This article offers an in – depth exploration of the lost foam casting process. It begins with an overview of the development and basic principles of the lost foam casting process. Then, it meticulously analyzes its technological characteristics, comparing them with traditional sand – casting methods to highlight its advantages. The production process is detailed, along with the functions of different production areas. The engineering design of lost foam casting plants is comprehensively covered, including considerations for fire protection, the layout of the mold – making workshop and the lost foam workshop, and other key aspects. Finally, the article looks at the current status and future trends of the lost foam casting process, aiming to provide a complete understanding of this technology for relevant professionals and enthusiasts.
1. Introduction
The lost foam casting process has emerged as a significant advancement in the field of casting technology. Derived from the full – mold casting process, it has experienced remarkable development over the past few decades. In 1981, the Chinese Academy of Sciences successfully developed China’s first lost foam casting production line. Since then, due to its unique technological advantages, the lost foam casting process has made great progress in various aspects such as technology, equipment, mold design, and raw materials in China.
This process has a wide range of applications, especially in the production of complex – shaped castings. It has become the main casting process for manufacturing motor shell castings. The continuous optimization of the engineering design of lost foam casting plants also reflects the industry’s pursuit of environmental protection, safety, green development, and energy – saving. Understanding the lost foam casting process and its engineering design is crucial for improving production efficiency, product quality, and reducing production costs.
2. Principles and Characteristics of Lost Foam Casting Process
2.1 Basic Principles
The lost foam casting process involves several key steps. First, a pattern made of paraffin or foamed resin, which is similar in size and shape to the final casting, is created. These patterns are then bonded together to form a pattern cluster. After that, a refractory coating is applied to the pattern cluster and dried. The coated pattern cluster is then buried in dry quartz sand and vibration – molded. During the pouring process, under negative pressure, the pattern gasifies as the liquid metal is poured in. The liquid metal fills the space previously occupied by the pattern, and after solidification and cooling, the final casting is formed.
2.2 Technological Characteristics
2.2.1 Design Freedom and Complex Shape Casting
One of the most significant advantages of the lost foam casting process is its ability to produce castings of various shapes and sizes with great design freedom. By using foam plastics, it can easily create complex – shaped products that are difficult to manufacture using traditional casting methods. For example, it is highly suitable for producing multi – ribbed, multi – core, and complex – geometric – shaped castings. This is in contrast to sand – casting, where complex shapes often require intricate sand – core designs and may still face challenges in achieving the desired shape accuracy. Table 1 compares the design flexibility of lost foam casting and sand – casting for complex – shaped parts.
| Comparison Items | Lost Foam Casting | Sand – Casting |
|---|---|---|
| Design Flexibility | High, can freely design complex structures | Limited by sand – core making and mold – opening difficulties |
| Applicability for Complex Shapes | Ideal for multi – ribbed, multi – core, and complex – geometric – shaped castings | Challenging for extremely complex shapes, requires complex sand – core preparation |
| Shape Accuracy | High, less distortion during casting | Lower than lost foam casting for complex shapes |
2.2.2 Environmental Friendliness
Compared with the green – sand casting process, the lost foam casting process is more environmentally friendly. In green – sand casting, the production of sand cores for complex castings often generates harmful flue gases. For instance, the cold – box core – making process produces triethylamine tail gas, and although the treatment technology for this gas is becoming more mature, the hot – box core – making process still faces difficulties in completely treating the generated soot, organic waste gas, and odor, which is both technically challenging and costly. In contrast, the lost foam casting process does not require sand cores, thus eliminating these pollution sources.
2.2.3 High Old – Sand Recovery Rate and Cost – Savings
The molding sand used in the lost foam casting process contains no chemical binders, which enables a high old – sand recovery rate, usually reaching over 90%. This not only reduces the consumption of new sand but also meets the strict environmental requirements of the current era. In terms of cost, the lost foam casting process can save about 15% of energy consumption in casting production, and the cost of castings can be reduced by approximately 30%. Table 2 shows a comparison of old – sand recovery rates and cost – savings between the two processes.
| Comparison Items | Lost Foam Casting | Sand – Casting |
|---|---|---|
| Old – Sand Recovery Rate | Over 90% | Generally lower, varies depending on the process |
| Energy Consumption Cost Savings | About 15% | Higher energy consumption, no significant savings |
| Casting Cost Reduction | About 30% | Higher production costs, less cost – reduction potential |
2.2.4 High – Quality Castings
Castings produced by the lost foam casting process have excellent quality characteristics. They have no flash, burrs, or draft angles, resulting in high – precision dimensions. This allows for a reduction in the machining allowance, and the amount of cleaning and grinding work can be reduced by more than 50%. Additionally, the surface quality of the castings is good, which is beneficial for subsequent processing and product performance.
