In aluminum, magnesium alloy die-casting molds, and gravity metal mold-casting molds, the design of the cooling system is also a key. The cooling system sometimes called the cooling pipe or the cooling circuit is composed of a series of high thermal conductivity materials. Its purpose is to take the heat away from the molten metal through direct heat conduction and realize the control of the mold temperature. Controlled, and directed cooling, to allow castings to cool as quickly as possible.
How does the Automatic Generation of Cooling Piping Systems Assist the Gravity-casting Mold Process?
In the metal casting process, the hot spot of solidification during casting forming usually forms shrinkage cavity defects. Therefore, when designing the casting plan, it is necessary to judge the position of the solidification hot spot and design a cool channel at this position to eliminate the shrinkage cavity with a rapid cooling effect occur. Using casting solidification simulation software, the position of the shrinkage cavity in casting forming can be interpreted, and the corresponding cooling system can be designed based on experience, but the time to complete the simulation is often more than several hours, resulting in delays in the development schedule. The system for automatically generating cooling pipelines can help the foundry industry to truly solve the cooling pipeline design of gravity-casting metal molds. It is important software that belongs to the special Computer-Aid for Cooling System Design. It allows the designer to obtain the correct and optimal cooling pipeline design through software calculation the first time, which improves the transformation of the foundry industry, shortens the development time of the foundry industry, and saves unnecessary costs and waste. The solidification simulation of casting has been widely used in the foundry industry. Many commercial solidification simulation software can solve the shrinkage problem through the cooling system and achieve considerable accuracy, and the actual casting defects have also been quite verified.
- The cooling system needs to be designed by experienced engineers.
- Engineers need many times of trial and error to test the best cooling pipeline design.
- Engineers need to know computer simulation and actual casting.
Many castings with complex shapes often need to go through many times of trial and error to gain experience, but these experiences cannot get a truly accurate design of the size and quantity of cooling pipes for each new development of castings.
To shorten this development time, the industry began to apply the so-called foundry knowledge-based expert system database to assist cooling system design. From the established cooling pipeline database system, the analysis suggests a possible mold temperature balance scheme design. However, this system only provides experience and reference materials, and cannot solve the problem of mold temperature balance in the actual casting process. If you want to solve the solidification problem of actual castings, you must first understand the way solidification defects are formed during the solidification process. Therefore, during the solidification process, the cooling efficiency can be used to change the mold temperature distribution to achieve directional solidification characteristics and shorten the solidification time, reducing the casting cycle time to increase production efficiency.
There are three forms of heat transfer during cooling in the casting process:
- Heat is transferred to the mold through the solidified metal to increase the temperature of the mold by heat conduction.
- The heat is transferred out of the mold to the air in the form of convection and heat radiation.
- Heat is quickly taken out of the mold to the air using cooling through water and air medium.
If the 3D drawing file of the casting scheme of the casting with a complex shape is loaded, the optimized cooling system design system can be directly and automatically generated: including the position, quantity, and size of the cooling pipeline, the following related work needs to be done:
- The total heat mode released by the solidification of the casting in the mold.
- Heat exchange capacity with the cooling pipeline when the heat is transferred into the mold.
- Guidelines for cooling system design and software for automatically generating cooling lines.
Theoretical Guidelines and System Design for Automatic Generation of Cooling Circuits:
Different from the previous simulation software (CAE) or suggestion system database, based on the theory of casting heat input and output, the 3D CAD file of the imported casting scheme is given, and the casting cooling system module design that solves the problem of casting defects is automatically generated.
Use the method of relational calculation of the temperature value in the cooling process to understand the following problems:
- The model relationship of the heat release of the casting from liquid to solid during the casting process.
- The heat exchange model relationship between the cooling pipeline and the mold.
- The heat flux model relationship for the rapid removal of heat through the cooling medium.
Based on the above problems, solidification theory, fluid mechanics, and computer fluid numerical simulation are discussed in many ways:
- Apply the heat content and latent heat formula of solidification theory to calculate. And numerically calculate the maximum heat released by the casting in the mold during the solidification process.
- Calculation of the interface heat transfer coefficient between the application flow medium and the mold under different conditions.
- Calculate the location, quantity, and size of cooling pipelines in the design system through the heat flux taken away per unit of time.
- Based on the heat balance, the optimized cooling algorithm in the mold is established. The Visual Basic code is used to connect to the CAD software to automatically analyze the heat produced by the casting plan and to use the most suitable mold production temperature and solidification time to construct an optimal cooling system design.
Using the heat transfer results of the casting solidification simulation process, the size and quantity of the cooling pipelines are determined by hot spot judgment analysis. And then combined with the cooling pipeline database and heat output relationship equation established in the previous item, the optimal three-dimensional cooling of the castings is automatically generated piping design. The basis of the calculation of the design rule is that the heat released by the solidification of the casting is equal to the sum of the heat absorbed by the mold steel and the heat that can be taken away by the cooling pipeline. The heat that can be taken away by the cooling pipeline is a certain proportion of the heat released by the solidification of the casting. This will change with different cooling media, so it is necessary to understand that the heat released by the casting during the solidification process includes the sensible heat and latent heat of the heat content.
Why does the Gravity-casting Mold Process Need to Automatically Generate the Cooling Piping System?
