Effect of tool geometry on ultraprecision machining of soft-brittle materials:a comprehensive review

Brittle materials are widely used for producing important components in the industry of optics,optoelectronics,and semiconductors.Ultraprecision machining of brittle materials with high surface quality and surface integrity helps improve the functional performance and lifespan of the components.According to their hardness,brittle materials can be roughly divided into hard-brittle and soft-brittle.Although there have been some literature reviews for ultraprecision machining of hard-brittle materials,up to date,very few review papers are available that focus on the processing of soft-brittle materials.Due to the‘soft’and‘brittle’properties,this group of materials has unique machining characteristics.This paper presents a comprehensive overview of recent advances in ultraprecision machining of soft-brittle materials.Critical aspects of machining mechanisms,such as chip formation,surface topography,and subsurface damage for different machining methods,including diamond turning,micro end milling,ultraprecision grinding,and micro/nano burnishing,are compared in terms of tool-workpiece interaction.The effects of tool geometries on the machining characteristics of soft-brittle materials are systematically analyzed,and dominating factors are sorted out.Problems and challenges in the engineering applications are identified,and solutions/guidelines for future R&D are provided.

DIFFUSION COUPLE BETWEEN HIGHSTRENGTH WEAR-RESISTING ALUMINUM BRONZE AND MACHINING TOOLS MATERIALS

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DESIGN AND PROPERTIES OF A FUNCTIONALLY GRADIENT CERAMIC TOOL MATERIAL

Based on the analyses of the severity of cutting process as well as the failure mechanisms of ceramic tools, a model for designing functionally gradient ceramic tool materials with symmetrical distribution is presented, by which a Al 2O 3/(W,Ti)C ceramic tool material FG 2 was developed. Multi objective optimization method was employed in designing the compositional distribution of this ceramic tool material. The results of both continuous and intermittent cutting tests are indicative of the much better cutting behavior of the functionally gradient ceramic tool FG 2 than that of the common ceramic tool SG 4.

Synergistically Toughening Effect of SiC Whiskers and Nanoparticles in Al_2O_3-based Composite Ceramic Cutting Tool Material

In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al2O3-SiCw-SiC np advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al2O3 matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al2O3-SiCw-SiCnp composite with both 20 vo1% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al2O3-SiCw-SiCnp is 730＋ 95 MPa and fracture toughness is 5.6 ± 0.6 MPa.m1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.

Strengthening and Toughening Effect of Yttrium on Al_(2)O_(3)/TiCN Ceramic Tool Material

The strengthening and toughening effect of yttrium on an advanced Al2O3/TiCN ceramic tool material was studied by means of SEM 9 TEM and energy spectrum analysis. Results showed that yttrium can react with the impurity elements such as W, Fe, Cr, etc. Thus, the interfaces between ceramic phases are purified and the interfacial binding strength is increased. As a result, the mechanical properties of the AL2O3/TiCN ceramic tool material reinforced with yttrium are improved significantly. In addition, the effect of yttrium on particle strengthening of the solid solution TiCN may partly contribute to the improvement of the mechanical properties.

Effects of Rare Earth Elements on Wear Resistance of Ceramic Tool Materials

Through the addition of Y, Sm and Ce in Al2O3/(W, Ti)C ceramic matrix, it was found that the amount and kind of the added rare earth elements have some different influences on the mechanical properties and wear resistance of the composite. Under the present experimental conditions, the flank wear curves of the selected ceramic tool materials when machining the hardened tool steel obeyed the wear law well. But wear resistance of different ceramic materials varied with each other. Wear resistance of rare earth ceramic tool materials was higher than that of the corresponding materials without rare earth. Wear modes of the developed Al2O3/(W, Ti)C series rare earth ceramic tool materials were mainly flank wear and accompanied with slight crater wear.

