why hot wire break when cutting foam

Hot wire is nichrome wire,its part number Cr20Ni80 is popularly used in hot wire cnc foam cutting machines for cutting eps foam,xps foam,sponge etc.Sometimes,the wire can be burned with red color and easily breaks,why it happens ?

Below are the two answers:

1. Quality of hot wire.Check the quality if the hot wire is Cr20Ni80 or if it is from qualified factory.
2. Electric current is relatively big.You need adjust the current with wire length.You need adjust current with your voltage for proper wire temperature.