This article delves deep into the world of integrated die – casting subframes in the automotive industry. It begins by introducing the significance of subframes in vehicle design and the growing trend towards lightweight and high – performance components. Through a comprehensive exploration of the design process, including optimization goals, structural optimization techniques, and new structure verification, the article demonstrates how integrated die – casting subframes offer substantial improvements over traditional designs. The use of tables and images aids in clearly presenting data and concepts, making it accessible to a wide range of readers, from automotive engineers to enthusiasts.
1. Introduction
In the automotive industry, the subframe is a crucial component of the vehicle’s chassis. It serves as a key link between the vehicle body and various suspension and drivetrain components, playing a vital role in load – bearing and vibration isolation. As the demand for more fuel – efficient, safer, and comfortable vehicles continues to rise, the design of subframes has become a focal point for automotive engineers.
The traditional approach to subframe design often involves the use of multiple components welded or bolted together. However, this method has several limitations, including higher weight, potential weak points at joints, and increased manufacturing complexity. The advent of integrated die – casting technology has presented a new and innovative solution to these challenges.
Integrated die – casting allows for the production of a single, monolithic subframe in one manufacturing process. This not only reduces the number of parts and assembly steps but also offers the potential for significant weight savings and improved structural integrity. Figure 1 shows a comparison between a traditional welded subframe and an integrated die – casting subframe.
[Insert Figure 1: Comparison between traditional welded subframe and integrated die – casting subframe]
2. Optimization Goals Extraction
2.1 Strength Analysis of the Welded Subframe
The strength of a subframe is a critical factor in ensuring its reliability and safety. To analyze the strength of the welded subframe, a multi – body dynamics analysis is first conducted in a specialized software. A multi – rigid – body model is created, and kinematic analysis is performed to extract the load information at each attachment point of the subframe. The load information is then input into the finite – element model of the subframe, and the strength is analyzed using the inertial release method.
Four envelope load cases, namely Case 1, Case 5, Case 6, and Case 9, are selected as the strength indicators, considering the actual requirements of subsequent structural optimization. The stress distribution in these four cases is presented in Figure 2, and the stress extreme values are summarized in Table 1.
[Insert Figure 2: Stress cloud diagrams of four envelope load cases]
| Load Case | Maximum Stress (MPa) |
|---|---|
| 1 | 141.3 |
| 2 | 303.4 |
| 3 | 269.0 |
| 4 | 318.4 |
Table 1: Strength calculation results of the welded subframe
2.2 Stiffness and Modal Analysis of the Welded Subframe
Stiffness and modal characteristics are also important performance indicators of the subframe. For stiffness calculation, three – item loads are applied at the attachment points of the lower control arm, motor, steering gear, and anti – roll bar, while the body mount installation points are constrained. The attachment point and constraint information is shown in Figure 3, and the stiffness values are calculated and recorded in Table 2.
[Insert Figure 3: Information of each attachment point]
| Load Case | F | Stiffness (N/mm) |
|---|---|---|
| arm1 | X | 58824 |
| Y | 62500 | |
| Z | 610.9 | |
| arm2 | X | 18519 |
| Y | 23810 | |
| Z | 5525 | |
| bar | X | 125000 |
| Y | 28571 | |
| Z | 17241 | |
| steering rack | X | 90909 |
| Y | 76923 | |
| Z | 13699 | |
| em1 | X | 25641 |
| Y | 4167 | |
| Z | 3410 | |
| em2 | X | 10870 |
| Y | 2597 | |
| Z | 15625 | |
| em3 | X | 7692 |
| Y | 2933 | |
| Z | 8929 |
Table 2: Stiffness of the welded subframe
For modal analysis, the six – degree – of – freedom at the body connection points is constrained, and the first three – order modal results are calculated and shown in Table 3.
| Order | Modal (Hz) |
|---|---|
| 1 | 274.8 |
| 2 | 366.3 |
| 3 | 374.1 |
Table 3: First three – order modal results of the welded subframe
2.3 Dynamic Stiffness Analysis of the Welded Subframe
The dynamic stiffness of the subframe affects the vehicle’s vibration and noise performance. Based on the actual connection methods of each installation point, the lower control arm and motor installation points are selected for dynamic stiffness calculation. The calculation results are shown in Figure 4 and summarized in Table 4.
