Abstract
The force relationships obtained in the machining of a series of low-carbon open-hearth steels containing various amounts of sulphur from 0.025 to 0.250 per cent were investigated in a constant-pressure lathe and in a conventional lathe. A wire-resistance, strain-gage dynamometer was used to measure the forces acting on a high-speed tool for various cutting conditions. In the constant-pressure test, sulphur additions increased the feed obtained with a given thrust load. The addition of sulphur reduced the forces acting on the tool for equivalent feeds in both test lathes. Theoretical calculations disclosed that the effectiveness of increased sulphur contents results from decreased friction between the chip and the tool and from an accompanying reduction in strain during chip formation. The decrease in friction and strain reduced the work required for removal of a unit volume of metal during machining. Shear stress was not a direct function of sulphur content, but generally decreased with feed. Results of conventional lathe tests generally corroborated those obtained in the constant-pressure lathe.
