Numerical Investigation of Thermal Behavior of CNC Machine Tool and Its Effects on Dimensional Accuracy of Machined Parts

The dimensional accuracy of machined parts is strongly influenced by the thermal behavior of machine tools (MT). Minimizing this influence represents a key objective for any modern manufacturing industry. Thermally induced positioning error compensation remains the most effective and practical method in this context. However, the efficiency of the compensation process depends on the quality of the model used to predict the thermal errors. The model should consistently reflect the relationships between temperature distribution in the MT structure and thermally induced positioning errors. A judicious choice of the number and location of temperature sensitive points to represent heat distribution is a key factor for robust thermal error modeling. Therefore, in this paper, the temperature sensitive points are selected following a structured thermomechanical analysis carried out to evaluate the effects of various temperature gradients on MT structure deformation intensity. The MT thermal behavior is first modeled using finite element method and validated by various experimentally measured temperature fields using temperature sensors and thermal imaging. MT Thermal behavior validation shows a maximum error of less than 10% when comparing the numerical estimations with the experimental results even under changing operation conditions. The numerical model is used through several series of simulations carried out using varied working condition to explore possible relationships between temperature distribution and thermal deformation characteristics to select the most appropriate temperature sensitive points that will be considered for building an empirical prediction model for thermal errors as function of MT thermal state. Validation tests achieved using an artificial neural network based simplified model confirmed the efficiency of the proposed temperature sensitive points allowing the prediction of the thermally induced errors with an accuracy greater than 90%.

Dynamic modeling of ultra-precision fly cutting machine tool and the effect of ambient vibration on its tool tip response

The dynamic performances of an ultra-precision fly cutting machine tool(UFCMT)has a dramatic impact on the quality of ultra-precision machining.In this study,the dynamic model of an UFCMT was established based on the transfer matrix method for multibody systems.In particular,the large-span scale flow field mesh model was created;and the variation in linear and angular stiffness of journal and thrust bearings with respect to film thickness was investigated by adopting the dynamic mesh technique.The dynamic model was proven to be valid by comparing the dynamic characteristics of the machine tool obtained by numerical simulation with the experimental results.In addition,the power spectrum density estimation method was adopted to simulate the statistical ambient vibration excitation by processing the ambient vibration signal measured over a long period of time.Applying it to the dynamic model,the dynamic response of the tool tip under ambient vibration was investigated.The results elucidated that the tool tip response was significantly affected by ambient vibration,and the isolation foundation had a good effect on vibration isolation.

A new method for deburring of servo valve core edge based on ultraprecision cutting with the designed monocrystalline diamond tool

Deburring of high-precision components to their micrometer features without any damage is very important but of great difficulty as the burr-to-functionality size ratio increases. To this end, this paper proposes a new deburring method in which the micro burr should be directly removed based on ultraprecision cutting with the designed monocrystalline diamond tool. To determine the feasibility of the proposed method, this paper applies it for deburring of the precision working edge of the servo valve core. Firstly, the monocrystalline diamond tool is carefully designed by covering a variety of topics like rake angle,clearance angle, edge radius. Then, the finite element(FE) simulation was conducted to characterize the deburring performance during the removal of the micro burr produced by the single abrasive grinding. Finally, an innovative self-designed deburring system was introduced and the deburring process was evaluated in terms of cutting forces, temperatures, tool wear mechanisms and deburring quality of the working edges by experiments. The FE simulation results indicate the suitability of the proposed deburring method. Meanwhile, the experimental findings agree well with simulation results and show that ultraprecision cutting with the specialized monocrystalline diamond tool could be successfully used for deburring of servo valve core edge without any damage. This work can provide technical guidance for similar engineering applications, and thus brings an increase to the machining efficiency for the manufacture of precision components.

Hybrid multibody system method for the dynamic analysis of an ultra‐precision fly‐cutting machine tool

The dynamics of an ultra‐precision machine tool determines the precision of the machined surface.This study aims to propose an effective method to model and analyze the dynamics of an ultra‐precision fly‐cutting machine tool.First,the dynamic model of the machine tool considering the deformations of the cutter head and the lathe head is developed.Then,the mechanical elements are classified into M subsystems and F subsystems according to their properties and connections.The M‐subsystem equations are formulated using the transfer matrix method for multibody systems(MSTMM),and the F‐subsystem equations are analyzed using the finite element method and the Craig-Bampton reduction method.Furthermore,all the subsystems are assembled by combining the restriction equations at connection points among the subsystems to obtain the overall transfer equation of the machine tool system.Finally,the vibration characteristics of the machine tool are evaluated numerically and are validated experimentally.The proposed modeling and analysis method preserves the advantages of the MSTMM,such as high computational efficiency,low computational load,systematic reduction of the overall transfer equation,and generalization of its computational capability to general flexible‐body elements.In addition,this study provides theoretical insights and guidance for the design of ultra‐precision machine tools.

