PCBN刀具车削镍基高温合金GH4169再生颤振仿真与试验研究

针对PCBN刀具车削镍基高温合金GH4169中颤振对加工效率和质量的影响,建立一种根据切削参数有效判定切削状态的方法。首先建立了二自由度外圆车削再生颤振模型,然后利用锤击法对数控车床的刀具系统进行模态试验,测定了1阶频率、模态阻尼、模态刚度、模态质量等模态参数;设计了二自由度外圆车削再生颤振MATLAB/Simulink仿真模型,根据仿真结果预测了稳定极限切削深度和颤振的主振方向。最后利用PCBN刀具进行变切深试验。试验结果表明,仿真模型正确。     

微铣削再生颤振动力学建模及稳定性分析

再生颤振是制约微铣削加工效率和加工质量的主要因素.以微铣削加工为研究对象,建立了考虑再生效应的微铣削颤振系统动力学模型和颤振稳定域解析模型,通过模态实验获得机床-刀具系统的频响函数,在此基础上综合使用铣削稳定性判据进行数值分析,获得了颤振稳定域解析解.最后进行了颤振稳定性加工实验,实验结果与仿真结果吻合良好,验证了建立的微铣削颤振系统动力学模型和颤振稳定域解析模型的正确性.     

基于动态切削过程仿真的外圆车削稳定性判定

建立考虑工件轴向和径向两个方向刀具刃倾角和模态方向的车削颤振模型。利用试验得到的切削力系数和模态参数,获得给定机床、刀具和工件组合下的颤振稳定域曲线。建立外圆车削轴类零件的动力学模型,主要包括刀具相对工件的动态切削力和动态位移模型。提出一种借助动态切削力和刀具动态位移时域仿真,以及相邻两转的切削力和位移动态成分映射截面来综合判断切削过程稳定性的方法。通过切削试验验证颤振稳定域判据和动态切削过程判据的准确性。利用该方法了解稳定切削和颤振切削的信号特点和分布规律。对比颤振稳定域和动态切削仿真两种稳定性判据的有效性、优缺点和适用场合,尤其通过典型零件的切削过程仿真说明动态切削仿真方法的优点。此外,还通过对动态切削过程的变模态参数仿真,分析模态参数对切削过程稳定性的影响。     

高速铣削再生颤振稳定性预测与验证

再生型颤振是制约高速铣削加工效率和零件加工质量的主要因素。以高速铣削加工为研究对象,建立了考虑再生效应的高速铣削动态铣削力模型和颤振稳定域解析模型,通过模态实验获得机床-刀具系统的频响函数,在此基础上综合使用铣削稳定性判据进行数值分析,获得了高速铣削颤振稳定域的解析解。最后,进行了零件颤振稳定性铣削加工实验,实验得到的结果与仿真结果吻合良好,由此验证了建立的颤振系统动力学模型和颤振稳定性解析模型的正确性。     

立铣加工钛合金颤振稳定域的研究

为了优化铣削加工中的切削参数来减小或避免再生颤振的发生,在切削加工再生颤振理论的研究基础上,以硬质合金立铣刀粗加工钛合金TA15为研究对象,建立了刀具的动力数学模型,对再生颤振稳定域在频域内进行求解;对再生颤振稳定域解析算法进行程序设计,通过提供由动态铣削实验获得的铣削力系数和由模态分析实验获得的模态参数等程序所需参数计算得到与主轴转速和轴向切深二者相关的颤振稳定域叶瓣图;最后通过对钛合金TA15进行立铣加工实验验证了颤振稳定域解析算法的准确性。     

基于数值模型的数控加工中切削力与稳定域仿真

针对数控铣削加工工艺参数选择存在的问题,以球头铣刀高速铣削过程为研究对象,建立了考虑机床-刀具-工件系统振动的非线性动力学模型,分析了铣削力中的动态分量对切削颤振的影响,在考虑再生颤振的基础上建立非线性动力学模型.基于动态铣削力建模和颤振稳定域分析计算,提出了机床切削系统稳定性极限预测方法,并对其进行仿真分析,为铣削加...     

