German Industry 4.0, the American Industrial Internet and the implementation of “Made in China 2025” confirm that the core of the Fourth Industrial Revolution in global manufacturing is smart production. This is particularly evident in China's sheet metal manufacturing industry, which consists of various processes such as laser cutting, sheet metal welding, shearing and bending.
This post will mainly focus on bending technology.
Common Bending Methods
Die doubling
Die bending is typically accomplished using a press brake (see Figure 1), which requires the assistance of workers or robots to complete the bending process.
The bending accuracy largely depends on the skill of the technicians or the quality of the robot. This bending method is commonly used in the production of small parts with a single product type and a simple manufacturing process.
Fig. 1 Die folding
Folding Machine Flange
A bending machine (see Figure 2) can be used to bend large parts with complex structures and various shapes.
Figure 3 shows the bending shapes that can be achieved using a single-knife automatic folder or a double-knife automatic folder.
Fig. 2 Working principle of folding machine
Fig.3 Foldable shape
Double knife bending and CNC bending
The double knife press brake is a type of press brake (see Figure 4) that operates on the same principle. It is capable of bending a wide variety of shapes and types, just like the press brake.
Fig. 4 Principle of double knife press brake
The CNC press brake is the most commonly used bending machine in the bending center (Fig. 5). Famous bending machine manufacturers can refer to this classification .
Fig. 5 Principle of CNC press brake
The flexibility of double knife press brake and CNC press brake is very high, making them suitable for “universal bending” and widely used in automatic production. Until 2018, both machines were powered by hydraulic power. However, since then, CNC press brakes have started to use servo drive and only hydraulic drive to clamp the tooling.
There are several main differences between these machines:
(1) Bending speed.
Under the same conditions, the CNC press brake will have a slightly faster bending speed.
For a 90° part structure, the CNC press brake takes 1.8 to 2 seconds to bend it, while for the double knife press brake it takes 2 to 3 seconds (depending on the profile size).
(2) Bending clearance.
The cutting way of double knife press brake differs from that of CNC press brake (see Fig. 6).
In cases where the clamping device is adjustable, the force area of the CNC press brake is relatively small, which may cause damage or scratches to the surface of the part (see Fig. 7).
Fig. 6 Bending clearance
Fig. 7 Surface scratch
(3) Flexion form.
Figure 8 shows the bending way of double knife press brake and CNC press brake.
Fig. 8 Flexion shape
Bending case analysis
Nowadays, punching technology has become more mature, especially with the popularity of punching units such as Trumpf and Amada. As a result, laser drilling and cutting technologies have also become increasingly popular.
Despite advances in various sheet metal production processes, bending remains a major bottleneck that significantly affects the overall workflow balance and limits improvements in shop capacity.
Elevator Hall Door Panel Bending Box
The elevator hall door panel has a relatively simple structure with a small number of holes.
Most manufacturers typically use punching centers and bending centers to complete production. However, the bottleneck in the production process is bending.
During bending, the part needs to rotate three times and the corresponding tool needs to be adjusted to complete the bending process. This takes about 35 to 45 seconds per piece.
To increase production speed and efficiency, manufacturers can add a bending center to the production line. Although this can reduce production time to 20 seconds per part, it also increases production cost.
Alternatively, manufacturers can adopt a double-knife press brake (as shown in Figure 9) that allows both sides of the part to be bent simultaneously. This reduces part rotation to just one turn, with a production rate of 12 to 15 seconds per part.
As an example, consider a part with the section shape shown in Figure 10 and a length of 2m. The calculated production beats are presented in Table 1.
Fig. 9 Double knife bending machine
Fig. 10 Cross section of the hall door
Table 1 Production pace
| Action | Time/s | Observation |
|---|---|---|
| Streaming | two | speed 1m/s |
| Alignment | 1.8 | |
| Doubling | 7.2 | 4×1.8s (CNC press brake) |
| +/-Changes | 1 | 1s |
| Cycle time | 12 |
An automatic hall door bending line equipped with a double knife bending machine offers highly flexible production capabilities while ensuring precision and repeatability. This production line can continuously and stably complete the bending process for hall doors with the highest production rate.
Electrical control cabinet/folding cabinet box
The production of electrical control cabinets is a highly complex process and their structure and materials vary greatly. Many manufacturers opt for the combination of a materials warehouse, punching and shearing machines, and robotic bending units to complete production.
The main advantage of this method is that as production capacity increases, manufacturers can add more robotic bending units to improve production efficiency. Furthermore, if a group of bending units is damaged, it will not affect the production of other units, ensuring uninterrupted production.
However, there are also some manufacturers who use tower punch and panel bender to produce electrical control cabinets. This approach produces greater production efficiency than robotic bending, but carries relatively high equipment costs.
In the cabinet industry, the case parts shown in Figure 11 must be taken into consideration.
Fig. 11 Box shape
The box shape is designed to increase the strength of sheet metal structures. However, when using a CNC press brake, the box height cannot be adjusted automatically and manual adjustment is required.
To enable automatic box height adjustment, a double knife press brake can be used, but installation of an additional module is required.
In many cabinets, sheathing, which refers to double-layer materials, is often used.
If bending 1.8-2.5 mm material using a CNC bending center, the situation depicted in FIG. 12 may occur. However, if a robot and press brake are used, this situation can be avoided.
Fig. 12 Water drop shape
Furthermore, the working table size of press brakes available on the market is limited to 4m. Therefore, if the length of the part is more than 4 m, the accuracy requirements for bend flatness become excessively high.
Conclusion
Bending is an art and choosing the right bending machine is a decision independent of the customer.
Signing a contract hastily can create regrettable situations and cause immeasurable losses to the enterprise.
Lastly, we aspire to help each customer build a satisfactory production line by offering powerful components in a modular way.
