When calculating for other copper alloys the machine rating is arrived at by assuming the 100 rating of 600 SFM . For example, phosphorus bronze ( grades A D ) has a machinability rating of 20.
32.
The most important material properties for the dies are thermal shock resistance and softening at elevated temperature; other important properties include hardenability, machinability, heat checking resistance, weldability, availability ( especially for larger dies ), and cost.
33.
Many of mangalloy's uses are often limited by its difficulty in machining; sometimes described as having " zero machinability . " The metal cannot be softened by annealing and hardens rapidly under cutting and grinding tools, usually requiring special tooling to machine.
34.
If a material has a machinability rating of 70 %, it can be determined, with the above knowns, that in order to maintain the same tool life ( 60 minutes ) the cutting speed must be 70 sfpm ( assuming the same tooling is used ).
