纳米切削过程中刀-屑接触区应力分布研究

高速切削时刀屑接触区的应力分布直接影响切削过程、切削温度及刀具磨损。利用分子动力学技术对纳米切削过程中刀屑接触区的应力分布特征进行研究,分别采用EAM势、Tersoff 势及Morse势计算单晶铜原子间、单晶硅原子间、工件原子与刀具原子间的相互作用力。分析纳米尺度下刀屑接触长度随切削距离变化的规律,探讨刀具前角对刀屑接触区应力分布的影响,通过描述刀屑接触区切屑原子的运动情况,为阐释刀屑接触区的应力分布特征提供依据。研究结果表明在刀-铜屑接触区,正应力在切削刃处最大,随着到切削刃距离的增大而减小,在刀-硅屑接触区,正应力以规则的波动形式逐渐减小。而切应力在切削刃处为负值,随着到切削刃距离的增大,切应力在刀屑接触长度的三分之二处增大到最大值后逐渐减小至零。     

微切削加工技术

在探讨切削技术发展动力的基础上给出了机械加工的尺度划分方法。通过综述微制造技术,介绍了微切削加工装备和微切削刀具,提出了利用应变梯度塑性理论进行微切削机理研究的设想,从分子动力学模拟仿真、最小切削厚度、切屑形态、微切削力、切削温度、工件材料的微量加工性、刀具变形、表面粗糙度与切削稳定性、毛刺、积屑瘤、刀具磨损等不同方面分析了微切削机理的研究现状和存在问题。最后介绍了微铣削CAD/CAM技术,并指出了微切削加工技术的发展趋势。     

超精密切削SiCp/Al复合材料有限元仿真研究

针对超精密切削SiC_p/Al复合材料加工时表面质量不高的问题,利用ABAQUS有限元分析软件建立三维仿真模型来动态模拟切削表面形成过程。分析了SiC颗粒破碎过程,研究工件表面形成机理;通过比对不同切削深度下的加工表面形貌,分析了刀具相对颗粒位置的变化对表面形貌的影响。结果表明:SiC颗粒存在轻微破损、破裂、断裂现象,加工表面出现空穴、凹坑、划痕三种不同类型的加工缺陷。     

微细铣削航空铝合金温度场试验研究

采用红外热像仪测量微细铣削加工航空铝合金材料中的切削温度。分析微刀具、工件及切屑的温度场分布规律;研究进给速度、主轴转速、背吃刀量对切削温度的影响。研究结果表明微细铣削加工中切削温度较低,最高切削温度出现在微刀具与工件的接触区域。进给速度对切削温度影响较大。该试验结果可用于微细铣削加工参数优化,也可为提高工件表面加工质量、合理设计与使用刀具提供理论依据。     

纳米切削多晶铜的分子动力学仿真研究

采用Voronoi方法建立了多晶铜切削模型,基于分子动力学方法实现了多晶铜纳米切削加工的二维分子动力学仿真。分别选用EAM势函数和Morse势函数来计算工件原子间以及工件原子和刀具原子间的相互作用。对切削过程和切削力的变化进行了分析,发现晶界会阻止位错向晶粒内部传播,在已加工区域表面,前一晶粒中的原子会随刀具运动到下一晶粒中形成晶界,切削过程中切削力随时间波动剧烈,并在晶界处会出现瞬时的峰值。     

车铣加工切削机理分析

车铣加工通过将车刀更换为铣刀,增加铣刀转动自由度,基于工件转动和铣刀转动的合成运动,完成对工件的加工.车铣加工具有断屑更容易、切削温度低、切削力小等优点,即使工件低速旋转,也能实现高速切削.对车铣加工的切削机理进行了分析,具体包括刀具磨损机理、切屑形成机理、工件表面质量、难加工材料切削等.     

