CHAPTER ONE
1.0    INTRODUCTION
1.1    Importance of Sheet Metal Work and Bending Machine
What is a metal? It is a strong shinny, which conducts electricity and melts when you make it hot enough. But surely metal must be something more than this because there are other substances such as carbon,, glass and rubbers, which are, obviously not metals but can also variously claim to have strength, elasticity or electrical conductivity.
Furthermore, most of the metals will melt when heated sufficient. What then is a metal? A study of simple metallurgy will show that there is one important factor, which distinguishes metals from non-metals and that is the neat, orderly arrangement of the atoms into regular geometric molecules. Metal is a good conductor of heat and electricity and forming basic oxides.
An alloy is a fused mixture or compound of two or more pure metals. The reasons for making these mixtures are many and various. Pure metals have certain desirable properties but are often lacking in other ways. Therefore it is necessary to mix other metals with them in order to preserve and improve their basic properties. To quote a well known example: Aluminum is a light weight metal which makes it useful for aircraft construction, but it is also soft and weak so a small quantity of copper is added to it to give the necessary strength and rigidity (Courtesy, 1980).
The subsequent development of iron and steel to suit its use in various forms enables it to serve effectively wherever used. Iron and steel remains the most vastly used material for structural works, enclosures and packages.  
The most popular forms of iron and steel remains the sheet form, mostly used in enclosure and vessel fabrication. The term metal sheet refers to lighter gauges of steel in rolled form ranging in thickness from approximately 0.4mm to 3.2mm. (Surenda singh, 1979).
Many engineering components are produced from flat sheets of metal which are cut to shape and then folded to form the finished article. The edges are then secured by a variety of methods such as welding, soldering and riveting. The accuracy of the size of drawing the shape on the flat sheet know as the development. Allowance is made at this stage for folding or bending, the amount varying with the radius of the bend and the metal thickness.
Quite a large of sheet metal is employed in the manufacturing industries, in building of aircrafts, automobiles and household appliances. Sheet metal to a large extent is used in the building industries for roofing, heating, prefabricated structures and air conditioning casings.
The base metal iron and bronze were appreciated for their strength especially for weapons and tools; copper, tin and lead came to be used mainly for their utility or durability- for cooking, for storage or for strengthening wooden construction of any kind.
The particular property of metals that can be mixed or alloyed in various combinations and proportions to make a better materials for particular purposes was understood in the ancient world. Copper and tin produces bronze; copper and zinc produces brass; lead and tin produces pewter. This property has been exploited with ingenuity and increasing scientific knowledge while the designation iron, copper, lead, silver and gold are still commonly used (Surenda, 1979).
All metals shares certain characteristic: a uniform smooth complexion; great strength and tenacity; but also easily worked surface; and malleability (their capacity to assume any desired shape).
All these are carried out with the help of sheet metal works, which involves fabrication of metallic objects by cutting, forming/ bending and fastening, welding etc. are referred as sheet metal works. (Oyewole and Agada, 2000).
The term bending refers to an operation in which metal is deflected from its original form to a new position generally at an angle or a curve and it remains so permanently. Bending is a common metalworking technique to process sheet metal. It is usually done by hand on a box and pan brake, or industrially on a press brake. Typical products that are made like this are boxes; such as electrical enclosures, rectangular ductwork and some firearm parts.
Usually, bending has to overcome both tensile stress as well as comprehensive stress. When bending is done the residual stresses make it spring back towards its original position, so we have to over bend the sheet metal keeping in mind the residual stresses.