[Insert Figure 4: Dynamic stiffness of the welded subframe]
| Load Case | F | Dynamic Stiffness (N/mm) |
|---|---|---|
| arm1 | X | 119409 |
| Y | 23273 | |
| Z | 72249 | |
| arm2 | X | 282524 |
| Y | 183388 | |
| Z | 2464991 | |
| em1 | X | 1130542 |
| Y | 148756 | |
| Z | 2237305 | |
| em2 | X | 35557 |
| Y | 14151 | |
| Z | 31061 | |
| em3 | X | 33050 |
| Y | 20478 | |
| Z | 32345 |
Table 4: Dynamic stiffness of each attachment point of the welded subframe
3. Subframe Structural Optimization
3.1 Topology Optimization of the Subframe
3.1.1 Basic Principles of Topology Optimization
Topology optimization is a powerful technique used to improve the structure’s performance by changing its shape and layout. Among the various topology optimization methods, the variable – density method is widely used. In this method, the design domain is divided into numerous small elements, each with a different pseudo – material density. Through iterative calculations, under the premise of meeting the constraint conditions, the material is transferred from areas where it is not needed to areas where it is required, achieving optimization goals such as stiffness, mass, and modal improvement.
3.1.2 Mathematical Model Building
The optimization of the subframe involves multiple performance indicators, including stiffness, strength, dynamic stiffness, and modal. According to different optimization strategies, these indicators can be grouped into two categories. Stiffness, strength, and modal can be normalized to the minimum compliance goal, while dynamic stiffness is aimed at the minimum mass goal.
A constraint set is established for each goal, and the MMO (Multi – Model Optimization) technology is used to superimpose the two optimization results to obtain the optimal subframe structure. The mathematical model for optimization is as follows:
\(\begin{cases} \min\overline{W}_{x},(x = 1,2,3\cdots\cdots)T\\ \min M_{x},(x = 1,2,3\cdots\cdots)T\\ St.\overline{V}_{s}\leq V_{m},(x = 1,2,3\cdots\cdots)T\\ \max\overline{S}_{x}\leq S_{m},(x = 1,2,3\cdots\cdots)T\\ \min\overline{K}_{a}\leq\sum_{i = 1}^{n}4\pi^{2}\overline{f}/\overline{IPI}_{i},(i = 1,2,3\cdots\cdots)T\\ V(x)=\sum_{i = 1}^{n}x_{i}\overline{v}_{i}\leq V_{x}C_{r} \end{cases}\)
In the two independent normalized goals, \(\overline{W}_{x}\) represents the target compliance value, x represents each volume optimization variable, M represents the target total mass, and x also represents each mass optimization variable. The compliance – normalized constraint function is represented by the volume fraction \(\overline{V}_{s}\) being less than the set target value \(V_{m}\) and the maximum stress \(\overline{S}_{s}\) being less than the set target value \(S_{m}\). The mass – normalized target function uses the weighted IPI for the second – type response constraint.
3.1.3 Optimization Results and Interpretation
After multiple rounds of process and parameter adjustments, an ideal subframe optimization result is obtained, as shown in Figure 5. The new subframe is structured with a one – way draft ribbing method, which is in line with the integrated die – casting design concept. The optimization result is clear, and the load – transfer path is reasonable. The optimized result is further interpreted and reshaped, as shown in Figure 6.
[Insert Figure 5: Subframe structure optimization result]
[Insert Figure 6: Subframe structure reshaping]
3.2 Parameter Optimization of the Subframe
After obtaining a reasonable subframe structure through topology optimization, in order to achieve a subframe with a rational thickness distribution and lightweight design, size – parameter optimization is carried out on the new structure. To obtain the extreme results of size changes, the outer contour and all the stiffeners of the subframe are completely discretized, and the percentage of the upper and lower limits of optimization is set according to the process requirements. A total of 32 design variables are obtained, and the optimization goals and constraints are set to be consistent with those of topology optimization. The final optimization result is shown in Figure 7, and the new structure is finally designed by updating the result into the model.