表面微织构刀具切削加工技术

刀面微织构改变了刀具与切屑之间的摩擦状态,表面微织构刀具在切削中能够降低刀具磨损、提高刀具寿命和切削性能,研究表面微织构刀具的切削加工技术具有重要意义。通过对表面微织构刀具切削加工技术进行综述,介绍了表面微织构刀具制备方法以及表面微织构刀具在切削加工过程中的切削力、切削温度、刀具磨损、工件加工表面粗糙度的影响规律,梳理了表面微织构在不同刀具上的应用,对表面微织构刀具切削加工技术的未来发展趋势进行了展望。     

虑及颗粒—基体摩擦行为影响的SiCp/Al切削仿真研究

摩擦系数是影响切削过程中切削力、切削热以及已加工表面形貌的重要参数。通过搭建力—热可控摩擦实验平台,探究温度—压力影响下SiC_p/Al切削过程中颗粒—基体两相摩擦行为。基于摩擦工件表面粗糙度与表面形貌,揭示了温度—压力影响机理。结果表明,温度—压力作用本质是影响SiC颗粒磨削深度;摩擦系数受压力影响较大,而温度、压力与颗粒自锐性三者的共同作用决定摩擦后工件表面粗糙度。考虑颗粒—基体摩擦行为影响的SiC_p/Al切削仿真模型能有效预测切削力,平均误差为3.28%;提高切削速度可有效改善SiC颗粒犁耕基体形成的三角形缺陷宽度,平均减少38.3%。该研究为进一步理解SiC_p/Al切削过程中的摩擦特性与提高仿真预测精度提供了理论基础。     

单晶Ni3Al切削过程的分子动力学仿真研究

采用分子动力学方法构建了单晶Ni3Al纳米块和球形金刚石刀具模型,模拟金刚石刀具对单晶Ni3Al工件的纳米切削过程并分析切削过程中切屑和已加工表面的形成,切削力、工件温度和系统势能的变化规律.结果 表明:在切削区域,由于刀具的剪切和挤压作用,工件原子发生滑移,部分原子脱离初始位置,形成切屑和已加工表面;切屑和已加工表面的形成主要与切向力和法向力的作用有关;切削过程中工件温度和系统势能在不断增加,而已加工表面工件原子的弹性恢复和晶格重组又会减弱其增加速率.     

工件旋转法磨削硅片的磨粒切削深度模型

半导体器件制造中,工件旋转法磨削是大尺寸硅片正面平坦化加工和背面薄化加工最广泛应用的加工方法。磨粒切削深度是反映磨削条件综合作用的磨削参量,其大小直接影响磨削工件的表面/亚表面质量,研究工件旋转法磨削的磨粒切削深度模型对于实现硅片高效率高质量磨削加工具有重要的指导意义。通过分析工件旋转法磨削过程中砂轮、磨粒和硅片之间的相对运动,建立磨粒切削深度模型,得到磨粒切削深度与砂轮直径和齿宽、加工参数以及工件表面作用位置间的数学关系。根据推导的磨粒切削深度公式,进一步研究工件旋转法磨削硅片时产生的亚表面损伤沿工件半径方向的变化趋势以及加工条件对磨削硅片亚表面损伤的影响规律,并进行试验验证。结果表明,工件旋转法磨削硅片的亚表面损伤深度沿硅片半径方向从边缘到中心逐渐减小,随着砂轮磨粒粒径、砂轮进给速度、工件转速的增大和砂轮转速的减小,加工硅片的亚表面损伤也随之变大,试验结果与模型分析结果一致。     

车辆转向的稳定性非线性分析方法

根据协同学和非线性动力学原理,通过对车辆－轮胎系统非线性模型的分析,利用轮胎魔术公式的逐点一阶Taylor展开式,建立车辆转向系统势能函数方程。通过对势能函数曲面的分析,发现车辆转向系统的稳定区域是由车身侧偏角和横摆角速度确定的极限环,并揭示出车辆转向失稳的机理。最后,利用李亚普诺夫函数对势能函数方程进行能量变化趋势验证,进而证实所建立转向系统势能函数方程的有效性和正确性。     

