A Simulation and Fabrication Works on Optimization of High Pressure Aluminum Die Casting Part

The content of this introduction paper is based on the article "A Simulation and Fabrication Works on Optimization of High Pressure Aluminum Die Casting Part" published by "Acta Physica Polonica A".

1. Overview:

• Title: A Simulation and Fabrication Works on Optimization of High Pressure Aluminum Die Casting Part
• Author: S.Ö. Ertürk, L.C. Kumruoğlu, A. Özel
• Year of publication: 2014
• Journal/academic society of publication: Acta Physica Polonica A (Vol. 125, No. 2)
• Keywords: High-pressure die casting, Simulation, Optimization, Aluminum alloys, Mold design, Air entrapment, Solidification, Radiographic testing, PACS: 81.20.Hy, 81.05.Bx

2. Abstract:

High-pressure die casting offers reduced costs due to its small tolerances and smooth surface finish. Casting parts produced are consumed by the automotive industry in millions. In this study, the use of computer aided engineering applications on design of high-pressure die-casting was studied. The influence of casting process steps in die design was studied and analyzed. The casting simulation software was used to improve design and solve problems. By using the simulation software in analyses of die design, the final design was reached in a few hours and thus the design process of pre-production was shortened and mold production was carried out with no revision on die material. Radiographic test was applied on the casting parts and the result shows good correlation between simulations of solidification result data. Also the results proved that the application of squeeze pressure in the intensification phase of high-pressure die casting process could be examined in the casting simulation.

3. Introduction:

The primary objective in manufacturing is process minimization for economical final product realization, often achieved through "net shape manufacturing". High-pressure die casting (HPDC), particularly using horizontal cold chamber machines, is a predominant process for near-net-shape components from aluminum and magnesium alloys, valued for its dimensional reproducibility. A significant portion of aluminum alloy castings, especially for automotive applications, utilize this method. The process involves injecting liquid metal at high velocities using a plunger through a shot sleeve, which can lead to turbulent flow and subsequent air entrapment, resulting in detrimental gas porosity that affects mechanical properties and pressure tightness. To mitigate these issues, ventilation channels and overflows are incorporated into die designs. The injection process comprises a slow shot phase, filling the shot sleeve, followed by a fast shot phase for rapid mold cavity filling. Computer simulation is crucial for managing cavity fill dynamics and optimizing the placement of ventilation channels and overflows. While various studies exist, few detail the step-by-step application of simulation in die design as an alternative to traditional trial-and-error approaches.

4. Summary of the study:

Background of the research topic:

High-pressure die casting is a critical manufacturing process for producing complex, near-net-shape aluminum components efficiently, particularly for the automotive sector. However, the process is susceptible to defects like gas porosity arising from air entrapment during high-velocity melt injection.

Status of previous research:

Existing theoretical and experimental work addresses HPDC die design, but there is a gap in literature demonstrating the systematic, step-by-step use of computer simulation throughout the design process to replace or augment traditional, often time-consuming, trial-and-error methods.

Purpose of the study:

This study aimed to utilize computer-aided engineering (CAE) simulation to optimize the design of a high-pressure aluminum die casting part. The objectives included analyzing the influence of process steps on die design, shortening the pre-production timeline by leveraging simulation, avoiding costly die revisions, and validating the simulation accuracy through fabrication and radiographic testing.

Core study:

The core investigation involved an iterative mold design process heavily reliant on casting simulation software. Key activities included:

1. Determining the optimal ingate location and type (emitter type selected) based on solidification simulation (Fig. 1) and analysis of filling patterns to minimize turbulence and air entrapment (Fig. 3, Fig. 4).
2. Defining the mold parting line (Fig. 2a) and necessary draft angles (Fig. 2b) considering part ejection mechanics.
3. Calculating required fill time based on part thickness (TABLE) and determining ingate dimensions using flow rate calculations (Q = V × A) to achieve a target velocity (30 m/s).
4. Simulating mold filling under defined plunger speeds (0.5 m/s slow phase, 2.5 m/s fast phase) to identify potential air entrapment zones (Fig. 4b, 4c).
5. Designing and positioning ventilation channels and overflows based on simulation results to manage trapped air and turbulent flow (Fig. 5).
6. Analyzing the final design simulation, including the effect of squeeze pressure during the intensification phase, to predict final part quality (e.g., shrinkage porosity, Fig. 6a).
7. Fabricating the mold based on the finalized simulation design.
8. Conducting radiographic tests on the cast parts to verify internal soundness (Fig. 6b).

