The function of a wiper die is to prevent wrinkles forming on the inside of the bend. You will find this is common when creating a 1D bend. The material wiper dies are made from will depend on the material to be bent. This item also plays a vital role in the production of bending thin-wall tubing.
The profile of the tube should be precisely manufactured to a true form within the wiper. The size and quality of the profile should permit the material to flow without any resistance. An oversized profile will allow the material to grow vertically and this may cause wrinkles, whilst a tight profile will cause drag, followed by clam slippage. This should be avoided. A badly fitted wiper die will probably result in failure to achieve a wrinkle-free bend and damage the wiper tip.