1. Introduction
Lost foam casting is an advanced manufacturing process that has been widely used in various industries. In the automotive industry, it has shown great potential in the production of engine cylinder block castings. This article will focus on the application of lost foam casting in engine cylinder block castings, discussing its process, advantages, challenges, and future prospects.
1.1 The Concept of Lost Foam Casting
Lost foam casting involves several key steps. First, a foam model that is similar in size and shape to the desired casting is created. This foam model is then assembled into a model cluster, coated with a refractory paint, and dried. After that, it is buried in dry sand and vibrated to create a mold. During the pouring process, either at atmospheric pressure or under negative pressure, the foam model is vaporized as the liquid metal is poured in, and the metal takes the place of the model. After solidification and cooling, the casting is formed.
1.2 The Importance of Engine Cylinder Block Castings
Engine cylinder block castings are crucial components in the automotive industry. They are complex structures that house various engine parts such as cylinders, piston bores, coolant passages, and oil galleries. The quality of the cylinder block casting directly affects the performance and reliability of the engine. High-quality cylinder block castings are required to ensure efficient combustion, proper lubrication, and effective cooling of the engine.
2. The Process of Lost Foam Casting for Engine Cylinder Block Castings
2.1 Mold Design
The design of the mold for engine cylinder block castings in lost foam casting is a critical step. Different design schemes may be adopted for diesel and gasoline engine cylinder blocks, but the parting scheme treatment is generally consistent. The parting scheme is mainly considered from the aspects of foam mold piece forming quality, ease of demolding, and overall model gluing quality. For engine cylinder block foam models, a common approach is horizontal layer-by-layer cutting. The principle is to ensure that the mold pieces containing the intake and exhaust passages can be smoothly demolded in a two-part mold structure. Based on several typical and representative lost foam casting process schemes for engine cylinder blocks and years of production experience, a horizontal parting scheme, along with local sealing of the crankcase in the direction of mold removal and equal-wall-thickness hollowed-out concave treatment on the outer wall of the crankcase at the locally sealed part, is considered an optimal parting and mold splitting scheme.
2.2 Foam Material Preparation
2.2.1 Pre-foaming and Maturation of the Foam Material
The selection of the foam material is crucial. In China, there are several manufacturers of expandable polystyrene beads suitable for lost foam casting. For engine cylinder block castings, after preliminary trials, the Jiachang brand B107 model EPS material is often chosen as the raw material for making the foam model. The density of the EPS foam model needs to be strictly controlled within the range of 23 – 24 g/L. To achieve this density requirement, the pre-foaming bulk density of the EPS beads must be strictly controlled within 20 – 21 g/L. After being foamed by the pre-foaming machine, the EPS material needs to be matured in a maturation bin for 4 – 8 hours before it can be used.
2.22. Foam Molding and Maturation
The foam molding process uses a hydraulic semi-automatic molding machine. By optimizing the design of the mold, the cylinder block sleeve model and the crankcase body can be molded in one step, solving the problems of deformation and dimensional accuracy. At the same time, the influence of adhesive on the casting quality is minimized. To reduce the adverse effects of residual water evaporation and blowing agent diffusion and evaporation in the foam model on the casting process, the foam model is required to be naturally aged for 20 days under normal temperature conditions.
2.3 Foam Model Processing
2.3.1 Drying of the Foam Model
Before the foam model and the forming pouring system are assembled and bonded into a complete model, they need to be dried in an independent drying room at a temperature of 55 °C ± 5 °C and a relative humidity of less than 30% until they are completely dry.
2.3.2 Finishing and Bonding of the Foam Model
After sufficient aging, the foam model needs to be carefully trimmed to remove burrs and flash, repair damaged surfaces, and flatten the joint surfaces. The geometric dimensions of the foam model are also checked. The fully qualified foam model and foam pouring system are then bonded into a model group using cold glue and hot melt glue. For engine cylinder block foam models with complex structures, manual bonding is currently used. To ensure sufficient operating time, cold glue is used to bond the parting and mold splitting surfaces of the cylinder block foam model, and the pouring system uses hot melt glue to bond the joint surfaces. The glue should be evenly applied during operation, and as little glue as possible should be used while ensuring a firm bond. After bonding, the joint is strictly sealed with double-sided tape.
2.4 Coating Application and Drying
The success rate of casting formation in lost foam casting is about 30% dependent on the lost foam coating and the application process. In tests, the lost foam coating produced by Sanmenxia Sunshine Casting Materials Co., Ltd. is often used for cylinder block castings. Two coatings are applied, and the foam model group is dried according to the number of coatings. The thickness of the coating is strictly controlled within 1.0 – 1.5 mm.
