Sheet metal processing is an essential part of mechanical machining, especially in industries such as aviation, appliances, automotive, and elevators, where sheet metal parts are widely used. As the only individual forming process in sheet metal processing, the bending process is one of the most critical processes, as the quality of the bending process directly affects the dimensional accuracy and appearance of the product. Therefore, ensuring the dimensional accuracy and angle of the workpiece during the bending process is a key research focus in bending technology.
With the development of the economy and the improvement of people's living standards, the pursuit of sensory goals has been increasing. In high-end metal decorations in certain places, the more complex the shape of the metal sheet decoration, the more it can reflect the designer's level of design and trendy style, thereby attracting the attention of customers. At the same time, the workpiece needs to meet process requirements such as having the smallest possible bending edge radius, no creases on the surface, and no pressure marks on the decorative surface. Traditional bending machines are unable to meet these special process requirements. Therefore, the groove milling bending process has emerged for metal sheet bending. This article mainly discusses the characteristics and slotting methods of the groove milling process, as well as how to ensure the dimensional accuracy and angle during the bending process.
The traditional bending process involves bending the metal sheet under the pressure of the upper and lower dies of the bending machine, using the two edges at the opening of the lower die and the edge at the top of the upper die to bend the metal sheet. The metal sheet undergoes elastic deformation to plastic deformation. The bending angle is determined by the depth to which the upper die enters the lower die, and the bending radius R ≥ sheet thickness t (Figure 1). In today's society, people have increasingly higher requirements for the shape of workpieces. Traditional free bending, bending machine bending, and even three-point bending processes are unable to bend workpieces with complex shapes, as shown in Figure 2. Additionally, the traditional bending method cannot control the radius of the bending corners, making it difficult to achieve the process requirements of seamless bending. Therefore, an emerging bending process called groove milling bending has emerged.
Characteristics of Groove Milling Bending Process
The groove milling bending process involves using a groove milling machine to mark and mill V-shaped grooves at the locations where the metal sheet needs to be bent, followed by bending the sheet on a regular bending machine according to the requirements. The characteristics of the groove milling bending process mainly include the following three aspects.
Small radius of curvature of workpiece edges, and no creases on the workpiece
According to the bending process, the size of the radius of curvature of the workpiece edges is directly proportional to the thickness of the sheet metal. The thicker the sheet metal, the larger the radius of curvature formed during bending. By V-grooving the metal sheet, the remaining thickness of the sheet is reduced to half or even smaller, significantly reducing the radius of curvature of the workpiece edges after bending. Additionally, due to the thinner remaining thickness at the bending location after grooving, the deformation force during bending is correspondingly reduced and does not spread to the unbent areas. As a result, there are no creases on the surface of the workpiece after bending. Furthermore, because the bending location has a thinner sheet thickness, the reduced pressure required during bending effectively avoids the risk of pressure marks on the decorative surface. This satisfies the process requirements of metal decoration in high-end places such as hotels, banks, commercial centers, and airports, where small edge radii, crease-free surfaces, and no pressure marks on the decorative surface are desired.
Reduction in equipment tonnage required for sheet metal bending
In the bending process, the bending force required for the metal sheet is directly proportional to its thickness. The thicker the sheet metal, the greater the bending force required, and the higher the equipment tonnage needed. By V-grooving the bending location of the metal sheet before bending, the remaining thickness of the sheet is significantly reduced. This reduces the bending force required during sheet metal bending, allowing thick sheets to be bent on bending machines with smaller tonnage. This reduces equipment investment, energy consumption, and space requirements.
Bending of complex-shaped workpieces and control of springback force
The part shown in Figure 2 cannot be bent into shape using traditional free bending, bending machine bending, or even three-point bending processes. However, it can be achieved by manually bending the part after V-grooving the bending location. In addition, control of the remaining sheet thickness can be used to control the springback force and springback angle. If the remaining thickness after grooving is controlled to be around 0.3mm, the springback angle becomes very small, and the springback can be essentially ignored.
Methods of Groove Milling
In sheet metal production, V-grooving of metal sheets is commonly performed using gantry planers and metal sheet slotting machines. The sheet to be grooved for bending is positioned on the slotting machine, and the thickness of the sheet is input for automatic tool alignment and grooving. When grooving, attention should be paid to the following two aspects.
