Abstract
This paper focuses on the design and optimization of the investment casting process for the rear floor of a car. Through structural analysis, performance testing, and process parameter optimization, a reasonable casting process is proposed, and the casting quality is improved. The research content includes structural analysis, wax pattern process design, low-pressure investment casting process design, and optimization. The results show that the designed process can meet the requirements of the rear floor and has certain innovation and practical value.
1. Introduction
1.1 Research Background and Significance
1.1.1 Research Background
With the development of the automotive industry, lightweight and high-strength materials are increasingly used. Aluminum alloy, with its advantages of low density, good thermal conductivity, and corrosion resistance, is widely used in automotive manufacturing. The rear floor of a car is an important part of the vehicle body, and its lightweight and high-strength requirements are becoming more and more prominent. At the same time, with the development of precision casting technology, investment casting has become an important method for manufacturing complex parts with high precision and good surface quality.
1.1.2 Research Significance
The research on the investment casting process of the rear floor of a car can improve the manufacturing accuracy and mechanical properties of the rear floor, and reduce the manufacturing cost and production cycle. At the same time, it can also provide a reference for the design and manufacturing of other automotive parts, and promote the development of the automotive industry.
1.2 Research Status at Home and Abroad
1.2.1 Forming Process of Car Rear Floor
The traditional forming process of the rear floor of a car is stamping and welding, which has the disadvantages of low production efficiency and poor product quality. In recent years, with the development of integrated forming technology, the rear floor of a car is increasingly manufactured by casting. At present, the casting processes used for the rear floor of a car mainly include die casting and investment casting. Die casting has the advantages of high production efficiency and good product quality, but it also has the disadvantages of high equipment investment and large die cost. Investment casting has the advantages of high precision and good surface quality, but it also has the disadvantages of long production cycle and high cost.
1.2.2 Investment Casting Process
Investment casting is a precision casting method that uses a soluble wax pattern to make a mold shell, and then pours molten metal into the mold shell to obtain a casting. The investment casting process has the advantages of high precision, good surface quality, and the ability to manufacture complex parts. However, the investment casting process also has the disadvantages of long production cycle, high cost, and difficult process control.
1.2.3 Numerical Simulation of Casting Process
Numerical simulation of the casting process is a computer-aided engineering technology that uses numerical simulation methods to simulate the filling, solidification, and cooling processes of molten metal in the mold cavity, and predicts the quality and performance of the casting. Numerical simulation of the casting process can help engineers optimize the casting process, improve the quality and performance of the casting, and reduce the cost and production cycle of the casting.
1.3 Research Contents and Methods
1.3.1 Research Contents
This paper mainly studies the investment casting process of the rear floor of a car, including the structural design of the rear floor, the design and optimization of the wax pattern process, the design and optimization of the low-pressure investment casting process, and the numerical simulation and experimental verification of the casting process.
1.3.2 Research Methods
This paper uses theoretical analysis, numerical simulation, and experimental verification methods to study the investment casting process of the rear floor of a car. The theoretical analysis method is used to study the structural characteristics and mechanical properties of the rear floor, and to establish a mathematical model of the casting process. The numerical simulation method is used to simulate the filling, solidification, and cooling processes of molten metal in the mold cavity, and to predict the quality and performance of the casting. The experimental verification method is used to verify the accuracy and reliability of the numerical simulation results, and to optimize the casting process parameters.
2. Structural Analysis and Performance Testing of Car Rear Floor
2.1 Structural Analysis of Car Rear Floor
The rear floor of a car is an important part of the vehicle body, which is mainly composed of a front crossbeam, a middle crossbeam, a rear crossbeam, and two longitudinal beams. The structural design of the rear floor should meet the requirements of strength, stiffness, and durability. In this paper, the structural characteristics of the rear floor of a car are analyzed by using SolidWorks software, and the finite element model of the rear floor is established by using HyperMesh software.
2.1.1 Geometric Model of Car Rear Floor
The geometric model of the rear floor of a car. The rear floor of a car is a complex thin-walled structure with many holes and grooves. The size of the rear floor is 1564mm * 1456mm * 619mm, and the average wall thickness is 3mm. The minimum wall thickness is 2.8mm, and the maximum wall thickness is 6mm.
2.1.2 Finite Element Model of Car Rear Floor
The finite element model of the rear floor of a car. The finite element model of the rear floor is established by using HyperMesh software. The element type of the finite element model is a triangular shell element, and the number of elements is 15452497. The material of the rear floor is ZL114A aluminum alloy, and the material properties are shown in Table 2.1.
Table 2.1 Material properties of ZL114A aluminum alloy
| Property | Value |
|---|---|
| Density (ρ) / (kg/m^3) | 2700 |
| Elastic modulus (E) / MPa | 69000 |
| Poisson’s ratio (v) | 0.36 |
2.2 Performance Testing of Car Rear Floor
The performance of the rear floor of a car mainly includes static performance and dynamic performance. The static performance of the rear floor mainly includes strength and stiffness, and the dynamic performance of the rear floor mainly includes modal analysis and vibration response analysis. In this paper, the static and dynamic performance of the rear floor of a car is tested by using ANSYS Workbench software.
2.2.1 Static Performance Testing
The static performance of the rear floor of a car is tested by using the static analysis module of ANSYS Workbench software. The loading conditions of the static performance test include bending load and torsional load. The bending load is applied to the rear floor by using a concentrated load and a uniform load, and the torsional load is applied to the rear floor by using a torque. The results of the static performance test Table 2.2.