2.2.5 Lower Equipment Investment
In general, the equipment investment for the lost foam casting process is relatively low. Compared with sand – casting, it can reduce equipment investment by 30% – 50%. This makes it an attractive option for small and medium – sized enterprises looking to enter the casting industry or for companies aiming to expand their production capacity while controlling costs.
3. Lost Foam Casting Production Process
3.1 Production Area Division
The production area of the lost foam casting process is mainly divided into the white area, the gray area, and the black area. The white area and the gray area are usually combined into a mold – making workshop, which is unique to the lost foam casting process. The black area is similar to a sand – casting workshop.
3.1.1 Mold – Making Workshop (White Area and Gray Area)
The mold – making workshop is responsible for producing qualified pattern clusters. It includes processes such as bead pre – foaming, maturation after pre – foaming, pattern – making, pattern aging, gluing, coating, and drying. Among them, steam pre – foaming is the commonly used method for pre – foaming. During pattern – making, steam is introduced into the mold to heat the beads, causing the foam to soften, expand, fill the mold cavity, and adhere to each other to form a whole.
- Pre – foaming: The foam beads are pre – expanded to a certain volume through methods such as steam pre – foaming. This process is crucial as it determines the density and quality of the final pattern. Different types of foam beads, such as expandable polystyrene resin beads (EPS), expandable methyl methacrylate – styrene copolymer resin beads (STMMA), and expandable polymethyl methacrylate resin beads (EPMMA), have different pre – foaming requirements.
- Maturation: After pre – foaming, the beads need to undergo a maturation process to stabilize their physical properties. This ensures that the beads can be effectively used in the subsequent pattern – making process.
- Pattern – Making: In this step, the matured beads are formed into pattern pieces. The steam – heating method is often used to make the beads fill the mold cavity and form a solid pattern piece.
- Pattern Aging: Pattern aging helps to further improve the dimensional stability of the pattern. It can be carried out in a natural environment or in a special aging chamber.
- Gluing and Coating: Pattern pieces are glued together to form a pattern cluster, and then a refractory coating is applied. The coating plays a crucial role in protecting the pattern during the casting process and improving the surface quality of the casting.
- Drying: The coated pattern cluster needs to be dried to remove moisture, ensuring that the pattern has sufficient strength and stability during the casting process.
3.1.2 Lost Foam Workshop (Black Area)
The lost foam workshop contains the melting department, the molding department, the sand – treatment department, and the cleaning department.
- Melting Department: Similar to that in sand – casting, it is responsible for melting the metal materials required for casting. Different metal materials, such as cast iron, steel, and non – ferrous metals, have different melting temperatures and requirements.
- Molding Department: The unique feature of the lost foam casting molding process is the use of dry sand to fill the sand box, and a vacuum pump is used to draw negative pressure to form a solid mold. The specific molding process includes steps such as adding bottom sand and vibrating for compaction, placing the pattern cluster, adding sand and vibrating for compaction on the molding vibrating table, covering with a film and adding top sand, adding a pouring cup, pouring, cooling, turning over the box, and sand – falling and conveying.
- Sand – Treatment Department: The sand used in the lost foam casting process is dry sand without any additives, and the sand – treatment equipment is relatively simple. The dry sand treatment process includes steps such as hydraulic box – turning, vibrating and conveying the sand – falling trough, using a high – temperature resistant bucket elevator, vibrating sand – falling screen, magnetic separator, automatic sand – adding door, air – cooling bed, bucket elevator, intermediate sand bin, bucket elevator, sand – temperature regulator, automatic sand – adding door, and bucket elevator to the molding sand bin.
- Cleaning Department: After casting, the castings need to be cleaned to remove sand and other impurities on the surface. This department is responsible for the cleaning work of the castings, and the cleaning methods may include vibration cleaning, shot – blasting cleaning, etc.
3.2 Specific Production Processes
3.2.1 Molding Process
The molding process in lost foam casting is a key link. As mentioned above, it starts with adding bottom sand to the sand box and vibrating it to a certain compaction degree. Then, the pattern cluster is carefully placed in the sand box. After that, more sand is added, and the molding vibrating table is used to make the sand quickly reach every part of the pattern, forming a suitable compaction degree. During this process, the deformation of the pattern cluster should be minimized to ensure the dimensional accuracy of the casting. After the sand is in place, a film is covered on the surface, and top sand is added. A pouring cup is also added for subsequent pouring.
