Sheet Metal Z-bending and N-bending (Precautions)

Definition: zigzag bending is called Z bending.

Standard bending process range: height of Z bending > apothem of V groove + Thickness

The minimum processing size is limited by the model used while the maximum processing size is determined by the shape of the machine table.

Z Processing Procedures

1. Processing to form a L bending
2. Bend the horizontal side of the L bending to form a Z bending (or bend the vertical side of the L bending to form a Z bending)

Workpiece Placement Principles for Z-bending

A: Convenient, good stability.

B: Generally is similar to L-bending.

C: The workpiece is flat with the lower die during the 2^nd placement.

Matters Need Attention for Z-bending

• The angle of L bending should be as accurate as possible, normally ranging from 89.5 °to 90 °.
• The back gauge should be set up to prevent deformation of the workpiece.

General Processing Methods of Z bending

• The processing sequence should be considered as shown in the following picture, first bend 1 and then bend 2.

• First bend to form an L bending and then further processed to form a Z bending (if interfere with machine worktable, first bend 1 to form a large angle, then bend 2 and then press 1)
• Using two acute angles to form Z bending: first bend into a right-angle, then insert 2 and then insert 1

1) If there is a collision, first bend 1 to form a large angle, then bend 2 and then press 1.

2) if no collision, as per general Z bending processing method, first bend 1 and then bend 2.

Special Processing Method of Z bending

A: lower die decenter processing

B: small V groove processing

C: bending to form a large angle, then pressing

D: choose grindable lower die

Other Z Bending Methods

A: process with offset die

B: process with the transformable die

N Bending Processing

Definition: continuously process the same machining surface twice to form N bending

Precautions for N-bending Processing

1. the angle of the first bending should be less than or equal to 90°
2. the back gauge of second bending should be based on the machining surface

Special Processing Method of N Bending

• if interfere with the top punch a little after Y sizes N-bending ==> flattening with hemming die after N-bending.
• if interfere with top punch very serious after Y sizes N bending ==> bend to collision position after A bend press line, positioning C and bending B point, then use hemming die + padding to form into shape.

• Processing with shaping punch and die.

Arc Processing

Arc processing is divided into two kinds: circular cutting with bending model and circular cutting with arc knife.

The arc knife is divided into two types: fixed and rod.

Precautions

A: when machining with  90°low die, there may be inadequate machining, so it is necessary to push the mold with hand or if possible, using  88°low die.

B: detect with detecting appliance to ensure the appearance size of the workpiece.

C: when processing 90°arc, the low die should choose 2 (R+T)

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