An analytical tim6 domain evaluation of the cutting forces in BTA deep hole machining using the thin shear plane model

This paper presents an analytical approach to describe the cutting forces in 1ST A deep hole machining processes in the time domain. The method takes into account the effect of different machining conditions. Since the cutting velocities employed in BTA deep hole machining process are relatively high, and since small chips are produced due to the presence of tool chip breakers, the analysis is developed on the basis of the thin shear plane model.

The cutting velocity is a linear function of radius and the rake angle. Cutting is different in the two regions of the cutting tool, so the total cutting force acting on the cutting tool is determined by integrating the force on a small incremental thickness of the cutting tool. This approach, to predict the value of the cutting forces without resorting to any empirical techniques, clearly illustrates the effect of various system parameters on the machining process.

The resultant force system on a new BTA cutting tool consists of an axial force and torque. But with the increase in the number of holes bored, not only does the cutting profile deteriorate, but the wear pads do too. The resultant force system will then consist of three force components and a torque, due to the fact that the forces are not balanced at the wear pads. Under such conditions, the cutting force equations derived in the latter half of the paper, coupled with the properties of the randomly varying component, can be used as the forcing function on the machine tool to evaluate not only the response but also the regions of stability and instability during the machining.     

On the prediction of the roundness error in BTA deep hole machining based on the stochastic description of the cutting tool motion

This paper presents a methodology of predicting the maximum possible out-of-roundness of the hole produced, in BTA deep hole machining, as a function of certain machining parameters. Based on the solutions of the stochastic differential equations representing the machine tool-workpiece system in BTA deep hole machining, and the true cutting tool motion, an index describing the upper bound of the roundness error is defined. A parametric analysis of the out-of-roundness index is carried out. This analysis points out that at a low length-to-diameter ratio of the cutting tool, the axial force is the predominant factor causing the tool-tip deviation from the ideal motion, and that the radial and tangential forces are the major causes for the tool tip deviation at high length-to-diameter ratio of the cutting tool. The experimental measurement of out-of-roundness of the specimens under different machining conditions shows that the roundness error obtained lies within the zone described by the theoretical prediction.     

A STOCHASTIC CHARACTERIZATION OF THE MACHINE TOOL WORKPIECE SYSTEM IN BTA DEEP HOLE MACHINING Part II: Response Analysis and Evaluation of the Tool Tip Motion

In this paper, the solutions to the stochastic differential equations, which mathematically represent the machine tool work-piece system in BTA deep hole machining are presented. The solutions to the parametric stochastic differential equations have been obtained using the well known averaging technique. The non-parametric inhomogeneous equations have been solved using the Fokker-Planck equation. Based on these solutions, the true motion of the tool tip has been described using the maximum, average and minimum deviation curves. These curves predict that helical grooves will be formed on the workpiece and such helical grooves were observed on the workpieces. Also, the maximum, average and minimum values of deviation of the tool tip which is a measure of the roundness error are established. Based on these results an upper bound for the roundness error as a function of depth of hole is derived. The measurement of roundness of the specimens reveals that the experimental values be in the zone predicted by the theory in a finite region. So it can be speculated that the resultant force system is not completely balanced at the pads.     

An experimental investigation for the stochastic modelling of the resultant force system in BTA deep hole machining

This paper presents the measurement and a statistical analysis of the resultant force system, consisting of an axial force and torque, in BTA deep hole machining. The measurements were performed using a specially designed two-component piezoelectric dynamometer and adopting the rotating cutting tool-stationary workpiece procedure. The dynamometer was calibrated for static and dynamic outputs and techniques were employed for increasing the measuring accuracy and reducing the cross-interference by obtaining the elements of the system transfer function. Experiments were carried out to measure the mean values and the dynamic fluctuations of the axial force and torque. The recorded data was processed and analysed to establish all major statistical properties of the axial force and torque. Results show that the dynamic fluctuations of the axial force and torque in BTA deep hole machining can be represented by a stationary wideband process with a gaussian density distribution function. Such a mathematical model is essential for evaluating the dynamic response of the machine-workpiece system as well as the true motion of the cutting tool tip, and to establish the reliability of the machining process.     

