Tube Bending
Tube bending is a term that refers to processes that permanently bend straight and rigid tubes or pipes. Angled tubing is used in countless applications, including agricultural, architecture, automotive engineering, construction, HVAC and plumbing, furniture, sports and recreation and even the arts. To make objects and structures like bridges, canopies, exhaust pipes, water pipes, trusses, exercise equipment, goal post frames, basketball hoop frames, bike frames and sculptures, manufacturers use both hot and cold-forming bending processes. During these processes, pipes and tubes can generally be bent up to 90° once or multiple times.
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Methods of Tube Bending
In addition to hot and cold-working processes, tube manufacturers use a mixture of manual and automatic bending methods. The most common of these methods include press bending, tube rolling and mandrel bending.
- Press Bending
- During press bending, a die pre-formed in the shape and angle of the desired bend is pressed against a pipe until it takes on that angle as well. A single die can be used to create multiple shapes, but it will only work with one size tube and tube radius, as it cannot be changed.
- Tube Rolling
- Next, tube rolling is an automated process performed in the span of three main steps. First, pre-impregnated metal materials are cut and rolled around a mold or mandrel. After this, manufacturers wrap the mandrel in a film sleeve that gets rid of any hidden air, ensuring the final product will not have any air-related imperfections, like bubbles, creases or wrinkles. Finally, the piece is heat-cured. Once this is done, the piece is removed from the mandrel, revealing a hollow formed tube. Similarly, some tubes are bent with the help machines that take them through a series of rollers, forcing them to take on their new angles gradually.
- Mandrel Bending
- Finally, mandrel bending, or mandrel tooling, is a sub-bending process that involves inserting a mandrel, aka a metal rod or ball, into a tube while it is still being bent. Depending on the main bending process being performed, mandrel bending can be a hot forming process or a cold forming process. Either way, it yields a uniform, wrinkle and kink-free bend.
- Rotary Draw Bending
- Other tube bending and pipe bending methods include rotary draw bending (RDB) and packing. Rotary draw bending equipment partners with CNC technology to create precise and complex bends. In addition, they can be programmed to produce multiple, varied bends and planes in one piece. RBD-formed tubes tend to be strong and aesthetically pleasing. As such, the process is frequently employed in the creation of bicycles, motor vehicle roll cages, handrails and frames, among others.
- Tube Bending Through Packing
- Packing is a more specific and less frequently used method of tube bending. Two common types of packing are ice packing and sand packing. During ice packing, a pipe is filled with a water soluble solution, frozen and then bent while still cold. This process, which is used to make trombones, works because the solute makes the ice flexible. Sand packing, also known as hot slab forming, is a bit more complicated. First, a pipe is filled with fine sand. Then, its ends are capped and it is placed inside a furnace heated to at least 1600F (870C). Once it has reached a level of malleability, the pipe is set on a slab with pins set in it and bent around the pins with a mechanical force like a crane or winch. In this case, the sand is useful because it reduces distortion in the pipe’s cross section.
Things to Consider When Choosing Tube Bending
Because tube bending methods change the properties of the pipes, they must be chosen with care. Some methods work through compression, which may leave behind waves or wrinkles. For some applications, this is not a problem, but others may find that such imperfections interfere with function. Note that, the wider a pipe, the smaller its ratio of distortion will be. Bending can also produce areas of weakness within a length of tube, but as long as the tube bending equipment used is high quality, and the workers operating it are skilled, this can be avoided.