Modification Of An Existing Metal Sheet-Bending Machine

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.
The machine used for bending operation is called sheet metal bending machine. This machine can be used to perform any type of bending. It consists of heavy beams, which are coupled together to bring about any shape of bending after the flat sheet has been marked out to a specific dimension of bending. This machine is extensively used in our community today by steel fabricators and production workshops for the fabrication of iron gates, security doors, burglary proofs, Louvre frames etc. (Oyewole and Agada 2000).
The street metal bending machine has great importance. It is used for bending metal sheet into shape and it is also used for giving out design.

1.2 Historical Review and Classification of Bending Machines
Over the years tremendous efforts have been made both in the study, design and development of tolls and machinery employed in manipulating sheet metal into desired shape mostly by bending.
The earliest approach to bending sheet metal to desire shape involves the use of stakes (thick or strong sharpened stick driven into the ground as a support, boundary, mark etc.) alongside hand tools of wood or rubber mallet, bench socket positioned at right angle to the craft-man. Stakes are of different types and forms corresponding from the type of bend to be made. The finishing achieved from this is generally poor and not very accurate. It’s other dements lie in the much labour required and limitation of the length of the sheet that can be bent.
To overcome these demerits and boost the fabrication industry, machine to carry out the bending operation were thereby developed. Bending machine in use include pinch bending rolls, power operated pyramid rolls, lock forming machine, Timman’s Jenny, Swing beam. The cramp folding machine; had operated geared bending machine, the box is the most versatile and easy to operate of all bending machines.
A top Vee-shaped blade descends on the plate, forming the necessary bend in vee- shaped bottom die. Top blades could be in varying width thus allowing box forms to be produced.

Fig 1.1: The press brake
The swing beam is a manually operated bending machine and it is extensively used in our community today by steel fabricators and production workshops. It is extensively used because it does not require electricity. The swing beam bending machine is easy to operate and it can bend a metal sheet of about 2.5mm.

DESIGN
The sheet metal bending machine that is designed and reported here is the swing beam type consisting of a clamping beam, bending beam, machine bed, supporting frame and the bend
Fig 1.2: Sketch o a metal the machine

1.3 Operation Characteristic of the Bending Machine
The design is such that will carry out vee-shape angle bend on a sheet metal of maximum thickness of 2.5mm and maximum width of 8ft (2 1 . e. a standard sheet metal plate length. A sheet metal thickness above 2.5mm cannot be bend by this machine but can be bent by a press brake. Press brake may be of either mechanical or hydraulic operation i.e. the power to drive the press is by a flywheel or by hydraulic rams (khurmi and Gupta, 1979).
1. The essential components of the bending machine are:
2. Clamping beam with threaded shaft, it hold the sheet metal to the machine bed.
3. Machine bed, it houses the sheet to be bent.
4. Bending beam, this ensures the folding of the sheet metal.
5. Pedestal, it supports the entire machine.
Turning the threaded shaft anti-clockwise, the bending beam lift up and an opening created, then, metal strip can be slotted into the machine for bending. Turning the shaft clockwise the bending beam comes or clamp down onto the machine bed, the sheet is clamped in between the clamping beam and the machine bed. By lifting the folding handle /bending lever up, the sheet metal bends into shape. The handle is released, the shaft (threaded) is turned anti-clockwise and the sheet is removed.
A back gauge is provided to control the length of sheet that enters into the machine for bedding in case where sheets to be cut are smaller in length between the back gauge and the bending zone. Metal sheets are measured and marked; the marked portion is placed alongside the edge of the folding blade.