1. Introduction
The automotive industry is constantly evolving, with components like the differential housing playing a crucial role in vehicle performance. Nodular cast iron differential housing, known for its excellent mechanical properties, has become a popular choice. This article delves deep into the casting technology development of nodular cast iron differential housing, covering aspects from its technical requirements to the final production results.
1.1 Significance of Differential Housing in Vehicles
The differential housing is a key part in the vehicle’s drivetrain. It houses the differential gears, which are responsible for allowing the wheels to rotate at different speeds during turns. This ensures smooth driving, reduces tire wear, and improves overall vehicle handling. A well – designed and properly cast differential housing is essential for the reliable operation of the vehicle.
1.2 Overview of Nodular Cast Iron as a Material
Nodular cast iron, also known as ductile iron, has unique characteristics. It contains graphite in a nodular or spherical form, which gives it better ductility, toughness, and strength compared to other cast irons. These properties make it highly suitable for applications like differential housing, where it can withstand mechanical stresses during vehicle operation.
2. Technical Requirements of the Differential Housing
2.1 Design and Dimensional Specifications
The 分体式 9AT differential housing has a distinct design. As shown in Figure 1 (please insert an image of the differential housing here, similar to the one in the original document), it has 4 windows and 3 pin holes, unlike the conventional design with 2 windows and 2 pin holes. Additionally, it features 3 non – symmetric bosses on the flange surface. The 成品单件设计重量 is 2.32 kg, and the 毛坯单件设计重量 is 3.32 kg. The diameter reaches 161 mm, and the 毛坯法兰厚度 is 8.3 mm. The dimensional tolerances adhere to ISO 8062 – CT9, and the casting has a strict 错边要求 ≤0.5 mm. These specifications pose challenges in the casting process, as any deviation can affect the functionality and fit of the part in the vehicle.
| Design Feature | Specification |
|---|---|
| Number of Windows | 4 |
| Number of Pin Holes | 3 |
| Bosses on Flange | 3 non – symmetric |
| Finished Part Weight | 2.32 kg |
| 毛坯单件设计重量 | 3.32 kg |
| Diameter | 161 mm |
| 毛坯法兰厚度 | 8.3 mm |
| Dimensional Tolerance | ISO 8062 – CT9 |
| 错边要求 | ≤0.5 mm |
2.2 Material and Chemical Composition Requirements
The material used for the differential housing is QT600 – M (企业标准). The chemical composition requirements are precisely defined, as shown in Table 1. Each element in the composition plays a vital role in determining the material’s properties. For example, carbon (C) affects the strength and hardness, while silicon (Si) influences the graphite formation and mechanical properties.
| Element | Content (Mass Fraction, %) |
|---|---|
| C | 3.3 – 3.9 |
| S | ≤0.02 |
| Si | 1.8 – 3.0 |
| Mn | 0.2 – 1.0 |
| P | ≤0.06 |
| Cu | 0.2 – 1.0 |
| Ti | ≤0.06 |
| Sn | ≤0.06 |
| Mg | 0.027 – 0.06 |
2.3 Mechanical and Metallurgical Property Requirements
The differential housing must meet specific mechanical and metallurgical property requirements. The mechanical properties, such as tensile strength, yield strength, elongation, and hardness, are crucial for its performance under load. The metallurgical properties, including 球化率，graphite type, 珠光体 percentage, and the limit of 碳化物 and 磷共晶，ensure the material’s integrity and durability. These requirements are detailed in Table 2.
| Property | Requirement |
|---|---|
| Tensile Strength /MPa | ≥650 |
| Yield Strength /MPa | ≥405 |
| Elongation (%) | ≥3 |
| Hardness (HBW) | 200 – 265 |
| 球化率 (%) | ≥80 |
| Graphite Type | V + VI |
| 珠光体 (%) | ≥55 |
| 碳化物和磷共晶 (%) | ≤3 |
2.4 Defect Requirements
Both internal and external defect requirements are strict for the differential housing. External defects are allowed within certain limits depending on the surface type (关键加工面，非关键加工面，and 毛坯面). Internal defects, such as porosity, must meet the D3/1 requirement, which means the defect area should be less than 3% of the maximum square area of the cross – section, and the maximum diameter of a single defect should be less than 1 mm. Additionally, 100% X – ray 探伤 is required at the sample stage, and it should meet ASTM E – 446 ≤level2. The customer also conducts CT 检测 on the processed product to ensure compliance with the internal defect requirements.
