Shigeo Zaima1, Shizuo Tada2 and Susumu Kamo1
1Department of Mechanical Science, Faculty of Engineering, Shizuoka University, Hamamatsu
Ten test pieces of different copper contents were first produced in the range of 66.5 ∼ 55.0%, which were then subdivided into five kinds of specimens with different lead contents in the range of 1 ∼ 4%. Fifty kinds of lead brass specimens thus prepared were cast to examine their drill-machinability under a constant load drilling. The experiment was carried out to investigate the effects of copper contents and lead contents in the free cutting brass whoes standard differs by countries and the relationship between the drill-machinability of the lead brass and its turn-machinability previously experimented. The drill-machinabilty was mainly investigated in the light of the drill resistance and the drilling time. The results obtained were as follows:
(1) In the drilling resistance, the thrust by drilling under a constant load was measured nearly constant regardless of the materials.
(2) When the copper content exceeded 60%, the torque increased distinctly with increase of the lead content, and below 60% the torque increased slightly. The torque increased with the copper content, and the increase in torque was remarkable in the vicinity of the α - or β -single phase in the (α+β) phase.
(3) The time needed to drill the unit thickness of a plate, that is, the drilling time was in close inverse-correalation with the torque.
(4) The tangential force in turning was in linear inverse-correlation with the torque, and the tangential force was in linear normal-correlation with the drilling time. Therefore, it may be said that there were some relations between the turn-machinability and the drill-machinability.
(5) The difference between the standard for the free cutting brass of different countries and the JIS standard was discussed in the light of the drilling.
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