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A term typically applied to a metal forming process. It is the creation of a formed feature by angular displacement of a sheet metal workpiece. The straining of material, usually flat sheet or strip metal, by moving it around a straight axis lying in the neutral plane. Metal flow takes place within the plastic range of the metal, so that the bent part retains a permanent set after removal of the applied stress. The cross section of the bend inward from the neutral plane is in compression; the rest of the bend is in tension.
Bending produces shapes in metal by the exertion of force beyond the material’s yield point but below it’s maximum tensile strength. During bending, the metal is stretched over it’s external radius and compressed through it’s internal radius. The mid-point between these points is called the neutral axis.
Bending can be performed in stamping dies designed for forming, but the greater majority of bends are made in “press brakes.”
In a typical bending operation, a piece of stock is placed between a set of upper and lower dies. Then a moving ram lowers the upper die, forcing the work into the fixed lower die. In some press brake designs, a lower die raises up against a fixed upper die.
Principle terms used in bending include:
• bend allowance refers to mathematical factors which determine the final part size
• bend angle is the final angle from 180o to which the part is bent
• bend radius refers to the distance from the tangents that extend from the remaining flat surfaces of the part
• springback is the tendency of the bent flange to return back to its
original shape. Such springback can amount from 2 to 4 degrees depending upon the material
Sheet metal fabrication is a very common method in industry for cheaply and repeatably manufacturing parts. The Stanford PRL has the tools to cut and bend sheet metal.
This photo shows metal being cut using the Jump Sheer. This machine is much like a very strong paper cutter for metal. It is operated by applying force to a large lever with the foot. Sometimes it requires so much force that you must jump on it to cut the metal, thus the name "jump sheer."
This picture shows a piece of metal cut by the jump sheer.
For accurate layout, sheet metal can be painted with a dye and marked with a scribe and punch.
This machine is called a turret punch. It has several punches mounted, in this case to make various diameter
The corner notcher can cut right angled "nibbles" in sheet metal. This is neccessary because the jump sheer can only cut a straight cut.
This is a photo of the sheet metal brake. It is used to put a constant small radius bend in sheet metal. The metal is lined up and clamped in place by a "finger." You can see the finger holding the metal in place.
The brake in action from another angle. You can see the metal is bent along the edge of the finger. By placing the finger closer or further from the bend plate, the radius of the bend can be controlled. If the finger is very close to the bend plate, it will be a small radius bend. This is an important parameter, because different materials require different bend radii or else cracks may form at the bend.
Here you can see the a finger being used to bend metal that already has other bends in it. The correct finger width must be used so that these other bends do not hit it as the metal is bent into a box.