Evaluation of a three-dimensional single-point turning at atomistic level by a molecular dynamic simulation

In this paper, a molecular dynamic simulation study was performed to study 3D single-point turning of a monocrystalline copper workpiece with rigid diamond tools at nanometric scale. Morse potential energy function was applied to model the copper/diamond and copper/copper interactions. Two-groove cutting was employed to simulate the surface creation in 3D single-point turning operations. Multiple machining conditions were investigated by considering the effects of rake angle, machining speed, depth of cut, and feed rate. Not surprisingly, in machining both grooves, the tool forces increase with the increase of feed rate and depth of cut, as well as the use of a smaller rake angle. These general observations are consistent with the conventional metal machining at longer length scales. On the other hand, it was found that the increase of machining speed also significantly causes the rise of tool forces. Moreover, the stress and instantaneous temperature distributions in the workpiece were analyzed. It was discovered that for all conditions investigated, the equivalent stress and temperature distributions actually resemble these reported for conventional machining. All cutting parameters affect the magnitude and distribution of stresses to a certain extent, while the machining speed appears to be the dominant factor for the machining temperature.     

基于分子动力学的单晶硅压痕过程计算机仿真研究

对单晶Si的压痕过程进行了分子动力学模拟.采用Morse势函数描述原子间的相互作用,以牛顿方程建立力学运动方程,使用改进后的Verlet算法解原子运动轨迹,通过对MD仿真结果的分析研究,将压痕过程分为三个特征阶段,即初期弹性变形阶段、中期塑性变形阶段及非晶层形成阶段.并从原子角度分析了压痕过程中原子间势能、磨削力的变化、应力状态、磨削温度等特征,解释了微观材料的去除和表面形成机理.     

单晶铜原子力显微镜加工过程亚表面变形层的分子动力学仿真

建立了原子力显微镜针尖切削单晶铜的三维分子动力学模型,采用嵌入原子势模拟工件原子之间的作用,采用Morse势模拟工件原子和刀具原子之间的作用.研究了工件材料的不同晶向和刀具切削方向、切削速度对工件亚表面变形层深度的影响.引入了原子势能变形判据,通过分析不同变形区域内原子的势能变化判断工件变形程度.观察了不同切削状态下亚表面原子势能的变化,发现工件材料晶向和切削方向对亚表面变形层深度有着显著影响.在切削速度为20～250 m/s范围内,切削速度对亚表面变形层深度没有影响.     

磨料水射流切割断面质量的研究

磨料水射流(AWJ)在难加工材料切割中得到广泛应用，但由于切割断面存在斜条纹限制了AWJ的应用。研究了射流压力和切割速度对塑性和脆性材料切割断面质量的影响规律，通过对AWJ切割机理和切割过程的分析，探讨了AWJ切割断面的形貌特征及其形成机理，认为是射流断面磨料动能的分布不均和射流的偏转滞后造成了AWJ切割断面斜条纹和曲线及尖角处的尖端，可以通过喷头摆动进给和切割速度补偿两种控制设计方案来实现AWJ的高效切割。     

Nano-milling on monocrystalline copper: A molecular dynamics simulation

Nano-milling is a promising technique for making miniaturized ultraprecision components. However, its underlying material removal mechanism is unclear and the accurate prediction of its performance is lacking. This study performs a systematic molecular dynamics analysis to reveal the material removal in the nano-milling of monocrystalline copper. It was found that the grooves by nano-milling, regardless of the machining parameters used, have two common features: (i) the groove top edge distortion is due to the effects of surface energy and high strain rate and (ii) the groove profile at the outlet side of the tool rotation aligns more closely with the designed geometry as a result of the atom flow variation and residual stress distribution. A dimensional analysis showed that the cutting speed factor and groove dimension factor significantly influence the specific energy and material removal rate in nano-milling. The groove quality can be improved by increasing the groove dimension factor or by decreasing the cutting speed factor. Finally, a machinability chart was developed for quality nano-milling processes.     

