1. Introduction
Sand casting is a traditional and widely used metal forming method with a long history. It has the advantages of low cost and high adaptability to complex shapes, making it an important process in modern manufacturing, especially in industries such as machinery manufacturing, automobiles, and aerospace. However, when it comes to casting complex structural parts, many challenges arise, which directly affect the quality and cost of the castings.
2. Complex Structural Parts Sand Casting Process Design
2.1 Casting Process Analysis
The use of furan resin self-hardening sand can help reduce surface defects of castings and enhance the overall tissue compactness. In the casting design process, the selection of dimensional tolerance directly affects the function of the casting and the complexity of subsequent processing. The commonly used dimensional tolerance level is CT11, considering the free shrinkage characteristics of the casting during the cooling process. The mass tolerance grade is set to MT10 to ensure the consistency of the casting’s weight and volume, with a tolerance range usually set to ±4% of the casting weight to adapt to slight changes in production. Considering the physical characteristics of HT250, the shrinkage rate should be preset to 0.9%. This parameter reflects the reduction in material volume during the transition from liquid to solid, and a reasonable setting of the shrinkage rate is crucial to avoid cracks or deformation of the casting during the cooling process.
2.2 Pouring Position Selection and Parting Surface Determination
In the sand casting process of complex structural parts, the selection of the pouring position and the determination of the parting surface are crucial, as they affect the crystallization quality and manufacturing efficiency of the casting. When the pouring direction is set with the dovetail guide surface facing down and the large plane facing up, this layout is conducive to using the gravity to promote the flow of the molten metal in the mold, helping to fill complex and elongated geometric shapes, and can also effectively avoid bubble and slag inclusion defects during the filling process, thereby improving the crystallization quality.
2.3 Pouring System Design
In the sand casting process design of complex structural parts, the design of the pouring system is a key link to ensure the quality of the casting and reduce defects, involving the position and form of the ingate and the reasonable placement of the riser. The ingate is usually designed in a stepped inclined pouring form. This method can effectively manage the flow and temperature distribution during the filling process by controlling the entry mode and speed of the molten metal, helping to achieve uniform filling and reduce sand mold damage and pore formation caused by liquid flow impact. The stepped design allows the molten metal to gradually fill each part of the cavity, optimizing the filling sequence from the bottom to the top, and preventing premature solidification and hot cracking. The setting of the riser is to capture the slag and gas that may float up during the pouring process and provide sufficient molten metal supply for the casting to avoid internal defects caused by the cooling and contraction of the molten metal. The riser is usually located at the top of the casting or above the important structure, so that the hot molten metal can continuously supply during the solidification process to ensure the integrity and performance of the key parts.
3. Complex Structural Parts Simulation Analysis
3.1 Preliminary Simulation Analysis
In the sand casting process design of complex structural parts, numerical simulation and optimization are key technical links to improve the casting quality and process efficiency. The preliminary simulation analysis using Anycasting software plays a central role. By simulating the filling process, the software can display in detail the flow path, speed, and temperature distribution of the molten metal in the mold, thereby identifying possible eddy currents, bubble generation, and cold shut areas, which are all key factors affecting the casting quality. The simulation of the solidification process provides important data on the temperature field and solidification rate of the casting during the cooling stage, helping engineers observe and predict the development of thermal stress and the tendency of shrinkage holes inside the casting, which is crucial for optimizing the structural strength of the casting and reducing subsequent processing.
When analyzing these simulation results, engineers can evaluate the effects of different pouring schemes and compare the impacts of various design changes on the filling quality and solidification uniformity. For example, if the simulation results show that the cold shut phenomenon is severe or the pores are concentrated in a certain area, the design of the pouring system may be adjusted, such as modifying the position or size of the ingate, or reconfiguring the riser to optimize the flow and solidification process of the molten metal. At the same time, the simulation can also reveal potential problems in the heat treatment and cooling process of the casting, allowing engineers to control the temperature gradient inside the casting by adjusting the cooling rate or changing the position and size of the chills, thereby optimizing the entire casting process.
3.2 Process Optimization Measures
First, adjusting the pouring system usually involves redesigning the position and shape of the ingate to improve the flow of the molten metal in the mold, avoid bubbles and slag inclusions caused by excessive speed, and ensure that each part of the casting can be filled evenly. Based on the data obtained from the simulation analysis, engineers can accurately identify the areas that perform poorly during the filling or solidification process and adjust the gating system accordingly to achieve the optimal flow of the molten metal and reduce casting defects.
Second, adding risers is to capture the floating slag and gas during the pouring process and provide additional molten metal to compensate for the solidification shrinkage. This measure is particularly important for castings with large or thick-walled parts, as these areas are more prone to shrinkage holes and porosity defects. The optimization of the configuration and size of the riser ensures that there is sufficient molten metal supplement during the solidification of the casting, thereby avoiding the generation of internal defects.
Third, the use of chills is to control the cooling speed of specific parts of the casting. By locally accelerating the cooling, the microstructure can be refined and the mechanical properties of the casting can be enhanced. Placing chills in the thicker or more complex structural areas of the casting can effectively guide the heat distribution and accelerate the solidification process of these areas, helping to reduce the internal stress and hot cracking caused by uneven cooling.
Finally, optimizing the solidification sequence of the casting is to ensure that the key structural parts of the casting solidify first by adjusting the entire casting system, such as the pouring temperature, pouring speed, and control of the cooling environment, thereby improving the structural integrity and performance of the entire casting.
4. Conclusion
In conclusion, by combining modern numerical simulation technology to optimize the traditional casting process, the casting quality and process efficiency of complex structural parts can be effectively improved, which also has a positive impact on the technological progress and sustainable development of the foundry industry. In the future, with the integration of artificial intelligence and machine learning technologies, casting process simulation will become more intelligent, able to automatically recommend the optimal casting parameters and achieve more efficient and accurate casting process design.
| Casting Method | Advantages | Disadvantages |
|---|---|---|
| Sand Casting | Low cost, high adaptability to complex shapes | Relatively low precision, possible surface defects |
| Investment Casting | High precision, good surface quality | High cost, complex process |
| Die Casting | High production efficiency, good dimensional accuracy | Limited to certain materials and shapes |
| Parameter | Value | Significance |
|---|---|---|
| Dimensional Tolerance | CT11 | Affects the function and subsequent processing of the casting |
| Mass Tolerance | MT10 | Ensures the consistency of the casting’s weight and volume |
| Shrinkage Rate | 0.9% | Avoids cracks or deformation during cooling |
| Element | Design Considerations | Function |
|---|---|---|
| Ingate | Stepped inclined pouring form | Controls the flow and temperature distribution of the molten metal |
| Riser | Located at the top or above important structures | Captures slag and gas, provides molten metal supplement |
| Chill | Placed in specific areas | Controls the cooling speed of the casting |
Table 4: Simulation Analysis Results and Optimization Measures
| Simulation Result | Optimization Measure |
|---|---|
| Severe cold shut or concentrated pores | Adjust the position or size of the ingate, reconfigure the riser |
| Non-uniform solidification | Optimize the pouring system, use chills |
| Potential heat treatment and cooling problems | Adjust the cooling rate, change the position and size of the chills |