基于四阶矩法车削颤振可靠性研究*

再生颤振是影响加工质量、加速刀具磨损、刀具破坏的主要原因。以车削加工为研究对象,针对具有不确定参数的车削加工颤振预测问题,研究车削加工系统结构动态特性参数具有随机特性的情况下颤振可靠性建模及求解问题。定义车削加工过程不出现颤振的概率为颤振可靠度,建立车削加工系统可靠性模型,研究四阶矩法求解可靠度的问题,提出利用颤振可靠性叶瓣图方法进行颤振预测。通过模态试验对一车床进行频响函数测试,采用四阶矩法计算获得了颤振可靠度,并与蒙特卡洛法获得的可靠度相比较。结果表明四阶矩法计算获得的可靠度与蒙特卡洛仿真结果一致性很好,但是四阶矩法计算精度高而且计算耗时远小于蒙特卡洛法。进行颤振可靠性切削试验,通过观察振纹和分析噪声功率谱识别颤振,对典型参数进行验证,试验结果与分析结果一致。     

立铣削过程中的颤振稳定性分析与研究

铣削过程中的颤振会导致刀具磨损、工件表面粗糙、产量下降等问题.分析和比较了一维动态铣削数学模型,结合已获得的试验数据,根据一维理论开发出动态铣削仿真软件.该软件预测了在特定铣削条件和模态参数下的稳定性曲线.研究表明,动态铣削仿真软件的开发对于数控铣床铣削参数的给定具有重要意义,仿真计算对铣削过程中稳定性判别是一种有效的方法.     

基于MATLAB的高速铣削加工再生型颤振的建模与仿真

针对国内高速铣削加工工艺参数选择存在的问题,基于动态铣削力建模和颤振稳定域分析计算,以MATLAB为开发工具,得到了铣削加工再生型颤振仿真算法.通过模态锤击实验获得频响函数,利用Visio Basic软件设计了圆柱立铣刀动力学仿真系统,对整个加工系统的颤振稳定域图形进行仿真,为铣削加工切削参数选择和优化提供了理论依据.实验验证了该仿真算法的有效性和准确性,并在实际应用中取得了良好的效果.     

车削Inconel 625锯齿形切屑形成对颤振影响的试验研究

为研究高温合金Inconel 625车削过程中锯齿形切屑的产生对颤振的影响,本文通过有限元软件对车削刀具、机床主轴等部件进行模态仿真,获取对应的模态频率;进行不同切削参数的车削试验,采集加速度信号并进行频域分析以获取其FFT功率谱。通过超景深显微镜观察切屑形态,并计算不同切削参数下的切屑锯齿化频率。对比仿真和试验结果发现:当切屑锯齿化频率接近于车床某部件的主振频率时,产生了较大的颤振峰值,这说明锯齿形切屑的产生会诱导切削颤振发生,对切削过程稳定性产生了不利的影响。     

Integration of cutting force control and chatter suppression control into automatic cutting feed adjustment system design

Abstract

This study designed an automatic cutting feed adjustment system for computer numerical control (CNC) turning machine tools, which integrate the operational characteristics of cutting force control and chatter suppression control to shorten the machining time and maintain the quality of workpieces. The setting of appropriate machining conditions (such as cutting feed, spindle speed and depth of cut) to consider both machining quality and efficiency often causes difficulties for machine tool operators. Therefore, this study uses cutting force control to design an automatic cutting feed adjustment method for cutting tools, and then, the chatter suppression control design is used to modify the cutting force command to suppress cutting chatter. The experimental results of the CNC turning machine tool show that the use of the cutting force control to adjust the cutting feed can shorten the machining time; however, the cutting chatter results in larger surface waviness on the workpiece surface. When the cutting force command is properly modified by actuating the chatter suppression control, the workpiece shows better surface roughness with prolonged machining time. Therefore, the cutting tests demonstrate that the proposed system is feasible for satisfying the machining requirements of the manufacturing processes of mechanical parts for high speed and high accuracy.     

