Quantifying machinability Machinability

1 quantifying machinability

1.1 tool life method
1.2 tool forces , power consumption method
1.3 surface finish method
1.4 machinability rating

quantifying machinability

there many factors affecting machinability, no accepted way quantify it. instead, machinability assessed on case-by-case basis, , tests tailored needs of specific manufacturing process. common metrics comparison include tool life, surface finish, cutting temperature, , tool forces , power consumption.

tool life method

machinability can based on measure of how long tool lasts. can useful when comparing materials have similar properties , power consumptions, 1 more abrasive , decreases tool life. major downfall approach tool life dependent on more material machining; other factors include cutting tool material, cutting tool geometry, machine condition, cutting tool clamping, cutting speed, feed, , depth of cut. also, machinability 1 tool type cannot compared tool type (i.e. hss tool carbide tool).

machineability index (

%

)

=


cutting speed of material 20 minute tool life
cutting speed of free-cutting steel 20 minute tool life


∗
100


{\displaystyle {\text{machineability index (}}\%{)}={\frac {\text{cutting speed of material 20 minute tool life}}{\text{cutting speed of free-cutting steel 20 minute tool life}}}*100}

tool forces , power consumption method

the forces required tool cut through material directly related power consumed. therefore, tool forces given in units of specific energy. leads rating method higher specific energies equal lower machinability. advantage of method outside factors have little effect on rating.

surface finish method

the surface finish used measure machinability of material. soft, ductile materials tend form built edge. stainless steel , other materials high strain hardening ability want form built edge. aluminium alloys, cold worked steels, , free machining steels, materials high shear zone don t tend form built edges, these materials rank more machinable.

the advantage of method is measured appropriate equipment. disadvantage of criterion is irrelevant. instance when making rough cut, surface finish of no importance. also, finish cuts require accuracy naturally achieves surface finish. rating method doesn t agree other methods. instance titanium alloys rate surface finish method, low tool life method, , intermediate power consumption method.

machinability rating

the machinability rating of material attempts quantify machinability of various materials. expressed percentage or normalized value. american iron , steel institute (aisi) determined machinability ratings wide variety of materials running turning tests @ 180 surface feet per minute (sfpm). arbitrarily assigned 160 brinell b1112 steel machinability rating of 100%. machinability rating determined measuring weighed averages of normal cutting speed, surface finish, , tool life each material. note material machinability rating less 100% more difficult machine b1112 , material value more 100% easier.

machinability rating= (speed of machining workpiece giving 60min tool life)/( speed of machining standard metal)

machinability ratings can used in conjunction taylor tool life equation,



v

t

n


=
c


{\displaystyle vt^{n}=c}

, in order determine cutting speeds or tool life. known b1112 has tool life of 60 minutes @ cutting speed of 100 sfpm. if material has machinability rating of 70%, can determined, above knowns, in order maintain same tool life (60 minutes) cutting speed must 70 sfpm (assuming same tooling used).