Influence of tool material and rotational speed on mechanical properties of friction stir welded AZ31B magnesium alloy

In this investigation,the effect of friction stir welding(FSW)parameters such as tool material rotational speed,and welding speed on the mechanical properties of tensile strength,hardness and impact energy of magnesium alloy AZ31B was studied.The experiments were carried out as per Taguchi parametric design concepts and an L9 orthogonal array was used to study the influence of various combinations of process parameters.Statistical optimization technique,ANOVA,was used to determine the optimum levels and to find the significance of each process parameter.The results indicate that rotational speed(RS)and traverse speed(TS)are the most significant factors,followed by tool material(TM),in deciding the mechanical properties of friction stir processed magnesium alloy.In addition,mathematical models were developed to establish relationship between different process variables and mechanical properties.

In-situ Fabricated TiB_2 Particle-whisker Synergistically Toughened Ti(C,N)-based Ceramic Cutting Tool Material

The mechanical properties of ceramic cutting tool materials can be modified by introducing proper content of nanoparticles or whiskers.However,the process of adding whiskers or nanoparticles has the disadvantages of high cost and health hazard as well as the agglomeration;although a new in-situ two-step sintering process can solve the above problems to some extent,yet the problems of low conversion ratio of the raw materials and the abnormal grain growth exist in this process.In this paper,an in-situ one-step synthesis technology is proposed,which means the growth of whiskers or nanoparticles and the sintering of the compact can be accomplished by one time in furnace.A kind of Ti（C,N）-based ceramic cutting tool material synergistically toughened by TiB_2 particles and whiskers is fabricated with this new process.The phase compositions,relationships between microstructure and mechanical properties as well as the toughening mechanisms are analyzed by means of X-ray diffraction（XRD）and scanning electron microscopy（SEM）.The composite which is sintered under a pressure of 32 MPa at a temperature of 1700℃in vacuum holding for 60 min can get the optimal mechanical properties.Its flexural strength,fracture toughness and Vickers hardness are 540 MPa,7.81 MPa·m（1/2）and 20.42 GPa,respectively.The composite has relatively high density,and the in-situ synthesized TiB_2 whiskers have good surface integrity,which is beneficial for the improvement of the fracture toughness.It is concluded that the main toughening mechanisms of the present composite are whiskers pulling-out and crack deflection induced by whiskers,crack bridging by whiskers/particles and multi-scale particles synergistically toughening.This study proposes an in-situ one-step synthesis technology which can be well used for fabricating particles and whiskers synergistically toughened ceramic tool materials.

X38CrMoV5 hot-work tool steel as tool material for thixoforging of steel:Numerical and experimental evaluation

Although thixoforming of low melting point alloys as aluminum or magnesium is now an industrial reality,thixoforming of high melting point alloys as steel is still at the research level.High working temperature,die wearing and production rate are problems that must be solved and are under investigation.The aim of this work is to evaluate the thermal and mechanical loadings applied to the tools during the steel thixoforging process in order to determine whether classical hot-work tool steel can be an appropriate tool material.This evaluation has been realized thanks to experimental trials and to simulations on the finite elements code Forge2008.The effect of the loadings on the tool's failure modes are highlighted and compared with the ones observed in classical hot forging.Beyond this,the failure modes of hot-work tool steel,the X38CrMoV5 or H11,were presented.

Experimental Study on Material Surface Modification of Tool Steel

This paper presents the surface temperature behavior of M42 high-speed tool steel samples during N+ implantation in an industrialized GLZ-100 metal-ion implantation machine. A detail study has been made on the parameters of N+ implantation. Optimized technical parameters have been presented. The microhardness of the sample surface implanted under these parameters has been increased by a factor of 2.3, and the wear-resistance has been improved by about 5.4 times. The research on the mechanism of surface modification of M42 steel by nitrogen ion implantation has also been made.

Microstructure and wear properties of YT758/CuZnNi hardfacing materials

Hardfacing materials containing YT758 hardmetal particles cemented by Cu-based alloy was deposited on the substrate to produce milling tools by oxy-acetylene flame process. Microstructure and wear properties of the hardfacing layers were analyzed by scanning electron microscopy(SEM) and electron dispersion X-ray spectroscopy(EDXS) and wear test. The results show that inter-diffusion zone is found at the interface of YT758/CuZnNi, which promises to improve the bonding strength of YT758/CuZnNi. The wear resistance of YT758/CuZnNi hardfacing layers is higher than that of YG8/CuZnNi hardfacing layers. The working efficiency of the milling tools strengthened by YT758/CuZnNi is approximately 23 times higher than that strengthened by YG8/CuZnNi.

