When physically bending a pipe, a pipe bending spring is put into (or above) the pipe to hold the pipe walls. A bendable, metallic spring known as a "bending spring" is often used to curve PVC conduit pipes by giving them the internal stability required to produce a clean, distortion-free curve. The spring features a ring end on one end and a tapered end on the other.
They are only somewhat smaller in diameter than the pipe's internal diameter. Typically, this type of extension springs are exclusively employed to bend 15-25 mm soft copper pipe (used in household plumbing). Once its center is approximately where the bend should be, the pipe bending spring is forced into the pipe.
Also, GL Metal can produce customized bending springs according to your requirements.