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A new prediction model was proposed to give the critical cutting condition of serrated chip in high speed machining, including cutting speed, depth of cut, and rake angle. Firstly, a critical criterion of serrated chip in high speed machining was obtained through the linear stability analysis of balance equations of continuum mechanics for primary deformation zone, which considers the influence of compression stress through stress equivalent. Secondly, the model of deformation in the primary deformation zone was proposed to build the corresponding relationships between the cutting conditions and the deformation conditions based on the model of parallel boundary shear zone. Lastly, the critical cutting condition of serrated chip in high speed machining can be predicted by combining the critical criterion and the calculation of deformation conditions in the primary deformation zone. For the validation of model, the critical cutting conditions of serrated chip on AISI 1045 steel were predicted and an orthogonal cutting experiment was performed for comparing with the prediction results. The comparison shows that the prediction results agree well with that of experiment. Therefore, the proposed model is available. This is very useful for the optimization of cutting parameters and precision control of high speed machining.

In multi-wire sawing, reducing the wire wear loss and increasing wire consumption are the common means to avoid the risk of saw wire breakage because the worn saw wire experiences a complex process with strength degradation and surface damage. So, it is urgent and necessary to give a reliable wire wear loss in theory. This paper focused on the surface topography and fracture strength of worn wire with different wire wear loss. Furthermore, the saw wire maximum safety wear loss model was presented based on the experimental results. By observing the surface topography of the worn saw wire, the dented traces were distributed on the whole surface and a few grooves with large depth were shown in the local zone. The cross-sections of the worn saw wires with different wear loss were circular. In addition, its fracture strength of the wore saw wires was not reduced with the increasing of the saw wire wear loss. On the contrary, the fracture strength of the wire with large wear loss was improved by hardening in comparison with fresh saw wire. This phenomenon suggested that surface damages did not affect the fracture strength of saw wire under the experimental condition. Furthermore, fracture photograph of the fracture test samples was divided into the crack propagation zone and final fracture zone. By analyzing these fracture topography, almost all the crack propagation zones were circular and its diameter was about 48.27 μm. It is not correlated with the amount of wear loss. However, the shape became non-circular in some samples with large depth damage on the surface. By summarizing these results, the model and calculation method of the maximum safety wear loss of saw wire were established, which could provide the theoretical basis for the determining the maximum safety wear loss.

The characterization of the microstructure and phase transformation in adiabatic shear bands (ASBs) within the serrated chips generated during high-speed machining of hardened 30CrNi3MoV steel has been performed. The observations showed that the microstructure gradually changes from the center of the ASB to the matrix of the chip, the fine equiaxed grains appear with size of about 0.4–0.6 μm in the center of the ASBs, the transitional region adjacent to the ASB is characterized by the broken and elongated martensite laths in shear direction. The analysis indicated that the serrated chip formation was likely due to adiabatic shear instability that occurred in the primary shear zones and the transformation to martensite within the ASB. Dynamic recovery and recrystallization are the dominant metallurgical processes during microstructural evolution of ASB.