艺术语言的更新与革命

各门类艺术史的后半段由艺术语言的更新和革命两个阶段构成,前者是量变,后者是质变。“更新”指特定门类艺术中艺术语言系统的材料、工具和技术三要素发生了独立或组合性革新,从而为该门类艺术带来一定程度或某种意义上的新改观。“革命”则指特定门类艺术的艺术语言系统围绕材料、工具、技术和视野四要素发生了独立或合成性重大变革,从而导致原门类艺术之衰微或崭新的门类艺术之产生,为艺术领域带来全局性的、持久的、深刻的影响。

“五位一体”创新教学模式在材料科学与工程基础教学中的应用

材料科学与工程基础是材料学专业的一门重要的专业基础课。作者针对当前学生思维活跃,接受能力强,但理论基础较差,偏好实践性、互动性、多样性教学过程的现状,对该课程采取融合实物演示、趣味课堂活动、科研工具软件演示、趣味实践作业和实物激励法的“五位一体”创新教学模式,从而在课程教学中做到以学生为主体,注重与学生的互动,提升学生学习热情和兴趣,让重难点知识点变得通俗易懂,充满趣味,还有效锻炼学生的动手能力,提高学生思考创新能力,激发、巩固、提升学生对专业的学习兴趣和综合素质。

硬质合金涂层刀具车削GFRP的切削力研究

研究了硬质合金涂层刀具车削玻璃纤维增强复合材料时,切削用量对切削力的影响,并通过正交试验建立了切削力经验公式。结果表明:切削速度引起的树脂软化对切削力的影响较大,切削分力随切削速度的增加先减后增,但切削速度由243 m/min增至342 m/min时,切削力变化趋于平缓;切削力随进给量和背吃刀量的增加而增大,但在进给量为0.05 mm/r时,由于涂层刀具刃口的挤压作用,轴向切削力反而较大。正交试验和极差分析表明,背吃刀量对切削合力及各切削分力的影响最大,切削速度对切削合力及轴向分力Fx和径向分力Fy的影响次之,进给量对主切削力Fz的影响较切削速度大。

考虑结合面特性影响的机床整机有限元静力学分析模型

针对机床数字化设计中典型结合面建模精度误差较大的问题,提出了一种采用虚拟材料等效结合面静力学特性的方法,建立了考虑结合面特性影响的机床整机有限元静力学分析模型,并完成了相应的静刚度测试实验。首先,综合考虑了弹塑性变形机制和摩擦力的影响,提出了一种新的结合面法向和切向刚度的分析模型;其次,根据不同类型结合面的特点,采用虚拟材料模拟结合面的刚度特性,建立了刚度特性与虚拟材料弹性模量和泊松比的关系,并将其应用于精密数控机床整机的静刚度分析;最后,开展了整机工艺系统的静刚度测试实验,得到了主轴末端X、Y、Z三个方向的刚度分别为26.60 N/μm、41.87 N/μm和40.17 N/μm,并将其与仿真数据进行了对比。研究结果表明:不考虑结合面影响的模型相对误差将近17%,而考虑结合面影响的模型相对误差在5%以内,验证了考虑结合面特性影响的机床整机有限元静力学分析模型的有效性;采用虚拟材料等效结合面静力学特性的方法可作为机床数字化设计的一种可行的方法。

贝壳仿生陶瓷刀具材料制备与力学性能研究

以Al_(2)O_(3)-(W,Ti)C为基体层,Al_(2)O_(3)-TiC为夹层,采用热压烧结工艺制备了力学性能较好的贝壳仿生陶瓷刀具材料,对材料的层数、层厚比和界面形状等叠层结构参数进行优化,测试材料的力学性能,并对其微观组织进行分析。分析结果表明,当层数为3、层厚比为3时,材料有较好的综合力学性能。在层间引入不同的界面形状,刀具材料的力学性能相较于无界面形状的刀具材料得到了提高,在所制备的试样中,最佳的断裂韧性、维氏硬度和抗弯强度分别为7.16MPa·m^(1/2)±0.04MPa·m^(1/2),20.40GPa±0.07GPa和981.72MPa±10.86MPa。

