Sheet Metal Grooving Process
Sheet metal processing is an essential part of mechanical manufacturing, especially in industries such as aviation, household appliances, automotive, and elevators, where sheet metal components are widely used. As the only forming process in sheet metal processing, bending is one of the most important processes, and the quality of the bending process directly affects the dimensional accuracy and appearance of the products. 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 aesthetics has also increased. In the metal decorations of upscale places, the more complex the shape of the metal sheet ornaments, the more it reflects the designer's level of design and trendy style, thus attracting the attention of customers. At the same time, the workpiece also needs to meet process requirements such as minimizing the bending edge radius, no creases on the workpiece surface, and no pressure marks on the decorative surface. Traditional bending machines are unable to meet these special process requirements, leading to the emergence of the grooving bending process on metal sheets. This article mainly discusses the characteristics and grooving methods of the grooving process, as well as how to ensure the dimensional accuracy and angle during the bending process.
Limitations of Traditional Bending Methods
The traditional bending process involves using the pressure from the upper and lower dies of the bending machine to bend the metal sheet by utilizing the two edges at the opening of the lower die and the edge at the top of the upper die. The metal sheet undergoes elastic deformation and then plastic deformation. The bending angle is determined by the depth of the upper die entering the lower die, with a bending radius R ≥ sheet thickness t. In today's society, there is an increasing demand for complex-shaped workpieces, and traditional methods such as free bending, bending machine bending, or even three-point bending processes are unable to achieve the desired shapes. Moreover, the traditional bending method cannot control the radius of the bending corners, making it difficult to achieve the requirements of seamless bending. As a result, a new emerging bending process called grooving bending has emerged.
Characteristics of Grooving Bending Process
The grooving bending process involves first using a grooving machine to cut V-shaped grooves at the locations where the metal sheet needs to be bent, and then performing the bending process on a regular bending machine according to the requirements. The characteristics of the grooving bending process mainly include the following three aspects.
1. Small radius of the workpiece edges and no creases on the workpiece surface
Reduced Radius of Workpiece Edges and No Creases on the Surface
From the bending process, it can be understood that the radius of the workpiece edges after bending is directly proportional to the thickness of the sheet metal. The thicker the sheet metal, the larger the radius of the bending arc. By grooving the metal sheet with a V-shaped groove, the remaining thickness of the sheet is reduced to half or even smaller. This significantly reduces the radius of the workpiece edges after bending. Additionally, due to the thinner remaining thickness at the bending area after grooving, the deformation force during bending is correspondingly reduced. It does not spread and affect the unbent areas, resulting in no creases on the surface of the workpiece. Furthermore, the reduced pressure required during bending, due to the thinner sheet thickness at the bending area, effectively avoids the risk of pressure marks on the decorative surface. This meets the process requirements for small radius of workpiece edges, no creases on the surface, and no pressure marks on the decorative surface in high-end places such as hotels, banks, commercial centers, and airports.
Reduced Equipment Tonnage Required for Sheet Metal Bending
In the bending process, the bending force required for the metal sheet is proportional to its thickness. The thicker the sheet metal, the greater the bending force required, and consequently, the higher the equipment tonnage needed. By grooving the bending area of the metal sheet before bending, the remaining thickness at that area is significantly reduced. This, in turn, reduces the bending force required during sheet metal bending, allowing thick sheets to be bent on lower-tonnage bending machines. This approach reduces equipment investment, as well as energy consumption and space requirements.
Bending Complex-Shaped Workpieces and Controlling Springback
Parts that cannot be bent into shape using general bending machines can be bent by manually bending the grooved area after V-grooving. Moreover, control of the remaining sheet thickness enables control over springback force and springback angle. If the remaining sheet thickness after grooving is controlled to be around 0.3mm, the springback angle becomes minimal, and springback can be ignored.
Methods for Grooving V-Shaped Slots
In sheet metal production, V-shaped slots on metal sheets are commonly created using gantry planers and metal sheet grooving machines. The process involves placing the sheet metal to be grooved on the grooving machine for positioning and then automatically grooving it by inputting the sheet thickness. When grooving, attention should be paid to the following two aspects.
