Research Article
Integrated Free-bulge Forming Method for Thin-walled Metallic Spherical Cap Structures
Issue:
Volume 13, Issue 3, June 2025
Pages:
86-97
Received:
3 April 2025
Accepted:
15 April 2025
Published:
14 May 2025
Abstract: The end surfaces of large storage tanks used in various industries are often composed of thin-walled metallic spherical cap structures. The ability to process these components at a low cost and with high manufacturing precision is an important research challenge. In this study, a new integrated free-bulge forming method is proposed to fabricate thin-walled metallic spherical cap structures. This method involves fixing the perimeter of a circular forming sheet, applying internal water pressure, and uniformly bulging the central portion of the sheet to achieve a spherical cap structure. To analyze the forming performance of the proposed method, formulas for calculating the plastic strain and average thickness during the process of forming the spherical cap from the circular sheet are derived, enabling a clear understanding of the workable range of the free-bulge forming method. Additionally, by deriving a prediction formula for the internal water pressure required for the free-bulge of the spherical cap structure, the key process design factors are identified. For verification, a free-bulge forming device is developed, and thin-walled metallic spherical cap structures are processed. The results confirm that the spherical cap shape is sufficiently precise and can be stably produced using the free-bulge forming method. Furthermore, a specialized device for measuring the shape accuracy of the spherical cap formed using the proposed free-bulge method is developed, and the surface shape of the spherical cap structure is measured. The results show that the formed spherical cap shape has a maximum deviation of 2.3% from the theoretical shape, demonstrating adequate precision for practical applications. To further verify the processing performance of the free-bulge forming method, the thickness distribution of the processed thin-walled metallic spherical cap is measured along its diameter. The results show that, compared to the original thickness of 1.0 mm, the minimum thickness of 0.858 mm occurs at the center of the spherical cap, representing a thickness reduction rate of -13.2%. It is confirmed that the free-bulge method can be stably applied to typical thin-walled press materials.
Abstract: The end surfaces of large storage tanks used in various industries are often composed of thin-walled metallic spherical cap structures. The ability to process these components at a low cost and with high manufacturing precision is an important research challenge. In this study, a new integrated free-bulge forming method is proposed to fabricate thi...
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Research Article
The Experimental Study of Reducing Cooling Fan Noise Using Test Bench
Andy Duan*
,
Jing Yu,
Siyuan Shao,
Dai Haijiang,
Changshui Zhou,
Perry Gu
Issue:
Volume 13, Issue 3, June 2025
Pages:
98-107
Received:
19 April 2025
Accepted:
3 May 2025
Published:
16 June 2025
DOI:
10.11648/j.ijmea.20251303.12
Downloads:
Views:
Abstract: The blade pass frequency (BPF) noise for axial flow cooling fans in Electrical Vehicles (EV) is much obvious in some of rotational speeds. The root cause of this BPF noise is due to the cooling fan loading which is caused by the pressure difference between inlet and outlet of the fan. The pressure difference is defined as the resistance value of the fan. The resistance value of fan in EVs is much higher than the value of internal-combustion engine (ICE) vehicles. It is very difficult to obtain the resistance value in full vehicle condition. A new method to estimate the vehicle resistance value is developed using bench tests. By assuming, on the same operating parameters of the same fan both in vehicle and in test bench, such as inlet voltage, current and rotational speed, the resistance value of the fan in vehicle is the same as in test bench, thus, the operating parameters are used in the bench testing to simulate the resistance value of the fan in vehicle. Once the resistance value is achieved, the noise values of the fan can be measured in the test bench under different rotational speeds. Several testing results of different fans show that the BPF noises in bench with the defined resistance value align with those in vehicle. Using this method, the cooling fan noise can be studied in bench, earlier fan prototypes can be evaluated before finalizing design parameters. From this study it is found that the deformation of blades under the operation is the main factor to affect BPF noise levels. During operation the blade deformation changes the gap between the blade and the shroud in axial direction. The gap is related to the initial gap and the strengthen of the fan blade. This gap can be designed and optimized to balance the BPF noise in the total rotational range. The guidelines for designing low noise fan are outlined in this paper also.
Abstract: The blade pass frequency (BPF) noise for axial flow cooling fans in Electrical Vehicles (EV) is much obvious in some of rotational speeds. The root cause of this BPF noise is due to the cooling fan loading which is caused by the pressure difference between inlet and outlet of the fan. The pressure difference is defined as the resistance value of th...
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