薄壁零件高速铣削实验

通过高速铣削单因素实验,研究高速铣削参数对工件表面质量和铣削力变化的影响规律,优化薄壁零件高速铣削参数.在此基础上进行了薄壁零件的高速铣削实验,结果表明,采用优化后的高速铣削参数加工薄壁零件,能够有效地提高薄壁零件的加工精度和加工效率.     

FV520B钢铣削参数优化及振动试验研究

高速铣削是航空材料加工制造中的关键技术之一。针对刀具大悬伸量加工时的振动抑制问题,通过高速铣削正交试验和不同刀具悬伸量下的高速铣削实验,研究铣削参数对铣削力及刀具悬伸量对铣削振动的影响规律。研究表明:采用12 mm平底刀,当铣削速度为75 m/min、每齿进给量为0.02 mm/齿、铣削宽度为5 mm、铣削深度为1 mm时,切削力最小,此参数下刀具最佳悬伸量为30～40 mm。研究结论为高速铣削工艺优化以及铣削振动控制提供了依据。     

薄壁零件的铣削加工稳定性研究

为控制薄壁结构零件加工过程中的变形和切削振动,在考虑刀具和工件两个方向的自由度的基础上,分析、建立了薄壁零件的动态铣削模型.针对2A12铝合金薄壁结构零件,利用Mikron高速加工中心和相关仪器,通过铣削力实验和模态实验,分别测得特定刀具和工件系统的动态铣削力系数和模态参数,从而绘制出高速铣削薄壁零件的稳定性叶瓣图,得到了不同径向切深条件下的极限轴向切深,并通过试验进行了验证.这种方法可用于相关薄壁零件加工时合理选择切削用量.     

TC4钛合金高速铣削力研究

钛合金高速铣削因具有高效率、高质量的优点,被广泛应用于航空航天制造业。为了研究高速铣削参数对钛合金高速铣削力的影响,利用专业金属切削加工有限元软件AdvantEdge,对TC4钛合金高速铣削过程进行二维模拟仿真,建立了高速铣削TC4钛合金时铣削力的预测模型,获得了不同铣削参数对铣削力的影响规律,并对仿真结果进行了试验验证。结果表明:高速铣削TC4钛合金的铣削力比较小,基本不超过100 N,铣削力最大值达到140 N;铣削合力对铣削宽度的变化最为敏感,对铣削速度和铣削深度变化的敏感次之,对每齿进给量最不敏感。研究结果为优化高速铣削工艺提供理论分析和试验依据。     

高速铣削加工表面位置误差的频域分析

在高速铣削加工过程中,提高轴向切削深度和主轴转速可以获得较高的材料去除率,然而限制轴向切削深度提高的一个因素是加工颤振.高速铣削系统动态失稳可能导致加工零件的表面几何精度偏差.分析高速铣削的表面位置误差对表征切削过程、刀具寿命估算和加工优化都起着重要作用.因此,在不考虑再生颤振影响的前提下,提出了一种数值分析和加工实验相结合的方法来研究表面位置误差.首先,构建了高速铣削加工过程模型,然后建立了动态铣削力模型,并推导了表面位置误差的分析方法.通过数值分析和铣削实验相结合,得到了高速铣削加工的稳定性叶瓣图.接下来,研究了逆铣削加工过程的表面位置误差,并详细分析了主轴转速和轴向切削位置对表面位置误差的影响规律.最后,把稳定性叶瓣和表面位置误差数据组合在同一个图里得到了高速铣削加工的综合分析图.借助综合分析图,能预测表面位置误差和优化高速铣削的工艺条件.     

高速铣削表面粗糙度的研究

通过在HSM－700型高速铣床上的正交铣削试验，联系平时实际的生产加工情况，分析高速铣削的切削加工参数对零件表面粗糙度的影响。通过分析不同铣削参数下的零件表面粗糙度和切屑变形，为高速加工切削参数的选择和表面质量的控制提供依据。     

高速铣削参数对工件表面质量的影响

切削参数对工件的表面质量有着重要的影响,本文通过单因素实验,研究高速铣削参数对已加工工件表面粗糙度、残余应力及残余应力分布的影响规律.实验表明,高速铣削能够获得较好的工件表面质量.     

