Experimental and Finite Element Study of Steady State Micro-cutting Characteristics of Aluminum Alloy (2A12)

This paper studies the micro-cutting characteristics of aluminum alloy (2A12) based on a series of orthogonal experiments and finite element method (FEM) simulations. An energy-based ductile failure law was proposed in the FEM simulation. The simulated cutting forces and chip morphology were compared with experimental results. The simulation result indicates that there is a close relationship between the cutting force and cutting heat. The micro-cutting force decreases as the heat flux vector increases. Both the cutting heat and the micro-cutting force need a finite time to achieve a steady state. It is observed that with the cutting speed of 169.95 m/min and uncut chip thickness of 6 μm, the heat flux vector in the workpiece increases to a stable value after 0.06 ms; meanwhile, the principal cutting force decreases to a steady state correspondingly, i.e., the micro-cutting process achieves the steady state. It is concluded that the steady state micro-cutting simulation can reflect the cutting process accurately.

Establishment and Growth of Potato Micro-Cuttings in Sand Trays

Two separate experiments were conducted to evaluate the success of the establishment and growth of micro-cuttings of potato (5 - 6 cm tall) in sand trays [38 cm (L) × 28 cm (W) × 7.5 cm (H) plastic trays] under controlled environment (22?C ± 2?C, 60 - 75 μmosm–1?s–1 light energy for 16 h daily). In the first experiment, micro-cuttings of potato cv. Diamant were planted at six populations (500, 600, 700, 800, 900 and 1000 cuttings per tray) in treated sand (sun dry, 1% formaldehyde, 0.2% Dithane M-45 and control). The mortality percentage of micro-cuttings was nil for sun dry sand while formaldehyde and dithane M-45 treated sand had 1% - 4% against 15% in the control with the highest population density. Mortality of micro-cuttings in formaldehyde and dithane M-45 treated sand trays were found not to be related to pathogenic organism rather toxic effect of these two chemicals. Micro-cuttings in Sun dry and control treatments showed better growth performance than these in chemically treated sand trays. In the second experiment, urea @ 1, 2 and 3 g per tray was applied as solid form after 15 days of planting the micro-cuttings and as liquid form @ 0.5, 1 and 2% solution sprayed in the micro-cuttings repeatedly after 15, 30, 45 and 60 days of planting. The micro-cuttings which received urea as solid state died within 2 - 3 days and 2% urea solution was also detrimental. Urea solution @ 0.5% found to be very effective for vegetative growth of micro-cuttings in sand trays. The control was also good for vegetative growth but at a slower rate.

Chip Formation in Micro-cutting

The miniaturisation context leads to the rise of micro-machining processes. Micro-milling is one of the most flexible and fast of them. Although it is based on the same principles as macro-cutting, it is not a simple scaling-down of it. This down-sizing involves new phenomena in the chip formation, such as the minimum chip thickness below which no chip is formed. This paper presents a review of the current state of the art in this field from an experimental and a numerical point of view. A 2D finite element model is then developed to study the influence of the depth of cut on the chip formation. After the model validation in macro-cutting, it highlights the phenomena reported in literature and allows to perform a minimum chip thickness estimation.

Magneto-plasticity in micro-cutting of single-crystal copper

The plasticity of metals can be significantly affected by the application of a magnetic field,otherwise known as the magneto-plastic effect.This paper investigates the magneto-plastic effect in the microcutting of a non-magnetic ductile material,single-crystal copper,under a weak magnetic field and reports the influence of the phenomenon on the cutting forces and machined surface quality.A softening effect was observed from the large reduction in cutting forces from 3.2 N to 1.5 N under the magnetic field.As compared to the magnetic field intensity and polarity,the variation in magnetic field orientations with respect to the cutting direction exhibited a stronger influence on the cutting force,chip morphology,machined surface texture,subsurface microstructure,surface roughness,and machined surface microhardness of the copper sample.An analytical model was developed based on the geometry of the cutting chips to correlate the orientation-dependent influence of the magnetic field on the cutting forces.On the surface quality,excessive folds with four different types of morphology produced under magnetic-free cutting were suppressed after applying the magnetic field with the most significant improvement achieved with the 90°magnetic field direction.The magnetic-assisted changes in machined surface morphology also led to the reduction in machined surface roughness and microhardness.The optimistic micro-cutting outcomes in this work establish a greater understanding of the magneto-plastic effect and demonstrate the applicability of magneto-plasticity in ultraprecision manufacturing.

