Effect Of Edge Radius Research Articles

Analytical modeling and experimental validation of micro end-milling cutting forces considering edge radius and material strengthening effects

This paper presents a novel micro end-milling cutting forces prediction methodology including the edge radius, material strengthening, varying sliding friction coefficient and run-out together. A new iterative algorithm is proposed to evaluate the effective rake angle, shear angle and friction angle, which takes into account the effects of edge radius as well as varying sliding friction coefficient. A modified Johnson–Cook constitutive model is introduced to estimate the shear flow stress. This model considers not only the strain-hardening, strain-rate and temperature but also the material strengthening. Furthermore, a generalized algorithm is presented to calculate uncut chip thickness considering run-out. The cutting forces model is calibrated and validated by NAK80 steel, and the relevant micro slot end-milling experiments are carried out on a 3-axis ultra-precision micro-milling machine. The comparison of the predicted and measured cutting forces shows that the proposed model can provide very accurate predicted results. Finally, the effects of material strengthening, edge radius and cutting speed on the cutting forces are investigated by the proposed model and some conclusions are given as follows: (1) the material strengthening behavior has significant effect on micro end-milling process at the micron level. (2) Cutting forces predicted increase with the increase of edge radius. (3) Considering varying sliding friction coefficient can enhance the sensitivity of the predicted cutting forces to cutting speed.

FEM analysis on the influence of rounded tool edge on micro-blanking of thin foil with negative clearance

This work studies the effects of the tool edge radius in a micro-blanking process with negative clearance by using finite element method. For the study, a simulation model of blanking of AL6061-T6 foil with tools (punch and die) having a large edge radius comparable to the thickness of the foil was prepared. Using the model, micro-blanking process with various tool edge radii are simulated to study the resultant blanking forces and blank quality. From the simulation studies, it is found that a large edge radius of a blanking punch have effect on the blanking forces. Especially, a projecting edge was observed at the edge of the finished blank. This projecting edge is considered to be caused by negative clearance and a large edge radius of a die. Overall summary and discussion on the effect of a rounded tool edge on the blanking force and blank deformation is presented.

Modeling Cutting Force in Micro-Milling of Ti-6Al-4 V Titanium Alloy

This work presents a finite element method (FEM) based micro-end milling cutting force modeling of Ti-6Al-4V titanium alloy microchannels. Ti-6Al-4V is one of the widely acceptable titanium based alloys for medical as well as aerospace applications due to its advantageous properties like; corrosion resistance, larger strength to weight ratio, non-toxic nature and bio-compatibility. Johnson-Cook constitutive equation is used for the FEM model with due consideration of effects of strain, strain rate and temperature on the material property and failure parameters considered as the chip separation criterion. Simulation of stress distribution, temperature distribution and cutting forces prediction during micro-end milling of Ti-6Al-4V alloy is performed by ABAQUS/Explicit 6.12 software with incorporation of tool edge radius effect, which is more common in downscaling of the process. Predicted cutting forces model results are validated by conducting micro-end milling experiments. The trend of the predicted cutting forces results shows in good agreement with experimental results.

Study on the micro-machining process with a micro three-sided pyramidal tip and the circular machining trajectory

In this paper a three-sided pyramidal tip was driven in a circular trajectory to perform micro-machining process. The circular trajectory was achieved by rotating the tip around a center point. Because of the asymmetry of the three-sided pyramidal tip, machining micro channels along different feeding directions would cause different cutting tracks, which influences the finish of channel sides. It was found that the variations of cutting rake angle and uncut chip thickness in each revolution mainly affected the burr formation. By studying effects of tip edge radius and tip geometry on machining process, a channel with slight burr at two sides was obtained. Using the optimized machining method and coordinating with feed motion of the work stage, perfect three-dimensional structures with well-finishing edges were obtained on aluminum alloy and polymethylmethacrylate (PMMA) surfaces. The dimension of fabricated 3D structures can be controlled in three dimensional directions, ranging from ten microns to several hundred microns.

Prediction of machining induced microstructure in Ti–6Al–4V alloy using 3-D FE-based simulations: Effects of tool micro-geometry, coating and cutting conditions

