切削参数对SiCp/Al复合材料切削变形的影响

为研究切削参数对SiC_p/Al复合材料切削变形的影响,通过试验测量的切削力和切屑厚度,计算得到SiC_p/Al复合材料的变形区参数,并分析了切削参数对变形区参数的影响规律,同时拟合得到了切削SiC_p/Al复合材料过程中剪切角与摩擦角的关系。研究结果表明:进给量增大,SiC_p/Al复合材料变形系数和剪应变减小,摩擦角减小,剪切角增大,且SiC_p/Al复合材料的摩擦角大于2024Al,剪切角小于2024Al;切削速度增大,SiC_p/Al复合材料变形系数、剪应变都减小,摩擦角减小但是不显著,剪切角增大; SiC_p/Al复合材料φ=B-C(β-γ)中B值大于2024Al,而斜率C(负值)小于2024Al。     

基于应变梯度塑性理论的微切削第一变形区应变分布研究

将应变梯度塑性理论应用于微切削仿真过程的材料本构模型中,表征材料的微观尺度变形特性。进行了45钢微切削过程仿真,研究微切削第一变形区内的有效流动应力、有效应变分布及其变化规律,分析了切削厚度与切削刃口圆弧半径比对第一变形区有效流动应力和有效应变分布的影响。设计了正交微铣削实验,获得了切屑根部试样,并通过金相试验和显微硬度测试证明了微切削过程中第一变形区应变梯度的存在和微切削变形仿真结果的有效性。     

微切削加工的切屑变形及切削力

本文从分析微切削加工表面的形成机理入手,在考虑刀具钝圆半径存在的条件下,分析了切削表面的形成过程和微切削加工中切削变形系数,在理论上阐明了微切削加工中的切屑变形及切削力情况。在进一步实验的基础上,探明了微切削加工中,切削速度、进给量、切削深度、刀具材料及工件材料等影响切屑变形及切削力的因素。得出了微切削加工中的切屑变形系数要大于常规切削加工的切屑变形系数,减小刀具钝圆半径会减小刀具后刀面与工件的接触长度,并且会减小切削刃以下部分金属的变形,有利于获得高质量的加工表面的结论。     

切削铝基复合材料时的切屑变形及影响因素研究

切屑形态特征和变形系数是研究切削变形程度的重要手段和参数,是计算其他切削过程参数的基础.通过硬质合金和聚晶金刚石(PCD)刀具车削SiC增强铝基复合材料,并观察切屑SEM照片,检测切屑的变形尺寸,研究切屑形态和变形系数.结果表明,切屑形态为小螺卷状,呈节状锯齿形.切削速度与变形系数的关系曲线呈驼峰形,随着进给量和刀具前角的增大,切屑变形系数减小.     

基于机器视觉的正交微切屑变形系数研究

切屑变形系数是描述切削变形程度的重要参数,是计算其它切削过程参数的基础。然而宏观的切削理论和试验技术不适用于微切削技术。研究微切屑变形系数对预测加工结果、优化切削过程、控制加工参数有着重要意义。本文应用机器视觉方法获得了微切削中切屑的几何形状,找出了切削厚度、厚度变形系数、宽度变形系数与进给量、背吃刀量的变化关系,为微切削过程的控制和预测提供了理论依据。试验方法简单、精确、效率高。     

金属纤维大刃倾角切削变形的三维有限元分析

基于有限元分析软件DEFORM-3D,对带状金属纤维的切削过程进行了三维有限元模拟.获得了在不同刃倾角和法向前角下的切屑变形系数和有效剪切角的变化曲线,并将模拟计算得到的变形系数和剪切角与试验作了对比,具有较好的一致性.     

