BENDING

BENDING???

BENDING Is the deformation of material about a

straight axis. There is little or no change in surface area of the work piece. Material on the outside of the bend tends to be stretched and material on the inside tends to be compressed. Bending is a very common sheet metal operation.

RAM AND PRESSING BENDING Is a method applicable to tubing, bar, and other sections, and is

illustrated in Figure 2H2c. A forming block is attached to the ram of a hydraulic press. Wing dies below the ram hold the tubing and pivot to wrap it around the forming block as press ram descends. A wiping action of the wing dies controls the flow of metal and provides a compression bend.

No mandrel is used. There is less control over the work piece than that provided by draw or compression bending, but the operation is relatively rapid. Bends to 165 degrees can be made. Automotive exhaust pipes and other tubing components used in large quantities are commonly bent by this method.

STRETCH BENDING The work piece is stretched longitudinally to the yield point and

then is wrapped around a bending die or form. A mandrel is not needed, but the method is not rapid. It is applicable to bends of non-uniform radius.

One common application of the process is the bending of structural members made from angle or channel sections when such members require a curved shape. The frame of rockets and other aerospace vehicles are bent this way. See Fig. 2H2d

WRINKLE BENDING is a method for bending large, heavy-wall, tubing or pipe. It is

applicable to field conditions since it can be done by hand with no special tooling. One side of the tubing is heated locally by gas torch to the point where the tubing wall softens .

A compressive force is applied to the pipe, causing the soft area to wrinkle and the tubing to shorten on that side, producing a shallow bend.

ROLL BENDING is means of putting gentle bends in tubing pipe, bars,

rolled or extruded shapes, plates and sheets. When used for pipe or tubing, the process is limited to

heavier-walled work pieces with bend radii usually not tighter than 6 times the diameter though 4 times is possible.

When the process is used with sheet metal, a common application is the production of cylindrical parts.

ROLL EXTRUSION BENDING This method is used for large, heavy- walled pipe. One

wall of the pipe is swaged from the inside, causing it to elongate and the pipe to bend. Pipes of 5 to 12 in (125 to 300mm) can be bent with this method to a minimum bend radius of 3 times the diameter.

BULGING, MECHANICAL is an operation that expands a portion of a tubular or

cylindrical part. When done mechanically, a segmented die with segments held together by springs- is inserted into the tubular part.

The process produces a patterned expansion (flat spots around the tubing) because of open spaces between the die segments when they are expanded. These flat spots can be minimized by rotating the segmented die and repeating the operation.

BULGING, HYDRAULIC expands tubing, pipe, or cylindrical part, by applying

internal force with a pressurized liquid or an elastomer (low-durometer rubber or polyurethane) punch. The work piece is contained by a die that is split so that the bulged part can be removed after the operation.

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