Machining process affects surface integrity of Ti–6Al–4V titanium alloyed end-products. During thermal-mechanical loading and subsequent processing that take place in machining, grain size is altered at the subsurface through dynamic recrystallization and subsequent recovery. This can cause softening or hardening of the machined surfaces affecting surface integrity depending on the resultant grain sizes and phase fractions. Prediction of machining induced surface integrity specifically microstructure and grain size can be achieved by using Finite Element-based process simulations and calculated temperature, strain, stress and strain rate fields. This study presents experimental and numerical investigations in machining induced subsurface microstructure, microhardness and grain size in Ti–6Al–4V titanium alloy. Machining surfaces are investigated by measuring subsurface microhardness and grain size and phase fractions in each cutting conditions through scanning electron microscopy and image processing. 3-D FE machining simulations are conducted at the same cutting conditions and tool geometry to predict dynamic recrystallization (DRx) and resultant grain size by utilizing the Johnson–Mehl–Avrami–Kolmogorov model for Ti–6Al–4V alloy. The study also presents investigations and discussions about the effects of machining conditions (tool geometry, coating, and cutting conditions) on the microhardness and grain size in machining Ti–6Al–4V. Numerical modeling results are compared with experimental results and distinct effects of tool edge radius, coating, and cutting conditions on machining induced subsurface microstructure specifically on the changes in grain size due to dynamic recrystallization and recovery have been reported.

Cutting Forces and Chip Morphology during Wood Plastic Composites Orthogonal Cutting

The effect of chip thickness, rake angle, and edge radius on cutting forces and chip morphology in wood plastic composites (WPCs) orthogonal cutting was investigated. Three types of WPCs, Wood flour/polyethylene composite (WFPEC), wood flour/polypropylene composite (WFPPC), and wood flour/polyvinyl chloride composite (WFPVCC), that were tested exhibited different behavior with respect to the machinability aspects. The cutting forces of WFPVCC were the highest, followed by WFPPC and WFPEC. The most significant factor on the parallel cutting force of these three types of WPCs was the chip thickness, which explained more than 90%, contribution of total variation, while rake angle, edge radius, and the interactions between these factors had small contributions. The most significant factor on the normal cutting force of WPCs was also the chip thickness, which accounted for more than 60% of the total variation. The chips produced included long continuous chips, short continuous chips, flake chips, and granule chips when cutting these three types of WPCs.

Modelling the effects of tool edge radius on micro machining based on smooth particle hydrodynamics simulation method

Smooth particle hydrodynamics (SPH) method is introduced to simulate the oxygen-free copper micro-cutting process. At the same cutting thickness r , several different a / r are employed to investigate the effects of tool edge radius on the micromachining mechanism. The simulation results indicate that the larger a / r was, the greater the transverse cutting force was, the smaller the vertical pressure was, which benefits for material removal and good quality surface generation. And it could also be found that the cutting heat was smaller with the smaller a / r , the flows along the rake face generated a large amount of friction heat and oxygen came into the contact slit easily, which caused chemical corrosion on diamond rake face seriously. When the a / r was bigger, chemical corrosion becomes difficult because the cutting tool contacted the material adequately and oxygen was difficult to enter the contact zone.

The effects of tool edge radius on drill deflection and hole misalignment in deep hole gundrilling of Inconel-718

Straightness control in gundrilling of deep, thin-walled holes on Inconel-718 is challenging due to insufficiently explored phenomena governed by the tool edge radius effects. Such effects are activated by conservative drilling conditions for Inconel-718, which transforms the chip formation mode to a thrust-dominated mechanism. Critical changes in force generation are thus resulted, which affect the characteristics of drill deflection and thin wall deformation. In consequence, the drill's self-piloting capability deteriorates – leading to uncontrollable deflection and hole misalignment. A mechanistic model uniting the underlying force, drill deflection, wall deformation and process kinematics is proposed and substantiated, as well.

Quasicontinuum analysis of the effect of tool geometry on nanometric cutting of single crystal copper

A dynamic multiscale simulation based on quasicontinuum method (QC) has been conducted to study the effect of tool geometry in nanometric cutting process of single crystal copper. In the simulation, the many-body EAM potential is used for the interactions between copper atoms in of the workpiece. The simulation captures the atomistic behaviors of material removal mechanisms from the free surface and the mobility of dislocations and their interactions with the computational cost of local atomistic simulation method. Simulations are performed on single crystal copper to study the atomistic details of material removal, chip formation, sub-surface deformation, and machining mechanism. The simulation results demonstrate that tool edge radius has significant effect on chip formation and subsurface deformation, because the effective rake angle varies with the tool edge radius. In addition, different effective rake angles result in different stress states and smoother surface can be obtained under bigger clearance angle. The variations of tangential force, normal force as well as the ratio of normal force to tangential force are obtained to analyze the effects of tool edge radius, rake angle and clearance angle in quantitative way.

Influence of Cutting Edge Radius in Micromachining AISI D2

Chip formation is a dynamic process that is often non linear in nature. A chip may not form when the depth of cut is less than a minimum chip thickness. This paper presents an investigation of cutting edge radius effect on micromachining AISI D2 tool steel via simulation. The chip growth, chip formation and material deformation mechanism was investigated using commercial finite element analysis software. A model is developed with consideration of the arbitrary LagrangianEulerian (ALE) method. The chip growth, chip formation and material deformation was investigate under three criteria such as a/r<1, a/r>1 and a/r=1. The model showed that the chip is formed at a/r >1 while material extrusion performed under a/r<1.

