Bending metal is a process in which metal is changed by deforming the material and then changing it to many different shapes. The metal is stressed beyond the yield strength but also below the complete tensile strength. This does not cause the surface area of the material to really change that much. The bending can refer to deformation about 1 axis.
A standard die set is used to produce a great variety of different shapes. Once the material is placed onto the die, it is then positioned in place with gages and stops. It can be held in place with things called, " hold-downs." The upper part of the press uses the ram with the right shaped punch that descends and forms the V-shaped bend in the metal.
The bending can be done using press brakes. Press brakes normally have a capacity of around 20 to 200 tonnes that allows them to accommodate stock from 1 millimetre to 4.5 millimetres. Bigger and smaller presses can be used for more specialised applications. Programmable back gages and multiple dies sets currently make it a very economical process.
Air bending, bottoming
One type of bending is air bending, it is done with the punch touching the piece of work in question and not bottoming in the lower cavity. As the punch gets released, the piece of work ends up bending under the pressure of the air. The amount of space that it springs back depend on the thickness of the material the grain, temper and the actual material itself. The spring back can usually range from five to ten degrees. Normally, the angle is used in the punch and the die to reduce the setup time. The inside radius of the bend will be the same as the radius of the punch.
Bottoming is also known as coining. It is the process of the punch and the workpiece bottom on the actual die. This controlled angle will give very little spring back. The pressure needed on this type of press is a lot more than air bending. The inside radius of the workpiece will be at least a minimum of one material thickness in bottoming.
Rolling
Rolling is the best known way to bend metal, perhaps because it is the least costly. Rolling uses an appropriate size die that adjusts to the steel tube, angle, pipe, channel, bar or steel beam and revolves at the same peripheral speed, turning in opposite directions. As the metal passes through the roll, the machine applies pressure to bend the tubing or the beam to the desired radius.
It is effective when the material, metal, must be bent a great deal. For instance, it can produce bends up to 360 degrees. This method is suitable for producing steel coils, spiral staircases and the like.
There are different kinds of rolling processes. Hot rolling, above the re-crystallisation temperature, mostly produces sheet metal. Most non-ferrous metal structures are rolled cold, but steel is usually rolled hot. Because rolling requires less set-up work and uses pre-made dies, the cost is less than other ways to bend and form steel, so companies often choose this when it suits their specifications.
Sometimes it may be necessary to be able to bend a metal when no heat or air is available. In this case, it will be possible to bend the metal providing you have a secure area to fix the metal to before you begin bending it. You can use similar steps to bending with hot metal, but take note not to use the cooling steps that you would normally use. If for example the metal was brass, you may not need to bend it when it is cold at all as you may even shatter it or crack it. Do not bend any type of rod or even rectangular bar when cold past sixty degrees as it will most probably crack the metal. The best way to bed the metal would be with an anvil, you could also use some tongs to make sure the metal is in place before you attempt to bend it.
Mandrel, press, table forming bending
Mandrel bending is also fairly well known. In this process, a metal shaft, or mandrel, is fitted inside the steel tube or pipe. As the mandrel moves, it bends the metal around the appropriate sized die to form the radius. Mandrel works best when the steel tube or pipe has a heavy wall and/or requires a tight radius because it prevents the material from rippling. Mandrel can only bend steel tubing up to 180 degrees, but it produces a bend that is uniform all the way up and down the pipe or tube. Obviously, this process is of little use for bending metal beams or sheets, however, it is used in bending exhaust pipes, molten glass and in very tiny cases, jewelry.
The press method is another way to bend metal. The steel tube, pipe, channel, bar or steel beam is fed through the press, which applies pressure every 6- or 7-inches until the material is bent to specifications. Press is used to bend bigger, heavier beams, pipes, channels, bars or tubes (24-inches or thicker) that do not require a very tight radius. This is a less common process than rolling or mandrel. However, it is capable of producing large, load-bearing steel support beams used for schools, roofing, skyscrapers, gymnasiums, malls and bridges.
In table forming, the steel tube, pipe, or beam is laid out straight and the ends are pulled around the appropriate sized die to form the radius. Table forming is used primarily to bend smaller, heavier steel tubes, pipes, channels, bars or steel beams that require a tight radius.
Bending expanded metal
In bending expanded metal, the sheet metal is slit thousands of times and then pulled to form diamond shaped expanded metal. Therefore, the same tools used to bend sheet metal are used to place a bend on expanded metal. Unlike sheet metal, it is easy to bend expanded metal without the use of sheet metal brakes or press brakes. You can place a uniform bend of a piece of expanded metal with a solid worktable, some hand tools and a little bit of time.
Lay the piece of expanded metal flat on top of the worktable. Stretch the tape measure across the face of the expanded sheet metal and mark the location of the bend with the paint marker. Repeat the procedure to mark the other edge of the expanded metal. Align both paint marks with the edge of the worktable. Place the two-by-four across the expanded metal, align it with the edge of the table and clamp the two-by-four by placing one pair of self-locking C-clamps on either side of the two-by-four. Starting a one end of the expanded metal, lightly tap the metal with the wooden or rubber mallet. After each tap, move over one-half inch until you reach the other end of the expanded metal. Do not attempt to place the full bend on the expanded metal, as this will distort the bent flange. Repeat the process of tapping the bend area until the flange is close to the angle that you need. Release the self-locking C-clamps, remove the two-by-four and flip the expanded metal over. Set the angle finder to the desired angle and place the angle finder against the bent flange. If the angle is too light, flip and secure the expanded metal as described earlier and continue tapping the metal until the angle of the bend is correct. (the finished)
Metal bending tips
Whether you are starting on a career as a blacksmith or simply repairing a car or building, it can be helpful to know the dynamics of bending metal. If you keep in mind a few basic principles, you can learn the best way to bend metal.
* Bending metal with heat-metal's crystalline structure makes it more malleable when heated. It can easily be bent when it's very hot. Sources you can use to heat metal include: propane or oxygen-acetylene torches, a forge and a hot fire. Some heat sources, however, may be too hot for a particular metal. For steel or aluminium, heat the metal until it is red hot. For most other metals, it usually is not necessary to use heat, but if you have to, heat them slightly and avoid heating metals, such as brass or copper, which melt very easily. Once, the metal is heated, use a hammer or tongs to beat a bend into the metal. This can be done with shear strength or with a mechanical aid, such as a press. When bending a hot metal, apply pressure to as small an area as possible to minimise strain on the metal. If you use a hammer, try to bend the metal around a template; hot metal is very easy to over-bend. Once the metal has been bent, let it cool slowly, so the crystals have time to reorganise and stay hard.
* Bending cold metal - sometimes, it is necessary to bend metal when heat is not available. In such cases, secure the met a l before bending it. Follow the same procedure as bending hot metal, but omit the heating and cooling steps. If the material is brass, you may not want to bend it while it's cold at all; it can shatter or crack. Never bend any rod or rectangular bar of cold metal past a 60-degree angle. Anything more will likely crack the metal. If you have a vise, use it to secure the metal, and then use tongs to hold the metal and bend it. If you have an anvil, you can use its horn as a template and bend the metal around it.
* Safety- wear heavy gloves and eye protection when bending metal. Do not touch hot metal with your hands. Use only tongs or a vise. If you know how to quench (rapidly cool hot metal in cold water or oil) metal and feel it is necessary after heating it, you may want to use more protection. Quenching can cause metal to shatter. Know the type of metal you are using before heating it. Never heat metals that are galvanised or that have zinc in them--unless you have access to a respirator that is certified to filter out poisonous gases. A simple facemask is not sufficient to block zinc fumes, which will kill you.