Zr基大块非晶合金铣削力实验研究

为了了解非晶合金的切削力学特性,以Zr基大块非晶合金和45钢为对比试样,通过正交实验探明非晶合金的铣削力特点以及铣削参数对切削力的影响,并利用线性回归方法建立了实验条件下的铣削力经验公式。实验结果表明:非晶合金Y轴铣削力最大,X轴最小,而且Y轴铣削力受铣削参数变化影响最大,其次为X轴,Z轴则几乎不受影响;轴向切削深度和径向切削深度对铣削力的影响明显,进给量和切削速度的影响较小。     

高速铣削钛合金Ti6A4V铣削力试验研究

采用涂层硬质合金刀具对钛合金Ti6A14V进行了高速铣削试验.通过分析正交试验直观图,研究了铣削参数的变化对铣削力的影响,为合理选择铣削参数提供了可靠的依据.高速铣削试验表明:采用小的轴向切削深度和每齿进给量及较大的径向切削深度和切削速度有利于减小铣削力.基于概率统计和回归分析原理,建立了铣削力回归方程,并对回归方程进行了显著性检验,检验结果表明:所建立的回归方程呈高度显著检验状态,与实际情况拟合的较好.     

基于BP神经网络的轮胎模具微铣削能耗预测

针对子午线轮胎模具微铣削加工过程中能耗计算问题,以主轴转速、每齿进给量、切削深度3个重要铣削参数作为变量,设计轮胎模具微铣削加工能耗实验.根据实验数据构建基于BP神经网络的微铣削能耗预测模型.通过改进预测模型的激活函数,提高模型的预测精度.结果表明:所提的预测模型有效,可以实现不同铣削参数组合下的能耗预测.     

机床再生颤振系统研究现状的综述

切削系统的稳定性是高速加工领域的一个重要研究内容,在工程实践中有着广泛的应用.本文在颤振机理与模型研究的基础上,分析了再生颤振产生的原因,以及目前国内外研究的发展状况.     

Mechanism of minimum quantity lubrication in high-speed milling of hardened steel

The rapid wear rate of cutting tools due to high cutting temperature is a critical problem to be solved in high-speed machining (HSM) of hardened steels. Near-dry machining such as minimum quantity lubrication (MQL) is regarded as one of the solutions to this difficulty. However, the function of MQL in HSM is still uncertain so far which prevents MQL from widely being utilized in the machining of hardened steels. In this paper, the mechanism of MQL in HSM of hardened steel is investigated more comprehensively. Comparing with dry cutting, the tool performance can be enhanced by MQL under all cutting speeds in this study. It is found that MQL can provide extra oxygen to promote the formation of a protective oxide layer in between the chip–tool interface. This layer is basically quaternary compound oxides of Fe, Mn, Si, and Al, and is proved to act as diffusion barriers effectively. Hence, the strength and wear resistance of a cutting tool can be retained which leads to a significant improvement of tool life. It is found that there exists an optimal cutting speed at which a stable protective oxide layer can be formed. When cutting speed is lower than this speed, there is less oxide layer and the improvement of tool life is less apparent. As the cutting speed is far beyond the optimal value, the protective layer is absent and the thermal cracks are apt to occur at the cutting edge due to large fluctuation of temperature. Resultantly, application of MQL is inappropriate in the extreme high-speed cutting condition irrespective of its little increase in tool life. Based on this study, it is concluded that the tool life can be effectively improved by MQL in HSM of NAK80 hardened steels when cutting parameters are chosen properly.     