Table 2.2 Results of static performance test
| Loading Condition | Maximum Deformation / mm | Maximum Stress / MPa |
|---|---|---|
| Bending Load | 2.23 | 82 |
| Torsional Load | 3.60 | 111 |
2.2.2 Dynamic Performance Testing
The dynamic performance of the rear floor of a car is tested by using the modal analysis module of ANSYS Workbench software. The first 16 natural frequencies and vibration modes of the rear floor are obtained by using the modal analysis module. The results of the modal analysis Table 2.3.
Table 2.3 Natural frequencies and vibration modes of car rear floor
| Mode Order | Natural Frequency / Hz | Vibration Mode |
|---|---|---|
| 1 | 0 | – |
| 2 | 0 | – |
| 3 | 6.7353E-006 | – |
| 4 | 7.9072E-005 | – |
| 5 | 1.1083E-004 | – |
| 6 | 1.891E-003 | – |
| 7 | 24.485 | Rear floor edge vibration |
| 8 | 63.891 | Middle vibration of front crossbeam of rear floor |
| 9 | 87.769 | Vibration on both sides of rear crossbeam of rear floor |
| 10 | 91.332 | Middle vibration of rear crossbeam of rear floor |
| 11 | 95.652 | Middle vibration of rear crossbeam of rear floor |
| 12 | 131.84 | Vibration on both sides of front crossbeam of rear floor |
| 13 | 146.45 | Middle vibration of rear crossbeam of rear floor |
| 14 | 163.39 | Rear floor edge vibration |
| 15 | 178.79 | Vibration on both sides and edge of rear crossbeam of rear floor |
| 16 | 189.25 | Middle vibration of rear crossbeam of rear floor |
3. Wax Pattern Process Design for Car Rear Floor
3.1 Pretreatment of Wax Pattern
The pretreatment of the wax pattern mainly includes grid division and material selection. In this paper, the grid division of the wax pattern is carried out by using HyperMesh software, and the material of the wax pattern is selected as F28 – 448 medium temperature wax.
3.1.1 Grid Division of Wax Pattern
The grid division of the wax pattern is carried out by using HyperMesh software. The grid type of the wax pattern is a double-layer grid, and the grid size is 2mm. The grid division result of the wax pattern.
3.1.2 Material Selection of Wax Pattern
The material of the wax pattern is selected as F28 – 448 medium temperature wax. The performance parameters of F28 – 448 medium temperature wax are shown in Table 3.1.
Table 3.1 Performance parameters of F28 – 448 medium temperature wax
| Performance | Parameter |
|---|---|
| Density of molten state (ρm) / (g/cm^3) | 1.0561 |
| Density of solid state (ρs) / (g/cm^3) | 1.1194 |
| Melt temperature range / °C | 61 – 66 |
| Mold temperature range / °C | 25 – 35 |
| Maximum shear rate (γmax) / (S^-1) | 40000 |
| Maximum shear stress (τmax) / MPa | 0.41 |
| Ejection temperature / °C | 30 |
| Transformation temperature / °C | 55 |
3.2 Process Design of Wax Pattern
The process design of the wax pattern mainly includes the design of the gating system and the cooling system. In this paper, the gating system of the wax pattern is designed by using Moldflow software, and the cooling system of the wax pattern is designed by using the cooling circuit module of Moldflow software.
3.2.1 Design of Gating System
The gating system of the wax pattern is designed by using Moldflow software. The gating system of the wax pattern mainly includes the sprue, the runner, and the gate. The design results of the gating system of the wax pattern Table 3.2.
Table 3.2 Design parameters of gating system of wax pattern
| Component | Parameter |
|---|---|
| Sprue diameter / mm | 16 (start), 18 (end) |
| Sprue length / mm | 80 |
| Runner type | Trapezoidal |
| Runner top length / mm | 20 |
| Runner bottom length / mm | 16 |
| Runner height / mm | 14 |
| Gate type | Point gate |
| Gate diameter / mm | 8 |
| Gate height / mm | 8 |
3.2.2 Design of Cooling System
The cooling system of the wax pattern is designed to ensure uniform cooling and minimize warpage. The cooling water pipe diameter is determined based on the wax pattern thickness, and the layout is optimized to achieve efficient heat transfer. The cooling water pump is selected to provide sufficient coolant flow rate. The cooling system design is evaluated by analyzing the coolant temperature distribution and the resulting warpage of the wax pattern. The goal is to achieve a balance between rapid cooling and minimizing internal stresses.
The coolant temperature distribution in the cooling circuit. It can be observed that the coolant temperature varies along the cooling path, which affects the cooling rate of different parts of the wax pattern. Areas with higher coolant temperature may experience slower cooling, leading to potential warpage issues.
To evaluate the impact of cooling on the wax pattern quality, the warpage deformation is analyzed. The warpage can be caused by uneven cooling, shrinkage differences, or orientation effects. In this case, the wax pattern material F28 – 448 is less prone to orientation deformation. The warpage deformation due to uneven cooling and shrinkage.
It can be seen that the maximum warpage due to uneven cooling is 0.55mm, mainly occurring in the red regions where the cooling effect is relatively poor. This indicates that the cooling water pipe layout in these areas may need to be optimized.That the maximum warpage due to shrinkage differences reaches 9.592mm, which is more significant. This is because the wax pattern is large, and the shrinkage varies greatly at different positions, especially in areas far from the gate. Considering this, it may be necessary to adjust the gate design, such as increasing the number of gates or optimizing their positions, to improve the filling and cooling uniformity and reduce shrinkage differences.
In summary, the cooling system design for the wax pattern of the car rear floor is crucial for obtaining a high-quality wax pattern with minimal warpage. The analysis of coolant temperature distribution and warpage deformation provides valuable insights for further optimizing the cooling system to meet the requirements of investment casting.