This method is popular in square tubing applications, for which many design the ram tool so that it deliberately compresses and slightly deforms the inside bend radius (see Figure 4). The workpiece ID isn’t supported, and a substantial amount of stretching occurs on the outside of the bend. You generally can achieve a centerline radius (CLR) that’s three to four times the workpiece OD. One of the oldest and simplest tube bending methods, it uses a hydraulically driven ram that forces a tube against rollers or pivot blocks. Visit any muffler shop and you’ll probably see a ram-style bender (see Figure 3). Pipe is specified by its nominal pipe size, while tube is specifiedīy its outside diameter. Most tubes, though, are bent one of four ways: ram-type bending, roll bending, compression bending, or rotary draw bending. Specialty tube bending processes abound, some old and some new. Like any other manufacturing technology, the application requirements drive the fabrication method of choice. That’s because as the outside stretches, the inside radius compresses and at a certain point starts to wrinkle. Some ovality is acceptable for certain applications, but unacceptable for precision work. This causes the outside surface of the bend to cave in, causing ovality, or a distortion of the cross section from its original round shape. That creates problems if you want to create the perfect bend.Įlongation occurs during bending, and the outside radius stretches (causing wall thinning), which the material resists. If the two edges of the joint don’t align perfectly, or if the weld bead is too large or inconsistent, these discontinuities will affect the tube’s roundness. In tube bending, the quality, size, and consistency of that weld seam matter.
Copper undergoes less radial growth than steel, which has less springback than stainless steel.Īlthough some are seamless, most tubes are produced with a longitudinal weld. Generally speaking, the harder the tube and the smaller the bend’s centerline radius, the greater the springback and resulting radial growth. Like in press brake forming, tubes experience springback after bending, producing a bend that undergoes radial growth. More specifically, it’s the distance between two tangent points, where a straight section begins to curve and the bend starts or finishes. The distance between bends (DBB) is just what it says. So if a tube is bent to “45 degrees,” that’s 45 degrees complementary, or a 135-degree included bend angle (see Figure 2). The bend angle refers to the complementary angle of bend. Other bending variables include the inside bend radius (sometimes called the intrados) the outside bend radius (or extrados) and the centerline radius or the neutral line, where neither compression nor stretching occurs. This variation should be accounted for, especially for bending processes using precise, tight-fitting tooling on small bend radii. There’s a tolerance, and the wall thickness can vary slightly. But when you’re specifying a bending machine, the centerline radius, the outside diameter, and wall thickness are critical variables.Īlso, every pipe schedule has a nominal wall thickness. Pipe, usually used to transport fluid or air, is specified by its nominal pipe size (see Figure 1). Fundamental Termsīending starts with knowing the properties of the tube or pipe you’re working with. Regardless of whether you’re working with tube or pipe, and regardless of the bending process, making the perfect bend boils down to just four factors: the material, machine, tooling, and lubrication. The technology used to bend tubular workpieces has evolved significantly, but all the mechanical magic can’t alter physics. But in reality, the basic principles have remained the same for decades.
TUBE BENDING CALCULATOR TRIAL
Many call tube bending a black art, a mysterious process with unavoidable trial and error. Editor’ Note: This article is based on the Tube Bending 101 FabCast, facilitated by the Fabricators & Manufacturers Association International (FMA) and presented by Danie Jacobs, president of i-Fab LLC.
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