刀具几何参数对金属钛纳米切削影响的分子动力学研究

基于分子动力学的基本原理,构建了钛的纳米切削分子动力学仿真模型。工件原子间采用嵌入原子势EAM（Embedded atom method）,工件原子与刀具原子间采用Morse势函数,研究了在不同刃口半径和刀具前角条件下,钛纳米切削过程中工件形态、系统势能、切削力以及工件温度等的变化规律。结果表明：随着刀具刃口半径增大,加工表面粗糙度增加,切削力和工件温度降低,切屑变薄;当刀具前角由负值增加到正值,钛工件承受的压应力逐渐变为剪应力,正前角刀具更有利于切削,同时在不同的刀具前角下,切向力和法向力的大小也有显著变化。     

Re-evaluation of the basic mechanics of orthogonal metal cutting: velocity diagram, virtual work equation and upper-bound theorem

This paper re-evaluates the known velocity relationships expressed in the form of a velocity diagram in orthogonal metal cutting, arguing that the metal cutting process be considered as cyclic and consisting of three distinctive stages. The velocity diagrams for the second and third stages of a chip-formation cycle are discussed. The fundamentals of the mechanics of orthogonal cutting, which are the upper-bound theorem applied to orthogonal cutting and the real virtual work equation, are re-evaluated using the proposed velocity diagram and corrected relationships are proposed. To prove the theoretical results, the equation for displacements in the deformation zone is derived using the proposed velocity relationships. To prove that the displacements in the deformation zone follow the derived equation and that this zone consists of two unequal parts, a metallographical study of chip structures has been carried out. To estimate the variation of stress and strain in the deformation zone quantitatively, a microhardness scanning test was conducted.Because it is proved that the chip formation process is cyclic, its frequency is studied. It is shown that when the noise due to various inaccuracies in the machining system is eliminated from the system response and thus from the measuring signal, and when this signal is then properly processed, the amplitude of the peak at the frequency of chip formation is the largest in the corresponding autospectra.     

切削参数对ZrO2陶瓷切削过程影响的数值模拟

采用有限元仿真方法对ZrO₂陶瓷工件进行三维切削过程的数值模拟,探讨工件材料切削过程中切屑去除机理、应力动态变化与分布规律以及切削力的演变规律等。结果表明：切削过程中刀具的硬接触行为显著影响材料去除,导致切屑崩落、材料开裂和裂纹扩展等失效形式出现。在切削深度分别为200和250 μm时,工件末端边缘出现大量裂纹,并朝垂直切削方向扩展,导致工件边缘出现大尺寸碎裂。增大切削速度可引起应力和切削力的上下波动,但在整体上没有明显变化。刀具刃圆半径影响切入初期裂纹的形成,随着刃圆半径增大,刀具前端的裂纹长度逐渐缩短,但其对切削力的影响不明显。负的刀具前角切削不会使工件内部产生裂纹,可获得较好的加工质量;此外,在刀具前角为0°时,其最大切削力最大,但随着刀具前角增加,其平均切削力变化不明显。     

Development of a chip flow model for turning operations

A model is presented which predicts the chip flow direction in turning operations with nose radius tools under oblique cutting conditions. Only the tool cutting edge geometry and the cutting conditions (feed and depth of cut) are required to implement the model. An experimental study has verified the chip flow model and shown that the model's predictions are in good agreement with the experimental results.     

Thermomechanical modelling of oblique cutting and experimental validation

An analytical approach is used to model oblique cutting process. The material characteristics such as strain rate sensitivity, strain hardening and thermal softening are considered. The chip formation is supposed to occur mainly by shearing within a thin band called primary shear zone. The analysis is limited to stationary flow and the material flow within the primary shear zone is modelled by using a one-dimensional approach. Thermomechanical coupling and inertia effects are accounted for. The chip flow angle is determined by the assumption that the friction force on the tool face is collinear to the chip flow direction. At the chip–tool interface, the friction condition can be affected by the important heating induced by the large values of pressure and sliding velocity. In spite of the complexity of phenomena governing the friction law in machining, a reasonable assumption is to consider that the mean friction coefficient is primarily function of the average temperature at the tool–chip interface. Comparisons between model predictions and experimental results are performed for different values of cutting speed, undeformed chip thickness, normal cutting angle and inclination angle. A critical study is presented in order to show the influences of the input parameters of the model including the normal shear angle, the thickness of the primary shear zone and the pressure distribution at the tool–chip interface. The model permits to predict the cutting forces, the chip flow direction, the contact length between the chip and the tool and the temperature distribution at the tool–chip interface which has an important effect on tool wear.     

A force model for nose radius worn tools with a chamfered main cutting edge

The three-dimensional cutting forces for nose radius tools with a chamfered main cutting edge incorporated with a tool-worn factor are presented in this paper. The variations in shear plane areas occurring in the tool-worn situation are used. The results obtained from the proposed model shows good agreement with the experimental data on both chip formation as well as cutting forces. In the experimental work the throwaway tips are locked onto the pocket of the tool holder. The holders for special tools are designed first. Next, the tool holders are manufactured by using medium carbon-steel bars and the mounting tips are designed based on various specifications. Finally, the nose radius tips mounting in the tool holder are ground to a wear depth, and the worn tool dimensions are measured by using a profile projector. The shear area and the friction area are calculated accordingly. Then the three-dimensional cutting forces will be obtained from those data.     