3.2.2 Pouring Process
Pouring in lost foam casting is usually carried out under negative pressure. The negative pressure environment makes the loose dry sand in the sand box form a hard mold, which has sufficient compressive strength to resist the impact of the liquid metal. At the same time, the pressure difference can enhance the effect of gas discharge after the pattern cluster gasifies. This helps to ensure the smooth filling of the liquid metal and the quality of the casting. The pouring speed and temperature need to be strictly controlled according to the type of metal and the size and shape of the casting.
3.2.3 Sand – Treatment Process
The sand – treatment process in lost foam casting focuses on recycling and reusing the dry sand. After the casting is completed and the sand is separated from the casting, the sand goes through a series of treatment steps. First, it is transported through a vibrating and conveying sand – falling trough, and then lifted by a high – temperature resistant bucket elevator. A vibrating sand – falling screen is used to remove large – sized impurities, and a magnetic separator is used to remove magnetic substances. The sand then passes through an air – cooling bed to reduce its temperature, and finally, it is stored in an intermediate sand bin and a molding sand bin for reuse.
4. Engineering Design of Lost Foam Casting Plants
4.1 Fire Protection Design
Since the lost foam casting process uses a large amount of resin – based raw materials, the fire risk is relatively high. Fire protection design is a crucial factor in the engineering design of lost foam casting plants, which is related to whether the project can be successfully accepted by the government. The fire – risk level of the mold – making workshop is higher than that of the lost foam workshop, and they have different fire – protection design requirements and investment costs.
- Mold – Making Workshop: The commonly used foam resin beads in the mold – making workshop, such as EPS, STMMA, and EPMMA, can volatilize flammable vapors. According to the latest GB50016 – 2014 (2018 Edition) “Code for Fire Protection Design of Buildings”, the storage room for these foam resin beads is classified as Class A in terms of fire risk, and the fire – resistance rating is Class II. If the area of the Class A bead storage room is greater than 5% of the workshop area, the entire workshop will be classified as Class A in terms of fire risk. Therefore, in the engineering design, it is necessary to strictly control the area of the bead storage room to be less than 5% of the workshop area. The production fire – risk of the mold – making workshop is Class C, and the workshop’s fire – resistance rating is Class II. In addition to setting up an indoor fire – hydrant system, an automatic sprinkler system also needs to be installed.
- Lost Foam Workshop: According to the “Code for Fire Protection Design of Buildings”, the production fire – risk of the lost foam workshop is Class D, and the workshop’s fire – resistance rating is Class II. Although the fire – risk level is relatively lower than that of the mold – making workshop, appropriate fire – protection measures still need to be taken, such as reasonable layout of fire – fighting facilities and evacuation routes.
4.2 Layout of the Mold – Making Workshop
4.2.1 Material Selection and Safety Considerations
As mentioned above, different types of foam resin beads are used in the mold – making workshop, and each type has its own characteristics and applicable casting materials. When choosing materials, it is necessary to consider the requirements of the casting product, such as the type of metal, the complexity of the shape, and the surface quality requirements. At the same time, strict safety measures should be taken for the storage and use of these flammable materials. For example, the storage room should be equipped with explosion – proof electrical equipment, and appropriate ventilation facilities should be installed to prevent the accumulation of flammable vapors.
4.2.2 Workshop Building Layout
The processes in the mold – making workshop, such as pattern – making equipment, pattern aging, gluing, coating, and drying, require a large area, but the process equipment is generally not very tall. Therefore, the mold – making workshop is usually designed as a multi – story building. A lifting ladder is set up for the transportation of pattern pieces. Designing the workshop as a multi – story building can effectively reduce the project’s land occupation area and make the height of the workshop consistent with that of the lost foam workshop, making the factory area more aesthetically pleasing. According to past design experience, a three – story design for the mold – making workshop is more appropriate.
- First Floor: The first floor is usually used for bead pre – foaming, maturation after foaming, and pattern – making equipment. Since the high – temperature steam – foaming molding process requires a large amount of high – temperature steam, and the condensed water volume after steam cooling is large, and the pattern – making equipment needs a traveling crane to replace the mold, these processes are arranged on the first floor for easy operation and drainage.
- Top Floor: A sunroom can be set up on the top floor to utilize solar energy for pattern aging, which saves energy. After the aging process, the white patterns can be glued on the top floor.
- Middle Floor: The middle floor can be used for white – pattern coating, drying, and pattern – cluster sending areas. It is also suitable to transport the pattern clusters to the lost foam workshop by an overhead chain at the height of the second floor. A fire – proof separation water curtain needs to be set up in the corridor between the mold – making workshop and the lost foam workshop to prevent the spread of fire. A boiler room should be arranged near the mold – making workshop to provide qualified steam for bead pre – foaming and pattern – making machines.