Cutting Force Analysis in Micro Milling of Steel

An analysis of cutting force performance in the micro milling on steel has been carried out based on an experimental work using micro flat end mills on a precision CNC machine tool. It has been found that cutting forces occurred at low feed per tooth are relatively high by assessing the averaged peak forces from the experiments. When feed per tooth is relatively close to tool edge radius, the forces were not growing in linearity with the increasing feedrate. This finding indicates the significance of ploughing phenomenon as an effect of tool edge radius in micro milling.

Numerical Study of Residual Stress Induced by Multi-steps Orthogonal Cutting

Residual stresses induced by material removal have a major influence on the lifetime of machined pieces especially in its corrosion resistance and fatigue life. For that reason, numerical prediction of residual stress profile was the subject of many works. But most of these models are developed only for a single step. They does not consider the effect of hardening and thermal softening on the residual stresses induced by the material removal which is, in the reality, a multi-steps operation such as milling and grinding. The cutting tool is in contact with a part of material that was the finished piece in the previous step. In this paper a multi-steps model for orthogonal cutting has been developed in order to study the influence of the cumulated strain and temperature induced by the different steps on the residual stresses. The effect of tool edge radius and heat generated by flank friction on the predicted stress profile is modeled. Commercial finite element software ABAQUS with its Explicit and Implicit modules was used. Computed Numerical predicted stress fields are compared against measured residual stresses obtained by X-Ray diffraction. Moreover, in order to take into account all the physics in the tool-work material interface, spring back simulation was performed using ABAQUS Implicit.

Mechanistic model for prediction of cutting forces in micro end-milling and experimental comparison

Micro end milling is an important process in the manufacture of micro and meso scale products and has an advantage of creating more complex geometry in a wider variety of materials in comparison with other micro-machining methods. In this paper, a new methodology for predicting the cutting coefficients considering the edge radius and material strengthening effects is presented. Further a mechanistic model is developed to predict the cutting forces in micro end milling operation taking into account overlapping tooth engagements. The mechanistic model, derived from basics considering material property and principles of metal cutting, is valid for a wider range of cutting parameters. The model is validated with the results from micro slot end-milling of mild steel carried out on the basis of full factorial design. On comparing the amplitudes of cutting forces, it is seen that mechanistic model predicts the transverse force with an average absolute error of 12.29%, while a higher prediction error of 19.49% is obtained for feed force. Additionally the mechanistic model is able to predict the variations in the cutting forces with rotation of the cutter and average absolute deviations of 13% and 11% are obtained for feed and transverse forces, respectively.

A Non-Dimensional Analysis of Tool Edge Radius Effect on the Mechanics of Micromachining

The effect of tool edge radius on the mechanics of micromachining, both in terms of plasticity and tribology is significant. Through an experimental study, the responses of normalized process variables namely tool-chip contact length, deformed chip thickness and machining force were evaluated for varying relative tool sharpness. A non-dimensional analysis of the interrelationship among the process variables indicate a transformation in chip formation mechanism under an extreme condition is reported.

Modeling the effect of tool edge radius on contact zone in nanomachining

The contact between tool and workpiece during nanomachining is a complicated phenomenon due to comparable tool edge radius, R, with cutting depth, a. This paper presents an investigation into the effects of tool edge radius on contact zone, chip formation mechanism, stagnation zone, tool forces and hydrostatic stress distributions. Molecular dynamics simulations of the nanometric cutting on single crystal copper were performed using EAM potential function with wide range from a/R=∞ to tools with various rounded tip. Results showed that although at a/R⩾1, both tool tip and rake edge participate in chip formation, at a/R<1 chip is formed only by rounded edge. Also, at a/R<1, a small fraction of atoms compared with a sharper tool are separated as chip and larger fraction is pressurized to pass beneath the tool edge. Indeed, in rounded edge tools, the stable stagnation zone is located in tool curvature tip that acts as the first effective cutting edge. The height of stagnation point from the bottom edge of tool increases with edge radius, where it is independent from undeformed chip thickness. In addition, cutting force is slightly increased at smaller a/R; however, the trust force is raised remarkably especially when cutting depth approaches to critical depth of cut. Smaller a/R, similarly, induced higher compressive hydrostatic stress in wider contact length. Finally, if cutting depth is lower than the height of stagnation zone, the cutting mechanism will change to sliding mechanism.

