Establishing Guidelines to Improve the High-Pressure Die Casting Process of Complex Aesthetics Parts

This introductory paper is the research content of the paper ["Establishing Guidelines to Improve the High-Pressure Die Casting Process of Complex Aesthetics Parts"] published by [IOS Press].

1. Overview:

• Title: Establishing Guidelines to Improve the High-Pressure Die Casting Process of Complex Aesthetics Parts
• Author: F.J.G. SILVA, Raul D.S.G. CAMPILHO, Luís Pinto FERREIRA and Maria Teresa PEREIRA
• Publication Year: 2018
• Publishing Journal/Academic Society: Transdisciplinary Engineering Methods for Social Innovation of Industry 4.0, M. Peruzzini et al. (Eds.), IOS Press
• Keywords: Die casting, Casting, Casting defects, Zamak, Aesthetic parts.

2. Abstracts / Introduction

The paper addresses the challenge of optimizing the High-Pressure Die Casting (HPDC) process for Zamak alloy aesthetic parts to minimize finishing operations. Zamak alloy is suitable for complex shapes due to its low melting temperature, but achieving a defect-free surface finish for aesthetic applications requires careful control of injection parameters and mould configuration. This study investigates the HPDC process and parameters through numerical simulations using SolidCast™ software and empirical tests to establish guidelines for improved results in casting complex aesthetic Zamak parts. The structure of the paper includes a literature review, methodology, experimental setup, results and discussion, and conclusions with suggestions for future work.

3. Research Background:

Background of the Research Topic:

The use of complex parts made of light-weight materials is increasingly common. High-Pressure Die Casting (HPDC) is frequently employed to produce these parts rapidly and cost-effectively. Zamak, a light-weight alloy, is widely used for mechanical components and can be adapted for aesthetic parts requiring complex finishing processes. The primary objective is to utilize HPDC for aesthetic parts, thereby reducing or eliminating finishing operations and lowering final costs.

Status of Existing Research:

Existing research acknowledges die casting as a prominent manufacturing technique for geometrically complex metal parts, particularly in the automotive industry. The HPDC process involves several parameters, including temperature of the molten material, injection pressure, injection time, over-pressure, and solidification time. Mould design elements such as sprue, gates, positioning, lubrication, thickness, and cooling systems are also critical. Prior studies have explored gate design, thermal flow, ejection processes, and injection condition optimization. Software based on Finite Element Methods (FEM) has improved the accuracy of simulating the die casting process. However, casting processes are still susceptible to defects, necessitating further research to correlate parameters, heat transfer, and material flow for optimal results.

Necessity of the Research:

Despite advancements in simulation and process optimization, achieving high surface quality in HPDC aesthetic parts remains challenging, often requiring extensive finishing operations. There is a need to optimize HPDC parameters and mould conditions specifically for aesthetic parts to minimize surface defects and reduce or eliminate costly finishing processes. This research aims to establish practical guidelines for achieving defect-free aesthetic Zamak parts through a single injected casting operation.

4. Research Purpose and Research Questions:

Research Purpose:

The research purpose is to establish guidelines to improve the High-Pressure Die Casting (HPDC) process of complex aesthetic parts made of Zamak alloy. The goal is to optimize injection parameters and mould configuration to obtain defect-free parts with good aesthetic appearance in a single casting operation, minimizing subsequent finishing processes.

Key Research:

The key research focuses on:

• Investigating the influence of injection parameters (pressure, injection time, cooling time) on the surface quality of Zamak aesthetic parts.
• Utilizing numerical simulation to understand material flow within the mould and optimize mould design, including runner systems and venting.
• Developing a hybrid methodology combining empirical testing and advanced simulation to identify optimal process parameters and mould configurations.
• Establishing practical guidelines for HPDC of complex aesthetic Zamak parts to minimize defects and finishing operations.

5. Research Methodology

Research Design:

The research employed a hybrid methodology, integrating "Empirical Approach" and "Advanced Approach" as depicted in "Figure 1". The "Empirical Approach" involved systematic experimentation by adjusting injection parameters such as pressure, injection time, and cooling time. The "Advanced Approach" utilized numerical simulation with SolidCast™ software to analyze material flow and optimize mould design.

Data Collection Method:

Empirical data was collected through a series of die casting trials using a ZM3 equipment manufactured by PR METAL, Ltd. For the first round of injection trials, "Table 1" shows the parameters established. A 3! factorial design was used, conducting three trials for each parameter set, totaling 81 trials. Numerical simulation data was generated using SolidCast™ software, modeling material flow and solidification under varying mould and runner configurations.

Analysis Method:

The quality of the cast parts was primarily evaluated through visual observation of surface defects and completeness of mould filling. Simulation results were analyzed to understand material flow patterns, identify potential defect areas, and assess the impact of mould design modifications. The "Ishikawa diagram" ("Figure 3") was used to systematically analyze potential factors contributing to surface quality issues.

