MOLECULAR DYNAMICS SIMULATION OF NANOMETRIC CUTTING

Molecular Dynamics (MD) simulations of nanometric cutting of single-crystal copper were conducted to predict cutting forces and investigate the mechanism of chip formation at the nano-level. The MD simulations were conducted at a conventional cutting speed of 5 m/s and different depths of cut (0.724–2.172 nm), and cutting forces and shear angle were predicted. The effect of tool rake angles and depths of cut on the mechanism of chip formation was investigated. Tools with different rake angles, namely 0°, 5°, 10°, 15°, 30°, and 45°, were used. It was found that the cutting force, thrust force, and the ratio of the thrust force to cutting force decrease with increasing rake angle. However, the ratio of the thrust force to the cutting force is found to be independent of the depth of cut. In addition, the chip thickness was found to decrease with an increase in rake angle. As a consequence, the cutting ratio and the shear angle increase as the rake angle increases. The dislocation and subsurface deformation in the workpiece material were observed in the cutting region near the tool rake face. The adhesion of copper atoms to the diamond tool was clearly seen. The same approach can be used to simulate micromachining by significantly increasing the number of atoms in the MD model to represent cutting depths in the order of microns.     

Numerical investigations of optimum turning parameters—AA2024-T351 aluminum alloy

Aerospace aluminum alloys have gained the prime significance due to their excellent machining characteristics. Numerous experimental and numerical studies have been conducted to establish the optimum cutting parameters of these alloys. In the numerical cutting models, the authenticity of computational results is suspected particularly because of the complex interaction at tool–chip interface, which involves a high material strain rate and thermal processes. The fidelity of cutting simulation results is appraised by a parametric sensitivity analysis and actual experimentation. In this research, the orthogonal turning of AA2024-T351 aluminum is simulated in Abaqus/Explicit by using a thermoviscoplastic damage model and Coulomb friction model for the contact interfaces. A parametric sensitivity analysis is performed to comprehend the chip morphology, tool–chip interface temperature, reaction force, and strain. Different simulations are performed with varied cutting speeds (200, 400, 600, and 800 m/min), rake angles (5°, 10°, 14.8°, 17.5°), feeds (0.3, 0.4 mm), and friction coefficients (0.1, 0.15). It is observed that an increased rake angle decreases the cutting force and increases tool–chip interface temperature. Similarly, the cutting depth has prominent effect on chip–tool interface temperature as compared to the friction. The computational results are found in close approximation with the published experimental data of AA2024-T351.     

基于黏结-滑移摩擦模型的304不锈钢切削力仿真研究*

通过预测加工304不锈钢时产生的切削力,从而对切削参数和刀具几何参数进行优化,是提高304不锈钢的加工精度、切屑控制及保障刀具寿命的基础。建立304不锈钢切削仿真模型,为提高模型的精确性,选择Johnson-Cook本构方程和黏结-滑移摩擦模型。结果表明：采用黏结-滑移摩擦模型的切削力预测结果更为准确,表明相对于纯剪切摩擦与库仑摩擦模型,黏结-滑移摩擦模型能更准确地描述刀-屑摩擦特性。展开不同参数下的切削力研究,研究发现：切削力随着刀具前角、后角和切削速度的增大而减小,随切削刃钝圆半径和切削厚度、宽度的增大而增大,其中切削宽度、厚度及前角对切削力大小影响较大。研究结果为304不锈钢切削效率的提高和切削机制的研究提供了理论依据。     

The influence of end mill helix angle on high performance milling process

The results of experimental research on the influence of the helix angle on high performance milling of AlZn5.5MgCu alloy are presented. End mills with a wavy shape of a cutting edge, dedicated to rough high performance machining, were used. The helix angle was changed in the range of 20° to 50° with a step of 5°. During the milling tests, three cutting force components were measured. After each test cutting, chips were collected and analyzed. A recording of the chip evacuation process using a high-speed camera was also conducted. The influence of the helix angle on cutting force components was determined and the mathematical models of the forces were calculated. The significance of coefficients in the obtained equations was analyzed as well. The recorded images of the chip evacuation were analyzed. The displacement and the angle of the chip evacuation were determined. Based on the analysis of the selected images the impact of the helix angle on the direction and evacuation velocity of chips was determined. The size and shape of the obtained chips was also analyzed.

