碳纤维复合材料小孔加工的试验研究

针对碳纤维复合材料小孔加工比常规尺寸的孔加工更困难,制孔质量和尺寸精度难易保证的问题,采用硬质合金麻花钻进行碳纤维增强树脂基复合材料直径3mm小孔的钻削试验,研究工艺参数、刀具磨损对切削力和制孔质量的影响。结果表明:转速和进给速度对制孔轴向力和孔径误差均有显著影响;回归分析得到了轴向力与转速和进给速度之间的关系式;转速对孔径误差的影响大于进给速度的影响;硬质合金麻花钻加工碳纤维复合材料的合格孔数为30个,孔径误差随刀具磨损量的增大而增大。研究结果可以对碳纤维复合材料小孔加工的切削力进行预测,为加工参数和刀具寿命的合理选择提供试验依据。     

T800级碳纤维复合材料螺旋铣磨制孔工艺研究

碳纤维复合材料由于具备强度高、各向异性、层间强度低等特点,加工时易产生毛刺、分层等损伤,是典型的难加工材料。本文针对碳纤维复合材料制孔出入口处易损伤的问题,对金刚石磨头端面进行锥角过渡改进设计,并采用螺旋铣磨工艺,探索T800级碳纤维复合材料轻量化低损伤加工方法,通过正交试验设计研究了刀具结构和工艺参数对制孔质量的影响。试验结果表明:与传统金刚石磨头相比,金刚石磨头端面锥角在60°时,轴向力从75N降至53.5N,降幅28.7%,径向力从35.5N升至128N,涨幅264%,并能获得较为理想的制孔质量,可以实现T800级碳纤维复合材料轻量化加工。     

复合材料叠层结构制孔技术

针对碳纤维复合材料与钛合金叠层制孔质量差、效率低的问题,通过有限元仿真计算和切削试验相结合的方法,研究了碳纤维复合材料与钛合金叠层制孔切削机理,分析了面向刀具结构、几何参数和制孔工艺参数等因素,建立刀具结构、切削力、刀具磨损等数学模型,实现了碳纤维复合材料叠层制孔的刀具设计技术。     

单向带复合材料ADU制孔刀具设计及验证

针对复合材料叠层ADU钻孔刀具开发测试周期长、样刀试制成本高以及制孔易损伤等问题,利用数控加工设备和ADU工具以相同的加工参数测试不同刃型的直柄硬质合金刀具,比较刃型结构对复合材料制孔质量的影响,确定最优结构后定制螺纹柄刀具开展ADU制孔验证,寻求一种便捷快速、成本较低的刀具开发路径,解决复合材料ADU制孔损伤问题,为复合材料叠层ADU钻孔刀具的选型测试提供参考,提高刀具开发效率,降低生产研发成本。     

TiSiC涂层钻头钻削CFRP/TC4钛合金叠层材料的研究

为解决碳纤维复合材料/钛合金叠层材料制孔刀具使用寿命短的问题,本文提出采用Ti Si C涂层来提高刀具耐用度,并研究了Ti Si C涂层钻头钻削碳纤维复合材料/钛合金叠层材料时的轴向力、刀具磨损和孔出口质量。结果表明,Ti Si C涂层刀具能减小钻削钛合金的轴向力,延长刀具寿命和改善孔出口质量,且制孔一致性良好,有利于提高钻孔质量和刀具寿命。     

C/E复合材料螺旋铣削制孔方法抑制缺陷产生的机理

传统钻削加工碳纤维/环氧树脂(Carbon/epoxy,C/E)复合材料时容易产生加工缺陷,而螺旋铣削作为一种新的制孔方法在航空材料的加工中逐渐受到关注。为分析螺旋铣削制孔方法抑制缺陷产生的机理,以传统钻削加工为参照,分别利用螺旋铣削及传统钻削两种方法对C/E复合材料进行制孔试验,并对螺旋铣削与传统钻削刀具的运动轨迹进行分析。在具有相同的加工效率及刀具切削速度的基础上,对两种加工方法的加工参数进行优化。进行制孔对比试验,并对制孔过程中的切削温度、切削力及加工质量进行检测与分析。结果表明,切削温度是影响C/E复合材料制孔质量的重要因素,且由于螺旋铣削制孔时的切削温度显著低于传统钻削制孔温度,因此螺旋铣削制孔质量明显优于传统钻削制孔质量。螺旋铣削制孔时的切削温度较传统钻削时降低69℃以上,降幅大于36%,因此有效避免了制孔出口处的撕裂及分层现象。     

