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Controlling Section Distortion in Bending Aluminum Profiles through the Application of Flexible Core Shafts

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Aluminum profiles have gained significant recognition in industrial production due to their lightweight, good formability, high strength, and high recyclability. In recent years, aluminum profiles have been extensively used in transportation equipment such as automobiles and rail vehicles, particularly in developed industrial countries like Europe, the United States, and Japan. However, the bending process of aluminum profiles often leads to section distortion issues. Effectively controlling section distortion and improving the accuracy of section shape has been a challenge in the bending process of aluminum profile components.

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Defects in Profile Bending

In this article, we analyze a specific aluminum profile component as an example. The cross-section of this component consists of a curved section and two straight sections, with a radius of 1,232.4 mm for the curved section and a length of 500 mm for the straight sections, all with an 8 mm wall thickness. The desired precision for the cross-section shape is high, with a flatness requirement of less than 1 mm for the outer surface and less than 2 mm for the inner surface. However, when using traditional mold pressing processes with either polyurethane boards filled with thin steel plates or sand filling, significant distortion occurs in the bent cross-section, preventing the achieved flatness on both sides of the profile from meeting the design requirements. Analysis indicates that the main cause of this defect is the lack of reliable support for the cross-section walls within the filling material, which fails to restrict the free deformation of the cross-section edges, resulting in substantial section distortion.

Top 6 common defects

  1. Wrinkling: This occurs when the material forms unwanted folds or wrinkles during the bending process. It can happen if the material is not properly supported or if the bending force is too high. Wrinkling can weaken the material and lead to a less aesthetically pleasing result.
  2. Springback: Springback is the tendency of a bent profile to partially return to its original shape after the bending force is removed. It can be challenging to predict and control, especially in materials with high elasticity. Proper tooling design and selection of bending parameters can help minimize springback.
  3. Cracking: Excessive deformation or improper material properties can lead to cracking in the bent profile. This defect can be caused by using the wrong bending technique, incorrect tooling, or using a material that is too brittle for the desired bend radius.
  4. Distortion: Distortion refers to the unintended changes in the cross-sectional dimensions of the profile after bending. This can result from uneven bending forces or inadequate support during the bending process.
  5. Buckle: Buckling occurs when the compressive forces during bending exceed the material’s ability to resist them. Buckling can lead to irregular shapes and can even cause the profile to collapse in extreme cases.
  6. Surface Imperfections: Profile bending can introduce scratches, marks, or other surface imperfections on the material. These defects can be caused by the interaction between the material and the bending tools.

Introduction of Flexible Core Shafts

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To address the section distortion problem, a flexible core shaft has been developed and introduced. It consists of rigid blocks and polyurethane pads arranged with spacing and connected and pre-tensioned using steel cables, as shown in Figure 2. The rigid blocks provide reliable support to the profile’s cross-section edges, effectively controlling section distortion, while the polyurethane pads provide the core shaft with flexibility, allowing it to bend along with the profile. The effectiveness of this flexible core shaft in controlling section distortion was investigated using numerical simulation techniques.

6 flexible core shafts in profile bending

1. Enhanced Precision: Flexible core shafts are designed to be adjustable and adaptable, allowing them to follow the desired curve accurately. This enhances the precision of the bending process, making it easier to achieve tight radii and intricate shapes without the risk of wrinkling, springback, or distortion.

2. Reduction of Wrinkling: One of the significant benefits of flexible core shafts is their ability to minimize wrinkling, a common defect in traditional bending methods. By providing more support along the length of the profile being bent, these shafts help distribute the bending forces more evenly, reducing the likelihood of unwanted folds or wrinkles.

3. Minimized Springback: Flexible core shafts can help mitigate springback, the tendency of the material to return to its original shape after bending. The adaptability of these shafts allows them to maintain the desired curvature even after the bending force is removed, leading to a more accurate final shape.

4. Complex and Variable Bends: With flexible core shafts, it becomes feasible to create profiles with complex and variable bends. The ability to adjust the shape of the shaft allows for the creation of multi-radius bends, S-curves, and other intricate configurations that would be challenging or impossible to achieve with rigid mandrels.

5. Improved Surface Quality: Flexible core shafts can contribute to better surface quality by reducing the chances of scratching or marring the material during the bending process. The smooth, adjustable surface of the shaft minimizes direct contact with the profile, leading to fewer surface imperfections.

6. Increased Versatility: Flexible core shafts are versatile tools that can be used with various materials and profiles. This versatility makes them suitable for a wide range of applications, from architectural and automotive components to aerospace and industrial designs.

Numerical Simulation and Forming Experiments

A finite element model incorporating the flexible core shaft was established for numerical analysis, simulating the bending process of the profile. A comparison was made with the case of no filling, and the simulation results demonstrated that the adoption of the flexible core shaft effectively controlled the section distortion, significantly improving the flatness of the cross-section edges.

Further Research

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Further research revealed that the filling gap between the flexible core shaft and the profile has a significant impact on the section distortion. Smaller gaps result in smaller section distortion. However, excessively small gaps can make it difficult to insert the core shaft and may cause scratching on the inner wall of the profile, leading to wall thinning and cracking. Therefore, in practical applications, the filling gap should be selected appropriately, with a recommended range of 0.2 to 0.4 mm.

The effectiveness of the flexible core shaft was further validated through forming experiments. A comparison was made between components formed with the filled flexible core shaft and those filled with polyurethane. The results showed that the use of the flexible core shaft achieved better control of section distortion.


Through numerical simulation and forming experiments, the following conclusions were drawn: the introduction of a flexible core shaft in the bending process of aluminum profiles effectively reduces section distortion and significantly improves the flatness of the cross-section edges. The control effect of the flexible core shaft surpasses that of traditional methods involving polyurethane filling. Additionally, the filling gap between the flexible core shaft and the profile has a notable influence on the amount of section distortion, requiring appropriate selection based on practical considerations.

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In summary, the proposed flexible core shaft approach provides an effective solution to the issue of section distortion in the bending process of aluminum profiles, demonstrating potential for practical applications.