Tube bending calculations
This is also the fabricators cut-off length. Once the location of all bends and lengths of bends are determined, the designer can calculate the raw-material length. Raw material length applies to straight stock. The constant is a conversion from radians to degrees. L = 0.01745 ur where L = length of bend, in., u = angle of bend, degrees, and r = radius of bend, in. Fibers at the centerline remain unchanged. Mechanical theory suggests that as a material bends, material fibers outboard of the centerline stretch, while material fibers inboard of the centerline compress. Remember that it is based on a bending radius through the centerline of the tube or rod. It is nothing more than the equation for the length of an arc. Length of bend is calculated from the previous information. More than one designer has miscalculated raw material length because the angle of bend concept was improperly understood. Although the angle sounds like a simple measurement, it is important that designers understand the concept because it greatly affects raw material calculations. Radius of bend is usually governed by the space the part must fit, the dies available to the fabricator, and the 33 OD guideline.īend angle is the number of degrees the material bends. Material identifier, 1020 HR steel or T6061 for example, along with the material’s OD and wall thickness. The drawing should contain at least the following elements: Now the designer can generate the production information needed by the metal fabricator. Several successful designs sport bending radii less than three times the material OD.Īfter choosing material size and bending dies, layout the overall shape of the part. The three-times rule, however, is only a guideline. For example, if using a 0.75-in.-OD tube, the bending radius should be at least 3 x 0.75 = 2.25 in. This usually avoids rupturing or tearing the material as it bends. Specifying a bend radius the manufacturer cannot produce can seriously delays projects committed to tight schedules.Ī good guideline regarding bending die selection is to choose a radius at least three times the tube’s outer diameter. When unknown, the designer should find this information before going any further. And the pressure die holds the tube in position as it feeds in and pulls around the forming die.ĭesigners usually know the material sizes (outer diameter and wall thickness) and bending dies available or commonly used by the metal fabricator. Additionally, toolmakers usually scribe the forming die with a tangency line to indicate the transition between the straight and curved portions of the die.Ī clamping die holds the tube tightly against the forming die so the tube does not slip during forming. The radius marked on the die usually indicates a radius to the centerline of the tube. Tool manufacturers usually stamp the die with its bending radius and tubing diameter. The forming die determines the tube’s bend radius.