4.3 Layout of the Lost Foam Workshop
4.3.1 Layout of the Molding Line
The core equipment of the molding line in the lost foam workshop is the molding vibrating table. Its function is to make the dry sand quickly reach every part of the pattern, forming a suitable compaction degree while minimizing the deformation of the pattern cluster to ensure the dimensional accuracy of the casting. When producing high – quality castings, the requirements for the vibrating table are relatively high. Since pouring is usually carried out under negative pressure, a vacuum pump room needs to be arranged in the lost foam workshop, and it should be close to the vacuum – pumping point to ensure effective negative – pressure generation.
4.3.2 Sand – Treatment Department
The cooling method of the dry sand used in the lost foam casting process is different from that of green – sand. In the sand – treatment department of the lost foam workshop, cooling equipment needs to be arranged nearby to provide circulating cooling water for cooling the high – temperature sand. Advanced molding – line equipment manufacturers usually arrange the molding and sand – treatment processes in a circular manner, which can improve production efficiency and reduce the transportation distance of sand.
5. Current Status and Future Trends of Lost Foam Casting
5.1 Current Application Status
Currently, the lost foam casting process has been widely used in various industries. In the automotive industry, it is used to produce engine parts, motor shell castings, and other components. In the machinery manufacturing industry, it is suitable for manufacturing complex – shaped parts with high precision requirements. In the field of aerospace, it also shows potential in the production of some high – performance components. However, although the lost foam casting process has many advantages, there are still some limitations. For example, the surface finish of some castings may not meet the requirements of high – end products, and the process control is relatively complex, requiring high – level technical operation and management.
5.2 Future Trends
5.2.1 Improvement of Automation Level
One of the future development directions of the lost foam casting process is to improve the automation level, especially in the mold – making workshop. Currently, the automation degree of the mold – making workshop is relatively low, and most of the processes rely on manual operation. In the future, through the application of advanced automation equipment through the application of advanced automation equipment, such as robotic arms for pattern assembly, automated coating systems, and intelligent control systems for pre – foaming and drying processes, the production efficiency and product quality can be significantly improved. Automated systems can precisely control process parameters, reducing human – error – induced variations in product quality. For example, robotic arms can assemble pattern clusters with high precision, ensuring consistent dimensions and better – fitting parts, which in turn leads to higher – quality castings.
5.2.2 Development of New Materials
The development of new materials is another important trend. Scientists and researchers are constantly exploring new types of foam materials with better performance, such as higher heat resistance, lower gas – generation during combustion, and improved mechanical properties. These new materials can further enhance the quality of castings and expand the application scope of the lost foam casting process. For instance, new foam materials with lower gas – generation can reduce the risk of porosity in castings, resulting in stronger and more reliable products. Additionally, the development of more environmentally friendly refractory coatings is also on the horizon. These coatings will not only protect the pattern during casting but also have a lower impact on the environment, aligning with the global trend towards sustainable manufacturing.
5.2.3 Integration with Advanced Manufacturing Technologies
The lost foam casting process is expected to be integrated with other advanced manufacturing technologies. For example, the combination of lost foam casting with 3D printing technology can bring new possibilities. 3D printing can be used to quickly produce complex – shaped patterns that are difficult to manufacture by traditional methods, and then these patterns can be used in the lost foam casting process. This integration can greatly shorten the product development cycle and reduce the cost of mold – making for small – batch and customized production. Moreover, integrating with virtual reality (VR) and augmented reality (AR) technologies can improve the process design and quality control. Designers can use VR/AR to simulate the lost foam casting process, predict potential problems, and optimize the process parameters before actual production, saving time and resources.
6. Conclusion
The lost foam casting process has distinct technological advantages, including design flexibility, environmental friendliness, high old – sand recovery rate, excellent casting quality, and relatively low equipment investment. Its production process is divided into different areas with specific functions, and each process step is crucial for ensuring the quality of the final casting.
In the engineering design of lost foam casting plants, fire protection design is of utmost importance. The layout of the mold – making workshop and the lost foam workshop needs to consider various factors such as material characteristics, process requirements, and safety regulations. By separating the mold – making workshop (white and gray areas) from the lost foam workshop (black area), the fire – protection investment can be reduced while meeting the fire – protection requirements.
Currently, the lost foam casting process has a wide range of applications in multiple industries. However, to meet the increasing demands of modern manufacturing, it is necessary to continuously improve the automation level, develop new materials, and integrate with advanced manufacturing technologies. These efforts will not only enhance the competitiveness of the lost foam casting process in the market but also promote the sustainable development of the casting industry. Future research and development should focus on these aspects to further optimize the lost foam casting process and expand its application scope in more high – end fields.
