Manufacturing of Aluminum Alloy Parts from Recycled Feedstock by PIG Die-Casting and Hot Stamping

This introductory paper is the research content of the paper ["Manufacturing of Aluminum Alloy Parts from Recycled Feedstock by PIG Die-Casting and Hot Stamping"] published by [MDPI].

1. Overview:

• Title: Manufacturing of Aluminum Alloy Parts from Recycled Feedstock by PIG Die-Casting and Hot Stamping
• Author: Tatsuhiko Aizawa, Takeshi Kurihara and Hiroki Sakayori
• Publication Year: 2022
• Published Journal/Society: Lubricants
• Keywords: upward recycling; aluminum and aluminum alloys; pin injection gate; die casting; hot stamping; mechanical parts; heatsink; nitrogen supersaturation; TiAlN coating

2. Abstract

PIG (Pin-Injection-Gate) die-casting and hot stamping was developed for fabrication of small-sized and thin-walled aluminum alloy parts from the recycled feedstock. The pure aluminum and aluminum alloy granules were utilized as a feedstock model of recycled materials. The measured mass of granules with the estimated weight from 3D-CAD (Computer Aided Design) of products was poured into the PIG-nozzles before injection. After quickly melting by induction heating inside the PIG-nozzle units, the aluminum melts were injected into a die cavity through the PIG-nozzle. No furnaces and no crucibles were needed to store the melt aluminum stock in different from the conventional die-casting system. No clamping mechanism with huge loading machine was also needed to significantly reduce the energy consumption in casting. Much less wastes were yielded in these processes; the ratio of product to waste, or, the materials efficiency was nearly 100%. Nitrogen supersaturation and TiAlN coating were used to protect the PIG-nozzle and the stamping die surfaces from severe adhesion from aluminum melt. The pure aluminum gears and thin-walled mobile phone case were fabricated by this process. X-ray tomography proved that both products had no cavities, pores and shrinkages in their inside. Using the hot stamping unit, the micro-pillared pure aluminum heatsink was fabricated to investigate the holding temperature effect on the aspect ratio of micro-pillar height to width.

3. Research Background:

Background of the research topic:

Green manufacturing is a growing need in sustainable, carbon-neutral societies [1]. Solid-state recycling offers a method to reprocess used aluminum alloys without remelting [2].

Status of previous research:

Previous research includes solid-state recycling methods like warm and hot extrusion of aluminum alloy debris [3]. Conventional die-casting [4] is effective for near-net shaping but is energy-intensive. Existing PIG die-casting systems address some limitations of conventional die-casting [5-7], particularly for small-sized and thin-walled parts.

Need for research:

Conventional die-casting requires large furnaces and significant clamping forces, leading to high energy consumption and material waste. There's a need for a more efficient process, especially for recycling aluminum.

4. Research purpose and research question:

Research purpose:

To develop an advanced PIG die-casting system integrated with hot stamping for the efficient production of aluminum alloy parts from recycled feedstock.

Core research:

To demonstrate the capability of the integrated PIG die-casting and hot-stamping system to produce small-sized, thin-walled, and micro-textured aluminum parts with minimal waste and high material efficiency.

5. Research methodology

The research employed a combined PIG die-casting and hot stamping system.
-Research Design: Experimental, combining PIG die-casting and hot-stamping.
-Data Collection:

• Weight measurement of feedstock.
• Temperature monitoring during induction heating.
• High-speed video recording of free injection.
• Short-shot experiments for flow analysis.
• X-ray tomography for defect analysis.
• Laser microscopy and profilometry for surface texture measurement.
• SEM-EDX for elemental composition analysis.
• Micro-Vickers hardness testing.
  -Analysis:
• Visual analysis of flow patterns.
• Quantitative analysis of injection speed.
• Dimensional analysis of cast and stamped parts.
• Defect analysis via X-ray tomography.
• Tribological characterization of nitrided surfaces.
  -Materials:
• Pure aluminum (99.7% purity) granules.
• AA5052 aluminum alloy particles.
• AISI420J2 for PIG-nozzles and casting dies.
• AISI316 for warm/hot stamping dies.
  -Surface Treatments:
• Low-temperature plasma nitriding.
• TiAlN coating.
• Plasma printing for micro-texturing.
  -Scope: Fabrication of pure aluminum gears, AA5052 mobile phone cases, and micro-pillared pure aluminum heatsinks.