2.5 Pouring System Design
For engine cylinder block castings with complex structures and thin walls, the design of the pouring system is very important. The design of the pouring system needs to consider two factors: the form of the pouring system and the location of the internal pouring gate. The pouring system for cylinder block castings is a closed type, that is, Fext>Fint>Fgate, with a ratio of (1.3 – 2):(1 – 1.5):1 chosen here. And one set of pouring system is designed to pour 2 cylinder block castings, with the pouring time controlled within 35 – 40 s. The location of the internal pouring gate for cylinder block castings is also very important, and a multi-point inlet internal pouring gate scheme is adopted as shown in Figure [Figure Number].
2.6 Molding
For the molding of cylinder block castings, 40 – 70 mesh dry sand is used. Before packing the foam model into the box, the coating needs to be carefully inspected. If any small cracks are found, they must be repaired with quick-drying paint. At the same time, the model is checked for deformation. If deformed, it must be returned. A five-draw negative pressure special sand box is used, with four foam models buried in each box. The vibrating table uses an airbag frequency modulation locking vibrating table. After the sand box is locked, a base sand layer with a thickness of 120 mm is added. After vibration, an inclined angle is scraped out and the foam model is placed. When placing the model, the pouring cup should be as close to the box edge as possible to facilitate the pouring operation. Sand filling is carried out in two steps. The first sand filling height is level with or slightly higher than the end of the cylinder block. The vibration frequency is adjusted appropriately, and the vibration time is controlled within 10 – 20 s. The second sand filling uses cover sand, and the cover sand should have sufficient thickness to ensure sufficient sand consumption and prevent box expansion. The pouring system for the cylinder block casting has been determined, and the sand filling height is such that the sand plane after vibration is 15 mm lower than the end surface of the pouring cup. After the molding sand is vibrated, the sand surface should be scraped flat and not in a hilly shape. A plastic film is covered by the sand filling and burying personnel, and after the film is covered, a protective sand layer is added. When the thickness of the protective sand layer is greater than 20 mm, it should also be scraped flat. The pouring cup should be fully exposed. During the burying process, the burying personnel should operate according to the process requirements. The sand box with the buried model should be inserted with a process card according to the process requirements and moved to the pouring station.
2.7 Pouring and Cooling and Sand Removal
Before pouring, the pouring personnel need to check whether the protective sand layer has sufficient thickness, whether the pouring cup position is suitable, whether it is aligned, whether the vacuum pump is operating normally, and whether the negative pressure is stable. A teapot ladle is chosen as the pouring ladle, and it should be baked to a dark red color before use. The pouring personnel and crane operators should be trained and hold certificates to work, and the pouring is carried out by a dedicated person. Before pouring the molten iron, the pouring ladle must be lowered to the best height and position, and the ladle spout should be as close to the pouring cup as possible so that the first drop of molten iron can be accurately poured into the center of the pouring cup. At the start of pouring, a small flow is used for a trial pour. When the pouring cup burns and emits black smoke and the sound of the molten iron being sucked is heard, the flow is increased. When the sound of the molten iron being sucked decreases and it is judged by experience that it is almost full, the flow is controlled in advance, changing from a large flow to a small flow so that the pouring cup is filled but not overflowing. A 1.5-ton intermediate frequency electric furnace is used as the pouring equipment, and the pouring vacuum degree is controlled within -0.035 – -0.040 MPa. The pouring temperature requires that the tapping temperature be controlled within 1600 – 1620 °C. Currently, on-site pouring shows that each ladle of molten iron pours 4 boxes, with 4 cylinder blocks in each box, and the final pouring temperature of the cylinder block casting should be >1480°C. The casting starts to be removed from the sand box after cooling for 1.5 h in the sand box.
3. Advantages of Lost Foam Casting in Engine Cylinder Block Castings
3.1 Simplified Process Flow
Compared with traditional casting processes, lost foam casting significantly simplifies the process flow for engine cylinder block castings. It reduces many complex and time-consuming steps such as core sand preparation, core making, molding, and core setting. In lost foam casting, each casting requires only one foam model, which reduces the number of operations and shortens the production cycle.
3.2 Material Savings
Lost foam casting can save a significant amount of raw and auxiliary materials. Since there is no need for a large amount of core sand and the foam model can be accurately molded, less material is wasted during the production process. Additionally, the recycling of used sand is also more convenient, which further reduces material costs.
3.3 Improved Casting Quality
3.3.1 Dimensional Accuracy
The use of foam models in lost foam casting allows for better control of the dimensional accuracy of the casting. The foam model can be precisely molded to match the desired shape of the cylinder block, reducing the errors caused by traditional molding methods. This results in a more accurate casting with tighter tolerances.
3.3.2 Surface Quality
The refractory coating on the foam model helps to improve the surface quality of the casting. It provides a smooth surface for the liquid metal to flow over, reducing surface defects such as porosity and roughness. The vaporization of the foam model during pouring also helps to fill any small gaps or voids, resulting in a more uniform and defect-free surface.
3.4 Environmental Benefits
Lost foam casting is a more environmentally friendly process compared to some traditional casting methods. It reduces the amount of dust and waste generated during the production process. The recycling of used sand and the reduction in the use of certain chemicals and materials contribute to a cleaner and more sustainable manufacturing environment.