[Insert Figure 7: Subframe size optimization]
4. New Structure Verification
4.1 Strength Analysis and Comparison of the Integrated Die – casting Subframe
The integrated die – casting subframe is analyzed under the same modeling standards and calculation load cases as the welded subframe. The stress cloud diagrams of the four envelope strength load cases of the new structure are shown in Figure 8, and the calculation results are compared with those of the welded subframe in Table 5. It can be seen from the calculation results that the maximum stress (Case 4) of the integrated die – casting subframe is reduced by 153.2 MPa, and the strength is increased by 48.1%.
[Insert Figure 8: Stress cloud diagrams of the integrated die – casting subframe]
| Load Case | Maximum Stress of Welded Subframe (MPa) | Maximum Stress of Integrated Die – casting Subframe (MPa) |
|---|---|---|
| 1 | 141.3 | 134.0 |
| 2 | 303.4 | 207.9 |
| 3 | 269.0 | 180.7 |
| 4 | 318.4 | 165.2 |
Table 5: Strength calculation results of the integrated die – casting subframe
4.2 Stiffness and Modal Analysis and Comparison of the Integrated Die – casting Subframe
The modal analysis results of the integrated die – casting subframe are shown in Figure 9, and the results are summarized in Table 6. By comparing the modal analysis results, it can be seen that the first – order modal of the integrated die – casting subframe is increased by 16.5%. The stiffness analysis results and comparisons of each attachment point are shown in Table 7, indicating that the stiffness of each attachment point has also been improved to varying degrees.
[Insert Figure 9: Modal cloud diagrams of the new subframe]
| Load Case | Modal of Welded Subframe (Hz) | Modal of Integrated Die – casting Subframe (Hz) |
|---|---|---|
| 1 | 274.8 | 320.1 |
| 2 | 366.3 | 367.7 |
| 3 | 374.1 | 389.8 |
Table 6: First three – order modal and comparison of the integrated die – casting subframe
| Load Case | F | Stiffness of Welded Subframe (N/mm) | Stiffness of Integrated Die – casting Subframe (N/mm) |
|---|---|---|---|
| arm1 | X | 58824 | 66666.66 |
| Y | 62500 | 71428.57 | |
| Z | 610.9 | 2857.40 | |
| arm2 | X | 18519 | 22727.27 |
| Y | 23810 | 32258.06 | |
| Z | 5525 | 5780.34 | |
| bar | X | 125000 | 125000.00 |
| Y | 28571 | 100000.00 | |
| Z | 17241 | 29411.76 | |
| steering rack | X | 90909 | 142857.40 |
| Y | 76923 | 66666.66 | |
| Z | 13699 | 16949.15 | |
| em1 | X | 25641 | 41666.66 |
| Y | 4167 | 4878.04 | |
| Z | 3410 | 3472.22 | |
| em2 | X | 10870 | 16949.15 |
| Y | 2597 | 4587.15 | |
| Z | 15625 | 28571.42 | |
| em3 | X | 7692 | 10204.08 |
| Y | 2933 | 4672.89 | |
| Z | 8929 | 11363.63 |
Table 7: Stiffness and comparison of the integrated die – casting subframe
4.3 Dynamic Stiffness Analysis and Comparison of the New Structure
The dynamic stiffness analysis results of the new structure are shown in Figure 10, and the calculation results are summarized in Table 8 and compared with the basic model. It can be seen from the comparison that the dynamic stiffness of the new structure has been improved to varying degrees, and the improvement of the attachment point of Swing Arm 2 has reached 3.2 times.
