With the rapid development of new energy vehicles, lightweight automotive components have become crucial for extending driving range. This study proposes an integrated precision investment casting process for aluminum alloy door bodies, replacing traditional stamping-welding methods. Through finite element analysis and process optimization, we systematically investigated structural performance, wax pattern formation, and casting parameters to achieve high-quality thin-walled castings.
1. Structural Performance Analysis
The door body structure was evaluated through modal and stiffness analysis using HyperMesh and ANSYS. The first-order natural frequency of 42.2 Hz exceeded typical vehicle excitation frequencies (1-30 Hz), preventing resonance. Key stiffness metrics met automotive standards:
| Stiffness Type | Max Deformation (mm) | Stiffness Value (N/mm) |
|---|---|---|
| Sagging | 2.7 | 296.3 |
| Torsional | 4.8 | 187.5 |
| Window Frame | 3.3 | 60.7 |
The modal analysis equation was expressed as:
$$[M]\{\ddot{x}\} + [C]\{\dot{x}\} + [K]\{x\} = \{f(t)\}$$
Where [M], [C], and [K] represent mass, damping, and stiffness matrices respectively.
2. Wax Pattern Optimization
Using Moldflow analysis, four gating systems were compared for precision investment casting:
| Scheme | Gates | Fill Time (s) | Shrinkage (%) |
|---|---|---|---|
| 1 | 3 | 7.275 | 5.138 |
| 2 | 5 | 7.299 | 5.180 |
| 3 | 7 | 7.295 | 5.242 |
| 4 | 10 | 7.313 | 5.211 |
Orthogonal experiments revealed optimal parameters:
$$\text{Shrinkage} = 3.863\% \text{ at } T_{\text{melt}}=56^\circ\text{C}, T_{\text{mold}}=33^\circ\text{C}, t_{\text{injection}}=8\text{s}$$
3. Precision Investment Casting Process
The low-pressure casting parameters were calculated as:
| Stage | Pressure (kPa) | Time (s) |
|---|---|---|
| Lifting | 21.84 | 8 |
| Filling | 49.4 | 8.3 |
| Pressurization | 98.8 | 4.94 |
The casting system design followed:
$$A_{\text{gate}} = \frac{G}{\rho vt} = 48 \text{ cm}^2$$
Where G=13.6kg, ρ=2.7g/cm³, v=120mm/s, t=8.3s.
4. Process Optimization
Liquid nitrogen spot cooling reduced shrinkage defects by 66.6%:
| Condition | Porosity Volume (cm³) |
|---|---|
| Initial | 14.68 |
| Optimized | 4.9 |
The cooling efficiency equation demonstrates:
$$G_{\text{LN2}} = \frac{\rho(V_0-V_1)(L+\Delta H)}{c\Delta t}$$
Where L=199kJ/kg (latent heat), ΔH=397kJ/kg (superheat).
5. Conclusion
This precision investment casting approach achieves 13.6kg door bodies with 1.5-3mm wall thickness, demonstrating 296.3N/mm stiffness and 42.2Hz natural frequency. The integrated process reduces production steps by 60% compared to traditional methods while maintaining structural integrity. Future work will focus on grain structure optimization and oxidation control during casting.