Bending, Bending Methods and Bending dies: Bending and bending dies

Bending, Bending Methods and Bending dies:

Bending and bending dies:

Bending is the metal working process by which a straight length is transformed into a curved length. It is very common forming process, for changing sheet and plate into channels, drums and tanks etc.

During the bending operation, the outer surface of the material is in tension and the inside surface is in compression. The strain in the bent material increases with decreasing the radius of curvature. The stretching of the bend causes the neutral axis to move toward the inner surface. In most cases, the distance of the neutral axis from the inside of the bend is 0.3 t to 0.5 t , where “t” is thickness of the part.

Bending terminology is illustrated in figure.

Bending Methods:

The two bending methods commonly used are v-bending and edge bending.

V- Bending:

In v-bending , a wedge shaped punch forces the metal sheet or strip into a wedge shaped die cavity, shown in fig.

The bend angle may be acute 90°, or obtuse. As the punch descends , the contact forces at the die corner produce a sufficiently large bending moment at the punch corner to cause the necessary deformation. To maintain the deformation to be plane strain , the side creep of the part during its bending is prevented or reduced by incorporating a spring loaded knurled pin in the die.

2: Edge Bending:

In edge bending , a flat punch forces the stock against the vertical force of the die. The bend axis is parallel to the edge of the die and the stock, is subjected.

Broach:

A broach is a multi point cutting tool having a series of cutting teeth or edges which gradually increase in size from the starting or entering end to the rear end. Broaches are used for machining either external or internal surfaces. These surfaces may be produced flat or circular. In broaching, the broach is pushed or pulled over or through a surface of work piece, Each tooth of the tool. A thin slice from surface broaching of inside surface is called internal or hole broaching and outside surfaces is called surface broaching.

Detail of an internal or hole broach:

A typical broach is shown in figure.

It is used to machine an internal hole. The broach is gripped by puller at the shank end. The front rake angle refers a rake angle of a single point cutting tool and back of the angle (relief angle) is provided to prevent rubbing of the tool with the work piece.

High speed steel (Hss) material is widely used to make the broach. It is also raised carbide of disposable inserts or sometime used for cutting edges then machining cost iron parts, which requires close tolerance. Carbide tools are also used to an advantage  on steel cutting. A broach may be either assembled or built up form shells.