飞秒激光加工单晶金刚石制备正前角磨削工具

目的制造一种磨粒有序排布、具有正前角的无结合剂端面金刚石磨削工具。方法采用波长为1030 nm、脉宽为250 fs的钛蓝宝石飞秒激光对单晶金刚石(SCD)进行烧蚀加工,首先研究加工工艺参数(特别是烧蚀轨迹间距)对金刚石加工效率及表面质量的影响。采用预先设计的激光扫描路径,基于优化后的工艺参数在SCD表面加工出微磨粒阵列结构,各磨粒呈方锥台形结构,其顶部倾斜角约为100°。在此基础上,对微磨粒阵列进行烧蚀加工,将所有微磨粒顶部的倾斜角减小至小于90°。结果当激光烧蚀轨迹间距为10.0μm时,烧蚀加工表面RMS粗糙度最小。确定了一种微磨粒边缘倾斜角小于90°且磨粒有序排布的新型无结合剂金刚石端面磨削工具的激光制备方法和工艺,采用该工艺加工的磨削工具表面质量好,轮廓精度高,磨粒平均正前角约为9.80°。结论采用飞秒激光可以高质量、高效率地制备出磨粒有序排布的新型正前角无结合剂金刚石端面磨削工具,该工具有望在硬脆材料磨削中减小磨削力,提高材料表面完整性。     

PCBN刀具干车淬硬钢时倒棱前角对切削力和刀具磨损的影响

PCBN刀具磨出负倒棱是为了加强刀具的刃口强度，以减少刀具加工时可能出现的破损情况。本文通过对PCBN刀具加工淬硬轴承钢GCr15的一系列试验数据加以分析，得出倒棱前角和切削力、刀具磨损之间的关系，进而得出在实际加工情况下应该采用的最佳倒棱前角值。试验表明：当倒棱前角取15度且切削速度为125m／s时，刀具具有最好的加工效果，不但切削力可以达到最小值，刀具磨损最轻，而且刀具寿命也达到了最大值。     

等螺旋角锥度刀具简易数控加工法

文章提出了一种在经济型数控机床上实现等螺旋角圆锥螺旋线的加工方法,其原理是用等导程螺旋线去逼近此种曲线.这个方法计算简单,结果精确,并可保证整段曲线上误差相等,而且其大小也可控制.     

The performance of CBN tools in the machining of titanium alloys

Advancements in the aerospace, nuclear and other industries require the enhanced in-service performance of engineering components. These requirements have resulted in the large scale development and use of heat-resistant and high-strength materials such as titanium alloys, which pose considerable machining problems. In this study on machining of titanium alloy using CBN tools, the machining performance was evaluated in terms of cutting force, specific cutting pressure, cutting temperature, chip strain and surface finish.     

A plane-strain UBET analysis of material flow in a filled deep die cavity in closed-die forging

When a deep die cavity is filled in closed-die forging, further movement of the dies will reduce the extension of the plastic region, a part of the workpiece in the cavity becoming rigid and forming dead zones. Consequently the plastic deformation is localized within a particular region, where the plastic deformation imparted could be much greater than the average. In this work, the upper-bound elemental technique (UBET) is applied to analyze the material flow in a filled deep cavity for plane-strain conditions. The boundaries between the dead zones and the deforming material are determined together with the velocity field by minimizing the total power dissipation. The boundaries are analyzed and presented numerically. Strain-rate hardening and inhomogeneous deformation in the UBET element are taken into account. A detailed formulation of the analysis is presented in the paper. The influences of flash-height and the strain-rate hardening exponent of the deforming material are studied theoretically. The results are compared with those of model-material experiments and those of commercial FEM software, satisfactory agreement being obtained.     

任意形状坯料反挤压成形内圆筒的上限单元技术的改善分析

提出了对任意形状坯料扳挤压成形内圆筒的运动许可速度场改善。     

空拔圆管拔制力复变函数法解析

利用复变函数解析空拔圆管问题是一种新方法。本文选取合适的坐标系,对空拔圆管的拔制力进行了解析,结果表明,在实践中与采用同样变形区形状的其他上界法解析的结果完全一致,且与实验结果相近,证明了这种方法的理论可靠性。     

Ti(C,N)基金属陶瓷刀具切削加工有限元模拟

介绍了本课题组研制的一种新的刀具材料--T(iC,N)基金属陶瓷的成分组成及其力学性能;基于大变形-大应变理论、增量理论以及更新拉格朗日算法、采用几何断裂分离准则,建立了二维弹塑性金属正交切削有限元模型,对金属正交切削过程进行了数值模拟;改变刀具前角,得出在不同的刀具前角下T(iC,N)基金属陶瓷刀具在正交切削过程中切削力以及刀具后刀面等效应力变化;分析了切削力、刀具表面等效应力对刀具磨损的影响;模拟结果与相关研究的实验数据吻合。本文的研究为后期研制新的刀具材料提供了理论依据,降低实验成本。     

FEA modeling and simulation of shear localized chip formation in metal cutting

The finite element analysis (FEA) has been applied to model and simulate the chip formation and the shear localization phenomena in the metal cutting process. The updated Lagrangian formulation of plane strain condition is used in this study. A strain-hardening thermal-softening material model is used to simulate shear localized chip formation. Chip formation, shear banding, cutting forces, effects of tool rake angle on both shear angle and cutting forces, maximum shear stress and plastic strain fields, and distribution of effective stress on tool rake face are predicted by the finite element model. The initiation and extension of shear banding due to material's shear instability are also simulated. FEA was also used to predict and compare materials behaviors and chip formations of different workpiece materials in metal cutting. The predictions of the finite element analysis agreed well with the experimental measurements.