4. Challenges and Solutions in Lost Foam Casting for Engine Cylinder Block Castings
4.1 Foam Model Quality Control
The quality of the foam model is crucial for the success of lost foam casting. However, ensuring consistent quality of the foam model can be a challenge. Some of the issues that may arise include inconsistent density, deformation during molding or aging, and poor bonding between different parts of the model. To address these issues, strict quality control measures need to be implemented. This includes careful selection of the foam material, precise control of the pre-foaming and molding processes, and regular inspection and testing of the foam models.
4.2 Coating Application and Adhesion
The application of the lost foam coating and ensuring its proper adhesion to the foam model can also be a challenge. The coating needs to be evenly applied with the correct thickness to ensure its effectiveness. Poor adhesion can lead to coating peeling during the pouring process, which can affect the quality of the casting. To solve this problem, proper coating application techniques need to be used, and the compatibility between the coating and the foam model should be ensured. Regular testing and optimization of the coating process are also necessary.
4.3 Pouring System Design and Optimization
The design of the pouring system for engine cylinder block castings is complex and requires careful consideration of various factors. In some cases, improper design of the pouring system can lead to problems such as incomplete filling of the casting, porosity, or excessive turbulence in the liquid metal. To optimize the pouring system, detailed simulations and experiments may be needed. The location and size of the internal pouring gates, as well as the flow rate and pressure of the liquid metal, need to be carefully adjusted to ensure a smooth and complete pouring process.
5. Future Prospects
5.1 Technological Innovations
In the future, there will likely be continued technological innovations in lost foam casting for engine cylinder block castings. This may include the development of new foam materials with better properties, more advanced coating technologies, and improved pouring system designs. These innovations will further improve the quality and efficiency of the casting process.
5.2 Application Expansion
The application of lost foam casting in engine cylinder block castings is expected to expand. As the automotive industry continues to grow and demand for high-quality engine components increases, lost foam casting will likely play an even more important role. It may also be applied to other types of engine components or in other industries with similar casting requirements.
5.3 Environmental and Sustainability Considerations
With increasing emphasis on environmental protection and sustainability, lost foam casting will need to continue to evolve to meet these requirements. This may involve further improvements in the recycling of used materials, reduction in the use of harmful chemicals, and development of more environmentally friendly processes.
6. Conclusion
Lost foam casting has shown great potential in the production of engine cylinder block castings. It offers several advantages such as simplified process flow, material savings, improved casting quality, and environmental benefits. However, there are also some challenges that need to be addressed, such as foam model quality control, coating application and adhesion, and pouring system design and optimization. Through continuous technological innovations and process improvements, lost foam casting is expected to play an increasingly important role in the future production of engine cylinder block castings, contributing to the development of the automotive industry and a more sustainable manufacturing environment.
The following tables summarize some of the key aspects of the lost foam casting process for engine cylinder block castings:
Table 1: Mold Design Considerations
| Consideration | Details |
|---|---|
| Parting Scheme | Horizontal layer-by-layer cutting, local sealing of crankcase, etc. |
| Mold Quality Impact | Affects foam model quality and ultimately casting quality |
Table 2: Foam Material Preparation
| Stage | Requirements |
|---|---|
| Pre-foaming | EPS beads density control within 20 – 21 g/L |
| Maturation | 4 – 8 h in maturation bin |
| Foam Molding | One-step molding of cylinder block sleeve and crankcase, natural aging for 20 days |
Table 3: Foam Model Processing
| Step | Actions |
|---|---|
| Drying | At 55 °C ± 5 °C and < 30% relative humidity until dry |
| Finishing | Remove burrs, repair surfaces, check dimensions |
| Bonding | Use cold glue and hot melt glue, seal with double-sided tape |
Table 4: Coating Application and Drying
| Aspect | Details |
|---|---|
| Coating Type | Lost foam coating from [Manufacturer Name] |
| Thickness | 1.0 – 1.5 mm |
| Drying | According to coating number |
Table 5: Pouring System Design
| Factor | Details |
|---|---|
| System Type | Closed type, with ratio (1.3 – 2):(1 – 1.5):1 |
| Inner Gate Location | Multi-point inlet scheme |
| Pouring Time | 35 – 40 s |
Table 6: Molding
| Step | Details |
|---|---|
| Sand Selection | 40 – 70 mesh dry sand |
| Model Placement | Close to box edge for pouring cup |
| Sand Filling | Two steps, first level with or higher than cylinder block, second with cover sand |
| Vibrating | 10 – 20 s at appropriate frequency |
Table 7: Pouring and Cooling and Sand Removal
| Aspect | Details |
|---|---|
| Pouring Ladle | Teapot ladle, baked to dark red |
| Pouring Conditions | Vacuum degree – 0.35 – – 0.040 MPa, temperature 1600 – 162 |