bending machine[′ben·diŋ mə‚shēn]
a machine used for the hot or cold bending of parts from flat sheet, bar, tubular, and rolled stock.
All-purpose bending machines are of several types, including three- and four-roll (rotary) machines, roller machines, and machines with a turning traverse, template, or arm. Three- and four-roll machines are used for bending sheet stock into cylindrical and conical shells and arc-shaped components. The thickness of the stock may be from tenths of a millimeter to several dozen millimeters. Stock thicker than 40-50 mm is bent hot. Machines of this type are usually made with horizontal orientation of the roll (see Figure 1). The position of the center roll or the side rolls is adjustable vertically, which produces bending in one or another part of the billet. Bending along the full length of the billet is caused by rotation of the center or side rolls. For making closed loop sections by this machine the rear bearing of the center roll is of the throw-out type, which permits the rear end of the roll to be tilted back by lowering the cantilevered end by the pressure mechanism. For bending sheet stock into conical shells of any angle, the vertically adjustable rolls are also adjusted to an angle. Roller bending machines are intended for bending formed billets into ring-shaped and arc-shaped parts. Strips 200 x 40 mm can be cold bent into ribs on the most powerful machines of this type. For ease of replacement, the three bending rollers are mounted on cantilever shafts. On smaller machines the axes of the rolls are positioned horizontally; on larger machines, vertically.
Machines with a turning traverse (see Figure 2) are mainly used for bending short billets with small radii of bends (such as boxes and thin-walled sections). This machine has three traverses: the stationary traverse (table), the holder, and the turning traverse. The stock is placed on the table against the stops and is clamped in place by the holder. As the edge of the sheet bar protrudes past the table and the holder, it is bent around the template—which determines the radius of the bend—by the rotation of the turning traverse. The traverses are fixed to two uprights. The turning traverse is mounted in two guide slots, which pivot on the journals of the bearings in the uprights. The maximum length of the edge that can be bent is determined by the length L. This type of machine is capable of bending sheets up to 15 mm thick and 5,000 mm wide.
Machines for bending around templates (see Figure 3) have a rotating table or template (less frequently a rotating arm) and an attached pressure roll. This type of machine is used to make flanges and stiffening ribs from formed billets and for bending pipe sections. The front end of the billet is first attached by a clamp to the template, which is mounted on the machine table. The pressure roll is then brought down onto the blank at a certain distance from the clamp. The template then begins to turn, and the billet, whose rear end is pressing against the pressure roll, is bent. The most powerful machines of this type are used for bending pipes. Bent parts are also made on special bending presses (bulldozers).
Bending machines are used in making boilers, in shipbuilding, in the chemical and petroleum industry, and in machine building.