There are many factors affecting the bending accuracy, among which the uneven plate thickness, the hardness of the plate, the deformation of the workbench and ram during bending, the selected die opening, the depth of the upper die into the lower die, the wear of the die and the convexity of the workbench will cause the error of the bending angle and straightness of the workpiece after bending.

The die opening and the depth of the upper die into the lower die are controlled by manual programming.

## Influence of material quality on accuracy #

The nominal bend is the free bend low carbon steel plate with tensile strength σb= 450N/mm² and bends the sheet into a 90 ° angle on the V-shaped die with opening distance V = 8 × S.

When the nominal bending is carried out with plates with uneven thickness, the angle error will appear;

When the hardness of the plate is not uniform, the springback of the workpiece during bending is not equal.

Therefore, the quality of materials has a great impact on the processing quality.

## Worktable convex compensation #

Under the action of load, the workbench and ram will produce elastic deformation.

The depth of the upper die into the lower die is uneven in the whole length, which affects the bending angle and straightness of the workpiece.

In order to solve this problem, the machine adopts the NC convex of the worktable to compensate its deformation, keep the depth of the upper die into the lower die basically uniform in the whole length, and improve the accuracy of bending angle and straightness of the workpiece.

## Eccentric load #

Eccentric load refers to load operation on the left or right side of the ram. The machine has strong ability to resist eccentric load.

Under the action of eccentric load force, the tilt will be generated between the workbench and the ram.

The grating detection mechanism at both ends of the ram will detect the deviation and feed it back to the computer, and the computer controls the proportional servo valve to adjust the amount of oil entering the oil cylinder, so as to keep the position of the two pistons synchronized and maintain a small parallelism error between the workbench and the ram.

If special parts are processed, the above eccentric load shall be understood. In general, it is necessary to avoid eccentric load operation.

## Correction of bending angle error #

When the bending part has been formed, the angle is about α °, measured angle error value △ α ° can be corrected by adjusting the position Y of the bottom dead center, and the correction value △ Y is approximately calculated according to the following formula:

**△Y=K × V × △a**

Where:

- △ Y – correction value of bottom dead center (mm)
- V – selected die opening (mm)
- △ α – Angle error value (degrees)
- K – Correction factor (degree /mm)

When α ≈ 90 °, K ≈ 0.0055; For folded 8 ~ 12 sided steel rod, when α ≈ 135 ° ~ 157.5 °, K ≈ 0.004.

If the inspected part angle is greater than the drawing requirements, adjust the bottom dead center position downward according to the correction value △ Y; Otherwise, adjust upward.

**Example 1:**

The angles at both ends are equal to the middle angle.

Fold dodecagon, α= 150 °, select the opening V = 200m, and measure the angle after bending α= 151.5 °, according to the above method: △ α = 1.5 °; K=0.004

△Y=K × V × △a=0.004 × 200 × 1.5=1.2mm

Input the bottom dead center Y + △ Y into the computer.

**Example 2:**

The angles at both ends are not equal to the middle angle.

Opening with V = 60mm, bend α= 90 ° workpiece. Actual measured angle at both ends α= 90 °, middle angle α = 91 ° (the convex amount is not enough).

According to the above method:

△α=1°； K=0.0055

△Y=K × V × △a=0.0055 ×60 × 1=0.33mm

Add △ Y to the original convex value and input it into the computer.

If the middle angle is smaller than the angle at both ends (the convex amount is too large), reduce the convex value by △ Y on the original basis and input it into the computer.

**Example 3:**

The angles at the lower ends of the column are not equal. Opening width V = 60mm, bend α= 90 ° workpiece.

Actual measured left end angle α= 90 °, right end angle α= 91 ° (lower left and higher right).

According to the above method:

△α=1, K=0.0055

△Y=K × V × △a=0.0055 × sixty × 1=0.33mm

Input the Y + △ Y value of the zero point at the right end upward to change its reference position.