     

Optimizing the geometric parameters of chamfered edge for rough machining Fe–Cr–Ni stainless steel

Geometry of cutting edge has great influence on performance and reliability of modern precision cutting tools. In this study, two-dimensional finite element model of orthogonal cutting of Fe–Cr–Ni stainless steel has been built to optimize the geometric parameters of chamfered edge. A method to measure the chip curl radius has been proposed. The effect of cutting edge geometric parameters on tool stress and chip curl radius has been analyzed. Then, the chamfered edge parameters have been optimized based on numerical simulation results. It finds that, keeping the equal material removal rate, the optimal geometric parameters of chamfered edge for rough machining Fe–Cr–Ni stainless steel are that the rake angle is from 16° to 17°, and the chamfer length is from 60 to 70 μm. Small (large) rake angle combined with small (large) chamfer length is more reasonable to reduce the tool stress. When the length of land is approximately equal to undeformed chip thickness and the rake angle is larger than 15°, the chip curl radius is minimal. The groove type with large radio of width to depth should be used in the chip breaking based on the optimization results.     

Research on chip formation parameters of aluminum alloy 6061-T6 based on high-speed orthogonal cutting model

Chip formation, an important aspect of the high-speed cutting (HSC) mechanism, is generally accepted as the result of shear deformation in the shear zone and tool-chip friction. In order to accurately study chip formation process in HSC, a theoretical model for the high-speed orthogonal cutting of aluminum alloy 6061-T6 was built, which can be used to calculate the important parameters of chip formation, such as shear angle, friction angle, length of shear plane, tool-chip contact length, and width of the first shear zone. A series of orthogonal cutting experiments, with the YG6 carbide tool and on a wide range of cutting speed (100–1,900 m/min) and feed (0.06–0.15 mm/r), were performed in order to obtain the parameters required in the model, including the cutting forces, the chip thickness, and the shear slip distance. Seven kinds of chip formation parameters were obtained with different cutting parameters in the experiment, and the built theoretical model can well explain the formation process and the morphology characteristics of these chips, which proves that the combined method of theoretical model and orthogonal cutting experiment is an effective and easy approach to obtain the parameters of chip formation in HSC, avoiding the cutting speed limitation and the safety risk in quick-stop test. Within the range of parameters set in the experiments, the chip mainly appears to be continuous chip, curling chip, or discontinuous chip. And the chip thickness, friction angle, length of shear plane, and width of the first shear zone decrease with the increase of the cutting speed; meanwhile, the shear slide distance and shear angle increase.     

An Improved Method for the Determination of 3D Cutting Force Coefficients and Runout Parameters in End Milling

A simple improved method is suggested for determining constant cutting force coefficients, irrespective of the cutting condition and cutter rotation angle. This can be achieved through the combination of experimentally deternimed cutting forces with those from simulation, performed by a mechanistic cutting force model and a geometric uncut chip thickness model. Additionally, this study presents an approach that estimates runout-related parameters, and the runout offset and its location angle, using only one measurement of cutting force. This method of estimating 3D end milling force coefficients was experimentally verified for a wide range of cutting conditions, and gave significantly better predictions of cutting forces than any other methods. The estimated value of the runout offset also agreed well with the measured value.     

高速车削镍基高温合金GH4169的切削力仿真研究

基于Deform 3D仿真软件建立了GH4169高温合金高速车削的有限元模型,采用四因素三水平正交试验方法研究了切削用量和刀具几何参数对切削力的影响规律,并建立了切削力经验公式。研究结果表明:在高速车削GH4169的过程中,对切削力影响最大的参数是切削深度,其次是进给量和前角,最后是刀尖圆弧半径;切削力随切削深度和进给量的增大而增大,随前角的增大呈现先降低又升高的趋势,而刀尖圆弧半径增大时切削力变化不大;最佳参数组合为:进给量0.2mm/r,切削深度0.4mm,前角10°,刀尖圆弧半径0.2mm。     

Slip-line field modeling of orthogonal machining pressure sensitive materials

The slip-line field methods are widely used in solving cutting problem; however, most of which were focused on the pressure-independent materials. In this work, a new slip-line field model for orthogonal cutting of pressure sensitive materials is developed. Analytical characterization for orthogonal cutting process is obtained, which can give the explicit expressions for the shear angle, cutting force, and chip thickness in terms of the tool geometry, the friction coefficients on the tool flat, and the internal friction angle of the materials. To investigate the effect of the material and cutting parameters on cutting process, the finite element simulation is performed as well. The comparisons between the shear angle and cutting force predicted by the theoretical model with those obtained from finite element model simulation are made. The good agreement of the predicted results with the numerical results clearly reveals that the proposed slip-line field model can satisfactorily characterize the orthogonal cutting behavior of the pressure sensitive materials. Further analysis has demonstrated that the pressure sensitivity of materials has a significant influence on cutting process.     