Real-time cutting simulation system of a milling operation for autonomous and intelligent machine tools

The conceptual architecture of autonomous and intelligent machine tools has been proposed not only to generate flexibly the process and operation plan but also to utilize the machine tools and cutting tools' performance while satisfying the requirements of the products and avoiding unexpected machining trouble. In order to realize the autonomous milling, machining strategy such as tool paths and cutting conditions must be decided, not in advance like current NC machining, but in a real-time manner. The objective of this research is to develop a real time machining optimization with machining simulation. Consequently, a cutting simulation system called a virtual machining simulator has been developed for this purpose. This simulator can calculate the changing geometry of the workpiece and estimate the instantaneous cutting force, torque, etc using the physical model. This estimated information enables the system to decide the suitable cutting conditions according to the machinability evaluated. In this paper, the machining status is evaluated and the cutting conditions are modified in real time so that the requirement of the machining operation is satisfied by referring to the physical model. The reliable and safe machining operation is carried out by maintaining the cutting force and torque desired value.     

测力刀柄系统标定技术研究

测力刀柄系统可实时监测切削过程的轴向力和扭矩的变化,为测试自主设计的测力刀柄系统的使用性能,设计并研制了一套标定辅助工装,搭建了标定实验平台,完成了静、动态标定实验.采用逐级加、卸载法,确定了测力刀柄系统的线性度、重复性和滞后性等静态特性指标;通过脉冲激励法获得了测力刀柄系统的固有频率、阻尼比和最大工作频率等动态特性指...     

Analysis on Simulation of Quasi-Steady Molecular Statics Nanocutting Model and Calculation of Temperature Rise During Orthogonal Cutting of Single-Crystal Copper

This paper uses quasi-steady molecular statics method to carry out simulation of nanoscale orthogonal cutting of single-crystal copper workpiece by the diamond tools with different edge shapes. Based on the simulation results, this paper analyzes the cutting force, equivalent stress and strain, and temperature field. For the three-dimensional quasi-steady molecular statics nanocutting model used by this paper, when the cutting tool moves on a workpiece, displacement of atoms is caused due to the effects of potential on each other. After a small distance that each atom moves is directly solved by the calculated trajectory of each atom, the concept of force balance is used. And Hooke-Jeeves direct search method is also used to solve the force balance equation, and obtain the new movement position. When chip formation and the size of cutting force during cutting are calculated, further analysis is made. After the position of an atom's deformation displacement is acquired, the shape function concept of finite element is employed to obtain the atomic-level equivalent strain. With the stress-strain curve obtained from experiment of the numerical tensile value of nanoscale copper film taken as the foundation, regression treatment is made, and then the flow stress-strain relational equation is acquired. The flow stress-strain curve is used to calculate the equivalent stress produced under equivalent strain of element. This paper further supposes that workpiece temperature is mainly produced from two heat sources: plastic deformation heat and friction heat. Thus, this paper uses the acquired equivalent stress and strain to calculate plastic deformation heat. Besides, this paper additionally develops a method to calculate the numerical value of friction heat produced by the workpiece atoms on the tool face and the numerical value of temperature rise of workpiece atoms on tool face. Finally, the temperature rise produced from the two heat sources is added up for calculation of temperature field of the cut single-crystal copper workpiece during nanoscale orthogonal cutting, and for making analysis.     

Intelligent design of cutting tools using smart material

Shaving metal from a workpiece to produce desired geometric shape is carried out in turning machine tool. Attenuating a micro level vibration of a cutting tool using smart materials can save old machines and enhance flexibility in designing new generations of machine tools. The finite element method is employed to investigate structural stiffness, damping, and switching methodology using smart material in tool error attenuation. In this work, a dynamic force model is deployed to investigate the effectiveness of using such technique in toolpost dynamic control. Effects of short and open circuit conditions on tool critical frequencies for different structural stiffness ratios are assessed. In the transient solution for tool tip displacement, the pulse width modulation (PWM) technique is implemented for smart material activation to compensate for the radial disturbing cutting forces. A Fuzzy Algorithm is developed to control actuator voltage level enhancing improved dynamic performance. The influence of minimum number of PWM cycles in each disturbing force cycle is investigated in controlling the tool error growth. A methodology is developed to utilize toolpost static force–displacement diagram to obtain required activation voltage to shrink error under different dynamic operating conditions. Time delay of applied voltage during error attenuation is evaluated at different frequencies.     

