Pipe and Tube Bending Machinery's Handbook, 31st Edition
1460
Roller
Roller
Workpiece
Pressing form block
F,v Fig. 68. Press Bending
Rotary Draw Bending.— Today, rotary draw bending is the most widely used method of bending tube and pipe, particularly for tight radii, good finishes, and thin-walled tubes. When rotary draw bending is used, the tube/pipe is inserted in the bending machine and fastened between the bend die and the clamp die. The rotation of both tools (the bending die and the clamp) around the bending axis bend the tube/pipe according to the radius of the bend die (Fig. 69).
Pressure bar
Pressure bar
Workpiece
F
F F
Clamp
v
Clamp
F
Rotating bending die
a) Starting Position
b) Ending Position
Fig. 69. Rotary Draw Bending. The pressure bar serves the purpose of receiving the radial stress generated during the forming process, and in addition it supports the straight tube/pipe end from outside. If a mandrel and a wiper shoe are applied additionally (mandrel bending), high workpiece quality can be achieved even in thin-walled pipes and tight-bending radii. The steel plug, or mandrel, fits inside the tube during rotary draw bending. The plug or mandrel supports the tube internally to reduce the amount of tube cross-sectional flatten - ing during tube bending. After the tube has been bent, the operator extracts the mandrel from the tube, releases the clamp, and then removes the workpiece from the machine. With modern mandrel bending machines, almost any kind of cold formable tube/pipe, depending on the material, can be safely bent to bending radii of approximately 1.5 D with the desired precision. The forming possibilities are not at all limited to bending only round pipes. Oval pipes and flat and mono-block material can be formed just as well by bending as square or other open profiles. Depending on the shape of the workpiece, the required forming tools are adapted accordingly. This method of bending tube/pipe is used in the manufacture of exhaust pipes, custom exhaust pipes, turbocharger exhaust and intake tubing, dairy tubing and process tubing, heat exchanger tubing, and all stainless and aluminum tubing where a nondeformed diam eter finish is critical. The main differences among rotary-draw-bending machines are the maximum workable outside pipe diameter and the degree of automation of the various functions. Only the bending function of the so-called “1-axis controlled bending machines” is automatic; in them, feeding and contortion are carried out manually. For the user of CNC
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