About the impact on gravity cast salt cores in high pressure die casting and rheocasting

1. Overview:

  • Title: About the impact on gravity cast salt cores in high pressure die casting and rheocasting
  • Authors: Andreas Schilling, Daniel Schmidt, Jakob Glück, Niklas Schwenke, Husam Sharabi, Martin Fehlbier
  • Year: 2022
  • Journal/Conference: Simulation Modelling Practice and Theory
  • Keywords:
    • Cast salt cores
    • Lost core
    • Core damage
    • Rheocasting
    • Flow-3D
    • Simulation
    • Core testing
    • High pressure die casting

2. Research Background:

  • Social/Academic Context:
    • High pressure die casting (HPDC) accounts for 60% of aluminum castings and over half of non-ferrous castings in Germany.
    • Increasing casting complexity with internal geometries, especially in e-mobility, demands new technologies beyond complex molds with sliders.
    • Lost salt core technology offers an alternative to slide systems for creating internal geometries.
    • Salt cores are advantageous due to water solubility, simplifying removal after casting.
  • Limitations of Existing Research:
    • Core viability is a decisive issue for process-safe use of salt cores.
    • Core loading in die casting is mainly attributed to the flow velocity of the impinging melt.
    • High mechanical demands are placed on cores due to high pressures and flow speeds in HPDC.
  • Research Need:
    • Explore alternative casting methods like rheocasting to lower melt temperature and potentially reduce core loading.
    • Investigate the application of rheocasting technology to salt cores to improve component quality and core durability.

3. Research Objectives and Research Questions:

  • Research Objective:
    • To investigate whether rheocasting technology can be applied to salt cores.
    • To assess if rheocasting can simultaneously improve component quality when using salt cores.
  • Core Research Question:
    • What is the impact of rheocasting on the durability of gravity cast salt cores in high pressure die casting compared to conventional high pressure die casting?
  • Research Hypothesis:
    • Salt cores used in rheocasting will experience reduced loads.
    • Salt cores in rheocasting will exhibit increased core viability compared to conventional HPDC. (This is implied by the expected lower core loading in rheocasting).

4. Research Methodology:

  • Research Design:
    • Simulation study using Flow-3D fluid-structure-interaction (FSI) simulations.
    • Experimental validation through three-point bending tests on salt cores.
    • Comparison of simulation results with experimental data.
  • Data Collection Method:
    • Simulation: Numerical data on core loading, stress distribution, and energy transfer during mold filling in both conventional HPDC and rheocasting simulations.
    • Experiment: Physical measurements of breaking strength and deformation of salt cores in three-point bending tests at 20 °C and 180 °C under different loading conditions (prism line load and area load).
  • Analysis Method:
    • FSI Simulation: Flow-3D Cast Version 5.0.1 was used to model mold filling and forces acting on the salt core. Rankine maximum-normal stress theory was used to predict core damage. Energy analysis was conducted to compare energy transfer to the core in different casting conditions.
    • Three-point Bending Test: Modified three-point bending test was used to determine the failure-critical material data of salt cores. Tests were conducted at different temperatures and loading types to characterize core strength and deformation.
  • Research Subject and Scope:
    • Salt Core Geometry: A simple geometry with a total length of 60 mm, square cross-section (10 mm side length), and a middle part with a 6 mm side length and 20 mm length was used.
    • Casting Processes: Conventional high pressure die casting and rheocasting were simulated and compared.
    • Material: A356 (AlSi7Mg0,3) alloy and a salt mixture of 50 wt-% sodium chloride and 50 wt-% sodium carbonate for the core.
    • Simulation Parameters: Piston speed of 6 m/s for conventional HPDC and 2 m/s for rheocasting. Melt temperature of 630 °C for conventional HPDC and 600 °C for rheocasting.

