International Journal of Machine Tools & Manufacture 73 (2013)1–8

Investigations ofyield stress, fracture toughness, and energy distribution in high speedorthogonal cutting

Bing Wang, ZhanqiangLiu*, Qibiao Yang

[Abstract] This paper presents a novelprediction method of the yield stress and fracture toughness for ductile metalmaterials through the metal cutting process based on Williams' Model [38]. Thefracture toughness of the separation between the segments in serrated chips inhigh speed machining is then deduced. In addition, an energy conservationequation for high speed machining process, which considers the energy of newcreated workpiece surfaces, is established. The fracture energy of serratedchips is taken into the developed energy conservation equation. Five groups ofexperiments are carried out under the cutting speeds of 100, 200, 400, 800 and 1500 m/min. The cutting forces are measuredusing three-dimensional dynamometer and the relevant geometrical parameters ofchips are measured with the aid of optical microscope. The experiment resultsshow that the yield stress of machined ductile metal material presents anobviously increasing trend with the cutting speed increasing from 100 to 800 m/min while it decreases when the cuttingspeed increases to 1500 m/minfurther. Meanwhile, the fracture toughness between the chip and bulk materialdisplays a slightly increasing tendency. In high speed machining, the fracturetoughness of the separation between the segments in serrated chips alsopresents increasing trend with the increasing cutting speed, whose value ismuch greater than that between the chip and bulk material. In the end, thedistribution of energy spent in cutting process is analyzed which mainlyincludes such four portions as plastic deformation, friction on the tool-chipinterface, new generated surface and chip fracture. The results show that theproportion of plastic deformation is the largest one while it decreases withthe cutting speed increasing. However, the proportions of energy spent on newcreated surface and chip fracture increase due to the increasing of both thechip's fracture area and the fracture toughness.

Keywords: Yield stress, Fracturetoughness, Plastic deformation, High speed machining, AISI 1045 steel

2013-Investigations of yield stress, fracture toughness, and energy distribution.pdf