Traditionally, mold cooling system design still relies on the designer's experience and limited knowledge accumulation. However, with castings becoming more and more complex and requiring higher cooling efficiency, designing a cooling system based on experience alone cannot ensure the optimal design and the most appropriate parameters. An excellent cooling system needs to fully consider the quality and thickness distribution of each part of the casting. In the area with larger wall thickness, that is, the area with more heat accumulation, the heat transfer capacity can be targeted to achieve an overall balance. In addition, the cooling process of the casting should be solidified as much as possible. Solidification starts from the farthest end of the gate to the inlet of the runner, and finally solidifies to the runner and the cake. Otherwise, hot spots will form inside the casting, leading to macroscopic shrinkage cavity defects.
Due to its high production efficiency and good maneuverability, high-pressure casting has become an important casting production process. The casting process includes a filling stage, a solidification stage, and a cooling stage. In this process, not only the filling stage is critical, but also the solidification and cooling stage, because it directly affects the production efficiency and the quality of the casting. An excellent cooling system can greatly reduce cooling time, improve casting productivity, and minimize various defects caused by uneven temperatures, such as hot spots, shrinkage cavities, uneven residual stress, warpage, etc. In addition, it is important for mold life, product release, etc. The mold itself can be regarded as a heat exchanger, which takes away the heat of the molten metal through the circulating cooling medium.
The casting cooling system consists of the following components:
- Temperature-controlling unit
- Pump
- Hoses
- Supply and collection manifolds
- Cooling channels in the mold
Drilling arrangement of cooling pipes:
- Parallel cooling pipes: There are multiple flow paths from the refrigerant supply manifold to the refrigerant collection manifold. According to the difference in flow resistance of each cooling channel, the flow rate of refrigerant in each cooling channel is also different, resulting in different heat transfer efficiency of each cooling channel, and there may be an uneven cooling effect between parallel cooling channels.
- Serial cooling pipes: From the refrigerant supply manifold to the refrigerant collection manifold to form a single flow path, which is the most commonly used cooling channel arrangement. If the cooling holes have a uniform pipe diameter, the refrigerant passing through the entire cooling system can be designed as the required turbulent flow to obtain the most efficient heat transfer. For large molds, multiple sets of cooling pipes in series may be required to obtain uniform cooling of the mold.
Basic principles of cooling system design:
- The layout of the pipes is evenly distributed in the metal filling area, and the influence on the heat balance of the mold should be considered.
- When the wall thickness of the casting is uniform, the distance between the cooling pipe and the cavity should be as equal as possible. When the wall thickness is uneven, the cooling water can be reasonably designed to be close to the cavity to enhance cooling.
- Reasonably choose the position of the cooling water pipe joint, in order not to affect the operation, it should be located on the back of the mold.
- The flow rate of the cooling medium in the cooling tube must be turbulent because the generation of turbulent flow can improve the heat dissipation rate.
The data structure of the cooling pipeline:
- Cooling system list: manage the established cooling pipelines and support grouping functions. For example, specify the cooling ducts on the movable side and the fixed side as two different groups. The program automatically displays the total length and surface area of the cooling channels. You can also use this classification management function to design different cooling water channel schemes.
- Detailed Data Sheet: Lists the detailed parameters of each segment in each cluster, including location coordinates, length, diameter, and orientation. Each segment is a separate CAD geometry unless the user performs a Boolean operation that automatically merges them.
- Design parameters for each segment: Displays the design parameters for each segment of the cooling duct.
Workflow for Online Cooling System Analysis:
- Step 1: EMDI (Casting Mass Distribution) Analysis
EMDI's MDI means Mass Distribution Index, which can be simply understood as the three-dimensional thickness distribution of castings. EMDI organizes the three-dimensional thickness distribution of castings and directly displays them on the surface of castings in cloud image mode. EMDI has no units, only grades. The larger the number of grades, the greater the thickness of the part. During the calculation process of EMDI, the system will automatically generate an analysis grid in the background. Users can customize the grid density, a smaller grid size can get more accurate results, but requires more CPU time and resources. After the EMDI calculation is completed, the system will use another smooth grid to directly display the EMDI result with the cloud image. All mesh generation is automatic without any user intervention. The resulting data from EMDI is easy to read and can be of great value in the cooling duct design process. This value intuitively describes the thickness distribution of the casting. The higher the value, the thicker it is, and the lower the value, it is thinner. In the design process of the cooling pipeline, it is hoped that the area with a thicker wall of the casting will have higher cooling efficiency, take away more heat to achieve a state of thermal balance, and reduce the generation of thermal knots.
- Step 2: Rapid Cooling Efficiency Analysis
The rapid cooling analysis is mainly used to evaluate the cooling efficiency of each part of the casting by the cooling pipeline. This efficiency can be simply understood as a function of the heat influence distance. The larger the diameter of the cooling channel and the closer it is to the casting, the more efficient the cooling. For the comprehensive effect of multiple cooling channels, this data has a high reference value. This indicator directly reflects the comprehensive influence and cooling efficiency of the cooling pipeline. The area with a higher value represents better cooling efficiency and more heat is taken away. On the contrary, the area with a lower value represents poor cooling efficiency and takes away more heat and fewer calories.
- Step 3: Cooling Impact Analysis
In the design process of the cooling pipeline, it should be considered that in the area where the wall thickness of the casting is larger, the higher the cooling efficiency is designed, the more heat is taken away, and the thermal knot is reduced. This approach takes into account both the geometry of the casting and the cooling efficiency of the cooling channels, and the result is useful for the design of the cooling system. When we adjust the display scale to a value less than 0.5, we can find insufficient cooling positions. These positions may not have sufficient cooling efficiency due to the excessive wall thickness of the casting. At this point, we need to adjust the design of the cooling pipeline to obtain a better heat balance. A cooling system design with a uniform heat effect can not only improve the quality of castings but also prolong the life of molds.