| Surface Type | Defect Allowance |
|---|---|
| 关键加工面 | Diameter ≤1 mm, Depth ≤1 mm |
| 非关键加工面 | Diameter ≤3 mm, Depth ≤1 mm |
| 毛坯面 | Diameter ≤4 mm, Depth ≤1 mm (visible bottom hole – like defects) |
| Internal Defects | Porosity meets D3/1, X – ray 探伤 meets ASTM E – 446 ≤level2 |
3. Initial Process Design
3.1 Riser Design
Considering the thin flange design, multiple windows and pin holes, and high – porosity requirements, the initial process design adopted a double – riser scheme. As shown in Figure 3 (please insert the corresponding figure here), two risers were placed at the flange positions corresponding to two of the pin holes. To improve the process yield, rectangular risers were designed with large rounded corners (R10) at the edges to reduce weight. A total of 3 risers were used for 2 castings, with the two single – use risers on the sides having dimensions of 120 mm×43 mm×50 mm. The riser neck was designed to be as large as possible, with a height of 7.7 mm (after removing 0.5 mm of the separation stop), a length of 55 mm, and a cross – sectional area of 423 mm². A 15 – mm – high weight – reducing pressure groove was designed at the top of the riser, and a 15 – mm – high separation block was added at the bottom. The single – use riser on the side had a weight of 2.1 kg and a modulus of 6 mm. The middle common riser was designed with reference to the single – use riser, with dimensions of 120 mm×55 mm×50 mm, a 15 – mm – high bottom pressure groove, and a 15 – mm – high separation block.
3.2 Gating System Design
To enhance the appearance quality of the differential housing, a lap – joint gating system was designed. The vertical and horizontal runners were lapped once, the vertical runners were further lapped through 6 – mm – thick flakes, and finally, the inner runner was lapped with the vertical runner. This multi – lap design, along with the use of thin and wide runners, served the purposes of flow restriction and slag – blocking. The inner runner introduced the molten iron from the bottom of the riser, which reduced the impact of the molten iron flow on the sand mold and prevented impurities from entering the casting cavity during the filling process.
3.3 Other Process Measures
To address the shrinkage porosity in the shaft head area, an innovative shaft head filling process was employed. Instead of fully filling the shaft head, only 60% of it was filled. Given the total shaft head height of 48 mm, filling 29 mm was sufficient to meet the requirements. This not only reduced the sand core consumption but also ensured that the shrinkage porosity in the shaft head could be removed by subsequent machining. The inner diameter of the shaft head cavity was ϕ39 mm, and part of it was formed by the outer mold with a 14 – mm – wide outer mold formation for easy mold removal, along with a 15° draft angle. Additionally, a 0.5 – mm – thick thickness subsidy was added to the flange position corresponding to the riser to improve casting feeding. Cold pins with dimensions of ϕ6 mm×25 mm and a 3° draft angle were also set at the pin hole positions.
4. Simulation and Optimization of the Process
4.1 Simulation of Shrinkage Cavity and Porosity Defects
The initial process design was simulated to predict shrinkage cavity and porosity defects. The simulation results, as shown in Figure 4 (please insert the figure here), indicated that there were shrinkage cavities in the pin hole positions (2.6 mm³ and 11.0 mm³), the flange position (0.7 mm³), and the blocked shaft head position (which could be machined away). To meet the requirement of zero – simulated internal shrinkage cavity defects, the process was further optimized.
4.2 Process Adjustment and Re – simulation
The casting was rotated 90°, which changed the relative positions of the bosses, risers, and pin holes. The new position placed two of the three bosses closer to the riser, and the riser was now facing the window instead of the pin hole. The cold pins were also removed. After these adjustments, the new process was simulated. The results, as shown in Figure 6, demonstrated that there were no shrinkage cavities in the pin hole and other critical positions. The shrinkage cavity in the blocked shaft head position was 77.8 – 80.00 mm³, which could be removed by machining.
5. Sample Trial – Production and Improvement
5.1 Problems Encountered during Trial – Production
During the trial – production using the optimized process, several issues were identified. The pouring time was long and unstable, ranging from 13 – 16 s, which affected the production rhythm of the molding line. Although the appearance, dimensions, full – mold material, and porosity of the samples passed the inspection, and 100% X – ray inspection showed no internal defects, and the third – party CT inspection by the client was also satisfactory, the long pouring time and low process yield (only 36.7%) were concerns that needed to be addressed.