[Insert Figure 10: Dynamic stiffness of the integrated die – casting subframe]
| Load Case | Dynamic Stiffness of Welded Subframe (N/mm) | Dynamic Stiffness of Integrated Die – casting Subframe (N/mm) |
|---|---|---|
| arm1 – X | 119409 | – |
| arm1 – Y | 23273 | – |
| arm1 – Z | 72249 | – |
| arm2 – X | 282524 | – |
| arm2 – Y | 183388 | – |
| arm2 – Z | 2464991 | – |
| em1 – X | 1130542 | – |
| em1 – Y | 148756 | – |
| em1 – Z | 2237305 | – |
| em2 – X | 35557 | – |
| em2 – Y | 14151 | – |
| em2 – Z | 31061 | – |
| em3 – X | 33050 | – |
| em3 – Y | 20478 | – |
| em3 – Z | 32345 | – |
4.4 Weight and Cost Comparison
The connection process of the optimized subframe structure is further optimized, and the cost and weight results of the basic structure and the new structure are tabulated in Table 9 and Table 10. Through a comprehensive analysis and comparison between the welded subframe and the integrated die – casting subframe, it becomes evident that the integrated die – casting subframe holds a significant edge in terms of both weight and cost.
The integrated die – casting subframe is 2.03 kg lighter than the welded subframe, representing a 16.3% reduction in weight. This weight reduction not only contributes to better fuel efficiency but also improves the vehicle’s overall performance. In terms of cost, the integrated die – casting subframe is 41.62 yuan cheaper, with an 8.6% cost reduction. This cost reduction is achieved through fewer manufacturing steps and a more streamlined production process.
| Part Number | Part Name | Quantity | Unit Price (yuan) | Total Price (yuan) | Weight (kg) |
|---|---|---|---|---|---|
| F33015 | Front Subframe Assembly | 1 | 456.53 | 456.53 | – |
| M10×1.25×50 – 4.5 | Aluminum Sleeve | 4 | 6 | 24 | – |
| M6x17.5 | Flat – Head Round – Body Knurled Split Rivet Nut | 9 | 0.08 | 0.72 | – |
| M8x19 | Flat – Head Round – Body Knurled Split Rivet Nut | 3 | 0.14 | 0.42 | – |
| – | Total Cost | – | – | 481.67 | 12.43 |
Table 9: Weight and Cost 核算 of the Welded Subframe
| Part Number | Part Name | Quantity | Unit Price (yuan) | Total Price (yuan) | Weight (kg) |
|---|---|---|---|---|---|
| – | Water Pump Bracket and Other Ancillary Structures | – | – | – | – |
| – | Total Cost | – | – | 440.05 | 10.4 |
Table 10: Weight and Cost 核算 of the Integrated Die – casting Subframe
5. Conclusion
5.1 Subframe Performance Enhancement
The integration of the parametric optimization method in the subframe design has proven to be highly effective. By precisely adjusting the thickness of the subframe’s stiffeners and outer contour, improvements in stiffness, dynamic stiffness, and modal characteristics have been achieved. The increase in dynamic stiffness notably reduces the vehicle body’s torsional deformation, enhancing driving stability and ride comfort. This optimization demonstrates that it is possible to achieve weight reduction while simultaneously enhancing performance. Therefore, a more rational structural design serves as a crucial approach to enhancing the subframe’s cost – effectiveness.
5.2 Subframe Structural Lightweighting
Topology optimization has successfully realized the lightweight design of the subframe. Compared with traditional designs, the newly designed subframe has achieved a 16.3% weight reduction while still meeting the requirements for stiffness, strength, dynamic stiffness, and modal performance. The comprehensive application of structural, process, and material lightweighting methods has established a complete lightweight technology roadmap, which can be used as a reference for the automotive industry.
5.3 Subframe Process Lightweighting and Cost Reduction
Replacing the welded subframe with an integrated die – casting subframe significantly reduces the number of processing steps. The non – welded structure not only improves the structural strength but also provides opportunities for further cost reduction through optimized connection methods. This change represents a significant step forward in automotive manufacturing, combining cost – effectiveness with enhanced performance.
