The influence of deformation compensation device on precision of WC67K-125T3200 Hydraulic Press Brake machine

When the sheet material is bent, because the die has made convex compensation, when WC67K-125T3200  Hydraulic Press Brake machine and unloading, the spring back will produce a new longitudinal flexure, and the two effects are superimposed to get the final flexure of the piece.

In this paper, the influence of two kinds of compensation devices on the precision of parts is analyzed, and the characteristics of common deflection compensation devices are compared. It is pointed out that the upper die plus convex compensation has more advantages. Therefore, the development of a new compensation structure which can quickly control the upper die plus convex is one of the development directions of the bending machine in the future.

1. Why do hydraulic Press Brake machine need compensation devices?

When the bending machine bends the workpiece, under the action of the bending force, the slider and the table will produce deformation. At this time, the depth of the upper die into the lower die opening is not consistent on the full length of the workpiece, which will seriously affect the precision of the workpiece.

For this reason, many kinds of deformation compensation devices have been developed. It can be roughly divided into two categories: one is a set of symmetric curves that convex the worktable into the middle of the upward uplift, which is called the convex compensation of the lower die; The other type is to convex the upper die or slider into the middle of the downward convex symmetric curve, called the upper die convex compensation.

The two kinds of compensation devices can effectively reduce the Angle error of the bending part. But the effect on straightness is different.

2. Natural deflection of the bending part

After the sheet material is bent, the edge of the bending part will appear natural deflection. Usually, it's denoted by its maximum deflection.

When the sheet metal is bending, the metal in the bending deformation area is in a highly plastic deformation state. The inner layer of the arc in the deformation area produces longitudinal compressive stress parallel to the OX direction, and the outer layer is longitudinal tensile stress.

These two stresses in opposite tension and compression form the longitudinal torque My rotating about the OY axis. It is the moment needed to keep the longitudinal (direction) of the bending part consistent with the longitudinal line corresponding to the die when the sheet material is bent.

When the slider returns after bending, the bending force and the longitudinal moment disappear at the same time, and the metal layers in the deformation area bounce back immediately, forming a longitudinal bending in the opposite direction to the longitudinal moment, that is, natural deflection.

For the convenience of expression, the bending deformation region is expanded into a plane. Under the bending force, the upper (inner arc) metal is longitudinally compressed, and the lower (outer arc) metal is tensioned.

3. Influence of two different convex compensation methods on straightness of bending parts

When the lower die is compensated with convex, the curve of compensating convex increases upward. When convex compensation is added to the upper die, the curve of convex amount is bent downward.

The natural deflection curve of a bending part is an upward bulge. The offset convex gen is small when the slider and table are bent. The convex deflection caused by compensating the convex deflection of the bending part should be somewhat reduced when unloading and springback. This makes the deflection caused by the convex increase usually lower than the natural deflection of the bending part.

4. Comparative analysis of four commonly used compensation devices

1) Convex compensation for lower beam hydraulic cylinder

After the cylinder passes through the pressure oil, the beam will uplift upward, forming a group of controllable convex curves, which is widely used in CNC bending machine. Its characteristics:

The cylinder is evenly distributed in the beam, and the convex curve is close to the deformation curve of the slider and the table on the full length of the table. Hydraulic system pressure control bump, easy to operate.

It can improve the precision of bending Angle. The structure is complex and the cost is high.

2) the wedge in the worktable is compensated with convex

A plurality of groups of wedges are arranged under the table, and the bevel Angle of each group of wedges is designed according to certain requirements. The horizontal position of the upper wedge of each wedge block is fixed, and the current wedge block moves to the left at the same time, so that the work table will uplift upward according to the design requirements. Has been widely used in various types of bending machine.

Its features:

The wedge is evenly distributed in the worktable, and the convex curve is designed into the deformation curve of the slider and the worktable, and the convex compensation is more accurate. @ Use the moving length of the lower wedge to control the convex amount, which can be manual or maneuverable, easy to operate.

It can improve the precision of bending Angle.

3) Upper die wedge plus convex compensation

There are multiple groups of wedges arranged between the slider and the upper die, each group of wedges has the same specification. The lower wedge connecting the plate and the wedge is fixed as a whole, and the upper wedge can be moved to obtain a convex curve of downward uplift, and finally they are fixed between the slider and the upper die with a press plate.

Its features:

Wedge evenly distributed under the slider, through the adjustment of each wedge, can obtain the best convex curve simple structure, low cost, but the operation is not convenient, in the middle and small common bending machine is widely used after accurate adjustment, can effectively improve the accuracy of bending Angle, the straightness of the workpiece is good.

4) Slider hydraulic cylinder plus convex compensation

A group of oil cylinders is arranged in the middle of the slider. After the cylinder is filled with pressure oil, the middle part of the slider rises downward, forming a controllable local convex curve. Due to the structure limitation, the two sides of the slider can not be effectively convex, and this compensation method has not been widely used.

Its characteristics are as follows: the convex compensation is concentrated in the middle of the slider, and a reasonable convex curve can not be formed on the full length of the upper die; Hydraulic system pressure control bump, easy to operate; It can improve the Angle and straightness accuracy of the parts properly.

When the bending machine is working, the convex amount of deformation compensation should be equal to the deformation amount of the slider and the table, which requires the compensation of convex amount can be adjusted on the full length of the mold, convenient and fast. However, the structure of upper die plus convex compensation is difficult to achieve this requirement, which limits its scope of use. In order to improve the working accuracy of the bending machine and give full play to the advantages of the upper die plus convex compensation, the development of a new type of fast control of the upper die increase of the new structure is one of the development directions of the future bending machine. At present, some departments have made useful attempts in this respect and achieved good results.