3D逆向技术在复杂曲面产品反求设计中的应用

运用3D扫描技术,结合正、逆向建模软件,对失效零件的较复杂表面进行逆向反求设计。对复杂曲面的特征情况进行数据采集和点云处理,并通过Geomagic Design X进行逆向数字建模,重构3D数字模型。对重构后的曲面进行精度与质量分析,并通过UG软件进行曲面优化。反求得到修复3D数字模型后,应用UG基于此数字模型对复杂表面进行数控编程,然后加工出复杂曲面产品模型实体来进行验证。研究表明,逆向设计技术是产品实现再生设计的重要手段,可以为曲面修复实现高质、高效、低成本提供指导意义。     

基于Geomagic Design Direct的正逆向混合建模创新设计

混合建模设计是正向设计与逆向设计的结合,提出了一种基于Geomagic Design Direct软件的正逆向混合建模的方法。通过数据采集、点云预处理、曲面重构,然后编辑曲面、实体特征造型以及参数化修改获得最终CAD模型。以游戏手柄模型为例,应用Geomagic Design Direct软件的强大功能对零件点云数据进行混合建模创新设计,实现了游戏手柄的快速还原以及对产品进行第二次创新。实验结果表明,通过Geomagic Design Direct软件实现混合建模技术,能高效的对原始模型进行创新设计。     

基于曲面和实体特征的混合逆向建模方法研究

当前,逆向工程中以还原原始设计意图和面向再设计为主要目的逆向建模方法是研究的热点方向。通过对基于曲面和基于实体特征的逆向建模方法进行分析和研究,提出一种基于曲面和实体特征的混合逆向建模方法,并阐述了这种混合逆向建模方法的建模流程和应用领域。以逆向建模软件Geomagic Studio和Geomagic Design Direct为平台,通过典型实例验证了这种混合逆向建模方法的可行性和优势所在,为基于逆向工程的复杂几何模型的重构和再设计提供了一种有效的解决方法。     

面向航空企业的工装快速准备研究

为了降低工装准备时间,缩短产品制造周期,在分析某航空企业工装准备业务流程的基础上,提出了基于制造资源集成平台的工装快速准备系统,建立了系统体系结构,划分了系统功能模块.最后对实现工装快速准备的相关关键技术进行了介绍.     

基于分层设计结构矩阵的航空产品工装模块划分

工装模块划分是航空产品工装模块化设计的关键环节。为提高航空产品工装模块划分的准确性,提出基于分层设计结构矩阵的航空产品工装模块划分方法。基于航空产品工装结构图建立分层设计结构矩阵,通过遍历构建全局设计结构矩阵,并运用聚类分析法得到工装模块划分的初始解,之后应用联系成本计算方法对划分结果进行评价,获得最优的模块划分方案。以某型号航空散热器焊接总装夹具为例,验证了该设计方法的有效性和可行性。     

基于CATIA二次开发的逆向工程曲面重构方法研究

针对利用逆向工程中扫描点云数据,提取特征轮廓曲线与生成曲面时,工作量较大且容易出问题,提出一种基于特征数据提取与CATIA二次开发的正逆向相结合的曲面重构方法。以Geomagic Studio软件完成对扫描点云数据的预处理,针对不同产品模型的特征,提取不同的截面线与轮廓线;分析模型特征,对于简单特征模型通过旋转、拉伸、扫琼等命令重新生成新模型;对于复杂曲面造型,提取特征点云数据并导出为ASC格式文件,通过对CATIA二次开发,读入存在EXCEL中的大量点数据坐标,快速生成三维模型。结果表明:以Geomagic Studio与CATIA软件为工具,完成特征曲线提取与特征点数据读取,实现了基于截面特征与曲面特征的正逆向相结合的建模方法,为产品造型创新设计与快速建模提供一种新方式。     

基于领域划分的逆向参数化建模

近年来,逆向工程中的参数化建模方法成为研究的重要方向。通过对目前应用比较广泛的基于曲面的逆向参数化建模和基于实体特征的逆向参数化建模的方法分别进行了分析,提出了基于领域划分的逆向参数化建模方法,并详细介绍了这种参数化建模方法的优势及其参数化建模的一般流程。以逆向参数化建模软件Geomagic Design X为平台,通过典型实例参数化建模及误差分析验证了该建模方法的优势,为逆向工程的参数化建模提供了一种更加有效、准确的建模方法。     