Effect of a weak magnetic field on ductile-brittle transition in micro-cutting of single-crystal calcium fluoride

Magneto-plasticity occurs when a weak magnetic field alters material plasticity and offers a viable solution to enhance ductile-mode cutting of brittle materials.This study demonstrates the susceptibility of non-magnetic single-crystal calcium fluoride(CaF_(2))to the magneto-plastic effect.The influence of magneto-plasticity on CaF_(2) was confirmed in micro-deformation tests under a weak magnetic field of 20 mT.The surface pile-up effect was weakened by 10-15 nm along with an enlarged plastic zone and suppressed crack propagation under the influence of the magnetic field.Micro-cutting tests along different crystal orientations on the(111)plane of CaF_(2) revealed an increase in the ductile-brittle transition of the machined surface with the aid of magneto-plasticity where the largest increase in ductile-brittle transition occurred along the[112]orientation from 512 nm to a range of 664-806 nm.Meanwhile,the subsurface damage layer was concurrently thinner under magnetic influence.An anisotropic influence of the magnetic field relative to the single-crystal orientation and the cutting direction was also observed.An analytical model was derived to determine an orientation factor M that successfully describes the anisotropy while considering the single-crystal dislocation behaviour,material fracture toughness,and the orientation of the magnetic field.Previously suggested theoretical mechanism of magneto-plasticity via formation of non-singlet electronic states in defected configurations was confirmed with density functional theory calculations.The successful findings on the influence of a weak magnetic field on plasticity present an opportunity for the adoption of magnetic-assisted micro-cutting of non-magnetic materials.

Calculation of the intracellular elastic modulus based on an atomic force microscope micro-cutting system

Better understanding of variations in the mechanical properties of cancer cells could help to provide novel solutions for the diagnosis,prevention,and treatment of cancers.We therefore developed a calculation model of the intracellular elastic modulus based on the contact pressure between the silicon tip of an atomic force microscope and the target cells,and cutting depth.Ovarian cells(UACC-1598) and colon cancer cells(NCI-H716) were cut into sequential layers using an atomic force microscope silicon tip.The cutting area on the cells was 8μm×8μm,and the loading force acting on the cells was increased from 17.523 to 32.126μN.The elastic modulus distribution was measured after each cutting process.There were significant differences in contact pressure and cutting depth between different cells under the same loading force,which could be attributed to differences in their intrinsic structures and mechanical properties.The differences between the average elastic modulus and surface elastic modulus for UACC-1598 and NCI-H716 cells were 0.288±0.08 kPa and 0.376±0.16 kPa,respectively.These results demonstrate that this micro-cutting method can be used to measure intracellular mechanical properties,which could in turn provide a more accurate experimental basis for the development of novel methods for the diagnosis and treatment of various diseases.

微细刀具研究现状分析与探讨

诸多行业对于微小零件、产品的迫切需求推动了微制造技术的高速发展。微细切削技术作为最具潜力的微制造技术之一,可在金属、陶瓷、聚合物和复合材料等中高效、准确地生成复杂特征,被广泛地运用于医疗、通信与航空航天等领域。微细刀具作为影响微细切削技术加工质量的关键因素,受到了业界与研究学者们的广泛关注。回顾并讨论了微细刀具相关的最新成果和发展,重点讨论分析了微细铣刀、微细车刀、微细钻头和微细磨头4种典型微细刀具的研制现状与使用性能,并对其失效分析与监测以及刀具涂层进行了详细介绍。最后,强调了微细刀具未来可能的发展趋势和研究方向,以期为微细刀具的研究学者提供重要的参考。

