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Bending Positioning Optimization For Narrow And Long Workpiece

Narrow and long workpiece is a kind of workpiece with large length-width ratio and positioning with short edge during bending.

The workpiece out of tolerance is often caused by the short contact size between the positioning edge of the workpiece and the back stop positioning of the press brake machine.

This post introduces a tooling structure for optimizing the bending and positioning of narrow and long workpieces, which basically solves the problems of difficult positioning and low precision of narrow and long workpieces.

With the rapid update of sheet metal deformation technology, CNC press brake has become one of the important production equipment for sheet metal cold deformation processing, which is widely used in the field of sheet metal processing.

Based on the consideration of safety and convenience, the existing press brake generally adopts the rear stop finger as the positioning device.

After simple programming, the rear stop linkage, single action and other functions can be realized, which is enough to meet the processing requirements of bending parts of various shapes.

However, the rear stop positioning used in CNC press brake also has its limitations.

If the width of the positioning edge of the workpiece to be processed is too narrow (such as narrow and long workpiece), when the rear stop finger is used for positioning, the contact size between the workpiece and the rear stop finger is too short, which is easy to lead to problems such as inaccurate positioning size, dislocation of bending position and design bending line, resulting in poor quality of formed products, frequent rework and repair, resulting in a huge waste of materials, energy and labor.

Bending deformation mechanism

In production, it is often necessary to fold the workpiece (steel plate) into a certain angle, and the bending radius at the bending position is small. This process is bending.

Bending is the process of applying an external force to the sheet metal by using the punch and die to bend it to a certain angle or shape.

The bending deformation of the workpiece is divided into several stages.

In the beginning, the material is free bending.

With the pressing down of the top punch, the material is gradually close to the surface of the lower die.

Then, when the punch continues to press down, the bending area of the material becomes smaller until it contacts the punch at three points.

When the punch is pressed down to the lowest point of the stroke, the material is completely close to the punch.

When the material is freely bent, the inner fiber is shortened due to longitudinal compression, and the outer fiber is elongated due to longitudinal tension, resulting in transverse shortening due to constant volume during plastic deformation.

Therefore, for workpieces with narrow width, the cross-section will be slightly fan-shaped after bending; For wide plate workpieces, the bending cross-section has no obvious deformation.

Bend positioning

Basic positioning of press brake

CNC press brake generally uses stop fingers to locate the workpiece.

The basic principle is that during bending processing, the bending program is prepared first, the workpiece shape is input into the machine controller, the bending line position of the workpiece is automatically calculated by the machine, and the CNC system controls the servo motor to move the two rear stops to the bending positioning position through the high-precision lead screw.

The operator only needs to align the positioning edge of the workpiece with the stop finger of the press brake to complete the positioning process.

At this time, the center line of the lower die of the press brake is the workpiece bending line. The state of workpiece positioning is shown in Fig. 1.

Workpiece positioning

Fig. 1 Workpiece positioning

Limitations of the positioning device of press brake

During production, it is found that when using the rear stopper positioning commonly used by the current bending machine, if the size of the positioning edge between the processed workpiece and the rear stopper is too short, it is difficult to align the workpiece with the rear stopper during positioning.

As shown in Fig. 2, the slight left-right offset of the workpiece will lead to inaccurate positioning, resulting in over tolerance scrapping of the workpiece or uneven bending edge size.

Positioning of narrow and long workpiece

Fig. 2 Positioning of narrow and long workpiece

Operators need to align repeatedly to ensure the primary forming effect, but the effect is often not ideal, which seriously affects the production efficiency and product quality.

Positioning optimization of narrow and long workpiece machining

Structure of positioning optimization device

Based on the consideration of the limitations of the positioning device of the CNC press brake, a positioning optimization device for the machine is designed, as shown in Fig. 3.

Positioning optimization device

Fig. 3 Positioning optimization device

The back plate is used to close to the side of the lower die of the bending machine;

The movable locking block is used to cooperate to lock the whole device on the lower die of the bending machine;

The front plate is used to install the screw, and the locking screw is used to fix the movable locking block on the lower die of the bending machine;

The positioning top plate is used for workpiece positioning.

Use of positioning optimization device

When using the above positioning optimization device, first align and clamp it on the lower die of the bending machine, and use a square to detect its state.

When positioning the workpiece with the positioning optimization device and the rear stop of the bending machine, the end of the workpiece is close to the rear stop of the bending machine, and the side of the workpiece is positioned with the positioning optimization device, so as to realize the accurate and stable positioning of the workpiece, As shown in Fig. 4.

Matching of rear retaining material and auxiliary positioning device

Fig. 4 Matching of rear retaining material and auxiliary positioning device

Implementation effect of the auxiliary positioning device

(1) The production efficiency is improved.

Before using this device, narrow and long workpieces often need to be measured repeatedly to ensure accurate positioning, and the error is often large.

After using the device, the operator can quickly find the workpiece to be processed, greatly improve the production efficiency of the product, and save more than half of the production and processing time for a single workpiece.

Improve the product quality.

Before using this tooling, the defective rate of narrow and long workpieces remains high, and the problems of over tolerance scrapping of the bending edge size of the processed workpieces and uneven bending edge size often occur.

After using the optimization device, the quality problems caused by inaccurate positioning of the bending line do not occur again, and the product quality is greatly improved.

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