Mechanistic modeling of cutting forces in high-speed microturning of titanium alloy with consideration of nose radius

Microturning is a micromechanical machining process used to produce microcylindrical or axially symmetrical parts. Microcylindrical parts are mainly used in microfluidic systems, intravenous micromotors, microsurgical applications, optical lens applications, and microinjection systems. The workpiece diameter is very small in microturning and therefore is greatly affected by the cutting forces. For this reason, it is important to predict the cutting forces when machining miniature parts. In this study, an analytical mechanistic model of microturning is used to predict the cutting forces considering the tool nose radius. In the semi-empirically developed mechanistic model, the tool radius was considered. A series of semi-orthogonal microturning cutting tests were carried out to determine the cutting and edge force coefficients. The mechanistic model was generalized depending on the cutting speed and depth of cut by performing multilinear regression analysis. In the study, the depth of cut (ap = 30–90 µm) and feed values (f = 0.5–20 µm/rev) were selected considering the nose radius and edge radius of the cutting tool. The experiments were carried out under high-cutting speeds (Vc = 150–500 m/min) and microcutting conditions. Ti6Al4V alloy was used as the workpiece material and the tests were carried out under dry cutting conditions. Validation tests for different cutting parameters were carried out to validate the accuracy of the developed mechanistic model. The results showed that the difference between the mechanistic model and the experimental data was a minimum of 3% and a maximum of 24%. The maximum difference between the experimental and the model usually occurs in forces in the tangential direction. It has been observed that the developed model gives accurate results even at a depth of cut smaller than the nose radius and at feed values smaller than the edge radius.

Numerical simulation of the influence of tool geometry on energy consumption during micro turning of titanium alloy

Fabrication of an axisymmetric biomedical implant with good dimensions, form and surface integrity features are a challenging task in the micro-manufacturing industry. This is due to workpiece deflection, vibrations, tool wear and adhesion of the chip on the cutting inset during the micromachining process. So experimental evaluation on the variation of tool geometry is expensive and difficult as stated in prior literature. So, in this work, a finite-element method simulation is developed to comprehend the physics of the process and predict the energy consumption by incorporating the effect of material strengthening caused by shearing of material across the grain, shear band pattern upon strain rate and tool geometry such as edge radius, nose radius and rake angle. The modified Johnson-Cook material model is used to state the flow stress and an adaptive remeshing technique is utilized to model the plastic deformation at a higher strain rate during the simulation process. Initially, the model is developed in a transient state and then modified to a steady-state to obtain the output process parameters. The proposed model is calibrated and validated with experimental results reported in the literature. It is inferred that the cutting force, thrust force and feed force acquired from finite-element method simulation have been confirmed experimentally with prediction accuracy of 94%, 82.66% and 87.02%, respectively. It is also inferred that energy consumption during machining reduces with an increase in rake angle because of the sharpness of the cutting edge and less friction between tool and chip. An increase of nose radius and edge radius produces high thrust force and energy consumption and impedes high radial depth of cut. For the same machining parameters with the increase of edge radius and decrease of rake angle the mechanism of material removal changes from shearing to ploughing.

Multi-objective Optimization of Turning Tool Geometric Parameters Based on Kriging Model

Cutting performance parameters of turning tool in different geometric parameters are obtained using finite element model, and the Kriging models of cutting stress and temperature are constructed, taking the cutting performance parameters as training samples. The multi-objective optimization model of turning tool geometric parameters is established based on the constructed cutting performance Kriging models, in which the design variables are rake angle, relief angle and cutting-edge radius, the objective parameters are cutting stress and temperature. The multi-island genetic algorithm is used to obtain the optimum turning tool geometric parameters: rake angle γo is 10.59°, relief angle λs is 6.15°and cutting-edge radius γE is 0.73mm. The simulation results after optimization demonstrate that the corresponding cutting temperature reduces 263.1°C, cutting stress drops by 550.8MPa.

