Sheet metal bending ,Among the forming operations, bending is one of the most common operations because of its very wide applications in making a variety of products, from a simple paper clip to a file cabinet. Bending is used for forming a workpiece to different angles for giving various shapes such as forming of flanges, corrugation, seams, etc. Common bending operations are described below.
1. V-die bending: V-die bending is done on or hydraulic presses. The bending force is a function of the strength of the metal, length of bend (L), i.e. the width of strip, thickness of sheet (t) and the die opening (W). For a V-die (included angle 90°), the maximum bending force (P) can be estimated as:
P=fult x L x t²/W
where
P = max. bending force, kg
fult= ultimate tensile strength, kg/cm²
L = length of bend (i.e. width of strip), cm
t = thickness of strip, cm
W = die opening, cm
2. Punch-press bends: Bend is made with a pressure pad holding the sheet metal over the top of a die while a punch forms it.
3. Roll forming (or contour roll forming or cold roll forming): The process is used for forming continuous lengths of sheet metal fed through a series of rolls, whereby the sheet is bent or formed in stages into the desired shapes. Typical products made by roll forming include: channels, gutters, panels, picture frames, pipes, etc. Roll formed sections can be used in the ‘as-formed’ condition or a closed section may be made by welding two separate roll formed part sections. The sheet thickness usually ranges from 0.125 mm to 20 mm.
4. Roll bending: In roll bending process, the sheet metal is bent to cylindrical shapes using a roll bending machine which carries three rolls of the same diameter, two are fixed and the third is adjustable. By adjusting the position of the adjustable roll, sheets can be bent to different curvatures.
5. Bending in sliding dies machine: A variety of these bending machines are available in different designs of dies. The lateral movements of the dies are controlled and synchronized with vertical die movement to make the component of desired shape. The technique is used for bending relatively short pieces.
6. Press brake forming: Press brake forming involves the use of a press and simple fixtures to bend sheet metal or plates and is suitable for bending longer jobs, for example, sheets having length 7 m or more are easily bent on this press. Long dies are adopted on either a mechanical press or a hydraulic press and a wide variety of shapes can be produced.
7. Beading: Beading consists of bending the periphery of a sheet stock. The operation can be completed using a single die or two dies.
8. Flanging, dimpling and hemming: Flanging is the process of bending the edges of sheet metals, usually to 90° Dimpling involves first punching a hole and later producing the flanges by piercing with a shaped punch Hemming or flattening involves folding the edges. of sheet over itself. Hemming increases stiffness of the part and improves appearance by eliminating sharp edge.
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