Mandrel bending or rotary-draw bending inserts a mandrel into a pipe or tube during bending so that the shape is maintained and the bends are not deformed.  Mandrel benders are machines designed to bend tube to a tight radius with little or no change in the shape of the tube, generally to a radius much tighter than the material can bend without collapsing or distorting. The mandrel refers to the part of the tooling which is inserted into the tube and remains inside the tube during the bend process, supporting the shape of the tube wall during the bending process. Vehicle exhaust pipe is a common application for a mandrel bender.

A common type of mandrel used in automotive exhaust pipe manufacturing is a series of metal balls linked together into an articulating mandrel in order to bend pipe in a certain pattern. The mandrel allows the exhaust pipes to be bent into smooth curves without undesirable creasing, kinking, or collapsing.