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The difference between hydraulic crowning and mechanical crowning

When customers buy CNC press brake, they are more concerned about the straightness of the metal plate. At this time, they will talk about whether to use mechanical or hydraulic crowning. Except for tonnage, length, throat depth, we also need to consider the press brake crowning system.

crowning system
Press brake crowning methods as following:

1. No crowning (if the press brake does not have a crowning function. When the angle error occurs, then it can only rely on manual methods to correct the work-piece angle. Such as hammering, etc.).
2. Hydraulic crowning which is a partial crowning function. It relying on the crowning cylinder of the workbench under the press brake for partial angle crowning. It can’t achieve the overall crowning effect).
3. Mechanical crowning, it is an overall crowning method. It solves the angle of the bending work-piece due to the unpredictable factors. Such as the difference of materials and the deflection of the equipment during the bending process.

When the CNC press brake exerts a force on the plate which will produce a reaction force on the machine. This reaction force will cause the machine to deform, thereby affecting the accuracy of the folded plate. To improve the bending accuracy, mechanical crowning and hydraulic crowning two press brake crowning methods came into being. The bending crowning modes of the two AVIDO press brakes have different requirements for operators. Such as different folding accuracy, and large differences. Buyers need to understand which crowning mode should be selected.
Through crowning, offset the deformation of the machine tool slider. Thereby ensuring the accuracy of the machining joint surface and improving the accuracy of the work-piece.

1. Crowning method of hydraulic cylinder:

Elector-hydraulic servo press brake + hydraulic deflection crowning

A group of oil cylinder composes the hydraulic automatic deflection crowning mechanism. It designs the position and size of each crowning oil cylinder. It is according to the deflection crowning curve of the slider and the finite element analysis of the worktable. Hydraulic crowning is through the relative displacement between the front, middle, and back three vertical plates. Then it can achieve the neutral version of the convex crowning. The principle is to achieve the convexity through the elastic deformation of the steel plate itself, so the crowning amount can be achieved within the elastic range of the worktable adjust.

Hydraulic crowning means that several small oil cylinders are placed under the workbench. When the machine is deformed, additional force is applied through these small oil cylinders to compensate, thereby reducing the influence of machine deformation on the folded plate. CNC hydraulic crowning is to set the parameters of the CNC system of the press brake according to the length and thickness of the folded sheet in the CNC system of the machine, calculate the required crowning amount through the computer system of the machine, and transmit the command to the crowning Amplifier. The hydraulic crowning proportional valve receives the signal sent by the crowning amplifier to control the small oil cylinder under the working table to bulge and reduce the deflection deformation of the plate.

However, many factors will affect the amount of crowning for hydraulic crowning. Such as whether the hydraulic oil leaks or the joint is loose, etc. It will affect the amount of hydraulic crowning every time, resulting in inconsistencies and differences in the processing of plates each time. The hydraulic crowning system is relatively complex, and problems such as oil leakage and loose seals may occur. The advantage of hydraulic crowning is that with the increasing use time, the machine will not have to wear problems, and mechanical crowning will have wear problems. Compared with mechanical crowning, the machine with hydraulic crowning is simple to operate and requires fewer workers. It can fold out the work-piece with higher precision.

Also, the machine with a hydraulic crowning system can ensure the full contact between the upper mold and the plate, so that the plate will not be displaced. From the perspective of machine durability and ease of operation, it is better to choose a machine with hydraulic crowning.

2. Mechanical crowning table method:

Double electric servo hybrid press brake + mechanical deflection crowning

The convex wedge is composed of a set of inclined convex wedges with an inclined surface. Each convex wedge is designed according to the deflection curve of the finite element analysis of the slider and the table. The CNC system calculates the required crowning amount according to the load force when the work-piece is bent (this force will cause the deflection deformation of the slider and the table vertical plate), and automatically controls the relative movement of the convex wedge, thereby effectively Crowning of the deflection deformation of the slider and the vertical plate of the worktable can obtain the ideal bending work-piece.

The mechanical deflection crowning is to achieve “pre-bump” by controlling the position. A set of wedge blocks form a curve of the actual deflection coincides, so that the gap between the upper and lower molds is consistent during bending, ensuring that the angle of the bending work-piece in the length direction is consistent.

Hydraulic crowning uses a small cylinder to compensate the worktable, while mechanical crowning uses an inclined wedge to compensate the worktable. The inclined wedge block can be divided into a single inclined wedge block and multiple groups of inclined wedge blocks. The mechanical crowning composed of multiple sets of inclined wedges has more crowning points, more than the three crowning points of ordinary hydraulic crowning, there is no crowning blind area, the accuracy of the folded work-piece is high, and the difference in each processing of the plate is small, suitable for mass production. Compared with the hydraulic crowning system, the mechanical crowning system is simpler, does not cause oil leakage and other conditions, and has a low failure rate and is environmentally friendly.

However, the mechanical crowning will wear out with the use of time, the inclined wedge will wear out, thus affecting the crowning effect. The requirements for mechanical crowning operations are high. If the same work-piece 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 work-piece does not need to be bent multiple times, and the worker has high technology, mechanical crowning can be selected from the perspective of work-piece accuracy. However, in actual production, the cost of high-tech workers is also high, so it must be considered comprehensively.

Mechanical crowning advantages:

1. Mechanical crowning can obtain accurate deflection crowning over the entire length of the table. Mechanical deflection crowning has long-lasting stability, reduces the maintenance frequency of hydraulic crowning (such as oil leakage). It is maintenance-free during the life of the machine tool.
2. Mechanical deflection crowning Because there are many crowning points, the press brake can achieve linear crowning when bending the work-piece. It also can improve the bending effect of the work-piece.
3. Mechanical crowning is to use the potentiometer to measure the return signal position, as a CNC axis, to achieve digital control so that the crowning value is more accurate.

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