Research on the nanometric machining of a single crystal nickel via molecular dynamics simulation

Molecular dynamics simulations are employed to study the nanometric machining process of single crystal nickel. Atoms from different machining zones had different atomic crystal structures owing to the differences in the actions of the cutting tool. The stacking fault tetrahedral was formed by a series of dislocation reactions, and it maintained the stable structure after the dislocation reactions. In addition, evidence of crystal transition and recovery was found by analyzing the number variations in different types of atoms in the primary shear zone, amorphous region, and crystalline region. The effects of machining speed on the cutting force, chip and subsurface defects, and temperature of the contact zone between the tool and workpiece were investigated. The results suggest that higher the machining speed, larger is the cutting force. The degree of amorphousness of chip atoms and the depth and extent of subsurface defects increase with the machining speed. The average friction coefficient first decreases and then increases with the machining speed because of the temperature difference between the chip and machining surface.     

Molecular dynamics simulation of single crystal Nickel nanometric machining

Molecular dynamics simulation is carried out to study the nanometric machining of single crystal Nickel (Ni). Through an investigation of atomic displacement and the variation of cutting force, it is found that the latter is in accordance with the number variation of elastic displaced atoms in the workpiece. It is further found that the generation of complex stacking faults is the predominant cause of cutting force fluctuation, and the stacking faults with complex structures lead to work-hardening. The temperature of the cutting tool and workpiece is studied during the machining process. It is concluded that the selection of averaging steps has a significant influence on the system temperature distribution. Thus, the time-spatial averaging method, which has a high accuracy and consistency in temperature distribution, is proposed.     

切削区温度分布研究

金属切削加工中,切削热与切削温度是一重要的物理现象,切削温度及其分布直接影响刀具磨损和工件的加工精度及表面质量.本文通过分析切削力和刀—屑接触长度的计算,建立了刀—屑接触区的正应力与剪应力的分布计算模型,采用有限元法对稳态切削过程中切削温度分布进行了计算,得到了切削区切削温度的分布情况.     

Chip formation dependence of machining velocities in nano-scale by molecular dynamics simulations

In this study, molecular dynamics simulations were carried out to study the effect of machining velocities on the mechanism of chip formation in nano-metric copper. A wide range of cutting velocities was performed from 10 to 2000 m/s, and the microstructure's evolution from a crystalline state to an amorphous state was studied. At the low machining velocity, dislocations were generated from the surface in front of the tool, and the immobile dislocation deduced by the cross slip of dislocation was observed. At the high machining velocity, no crystal dislocation nucleated, but instead disorder atoms were found near the tool. Temperature near the tool region increased with the increasing machining velocities, and the temperature had an important effect on the phase transition of the crystal structure.     

微切削加工Al7050-T7451过程切屑形貌及尺度效应研究

采用硬质合金刀具,通过一系列的单因素直角切削试验对铝合金7050-T7451微切削加工中的切屑形貌、切削力以及尺度效应等进行了研究。为了便于使用Kistler9257B型测力仪进行加工过程切削力的测量,对工件进行处理,使用数控铣削中心实现直角车削。试验方案在不同切削速度下变换切削深度,考虑刀具刃口半径的存在对微切削加工过程的影响。试验中收集不同切削参数下的切屑,得到切屑的宏观形貌;对切屑进行抛光腐蚀,在高倍光学显微镜下获取切屑的微观形貌,研究了切削参数对切屑厚度和卷曲程度等的影响规律。试验过程中实时测得不同切削条件下的切削力,讨论了微切削加工过程切向力和径向抗力受刀具刃口半径影响下的变化规律,并从单位切削力的角度出发研究了刀具刃口半径对微切削加工过程中尺度效应的影响规律。     

硼砂熔盐被覆VC机理的探讨

探讨在硼砂熔盐中被覆VC时的化学反应及其动力学过程。系统地讨论硼砂熔盐特性及主要成分、操作温度、合金元素等对反应速度的影响。并提出VC形成时的碳原子扩散途径:开始碳原子从固溶体中扩散至基体金属表面直接与钒结合,以后的碳原子扩散至基体金属表面,需再穿过VC晶格间隙,扩散至被覆层表面,才与钒结合成VC,使被覆层逐渐加厚。     

ZrO_2陶瓷激光加热辅助切削加工技术

为了解决高强度、高脆性氧化锆(ZrO2)陶瓷材料加工困题的问题,对激光加热辅助切削(Laser-assisted machining,LAM)ZrO2陶瓷加工技术进行了研究。建立了热传递的三维模型,并采用ANSYS软件进行了温度场有限元仿真。搭建了切削试验系统并进行了加工试验。试验采用Nd:YAG激光器进行连续加热,红外线测温仪测量表面温度,压电式测力仪在线测量切削力,并对切屑形状、刀具磨损状态和加工质量做了研究。结果表明:相对传统切削加工技术,LAM加工技术能够有效地减小切削力,减缓刀具磨损和改善加工表面质量。     

