Optimization of Cutting Parameters for Trade-off Among Carbon Emissions, Surface Roughness, and Processing Time

As the manufacturing industry is facing increasingly serious environmental problems, because of which carbon tax policies are being implemented, choosing the optimum cutting parameters during the machining process is crucial for automobile panel dies in order to achieve synergistic minimization of the environment impact, product quality, and processing efficiency. This paper presents a processing task-based evaluation method to optimize the cutting parameters, considering the trade-off among carbon emissions, surface roughness, and processing time. Three objective models and their relationships with the cutting parameters were obtained through input–output, response surface, and theoretical analyses, respectively. Examples of cylindrical turning were applied to achieve a central composite design(CCD), and relative validation experiments were applied to evaluate the proposed method. The experiments were conducted on the CAK50135 di lathe cutting of AISI 1045 steel, and NSGA-Ⅱ was used to obtain the Pareto fronts of the three objectives. Based on the TOPSIS method, the Pareto solution set was ranked to find the optimal solution to evaluate and select the optimal cutting parameters. An S/N ratio analysis and contour plots were applied to analyze the influence of each decision variable on the optimization objective. Finally, the changing rules of a single factor for each objective were analyzed. The results demonstrate that the proposed method is effective in finding the trade-off among the three objectives and obtaining reasonable application ranges of the cutting parameters from Pareto fronts.

Hardening Effect on Machined Surface for Precise Hard Cutting Process with Consideration of Tool Wear

During hard cutting process there is severe thermodynamic coupling effect between cutting tool and workpiece, which causes quenching effect on finished surfaces under certain conditions. However, material phase transformation mechanism of heat treatment in cutting process is different from the one in traditional process, which leads to changes of the formation mechanism of damaged layer on machined workpiece surface. This paper researches on the generation mechanism of damaged layer on machined surface in the process of PCBN tool hard cutting hardened steel Cr12MoV. Rules of temperature change on machined surface and subsurface are got by means of finite element simulation. In phase transformation temperature experiments rapid transformation instrument is employed, and the effect of quenching under cutting conditions on generation of damaged layer is revealed. Based on that, the phase transformation points of temperature under cutting conditions are determined. By experiment, the effects of cutting speed and tool wear on white layer thickness in damaged layer are revealed. The temperature distribution law of third deformation zone is got by establishing the numerical prediction model, and thickness of white layer in damaged layer is predicted, taking the tool wear effect into consideration. The experimental results show that the model prediction is accurate, and the establishment of prediction model provides a reference for wise selection of parameters in precise hard cutting process. For the machining process with high demanding on surface integrity, the generation of damaged layer on machined surface can be controlled precisely by using the prediction model.

Adiabatic Shear Mechanisms for the Hard Cutting Process

The most important consequence of adiabatic shear phenomenon is formation of sawtooth chip. Lots of scholars focused on the formation mechanism of sawtooth, and the research often depended on experimental approach. For the present, the mechanism of sawtooth chip formation still remains some ambiguous aspects. This study develops a combined numerical and experimental approach to get deeper understanding of sawtooth chip formation mechanism for Polycrystalline Cubic Boron Nitride（PCBN） tools orthogonal cutting hard steel GCr15. By adopting the Johnson-Cook material constitutive equations, the FEM simulation model established in this research effectively overcomes serious element distortions and cell singularity in high strain domain caused by large material deformation, and the adiabatic shear phenomenon is simulated successfully. Both the formation mechanism and process of sawtooth are simulated. Also, the change features regarding the cutting force as well as its effects on temperature are studied. More specifically, the contact of sawtooth formation frequency with cutting force fluctuation frequency is established. The cutting force and effect of cutting temperature on mechanism of adiabatic shear are investigated. Furthermore, the effects of the cutting condition on sawtooth chip formation are researched. The researching results show that cutting feed has the most important effect on sawtooth chip formation compared with cutting depth and speed. This research contributes a better understanding of mechanism, feature of chip formation in hard turning process, and supplies theoretical basis for the optimization of hard cutting process parameters.