Modeling of the effect of tool edge radius on surface generation in elliptical vibration cutting

The elliptical vibration cutting (EVC) technique has been found to be a promising technique for ultraprecision machining of various materials. During the EVC process, two-dimension vibration movement of the cutting tool generates consecutively overlapping EVC cycles. In each cycle, the tool position relative to the workpiece gets continuously varied, and meanwhile, cusps are left along the nominal cutting direction. Such vibration marks, which have never been found in conventional cutting process, are considered to be a critical characteristic for the EVC technique. In order to analyze this unique characteristic, an analytical model based on geometrical relationships in the EVC process was developed to calculate the theoretical roughness, where the tool edge is assumed to be perfectly sharp. However, the effect of tool edge radius is probably significant, especially in the situation where the tool edge radius is comparable to the vibration amplitudes. Hence, in the present research, an analytical surface generation model for the EVC process is developed to better understand the surface generation process and predict the surface roughness. The tool edge radius is considered and investigated in detail in this new approach. Mathematical evaluation shows that the surface roughness value along the nominal cutting direction decreases with the increase of the edge radius. In order to validate the proposed model, a series of EVC grooving tests on soft and hard work materials were conducted using a polycrystalline diamond (PCD) tool by applying the ultrasonic EVC technique. The results show that the predicted roughness based on the proposed model correlates well with the experimental results measured by a white light interferometer, and the model considering the tool edge radius performs significantly better than the one without considering the edge radius in predicting the roughness along the nominal cutting direction.

ANALYTICAL MODELING OF MICRO END-MILLING FORCES WITH EDGE RADIUS AND MATERIAL STRENGTHENING EFFECTS

The study aims at developing a predictive analytical force model for the micro end-milling operation taking into account the material strengthening as well as the edge radius effects that come into play at the micro level. The mechanistic models for macro end-milling process have been extensively reported in literature and such models predominantly use milling force coefficients which are empirically determined from end-milling experiments. The proposed model for micro end-milling is based on determination of milling force coefficients from fundamental oblique cutting approach. The edge radius effect has been accounted by analyzing the rubbing action similar to the rolling of a cylinder over work surface. Johnson-Cook material model has been modified based on the strain gradient plasticity theory incorporating the increase in material strength with decreasing uncut chip thickness. From the micro orthogonal cutting experiments, a good agreement between the experimental and predicted shear strength values is observed. The force model is validated against measured forces in end-milling experiments carried out on the KERN Evo 5 axis micro machining center. The feed and lateral forces are predicted within 10% deviation on an average.

Finite Element Analysis of Cutting Force and Burr Formation in Micro-Cutting of Titanium Alloy Considering Tool Edge Radius

In recent years, with the development of machinery industry, micro-cutting technologies have been gradually moving into engineering realization. The paper carries out a series of works on simulation modeling of micro-cutting of Ti-5Al-5V-5Mo-3Cr considering tool edge radius. Unlike conventional cutting, in micro-cutting the effect of tool edge radius which has a marked impact on cutting force, specific cutting energy, burr formation and burr size can no longer be neglected.

Prediction of machining induced residual stresses in turning of titanium and nickel based alloys with experiments and finite element simulations

Titanium and nickel alloys represent a significant metal portion of the aircraft structural and engine components and the residual stresses induced by machining are very critical due to safety and sustainability concerns. This paper presents experimental investigations and finite element simulations on turning of Ti–6Al–4V titanium alloy and IN100 nickel based alloy with uncoated and TiAlN coated tools. Face turning of Ti–6Al–4V and IN100 using uncoated tools with various edge radii and TiAlN coated carbide tools is conducted; and residual stresses are measured in radial and circumferential directions using X-ray diffraction technique. 3-D finite element (FE) modeling is utilized to predict forces and machining induced stress fields. The feasibility and limitations of predicting machining induced residual stresses by using viscoplastic finite element simulations and temperature-dependent flow softening constitutive material modeling are investigated. A friction determination method is utilized to identify friction coefficients in presence of tool edge radius. The predicted stress fields are compared against measured residual stresses. Effect of tool edge radius and coating on the predicted stress profiles is also investigated. The results are found useful in predicting machining induced surface integrity that is critical to determine the fatigue life of nickel and titanium alloy components.

Study of edge radius effects in mechanical micro-machining

In mechanical micro–machining, the feature size ranges from tens of micrometres to less than a millimetre in size. At this level of cutting, the tool cannot be considered as a sharp tool, as the uncut chip thickness is comparable to the tool edge radius. Due to technological limitations, it is not possible to manufacture a perfectly sharp tool. Researchers have studied various aspects of edge radius of tools, such as size effect, minimum chip thickness effect, ploughing phenomena, etc. In the present study, FEM analysis of the orthogonal machining is presented to study the stress state ahead of the tool, in the machined surface and in the layers encompassing the chip. The uncut chip thickness in this study is chosen to be more than the edge radius of the tool. The study indicates, an optimum value for edge radius can be found and used for processes of constant uncut chip thickness.