基于Deform-3D的镍基高温合金残余应力仿真分析

GH4169镍基高温合金应用广泛,但是属于难以加工的材料,而且已加工表面的残余应力很容易导致工件变形,从而影响工件的加工质量。应用Deform 3D软件,研究了不同切削用量下残余应力的变化规律。研究结果表明,切削速度的变化对表面残余应力的影响甚小|背吃刀量和进给量增大,表面残余应力随之增大|随着切削用量的增加,工件内部残余应力亦随之增加。     

一种基于FTS车削的微切削力模型

机械加工中的切削力模型建立对于研究工件表面形貌成型,探究切削理论有着深远的意义。在微切削加工领域,伺服车削通常用来加工自由曲面,但是考虑到尺寸效应,传统宏观领域的切削力模型无法真实地描述切削过程。针对微切削加工领域,提出了一种切削力模型,模型充分考虑了最小未成型切屑厚度,刀具切削刃钝圆以及工件对后刀面回弹引起的摩擦力。由于切削深度不同,所对应的切削原理也不同,将切削过程分为多个区域建模。当刀具切入工件后,随着切屑厚度的减小,切屑在前刀面分别经历宏观剪切、大负前角切削以及耕梨过程,而同时工件未切下的部分在后刀面的进一步作用下形成已加工表面,对应上述过程,将分为4个区域建模。最后,基于自主设计的能够精确测量两个方向切削力的快刀伺服装置(DFT-FTS)设计实验。     

Effects of mask wall angle on matrix-hole shape changes during electrochemical machining by mask

The influences of the mask wall angle on the current density distribution,shape of the evolving cavity and machining accuracy were investigated in electrochemical machining(ECM) by mask.A mathematical model was developed to predict the shape evolution during the ECM by mask.The current density distribution is sensitive to mask wall angle.The evolution of cavity is determined by the current density distribution of evolving workpiece surface.The maximum depth is away from the center of holes machined,which le...     

SiCp/Al复合材料的ELID精密加工工艺

针对高体积分数SiCp/Al复合材料的加工难题,采用在线电解修整精密磨削加工工艺对其进行精密磨削实验研究.首先,通过建立单颗粒磨削模型,得到磨粒的最大变形磨屑厚度,进而利用Matlab软件,得到SiCp/Al复合材料塑性域磨削的试验参数范围.然后,通过单因素试验探究磨削深度、砂轮转速以及工件移动速度对加工表面粗糙度的影响,利用正交试验最优参数与理论分析得到的塑性域磨削的试验参数范围进行对比,确定了最优工艺参数.最后,以最优试验参数对体积分数40%的SiCp/Al复合材料进行精密磨削加工,获得表面粗糙度Ra 0.030μm的加工表面.研究表明:应用ELID精密磨削加工工艺,采用W5铸铁基金刚石砂轮,当砂轮转速为1 500 r/min,磨削深度在0.1μm,工件移动速度为2 m/min时,磨削效果最佳.     

高速硬加工中切屑成形的有限元模拟

为了研究AISI4340钢高速加工中切屑形成机理，建立了高速加工的有限元模型.该模型采用Johnson-Cook（JC）模型作为工件材料模型，采用JC破裂模型作为工件材料失效准则，刀-屑接触摩擦采用可自动识别滑动摩擦区和黏结摩擦区的修正库仑定律，并采用任意拉格朗日-欧拉方法实现切屑和工件的自动分离.利用建立的有限元模型模拟了四种切削条件下的材料加工，分析了切屑形成过程，模拟得到了不同切削条件下的切削力，并对其进行了比较.研究结果表明，在高速加工条件下形成了不连续状切屑，不连续状切屑形成机理与基于自由表面破裂的锯齿状切屑形成机理不同.     

单晶硅和单晶铝纳米切削过程比较

采用分子动力学模拟方法进行了单晶硅和单晶铝纳米切削过程的比较研究．硅原子间相互作用力采用Tersoff势计算，铝原子间和工件与刀具原子间相互作用力采用Morse势计算．通过对切削过程中切屑和加工表面、能量和切削力的分析，发现硅发生非晶态相位变换和切屑体积改变，但没有位错和弹性恢复产生；而铝发生的现象却与硅相反．     

Experimental investigation and numerical simulation on interfacial carbon diffusion of diamond tool and ferrous metals

We numerically simulated and experimentally studied the interfacial carbon diffusion between diamond tool and workpiece materials. A diffusion model with respect to carbon atoms of diamond tool penetrating into chips and machined surface was established. The numerical simulation results of the diffusion process reveal that the distribution laws of carbon atoms concentration have a close relationship with the diffusion distance, the diffusion time, and the original carbon concentration of the work material. In addition, diamond face cutting tests of die steels with different carbon content are conducted at different depth of cuts and feed rates to verify the previous simulation results. The micro-morphology of the chips is detected by scanning electron microscopy. Energy dispersive X-ray analysis was proposed to investigate the change in carbon content of the chips surface. The experimental results of this work are of benefit to a better understanding on the diffusion wear mechanism in single crystal diamond cutting of ferrous metals. Moreover, the experimental results show that the diffusion wear of diamond could be reduced markedly by applying ultrasonic vibration to the cutting tool compared with conventional turning.     

