Press brake machine is an important equipment in sheet metal processing, and its working accuracy directly affects the bending accuracy of work pieces. In the bending process of the work pieces, because the two ends of the ram are stressed mostly. the reaction force when the plate is bent leads to concave deformation of the lower surface of the ram, and the deformation of the middle part of the ram is the most, the final bent work pieces have different angles in the whole length direction. In order to eliminate the adverse effects of ram deformation. it is necessary to compensate the deflection deformation of ram. The usual Crowning Systems are hydraulic Crowning and mechanical Crowning, which make the middle part of the workbench produce upward elastic deformation to offset the deformation of the ram of Press Brake, ensure the precision of machining joint surface and improve the precision of work piece. At present, major foreign press brake manufacturers have adopted mechanical crowning devices. Domestic manufacturers will choose the appropriate Crowning method according to the actual situation.

The difference between mechanical crowning and hydraulic crowing

1. Mechanical crowing

The convex wedge consists of a set of projecting inclined wedges with beveled surfaces. Each projecting wedge is designed by finite element analysis according to the deflection curve of slider and table.

The CNC controller system calculates the required amount of crowning based on the load force. This force causes deflection and distortion of the vertical plate of the slider and table. And the relative motion of the convex wedge is automatically controlled, so that the deflection deformation generated by the slider and table vertical plate can be effectively crowning and the ideal bending work pieces can be obtained.

The actual deflection curves overlap, so that the upper and lower tool clearance is consistent during bending and the angle in the length direction of the bent work piece is consistent.

The mechanical camber allows accurate deflection crowning over the full length of the table. Mechanical deflection crowning provides long-lasting stability and reduces the frequency of maintenance (e.g., oil leaks) for hydraulic crowning, making it maintenance-free for the life of the machine.

Mechanical deflection crowning allows the bending machine to achieve linear crowning when bending work pieces in operation due to the high number of compensation points, which can improve the bending effect of work pieces. Mechanical crowning is driven by the motor as the CNC control axis to achieve CNC control, so that the crowning is more accurate.

2. Hydraulic crowing

Automatic hydraulic deflection crowning of the worktable consists of a set of cylinders mounted on the lower worktable. According to the deflection crowning curve of the slider and the finite element analysis of the table, the position and size of each crowning cylinder are designed.

The hydraulic is to achieve the convex compensation of the neutral plate by the relative displacement between the front, middle and back three vertical plates. The principle is to realize the convexity through the elastic deformation of the plate itself, so the crowning amount can be adjusted within the elastic range of the table.

How to choose the correct crowning system?

Due to the difference in operator requirements and product accuracy between the two bending machine crowning methods, it is important to choose the correct bending crowning.

Hydraulic crowning uses a small cylinder to compensate the table, while mechanical crowning uses a tilting wedge to crowning the table. Slanting wedge can be divided into single slanting wedge and multiple groups of slanting wedge. The mechanical crowning composed of multiple groups of inclined wedges has more crowning points, more than the ordinary hydraulic crowning of 3 crowning points, there is no crowning blind area, the work piece folded with high precision, each processing plate difference is small, suitable for batch production.

CNC control hydraulic crowning: we set bending parameters in the cnc controller, such as plate thickness, plate length, material. cnc controller will automatically calculate the required compensation value, and then send the command to the crowning amplifier. The crowning amplifier sends the signal to the hydraulic crowning proportional valve, which controls the small cylinder bulge under the worktable to reduce the deflection of the plate.

However, the hydraulic crowning value is affected by various factors, such as whether the hydraulic oil is leaking or not, whether the joint is loose or not, which can affect the amount of hydraulic crowning each time, resulting in inconsistency and variation in the processing of each sheet. Time.

The hydraulic system is more complex and may have problems such as oil leakage and loose seals. The advantage of hydraulics is that the machine does not experience wear problems with increased use time, whereas mechanical crowning can experience wear problems.

Compared to mechanical crowning, hydraulically crowning machines are easy to operate and therefore can help bend with greater accuracy. In addition, the machine has higher durability.Hydraulic crowning uses small cylinders to compensate the table, while mechanical crowning uses wedges to compensate the table. Slanting wedges can be further divided into single slanting wedges and multiple sets of slanting wedges.

Multi-group inclined wedge mechanical crowning has more crowning points than hydraulic crowning, while common hydraulic crowning has only 3 crowning points, no compensation blind zone, higher accuracy of folding work piece, small processing plate each time, and suitable for mass production.

Compared with the hydraulic crowning system, the mechanical crowning system is simpler, will not cause oil leakage and other situations, low failure rate, and environmental protection.

However, after long-term use, the mechanical convex bevel wedge will wear out and affect the crowning effect. Mechanical crowning has higher requirements for operation. If the work piece needs to be bent in multiple steps, workers need to make real-time adjustments.

If the work piece needs only one step of bending, our workers are highly skilled. We can choose mechanical crowning from the perspective of work piece accuracy. In actual production, we must consider the ability of workers, the cost of highly skilled workers, etc.

To sum up, both hydraulic crowning and mechanical arch crowning have their own advantages. We can consider configuring the table crowning of our ZFY CNC press brake according to the above aspects.