5.2 Process Optimization Measures
To solve the problems, a series of optimization measures were implemented. First, considering the influence of gas generated during the pouring process due to the large volume of the sand core, exhaust sheets were added to the horizontal runner, and the bottom of the exhaust sheet was made into a separation block. Second, to increase the process yield, two sections of vertical runners were removed, and the horizontal runner was lightened. The inner runner was changed to enter the iron from the top of the riser, and a lap – joint treatment was carried out on the inlet riser inner runner.
5.3 Results of Process Improvement
After the improvement, the simulated pouring filling time was 8.539 s, and the actual production pouring filling time was 10.2 – 10.3 s, which met the requirements of the production line. The process yield increased from 36.7% to 42.7%. The increase in the process yield was mainly due to the reduction of the runner and the optimization of the gating system, although the overall yield was still affected by the large diameter and thin thickness of the casting, which required more risers for feeding to meet the internal defect requirements.
6. Mass Production and Quality Control
6.1 Mass Production Results
The differential housing entered mass production after successful trial – production and improvement. In a certain month, 1887 pieces were inspected for appearance, and 62 pieces were rejected, resulting in a qualification rate of 96.71%. The main reasons for rejection were appearance sand holes (37 pieces, with a rejection rate of 1.96%), 磕碰伤 (18 pieces, with a rejection rate of 0.95%), and unclear casting characters after shot – blasting (7 pieces, with a rejection rate of 0.37%). The processing rejection rate at the client’s end was less than 1%, achieving the product development goals.
6.2 Quality Control Measures
To maintain the high – quality production of the differential housing, strict quality control measures were implemented. Regular inspections were carried out during the production process, including inspections of the raw materials, the casting process parameters, and the final product quality. The use of advanced inspection equipment, such as X – ray and CT scanners, ensured that the internal defects met the requirements. Any deviation from the quality standards was promptly identified and corrected to prevent defective products from entering the market.
7. Conclusion
The development of the casting technology for nodular cast iron differential housing is a complex and multi – step process. By meeting the strict technical requirements, through continuous process design, simulation, optimization, and improvement, high – quality differential housings can be produced. The final product not only meets the performance requirements of the automotive industry but also has a high qualification rate in mass production. This development process provides valuable experience for the production of similar castings and promotes the development of the casting industry.
In the future, with the continuous development of automotive technology and the increasing demand for high – performance components, further research and improvement in the casting technology of differential housing are expected. This may involve exploring new materials, improving the casting process, and enhancing the quality control system to meet the ever – growing challenges in the automotive market.
8. Future Outlook and Research Directions
8.1 New Material Exploration
As the automotive industry trends towards lightweight and high – performance, exploring new materials for differential housing casting becomes crucial. Advanced high – strength alloys or composite materials with lower density and better mechanical properties could be considered. For example, aluminum – based composites reinforced with ceramic particles might offer a combination of low weight and high strength, which could potentially reduce the overall weight of the vehicle while maintaining or even improving the performance of the differential housing.
8.2 Process Improvement
The casting process can be further optimized. Advanced casting techniques such as vacuum casting or precision casting could be explored. Vacuum casting can reduce the presence of gas – related defects by removing air from the casting environment, while precision casting can improve the dimensional accuracy and surface finish of the differential housing, reducing the need for post – processing and improving production efficiency.
8.3 Quality Control System Enhancement
The quality control system can be enhanced with the application of artificial intelligence and machine learning technologies. These technologies can analyze large amounts of production data in real – time, predict potential quality issues, and adjust the production process accordingly. For example, by monitoring the temperature, pressure, and flow rate data during casting, machine learning algorithms can detect early signs of defects and alert operators to take corrective actions, ensuring consistent product quality.
9. Industry Impact and Significance
9.1 Contribution to the Automotive Industry
The successful development of nodular cast iron differential housing casting technology contributes significantly to the automotive industry. High – quality differential housings ensure the reliable operation of vehicles, improving vehicle safety and performance. The increased production efficiency and reduced cost through process optimization also help automotive manufacturers to be more competitive in the market.
9.2 Promotion of the Casting Industry Development
This technology development sets a good example for the casting industry. The innovative process design, simulation – based optimization, and quality control methods can be applied to the production of other castings. It promotes the overall technological progress of the casting industry, enabling it to meet the growing demands of various industries for high – quality castings.
10. Conclusion
The development of nodular cast iron differential housing casting technology is a comprehensive project that involves multiple aspects from technical requirements to production and quality control. Through continuous efforts in process design, simulation, trial – production, and improvement, high – quality products with high qualification rates can be achieved. Looking ahead, further exploration in new materials, process improvement, and quality control system enhancement will drive the continuous development of this technology, bringing more benefits to the automotive and casting industries.
