Abstract: This article focuses on the lost foam casting process of ductile iron castings. It includes an analysis of the pouring system design, common defects such as shrinkage porosity, and their prevention methods. Through experiments and simulations, the optimal process parameters and defect prevention measures are determined, aiming to improve the quality and qualification rate of ductile iron castings produced by lost foam casting.
1. Introduction
Lost foam casting is a modern casting method that has gained significant popularity in recent years. It offers several advantages over traditional casting processes, such as better dimensional accuracy, reduced machining requirements, and the ability to produce complex shapes. Ductile iron, on the other hand, is a widely used material known for its excellent mechanical properties. In this article, we will explore the lost foam casting process for ductile iron castings, with a particular focus on process design and defect prevention.
2. Structure Analysis of Ductile Iron Castings for Lost Foam Casting
The ductile iron castings considered in this study have a weight of 180 kg and specific structural characteristics. The material is QT400 – 15, and the contour dimensions are 430 mm × 620 mm × 684 mm. There are two thick regions and oil passages with a total length greater than 500 mm. These structural features play a crucial role in determining the casting process and potential defects.
| Casting Characteristics | Details |
|---|---|
| Weight | 180 kg |
| Material | QT400 – 15 |
| Dimensions | 430 mm × 620 mm × 684 mm |
| Thick Regions and Oil Passages | Two thick regions, oil passages > 500 mm |
3. Pouring System Design and Simulation
3.1 Design of Pouring System Schemes
Four pouring system schemes were considered for the lost foam casting of ductile iron castings: side – bottom pouring, top pouring, stepped pouring, and bottom pouring. Each scheme has its own characteristics and potential effects on the casting quality.
| Pouring System Scheme | Description |
|---|---|
| Side – Bottom Pouring | Combination of side and bottom pouring directions |
| Top Pouring | Pouring from the top of the mold |
| Stepped Pouring | Multiple levels of pouring |
| Bottom Pouring | Pouring from the bottom of the mold |
3.2 Simulation Results of Different Pouring System Schemes
MAGMA simulation software was used to simulate the solidification and feeding of different pouring system schemes. The simulation results showed that each scheme had different shrinkage porosity risks and solidification behaviors.
4. Defect Analysis of Lost Foam Casting for Ductile Iron Castings
4.1 Main Defects Observed
The main defects observed in the ductile iron castings produced by lost foam casting were shrinkage holes, especially on the upper end face at the intersection of the parallel plate structure.
| Defect Type | Location |
|---|---|
| Shrinkage Holes | Upper end face at parallel plate intersection |
4.2 Causes of Defects
4.2.1 Shrinkage Hole Formation Mechanism
The formation of shrinkage holes in ductile iron castings is related to the solidification characteristics of ductile iron. Ductile iron solidifies in a mushy state. During solidification, the thick regions solidify slower than the surrounding thin regions. After the surrounding regions solidify, the thick regions lack the supply of molten iron, resulting in shrinkage porosity or shrinkage holes. Additionally, the eutectic expansion during solidification can also cause adverse effects such as volume increase of the molten iron and pressure on the mold wall.
4.2.2 Role of Risers in Defect Prevention
Risers play an important role in preventing shrinkage defects. There are two types of risers used in this experiment: slag – collecting risers and feeding risers. The feeding risers are mainly used to supply molten iron and control pressure. The pressure changes in the riser and the mold during the casting process can be divided into three typical stages: when the ingate solidifies, the casting and the riser form a whole; when the liquid metal contracts, the pressure in the riser is the lowest; and with the precipitation of graphite and the formation of austenite, the riser is refilled due to expansion.
5. Improvement Schemes for Lost Foam Casting of Ductile Iron Castings
5.1 Improvement of Riser Parameters
Based on the traditional sand casting riser design principle, two types of risers were set up. The parameters of the risers were adjusted according to the modulus of the hot spot area of the casting and the riser itself.
| Riser Type | Modulus Relationship |
|---|---|
| 1# Riser | Mn=Ms , MN=0.8MR |
| 2# Riser | MR=1.5MS, MN=0.6MR |
5.2 Improvement Effects
The effects of different risers on the casting quality were verified through full – process trials. The results showed that the choice of the bottom pouring system and 2# riser had better effects on reducing defects.
6. Process Control and Quality Improvement in Lost Foam Casting of Ductile Iron Castings
In addition to optimizing the pouring system and riser parameters, process control throughout the entire process is crucial for improving the quality of ductile iron castings produced by lost foam casting. This includes preventing collisions, controlling the drying of coatings, pouring negative pressure, and maintaining pressure.
7. Conclusion
In conclusion, the lost foam casting process for ductile iron castings requires careful consideration of the pouring system design and defect prevention. Through a combination of simulation and experimental studies, the optimal pouring system (bottom pouring) and riser parameters (matching the casting structure) have been determined. Strengthening process control throughout the entire process is also essential for ensuring high – quality castings. By following these guidelines, the quality and qualification rate of ductile iron castings produced by lost foam casting can be significantly improved.
Throughout the article, we have emphasized the importance of lost foam casting in the production of ductile iron castings and provided a comprehensive understanding of the process design and defect prevention aspects. Future research could focus on further optimizing the process parameters and exploring new techniques for even better casting quality.