Simulation-based solid carbide end mill design and geometry optimization

Designing a high-performance solid carbide end mill is difficult due to the complex relationship between end mill geometry and numerous or conflicting design goals. Earlier approaches of computer-aided solid end mill design are limited to only a few design aspects. This article presents a three-dimensional finite element method of milling process for solid carbide end mill design and optimization. The software was secondarily developed based on UG platform, integrating the parametric design with the development of the two-dimension drawing of solid carbide end mill. The three-dimension finite element simulation for milling Ti-6Al-4V alloy was performed and the geometrical parameters were optimized based on the objective of low cutting force and cutting temperature. As a result, a simulation-based design and optimization of geometrical parameters of tool structure and cutting edge is possible. The optimized results, for the geometrical parameters of tool structure and cutting edge when milling titanium alloy using a 20-mm diameter solid carbide end mill, is a 12-mm diameter of inner circle, four flutes, a 45 ° helix angle, and a 9 ° rake angle of the side cutting edge.     

一种新型的广义铣削力模型

基于微分几何理论建立了任意形状铣刀的数学模型,给出适用于任意形状铣刀的三维单元铣削力模型。该铣削力模型考虑了铣刀的法向前角,认为作用单元体上的铣削力由作用于前后刀面上的正压力和摩擦力组成,并表示为与瞬时切厚有关的非线性函数。     

基于三相微观结构的纤维复合材料切削仿真研究

为了研究纤维增强复合材料在切削过程中的材料去除机理及切削性能,本文建立了基于三相微观结构的纤维增强复合材料的二维有限元切削模型。针对纤维、基体和界面相组成三相微观结构,分别建立了它们的本构模型和失效准则,并完成复合材料二维正交切削的动态物理仿真。通过切削力仿真值与实验值的比较,验证了该模型的准确性和有效性。并基于此模型,分析材料的切屑形成机理、切削损伤及加工参数对切削力的影响。结果表明,纤维增强复合材料的切屑形态、损伤模式和切削力具有明显的各向异性。     

Investigate on milling force of cryogenic cooling processing aluminum honeycomb treated by ice fixation

Aerospace metal honeycomb materials with low stiffness had often the deformation, burr, collapse, and other defects in the mechanical processing. They were attributed to poor fixation method and inapposite cutting force. This paper presented the improvement of fixation way. The hexagonal aluminum honeycomb core material was treated by ice fixation, and the NC milling machine was used for a series of cryogenic machining. Considering the similar structure of fiber-reinforced composite materials, the milling force prediction model of ice fixation aluminum honeycomb was established, considering tool geometry parameters and cutting parameters. Meanwhile, the influence rule on milling force was deduced. The results show that compared with the conventional fixation milling method, the honeycomb processing effect is improved greatly. The machining parameters affect order on milling forces: the cutting depth is the most important, followed by the cutting width, then the spindle speed and the feed. Moreover, too small cutting depth (a_p?=?0.5 mm) will cause insufficient cutting force, while a_p?>?2 mm with higher force will reduce the processing quality of honeycomb. Simultaneously, the honeycomb orientation (θ) has a great influence on processing quality. Using the model, the predicted and measured error values of the feed and main cutting force are all small in θ?<?90°. But, the rate is 33 and 26% for the main cutting force and feed force error in θ?>?90°, respectively, while they all exhibit the smallest error in θ?=?60°. This bigger error mainly is due to unstable cutting force with obtuse angle. In addition, the tool rake angle has little influence on cutting quality in θ?<?90°, but bigger on that in θ?>?90°. Furthermore, the calculation model successfully conforms to the main deformation mechanism and influences parameters of the cutting force in the milling process, and it can accurately predict the cutting force in θ?<?90° and guide the milling process.     