5. Research Methodology

Research Design:

The study employed an iterative design methodology integrating CAE simulation with experimental validation. The mold design for an aluminum HPDC part was progressively developed and optimized using casting simulation software. The final design derived from simulation was then used for mold fabrication, followed by casting production and non-destructive testing for validation.

Data Collection and Analysis Methods:

• Simulation: Casting simulation software was utilized to analyze mold filling dynamics (flow patterns, velocity), air entrapment potential, solidification behavior (Fig. 1), and the influence of intensification pressure on shrinkage defects (Fig. 6a). Simulation results guided design decisions regarding parting line (Fig. 2a), draft angles (Fig. 2b), ingate geometry and location (Fig. 4a), and the placement of ventilation channels and overflows (Fig. 5).
• Experimental Validation: After mold fabrication based on the final simulation, casting trials were performed. The resulting parts, after removal of runners and overflows, underwent radiographic examination using a Baltospot GFD Industrial X-ray device with a Kodak MX123 screen, following EN 12681 and EN 444 standards. The radiographic results (Fig. 6b) were compared with simulation predictions to assess internal quality and validate the simulation's accuracy.

Research Topics and Scope:

The research focused specifically on the optimization of a high-pressure die casting process for a particular aluminum component. The scope encompassed the detailed design of the die casting mold elements (ingate, runners, overflows, vents, parting line, draft angles), the application of simulation tools to predict and mitigate casting defects (turbulence, air entrapment, shrinkage), analysis of process parameters (plunger speed, intensification pressure), and the validation of the simulation-driven design through radiographic inspection of the fabricated part.

6. Key Results:

Key Results:

The application of casting simulation software enabled the final die design to be achieved rapidly ("in a few hours"), significantly shortening the pre-production design phase compared to traditional trial-and-error methods. This simulation-driven approach allowed for mold production without the need for subsequent revisions. Simulation effectively predicted potential filling issues, such as air entrapment (Fig. 4b, 4c), and guided the strategic placement of overflows (Fig. 5) to manage colliding melt streams and turbulence. The final simulation, incorporating the effect of solidification compression force (squeeze pressure), predicted the absence of shrinkage defects (Fig. 6a). Subsequent radiographic examination of the parts produced using the simulation-optimized design confirmed the absence of detrimental internal defects (Fig. 6b), thereby validating the accuracy of the design and the simulation parameters employed. A good correlation was observed between the solidification simulation results and the radiographic test findings. The study successfully demonstrated that computer simulation can be used to examine the effect of the squeeze pressure applied during the intensification phase of the HPDC process.

Figure Name List:

• Fig. 1. Solidification steps of casting part.
• Fig. 2. (a) Mold parting line, (b) draft analyses of casting part.
• Fig. 3. (a) Mold filling of model with three ingate, (b) mold filling of model with single and thin ingate.
• Fig. 4. (a) The solid model of casting part with emitter type ingate, (b) possible air entrapments in part, (c) possible air entrapments from section.
• Fig. 5. (a) Mold filling with three overflows attached model, (b) mold filling of part with five overflows.
• Fig. 6. (a) The shrinkage view from simulation result, (b) the radiographic result of casting part.
• TABLE Fill times due to section thickness of casting part.

7. Conclusion:

This study demonstrates the efficacy of utilizing computer simulation as an integral tool in the design and optimization of high-pressure die casting processes. The primary advantages highlighted include the significant reduction in design time and the prevention of economic and time losses associated with traditional trial-and-error methods by proactively identifying and mitigating potential casting defects like turbulence and air entrapment. The step-by-step simulation approach facilitated a robust die design, leading to the successful production of castings free from major internal defects, as confirmed by radiographic testing. The strong correlation between simulation predictions (including solidification behavior and the effect of compression force) and experimental results validates the use of simulation as a reliable tool for optimizing HPDC processes and ensuring part quality.

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9. Copyright:

• This material is a paper by "S.Ö. Ertürk, L.C. Kumruoğlu, A. Özel". Based on "A Simulation and Fabrication Works on Optimization of High Pressure Aluminum Die Casting Part".
• Source of the paper: https://doi.org/10.12693/APhysPolA.125.449

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