Setting the Grooving Depth and Remaining Thickness
Under a certain sheet thickness, the grooving depth and remaining thickness correspond to each other. First, set a value for the remaining thickness, typically around 0.8mm, with a minimum value not less than 0.3mm, based on the bending process requirements. Then, set the number of passes and the feed depth according to the sheet metal thickness. To control burrs and protect the cutting tool, the feed amount should not be too large. Generally, the depth of the first groove should not exceed 0.8mm, and it should be divided into at least two passes instead of completing it in one pass. For example, when grooving a stainless steel sheet with a thickness of 1.2mm and a remaining thickness of 0.5mm, set a feed amount of 0.5mm for the first pass and 0.2mm for the second pass. After two passes, the remaining thickness will be exactly 0.5mm, with relatively small burrs.
Setting the Grooving Angle
It is known from the bending process that metal sheets undergo varying degrees of springback deformation during bending, resulting in deviations in the bending angle. When grooving the V-shaped slot, the grooving angle can be rationalized based on the required bending angle of the workpiece. Generally, the grooving angle of the V-shaped slot should be 1° to 2° larger than the desired bending angle. For example, when bending a 90° workpiece, the grooving angle of the V-shaped slot can be set to 92°. This effectively avoids angle errors caused by bending springback.
Selection and Setting of Grooving Tools
Types and Selection of Grooving Tools
Grooving tools are mainly categorized as diamond-shaped corner groove tools, square groove tools, triangular groove tools, circular groove tools, etc. Suitable tools can be selected based on the different shapes and angles of the V-groove during grooving. When grooving a regular V-groove, the tool angle should be smaller than the angle of the V-groove. For example, for V-groove angles of 45° to 60°, a groove tool with a diamond-shaped corner angle of 35° should be selected. For angles of 60° to 80°, a triangular groove tool should be chosen. For angles of 80° to 90°, a groove tool with a diamond-shaped corner angle of 80° is suitable. For angles greater than 90°, a square groove tool should be used. For creating circular grooves, a circular groove tool is selected.
Setting the Number of Tools
When grooving long-sized sheets with deep grooves, using a single tool for a long continuous grooving path can lead to problems such as excessive heat generation and tool wear, poor grooving results, and larger burrs. For example, when grooving a stainless steel sheet with a length of 2m and a groove depth of 2mm, if the feed amount for the first pass is set to 0.5mm and the tool is continuously used for 2m, the tool may become softer due to excessive heat, resulting in lower grooving quality and larger burrs after 1.5m. On the other hand, if the feed amount is set to 0.2mm, it would require 10 passes to complete the 2mm V-groove, significantly affecting the processing efficiency. Therefore, when grooving long-sized sheets, in addition to setting the feed amount, it is necessary to determine the number of tools working simultaneously. In such cases, it is common to use 3 to 4 tools simultaneously, with each tool having a feed amount difference of around 2mm. For example, if the feed amount for the first tool is set to 5mm, the second, third, and fourth tools would have feed amounts of 7mm, 9mm, and 11mm, respectively. This ensures grooving quality while improving work efficiency.
Avoiding Deviations in Bending Angle and Dimension
For the bending process, the quality of the bending depends mainly on two important parameters: the bending angle and dimension. To ensure the dimensional accuracy and angle during bending, attention should be paid to the following aspects:
1. Misalignment between the upper and lower dies can result in dimensional errors during bending. Therefore, the alignment of the upper and lower die tools should be adjusted before bending.
2. The movement of the backstop block can change the relative position between the sheet and the lower die, affecting the bending dimension. Therefore, the distance of the backstop block position should be re-measured before bending.
3. Insufficient parallelism between the workpiece and the lower die can cause bending springback, affecting the bending angle. Therefore, the parallelism should be measured and adjusted before bending.
4. Insufficient bending angle in one bending operation can also affect subsequent bending operations. The accumulation of bending errors can result in larger dimensional and angular errors in the workpiece. Therefore, ensuring accuracy in single-side bending is particularly important.
5. During bending, the size of the V-notch in the lower die is inversely proportional to the bending pressure. When processing different thicknesses of metal sheets, the appropriate V-notch in the lower die should be selected according to the specifications. Generally, a notch size of 6 to 8 times the sheet thickness is suitable.
6. When bending the workpiece on the bending machine after grooving, it is important to ensure that the top die edge, the bottom edge of the workpiece V-groove, and the bottom edge of the lower die V-groove are in the same vertical plane.
7. To prevent tool clamping, it is preferable to control the angle of the upper die to be around 84° during grooving.
The grooving process, as a new type of processing technology in the bending process, is the result of market selection. With the continuous development of process technology, the requirements for process personnel in companies are also increasing. As process technicians, only by mastering various processing techniques can we produce better products. Only through continuous exploration and pursuit of new processes can we produce more excellent products. In the competitive market, those who do not innovate and break through will be left behind.
