Traditional chamfers must be avoided because they need extremely fragile tools.
Image 8 is a schematic drawing of the punch which would produce traditional chamfers: it is easy to understand that it’s shape makes it very fragile. 
Image 9 shows the solution which is commonly adopted: inserting a small flat makes the punch much stronger.
Another possible solution, for chamfers around holes, is to insert a short cylindrical section before the chamfer: the shaft (or core) which produces the hole would then be stronger.