What is wiper die of pipe bending machine?

What is wiper die of pipe bending machine?

The wiper die of the pipe bender is placed behind the bending die. The goal is to avoid any bumps on the inner radius.
During the molding process, the material becomes plastic during the bending process. May cause large wrinkles and deformation. Therefore, adding a wiper mold after bending the mold helps smooth the surface.