弹性基体软固结磨料磨具的材料去除机理

基于弹性磨具的磨抛工艺为硬脆材料超精密加工效率与加工质量的兼顾平衡提供了新的解决思路,但其磨抛过程的材料去除机理尚未明确。为研究弹性磨抛过程中的材料去除行为,以硅橡胶作为磨具基体材料,混合微米级金刚石磨料制备弹性基体软固结磨料磨具,利用有限元仿真分析方法研究弹性基体软固结磨粒的受力状态,结合接触力学与运动学分析建立考虑单颗磨粒磨损行为与有效磨粒数量的材料去除模型,通过石英玻璃试件的弹性磨抛加工试验验证预测模型的准确性。结果表明:石英玻璃试件的材料去除率随着磨抛压力、主轴转速、磨具偏角的增大而显著增加,而磨料粒径对其影响程度较小;当工艺参数组合为磨料粒径100μm、磨抛压力7 N、主轴转速1500 r/min、磨具偏角20°时,经60 min磨抛后,工件已加工表面粗糙度由1.069μm降至0.089μm,材料去除率为8.893×10^(8)μm^(3)/min;该试验条件下,建立的材料去除模型预测准确度相比Preston经典模型提高36.7%。研究成果可为实现硬脆材料的确定性材料去除提供技术支持和理论依据。

先进复合材料用模具材料及结构形式现状与发展趋势

复合材料制件的制备一般在模具中进行,在材料固化的同时完成复合材料制件成型,因而模具直接影响复合材料制件的尺寸及表面精度。随着先进复合材料制件在航空航天等领域应用的显著增长,为满足对复合材料产品不断提高的性能和精度要求,多种模具材料及结构形式应运而生,为复合材料制件的高精密制造提供了丰富的加工方式。总结了用于复合材料制造的模具材料由使用传统材料到殷钢、轻质复合材料及新型材料的发展过程,针对不同成型工艺及复合材料制件结构类型,对复合材料成型模具的结构形式进行了论述,并探讨了复合材料成型模具的发展方向。

用于碳纤维复合材料钻削的金刚石涂层刀具制备及结构优化

本文针对传统硬质合金涂层刀具钻削碳纤维复合材料(CFRP)使用寿命短、加工后工件易产生毛边等缺陷、孔加工粗糙度波动大的问题,制备并对比了不同涂层结构和不同刃口结构的金刚石涂层刀具的加工性能。结果表明,利用金刚石涂层刀具进行CFRP材料的钻削加工时,微晶金刚石(MCD)/纳米金刚石(NCD)复合结构比单一MCD涂层结构的耐磨性更好,使用寿命更长;通过减小钻头倒锥、钻尖角,增大槽前角、钻尖容屑槽前角和背宽优化刃口结构后,金刚石涂层刀具加工孔径粗糙度平均值显著降低,粗糙度极差由4.105µm下降至0.848µm。

医用防护服粉碎装置设计

为提升粉碎装置对医用防护服混合物的粉碎性能,需对粉碎装置进行优化设计。采用模块化设计与粉碎过程分析的方法,对医用防护服粉碎装置的动刀安装角度与刀架安装布局进行改进设计,使用ADAMS对优化前后的粉碎装置进行仿真模拟。结果表明:将粉碎动刀的安装角度由水平安装提升至与水平方向呈60.8°的夹角后,粉碎装置对医用防护服的剪切力提升了34%;动刀刀架以间隔15°的方式进行布局,刀架工作时所受到的应力由3960 N下降至660 N;对医用防护服混合物剪切时,优化后的单辊式粉碎机刀架布局角速度波动范围由625~820°/s降低至700~800°/s,角加速度无明显波动,振动明显降低。