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When the customer bends a thicker plate and a longer length, the model of the bending machine that needs to be selected is larger. In practical applications, the accuracy of the bending machine will be affected by many factors. Such as the uneven pressure distribution caused by the elastic deformation of the slider and the worktable of the bending machine.
For this reason, it is necessary to take corresponding measures to compensate or eliminate the deflection and deformation, and the more effective is the deflection crowning device.
As long as the bending machine is preset between the slider and the upper mold or the worktable and the lower mold worktable, a deformation amount opposite to the force deformation direction is preset. Because this deformation amount is the same as the relative deformation amount produced during actual work, so it can realize the crowning of the relative deformation of the slider pole table, make the pressure distribution between the dies more uniform, and improve the bending quality of the sheet metal.
Type of Crowning Device
- Geometric crowning
This method is not commonly used. When bending, the working plane of the worktable is processed into a slightly convex arc in the middle to compensate for the deflection generated during bending. At the same time, make appropriate corrections to the upper die of the bending machine, so that the middle part of the upper die is slightly curved.
- Hydraulic crowning
Two auxiliary hydraulic cylinders are arranged in the middle of the frame of the bending machine. When the equipment is idle downward, the auxiliary cylinder is only filled with liquid to follow the downward direction; when bending, the auxiliary cylinder enters pressure oil to make the slider produce downward deflection to compensate.
- Mechanical crowning
It adopts a triangular oblique wedge structure. In this way, the deflection crowning between the worktable of the bending machine and the slider can be increased or decreased according to the size of the bending force.
The Difference Between Hydraulic Crowning And Mechanical Crowning
- Crowning method of hydraulic cylinder
The hydraulic automatic deflection crowning mechanism of the workbench is composed of a group of oil cylinders installed in the lower workbench. The position and size of each crowning cylinder are designed according to the deflection crowning curve of the slider and the workbench finite element analysis.
Hydraulic crowning the bulge crowning of the neutral version is realized by the relative displacement between the front, middle and rear three vertical plates. The principle is to realize the bulge through the elastic deformation of the steel plate itself, so the crowning can be realized within the elastic range of the worktable adjust.
- Mechanical crowning with workbench mode
The protruding wedges are composed of a group of protruding oblique wedges with inclined surfaces. Each protruding wedge is designed according to the deflection curve of the sliding block and the working table by the finite element analysis. The numerical control system calculates the required crowning amount according to the load force when the part is bent (this force will cause the deflection and deformation of the slider and the table vertical plate). And automatically controls the relative movement of the convex wedge, thereby effectively compensate the deflection deformation produced by the sliding block and the vertical plate of the worktable, and can obtain the ideal bending parts.
The mechanical deflection crowning is realized by controlling the position of the “pre-protrusion”, and a set of wedges is formed in the length direction of the worktable. The curve with the actual deflection coincides with the gap between the upper and lower molds during bending, ensuring the same angle of the bending workpiece in the length direction. Make sure that the angle of the bent workpiece in the length direction is consistent. Mechanical crowning can obtain accurate deflection crowning over the full length of the worktable.
Dynamic Hydraulic Crowning Function
- Dynamic adjustment of bending force
In order to improve the efficiency of multi-station bending processing and reduce the difficulty of adjusting bending parameters, the dynamic adjustment function of bending force can automatically detect the load of the left and right cylinders in real-time. Automatically adjust the pressure of the left and right oil cylinders, eliminating the tedious process of preliminary debugging.
- Sheet thickness crowning function
Plates of the same model will have thickness deviations in different batches. Once the thickness changes, the use of the previously adjusted processing parameters will result in angular errors. The operator needs to repeatedly adjust the parameters, and the actual processing time of the machine tool will be wasted. The plate thickness crowning function can monitor the plate thickness in real-time.
When the deviation is detected, the pressing depth of the movable beam is automatically adjusted to compensate for the thickness deviation. There is no need to repeatedly adjust the processing parameters, which can improve the processing efficiency and reduce the difficulty of debugging the workpiece. The processing quality of the product.
