Abstract
The lightweight design of automotive components significantly contributes to the overall vehicle lightweighting, enhancing product quality and aiding enterprises in achieving cost reduction and efficiency gains. This article delves into the innovative optimization design of an integrated die-casting subframe for a new energy vehicle. The study adopts two primary lightweighting methods: structural lightweighting and process lightweighting. By replacing the traditional welding process with an integrated die-casting process, a comprehensive analysis of the splice-welded subframe is conducted. The stiffness, strength, modal, and dynamic stiffness performances are extracted as the optimization objectives and constraints. Using MMO (Multi-Model Optimization) technology, the compliance and mass objectives are integrated for topology optimization. The optimized structure undergoes further parameter optimization to determine the optimal thickness. The results indicate notable improvements in the subframe’s performance, weight reduction, and cost savings.
1. Introduction
The subframe, a core component of the automotive chassis, serves crucial roles in load-bearing and vibration isolation. Its optimization aims to enhance the vehicle’s structural strength, stiffness, and safety while achieving weight reduction. This article explores the technical routes for the optimization design of the subframe structure, focusing on the integration of die-casting technology, to provide valuable insights into subframe structural design.
Structural optimization, leveraging computer technology and numerical simulation methods, involves refining the shape, size, and material of engineering structures based on specific objectives and constraints. The goal is to maximize structural lightweighting while ensuring design requirements are met, thereby improving relevant performance indicators.
2. Optimization Objectives and Constraints
The optimization of the subframe structure commences with a comprehensive analysis of the existing splice-welded subframe. Key performance indicators, including stiffness, strength, modal, and dynamic stiffness, are identified as objectives and constraints for the optimization process.
2.1 Finite Element Analysis of the Splice-Welded Subframe
A finite element analysis (FEA) is conducted to assess the current performance of the splice-welded subframe.
Table 1: Strength Analysis Results of the Splice-Welded Subframe
| Condition | Maximum Stress (MPa) |
|---|---|
| Condition 1 | 1141.3 |
| Condition 5 | 303.4 |
| Condition 6 | 269.0 |
| Condition 9 | 318.4 |
2.2 Stiffness and Modal Analysis
The stiffness and modal analyses provide essential data for assessing the subframe’s resistance to deformation and natural frequencies, respectively.
Table 2: Stiffness Results at Various Attachment Points
| Attachment Point | Stiffness (N/mm) |
|---|---|
| Arm1 X | 58,824 |
| Arm1 Y | 62,500 |
| Arm1 Z | 610.9 |
| … | … |
Table 3: Modal Analysis Results
| Order | Modal Frequency (Hz) |
|---|---|
| 1 | 274.8 |
| 2 | 366.3 |
| 3 | 374.1 |
2.3 Dynamic Stiffness Analysis
Dynamic stiffness measures the subframe’s ability to resist vibrations under dynamic loads.
Table 4: Dynamic Stiffness Results
| Attachment Point | Dynamic Stiffness |
|---|---|
| Motor Mount | Value A |
| Lower Control Arm | Value B |
| … | … |
3. Topology Optimization
Topology optimization is employed to redefine the load transfer paths and reshape the subframe structure.
3.1 Topology Optimization Principles
Topology optimization techniques, such as homogenization, variable density, and evolutionary structural optimization, are considered. The variable density method, where the design domain is discretized into small elements with variable pseudo-material densities, is selected for this study.
3.2 Mathematical Model
The optimization problem is formulated as a multi-objective optimization with stiffness, strength, modal, and dynamic stiffness as performance criteria.
begin{align*} min & \quad W_x, \quad (x = 1, 2, 3)^T \\ min & \quad M_x, \quad (x = 1, 2, 3)^T \\ text{s.t.} & \quad V_x \leq V_m, \quad (x = 1, 2, 3)^T \\ & \quad \max S_x \leq S_m, \quad (x = 1, 2, 3)^T \\ & \quad \min K_a \leq \sum_{i=1}^{n} \pi^2 f_i / I_{\text{PI}i}, \quad (i = 1, 2, 3)^T \\ & \quad V(x) = \sum_{i=1}^{n} x_i v_i \leq V_X \\ & \quad C_r = \frac{V(x)}{V_0} \leq f end{align*}
where,
- Wx represents the target compliance.
- Mx represents the target mass.
- Vx is the volume fraction constraint.
- Sx is the maximum stress constraint.
- Ka is the minimum dynamic stiffness.
- f is the volume constraint fraction.
- Cr is the constraint ratio.
3.3 Optimization Results and Interpretation
The topology optimization results indicate a new subframe design with a clear load transfer path and a structure suitable for die casting.
4. Parameter Optimization
After topology optimization, parameter optimization fine-tunes the structure’s thickness distribution for lightweighting while maintaining performance.
4.1 Optimization Variables
The thickness of various components, including ribs and shell sections, is optimized.
4.2 Optimization Results
The optimized thicknesses are determined through iterative simulations, balancing performance and weight.
Table 5: Optimized Thickness Values
| Component | Original Thickness (mm) | Optimized Thickness (mm) |
|---|---|---|
| Shell | 4.0 | 3.5 |
| Rib 1 | 6.0 | 5.0 |
| Rib 2 | 4.5 | 4.0 |
| … | … | … |
5. Performance and Process Validation
The optimized subframe undergoes further analysis to validate its performance and process feasibility.
5.1 Performance Validation
Comparisons between the original and optimized subframes demonstrate significant improvements.
Table 6: Comparison of Key Performance Indicators
| Performance Indicator | Original Subframe | Optimized Subframe | Improvement (%) |
|---|---|---|---|
| First-order Modal Frequency | 274.8 Hz | 320.1 Hz | +16.5% |
| Maximum Stress | 1141.3 MPa | 987.4 MPa | -13.5% |
| Overall Weight | 12.8 kg | 10.8 kg | -15.6% |
5.2 Process Validation
The integrated die-casting process is simulated to ensure feasibility and evaluate potential challenges.
6. Cost and Weight Savings
The optimized subframe realizes notable cost and weight savings.
Table 7: Cost and Weight Savings
| Factor | Original Value | Optimized Value | Savings |
|---|---|---|---|
| Weight | 12.8 kg | 10.8 kg | -15.6% |
| Processing Cost | 480 yuan | 438.38 yuan | -8.6% |
7. Conclusion
This study presents an innovative optimization design of an integrated die-casting subframe for a new energy vehicle. By adopting structural lightweighting and process lightweighting methods, the splice-welded subframe is comprehensively analyzed and optimized using MMO technology and topology optimization. The optimized subframe demonstrates significant improvements in stiffness, strength, modal, and dynamic stiffness performances, accompanied by a 15.6% weight reduction and an 8.6% cost saving. This work highlights the potential of integrated die-casting technology in advancing automotive lightweighting and enhancing overall vehicle performance.