1. Introduction
The front bearing seat is an essential component in various mechanical systems, such as automotive front suspension systems and aircraft landing gears. The upper half of the front bearing seat, being a shell-like structure, has its own unique characteristics and requirements in the casting process. This article focuses on the design and simulation optimization of the casting process for the upper half of the front bearing seat made of HT250 gray iron.
1.1 Importance of Front Bearing Seat
The front bearing seat plays a crucial role in maintaining the stability of the wheel and suspension system connection. It provides support for the wheel and the bearing for its movement, ensuring a smooth and comfortable ride in vehicles. In aircraft, it is equally important for the proper functioning of the landing gear.
1.2 Significance of Casting Process Optimization
To produce a high-quality front bearing seat upper half casting, it is necessary to optimize the casting process. This helps in avoiding defects such as shrinkage cavities, porosity, and gas holes, which can affect the performance and durability of the final product.
2. Part Analysis
2.1 Structural Characteristics
The upper half of the front bearing seat has a three-dimensional structure with an outer dimension of . It has a maximum wall thickness of and a minimum wall thickness of , with a net weight of . The cavity structure is complex, and the metal liquid filling process is difficult. The part has a relatively symmetric overall structure, and both the upper and lower large planes are important machining surfaces. The injection hole is an elongated arc-shaped cavity, which makes the sand core vulnerable during metal liquid filling.
2.2 Technical Requirements
The casting is required to have no defects such as shrinkage cavities, porosity, gas holes, and sand inclusions that affect its performance. It is a medium-sized casting produced in small batches, and the manual molding production method is adopted. The molding material selected is furan-urea aldehyde resin sand with high bonding strength, good heat resistance, and low gas generation.
2.3 Process Parameters
The following are the selected casting process parameters:
| Parameter | Value |
|---|---|
| Dimension tolerance grade | CT13 |
| Machining allowance | G |
| Casting shrinkage rate | 0.9% |
| Cutting allowance for pouring and riser | |
| Cooling time | 1 h |
3. Casting Process Design
3.1 Pouring Position and Parting Surface Selection
Two pouring positions and parting surfaces were considered.
| Scheme | Advantages | Disadvantages |
|---|---|---|
| Scheme One | Ensures the accuracy of the bearing groove, convenient for mold closing, stable filling, and avoids uneven pouring | Results in low surface accuracy of the bearing base, requires additional machining allowance, and has a large number of thick walls at the bottom, prone to forming hot spots |
| Scheme Two | Places the bearing seat bottom at the bottom, ensuring the accuracy of the bearing seat bottom, and preventing sand holes, gas holes, and slag inclusions | Requires flipping the upper sand box during mold closing, which may damage the sand mold |
After comparison, Scheme Two was chosen as it is more favorable for the overall quality of the casting.
3.2 Pouring System Design
3.2.1 Type Selection
A bottom-injection pouring system with a semi-closed type was selected. This type of pouring system ensures stable metal liquid filling, smooth exhaust, good slag blocking ability, and can regulate the temperature field during solidification, reducing casting defects. The area ratio of each runner was selected as 直横内.
3.2.2 Calculation of Restricted Flow Section
The pouring time was calculated to be . The height of the straight runner and the minimum cross-sectional area of the pouring system were also calculated. The straight runner has a height requirement to ensure sufficient pressure for clear casting contours. The minimum cross-sectional area was calculated using relevant formulas, and the resulting value was .
3.2.3 Design of Each Runner Size
Based on the area ratio and calculations, the dimensions of the straight runner, cross runner, and inner runner were determined as follows:
| Runner | Dimensions |
|---|---|
| Straight Runner | Area: , Small diameter: , Large diameter: , Length: about |
| Cross Runner | Total area: , Two trapezoidal cross runners, one with an area of |
| Inner Runner | Total area: , Four trapezoidal inner runners, one with an area of |
3.2.4 Design of Sprue Cup
A pool-type sprue cup was adopted with a capacity of and specific dimensions as follows:
| Dimension | Value |
|---|---|
| A | (mm) |
| B | (mm) |
| I | (mm) |
| H | (mm) |
| H1 | (mm) |
| d | (mm) |
| a | (mm) |
| R | (mm) |
| R1 | (mm) |
| H2 | (mm) |
4. Casting Process Simulation and Analysis
4.1 Simulation Setup
The UG three-dimensional modeling software was used for entity drawing, and the model was imported into ProCAST for mesh division. The pouring temperature was set to , and the pouring time was .
4.2 Simulation Results and Analysis
4.2.1 Filling Process
The metal liquid entered the casting at around and filled the bottom of the casting at around . The entire cavity was filled in . The filling speed field and temperature field were analyzed. It was found that there was no convection between the two sides of the casting at the beginning, but convection occurred in the middle ring. The gas was concentrated at the top of the casting. The temperature of the thin-walled part at the top of the casting was low during filling, and an overheated area was formed in the middle part between the square hole and the casting base.
4.2.2 Solidification Process Defect Analysis
Defects mainly existed in four places: on the three small bosses on the right side of the top, on the thicker boss at the top, at the overheated area between the side hole and the base of the casting, and in the pouring system. The volume percentage of shrinkage cavities was calculated to be . The top of the casting was thick, and there was a depression phenomenon due to insufficient shrinkage compensation, and a hot spot was present as it was the last part to solidify.