An experimental investigation of oblique cutting mechanics

In this study, an experimental investigation of oblique cutting process is presented for titanium alloy Ti-6Al-4V, AISI 4340, and Al 7075. Important process parameters such as shear angle, friction angle, shear stress, and chip flow angle are analyzed. Transformation of the data from the orthogonal cutting test results to oblique cutting process is applied, and the results are compared with actual oblique cutting tests. Effects of hone radius on cutting forces and flank contact length are also investigated. It is observed that the shear angle, friction angle, and shear stress in oblique cutting have the same trend with the ones obtained from the orthogonal cutting tests. The transformed oblique force coefficients from orthogonal tests have about 10% discrepancy in the feed and tangential directions. For the chip flow angle, the predictions based on kinematic and force balance results yield better results than Stabler's chip flow law. Finally, it is shown that the method of oblique transformation applied on the orthogonal cutting data yields more accurate results using the predicted chip flow angles compared to the ones obtained by the Stabler's rule.     

A 3D Predictive Cutting-Force Model for End Milling of Parts Having Sculptured Surfaces

A comprehensive, 3D mathematical model of desired/optimal cutting force for end milling of freeform surfaces is proposed in this paper. A closed-form predictive model is developed, based on a perceptive cutting approach, resulting in a cutting force model having a comprehensive set of essential cutting parameters. In particular, the normal rake angle, usually missing in most existing models of the same sort, is included in the developed model. The model also permits quantitative analyses of the effect of any parameters on the cutting performance of the tool, providing a guideline to improving the tool performance. Since the axial depth of cut varies with time when milling sculptured surface parts, an innovative axial depth of cut estimation scheme is proposed for the generation of 3D cutting forces. This estimation scheme improves on the practicality of most existing predictive cutting-force models for milling, in which the major attention has been focused on planar milling surface generation. In addition, the proposed model takes the rake surface on the flute of mills as an osculating plane to yield 3D cutting force expressions in only two steps. This approach greatly reduces the time-consuming mathematical work normally required for obtaining the cutting-force expressions. A series of milling simulations for machining freeform parts under specific cutting conditions have been performed to verify the effectiveness of the proposed cutting-force model. The simulation results demonstrate the accurate estimating capability of the proposed method for axial depth of cut estimation. The cutting force responses from the simulation exhibit the same trends as can be obtained using the empirical mechanic’s model referenced in the literature. Finally, from the simulation results it is also shown that designing a tool with a combination of different helix angles, having cutting force signatures similar to those of the single helix angle counterparts, is particularly advantageous.     

单晶硅料摆辅助多金刚线切片的锯切力模型研究

料摆辅助多金刚线切片技术是实现硬脆材料高精高效加工行之有效的工艺技术,探明其工艺参数、锯切力和切片质量的定量关系,具有重要的现实意义。在研究金刚线运动轨迹的基础上,推导了考虑线弓影响的切割长度变化公式;结合压痕断裂力学和试验研究,建立并验证了料摆辅助切片的锯切力模型。开展了不同工艺参数对锯切力的影响分析,结果表明,料摆辅助加工可以降低锯切力近50%;摆动角度对最大切割力的影响较小,但摆角增大会加剧"锯齿形波动"周期内的锯切力极值幅度,摆动角速度对"锯齿形波动"的周期影响较大;在恒定进给速度条件下,进给速度越高,锯切力越大;在变速进给条件下,最大锯切力可降低12%左右。进一步进行了摆角分别为0°、3°、5°和7°的多金刚线切割单晶硅实验,试验表明,料摆辅助切片加工有助于减少硅片表面因脆性崩裂产生的表面材料破损、深凹坑等缺陷;相较于普通切片加工,在摆角5°工况时,工件的表面粗糙度和硬化层厚度最大分别降低30.1%和20.1%。     

A new method for cutting force prediction in peripheral milling of complex curved surface

The instantaneous uncut chip thickness and entry/exit angle of tool/workpiece engagement vary with tool path, workpiece geometry and cutting parameters in peripheral milling of complex curved surface, leading to the strong time-varying characteristic for instantaneous cutting forces. A new method for cutting force prediction in peripheral milling of complex curved surface is proposed in this paper. Considering the tool path, cutter runout, tool type(constant/nonconstant pitch cutter) and tool actual motion, a representation model of instantaneous uncut chip thickness and entry/exit angle of tool/ workpiece engagement is established firstly, which can reach better accuracy than the traditional models. Then, an approach for identifying of cutter runout parameters and calibrating of specific cutting force coefficients is presented. Finally, peripheral milling experiments are carried out with two types of tool, and the results indicate that the predicted cutting forces are highly consistent with the experimental values in the aspect of variation tendency and amplitude.     

