. This suggests a need for further investigation of how to define boundary conditions that more accurately describe the conditions in the foundry. The aim of this research is to investigate how the uncertainty in variation of foundry parameters can be accounted for when defining initial boundry conditions in order to improve accuracy of simulation. Characterization measurement has been performed on mould and alloy materials to eliminate uncertainties that can potentially be introduced in simulation from inaccurate material data. The discrepancy between experiments and simulations were analyzed and discussed to identify how variation in foundry parameters influence accuracy in simulation of the filling of a thin-walled mould.

Place, publisher, year, edition, pages
Sweden: Springer , 2017. Vol. 12, no 42, p. 1-11
Keywords [en]
casting thin-walled filling simulation prediction inconel
National Category
Production Engineering, Human Work Science and Ergonomics
Identifiers
URN: urn:nbn:se:mdh:diva-38643DOI: 10.1007/s40962-017-0189-9ISI: 000436927100014Scopus ID: 2-s2.0-85049332591ISBN: 1939-5981 OAI: oai:DiVA.org:mdh-38643DiVA, id: diva2:1186063
Projects
INNOFACTURE - innovative manufacturing developmentAvailable from: 2018-02-27 Created: 2018-02-27 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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Raza, MohsinFagerström, Björn

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