Effect of cutting edge geometry change due to tool wear on hole quality in drilling of carbon fiber reinforced plastics using advanced ceramic coated tools

This paper aims to study the evolution of cutting edge geometry due to tool wear and discuss its impact on the hole quality of a carbon fiber reinforced plastic (CFRP) laminate. A drilling experiment was conducted using three types of twist drills: uncoated, BAM (AlMgB14) coated, and (AlCrSi/Ti)N nanocomposite coated tungsten carbide tools. After generating 120 holes, the uncoated drill had the largest cutting edge radius (∼36 µm), while the BAM coated drill had the most extensive flank wear (∼287 µm) among the three drills. This relatively rapid tool wear results in a reduction of average hole size and a considerable variation on the hole profiles. The worn drills with the cutting edge radius greater than 19.3 µm form the fiber pull-outs in not only the 135° plies but also the adjacent 45° and 90° plies from the cutting direction, creating deep void networks. This type of networked fiber pull-out damage was observed with the holes machined by the uncoated and BAM coated drills. The (AlCrSi/Ti)N coated drill, which experienced the least amount of flank wear and the least increase of cutting edge radius, generated consistently sized holes up to 120 holes. However, the relatively sharp (AlCrSi/Ti)N coated tool results in the higher arithmetic roughness average (Ra) and the maximum roughness height (Rz) values than the other tools due to the localized fiber pull-outs and the absence of severe matrix smearing.

An Improved Cutting Force Model in Micro-milling Considering the Comprehensive Effect of Tool Runout, Size Effect and Tool Wear

Tool runout, cutting edge radius-size effect and tool wear have significant impacts on the cutting force of micro-milling. In order to predict the micro-milling force and the machining performance related to the cutting force, it is necessary to establish a cutting force model including tool runout, cutting edge radius and tool wear. In this study, an instantaneous uncut thickness (IUCT) model considering tool runout, a nonlinear shear/ploughing coefficient model including cutting-edge radius and a friction force coefficient model embedded with flank wear width, are constructed respectively. By integrating the IUCT, the nonlinear shear/ploughing coefficient and the friction force coefficient, a comprehensive micromilling force model including the tool runout, size effect and tool wear is derived. Experiment results show that the proposed comprehensive model is efficient to predict the micro milling force.

Accurate preparation of mesoscopic geometric characteristics of ball end milling cutter and optimization of cutting performance

According to the difficult machinability of titanium alloy, the research shows that the surface micro-textured technology can reduce the friction force and cutting temperature in the cutter-workpiece contact area. Starting with the precise preparation of micro textures by laser processing technology, this paper takes ball-end milling cutter milling titanium alloy as the research object, studies the influence of laser processing parameters on micro-textured size parameters, and optimizes the laser processing parameters as follows: laser power P = 40 W, scanning speed V = 1700 mm/s, scanning times N = 7 times, and spot diameter D = 40 μm. The distribution of temperature field and stress field during laser processing is analyzed, and the accuracy of the influence rule of laser processing parameters on micro-textured size parameters is verified, thus realizing the purpose of accurately preparing micro textures. The interactive influence of mesoscopic geometric features on the cutting performance of ball-end milling cutter is analyzed, and the genetic algorithm is used to optimize the parameters. The results show that the main factor affecting the force-heat characteristics of the tool is the blunt edge radius, and the interaction between the blunt radius of the cutting edge and the distance from blade is obvious. The optimized mesoscopic geometric parameters are as follows: the blunt edge radius is 20 μm, and the distance from blade is 110 μm, the micro-textured diameter is 30 μm, and the micro-textured spacing is 175 μm. The research content of this paper lays a foundation for efficient cutting of titanium alloy materials.

Change in Edge Radius of Cutting Tool from Surface Tension Between Solid Materials

In this study, the “surface tension defined from stress” was used to predict the change in the cutting edge radius in the tool’s initial-stage wear regime. An analysis of the “surface tension defined from the stress” between solids showed that the flow of the material and the adhesion phenomenon must occur simultaneously at the interface. From the experimental and simulation results, it was confirmed that the proposed model can be used to predict the stress distribution acting on the cutting tool and evaluate the “surface tension defined from the stress” at the tool and workpiece interface. It was also verified that the cutting-edge radius under a state of equilibrium changes based on the cutting condition. These results indicate that simply using a cutting tool with a smaller cutting-edge radius will lead to a rapid increase in the cutting-edge retreat at the beginning of the cutting. For the unmanned operation of the cutting processes, it is desirable to use a cutting tool with a cutting-edge radius under a state of equilibrium at the beginning of the cutting to improve the cutting efficiency and reduce the cutting cost.