5. Major Research Findings:

  • Core Research Findings:
    • Rheocasting significantly reduces the load on salt cores compared to conventional HPDC.
    • The highest core load occurs at the first impact of the melt.
    • Core loads remain approximately constant during further mold filling after the initial impact.
    • Salt cores in rheocasting show reduced stress levels, well below the failure limit observed in bending tests.
  • Statistical/Qualitative Analysis Results:
    • Bending Tests:
      • Higher core temperature leads to a decreasing breaking load with triangular fin.
      • Compression increases slightly at higher temperatures.
      • Full load tests show higher breaking load and breaking elongation with higher variance.
      • Fine-grained microstructure of the edge zone (0.8 - 1.0 mm thick) is decisive for bending strength.
      • Breaking strength and compression data are presented in Fig. 5 for Prism 20°C, Prism 180°C, and Full face 20°C loading conditions.
    • Simulation:
      • Mesh dependency study showed that 0.5 mm mesh size for the salt core is a reasonable compromise between accuracy and computation time.
      • Maximum normal stress in conventional HPDC (6 m/s piston speed) reaches up to 13 MPa immediately after melt impact (Fig. 10).
      • Maximum normal stress in rheocasting (2 m/s piston speed) is significantly lower, around 2.3 MPa (Fig. 12).
      • Calculated displacement in melt flow direction is 0.17 mm, comparable to bending test results.
      • Energy analysis indicates lower energy transfer to the salt core in rheocasting.
  • Data Interpretation:
    • Simulation results are consistent with the experimental bending test data, suggesting the simulation model is reasonably accurate.
    • The significantly lower core loads in rheocasting, as indicated by simulations, suggest improved core viability compared to conventional HPDC.
    • The initial melt impact is the most critical phase for core loading.
  • Figure Name List:
    • Fig. 1. Salt core geometry and casting die.
    • Fig. 2. Modified three-point bending test.
    • Fig. 3. Simulation model for the fluid structure interaction (FSI) calculation.
    • Fig. 4. Detail of the core balance volume.
    • Fig. 5. Breaking strength and compression resulting from three-point bending tests.
    • Fig. 6. Sectional view of the salt core (6 x 6 mm) at 40x magnification.
    • Fig. 7. Mesh dependency of the stresses in the salt core after the impact of the melt.
    • Fig. 8. Balance volume of the salt core for energy consideration (purple).
    • Fig. 9. Simulated impact of the melt on the salt core.
    • Fig. 10. Stress condition on salt core surface immediately after the first impact of the melt.
    • Fig. 11. Deformation of the salt core after first impact of the melt.
    • Fig. 12. Stress condition on salt core surface immediately after the first impact of the semi solid melt.
Fig. 1. Salt core geometry and casting die.
Fig. 1. Salt core geometry and casting die.
Fig. 2. Modified three-point bending test.
Fig. 2. Modified three-point bending test.
Fig. 4. Detail of the core balance volume.
Fig. 4. Detail of the core balance volume.
Fig. 11. Deformation of the salt core after first impact of the melt. The displacement in the middle of the core is in direction Z nearby 0.17 mm.
Fig. 11. Deformation of the salt core after first impact of the melt. The displacement in the middle of the core is in direction Z nearby 0.17 mm.
Fig. 12. Stress condition on salt core surface immediately after the first impact of the semi solid melt. The flow velocity before impact is 4.55 m/s. The maximum stress on the lower core side is approximately 2.3 MPa.
Fig. 12. Stress condition on salt core surface immediately after the first impact of the semi solid melt. The flow velocity before impact is 4.55 m/s. The maximum stress on the lower core side is approximately 2.3 MPa.