复合叠层材料制孔过叠层阶段声发射分析

复合叠层材料钻孔加工时,伴随着刀具的磨损,会产生丰富的声发射信号。刀具在加工叠层材料接触面时会引起声发射信号突变,为研究该过程信号的突变规律,采用硬质合金钻头与碳纤维复合材料-铝合金叠层板件开展了一系列实验,采集制孔过程中刀具的声发射信号,对信号进行了时频域多分辨率分析。研究表明,在刀具从复合材料加工至铝合金过程中,信号强度逐渐降低,高频段成份逐渐增加。     

钻头几何角度对CFRP和钛合金叠层制孔的影响

针对碳纤维复合材料(CFRP)与钛合金叠层结构钻孔刀具寿命低、出入口质量不易保证、影响加工质量和制孔效率等问题。以钻头螺旋角、外缘后角和顶角为主要研究对象,进行试验方案设计,揭示钻头几何角度对叠层结构制孔切削力及出入口质量的影响规律,表明:碳纤维复合材料与钛合金叠层结构制孔的钻头最佳几何角度:螺旋角25°左右,顶角140°左右,外缘后角12°左右。     

复合材料成型分层缺陷在钻削横刃挤压阶段的扩展行为

碳纤维增强复合材料由于具有高比强度、高比模量等优异性能,广泛应用于先进装备的承力构件中。此类复材构件在铺放固化成型过程中易产生随机分布的分层缺陷,若缺陷区域与构件连接孔加工区域交叠,将使制孔损伤产生机制更加复杂、加工质量更难以保证。为保障碳纤维复合材料构件的加工质量,揭示成型分层缺陷对制孔质量的影响机制,针对钻削过程中成型分层缺陷的动态演化行为进行研究,得到其在钻削过程中轴向力最大的横刃挤压阶段发生扩展的临界条件以及扩展长度的计算方法。基于此,结合钻削试验对预埋分层缺陷在制孔过程中的扩展行为进行在线观测,最终获得刀具作用位置对缺陷扩展行为的影响。该研究成果将为后续有关复材成型缺陷在钻削过程中扩展的抑制方法研究提供基础,也将为丰富复材损伤抑制理论作出贡献。     

航空叠层材料制孔技术研究现状与发展趋势分析

为有效的减轻飞机质量和燃料成本,复合材料/金属叠层材料已广泛应用于现代飞机的高科技部件。综述了包括CFRP/铝和CFRP/钛叠层材料制孔技术的最新进展,主要涵盖了制孔加工刀具、金属切屑排除、金属材料毛刺、切削温度等方面。文献综述表明,有多种方式可改善加工品质:1)改善航空叠层材料的制孔刀具;2)有效的排除金属切屑,减少对复合材料的损伤;3)预防和减少钛合金和铝合金毛刺的形成;4)有效的冷却方式,减少复合材料的热损伤。     

液体润滑剂的黏度对边界滑移影响的实验研究

为了了解微纳米间隙中流体的流动特性,采用原子力显微镜对微纳米间隙中的固体和液体边界滑移进行了实验研究,主要研究了液体润滑剂的黏度对边界滑移的影响。实验中采用的固体样品为SiO2,液体样品为两种不同黏度的季戊四醇油酸酯,分子式为C77H140O8,黏度分别为32mm2/s和150mm2/s。采用相对速度法对实验数据进行了处理,结果表明,不同黏度的季戊四醇油酸酯和SiO2表面作用时都会发生边界滑移,黏度大,产生的滑移大。其原因是,随着黏度升高,邻近固体表面的液体分子与和固体表面相接触的液体分子之间的剪切力增大,可更加容易地克服固液界面间的作用力,更加容易产生边界滑移。     

