Research on Three-Dimensional Freeform Bending Technology
Three-dimensional freeform bending technology has revolutionized the field of plastic forming in recent decades. This innovative technique combines advanced multi-axis servo control with plastic forming processes, enabling the one-time integral forming of complex components with high precision and efficiency. It has found extensive applications in aerospace, rail transportation, automotive, petrochemical, and construction industries.
Research Objectives
The aim of this study was to investigate the three-dimensional freeform bending technology for the production of a complex aluminum alloy skeletal structure used in the front window glass installation of a certain type of high-speed train locomotive. The skeletal structure, composed of JIS H 4100A5083 H112 AL-Mg deformed aluminum alloy extruded solid profiles, presented significant challenges due to its intricate three-dimensional geometry.
Manufacturing Process
To reduce construction complexity and improve production efficiency, the manufacturing process was divided into several stages. First, the front window skeletal structure was segmented into two parts. After three-dimensional forming, the segments were assembled, welded, and subjected to mechanical processing for gap fitting. The individual component length was approximately 4500mm, with the segmented lines located at both ends. Specialized molds were designed and fabricated based on the solid extrusion profile section of the CRH2 locomotive’s front window skeletal structure. These molds were installed on the equipment control head, with the notch shape on the mold aligning with the bent profile section. This allowed the profiles to be smoothly and accurately bent during the forming process. To enhance formability and precision, the aluminum alloy extruded profiles were treated to achieve the mechanical properties specified by the H112 standard.
Process Observations and Control
The accompanying diagram illustrates the process and the main body of the mold during the three-dimensional forming of the segmented front window skeletal structure using extruded profiles and the three-dimensional freeform bending system. It provides insight into the installation and configuration of the specialized molds, the interaction between the profiles and the molds during bending, and the control of the forming process based on the desired geometry.
Measurement and Quality Assurance
During the fabrication process, a manual coordinate measuring device was used to measure and collect data from the test specimens. The measurement data was imported into the control system and compared with the three-dimensional models using analysis software. By refining the control program, the dimensional accuracy of the three-dimensional freeform bending of solid aluminum profiles was improved, resulting in the production of qualified components.
NSB-S six-axis linkage freeform bending system of German J.NEU company
In recent years, 3D freeform bending technology has attracted widespread attention in the manufacturing industry. The NSB-S six-axis linkage freeform bending system of German J.NEU company has made a significant breakthrough in this field with its advanced performance and precise control ability. At the same time, the flexible forming technology and equipment team of Nanjing University of Aeronautics and Astronautics in China has also achieved remarkable results in this field.
The NSB-S six-axis linkage freeform bending is an independent research and development achievement of J.NEU. It has the following characteristics:
- Highly flexible: The system adopts a six-axis linkage structure, which can realize freeform bending in multiple directions, making the forming process more flexible and diverse.
- High-precision control: Through advanced control algorithms and sensor technology, the forming process can be sensed and adjusted in real-time to achieve precise bending control.
- High efficiency: The system has the ability to quick response and high-speed forming, which can greatly shorten the forming cycle and improve production efficiency.
- Wide applicability: suitable for forming various materials, including metals, alloys, composite materials, etc.
The following table summarizes the main parameters of the NSB-S six-axis linkage freeform bending system:
| No | Feature name | Technical Parameters |
| 1 | Processing capacity (φ, mm) | 10-90 |
| 2 | The maximum radius of the workpiece | Unlimited |
| 3 | Workpiece minimum radius value | 2.0D～2.4D(D is the outer diameter of the curved pipe) |
| 4 | bending angle | 0°～ 360° |
| 5 | Bending axis positioning accuracy | ≤ 0.01mm |
| 6 | Feed axis positioning accuracy | ≤ 0.05mm |
| 7 | Maximum speed | 400 mm/sec |
| 8 | Weight (kg) | 6000 |
3D Freeform Bending System at Nanjing University of Aeronautics and Astronautics, China
The three-dimensional freeform bending system developed by the flexible forming technology and equipment team of Nanjing University of Aeronautics and Astronautics has the following characteristics:
High precision: The system adopts GTS high-performance multi-axis plug-in motion controller, which can realize high-precision forming and meet the requirements of complex components.
Multi-axis linkage: the system supports multiple structures, including 3-axis, 6-axis, 6-axis parallel structure and 7-axis parallel structure, etc., with greater flexibility.
Modular design: The system adopts a modular design, with the help of intelligent pipe bending workstations for process control, improving work efficiency and optimizing production processes.
Wide application: Widely used in aerospace, rail transit, automobile, petrochemical, construction and other fields, suitable for various pipe diameters and workpiece sizes.
The following table lists the two models and their main parameters of the 3D freeform bending system of Nanjing University of Aeronautics and Astronautics:
Parameters and Features
The Chinese team’s system offers the following parameters and features:
| Parameter | TFB-S60 | TFB-S90 |
|---|---|---|
| Maximum Processing Diameter | 30-60 mm | 60-90 mm |
| Maximum Bending Radius | Infinite | Infinite |
| Minimum Bending Radius | 3.5D | 3.5D |
| Bending Angle | 0-360 degrees | 0-360 degrees |
| Feed Axis Positioning Accuracy | ≤0.05 mm | ≤0.05 mm |
| Bending Axis Positioning Accuracy | ≤0.02 mm | ≤0.02 mm |
| Maximum Speed | 330 mm/s | 330 mm/s |
| Standard Machine Model | Maximum Processing Length 3000mm, customizable up to 6000mm in increments of 1000mm. |
In order to overcome the technical challenges caused by the high-speed operation of trains, innovative technologies have been applied in the design of high-speed trains in China, such as aerodynamic reduction, aerodynamic noise reduction, airtightness and strength, modal matching, vibration reduction and noise reduction, and lightweight. The use of three-dimensional structures in the internal load-bearing components of the trains has become increasingly popular. This article will explore the application of three-dimensional freeform bending technology in high-speed train manufacturing.