Modelling the cutting forces in micro-end-milling using a hybrid approach

This paper presents the development of a cutting force model for the micro-end-milling processes under various cutting conditions using a hybrid approach. Firstly, a finite element (FE) model of orthogonal micro-cutting with a round cutting edge is developed for medium-carbon steel. A number of finite element analyses (FEA) are performed at different uncut chip thicknesses and velocities. Based on the FEA results, the cutting force coefficients are extracted through a nonlinear algorithm to establish a relationship with the uncut chip thickness and cutting speed. Then, the cutting force coefficients are integrated into a mechanistic cutting force model, which can predict cutting forces under different cutting conditions. In order to account for the cutting edge effect, an effective rake angle is employed for the determination of the cutting force. A comparison of the prediction and experimental measured cutting forces has shown that the developed method provides accurate results.     

Analysis of the machining characteristics in reaming AlSi12 alloy with PCD reamer

Machining characteristics were studied for the reaming AlSi12 alloy using six flutes polycrystalline diamond reamer on DMG DMU 50 linear five-axis CNC machine. The output measures for this experiment comprise of cutting torque, cutting thrust, hole diameter, hole cylindricity, and workpiece surface finishing. Cutting forces were in real time monitored by Kistler Dynamometer during the experiments. Hole diameter, hole cylindricity, and surface finishing (surface roughness and surface integrity) of the machined surfaces were measured after machining. It is indicated that the cutting force of thrust and torque decreased with increase of cutting speed and decrease of cutting feed. High accuracy of hole was achieved because the hole measurements satisfied the standard deviation. Hole diameters were within tighter tolerance value of 33₀ ^0.025, and cylindricalities varied in the range from 0.002 to 0.014 um (less than 0.02 um). As to surface finishing, high surface performance could be obtained by eliminating surface defects on initial hole such as cavities and voids after subsequent finishing operating of reaming. However, the reamed surface damages of AlSi112 alloy under inapposite cutting conditions were involved with re-deposited work material (chip), surface grooves and notch, feed marks, surface shrinkage cavities and porosities, metal debris, and micro-pits. Moreover, surface roughness improved with an increase in the cutting speed from 2,000 to 6,000 rpm, but it deteriorated evidently when the cutting speed increased from 6,000 to 10,000 rpm. Cutting speed of 6,000 rpm and cutting feed of 3,000 mm/min were the recommendable cutting parameters to ream AlSi12 alloy because best hole quality could be produced in comparison of other cutting parameters.     

3D FE modelling of high-speed ball nose end milling

The paper details research and development of a Lagrangian-based, 3D finite element (FE) model to simulate the high-speed ball nose end milling of Inconel 718 nickel-based superalloy using the commercial FE package ABAQUS Explicit. The workpiece material was modelled as elastic plastic with isotropic hardening and the flow stress defined as a function of strain, strain rate and temperature. Workpiece material data were obtained from uniaxial compression tests at elevated strain rates and temperatures (up to 100/s and 850°C, respectively) on a Gleeble 3500 thermo-mechanical simulator. The data were fitted to an overstress power law constitutive relationship in order to characterise flow behaviour of the material at the level of strain rates found in machining processes (typically up to 10⁵/s). Evolution of the chip was initially seen to progress smoothly, with the predicted machined workpiece contour showing good correlation with an actual chip profile/shape. Cutting force predictions from the FE model were validated against corresponding experimental values measured using a piezoelectric dynamometer, while modelled shear zone/chip temperatures were compared with previously determined experimental data. The model was successful in predicting the forces in the feed and step-over direction to within 10% of corresponding experimental values but showed a very large discrepancy with the thrust force component (～90%). Modelled shear-plane temperatures calculated at the point of maximum cutting force were found to demonstrate very good agreement with measured values, giving a discrepancy of ～5%. The simulation required a computational time of approximately 167 h to complete one full revolution of the ball end mill at 90 m/min cutting speed.