A dual-purpose positioner-fixture for precision six-axis positioning and precision fixturing: Part II. Characterization and calibration

The kinematics, stiffness, and repeatability of a moving groove, dual-purpose positioner-fixture were determined experimentally. A dual-purpose positioner-fixture is an alignment device that may be operated in a fixture mode or a six-axis nanopositioning mode. When operated in fixture mode, experiments show standard deviation in repeatability of 11, 11, and 38 nm in x, y, and z; and 0.7, 0.3, and 0.3 μrad in θ_x, θ_y, and θ_z. The stiffness characteristics were shown to match predictions within 5%. When operated in nanopositioner mode, the device demonstrated 4 nm resolution and a range, of 40 μm × 40 μm × 80 μm in translation and 800 μrad × 800 μrad × 400 μrad in rotation. The fixture possesses a load capacity of 450 N and a natural frequency of 200 Hz when the fixture is preloaded to 225 N.     

A Further Discussion on Trends in the Development of Advanced Manufacturing Technology

This paper is a supplement to “Trends in the Development of Advanced Manufacturing Technology” (Yang and Wu in Chin. J. Mech. Eng., 39: 73, 2003) but delves deeper into it. It first points out the strategic status of manufacturing industry in state development. Then, a detailed analysis is given on the features and trends in the development of advanced manufacturing technology in a total of 12 points from three aspects: “precision,” “extreme,” and “culture” from the aspect of the product itself; “green,” “rapidness,” “saving,” and “efficiency” during the manufacturing process; and “digit,” “auto,” “integration,” “networking,” and “intelligence” in view of the manufacturing method. In addition, it emphasizes that all the above aspects should be based on two base points: “manufacture” and “machinery.” Finally, it puts forth the guiding ideologies for the development of advanced manufacturing technology and the aspects China should give priority to in development, while stressing on the principles of independence, innovation and “human orientation.”     

Loading strategies for a class of just-in-time manufacturing system

In this paper, based on the group technology and the just-in-time manufacturing concepts, two loading models for optimal utilisation of the processing capabilities of an integrated manufacturing system consisting of a set of heterogeneous workstations are developed. These loading models are developed to integrate and utilise the available information from both the bill of materials and the process plans. The objective functions for these models are: the maximum tardiness and the makespan. In these models, the production quantity of each customer order for any part or product always equals its corresponding demand quantity; each part requires a finite number of aggregated stages of operation; job splitting is allowed; and the processing priorities of all the jobs during the planning time horizon are specified based on a desirable dispatching rule. The proposed mathematical programming models are fixed charge problems which are solved by compatible mixed integer programming algorithms. Finally, to provide additional decision-making capabilities, based on these models and their corresponding solution algorithms, a compatible decision support system is suggested.Notation l(1 toL) the product index - t(1 toN) the component (e.g., job type) index - i(1 toN) the job type priority index - j(1 toM) the workstation index - r(1 toR) the processing stage priority index - k(1 toK) the due date priority index - J _i,j,r,k the job with the job type priority indexi of the customer with the processing stage priority indexr and the due date priority indexk which has to be processed at the workstationj - L _i,r,k the number of units of the job with the job type priority indexi of the customer with processing stage priority indexr and the due date priority indexk (e.g. demand quantities) - t _i,j,r the required time to perform the processing stage priority indexr of each unit of the job with the job type priority indexi at the workstationj - D _i,r,k the due date of the job with the job type priority indexi of the customer with the processing stage priority indexr and the due date priority indexk - s _i,j,r the required time for setting up the workstationj for processing the job with the processing stage priority indexr, and the job type priority indexi - X _i,j,r,k the number of units of the job with job type priority indexi of the customer with the processing stage priority indexr, and the due date priority indexk to be produced at the workstationj - l _i,j,r,k the idle time at the workstationj prior to processing the job with the job type priority indexi and the processing stage priority indexr with the due date priority indexk - V the maximum tardiness - W the makespan of the operation - Y _i,j,r,k=1 ifX _i,j,r,k>0 - Y _i,j,r,k=0 ifX _i,j,r,k=0 - _i,j,r,k a sufficiently large constant (e.g. _i,j,r,kL _i,r,k)     