NUMERICAL SIMULATIONS OF DUCTILE MACHINING OF SILICON NITRIDE WITH A CUTTING TOOL OF DEFINED GEOMETRY

Recent experiments involving machining of silicon nitride at the micrometer scale has shown that silicon nitride behaves in a ductile fashion under high pressures and when the depth of cut is small. In this paper, a preliminary study of ductile machining of Silicon Nitride (Si₃N₄) using numerical simulations is reported. The commercial software package ADVANTEDGE is used to model the cutting process. The numerical simulations involve a parametric study carried out to understand the effects of cutting speed, feed, rake angle and tooltip radius to evaluate conditions that are conducive to brittle-to-ductile phase transition. The feed, tooltip radius and depth of cut are of the order of tens of micrometers and the cutting speeds range from 0.5 m/min to 300 m/min. The results indicate that machining of silicon nitride may be carried out in a ductile fashion for small tooltip radii, high negative rake angles and small depths of cut.     

Measurement and simulation of regenerative chatter in diamond turning

In this work, the stability of outer diameter turning is explored to extend previous results from the orthogonal turning geometry. The work begins with a numerical approach to the determination of the stability limit using a nonlinear chip area model. A complete experimental verification follows for turning of 6061-T aluminum with single crystal, synthetic diamond tools. Although diamond-turning operations are not particularly susceptible to chatter, the cutting process is well understood, and experimental tests may be conveniently carried out. Recent work to define the specific cutting energy better at small depths of cut is incorporated. The results show qualitative differences from the orthogonal cutting geometry. The role of machine parameters and tool geometry is explored using the verified model.     

Three-dimensional chatter stability prediction of milling based on the linear and exponential cutting force model

Stability lobes are widely used to avoid chatter which restricts the machining quality and productivity. A lot of work has been done to predict the stability lobes fast and accurately. However, most of them are based on the linear force model, and the chatter stability limit is formulated as independent on the feed rate, which is inconsistent with the machining practice. By referencing with the zero-order solution, this paper investigates the chatter stability prediction based on the exponential force model. Focusing on the cutters with a lead angle (i.e., inserted face mill, the ball-end mill, and bull-nose end mill) where chatter is likely to be brought up in Z direction, the stability model is extended to three-dimensional. Taylor equation is utilized to linearize the exponential expressions when computing the directional coefficients in order to solve the stability limit analytically as the linear force model. Simulation results show that the exponential force model agrees with the measurements as well as the linear force model in the cutting force prediction, and it is able to demonstrate the feed rate effect on the stability limit. The stability limit is found to be increased as the feed rate increases, which is evidenced by the time domain simulation. Cutting tests are performed in the end to verify the stability model. The proposed model could be reduced to either X/Y dimensional or linear force model-based stability model by further simplifications.     

A study on the effect of rectangular cut out on laser forming of AISI 304 plates

Laser bending of a rectangular AISI 304 plate with a rectangular cut out is investigated in the present work. In particular, effects of process parameters: laser power, scanning speed, and geometric parameters: dimensions of the cut out of sheet metal on temperature distribution and bending angle are explored with the help of numerical simulation. Analyses are carried out through a coupled thermo-mechanical formulation with finite element method using COMSOL MULTIPHYSICS. The temperature distribution and deformation of sheet metal have been obtained from numerical simulations. The bending angle is affected by process parameters, namely, laser power, scanning speed, and width of the cut out of the sheet metal. Position of the cut out vis-à-vis the scanning path and length of the cut out have very little effect on the bending angle.     