A comparative study of the cutting forces in high speed machining of Ti–6Al–4V and Inconel 718 with a round cutting edge tool

Titanium alloy Ti–6Al–4V and nickel-based superalloy Inconel 718 have been widely employed in modern manufacturing. The published literature on high speed machining (HSM) of the two materials often involves different machining set-up, which makes it difficult to directly apply the research findings from one material to the other to select the most appropriate tool geometry and cutting conditions. A comparative experimental study of HSM of Ti–6Al–4V and Inconel 718 is conducted in this paper using the same machining set-up. The scope of this study is limited in high speed finish machining, where the tool edge geometry plays a significant role. The experimental set-up and the methods of measuring the cutting forces and the tool edge radius are introduced. A total of 40 orthogonal high speed tube-cutting tests were performed, involving five levels of cutting speeds and four levels of feed rates. Based on extensive experimental data, the similarities and differences between HSM of Ti–6Al–4V and Inconel 718 are quantitatively compared and qualitatively explained in terms of four quantities: (1) the cutting force F_c, (2) the thrust force F_t, (3) the resultant force R, and (4) the force ratio F_c/F_t. A total of 12 empirical regression relationships are obtained.     

薄壁筒车削颤振稳定性预测

切削颤振是制约薄壁筒工件加工质量和效率的主要因素之一。采用半离散法对含有时滞项的动力学方程进行稳定性预测分析,结合薄壁筒工件切削振动试验,研究刀具、工件动力学参数匹配关系变化对切削加工稳定性的影响。通过仿真分析得出:随着刀具刚度或固有频率的提升,切削系统稳定性呈上升趋势,但过度提升刀具刚度并不会有效提升切削稳定性;在刀具与工件固有频率接近处,切削系统的稳定性较差;适当调整刀具动态特性参数有利于提高柔性工件切削加工的稳定性;切削过程中,时变的切削位置和工件尺寸会引起切削系统动态特性的变化。根据时变稳定性预测图,从稳定性分析角度解释了一次走刀切削试验中薄壁筒工件表面出现不同加工形貌的原因。     

Milling force prediction using a dynamic shear length model

Modelling of cutting forces in milling is often needed in machining automation. In this paper, a new method for the determination of the cutting forces in face milling is presented, which applies a predictive machining theory originally developed for orthogonal cutting to milling operations, with a dynamic shear length model developed and incorporated. The proposed dynamic shear length model is developed based on the analysis for the true tooth trajectories of a milling cutter, taking into account of the characteristic wavy surface effects in milling. The prediction for the cutting forces is carried out at each step of the angular increment of cutter rotation from input data of fundamental workpiece material properties, tool geometry and cutting conditions. Cutting forces at a cutter tooth can be predicted once the shear angle, shear length, shear plane area, and the shear flow stress along the shear length have been determined. The milling force prediction using the dynamic shear length model is verified through milling experimental tests. The sensitivity of the difference between the static and dynamic shear length models with respect to the feed per tooth and the cutter diameter is discussed.     

Chatter milling modeling of active magnetic bearing spindle in high-speed domain

A new dynamical modeling of Active Magnetic Bearing Spindle (AMBS) to identify machining stability of High Speed Milling (HSM) is presented. This original modeling includes all the minimum required parameters for stability analysis of AMBS machining. The stability diagram generated with this new model is compared to classical stability lobes theory. Thus, behavior's specificities are highlighted, especially the major importance of forced vibrations for AMBS. Then a sensitivity study shows impacts of several parameters of the controller. For example, gain adjustment shows improvements on stability. Side milling ramp test is used to quickly evaluate the stability. Finally, the simulation results are then validated by HSM cutting tests on a 5 axis machining center with AMBS.     

Self-Excited Vibration Drilling Models and Experiments

A nonlinear dynamical model of vibration drilling is presented. It takes in consideration cutting interruption through surface generation equations. The linear stability analysis yields stability charts and the nature of Hopf bifurcation is discussed at critical values of cutting parameters. Dimensionless equations have been employed in order to obtain graphical charts that completely describe the dynamics of a pair of vibration-drilling head - workpiece material. The analysis of “finite amplitude instability” phenomenon is carried out in time domain by computer simulations. A dynamic cutting fixture was used to run vibration drilling experiments. Based upon simulations and general vibration cutting model described here, the dispersion of the results from experimental work was explained. Important conclusions are drawn concerning forthcoming experiments in vibration drilling.     