Modeling of the minimum cutting thickness in micro cutting with consideration of the friction around the cutting zone

Friction modeling between the tool and the workpiece plays an important role in predicting the minimum cutting thickness during TC4 micro machining and finite element method(FEM)cutting simulation.In this study,a new three-region friction modeling is proposed to illustrate the material flow mechanism around the friction zone in micro cutting;estimate the stress distributions on the rake,edge,and clearance faces of the tool;and predict the stagnation point location and the minimum cutting thickness.The friction modeling is established by determining the distribution of normal and shear stress.Then,it is applied to calculate the stagnation point location on the edge face and predict the minimum cutting thickness.The stagnation point and the minimum cutting thickness are also observed and illustrated in the FEM simulation.Micro cutting experiments are conducted to validate the accuracy of the friction and the minimum cutting thickness modeling.Comparison results show that the proposed friction model illustrates the relationship between the normal and sheer stress on the tool surface,thereby validating the modeling method of the minimum cutting thickness in micro cutting.

Chip-ejection interference in cutting processes of modern cutting tools

Based on the “principle of minimum energy”, the basic characteristics of non-free cutting are studied; the phenomenon and the nature of chip-ejection interference commonly existing in the cutting process of modern cutting tools are explored. A “synthesis method of elementary cutting tools” is suggested for modeling the cutting process of modern complex cutting tools. The general equation governing the chip-ejection motion is deduced. Real examples of non-free cutting are analyzed and the theoretically predicted results are supported by the experimental data or facts. The sufficient and necessary conditions for eliminating chip-ejection interference and for realizing free cutting are given; the idea and the technical approach of “the principle of free cutting” are also discussed, and a feasible way for improving or optimizing the cutting performance of modern cutting tools is, therefore, found.

Experimentation on Tool Wear and Surface Roughness in AISI D2 Steel Turning with WC Insert

The Taguchi method, based on an orthogonal arrangement (L9, 33), the vari-ance analysis, the signal-to-noise ratios and the response surface methodol-ogy have been used to optimize maximum flank wear (VBmax) and surface roughness (Ra) of the cutting tool when turning a hardened steel AISI D2 (65 HRC) with PVD—TiAlN coated WC insert upon dry environment. By em-ploying regression models;cutting speed, cutting depth and feed rate, which optimize maximum flank wear and surface roughness were validated. Results of relation signal-to-noise ratios, showed that with cutting speed of 200 m/min, cutting depth of 0.2 mm and feed rate of 0.20 mm/rev, Ra is opti-mized. With cutting speed of 150 m/min, cutting depth of 0.4 mm and feed rate of 0.3 mm/rev, VBmax is optimized. Through the variance analysis it was concluded that the depth of cut was the main parameter that affected on the surface roughness;whereas, the feed rate was the most influential parameter on the flank wear. Confirmation test results showed that the Taguchi method was very successful in the optimization of machining parameters for mini-mum surface roughness and flank wear in the turning of the D2 steel.

变曲率曲面构型前刀面车刀的减阻性能研究

为了降低切削过程中的阻力,通过对河狸牙齿前刀面的构型分析,设计出了具有变曲率准线曲面构型前刀面的车刀。在0.15~0.5 mm背吃刀量下,选取4种前刀面构型进行仿真切削对比分析。仿真结果表明,余弦函数准线构型前刀面刀具的切削力相对于其他构型前刀面刀具的降低了3.5%~11.96%,并通过直角切削实验对仿真结果进行了验证。随后通过仿真实验对余弦准线函数进行参数优化,得出了切削力随周期和幅值改变的变化规律。优化结果表明:当背吃刀量与前刀面余弦函数准线一个周期的比值为40%左右时,减阻效果最为显著。所设计的变曲率构型前刀面车刀不仅有效降低了切削力,还为金属切削刀具的构型设计提供了新思路,具有较强的应用价值。

