Unit IV-manufacturing Technology

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UNIT IV

SHEET METAL PROCESS

Typical shearing Operations

1. Punching: shearing process using a die and punch where the interior portion of the sheared

sheet is to be discarded.

2. Blanking: shearing process using a die and punch where the exterior portion of the shearing

operation is to be discarded.

3.

Perforating: punching a number of holes in a sheet

4. Parting: shearing the sheet into two or more pieces

5. Notching: removing pieces from the edges

6. Lancing: leaving a tab without removing any material



Shearing

• Shearing is the cutting action along a straight line to separate metal by two moving blades.

• In shearing, a narrow strip of metal is plastically deformed to the point where it fractures at thesurfaces in contact with the blades.

• The fracture then propagates inward to provide complete separation. It is used for production of

blanks.

Shaving Process

Bending



Types of Bending

1. Air Bending,

2. Die Bending, And

3. Edge Bending.

In air bending, the work piece is supported only at the outer edges so that the length of the ram stroke

determines the bend angle of the part.

In die bending, the sheet is forced into a female die cavity of the required part angle.

In edge bending, the base of the sheet is held between a pressure pad and a die while the sheet is

forced to yield and bend over the edge of the die.



Bending Terminology

Stretch Forming

• Stretch forming is very similar to deep drawing. It differs from deep drawing in that the material

is clamped tightly between the binder and die. Deformation is restricted to the area within the

lock beads. Stretch forming is used to form compound curves in sheet stock.

Deep Drawing

• In deep drawing, a sheet blank (hot or cold), is forced by a punch into and through a die to form

a deep recessed part having a wall thickness essentially the same as that of the blank.



• If the amount of shape change required in deep drawing is too severe, then more than one

drawing operation is required to form the part completely.

Special Forming Process

Hydro Forming Process

Spin Forming

Spinning is the process of shaping seamless hollow cylinders, cones, hemispheres, or other

axially symmetrical metal shapes by the combined forces of rotation and pressure.

Spinning does not result in any significant change in thickness.



Rubber Pad Forming

Explosive Forming

• Explosive forming changes the shape of a metal blank or preform by the instantaneous

high pressure that results from the detonation of an explosive.

• The work piece is clamped and sealed over a die and the air in the die cavity is

evacuated.

• The work piece is then placed in a tank filled with water.

• An explosive charge detonated at a certain distance generates a shock wave whose

energy is high enough to form the metal.

• Explosive forming is reserved for large parts, typical of the aerospace industry.



Magnetic Pulse Forming

Super plastic forming

In Superplastic forming, a sheet of metal is clamped between a die cavity and a plate which

are kept at the convenient temperature. Gas pressure is applied to deform the sheet by

forcing it against the walls of the die cavity, under suitable stress and deformation rate

This process applies to Titanium, Aluminum, some Inconel and magnesium alloys.

Step 1 : Plastic deformation, then creep of irregular zones. In this stage, surfaces are brought

unto further contact and phenomena such as oxide film rupture occur.



Step 2 : Grain growth across the interface, whereby new joints tend toward equilibrium.

Remaining pores begin to disappear by diffusion at grain boundaries.

Step 3 : Elimination of last pores by diffusion through the metal volume.

Peening

Shot peening is a process specifically designed to enhance the fatigue strength of components

which are subject to high alternating stress. Surface treatment procedures like grinding,

milling, bending or heat treatment procedures cause Tensile Residual Stress. This Tensile

Residual Stress leads to low life cycles of the parts. Shot Peening converts Tensile Residual

Stress into Compressive Residual Stress which leads to significant increases in the life cycle ofparts and their maximum load capacities.

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Unit IV-manufacturing Technology