Heat generation and temperature prediction in metal cutting: A review and implications for high speed machining

Determination of the maximum temperature and temperature distribution along the rake face of the cutting tool is of particular importance because of its controlling influence on tool life, as well as, the quality of the machined part. Numerous attempts have been made to approach the problem with different methods including experimental, analytical and numerical analysis. Although considerable research effort has been made on the thermal problem in metal cutting, there is hardly a consensus on the basics principles. The unique tribological contact phenomenon, which occur in metal cutting is highly localized and non-linear, and occurs at high temperatures, high pressures and high strains. This has made it extremely difficult to predict in a precise manner or even assess the performance of various models developed for modelling the machining process. Accurate and repeatable heat and temperature prediction remains challenging due to the complexity of the contact phenomena in the cutting process. In this paper, previous research on heat generation and heat dissipation in the orthogonal machining process is critically reviewed. In addition, temperature measurement techniques applied in metal cutting are briefly reviewed. The emphasis is on the comparability of test results, as well as, the relevance of temperature measurement method to high speed cutting. New temperature measurement results obtained by a thermal imaging camera in high speed cutting of high strength alloys are also presented. Finally, the latest work on estimation of heat generation, heat partition and temperature distribution in metal machining is reviewed. This includes an exploration of the different simplifying assumptions related to the geometry of the process components, material properties, boundary conditions and heat partition. The paper then proposes some modelling requirements for computer simulation of high speed machining processes.     

Theoretical and experimental analysis of nano-surface generation in ultra-precision raster milling

The fabrication of high-quality freeform surfaces is based on ultra-precision raster milling, which allows direct machining of the freeform surfaces with sub-micrometric form accuracy and nanometric surface finish. Ultra-precision raster milling is an emerging manufacturing technology for the fabrication of high-precision and high-quality components with a surface roughness of less than 10 nm and a form error of less than 0.2 μm without the need for any additional post-processing. Moreover, the quality of a raster milled surface is based on a proper selection of cutting conditions and cutting strategies.Due to different cutting mechanics, the process factors affecting the surface quality are more complicated, as compared with ultra-precision diamond turning and conventional milling, such as swing distance and step distance. This paper presents a theoretical and experimental analysis of nano-surface generation in ultra-precision raster milling. Theoretical models for the prediction of surface roughness are built. An optimization system is established based on the theoretical models for the optimization of cutting conditions and cutting strategy in ultra-precision raster milling. A series of experiments have conducted and the results show that the theoretical models predict well the trend of the variation of surface roughness under different cutting conditions and cutting strategies.     

Effect of temperature of annealing below 900 °C on structure, properties and tool life of an AlTiN coating under various cutting conditions

In this study the cemented carbide cutting tools with a nano-crystalline Al_0.67Ti_0.33N hard PVD coating deposited by cathodic arc evaporation were annealed within a range of temperatures 700-800 °C during 2 h in vacuum. The changes in structure and properties of the coating vs. temperature have been analyzed using TEM as well as high temperature nano-indentation methods. Cutting tools with the annealed AlTiN coating have been run through a number of cutting tests with varying conditions. The conditions were as following: 1) continuous cutting: turning of annealed 1040 steel (HB 220); 2) interrupted cutting: turning of 4340 steel (HRC 40); 3) end milling: ball nose end milling of hardened H13 steel (HRC 50). The cutting tool life has been investigated before and after annealing of the Al_0.67Ti_0.33N coatings at different temperatures. The relations between high temperature hardness and plasticity of the Al_0.67Ti_0.33N coating and tool life under varying cutting conditions was outlined.