6. Conclusion and Discussion:

  • Summary of Major Findings:
    • Simulation results indicate that rheocasting significantly reduces the load on salt cores during die casting compared to conventional HPDC.
    • The load from the impacting melt is directly related to piston speed and melt flow rate, with higher speeds leading to higher loads.
    • In conventional HPDC (6 m/s piston speed), the tension on the salt core can reach around 13 MPa, exceeding the tensile strength of the salt core (11 MPa), suggesting potential core failure.
    • In rheocasting (2 m/s piston speed), the maximum stress is significantly reduced to approximately 2.3 MPa, well below the tensile strength.
  • Academic Significance:
    • This study demonstrates the potential of rheocasting as a viable alternative to conventional HPDC for applications using lost salt core technology.
    • The research provides valuable insights into the core loading mechanisms in both HPDC and rheocasting processes.
    • The use of FSI simulation combined with experimental validation offers a robust methodology for analyzing and optimizing salt core die casting processes.
  • Practical Implications:
    • Rheocasting offers a promising approach to enhance the process safety and reliability of salt core die casting by reducing core damage.
    • Lower core loads in rheocasting can potentially enable the production of more complex and delicate internal geometries using salt cores.
    • The findings suggest that adjusting casting parameters, particularly piston speed and melt temperature in rheocasting, can significantly improve core viability.
  • Limitations of the Research:
    • The simulation model simplifies the casting process and assumes isothermal flow and homogeneous salt core material properties.
    • The deformation speed in the three-point bending test (5 mm/min) is significantly slower than the deformation rate in the casting process (deformation occurs within about 0.001 s), which might affect the direct comparability of failure limits.
    • Experimental verification of the simulation results in real casting trials is still needed.

7. Future Follow-up Research:

  • Future Research Directions:
    • Experimental validation of the simulation results through real die casting and rheocasting trials in a casting laboratory.
    • Investigation of the influence of various rheocasting parameters on core loading and component quality.
    • Exploration of different salt core materials and compositions to further enhance core strength and viability in rheocasting.
    • Evaluation of the impact of rheocasting and salt core technology on the microstructure and overall quality of cast components.
  • Areas that need further exploration:
    • Detailed analysis of the solid phase formation and its influence on core loading in rheocasting.
    • Optimization of salt core design and casting process parameters for rheocasting applications.
    • Investigation of the long-term durability and performance of components produced using rheocasting and salt core technology.

8. References:

  • [1] B. Nogowizin, Theorie Und Praxis des Druckgusses, Fachverlag Schiele&Schön, Berlin, 2011.
  • [2] Jelínek, P.; Adámková, E.: Lost Cores for High-Pressure Die Casting, Archives of Foundry Engineering, 14(2) 101-104, 2014, doi:10.2478/afe-2014-0045.
  • [3] B. Fuchs, Salzkerntechnologie Für Hohlgussbauteile im Druckguss, Cuvillier Verlag, PhD, Erlangen, Nürnberg, 2014.
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  • [7] Kohlstädt, S.; Vynnycky, M.; Goeke, S.: On the CFD Modelling of Slamming of the Metal Melt in High-Pressure Die Casting Involving Lost Cores, Metals 2021, 11 (1), 78, doi:10.3390/met11010078.
  • [8] Uggowitzer, P.J.; Gullo, G.; Wahlen, A.: Metallkundliche Aspekte bei der semi-solid Formgebung von Leichtmetallen, In: Vom Werkstoff zum Bauteil, ed. H. Kaufmann und P.J. Uggowitzer, LKR-Verlag Ranshofen, 95-107, 2000.
  • [9] P. Das, Rheological Characterization of Semi-Solid A356 Aluminium Alloy, In: Solid State Phenomena, Vols. 192-193, Trans Tech Publications, Switzerland, 2013, pp. 329-334.
  • [10] Fickel, P.: Hohl- und Verbundguss von Druckgussbauteilen – Numerische Auslegungsmethoden und experimentelle Verifikation, PhD, Stuttgart, 2017.
  • [11] R.K. Freier, Aqueous Solutions, Data Inorg. Org. Compd. 2 (1978). Supplements, Gruyter, Berlin.

9. Copyright and Source Material:

This summary is based on the paper "About the impact on gravity cast salt cores in high pressure die casting and rheocasting" by Andreas Schilling.

Paper Source: https://doi.org/10.1016/j.simpat.2022.102585

This summary is for informational purposes only and should not be used for commercial purposes without permission from the author.
Copyright © 2025 CASTMAN. All rights reserved.

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Tags: Aluminum Casting; ,CAD; ,Casting Technique; ,CFD; ,Die casting; ,FLOW-3D; ,High pressure die casting; ,High pressure die casting (HPDC); ,Microstructure; ,Salt Core