Sheet Metal Bending Tool Design

V- bending Tool:-

V-bending tools are used to bend a component in v-shape. The tool consist of a v-shape punch and v-die. The punch and die is mounted in die sets or punch can be directly fixed to the press ram.

V- bending is classified in three groups:

Air bending
Bottoming
Coining

Air Bending:-

Air bending is also known as partially bending because while bending, component does not touch the die entirely. In air bending the component blank is placed on two points of bending die and the punch moves downward to pushes the bend. The bend angle is controlled by the length of the punch travel. In this bending process the component have slightly greater springback. This method is less accurate than bottoming and coining process.

Bottoming:-

In this process punch presses the component blank onto the surface of the die. In bottoming the inner radius of component is depends upon the die radius. The effect of spring back is lessen by compressing the inner line.This is most commonly used method in the bending. Die opening is generally taken as 6 to 8t for sheet thickness less than 2.5 mm and 8 to 10t for sheet thickness above 2.5 mm (where, t is sheet thickness of component).

The inner radius of bending is depends upon die opening. It is generally equal to 1/6 times of the die opening width.

R = W/6

Where, R = inner radius

W = die opening.

Coining:-

In coining process punch and die are made exactly with the same angle as required. In coining process both punch tip & punch penetrates into the work piece, due to this the bend radius is always equal to the punch tip.The penetration of punch also relieves the internal stresses and eliminate the spring back. Coining is very good method to control the springback.

U- Bending Tool :-

U-bending tools are used to bend a flat strip to U shape.The tool consist of a punch, U shaped die and a pressure pad. U bending tools without pressure pad can be used for rough work. But the bottom of the work piece will not be straight, it can be straightened by applying the pressure at the bottom corner. This pressure should be 0.3 x bending force. To get the straight bottom a convex radius can be provided at the bottom face of the die (pressure pad) and corresponding concave radius on the punch. The concave radius should be more than or equal to Rmax.

The pressure pad performs three functions:-

Holding the workpiece during bending.
Serves as bottoming block for setting the bend.
Act as a stripper or ejector.

The face of the pressure pad should be flush with the die face when the tool is in open condition. The fit between the pad and the die walls is slide fit (H7g6). This fit avoid the entry of foreign particles. During the bending operation strong lateral forces act on the die, so the construction of die should be strong.

Wipe Bending Tool:-

Wipe bending is also known as edge bending. This tool is used to bend the edge of sheet metal. The construction of this tool is very simple. The bend radius is depends upon the radius of wiping die. A pressure pad is used to hold the workpiece tightly during the bending process.

Bending Force Calculation formula:-

The amount of force required to bend the sheet is called bending force. This force directly proportional to the tensile strength of sheet metal, thickness of sheet metal and bending length of the workpiece. And inversely proportional to the die opening.

Bending force, U-bending, V- bending, edge bending

SHEET METAL BENDING FORCE