医用钛合金切削加工中切屑变形机理研究

在分析医用钛合金材料Ti-6Al-4V特性的基础上,首先从理论上阐明了钛合金切削加工的切屑变形机理,然后采用试验研究方法,从切屑变形系数ξ与刀具前角γ0的关系、显微组织结构特征两方面对切屑变形机理进行深入研究,发现钛合金Ti-6Al-4V高速切削时切屑变形的主要特征是集中剪切滑移;切屑变形系数ξ随刀具前角γ0的增大而减小,在保证切削刃强度的前提下,增大刀具前角可改善钛合金的切削性能;同时Ti-6Al-4V钛合金的典型（α-β）相金相组织使其成为难切削加工材料,应积极采取措施减少其给切削加工带来的不利因素。     

NiTi形状记忆合金切削仿真变形行为研究

利用ABAQUS软件对NiTi形状记忆合金不同切削速度和进给量时的切屑和已加工表面层热力载荷分布进行仿真分析。结果表明：切削速度和进给量增加都会导致切屑温度升高,塑性应变和损伤加剧;切削速度对温度影响较大,而进给量对塑性应变和损伤影响明显;切削速度增加,已加工表面层温度变化速率变大,表层残余应力增大,深层残余应力减小;进给量增加,应变层深度增加,残余应力逐层变大。     

钛合金TC4超声波振动切削有限元仿真

采用Johnson-Cook材料模型,以任意拉格朗日欧拉网格算法（ALE）实现切屑分离,建立了热应力耦合二维正交振动切削模型,并进行了钛合金TCA超声波振动稳态切削的有限元仿真,得到了振动切屑形状和切削力、切削温度的变化曲线,同时将振动切削与普通切削进行了对比分析,分析结果表明,振动切削中切屑变形系数、切削力、切削温度明显降低,剪切角增大。     

钛合金TC4超声波振动切削有限元仿真

采用Johnson-Cook材料模型,以任意拉格朗日欧拉网格算法(ALE)实现切屑分离,建立了热应力耦合二维正交振动切削模型,并进行了钛合金TC4超声波振动稳态切削的有限元仿真,得到了振动切屑形状和切削力、切削温度的变化曲线,同时将振动切削与普通切削进行了对比分析,分析结果表明,振动切削中切屑变形系数、切削力、切削温度明显降低,剪切角增大.     

Mesoplasticity approach to studies of the cutting mechanism in ultra-precision machining

There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by Lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale.     

Modeling of flow stress in orthogonal micro-cutting process based on strain gradient plasticity theory

The rapidly increasing demand for miniature components machining processes has drawn more attention to micro-machining research. Flow stress has always been a significant base for analyzing plastic deformation in machining processes. However, few studies have been conducted to predict accurately the material flow stress in the micro-cutting processes. In order to describe size effect in micro-cutting, this paper discusses the development of a circular primary deformation zone model, calculates the strain gradient in the primary zone, and presents a new flow stress model based on the theory of strain gradient plasticity. First, a series of orthogonal cutting experiments are performed and flow stress is calculated from the experiment data. Results from the proposed model have been successfully validated with experimentally determined results. It shows that the flow stress in micro-cutting is influenced greatly by the feed rate and the cutting edge radius.     

INVESTIGATION OF SIZE-EFFECTS IN MACHINING WITH GEOMETRICALLY DEFINED CUTTING EDGES

The miniaturization of cutting processes shows process specific size-effects like the exponential increase of the specific cutting force k_c with decreasing depth of cut h. Experiments were carried out in an orthogonal turning process. The influence of different process parameters on the results was investigated separately to identify process specific size-effects. Two materials were studied: a normalized steel AISI 1045 and an annealed AISI O2. To complement the experiments, parameter variations were performed in two-dimensional, thermo-mechanically coupled finite element simulations using a rate-dependent material model and analyzed by similarity mechanics. The influence of rounded cutting-edges on the chip formation process and the plastic deformation of the generated surface were determined numerically. The complex physical effects in micro-cutting were analyzed successfully by finite element simulations and compared to experiments.     