Application of Three-Dimensional Freeform Bending Technology in High-Speed Train Manufacturing
Three-dimensional freeform bending technology is an important innovation based on three-dimensional trajectory control flexible forming technology, which can achieve accurate forming of hollow components with complex axial lines and complex sections. Since its invention in the 1990s, with the improvement of relevant basic research, commercial freeform tube bender equipment has been developed by companies in Japan and Germany, and it has been widely used in aerospace, automotive, and especially military industries, receiving unanimous praise.
In the field of aviation manufacturing, Chinese researchers have demonstrated the immense potential of three-dimensional freeform bending technology. In 2014, Yuan Song, a researcher at the Beijing Aerospace Manufacturing Engineering Institute of Aviation Industry Corporation of China, introduced the technology for the first time in China in his work “Aircraft Sheet Metal Manufacturing Technology,” highlighting its potential technological advantages and application prospects. In 2016, Associate Professor Guo Xunzhong from Nanjing University of Aeronautics and Astronautics wrote an article titled “Three-dimensional Freeform Bending Technology and Its Potential Application in Aircraft Manufacturing Industry,” analyzing and looking forward to the application prospects of the technology in the manufacturing of complex curved components. In 2018, Professor Tao Jie from Nanjing University of Aeronautics and Astronautics systematically introduced the development process, key technologies, and five typical configurations of freeform bending equipment/freeform tube bender developed by companies such as Germany’s J.Neu, and their mechanism of motion in his work “Three-dimensional Freeform Tube Bender and Its Key Technologies.”
Table 1: The Advantages of Three-dimensional Freeform Bending Technology
| Advantages | Description |
|---|---|
| High accuracy | Precise forming of complex axial line and section profile |
| High efficiency | Single-time forming of hollow components |
| High flexibility | Accommodates complex shapes and profiles |
| High controllability | The impact of heat treatment on the shape of components is controllable |
In high-speed train manufacturing, three-dimensional aluminum extrusions are widely used to meet the requirements of lightweight and long service life. AL-Mg (5000 series), AL-Mg-Si (6000 series), and AL-Mg-Zn (7000 series) aluminum alloys are commonly used due to their structural strength, stiffness and lightness, corrosion resistance, easy processing and welding, complex extrusion of hollow profiles, and recyclability. AL-Mg aluminum alloy has good welding and corrosion resistance, but poor extrusion workability. AL-Mg-Zn aluminum alloy was developed for thin-walled and lightweight development, and has good extrusion workability, material strength, and weldability. AL-Mg-Si is a new aluminum alloy material developed to overcome the stress corrosion of AL-Mg-Zn series aluminum alloy materials.
Table 2: Comparison of Different Aluminum Alloys Used in High-Speed Train Manufacturing
| Parameters | AL-Mg | AL-Mg-Zn | AL-Mg-Si |
|---|---|---|---|
| Features | Good welding and corrosion resistance | Good extrusion workability, strength, and weldability | Monogenic solid solution strengthening and increase elongation |
| Suitable for | Components and joints requiring good welding performance | Structural parts with complex sections and profiles | High-precision components requiring high strength and stiffness |
| States | T5, T6 | T5, T6 | T5, |
To enhance the strength of aluminum extrusions, a heat treatment is often applied to induce desired mechanical and physical properties. The status of aluminum extrusions is mainly classified into the H112, T5, and T6 states. Different aluminum alloy states have different properties, and the impact of heat treatment on the shape of components is controllable. Although H112, T5, and T6 aluminum extrusions have sufficient strength, their forming performance is poor. Therefore, for complex three-dimensional aluminum extrusion profiles, the O-state extrusion can be firstly used for bending, followed by a heat treatment to H112, T5, or T6 which is proven to be feasible.
In conclusion
Teams in Germany and China have made significant progress in the field of 3D free-bending technology. The NSB-S six-axis linkage freeform bending system of German J.NEU company has become a leader in the industry with its advanced performance and precise control capabilities. The flexible forming technology and equipment team of Nanjing University of Aeronautics and Astronautics has achieved efficient and accurate three-dimensional freeform bending through innovations such as adaptive control and material adaptability.
These achievements have provided strong technical support for the manufacturing industry of high-speed EMUs and other fields, and promoted the development and progress of the industry. With the deepening of further research and practice, it is believed that 3D freeform bending technology will play a greater role in the future development and bring more innovations and breakthroughs to the manufacturing industry.
References
- [1] J.NEU GmbH. (2022). NSB-S 6-axis linkage freeform bending system. Retrieved from http://www.jneu.eu/
- [2] Nanjing University of Aeronautics and Astronautics. (2021). Research on three-dimensional freeform bending technology. Retrieved from http://en.nuaa.edu.cn/