工业机器人自动钻孔及锪窝一体化加工

为了提高工业机器人制孔的位姿精度,控制锪窝深度误差,利用激光跟踪仪跟踪机器人位姿,获得位姿偏差,并对机器人位姿偏差进行补偿,提高机器人制孔的位姿精度;利用光栅尺构成闭环控制系统,将制孔过程中机器人与工件变形引起的误差补偿到制孔刀具的进刀位置,从而保证埋头螺栓孔的锪窝深度.采用该跟踪、补偿系统在平面试验件和曲面试验件上进行了工业机器人制孔位置精度和锪窝深度补偿加工试验.结果表明,机器人的位置精度和角度精度达到0.05 mm和0.05°,锪窝深度误差控制在0.03 mm以内.     

钛合金正交切削过程数值模拟

为了研究刀具磨损、加工表面残余应力分布,优化高速切削参数,基于切削条件下材料屈服流动特性、刀具-切屑界面接触摩擦行为以及单元网格划分,建立切削加工过程的有限元仿真模型.通过此模型模拟了钛合金连续状和锯齿状切屑的形成过程.以观察实际切屑形态,验证了该模型的有效性.     

端铣切削可转位铣刀片刃前区温度场分析

端铣切削难加工材料3Cr1Mo1/4V过程中产生切削高温,导致刀片破损速度加快,使用寿命降低.因此精确控制切削热和准确测量切削温度成为决定此类难加工材料切削性能的关键因素.通过可转位铣刀片断续车削模拟端铣切削的实验方案,利用红外辐射测温法分析切屑自由端表面的温度分布规律,并借助有限元软件的热传导单元获得刀-屑接触区及切屑内部的温度场分布.研究结果表明,断续切削实验方案及有限元模拟可有效用于铣刀片刃前区温度场分析,从切屑一侧研究切削热及切削温度,为优化设计铣刀片槽型,提高刀具寿命和加工效率等奠定基础.     

Study on the Key Influencing Factors in Atmospheric Pressure Plasma Processing of Fused Silica

In order to get ultra-smooth fused silica surface without subsurface damage efficiently, the atmospheric pressure plasma processing （APPP） method has been developed. It is based on chemical reaction between active radicals excited by plasma and workpiece surface atoms, so the subsurface damage caused by contact stress can be avoided and atomic-level precision can be ensured. In this paper, based on the spectral quantitative analysis theory, the influence laws on material removal rate by the key factors of APPP including the flow rate of reaction gases, the input power, the processing distance and time are discussed. In addition, the results that APPP can remove the damaged surface layer and do not introduce secondary damage are proved via the nanoindentation technology＇.     

热处理对桑蚕丝分子组成和性能的影响

以市售桑蚕丝织物为研究对象,分别在50℃、100℃、150℃、200℃和不同处理时间条件下,对丝织物进行加速热老化.利用红外、热重和氨基酸测定手段考察了热老化处理对其组成和性能的影响.结果表明:热老化处理后,桑蚕丝纤维样品的红外特征峰峰值强度随着温度的提高和处理时间的延长而变化,且产生微小位移;热处理使丝纤维的热分解温度降低,缘于热老化后纤维晶区受到破坏、结晶度下降;丝纤维的氨基酸含量随着热处理时间的延长以及热处理温度的增加而变化,表明热老化处过程有化学反应发生.由于化学反应的发生使纤维组成发生变化,致使纤维结构产生破坏和损伤,织物断裂强度下降.     

速度效应对淬硬钢最小切削厚度的影响

塑性材料加工中,存在一个最小切削厚度,当切削加工中实际有效切削厚度小于工件材料的最小切削厚度时,将造成刀具与工件无法正常切削,而主要以滑擦为主,此时加工精度很难保证,确定材料的最小切削厚度对提高工件的加工质量及精度具有重要意义.针对以上问题以淬硬钢Cr12Mo V材料为研究对象,提供了一种确定工件材料最小切削厚度的试验方法,并通过提供的试验方法,确定了淬硬钢Cr12Mo V(58 HRC)不同切削速度下的最小切削厚度值,试验结果表明:在所选的速度范围内,热软化效应对淬硬钢Cr12Mo V(58 HRC)成屑机制的影响大于应变率效应的影响,淬硬钢Cr12Mo V(58 HRC)最小切削厚度值的确定,为汽车覆盖件模具精加工余量的选取提供了理论依据.