text: A tube can be bent in multiple directions and angles. Common simple bends consist of forming elbows, which are 90° bends, and U-bends, which are 180° bends. More complex geometries include multiple two-dimensional (2D) bends and three-dimensional (3D) bends. A 2D tube has the openings on the same plane; a 3D has openings on different planes.
  A two plane bend or compound bend is defined as a compound bend that has a bend in the plan view and a bend in the elevation. When calculating a two plane bend, one must know the bend angle and rotation (dihedral angle).
  One side effect of bending the workpiece is the wall thickness changes; the wall along the inner radius of the tube becomes thicker and the outer wall becomes thinner. To reduce this the tube may be supported internally and or externally to preserve the cross section. Depending on the bend angle, wall thickness, and bending process the inside of the wall may wrinkle.