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On determining lost core viability in high-pressure die casting using Computational Continuum Mechanics
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Casting of Metals.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The subject of this thesis work is to investigate whether Computational ContinuumMechanics (CCM) can serve as a valuable tool for the casting engineerto determine a priori whether a housing concept with inlying geometries thatso far only exists in Computer Aided Design (CAD) will have the desired coolingperformance and will be manufacturable with an acceptable number ofrejects.As of spring 2019, no application in serial production of lost cores, i.e.cores that are destroyed during deforming, in high-pressure die casting isknown. The reason for this is believed to be the absence of an engineeringtool that can tell upfront whether a concept of casting and process combinedwill be viable. This thesis aims to ll precisely that void by presenting, implementingand testing a CCM model inside the OpenFOAM toolbox in order todetermine upfront whether a design of a housing will be manufacturable withlost cores. The two-phase ow of air and melt is modeled with the volumeof-uid-concept. Turbulence modeling is done via the Reynolds-Averaged-Navier-Stokes (RANS) approach, mostly using the Menter SST k-omega-model.An isotropic linear elastic model was assumed for the solid mechanics.Industrial operators and managers like short and easy to grasp conclusions. As it, however, turned out during the process of this research project, there is no clear and easy answer to the question whether salt cores in high-pressuredie casting are a viable concept and will lead to sound castings. First of all, it was proven that housings made with lost cores can improve the heat transfer capabilities of castings. It was possible to produce castingswith cores up to an impact velocity of 30 ms^-1. The impact velocity wasfound to be the most decisive parameter. But the reader should bear in mindthat this limit is only valid for the given setup. Each conguration has to betested with the introduced model separately. The slamming events at rstimpact of the melt were found to be not failure-critical if crack-free coresare used. It was also found that the approach of evaluating only the peakforce does not go far enough. Eects later in the process may have a moreimportant impact due to larger force-time integrals. Also, dierent from theoriginal assumptions, the heat transferred from the melt to the core maynot be neglected even though filling times are below 0.1 s. Dening generalnumerical constraints for conditions under which salt cores are a viabletechnology is very dicult as geometry alterations play an important roletoo. This underscores the power and usefulness of the presented model evenIfurther as the engineer is now capable of testing each setup individually.It soon became clear that a fully comprehensive model is still for futureresearchers to develop. It was found that it is not benecial to attach the shotsleeve to the casting model with currently available open-source CFD technology.The presented strategy in this thesis together with the developed CCMtools can therefore provide a powerful tool for the casting or CAD-engineerto decide case by case whether a concept for a casting will be producible ornot. The tools range from a limited CFD approach for evaluating only theforces to a fully coupled FSI methodology describing the core deformationover time. All models have been tested and validated with high-pressure diecasting experiments and are in line with previously published ndings withdeviations of 5-10 % at maximum.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. , p. 88
Series
TRITA-ITM-AVL ; 2019:17
Keywords [en]
high-pressure die casting, lost salt cores, computational continuum mechanics, two-phase compressible flow, OpenFOAM, CFD, fluid-structure interaction, volume-of-fluid method
National Category
Manufacturing, Surface and Joining Technology
Identifiers
URN: urn:nbn:se:kth:diva-251022ISBN: 978-91-7873-206-7 (print)OAI: oai:DiVA.org:kth-251022DiVA, id: diva2:1314216
Public defence
2019-05-31, Lecture Hall F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2019-05-08 Created: 2019-05-08 Last updated: 2019-05-08Bibliographically approved
List of papers
1. Experimental and numerical CHT-investigations of cooling structures formed by lost cores in cast housings for optimal heat transfer
Open this publication in new window or tab >>Experimental and numerical CHT-investigations of cooling structures formed by lost cores in cast housings for optimal heat transfer
2018 (English)In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 54, no 11, p. 3445-3459Article in journal (Refereed) Published
Abstract [en]

This paper investigates the cooling performance of six different lost core designs for automotive cast houses with regard to their cooling efficiency. For this purpose, the conjugate heat transfer (CHT) solver, chtMultiregion, of the freely available CFD-toolbox OpenFOAM in its implementation of version 2.3.1 is used. The turbulence contribution to the Navier-Stokes equations is accounted for by using the RANS Menter SST k - model. The results are validated for one of the geometries by comparing with experimental data. Of the six investigated cooling structures, the one that forces the fluid flow to change its direction the most produces the lowest temperatures on the surface of the cast housing. This good cooling performance comes at the price of the highest pressure loss in the cooling fluid and hence increased pump power. It is also found that the relationship between performance and pressure drop is by no means generally linear. Slight changes in the design can lead to a structure which cools almost as well, but at much decreased pressure loss. Regarding the absolute values, the simulations showed that the designed cooling structures are suitable for handling the cooling requirements in the particular applications and that the maximum temperature stays below the critical limits of the electronic components.

Place, publisher, year, edition, pages
SPRINGER, 2018
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-238528 (URN)10.1007/s00231-018-2372-9 (DOI)000447509900020 ()
Note

QC 20181106

Available from: 2018-11-06 Created: 2018-11-06 Last updated: 2019-05-10Bibliographically approved

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