6. Key research results:

Key research results and presented data analysis:

• Efficient Material Use: The PIG die-casting process achieved nearly 100% material efficiency.
• Free Injection: Free injection experiments showed an average injection velocity of 0.8 m/s (Figure 10).
• Aluminum Flow: Short-shot experiments demonstrated a flow pattern similar to plastic mold injection (Figure 11).
• Defect-Free Products: X-ray tomography confirmed the absence of cavities, pores, and shrinkages in the cast parts (Figure 12, Figure 13).
• Micro-Texturing: Hot stamping successfully created micro-pillars on a pure aluminum heatsink (Figure 14, Figure 15). The holding temperature significantly affected the aspect ratio of the micro-pillars.
• Tribological properties: The nitrogen supersatruation process was mainly utilized for protection of the PIG-nozzle and die surfaces from the adhesion of aluminum remelts. TiAlN coating onto the nitrided PIG-nozzle wrought well to protect the PIG-nozzle inner surface from severe adhesion of aluminum melts.

List of figure names:

• Figure 1. Two procedures to yield the aluminum products.
• Figure 2. Manufacturing system including the PIG die-casting and hot stamping unit.
• Figure 3. PIG-nozzle unit including the weight-measuring section, the plunger, the pressurizing tools, and the heating section.
• Figure 4. A low temperature plasma nitriding system.
• Figure 5. A plasma printing procedure with aid of the low temperature plasma nitriding.
• Figure 6. The mesh-textured AISI316 punch by the plasma printing.
• Figure 7. Nitrogen solute content and hardness depth profiles in the nitrided AISI20J2 materials for PIG-nozzles and dies.
• Figure 8. Comparison of the corrosion and erosion toughness between the un-nitrided and nitrided AISI420J2 surfaces.
• Figure 9. Distribution of chromium and nitrogen contents on the dipped AISI420J2 surfaces from "A" to "B" across "X".
• Figure 10. Dynamic behavior in the free injection of the aluminum melt from the PIG-nozzle outlet gate.
• Figure 11. A short-shot experiment by using the double PIG-nozzle units for PIG die-casting.
• Figure 12. PIG die-cast, small-sized gear block by using a single PIG-nozzle unit.
• Figure 13. PIG die-cast, thin-walled AA5052 mobile phone case by using the double PIG-nozzle units.
• Figure 14. Warm stamping of pure aluminum solidified preform for microtexturing its surface.
• Figure 15. Effect of the holding temperature during the hot stamping on the microtexture formation.

7. Conclusion:

Summary of key findings:

The integrated PIG die-casting and hot stamping system successfully fabricated small-sized, thin-walled, and micro-textured aluminum parts from recycled feedstock with high material efficiency and minimal defects. Nitrogen supersaturation and TiAlN coating effectively protected the tooling from adhesion wear. The holding temperature in hot stamping significantly influenced the micro-pillar aspect ratio.

• Academic significance: The research demonstrates a novel approach to aluminum recycling and manufacturing, combining PIG die-casting and hot stamping. It provides insights into the flow behavior of aluminum melts in the PIG system and the effect of surface treatments on tool life.
• Practical implications: The developed system offers a more sustainable and efficient alternative to conventional die-casting, reducing energy consumption and material waste. It is suitable for producing small, complex aluminum parts with high precision.

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9. Copyright:

• This material is a paper by "Tatsuhiko Aizawa, Takeshi Kurihara and Hiroki Sakayori": Based on "Manufacturing of Aluminum Alloy Parts from Recycled Feedstock by PIG Die-Casting and Hot Stamping".
• Source of paper: https://doi.org/10.3390/lubricants11010013

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