切削液扰动对BTA深孔加工系统横向振动频率的影响

为探究切削液扰动下BTA深孔镗削系统横向振动频率的影响,通过建立BTA深孔镗杆系统计及内、外切削液流固耦合及其自由液面效应的横向振动模型,解析系统不同情况下的横向振动的一、二阶频率表达式,并以不同情况下,深孔镗杆内、外切削液的横截面面积及其对深孔镗杆的附加质量来表征对应的自由液面变化,通过计算,明确了BTA深孔镗杆的横向振动频率对切削液流速、轴向力的敏感性及其运动转换趋势。BTA深孔镗杆横向振动频率对轴向力的敏感性规律为:在共振脊区域,在内、外切削液都无自由液面时最大;内、外切削液都有自由液面时最小;在共振翅区域,只内切削液有自由液面时最大,内、外切削液都无自由液面时最小。BTA深孔镗杆横向振动频率对切削液流速的敏感性规律为:在共振脊区域,只内切削液有自由液面时最大,内、外切削液都无自由液面时最小;在共振翅区域,内、外切削液都无自由液面时最大,只内切削液有自由液面时最小。系统在切削液流速、轴向力达到临界等效值时,发生弯曲或屈曲;在静力失稳后,系统将会在更高的切削液流速值以混阶模态形式发生耦合颤振等复杂运动。该研究结果可为BTA深孔镗削加工的生产实践提供一定理论指导。     

A finite-element model with closed-form solutions to workpiece deflections in turning

Simulation models for workpiece deflections play an important role in determining conditions to maximize the part accuracy in machining processes as well as in analysing the dynamic response of the machining system. In this paper, the crosssectional deflection of the workpiece due to all cutting force components (radial, axial and tangential) is determined using the finite-element method. Three workpiece mounting types generally used in industrial practice are considered. The change in the workpiece diameter during machining can easily be taken into account with this model. Furthermore, the finite-element reponses are derived in closed form which enables rapid and continuous solutions along the part length. Numerical examples are treated for which the workpiece deflections calculated from this model are compared with those computed only from the radial cutting force component as usually done by several simplified models. From the results obtained, the proposed model is generally recommended to improve turning simulations.     

The Axial Nonlinear Vibration Analysis of Ball-screw about Machine Tool Feeding System

The forced state of the ball-screw of machine tool feeding system is analyzed. The ball-screw is simplified as Timoshenko beam and the differential equation of motion for the ball-screw is built. To obtain the axial vibration equation,the differential equation of motion is simplified using the assumed mode method. Axial vibration equation is in form of Duffing equation and has the characteristics of nonlinearity. The numerical simulation of Duffing equation is proceeded by MATLAB / Simulink. The effect of screw length,exciting force and damping coefficient are researched,and the axial vibration phase track diagram and Poincare section are obtained. The stability and period of the axial vibration are analyzed. The limit cycle of phase track diagram is enclosed. Axial vibration has two type-center singularity distributions on both sides of the origin. The singularity attracts vibration to reach a stable state,and Poincare section shows that axial vibration appears chaotic motion and quasi periodic motion or periodic motion. Singularity position changes with the vibration system parameters,while the distribution doesn' t change. The period of the vibration is enhanced with increasing frequency and damping coefficient. Test of the feeding system ball-screw axial vibration exists chaos movement. This paper provides a certain theoretical basis for the dynamic characteristic analysis of machine feeding system ball-screw and optimization of structural parameters.     