INVESTIGATION OF SIZE-EFFECTS IN MACHINING WITH GEOMETRICALLY DEFINED CUTTING EDGES

The miniaturization of cutting processes shows process specific size-effects like the exponential increase of the specific cutting force k _c with decreasing depth of cut h. Experiments were carried out in an orthogonal turning process. The influence of different process parameters on the results was investigated separately to identify process specific size-effects. Two materials were studied: a normalized steel AISI 1045 and an annealed AISI O2. To complement the experiments, parameter variations were performed in two-dimensional, thermo-mechanically coupled finite element simulations using a rate-dependent material model and analyzed by similarity mechanics. The influence of rounded cutting-edges on the chip formation process and the plastic deformation of the generated surface were determined numerically. The complex physical effects in micro-cutting were analyzed successfully by finite element simulations and compared to experiments.     

切削温度对微细切削加工影响的有限元分析研究

建立微细切削仿真模型,对二维正交切削加工过程进行了热力耦合有限元数值分析,采用有限元模拟与微细切削加工实验验证相结合的方式,深入研究了切削温度对微细切削加工的影响,揭示了在高速、大切厚加工条件下,随着切削厚度的减小,刀—屑接触区切削温度降低,增加了材料的截切强度,从而引起材料的强化,导致单位切削力显著增加。     

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。     

光学玻璃微切削时材料去除机理和表面质量的研究

通过显微压痕和纳米压痕试验,研究了Soda-lime光学玻璃在微/纳米尺度下的材料去除机理,发现外加载荷的幅值对脆性材料变形方式有直接影响。对光学玻璃的金刚石普通切削和超声振动切削试验结果表明,超声振动切削的实际有效切削深度与名义切削深度有着较好的一致性,合理选择金刚石超声振动切削参数可实现光学玻璃的塑性域切削。     

Damaged layer characteristics in micro-endmilling of copper using an ultrahigh-speed air spindle

This paper presents an investigation on the characteristics of damaged layer in micro-machining by using the ultrahigh-speed air spindle. The damaged layer in metal cutting is derived from plastic deformation and transformation of metal structure. In this study, micro-cutting force, surface roughness, and plastic deformation layer according to the variation of machining conditions were investigated by experiments. The damaged layer was measured using optical microscope for the samples prepared by metallographic techniques. Its scale was dependent on cutting process parameters, especially feed per tooth. According to experimental results, it was verified that the thickness of damaged layer was increased with increasing of feed per tooth and cutting depth, also thickness of damaged layer was reduced in down-milling compared to upmilling during micro-endmilling operation.     

单颗CBN磨粒微切削硬质合金YG8磨损研究

微小孔用铰珩工具长径比大,刚度差,可以采用加工工艺方法对其进行修整.为揭示铰珩工具修整过程中CBN磨粒的磨损特性,采用光滑粒子流体动力学法,建立CBN磨粒微切削YG8硬质合金的仿真模型,并通过试验验证该模型的可行性.结果表明:在微切削YG8硬质合金过程中,随着累积材料去除体积的增加,CBN磨粒不断发生微破碎而使其磨损体...     

A study on critical depth of cuts in micro grooving

Ultra precision diamond cutting is a very efficient manufacturing method for optical parts such as HOE, Fresnel lenses, diffraction lenses, and others. During micro cutting, the rake angle is likely to become negative because the tool edge radius is considerably large compared to the sub-micrometer-order depth of cut. Depending on the ratio of the tool edge radius to the depth of cut, different micro-cutting mechanism modes appear. Therefore, the tool edge sharpness is the most important factor which affects the qualities of machined parts. That is why diamond, especially monocrystal diamond which has the sharpest edge among all other materials, is widely used in micro-cutting. The majar issue is regarding the minimum (critical) depth of cut needed to obtain continuous chips during the cutting process. In this paper, the micro machinability near the critical depth of cut is investigated in micro grooving with a diamond tool. The experimental results show the characteristics of micro-cutting in terms of cutting force ratio (Fx/Fy), chip shape, surface roughness, and surface hardening near the critical depth of cut.