基于神经网络的并联机床位姿误差分析与补偿研究

为了解决并联机床位姿误差补偿这一难题,以六自由度并联机床为研究对象,基于并联机床的运动学逆解建立了位姿误差模型,得到了并联机床驱动杆杆长误差和铰链点位置误差与并联机床动平台位姿误差的关系。铰链点位置误差可以通过调整杆长来弥补,由于驱动杆杆长误差难以测量,所以基于BP神经网络设计了一种改进的修正系统输入法对并联机床动平台的位姿误差进行补偿。仿真结果表明,经过补偿后的位姿误差明显小于补偿前的位姿误差,验证了并联机床位姿误差分析与补偿方法的可靠性。

基于响应面法的环网柜接线套管干切削工艺参数优化研究

采用干切削加工是修复环网柜接线套管表面烧蚀、裂痕的一种有效方法。利用单因素试验研究切削用量在未涂层、TiAlCrN涂层和TiAlSiN涂层刀具下对切削力的影响规律。在单因素试验的基础上运用Box-Behnken中心组合试验方法,采用性能最优的TiAlSiN涂层刀具对环网柜接线套管切削工作参数进行试验研究,以切削速度、进给量和背吃刀量为试验因素,以刀具切向力、轴向力、径向力为试验指标进行三因素三水平二次旋转回归正交试验。通过建立响应面数学模型,分析各切削工艺参数对切削性能的影响,并对试验因素进行综合优化。试验结果表明:影响切削力显著顺序为背吃刀量>进给量>切削速度;最优参数组合为切削速度94.589 m/min、进给量0.097 mm/r、背吃刀量0.501 mm,此时刀具切向力为11.75 N、轴向力为34.80 N、径向力为19.53 N;验证试验结果与理论优化值基本吻合。

基于法向等距法的刀具半径补偿算法及加工应用

刀具补偿技术是根据零件轮廓和预先设定的偏置参数获得铣削程序,在提高编程效率和机床制造精度的同时避免了过切现象。为解决SIEMENS系统在实际加工中采用展成法(X-C插补)加工涡旋盘时无法直接添加刀具半径补偿指令的问题,针对软件获取刀补点方法存在步距大、精度低、通用性差等缺点,提出一种基于法向等距法的刀具半径补偿算法。计算涡旋盘刀具补偿点位置坐标,并对涡旋盘外壁曲线刀补点坐标进行参数化编程。利用NX软件生成刀路轨迹,对整个涡旋型线进行程序仿真,轨迹一致且程序无误,最后在涡旋铣专机上进行了粗、精加工实际验证。结果显示,轨迹满足加工要求,表明本文提出的算法所计算的刀补点可以实现涡旋盘曲线加工,验证了算法的合理可行性,有效解决了生产实际难题,也为其他采用展成法无法直接增加刀补指令的参数化编程提供了有效的方案。

基于干扰观测器的非轴对称表面零件加工快速刀具伺服控制方法

非轴对称表面零件具有复杂的表面形状,刀具控制过程中难以应对加工过程中的等效干扰,使得加工精度不高。针对上述问题,提出基于干扰观测器的非轴对称表面零件加工快速刀具伺服控制方法。基于快速伺服刀具动态行为分析结果,干扰观测器计算等效干扰并以此得出扰动补偿量。以扰动补偿量和动态行为分析为基础,分别设计等效控制律和切换控制律,通过增量滑模控制器实现非轴对称表面零件加工快速刀具伺服控制。实验结果表明,所研究方法刀具伺服控制边界与监控边界高度重合,且跟踪偏移量数值为±0.02μm,具备更高的加工精度和跟踪稳定性能。

数控车床加工的产品质量控制

使用数控车床在加工过程中,经常会碰到尺寸精度不稳定、位置精度不稳定、表面粗糙度不稳定等产品质量难以控制的问题,甚至会碰到不明原因的振刀、断刀、缠屑、零件变形等问题,本文主要从三个大方面阐述数控车床加工的产品质量控制方法,数控车床设备,工艺方法、刀杆、刀片的选择和切削用量。

Edge preparation methods for cutting tools:a review

Edge preparation can remove cutting edge defects,such as burrs,chippings,and grinding marks,generated in the grinding process and improve the cutting performance and service life of tools.Various edge preparation methods have been proposed for different tool matrix materials,geometries,and application requirements.This study presents a scientific and systematic review of the development of tool edge preparation technology and provides ideas for its future development.First,typical edge characterization methods,which associate the microgeometric characteristics of the cutting edge with cutting performance,are briefly introduced.Then,edge preparation methods for cutting tools,in which materials at the cutting edge area are removed to decrease defects and obtain a suitable microgeometry of the cutting edge for machining,are discussed.New edge preparation methods are explored on the basis of existing processing technologies,and the principles,advantages,and limitations of these methods are systematically summarized and analyzed.Edge preparation methods are classified into two categories:mechanical processing methods and nontraditional processing methods.These methods are compared from the aspects of edge consistency,surface quality,efficiency,processing difficulty,machining cost,and general availability.In this manner,a more intuitive understanding of the characteristics can be gained.Finally,the future development direction of tool edge preparation technology is prospected.