FUZZY CLUSTERING MODELLING FOR SURFACE FINISH PREDICTION IN FINE TURNING PROCESS

ABSTRACT

In this paper, fuzzy subtractive clustering based system identification and Sugeno type fuzzy inference system are used to model the surface finish of the machined surfaces in fine turning process to develop a better understanding of the effect of process parameters on surface quality. Such an understanding can provide insight into the problems of controlling the quality of the machined surface when the process parameters are adjusted to obtain certain characteristics. Surface finish data were generated for aluminum alloy 390 (73 BHN), ductile cast iron (186 BHN), and inconel 718 (BHN 335) for a wide range of machining conditions defined by cutting speed, cutting feed rate and cutting tool nose radius. These data were used to develop a surface finish prediction fuzzy clustering model as a function of hardness of the machined material, cutting speed, cutting feed rate, and cutting tool nose radius. Surface finish of the machined part is the output of the process. The model building process is carried out by using fuzzy subtracting clustering based system identification in both input and output space. Minimum error is obtained through numerous searches of clustering parameters. The fuzzy logic model is capable of predicting the surface finish for a given set of inputs (workpiece hardness, cutting speed, cutting feed rate and nose radius of the cutting tool). As such, the machinist may predict the quality of the surface for a given set of working parameters and may also set the process parameters to achieve a certain surface finish. The model is verified experimentally by further experimentation using different sets of inputs. This study deals with the experimental results obtained during fine turning operation. The findings indicate that while the effects of cutting feed and tool nose radius on surface finish were generally consistent for all materials, the effect of cutting speed was not. The surface finish improved for aluminum alloy and ductile cast iron but it deteriorated with speed for inconel.     

FUZZY CLUSTERING MODELLING FOR SURFACE FINISH PREDICTION IN FINE TURNING PROCESS

In this paper, fuzzy subtractive clustering based system identification and Sugeno type fuzzy inference system are used to model the surface finish of the machined surfaces in fine turning process to develop a better understanding of the effect of process parameters on surface quality. Such an understanding can provide insight into the problems of controlling the quality of the machined surface when the process parameters are adjusted to obtain certain characteristics. Surface finish data were generated for aluminum alloy 390 (73 BHN), ductile cast iron (186 BHN), and inconel 718 (BHN 335) for a wide range of machining conditions defined by cutting speed, cutting feed rate and cutting tool nose radius. These data were used to develop a surface finish prediction fuzzy clustering model as a function of hardness of the machined material, cutting speed, cutting feed rate, and cutting tool nose radius. Surface finish of the machined part is the output of the process. The model building process is carried out by using fuzzy subtracting clustering based system identification in both input and output space. Minimum error is obtained through numerous searches of clustering parameters. The fuzzy logic model is capable of predicting the surface finish for a given set of inputs (workpiece hardness, cutting speed, cutting feed rate and nose radius of the cutting tool). As such, the machinist may predict the quality of the surface for a given set of working parameters and may also set the process parameters to achieve a certain surface finish. The model is verified experimentally by further experimentation using different sets of inputs. This study deals with the experimental results obtained during fine turning operation. The findings indicate that while the effects of cutting feed and tool nose radius on surface finish were generally consistent for all materials, the effect of cutting speed was not. The surface finish improved for aluminum alloy and ductile cast iron but it deteriorated with speed for inconel.     

激光辅助精密微铣床的研制与有限元分析

激光辅助切削作为一种先进的特种加工技术,具有能量密度高、升温速度快、加热范围小、对材料热影响小等优点。介绍了自主设计的激光辅助精密微铣床,通过对横梁和立柱进行有限元分析得知,横梁和立柱静态时具有极小变形量,动态时具有较高固有频率,满足设计要求,可以保证加工系统的整体稳定性,进而确保零件的表面加工质量和精度。