杜梨组培快繁及组培苗微扦插技术研究

以种子来源的4个杜梨株系组培苗为试材,采用植物组织培养和组培苗微扦插的方法,研究了不同浓度细胞分裂素6-BA和IBA处理对杜梨丛生芽增殖的影响以及不同浓度IBA和生长素(NAA)处理对杜梨组培苗离体生根和微扦插生根的影响,以期为稳定高效杜梨组培快繁体系的建立提供参考依据。结果表明:基因型和6-BA浓度对杜梨增殖系数具有极显著影响,IBA浓度对增殖系数具有显著影响;低浓度的生长素更适合用于杜梨组培苗的生根诱导。综合考虑组培苗增殖和生根情况,DL30株系表现最优,其适宜的增殖培养基为MS+1.0 mg·L^(-1)6-BA+0.2 mg·L^(-1)IBA,增殖系数为3.4±0.35,适宜的生根培养基为1/2MS+0.2 mg·L^(-1)IBA,生根率达60.0%±20.0%。IBA和NAA蘸根处理对杜梨组培苗微扦插生根有显著影响,杜梨株系DL30组培苗通过1000 mg·L^(-1)的IBA蘸根处理后微扦插生根率为46.7%±8.8%。

任豆组培再生研究

为完善任豆Zenia insignis组培快繁技术,研究采用微枝扦插的组培再生方式,探讨了基本培养基中NO-3、K+、Ca2+不同含量,以及不同植物生长调节剂种类与浓度对任豆组培芽增殖与生根效果的影响,结果表明:(1)任豆种子用75%酒精、0.1%升汞分别浸泡灭菌10,30 min,再用始温为85℃无菌水浸种24 h效果最好,种子萌芽快,种子发芽率可达92.16%;(2)RD基本培养基中NO^(-)_(3)、K^(+)、Ca^(2+)含量分别以600,360,330mg/L为最优配比,最佳继代培养基配比为RD+6-BA 0.2 mg/L+NAA 0.01 mg/L,20 d增殖系数可达3.32;(3)NAA对任豆组培芽生根以及生长有极显著的影响,最佳生根培养基配比为1/2 MS+NAA 0.5 mg/L+AC 1.0 g/L,生根率可达100%,且根系粗壮发达,组培苗生长健壮,叶片浓绿舒展。

基于ABAQUS的YW1织构刀具切削仿真与试验研究

在硬质合金刀具表面植入微织构有利于提高刀具的切削性能。为深入探究织构化刀具对TC4钛合金加工性能的影响,设计一定几何参数的织构化刀具,通过调整刀具织构参数和加工参数对TC4钛合金进行切削仿真与试验分析,从切削力、切削温度、刀具磨损、切屑形貌、加工工件表面质量等方面评价刀具的切削性能。结果表明:带有微织构的硬质合金刀具对改善工件应力分布状态有积极作用,能降低切削力,缓解刀具瞬间的高温聚集,减小磨损面积,改善切屑的形貌,形成良好的工件表面质量;在不同形态织构刀具中,横向沟槽织构刀具(T3)改善切削力和降温效果最优,圆形织构刀具(T4)温度梯度分布最优;微织构的存在一定程度上提高了刀具的抗黏附性能,其中,横向沟槽织构刀具(T3)前刀面处磨损面积最小,减摩抗黏性能最好,能形成较好的工件表面质量。

基于ABAQUS的微织构刀具切削钛合金仿真研究

构建无织构刀具和呈微凹坑、平行槽、垂直槽、斜向槽形貌的微织构刀具模型,并利用有限元分析软件ABAQUS研究了微织构刀具对钛合金车削过程的影响。通过分析不同形貌微织构刀具在切削过程中的切削力、摩擦系数、切削温度和工件表面残余应力,确定了较优的微织构形貌;研究了切削速度对微织构刀具切削钛合金性能的影响。结果表明,微织构刀具能有效降低切削力、摩擦系数和切削温度,使工件表面残余应力由拉应力转变为压应力,其中垂直槽微织构刀具能最有效地改善切削质量;随着切削速度的提高,切削力和切削温度增大,摩擦系数减小,工件表面残余应力由压应力向拉应力转变并有增大的趋势。

