Effect of Applying Pressure of High Pressure Diecasting Process Using Salt core

This article introduces the paper "Effect of Applying Pressure of High Pressure Diecasting Process Using Salt core".

1. Overview:

• Title: Effect of Applying Pressure of High Pressure Diecasting Process Using Salt core
• Authors: Jun-Ho Lee, J. H. Moon, Dock-Young Lee
• Publication Year: 2008
• Journal/Conference: Journal of the Korean Foundrymen's Society, Vol. 28, No. 3 (한국주조공학회지, 제28권 제3호)
• Keywords: Salt core, Squeeze casting, High pressure die casting, Net-shape forming

2. Research Background:

• Social/Academic Context of Research Topic:
  • Increased application of pressure casting methods like die casting, low pressure casting, and squeeze casting in manufacturing aluminum and magnesium castings.
  • Pressure casting methods offer advantages in productivity, reduced defects, and improved dimensional accuracy compared to gravity casting.
  • Low temperature melting salt core composite casting technology is a core technology for lightweighting and modularizing integrated components.
• Limitations of Existing Research:
  • Conventional shell cores have weaknesses: fragility, damage during handling, resin odor, difficult recycling, and poor surface finish.
  • Shell cores are prone to melt penetration in high pressure casting, limiting their use in die casting and squeeze casting.
  • Previous research on high pressure solidification and squeeze casting mainly focused on the effects of pressure and pressure conditions on solidification structure and mechanical properties of aluminum and copper alloys.
  • Research on the effect of pressure on solidification phenomena is limited.
• Necessity of Research:
  • Increasing demand for casting technologies to manufacture high-quality integrated components with complex internal shapes.
  • Need to develop fusible core technology to overcome shell core limitations and be applicable to high pressure casting processes.
  • In-depth study needed on the effect of pressure during squeeze casting on solidification phenomena and core behavior.

3. Research Objectives and Research Questions:

• Research Objectives:
  • To evaluate the suitability of molten metal and fusible cores by applying low melting point cores in squeeze casting under varying pressures (gravity, 1000 kg/cm²).
  • To measure changes in heat transfer coefficient with increasing punch pressure.
  • To observe and analyze the microstructure of pressurized molten metal.
  • To develop high-performance fusible core materials and optimize alloy-core combinations through fusible core manufacturing and characterization.
• Core Research Questions:
  • What is the effect of pressure variation in squeeze casting on the interaction between low-temperature salt fusible cores and molten metal?
  • How does increased pressure alter the heat transfer characteristics at the molten metal-core interface?
  • Can fusible cores function as suitable core materials for realizing complex internal shapes under pressure conditions?
• Research Hypotheses:
  • Increased pressure will accelerate core melting by enhancing heat transfer at the molten metal-core interface, potentially increasing casting defects.
  • Low-temperature salt fusible cores can achieve complex shapes within a specific pressure range, and the optimal pressure depends on core material and process parameters.

4. Research Methodology:

• Research Design:
  • Experimental study using a 50-ton vertical hydraulic press for squeeze casting.
  • Experiments divided into gravity solidification and pressure solidification (1000 kg/cm²) conditions.
• Data Collection Methods:
  • Temperature measurement: Thermocouples placed in molten metal, core, and mold wall to record temperature changes using a Data Acquisition System.
  • Microstructure and Macrostructure Analysis: Specimens sectioned, polished, and etched. Microstructure observed using optical microscopy. Macrostructure visually inspected.
• Analysis Methods:
  • Cooling curve analysis: Analyzing temperature data to understand solidification behavior under different pressures.
  • Microstructure analysis: Examining grain size and phase distribution to assess the effect of pressure on solidification structure.
  • Macrostructure analysis: Observing core shape retention and surface quality to evaluate core performance under pressure.
• Research Subjects and Scope:
  • Alloy: Al-7 wt%Si alloy (A356 alloy). Chemical composition detailed in Table 2.
  • Core: Ceramic weight% 60% core (Ø20 mm diameter, 75 mm height) made of low melting point salt with ceramic particle addition.
  • Casting Equipment: 50 ton vertical hydraulic press (Squeeze casting device) shown in Figure 1.
  • Mold: SKD61 steel mold. Chemical composition detailed in Table 1.
  • Pressure Conditions: Gravity casting and pressure casting at 1000 kg/cm².
  • Experimental conditions summarized in Table 3.

