German industry 4.0, American industrial Internet and the implementation of “made in China 2025” all confirm that the core of the fourth industrial revolution in the global manufacturing industry is intelligent manufacturing, which is particularly obvious in China’s sheet metal manufacturing industry.
It is composed of laser cutting, sheet metal welding, cutting, cutting, welding and so on.
This post mainly discusses bending technology.
Table of Contents
Common bending methods
Die bending
Die bending is usually completed on the press brake machine (Fig. 1). Workers or robots are needed to assist in the bending process.
Its bending accuracy depends on the skilled operation of technicians or the quality of the robot.
This kind of bending method is widely used in the production of small parts with single product type and simple process.
Folding machine (Fig. 2) can be applied to the bending of large parts with many kinds and complex structures.
The bending shape that single knife automatic folding machine and double knife automatic folding machine can complete is shown in Figure 3.
Fig. 2 Working principle of folding machine
Fig. 3 Folding shape
Double knife bending and CNC bending
The double knife bending machine is a variant of the folding machine (Fig. 4). Its working principle is the same as the folding machine, and it can bend a wide range of shapes and types.
Fig. 4 Principle of double knife bending machine
CNC press brake is the most commonly used bending machine in bending center (Fig. 5). The famous bending machine manufacturers can refer to this ranking.
Fig. 5 Principle of CNC press brake
The flexibility of the double knife bending machine and CNC bending machine is very high, basically equivalent to “universal folding”, which is widely used in automatic production.
Until 2018, both will be powered by hydraulic power.
After that, the CNC bending machine began to use servo drive, and only use the hydraulic drive to clamp the toolings.
There are several main differences between them:
(1) Bending speed.
Under the same conditions, the bending speed of the CNC bending machine will be slightly faster.
It takes 1.8 ~ 2 s to bend a 90 ° workpiece structure, while it takes 2 ~ 3 s for double knife bending machine (according to the size of the profile).
(2) Bending clearance.
The cutter shape of the double knife bending machine is different from that of CNC bending machine (Fig. 6)
When the clamping device can be adjusted, the force area of the CNC bending machine is relatively small, resulting in damage or scratch on the surface of the workpiece (Fig. 7).
Fig. 6 Bending clearance
Fig. 7 Surface scratch
(3) Bending shape.
Figure 8 shows the bending shape of the double knife bending machine and CNC bending machine.
Fig. 8 Bending shape
Bending case analysis
Now punching technology is more mature, especially with the popularity of punching units represented by Trumpf and Amada, laser drilling and laser cutting technology have become popular.
In the whole sheet metal production process, bending is still a major process bottleneck, which seriously affects the beat balance between processes and restricts the improvement of workshop capacity.
Bending case of elevator hall door panel
The structure of the elevator hall door panel is relatively simple, and the number of punching holes is small.
Most manufacturers usually use punching center + bending center to complete production.
The bottleneck of this production mode is bending.
When bending, the workpiece needs to rotate three times, and adjust the corresponding tool to complete the bending process, the time is 35 ~ 45 seconds/piece.
If a bending center is added after the production line, the production time is 20 seconds/piece, the speed and efficiency are increased, and the production cost is also increased.
If the double knife bending machine (shown in Fig. 9) is adopted, both sides of the workpiece can be bent at the same time. At this time, the workpiece only needs to rotate once, and its production rhythm is 12-15 seconds/piece.
We take the workpiece with the section shape as shown in Figure 10 and the length of 2m as an example, and the calculated production beat is shown in Table 1.
Fig. 9 Double knife bending machine
Fig. 10 Cross-section of the hall door
Table 1 Production rhythm
Action
Time/s
Note
Transmission
2
speed 1m/s
Alignment
1.8
Bending
7.2
4×1.8s (CNC press brake)
+/-Changes
1
1s
Cycle Time
12
An automatic hall door bending line with double knife bending machine can not only provide highly flexible production, but also ensure accuracy and repeatability, and can continuously and stably complete the hall door bending production with the highest output rate.
Electric control cabinet/cabinet bending case
The electric control cabinet is a very complex product, its structure and material change greatly
The advantage is that with the increase of production capacity, the number of robot bending units can be increased, so as to improve production efficiency.
When a group of the bending units is damaged, it will not affect the production of other units, and ensure uninterrupted production.
There are also some manufacturers using turret punch + panel bender to produce electric control cabinet, its production efficiency is higher than robot bending, of course, the equipment cost is relatively high.
In the cabinet industry, box parts shown in Figure 11 need to be considered.
Fig. 11 Box shape
Box shape is to increase the strength of sheet metal structure. In the case of CNC bending machine, the height of the box cannot be adjusted automatically (the manual adjustment is required).
The double knife bending machine can automatically adjust the height of the box, but the module needs to be installed.
In a lot of cabinets, there will be hemming (that is, double-layer materials).
If CNC bending center is used to fold 1.8-2.5mm material, the situation shown in FIG. 12 will appear, but if robot + press brake machine is used, this situation will not occur.
Fig. 12 Water drop shape
In addition, the worktable of press brake machine on the market is within 4m. If the length of the workpiece is more than 4 m, the accuracy requirement for the bending flatness will be very high.
Hi, I'm Shane—founder of MachineMfg. I have worked in the metalworking industry for more than 10 years. I do a lot of thinking, reading, and writing around sheet metal fabrication, machining, mechanical engineering, and machine tools for metals.