5. Optimization of Casting Process
5.1 First Optimization
5.1.1 Preliminary Design and Calculation of Riser
The size of the riser was calculated based on relevant formulas. According to the design principles of the top-open riser for gray iron parts, the size of the riser was determined. Three risers were set on the left boss, and one riser was set on the right boss.
| Location | Riser Dimensions (, ) |
|---|---|
| Left Boss | About , |
| Right Boss | About , |
5.1.2 Position Design of Cold Iron
Cold iron was designed to be placed at the center of the two square holes on both sides of the casting and the bearing base. The thickness and length of the cold iron were calculated, and the thickness was , and the length was .
5.2 First Optimization Results and Analysis
After the first optimization by adding risers, the number of defects decreased significantly. However, there were still some problems: there were still obvious defects on both sides of the casting; the distribution of risers was unreasonable, resulting in slow solidification and shrinkage porosity on the right small boss at the top; the number of risers on the top was a bit too many, causing slow solidification and a hot spot, and the size of the left riser was too small.
5.3 Second Optimization
5.3.1 Adjustment of Cold Iron and Riser
The number of cold irons was increased from two to four. Two small risers were added on the other two small bosses at the top, and the three risers on the larger boss were combined into two risers with an increased size.
| Location | Riser Dimensions (, ) |
|---|---|
| Left Boss (adjusted) | About , |
| Right Boss (adjusted) | About , |
6. Discussion on the Impact of Process Parameters on Casting Quality
6.1 Pouring Temperature
The pouring temperature of was selected for this casting process. A higher pouring temperature can improve the fluidity of the metal liquid, making it easier to fill the complex cavity of the casting. However, if the pouring temperature is too high, it may lead to excessive oxidation of the metal liquid, resulting in defects such as gas holes and inclusions. On the other hand, a lower pouring temperature may cause the metal liquid to solidify prematurely, resulting in incomplete filling of the cavity.
6.2 Pouring Time
The calculated pouring time was . An appropriate pouring time is crucial for ensuring the quality of the casting. If the pouring time is too short, the metal liquid may not be able to fill the cavity evenly, resulting in defects such as misruns and cold shuts. If the pouring time is too long, the metal liquid may be exposed to air for a longer time, increasing the risk of oxidation and gas hole formation.
6.3 Cooling Rate
The cooling rate of the casting affects the solidification process and the formation of defects. A faster cooling rate can help to reduce the formation of shrinkage cavities and porosity by promoting a more directional solidification. However, if the cooling rate is too fast, it may cause thermal stress in the casting, leading to cracking and distortion. The addition of cold irons in the casting process helps to control the cooling rate and improve the solidification quality.
7. Comparison with Other Casting Processes
7.1 Sand Casting vs. Die Casting
Sand casting, as used in this study for the front bearing seat upper half, has several advantages. It is a versatile process suitable for a wide range of part sizes and geometries, including complex structures like the front bearing seat. It also has relatively lower tooling costs compared to die casting. However, die casting offers higher production rates and better dimensional accuracy for some parts. The choice between sand casting and die casting depends on factors such as production volume, part complexity, and cost requirements.
7.2 Gray Iron Casting vs. Other Alloys
Gray iron, specifically HT250 in this case, was chosen for its good casting properties, mechanical performance, and cost-effectiveness. Compared to other alloys such as aluminum alloys or steel alloys, gray iron has better vibration damping properties and is more suitable for applications where shock absorption is important, like in the front bearing seat. However, other alloys may offer higher strength or better corrosion resistance in different applications.
8. Future Research Directions
8.1 Optimization of Casting Process for Different Materials
The current research focused on the casting process optimization for HT250 gray iron. Future studies could explore the optimization of casting processes for other materials, such as advanced alloys with higher strength and better performance characteristics. This would involve understanding the unique properties of these materials and adapting the casting process parameters accordingly.
8.2 Incorporation of Advanced Simulation Techniques
While ProCAST was used for the numerical simulation in this study, there is room for improvement in simulation accuracy and efficiency. Future research could explore the incorporation of more advanced simulation techniques, such as multi-scale simulations or real-time simulations, to better predict the casting behavior and optimize the process further.
8.3 Application of Additive Manufacturing in Casting
Additive manufacturing has the potential to revolutionize the casting industry. Future research could investigate the integration of additive manufacturing techniques with traditional casting processes. For example, using 3D printed molds or cores could offer more design flexibility and potentially improve the quality of the casting.
9. Summary
The casting process for the upper half of the front bearing seat has been thoroughly studied and optimized. The process design, including the selection of pouring position, parting surface, pouring system, and the addition and optimization of risers and cold irons, was based on the analysis of the part’s structure and technical requirements. The simulation results provided valuable insights into the filling and solidification processes, enabling the identification and elimination of defects. The final casting process scheme achieved a high-quality casting with minimal defects. Future research directions offer opportunities for further improvement and innovation in the casting field.
In conclusion, the optimization of the casting process for the upper half of the front bearing seat is an important step towards ensuring the performance and reliability of this critical component. By continuously exploring and improving the casting process, we can meet the evolving demands of various industries and contribute to the development of high-quality mechanical products.