5. Main Research Results:

• Key Findings:
  • Increased pressure led to faster cooling rates and shorter solidification times for the molten metal.
  • Chill zone formation was observed in pressure casting, indicating rapid initial solidification.
  • Increased pressure caused enhanced heat transfer, leading to melting of the core surface and increased surface roughness.
  • Fusible cores exhibited unstable behavior with increased pressure, making shape maintenance difficult.
  • Gravity casting with low-temperature salt cores resulted in good shape retention and sound casting specimens.
  • Core surface dissolution was observed at 1000 kg/cm² pressure.
  • Heat transfer coefficient at the molten metal-core interface was approximately 10 times higher in pressure casting compared to gravity casting.
  • Core temperature increased rapidly under pressure, reaching melting point temperatures quickly.
• Statistical/Qualitative Analysis Results:
  • Cooling curve analysis indicated significantly reduced solidification time under pressure casting compared to gravity casting (no specific numerical data provided).
  • Microstructure analysis showed a tendency for finer grain structures in pressure cast specimens (qualitative observation).
  • Macrostructure analysis revealed increased core surface roughness and shape defects with higher pressure (qualitative observation).
• Data Interpretation:
  • Increased pressure accelerates molten metal cooling and solidification but also enhances heat transfer to the core, potentially causing core melting.
  • Low-temperature salt fusible cores are effective for complex shapes in gravity casting but have limitations in high-pressure squeeze casting due to heat resistance and strength.
• Figure Name List:
  • Fig. 1. Squeeze casting device.
  • Fig. 2. Flow chart of experiment procedure.
  • Fig. 3. Cooling curve of A356 alloy.
  • Fig. 4. Microstructures of gravity cast specimen using fusible core added 60 wt% ceramic powder.
  • Fig. 5. Microstructures of squeeze cast specimen at a pressure of 1000 kg/cm² using fusible core added wt 60 wt% ceramic powder.
  • Fig. 6. Cooling curves of gravity cast specimen using fusible core added 60 wt% ceramic powder.
  • Fig. 7. Cooling curves of squeeze cast specimen at a pressure of 1000 kg/cm² using fusible core added 60 wt% ceramic powder.

6. Conclusion and Discussion:

• Summary of Main Results:
  • In squeeze casting with low-temperature salt fusible cores, increased pressure accelerates molten metal cooling but can induce core melting, degrading casting surface quality.
  • Low-temperature salt cores maintain shape and produce good castings under gravity conditions, but their heat resistance and strength are limited under pressure casting.
  • Rapid increase in heat transfer at the molten metal-core interface in pressure casting leads to rapid core temperature rise and melting.
• Academic Significance of Research:
  • Experimentally demonstrated the effect of pressure on low-temperature salt fusible cores in squeeze casting.
  • Provided fundamental data for process optimization by analyzing heat transfer characteristics at the molten metal-core interface under pressure.
  • Highlighted the applicability and limitations of low-temperature salt fusible cores in high-pressure casting processes.
• Practical Implications:
  • Emphasized the importance of pressure control when using low-temperature salt fusible cores in squeeze casting.
  • Suggested the need for technologies like core surface coating, pressure reduction, and core material improvement to maintain core surface quality in high-pressure casting.
  • Provided guidance for process design and core material development for manufacturing high-quality cast components with complex internal shapes.
• Limitations of Research:
  • Results are specific to Al-7wt%Si alloy and Ceramic weight% 60% core, limiting generalizability.
  • Experiments were limited to gravity and 1000 kg/cm² pressure conditions, lacking investigation of a wider pressure range.
  • In-depth analysis of core material's thermal and mechanical properties is limited.

7. Future Follow-up Research:

• Future Research Directions:
  • Expand squeeze casting experiments with various alloy and core material combinations.
  • Investigate core material composition and manufacturing process modifications to improve heat resistance and strength.
  • Develop and apply core surface coating technologies to control heat transfer and verify their effectiveness.
  • Study molten metal and core behavior under various pressure conditions and process parameters.
  • Evaluate thermal and mechanical properties of fusible cores and establish a comprehensive database.
• Areas Requiring Further Exploration:
  • Clarify the heat transfer mechanism between the core and mold during squeeze casting.
  • In-depth analysis of core melting behavior and casting defect formation mechanisms.
  • Simulation-based optimization of squeeze casting processes.
  • Development of environmentally friendly core materials and removal technologies.

8. References:

• [1] Fatih Cay, S. Can Kurnaz, Mater. & Design, "Hot tensile and fatigue behaviour of zinc-aluminum alloys produced by gravity and squeeze casting", 26 (2005) 479-485.
• [2] T. M. Yue, Jour. of Mater. Process. Tech., "Squeeze casting of high-strength aluminium wrought alloy AA7010", 66 (1997) 179-185.
• [3] Z.W. Chen, W.R. Thorpe, Mater Sci. and Eng. A, "The effect of squeeze casting pressure and iron content on the impact energy of Al-7Si-0.7Mg alloy", 221 (1996) 143-153.
• [4] M.A. Sava, S. Altintaş, Mater. Sci. and Eng. A, "Effects of squeeze casting on the wide freezing range binary alloys", 173 (1993) 227-231.
• [5] P.V. Evans, R. Keyte, R.A. Ricks, Mater. &Design, "Squeeze casting of aluminium alloys for near net shape manufacture", 14 (1993) 65-67.
• [6] A Bloyce, J.C Summers, Mater. Sci. and Eng. A, "Static and dynamic properties of squeeze-cast A357-SiC particulate Duralcan metal matrix composite", 135 (1991) 231-263.
• [7] M. R. Ghomashchi, K. N. Strafford, Jour. of Mater. Process. Tech., "Factors influencing the production of high integrity aluminium/silicon alloy components by die and squeeze casting processes", 38 (1993) 303-326.

9. Copyright:

• This material is based on the paper by [Jun-Ho Lee, J. H. Moon, Dock-Young Lee]: [Effect of Applying Pressure of High Pressure Diecasting Process Using Salt core].
• Paper Source: DOI information not available in the paper

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