Research Subjects and Scope:

The research focused on High-Pressure Die Casting of Zamak 5 alloy. The material composition was: 3.8%Al, 0.95%Cu, 0.6%Mg, 0.04%Fe, balance Zn. The case study part was an aesthetic component typically used in women's wallets. Experiments were conducted using a single-cavity mould. The study explored the influence of pressure, injection time, and cooling time, while keeping mould geometry, gate positioning, and venting channels constant initially, and then modifying mould design based on simulation results.

6. Main Research Results:

Key Research Results:

The research led to the establishment of guidelines for improving the HPDC process for aesthetic Zamak parts. "Table 2" summarizes characteristic results from the first round of trials, showing defects like "Lack of filling", "Small surface depression and crack", and "Really bad surface quality" under different parameter sets. Through simulation and iterative empirical testing, optimized parameters and mould design were identified. "Table 3" presents the most characteristic results from the optimized conditions, achieving improved part quality. "Figure 6" shows parts obtained with optimized mould design and parameters, demonstrating improved surface quality sufficient to avoid intermediate finishing steps before coating.

Analysis of presented data:

Initial empirical trials ("Table 2") revealed that low cooling times resulted in poor surface quality. While medium cooling times also showed defects, it was inconclusive for direct correlation. Injection time did not show a clear trend initially, but reducing injection time, leading to higher metal speed, resulted in increased turbulence and poor surface quality. Lower pressure was identified as crucial to reduce turbulence during mould filling. Simulations ("Figure 4" and "Figure 5") indicated that inverting the mould position, using a central runner, and incorporating risers improved material flow and reduced turbulence. Optimized parameters (Pressure: 2 bar, Injection time: 0.5 s, Cooling time: 1 s) combined with mould modifications resulted in parts with significantly improved surface quality.

Figure Name List:

• Figure 1. Flow diagram of the hybrid methodology used in this work.
• Figure 2. (a) Part used as case study in this work. (b) Contextualization of the part in the final product.
• Figure 3. Ishikawa diagram corresponding to problem root-causes analysis.
• Figure 4. Parameters used in the simulations process and some tests carried out with different runner positioning.
• Figure 5. (Right hand) Simulation after the mould has been inverted and using a central runner; (Left hand) Simulation after the mould has been inverted and using a central runner and a posterior riser.
• Figure 6. Parts obtained with the inverse positioning of the mould, central runner and three risers in the other sides of the part. The part is not perfect, but the quality is enough to avoid intermediate steps before coating.

7. Conclusion:

Summary of Key Findings:

This study successfully developed and validated a hybrid approach for optimizing HPDC parameters for aesthetic Zamak parts. Key guidelines established include:

• Material Definition: Correct material selection is crucial due to its influence on material fluidity and distribution during filling.
• Pressure: Lower pressure is recommended to minimize turbulence, especially for complex part shapes.
• Filling Time: Short filling times, around 0.5 seconds for ~25g parts, are suitable.
• Cooling Time: Medium cooling times are necessary for part consolidation.
• Mould Design: For curved parts, orienting the central part downwards facilitates material flow to upper areas. Simulation is essential for mould design optimization.
• Runner Design: Central runners are preferable to minimize turbulence compared to multiple runners.
• Risers: Risers should be considered for parts prone to turbulence, particularly in areas with high area-to-thickness ratios.

Academic Significance of the Study:

The study demonstrates the effectiveness of a hybrid methodology combining empirical testing and advanced simulation for optimizing complex manufacturing processes like HPDC. It provides a structured approach to problem-solving in die casting and contributes to the understanding of parameter interactions and mould design influences on the quality of aesthetic parts.

Practical Implications:

The established guidelines offer practical insights for die casting engineers and manufacturers to improve the HPDC process for aesthetic Zamak parts. Implementing these guidelines can lead to:

• Enhanced surface quality of cast parts.
• Reduction or elimination of intermediate finishing operations like blasting and manual polishing.
• Time and cost savings in production.
• Improved efficiency in achieving desired aesthetic outcomes in HPDC parts.

Limitations of the Study and Areas for Future Research:

The study acknowledges limitations and suggests future research directions, including:

• Exploring the influence of different vents positioning to further optimize material flow and reduce defects.
• Investigating surface treatments of the mould cavity to enhance part surface quality.
• Further research could explore the application of these guidelines to different aesthetic part geometries and Zamak alloys.

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9. Copyright:

• This material is "F.J.G. SILVA et al."’s paper: Based on "Establishing Guidelines to Improve the High-Pressure Die Casting Process of Complex Aesthetics Parts".
• Paper Source: doi: 10.3233/978-1-61499-898-3-887

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