多线切割保公差工艺对烧结钕铁硼永磁体表面质量的影响

采用多线切割保公差工艺切割烧结钕铁硼永磁体,利用SJ-410粗糙度仪、JMS-6010LA型扫描电子显微镜对微观形貌及表面粗糙度R_(a)进行表征。结果表明:随着进给速度增高和线速度的降低,金刚石磨粒压入深度减小,微观形貌由深犁沟、凹坑、破损变为浅犁沟、浅凹坑和破碎,材料去除机理由塑性去除变为塑性变形。粗糙度R_(a)随着进给速度和线速度的增高而减小;进给速度和线速度对法向载荷呈相反作用,在不同工艺参数下的材料去除方式中,塑性变形和塑性去除占据主导作用,进给速度10 mm/h和线速度1190 m/min的粗糙度最低,表面质量最优。切割时间只与进给速度有关,线弓随着进给速度增加,随线速度降低。

微坑织构刀具切削Ti-6Al-4V性能仿真研究

为揭示刀具表面织构形貌对刀具切削性能的影响,以微坑织构和无织构硬质合金刀具为研究对象,使用仿真软件AdvantEdge建立Ti-6Al-4V三维正交切削模型,研究不同微坑直径对刀具切削力、切削温度的影响。结果表明,直径为70μm的微坑织构刀具的综合切削性能更好,主切削力和背向力分别降低了14.3%和15.2%,同时前刀面高温区域面积小且峰值温度低。微坑织构刀具在不产生衍生切削的前提下,微坑直径越大,刀—屑接触面积越小,刀具切削性能越好。

微型排桩支护结构在隧道明洞段的应用

为探索微型排桩在高陡边坡明洞段支护结构中的适应性,基于二维杆系荷载-结构模型,提出三排桩支护结构设计计算方法;结合工程案例拟定多种钢管排桩+锚索支护方案,对排桩支护结构的内力及变形特征、不同方案的适应性、钢管桩直径的影响等进行深入研究。结果表明:1)排桩支护中,前排桩、中排桩、后排桩具有几乎相同的内力和变形特征,但前排桩的变形和内力值略大于其他2排桩,前排桩坑底位置是整个支护结构中最不利部位;2)采用增设锚索、预留压脚岩体等方式降低相邻支撑间的竖向间距,可以有效降低支护结构位移和内力,从而使支护结构变形满足相关规范要求;3)随着桩径的增大,钢管桩刚度增大,支护结构水平位移呈指数形式降低;4)增加三排桩直径和仅增加前排桩直径均可以有效降低支护结构变形。支护结构设计中,可以根据开挖高度、施工机械、地形地貌等,选择合适的支撑方式和钢管桩直径,从而实现支护结构快速、机械化施工。

微纳织构涂层刀具切削性能研究进展

刀具磨损严重、服役寿命短仍然是切削加工所面临的难题。随着现代制造业的发展,钛合金、高温合金等难加工材料在工业中广泛运用。但由于这些材料具有低导热系数、变形系数小等特点,在机械加工中存在切削力和切削温度高、刀具磨损严重等问题,严重缩短了刀具的服役寿命。通过表面织构技术和表面涂层技术在刀具切削表面置入微纳织构和涂层可以显著改善切削性能;特别是在减小刀具磨损、降低切削力、切削温度以及刀-屑接触界面摩擦因数等方面具有显著效果。系统概述微纳织构涂层刀具的作用机理、切削性能以及应用领域,对微纳织构涂层刀具后续发展有重要推动意义。首先,介绍微纳织构涂层刀具的制备方式。其次,分析总结微纳织构涂层刀具的作用机理,并从抗磨损性、抗粘结性和刀具寿命三个方面总结微纳织构涂层刀具的自身性能。随后,从切削力、切削温度、刀-屑接触处的摩擦因数三个方面总结微纳织构涂层刀具的切削性能。最后对微纳织构涂层刀具在现代制造业中的应用进行阐述。提出在刀具切削表面同时置入微纳织构和涂层的当前研究现状以及未来发展方向,可为进一步研究微纳织构涂层刀具在切削加工中改善切削性能以及加工表面质量与性能提供参考。