Preparation of ultrafine α -Al2O3 using precipitation-azeotropic distillation method

Ammonium aluminum carbonate hydroxide (AACH) was prepared by a precipitation-azeotropic distillation method, which uses aluminum sulfate as the Al source and ammonium carbonate as the precipitant. Then, AACH was calcined into ultrafine α-Al₂O₃ powder. The factors that influence the dispersion property of ultrafine α-Al₂O₃ powder are discussed in this paper, such as the methods of adding materials, surfactant, and drying methods. The changes of the structure and property of ultrafine alumina in the thermal treatment process are also studied. The morphological structure and properties of AACH are characterized by DTA/TGA, SEM, XRD, and ICP measurements. The results show that ultrafine α-Al₂O₃ powder with a uniform particle size and well-distributed property can be synthesized only after aluminum sulfate atomizes into ammonium carbonate, proper amount of PEG1000 is added as the dispersant, and the product is treated by azeotropic distillation. The phase transformation of alumina during the calcination process can be described as amorphous Al₂O₃→γ-Al₂O₃→ϑ-Al₂O₃→α-Al₂O₃. The crystal grain size and density of ultrafine alumina powder increase with the increase of the calcination temperature. After AACH has been calcined at 1200°C for 2 h, the ultrafine α-Al₂O₃ with uniform particle size, spherical shape, and more than 99.97% purity is obtained and its powder is well dispersed. __________ Translated from Journal of Hunan University of Science & Technology (Natural Science Edition), 2007, 22(2): 35–39 [译自: 湖南科技大学学报(自然科学版)]     

高速数控加工中NURBS曲线拟合及插补技术的研究

通过分析现代数控系统中自由曲面插补算法的特点,提出了基于最小二乘法的NURBS曲线拟合算法和基于弧长参数补偿的NURBS插补技术。采用最小二乘法拟合NURBS曲线,能获得光滑的刀具加工路径,并且在一定范围内能复原曲线的设计轮廓。参数补偿的NURBS插补方法,以泰勒展开法得到的插补参数作为临时插补点,利用该插补法能显著减小速度波动,可将速度控制在理想的范围内,可进一步提高加工精度并减小数控机床的振动。仿真实验表明：该算法简明高效、易于实现,能够满足现代数控系统的要求。     

Antimicrobial effect,frictional resistance,and surface roughness of stainless steel orthodontic brackets coated with nanofilms of silver and titanium oxide: a preliminary study

Nano‐silver and nano‐titanium oxide films can be coated over brackets in order to reduce bacterial aggregation and friction. However, their antimicrobial efficacy, surface roughness, and frictional resistance are not assessed before. Fifty‐five stainless‐steel brackets were divided into 5 groups of 11 brackets each: uncoated brackets, brackets coated with 60 µm silver, 100 µm silver, 60 µm titanium, and 100 µm titanium. Coating was performed using physical vapor deposition method. For friction test, three brackets from each group were randomly selected and tested. For scanning electron microscopy and atomic‐force microscopy assessments, one and one brackets were selected from each group. For antibacterial assessment, six brackets were selected from each group. Of them, three were immediately subjected to direct contact with S. mutans. Colonies were counted 3, 6, 24, and 48 h of contact. The other three were stored in water for 3 months. Then were subjected to a similar direct contact test. Results pertaining to both subgroups were combined. Groups were compared statistically. Mean (SD) friction values of the groups 'control, silver‐60, silver‐100, titanium‐60, and titanium‐100' were 0.55 ± 0.14, 0.77 ± 0.08, 0.82 ± 0.11, 1.52 ± 0.24, and 1.57 ± 0.41 N, respectively (p = .0004, Kruskal–Wallis). Titanium frictions were significantly greater than control (p < .05), but silver groups were not (p > .05, Dunn). In the uncoated group, colony count increased exponentially within 48 h. The coated groups showed significant reductions in colony count (p < .05, two‐way‐repeated‐measures ANOVA). In conclusions, all four explained coatings reduce surface roughness and bacterial growth. Nano‐titanium films are not suitable for friction reduction. Nano‐silver results were not conclusive and need future larger studies.     