In conclusion, the design optimization of subframes is a crucial aspect of modern automotive engineering. Through the combined application of topology optimization, material optimization, and structural parameter optimization, the structural performance of subframes can be effectively improved, meeting the automotive industry’s demands for lightweighting, safety, and economy. As technology continues to evolve, subframe optimization design will play an increasingly important role in automotive engineering, contributing to the development of intelligent, green, and sustainable automotive manufacturing.
6. Future Outlook
The development of integrated die – casting subframes is still in its early stages, and there is significant potential for further improvement. Future research could focus on exploring new materials and manufacturing processes to further enhance the performance and cost – effectiveness of subframes. For example, the use of advanced high – strength alloys or composite materials may offer even greater weight savings without sacrificing strength.
In addition, with the increasing trend towards electric vehicles, subframes will need to be designed to accommodate new components such as larger batteries and electric motors. This will require a more comprehensive approach to subframe design, considering factors such as heat management and electromagnetic compatibility.
Furthermore, the application of artificial intelligence and machine learning in subframe design could revolutionize the optimization process. These technologies can analyze vast amounts of data to identify the most optimal design solutions more quickly and accurately, reducing the time and cost required for development.
7. Challenges and Solutions
Despite the numerous advantages of integrated die – casting subframes, there are also several challenges that need to be addressed. One of the main challenges is the high initial investment required for die – casting equipment. The cost of purchasing and maintaining large – scale die – casting machines can be a significant barrier for some automotive manufacturers.
Another challenge is the complexity of die – casting molds. Designing and manufacturing molds that can produce high – quality subframes with complex geometries requires advanced technical expertise and precision manufacturing capabilities. Any defects in the mold can lead to product quality issues and production delays.
To overcome these challenges, automotive manufacturers can consider collaborating with specialized die – casting suppliers. By leveraging the suppliers’ expertise and economies of scale, manufacturers can reduce the cost of die – casting equipment and molds. Additionally, continuous research and development in mold – making technology can help improve the quality and efficiency of mold production.
8. Industry Impact
The adoption of integrated die – casting subframes has far – reaching implications for the automotive industry. It not only improves the performance and quality of individual vehicles but also has the potential to transform the entire manufacturing process.
For automotive manufacturers, the use of integrated die – casting subframes can lead to significant cost savings in the long run. Fewer parts and assembly steps mean reduced production time and labor costs. This can enhance the competitiveness of manufacturers in the global market.
From an environmental perspective, the lightweighting of subframes contributes to lower fuel consumption and emissions. As the automotive industry moves towards more sustainable practices, this reduction in environmental impact is becoming increasingly important.
Moreover, the development of integrated die – casting subframes also promotes innovation in related industries, such as die – casting equipment manufacturing and mold design. This can lead to the creation of new jobs and the growth of the overall economy.
9. Case Studies of Leading Automotive Brands
Many leading automotive brands have already recognized the potential of integrated die – casting subframes and have started to incorporate them into their vehicle designs. For example, Tesla has been at the forefront of using large – scale integrated die – casting technology in its Model Y. By using a single piece of die – cast aluminum for the rear subframe, Tesla has achieved significant weight reduction and cost savings.
Another example is Volvo, which has also been exploring the use of integrated die – casting in its vehicles. Volvo’s focus on safety and sustainability aligns well with the benefits of integrated die – casting subframes, such as improved structural integrity and reduced environmental impact.
These case studies demonstrate the practical application and effectiveness of integrated die – casting subframes in real – world automotive manufacturing. They also serve as inspiration for other automotive brands to follow suit and embrace this innovative technology.
10. Conclusion
The integrated die – casting subframe represents a significant advancement in automotive design. Through its innovative structure and manufacturing process, it offers a wide range of benefits, including performance improvement, weight reduction, and cost savings. While there are still challenges to overcome, the future of integrated die – casting subframes looks promising. With continued research, development, and industry collaboration, this technology has the potential to play a crucial role in the future of automotive manufacturing, driving the industry towards a more sustainable and efficient future.