Modeling and Analytical Solution of Chatter Stability for T-slot Milling

T-slot milling is one of the most common milling processes in industry. Despite recent advances in machining technology, productivity of T-slot milling is usually limited due to the process limitations such as high cutting forces and stability. If cutting conditions are not selected properly the process may result in the poor surface finish of the workpiece and the potential damage to the machine tool. Currently, the predication of chatter stability and determination of optimal cutting conditions based on the modeling of T-slot milling process is an effective way to improve the material removal rate(MRR) of a T-slot milling operation. Based on the geometrical model of the T-slot cutter, the dynamic cutting force model was presented in which the average directional cutting force coefficients were obtained by means of numerical approach, and leads to an analytical determination of stability lobes diagram(SLD) on the axial depth of cut. A new kind of SLD on the radial depth of cut was also created to satisfy the special requirement of T-slot milling. Thereafter, a dynamic simulation model of T-slot milling was implemented using Matlab software. In order to verify the effectiveness of the approach, the transfer functions of a typical cutting system in a vertical CNC machining center were measured in both feed and normal directions by an instrumented hammer and accelerators. Dynamic simulations were conducted to obtain the predicated SLD under specified cutting conditions with both the proposed model and CutPro?. Meanwhile, a set of cutting trials were conducted to reveal whether the cutting process under specified cutting conditions is stable or not. Both the simulation comparison and experimental verification demonstrated that the satisfactory coincidence between the simulated, the predicted and the experimental results. The chatter-free T-slot milling with higher MRR can be achieved under the cutting conditions determined according to the SLD simulation.     

Drilling of woven glass fiber-reinforced plastic—an experimental and finite element study

Drilling in woven fiber-reinforced plastics is a well-known practice in modern-day manufacturing. The high fracture toughness of woven fiber-based composites over unidirectional counterparts is increasing demand in aviation and electronics industries. Hence, failure of these materials at harsh environments is a matter of concern. Very few numerical studies on drilling of these composites have been carried out; hence, the present scope may be considered as a trial de novo. Delamination was studied in the present work at different feed–speed combinations. Drilling responses were estimated using finite element as a numerical simulation tool. An equivalent elastic macromechanical model was assumed for the woven composite workpiece. A 3D drill bit was modeled using commercial CAD package Pro-Engineer and Ansys Autodyn was used as the solver environment. The simulation and validation experiments were carried out at planned feed–speed combinations. The effect of process parameters on exit and entry delamination is also documented. The thrust determined by finite element techniques showed good prediction with the experimental results.     

基于工件材料去除率的滚齿机床能耗模型

开展了滚齿机床能耗建模与参数分析的研究。基于滚刀和工件的几何参数与空间运动分析,进行未变形切屑的数值计算,求取了滚齿加工过程中材料去除率的数值,建立了滚齿机床能耗预测模型,并通过正交试验进行了验证,平均预测准确率超过95%。基于实验结果与所提出的数值模型,对比分析了进给速度、滚刀转速与切削深度对表征能量利用效率的比能耗的影响,结果表明,所提出的模型可以准确预测滚齿加工过程中的机床能耗。     

XH6650加工中心动态仿真与模态测试分析

随着机床加工速度的提高,对机床的动态特性要求越来越高,文中以XH6650的高速卧式加工中心为对象,提出了简化结构细小特征,建立界面特性的有限元建模方法,建立了该机床的数字化模型,并进行动力学仿真,为验证建模方法的可靠性,对整机进行了动态测试,结果表明该方法有很好的精度.     

正交车铣偏心加工三维颤振稳定性的研究

针对正交车铣复杂运动产生变深度、变厚度的切削特性,基于其加工原理采用解析法提出三维颤振稳定域的理论模型.在模态试验基础上,仿真分析正交车铣偏心加工颤振稳定域叶瓣图,结果表明正交车铣加工产生颤振的条件除了与铣刀几何形状和啮合条件、机床结构的频响应函数、工件材料特性等有关外,主要与铣刀轴转速和切削深度密切相关.在正交车铣切削颤振稳定域试验过程中,切削力频谱分析的结果表明:当刀齿切入频率在力频谱中起主导作用时,切削过程是无颤振和稳定的;当系统结构模态频率在力频谱中起主导作用时,将产生颤振并测得切削力和表面粗糙度值都大于或高于无颤振情况.因此该理论模型及仿真结果可以有效预测正交车铣偏心加工颤振稳定性,为其加工表面质量和加工效率提供理论指导.