Wear behavior of low-cost, lightweight TiC/Ti–6Al–4V composite under fretting: Effectiveness of solid-film lubricant counterparts

The wear behavior of low-cost, lightweight 10 wt% titanium carbide (TiC)-particulate-reinforced Ti–6Al–4V matrix composite (TiC/Ti–6Al–4V) was examined under fretting at 296, 423, and 523 K in air. Bare 10 wt% TiC/Ti–6Al–4V hemispherical pins were used in contact with dispersed multiwalled carbon nanotubes (MWNTs), magnetron-sputtered diamond-like carbon/chromium (DLC/Cr), magnetron-sputtered graphite-like carbon/chromium (GLC/Cr), and magnetron-sputtered molybdenum disulfide/titanium (MoS₂/Ti) deposited on Ti–6Al–4V, Ti–48Al–2Cr–2Nb, and nickel-based superalloy 718. When TiC/Ti–6Al–4V was brought into contact with bare Ti–6Al–4V, bare Ti–48Al–2Cr–2Nb, and bare nickel-based superalloy 718, strong adhesion, severe galling, and severe wear occurred. However, when TiC/Ti–6Al–4V was brought into contact with MWNT, DLC/Cr, GLC/Cr, and MoS₂/Ti coatings, no galling occurred in the contact, and relatively minor wear was observed regardless of the coating. All the MWNT, DLC/Cr, GLC/Cr, and MoS₂/Ti coatings on Ti–6Al–4V were effective from 296 to 523 K, but the effectiveness of the MWNT, DLC/Cr, GLC/Cr, and MoS₂/Ti coatings decreased as temperature increased.     

Design of a six-axis micro-scale nanopositioner—μHexFlex

This paper presents the design of a small-scale nanopositioner, the μHexFlex, which is comprised of a six-axis compliant mechanism and three pairs of two-axis thermo-mechanical micro-actuators. In this paper, we cover the modeling, design and fabrication of the μHexFlex. Specific attention is given to: (1) the use of constraint-based design in generating the compliant mechanism design, (2) the modeling of the actuators, and (3) the system model which links the actuator input and mechanism response. The measured, quasi-static performance of a 3 mm diameter prototype shows a maximum range of 8.4 μm × 12.8 μm × 8.8 μm and 19.2 mrad × 17.5 mrad × 33.2 mrad (1.1° × 1.0° × 1.9°). Experimental results indicate that a constant mechanical/electrical material property system model may be used to predict the position and orientation over a range of 3.0 μm × 4.4 μm × 3.0 μm and 6.3 mrad × 6.3 mrad × 8.7 mrad (0.36° × 0.36° × 0.5°). The dynamic characteristics of the device were investigated experimentally. Experimental results show a lowest natural frequency of 4 kHz. The resolution characteristics of the device have been measured at 1 Å/mV. The device was created using deep reactive ion etching (DRIE). Bulk fabrication costs are estimated at less than $ 2 per device.     

Microstructure and electrical properties of NaNbO3-BaTiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x) NaNbO3-xBaTiO₃ have been fabricated by a traditional ceramic sintering technique. The effects of BaTiO₃ (BT) synthesized by hydrothermal method on crystal structure, density, dielectric, piezoelectric, and electromechanical properties were investigated. Results show that the phase structure transforms from the orthorhombic phase to the tetragonal phase with the increase of the content of BT, and the two phases co-exist when 0.08<×⩽0.10. However, the optimum composition for (1 − x)NaNbO₃-xBaTiO₃ ceramics is 0.90NaNbO₃-0.10BaTiO₃. The 0.90NaNbO₃-0.10BaTiO₃ ceramics sintered at 1250°C have higher properties: piezoelectric constant d ₃₃ of 120 pC/N, dielectric constant ε_τ of 718, planar electromechanical coupling factor k _p of 24%, planar frequency N _d of 3 MHz·mm, and the mechanical quality factor Q _m of 138, respectively. The results show that the (1−x)NaNbO₃-xBaTiO₃ ceramics is one of the promising lead-free materials for high-frequency applications.