微量润滑工况下纳米粒子协同微织构对刀具切削性能的影响

目的探究微量润滑工况下纳米粒子与织构协同作用对刀具切削性能的影响及其变化规律。方法通过有限元数值模拟软件ABAQUS对不同工况下刀具的等效塑性应变、等效应力以及切削力的变化进行仿真和预测评估。同时,通过切削试验进行验证分析,并结合刀具前刀面的磨损状态、前刀面磨损区主要元素含量、切屑形貌及其变化以及已加工表面质量对刀具的切削性能进行综合评价,以探究纳米粒子与织构刀具的协同作用对刀具切削性能的影响机制。结果仿真结果表明,N-O-M切屑的等效塑性应变较小,切屑层较薄,与N-O-T相比,最大等效应力值降低了26.4%,平均切削力为232N,刀具减摩效果最为明显;不同工况下平均切削力误差均控制在10%以内,试验值与仿真值高度一致;N-O-M磨损面积仅为1.95×10^(-2) mm^(2),刀具表面无明显的黏结物和崩刃现象,磨损面积仅为N-O-T的39.8%;N-O-M切屑卷曲半径最小,已加工工件表面脊线较长,工件表面质量较优。结论微量润滑工况下纳米粒子与表面织构的协同作用对提高刀具切削加工性能具有重要意义。微液滴在一定的压力下能渗入刀-屑界面接触区形成液膜,织构沟槽中的纳米粒子随着液膜中润滑介质的流动能够周期性释放到摩擦副的接触表面,持续作用于切削区域改变原有的摩擦接触状态和润滑方式,促进摩擦副间摩擦形式由滑动摩擦向滚动摩擦状态转变,实现减摩降磨的目标。

组合微织构刀具切削钛合金仿真研究

为提升刀具切削钛合金过程中的切削性能,考虑微织构形貌之间的交互作用,设计了微坑-微槽组合微织构刀具,并利用DEFORM-3D有限元模拟软件模拟组合微织构刀具切削钛合金的过程。以微织构刀具的刀具前角、切削速度和背吃刀量为因素变量设计了三因素三水平的正交试验,分析各试验因素对切削过程中主切削力的影响。结果表明:在组合微织构刀具切削钛合金过程中背吃刀量对切削力的影响最大,刀具前角次之,切削速度对切削力的影响程度最小,其最优组合为刀具前角为10°,切削速度为60 m/min,背吃刀量为0.1 mm;同时,组合微织构刀具在切削钛合金过程中,背吃刀量越小,切屑的卷曲程度越好;在不同背吃刀量的条件下,刀具前角对切屑形态的影响较为明显。

不同工艺参数对FeCoNiCrMnAl_(x)高熵合金微铣削加工性能影响研究

为探究FeCoNiCrMnAl_(x)(x=0、0.6、1)高熵合金的微铣削加工性能,采用单因素实验法,分析不同主轴转速、每齿进给量、铣削深度等工艺参数对其微铣削力、切削比能和表面粗糙度的影响。结果表明:Al_(1)合金的铣削力最大,表面质量最差;Al_(0)合金由于较低的铣削力、切削比能和表面粗糙度而具有更好的可加工性;3种合金的微铣削力和表面粗糙度均随主轴转速和每齿进给量的增加先增大后减小,随铣削深度的增加而增大;为降低合金的铣削力和表面粗糙度,可以适当提高主轴转速和每齿进给量,降低铣削深度。

SLM成形件切削比能模型建立及影响因素分析

选区激光熔融(SLM)成形件在通过后处理加工提升表面质量时会消耗大量能量,而通过优化切削比能可以提高材料去除率和降低切削力,进而减小加工过程中的能量消耗。因此以SLM Inconel 718成形件为研究对象,建立基于切削力的切削比能模型。结合微铣削正交实验,拟合得到SLM Inconel 718微铣削切削比能与铣削参数的经验公式,并研究不同铣削参数对切削比能的影响规律。结果表明,SLM Inconel 718切削比能经验公式拟合程度在95%以上,切削深度对切削比能影响很小,切削比能随主轴转速和每齿进给量的增加而增加。

巧设Δ用微元思想解决物理问题

微元法是分析、解决物理问题常用的方法,微元法可以把复杂的物理过程简化为学生熟知的简单的物理过程、物理规律.以3个问题为例,在分析和解决问题过程中通过微元法巧妙设置Δl、ΔT、Δθ,避开繁杂运算过程,旨在培养学生从局部到整体的科学思维和提高学生运用核心知识解决问题的能力.