Prediction of cutting force based on machining parameters on AL7075-T6 aluminum alloy by response surface methodology in end milling

Cutting forces modeling is the basic to understand the cutting process, which should be kept in minimum to reduce tool deflection, vibration, tool wear and optimize the process parameters in order to obtain a high quality product within minimum machining time. In this paper a statistical model has been developed to predict cutting force in terms of geometrical parameters such as rake angle, nose radius of cutting tool and machining parameters such as cutting speed, cutting feed and axial depth of cut. Response surface methodology experimental design was employed for conducting experiments. The work piece material is Aluminum (Al 7075-T6) and the tool used is high speed steel end mill cutter with different tool geometry. The cutting forces are measured using three axis milling tool dynamometer. The second order mathematical model in terms of machining parameters is developed for predicting cutting forces. The adequacy of the model is checked by employing ANOVA. The direct effect of the process parameter with cutting forces are analyzed, which helps to select process parameter in order to keep cutting forces minimum, which ensures the stability of end milling process. The study observed that feed rate has the highest statistical and physical influence on cutting force.     

Simulation Analysis and Experiment Study of Nanocutting with AFM Probe on the Surface of Sapphire Substrate by Using Three Dimensional Quasi-steady Molecular Statics Nanocutting Model

The three-dimensional quasi-steady molecular statics nanocutting model is used by this paper to carry out simulation analysis of nanocutting of sapphire in order to explore the effects of conical tools with different tip radii of probe and straight-line cutting at different cutting depths, on cutting force. Meanwhile, this paper uses a cutting tool of atomic force microscopy (AFM) with a probe tip similar to a semisphere to conduct nanocutting experiment of sapphire substrate. Furthermore, from the experimental results of nanocutting sapphire substrate, this paper innovatively proposes the theoretical model and equation that the specific down force energy (SDFE) during nanocutting by using AFM probe as the nanocutting tool, is approximately a constant value. This paper uses three-dimensional quasi-steady molecular statics nanocutting model to simulate calculation and obtain nanocutting down force. It is compared with the down force calculated by SDFE theoretical equation proposed for verification. As a result, the down force obtained by the paper's simulation is very close to the down force calculated by SDFE theory. Therefore, it can be verify that the three-dimensional quasi-steady molecular statics nanocutting theoretical model used by this paper is feasible. The SDFE proposed by this paper is defined as equating to down force energy dividing the removed volume of down press of the workpiece by the AFM probe. From the experimental data and the calculation results, it is found that the values of SDFE under different down force actions are almost close to a constant value. The three-dimensional quasi-steady molecular statics nanocutting sapphire workpiece model is to find the trajectory of each atom of the sapphire workpiecs being cut whenever the diamond cutter goes forward one step. It uses the optimization search method to solve the force equilibrium equation of the Morse force in the X, Y and Z directions when each atom moves a small distance, so as to find the new movement position of each atom, and step by step calculates the behavior during cutting.     

Experimental investigation into the effects of nozzle position,workpiece hardness,and tool type in MQL turning of AISI 1045 steel

Minimum quantity lubrication (MQL) is a replacement for dry machining in which a minimum quantity of lubricant fluid is mixed up with compressed air and sprayed periodically on the machining area. In this research the effects of different parameters on the MQL turning of AISI 1045 steel have been investigated to evaluate the cutting force, surface roughness, and tool wear in comparison with the wet and dry machining. The research is aimed to study the effect of the MQL nozzle position, workpiece hardness and tool type on the output parameters. During MQL machining experiments, the nozzles were placed in three different arrangements relative to the tool to investigate the effect of the nozzle position. The effect of workpiece hardness and tool type were also studied experimentally for different lubrication conditions. The results indicated that the MQL system significantly increases the cutting efficiency in AISI 1045 steel machining. The experiments results have also confirmed a significant influence of the nozzle position, workpiece hardness, and tool type on the outputs. Machining with MQL is also beneficial to the environment and machine tool operator health as lubricant consumption during operation with MQL is 7-fold lower than in the conventional system.     

