Experimental investigation and mechanistic modeling of the effects of tool edge hone effects in turning operations

Cutting force predictions from machining process models are generally accurate to within 20% for a specific tool and work material combination over a wide range of cutting conditions when calibrations are accurately performed. The calibration implicitly assumes that the tool used in the cut has a sharp cutting edge (zero radius) or identical (and maybe unknown) cutting edge radius. Significantly higher errors (more than 20%) in force calculations are seen when the same calibration data is used for predictions across a wide range of edge radii, also referred to as an edge hone. This paper describes the preliminary experimental work done to understand the impact of a honed cutting edge on the calibration of the force coefficients used by mechanistic models. Tube turning tests were performed on gray cast iron using tools of varying edge radii, and the cutting and thrust forces measured. Useful correlations between the edge radius and the machining force were observed although some of the results were confounded by variations in the temperature at the cutting edge. A new mechanistic calibration approach is applied to obtain the force coefficients from the measured forces that gives accurate results when the ratio of chip thickness to edge radius is used to calibrate the forces. This method has the advantage of being dependent only on the geometric size of the honed edge in relation to the thickness of the chip that is being removed. This allows the calibration to be performed with lesser experimental effort, while still being valid for predictions over a wide range of edge radii. Validation of this approach was performed using a range of edge hone sizes with peak force prediction errors less than 17%.