Cutting Speed Effects on Surface Topography in High-Speed Broaching of 42CrMo4 Steel

Broaching is a key machining process used for manufacturing components with tight geometric and dimensional tolerances. As most cutting parameters are defined by tool geometry, process optimization primarily depends on cutting speed and lubrication conditions. To increase productivity, higher cutting speeds are required; however, their effects on surface quality remain insufficiently understood. This work investigates the influence of cutting speed (7.5–210 m/min), lubrication condition (dry and oil-lubricated) and clearance angle (1° and 2°) on fundamental variables and surface topography when external broaching of 42CrMo4 steel (AISI 4140) using T15 High-Speed Steel (HSS) tools. Experiments were performed on a High-Speed (HS) linear testbench for cutting, with synchronised in-process measurement of force components, accelerations, cutting speed, and HS imaging. Workpiece position from accelerometer data was calculated to explain surface irregularities, while surface topography and geometric errors were characterized post-process and correlated with the in-process data. The results show that increasing the cutting speed up to 90 m/min significantly reduces the specific cutting force and improves surface roughness. In particular, 90 m/min appears to be an optimal processing condition, as it enhances surface finish and reduces surface irregularities, thereby minimizing geometric errors. These findings contribute to a better understanding of HS broaching mechanisms and support assessment of its industrial applicability.