一种由干摩擦引起的车床切削颤振

建立了由刀架弹性子系统及工件弹性子系统在非线性动态切削力耦合下的多自由度颤振模型。通过数值模拟显示了此系统存在内共振现象,此时两个子系统的振幅会相互影响显著增大。同时利用平均法求出了此系统的1:2内共振的近似解析解,相应求得两个子系统的一组稳态振幅曲线,通过分析解释了系统发生切削颤振的原因及条件,为解决切削颤振问题提供了新的途径。     

薄壁结构件铣削加工振动稳定性分析

针对如何考虑刀具与工件相互耦合作用及加工位置对系统稳定性影响,通过对切屑厚度、铣削力建模,建立薄壁件铣削系统动力学模型,考虑薄壁件铣削稳定性受铣削位置影响,获得以轴向铣削深度、转速、铣削加工位置为参数的三维稳定性图。通过对曲面图分析,可确定在不同主轴转速、不同铣削区域内薄壁件各模态对铣削稳定性影响。通过时域模拟分析加工位置对系统失稳机制影响,揭示稳定铣削与不稳定铣削、不同模态在不稳定铣削时铣削力、铣削位移的变化规律。     

基于ALE方法的钛合金超声振动车削仿真

采用ALE方法建立了钛合金超声振动车削有限元仿真模型。预测了超声振动车削过程中切削力变化规律,并将模拟获得的切削力平均值与相同条件实验获得的切削力平均值比较,验证了有限元模型的正确性。将超声振动主切削力模拟平均值与普通切削主切削力实验平均值比较,结果表明,采用超声振动辅助手段可以明显降低切削力平均值。预测了超声振动车削一个周期内工件及刀尖温度变化规律,结果表明,刀具切入阶段,工件及刀尖温度迅速升高,当刀具到达运动轨迹最大位移时,工件及刀尖温度达到最大值,随后进入分离阶段,工件及刀尖温度迅速降低。研究了超声振动振幅、频率对切削力及刀尖温度的影响规律,结果表明,随着超声振动振幅及频率的增大切削力有较明显的降低,刀尖温度有小幅降低。     

An investigation on the mechanics of nanometric cutting and the development of its test-bed

The mechanics of machining at a very small depth of cut (100 nm or less) is not well understood. The chip formation physics, cutting forces generation, resulting temperatures and the size effects significantly affect the efficiency of the process and the surface quality of the workpiece. In this paper, the cutting mechanics at nanometric scale are investigated in comparison with conventional cutting principles. Molecular Dynamics (MD) is used to model and simulate the nanometric cutting processes. The models and simulated results are evaluated and validated by the cutting trials on an atomic force microscope (AFM). Furthermore, the conceptual design of a bench-type ultraprecision machine tool is presented and the machine aims to be a facility for nanometric cutting of three-dimensional MEMS devices. The paper concludes with a discussion on the potential and applications of nanometric cutting techniques/equipment for the predictabilty, producibility and productivity of manufacturing at the nanoscale.     

单晶铜纳米切削过程的研究

采用分子动力学三维模型研究单晶铜纳米切削过程，工件原子间相互作用力和工件与刀具原子间相互作用力采用Morse势计算．通过分析切削过程中瞬间原子图像、切削力、单位切削力和轴向切削力与切向切削力比值。发现在整个切削过程中有位错产生，在加工表面发生弹性恢复，但未发生切屑体积的改变，切屑以原子团方式去除，单位切削力和轴向切削力与切向切削力的比值比传统切削时大得多．单晶铜纳米切削过程是位错在晶体中运动产生的塑性变形．     

Optimal machining conditions with costs of quality and tool maintenance for turning

Although there is a voluminous literature on machine tool economics, the cost of machining quality has received little attention. In this paper, we develop a timedynamic economic model for single-pass turning. The model incorporates considerations on the stochastic nature of tool-life and such tool maintenance activities as tool replacement and tool regrinding. We model the quality cost of tool-cutting in terms of deviation from target roughness and deviation from target dimension. The cost of deviation is either the Taguchi type under continuous assumption or in terms of the cost to the entire workpiece under discrete assumption. The connection between quality cost and tool maintenance cost is explicitly addressed. Essentially, quality cost as well as machining cost is a function of two sets of decisions: machining conditions as defined by the choice of cutting speed and feed rate (depth of cut is a constant in single-pass operations), and the condition of the cutting tool as defined by the tool retirement and regrinding policy. The cost of tool failure is also incorporated.