- Dynamic adjustment of the deflection crowning of the workbench
Within the set bending length, if the bending force of the machine tool and the deformation of the frame change, it is necessary to manually adjust the bending parameters. When processing complex workpieces, it will cause debugging time and waste of raw materials. The machine tool adopts dynamic deflection crowning.
According to the change of the bending force, the deflection crowning amount of the worktable is adjusted in real-time to ensure that the angle of the processed workpiece remains stable under different loads.
Advantages And Disadvantages of Crowning Devices
- Geometric crowning device
Although this crowning method is low in cost and easy to manufacture, it has the disadvantages of only realizing crowning for a fixed amount of deformation and low crowning flexibility. So although it can achieve the effect of deflection crowning, it is still relatively difficult to realize.
- Hydraulic crowning device
At the same time, an auxiliary hydraulic cylinder should be arranged at the lower part of the worktable on the bending machine to generate a corresponding upward force on the worktable during bending to form an automatic deflection crowning system. This crowning method can realize the deflection crowning for the continuously changing amount of deformation. The crowning flexibility is relatively large, but the structure is complicated and the cost is relatively high.
- Mechanical crowning device
- Mechanical crowning can obtain accurate deflection crowning over the full length of the worktable. Mechanical deflection crowning has long-lasting stability, reduces the maintenance frequency of hydraulic crowning (such as oil leakage), and is maintenance-free during the life of the machine tool.
- Mechanical deflection crowning because there are more crowning points, so that the bending machine can achieve linear crowning when bending the workpiece while working, and can improve the bending effect of the workpiece.
- Mechanical crowning uses a potentiometer to measure the position of the return signal. As a numerical control axis, it realizes digital control and makes the crowning value more accurate.
How to Choose Crowning Device
Since the two bending crowning modes have different requirements for operators and different product accuracy, it is very important for buyers to understand which crowning mode should be selected.
The crowning amount of hydraulic crowning is affected by many factors, such as whether the hydraulic oil is leaking, the joint is loose, etc., which will affect the amount of hydraulic crowning each time, resulting in inconsistencies and differences in the processing of plates each time. The hydraulic crowning system is more complicated, and problems such as oil leakage and loose sealing rings may occur. The advantage of hydraulic crowning is that as the use time increases, the machine will not have wear problems, while mechanical crowning will have wear problems.
Compared with mechanical crowning, the machine using hydraulic crowning is simple to operate and does not require high workers, and can produce workpieces with higher precision. In addition, the machine with hydraulic crowning system can ensure full contact between the upper die and the plate. So as not to allow the plate to shift. From the perspective of machine durability and ease of operation, it is better to choose a hydraulically compensated machine.
The mechanical crowning composed of multiple sets of oblique wedges has more crowning points than the 3 crowning points of ordinary hydraulic crowning, there is no crowning blind zone, the precision of the folded workpiece is high, and the difference between each processing plate is small, which is suitable for mass production. Compared with the hydraulic crowning system, the mechanical crowning system is simpler, will not leak oil and other conditions, has a low failure rate and is environmentally friendly.
However, mechanical crowning will wear out the oblique wedge with the passage of time, which will affect the crowning effect. Mechanical crowning operations require high requirements. If the same workpiece needs to be bent multiple times, workers need to make real-time adjustments. Even if the workers have sufficient experience, unpredictable errors will occur. If the folded workpiece does not need to be bent multiple times and the workers have high skill, mechanical crowning can be selected from the perspective of the accuracy of the workpiece. However, in actual production, the cost of high-skilled workers is also high, so comprehensive consideration must be given.
Generally speaking, mechanical crowning and hydraulic crowning have their own advantages, but there are deficiencies, so you can choose the appropriate crowning method according to your actual needs. However, most of the current bending manufacturers choose mechanical crowning because of the advantages of good flexibility, low cost, and continuous crowning of deflection.