二维金属切削过程的数值模拟

本文基于数值模拟技术,借助于有限元软件成功地模拟了二维金属切削过程中切屑形成及切削区应力、应变变化的过程,计算出了剪切角及切削起始阶段切削力的变化,并通过实验验证了这一规律的正确性。该方法新颖、独特,从而为金属切削理论研究和刀具产品开发领域中提出一种更为有效、更为可靠的研究方法。

现代刀具涂层制备技术的研究现状

刀具涂层是一种机床工具行业的重要材料,其性能直接影响数控机床的机械加工精度。概述了刀具涂层材料的特点、要求及涂层制备技术的发展,分析了化学气相沉积法、物理气相沉积法、等离子体增强化学气相沉积法及溶胶-凝胶法等几种涂层制备方法的优缺点。结合国内外刀具涂层的研究现状及发展趋势,指出在大力发展化学气相沉积涂层和物理气相沉积涂层技术的同时,开发两者相结合的新型工艺,推动国内刀具涂层技术的快速发展。

空载状态下往复式棉秆切割器动力学仿真与试验

为了能够迅速、可靠地确定空载状态下往复式棉秆切割器的切割阻力和功耗等数据从而优化其设计,选择一种以偏置式曲柄连杆机构驱动的往复式棉秆切割器作为仿真与试验研究对象。采用SolidWorks进行了虚拟样机设计,利用ADAMS对空载状态下往复式棉秆切割器进行了动力学仿真研究,依据仿真数据应用响应面方法对切割峰值阻力与机架所受振动力进行了试验分析,确定了割刀平均切割速度为0.8m/s、配重块质量为1.5kg、安装位置滞后于曲柄位置170°时切割峰值阻力与机架所受振动力最小,分别为450和380N。利用研制的往复式棉秆切割试验台,对空载状态下的切割阻力随着割刀平均切割速度的变化进行了试验研究,并与仿真数据进行了对比分析。结果表明,切割峰值阻力的实测值与模拟值相对误差为7%,机架所受振动力的实测值与模拟值相对误差为7.7%,仿真数据可靠,能替代试验数据作为参考依据,为低功耗棉秆切割收获装备的研发提供了一种设计参考。

硬态切削机理研究的现状与发展

对国内外硬态切削机理研究的内容和成果进行了综合评述 ,讨论了硬态切削的概念和特点、切削力、金属软化效应、刀具磨损机理、切屑形成机理、冷却方式以及已加工表面完整性 ,提出了硬态切削研究中的热点问题。

铝合金整体壁板时效成形模具型面构造

时效成形是飞机整体壁板的主要成形工艺之一,由于成形过程中回弹量大的特点,需要对模具进行补偿以消除回弹对零件成形精度的影响。为了有效消除回弹影响,提出一种有限元模拟与物理试验相结合的思路,基于有限元模具型面回弹补偿—试验迭代的频域模具型面修正方法。以2124铝合金材料为例,以零件理论外形作为初始模具型面对整体壁板进行仿真回弹补偿迭代,经过6次补偿,零件成形误差减小到0.47 mm,把有限元迭代所得模具型面进行工艺试验,验证结果表明,仿真迭代所得模具型面成形零件的误差为0.63 mm;达不到0.5 mm的外形误差要求。进一步采用模具'频域'修正算法对时效成形模具型面进行修正,经过2次修正,成形零件误差降低至0.484 mm,满足使用要求,结果表明该方法可行。

金属切削刀具后刀面的切削热研究

在以往的金属切削热研究中,认为刀具后刀面处产生的切削热很小而被忽略。文章应用平面热源法,建立了刀具后刀面与工件摩擦面的切削热模型,推导了该摩擦面的切削热分配和切削温度理论计算公式,对影响后刀面切削热的主要因素进行了分析。研究结果表明,当刀具后刀面磨损带宽度达到一定程度时,则刀具后刀面处产生的切削热不能忽略。