Formability of sheet metal

FORMABILITY OF SHEET METAL

Formability is the ability of the sheet metal to undergo the desired shape change without failure.

Generally, the sheet metal is specified in terms of gauge and mechanical properties. The behaviour of sheet metal may be altered in actual working conditions. The reason behind this alteration of its behaviour is mainly due to the change in material variables and process variables. So, the formability of sheet metal is a function of material variables and process variables.

Formability = f(f1, ƒ2)

where

f1 = Material variables and

ƒ2 = Process variables

Material variables are the basic variables that govern the ductility of material. Process variables are the applied stress system, interface friction, lubrication at the interface, die- design, product shape etc.

There are two universal laws exist which govern the material properties or variables.

Law 1: Process of fracturing

The ductility of the material will be lower if the section size is large.

Law 2: Law of geometrical similitude

This law is applicable for the fabrication of sheet and strip which is expressed by the following statements:

1. Blanks are geometrically similar in all aspects with respect to another blank such as dimension, thickness, width, length etc. These geometrically similar blanks should be fabricated by using similar tools.

2. Unit strains at corresponding locations are identical for geometrically similar blanks. 

3. The forces required to form any required shape on geometrically similar blanks are directly proportional to the square of the thickness.

4. The consumption of work for forming the required shape is also proportional to the cube of its thickness for geometrically similar blanks,

The formability of sheet metal or blank obeys these two laws while the corresponding test is carried out. The various tests should be carried out so as to acquire thorough knowledge about the formability.