Abstract
This comprehensive article delves into the challenges associated with shrinkage cavity and porosity defects in main reducer shell castings produced using the KW horizontal molding line. By analyzing the existing casting process and conducting detailed simulations, we identify the root causes of these defects. Subsequently, we propose and implement various process improvements, including optimizing the pouring system, increasing and modifying risers, and introducing heating risers. The successful implementation of these measures has eliminated the defects, enabling the stable production of qualified products. The article highlights the significance of understanding casting defects and their remediation strategies for enhancing product quality and meeting evolving customer requirements.
Keywords: main reducer shell, casting defects, shrinkage cavity, porosity, pouring system, risers, process improvement
Introduction
The main reducer shell (hereinafter referred to as “main reducer housing”) is a critical component in heavy-duty truck axles, which has been adapted from German technology since the late 20th century. Its demand remains stable in the market, with minor dimensional variations across different truck models. However, with advancements in automotive technology and stringent quality standards, customers have imposed new requirements on this product, particularly the elimination of shrinkage cavity and porosity defects.
This article presents a detailed analysis of these casting defects in main reducer housings, their root causes, and the process improvements implemented to address them. We will explore the existing casting process, analyze the structural and process hot spots, and propose optimized solutions validated through simulations and actual production runs.
Current Production Overview
Casting Process and Equipment
The main reducer housings are produced using the KW horizontal molding line, which employs airflow pre-compaction followed by high-pressure multi-touch compaction. The maximum compaction pressure is 1.25 MPa, and the mold box dimensions are 1100 mm x 900 mm x 350/250 mm, yielding a production rate of 90 castings per hour.
Material and Design
The housings are made from QT450-10 ductile iron, with a single casting weighing 37.5 kg and maximum dimensions of 548 mm x 360 mm x 180 mm. The primary wall thickness is 12 mm, and the product exhibits several thick, hot spots, particularly in areas distant from the flanges. The casting layout employs a one-pattern-three-casting design with a central gating system and strategically placed risers to optimize product quality, production efficiency, and yield rates.
Casting Parameters
The casting position is set with the flange face down, utilizing two internal gates in an open pouring system. Hot spots are complemented with risers, and venting pins are installed in the upper mold to facilitate gas escape. Cold irons are placed at protruding areas, and sand cores are prepared using the hot core process. The molten iron is poured at temperatures ranging from 1380°C to 1420°C, with chemical composition monitored using carbon-sulfur analyzers and direct-reading spectrometers (see Table 1).
| Chemical Composition (Mass Fraction, %) | QT450-10 |
|---|---|
| Carbon (C) | 3.65 – 3.95 |
| Silicon (Si) | 2.55 – 2.85 |
| Manganese (Mn) | 0.1 – 0.4 |
| Phosphorus (P) | ≤ 0.06 |
| Sulfur (S) | ≤ 0.02 |
Table 1: Chemical Composition of QT450-10 Iron
Defect Analysis
Through dissections of products manufactured using the existing process, we identified shrinkage cavity and porosity defects primarily in two areas: the vertical-horizontal junction near the bearing seat mounting surface and within the shift fork hole boss. These defects necessitated a targeted approach to optimizing the casting process.
Structural and Process Hot Spots
Casting hot spots can be classified into structural and process hot spots. Structural hot spots are inherent to the casting geometry, while process hot spots arise due to casting design choices like the placement of risers, gates, and vents. These hot spots exhibit prolonged solidification times, leading to excessive shrinkage and, consequently, defects if not adequately compensated.
Discussion and Future Work
The successful elimination of shrinkage cavity and porosity defects in the main reducer shell casting through the optimized casting process highlights the importance of comprehensive defect analysis and simulation-driven process improvements. The implementation of the semi-closed and semi-open pouring system, along with the strategic placement of enlarged and heated risers, has significantly improved the quality of the castings.
The key factors contributing to the success of this project include:
- Accurate Identification of Defect Locations: By conducting detailed dissection and analysis, the critical areas prone to shrinkage defects were precisely identified. This allowed for targeted process modifications.
- Simulation-Based Process Optimization: The use of solidification simulation tools enabled the prediction of casting behavior and the identification of potential hot spots. This informed the design of the optimized pouring system and riser placement.
- Innovative Riser Design: The introduction of heated risers and the strategic use of oversized risers, coupled with the innovative design of the riser assembly, significantly enhanced the feeding efficiency and prevented the formation of isolated liquid zones.
- Comprehensive Validation: The multi-round validation process, including both simulation and physical testing, ensured the reliability and effectiveness of the optimized process.
Looking forward, there are several avenues for further improvement and research:
- Advanced Simulation Tools: The continued development of advanced simulation software can enable more precise predictions of casting behavior, allowing for even more refined process optimizations.
- Automation and Digitization: The integration of automation and digitization technologies, such as the “robotic automatic investment shell production line” mentioned in the reference, can further enhance production efficiency and product quality consistency.
- Sustainable Casting Practices: Exploring sustainable casting practices, such as reducing waste and emissions, can align the casting industry with environmental regulations and promote green manufacturing.
- Material Innovations: Research into new casting materials with improved properties can offer additional solutions to casting defects and enhance the overall performance of cast components.
In conclusion, the successful elimination of shrinkage cavity and porosity defects in the main reducer shell casting demonstrates the effectiveness of a comprehensive approach that combines defect analysis, simulation-driven process optimization, and rigorous validation. This work not only improves the quality of the castings but also provides valuable insights for future.