基于Geomagic Studio的特征建模技术研究

对逆向建模方法中的特征建模方法与非特征建模方法进行了研究。以基于Geomagic studio软件的连杆模型重建为例,通过与非特征建模方法的对比,重点对特征建模过程进行了介绍和分析。并利用Geomagic Studio软件的参数转换功能,将特征建模后得到的CAD曲面导入SolidWorks软件中,实现了对特征模型的参数化修改。实际建模结果表明：特征建模能更好地表达原始产品模型的设计意图,而且其具有进一步参数化修改的能力可更好地支持产品的创新设计。     

逆向技术在模具型腔修复中的应用研究

基于逆向技术,对失效的型腔曲面特征进行数据采集、点云处理,并重构3D数字模型,并通过CAM进行数控加工。研究表明,逆向建模与制造能使模具型腔这类关键零件失效后得到复原再现,降低了生产成本,并为工艺提升与创新提供了新的有效手段。     

复杂曲面零件的逆向建模及数控加工仿真的研究

通过对逆向工程技术及CAD/CAM技术的分析,结合鼠标曲面自身特点,采用三坐标测量机对其扫描得到点云数据,利用Imageware强大的点云处理和曲面建模功能进行点云数据处理、曲线处理、曲面处理,重构曲面模型并进行误差分析。采用UG/CAM模块对Imageware生成的CAD模型进行数控加工自动编程,并通过后置处理操作得到能被机床控制器所识别的NC代码。最终经VERI-CUT实现数控加工过程仿真以验证数控程序的正确性。证明了将Imageware、UG、VERICUT结合以实现复杂曲面零件的逆向制造的方法不仅软件兼容性好、而且操作便捷,从而大大缩短了产品的设计开发周期,并提高了加工效率,为复杂曲面零件的仿制加工提供了依据。     

超声辅助对共沉淀法制备富锂锰基正极材料Li[Li_0.144Ni_0.136Co_0.136Mn_0.544]O₂性能影响的研究

通过超声辅助共沉淀法成功制备了富锂锰基正极电极材料,研究了不同的超声时间对材料形貌、结构和电化学性能的影响。研究发现,超声辅助能够使材料颗粒更加均匀,结构更合理,有利于材料电化学性能的提升。当合成前躯体材料超声时间为8h时,复合材料的放电比容量最好,在0.1C的初始放电比容量为327.8 mAh g_-1,均高于未超声的复合材料的265.2 mAh g_-1,1C下循环50圈后放电容量为181.6 mAh g_-1,保持率为84.8%。通过循环伏安法测试和电化学交流阻抗测试,发现超声后的复合材料还原氧化峰电流更大,电荷转移阻抗更小,具有较好的倍率性能。     

Investigation of the microwave dielectric properties of Ca1−xMgxLa4Ti5O17 ceramics for application in coplanar patch antenna

In this paper, the dielectric properties of Ca_1−xMg_xLa₄Ti₅O₁₇ ceramics at microwave frequency have been studied. The diffraction peaks of Ca_(1−x)Mg_xLa₄Ti₅O₁₇ ceramics nearly unchanged with x increasing from 0 to 0.03. Similar X-ray diffraction peaks of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic were observed at different sintering temperatures. A maximum density of 5.3 g/cm³ can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. A maximum dielectric constant (_r) and quality factor (Q × f) of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h are 56.3 and 12,300 GHz (at 6.4 GHz), respectively. A near-zero temperature coefficient of resonant frequency (τ_f) of −9.6 ppm/°C can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. The measurement results for the aperture-coupled coplanar patch antenna at 2.5 GHz are presented. With this technique, a 3.33% bandwidth (return loss <−10 dB) with a center frequency at approximately 2.5 GHz has been successfully achieved.     

Structure, microstructure and electrical properties of (1 − x − y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBi0.5Li0.5TiO3 lead-free piezoelectric ceramics

The ternary system (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBi_0.5Li_0.5TiO₃ (abbreviated to BNKLT-x/y) was synthesized by conventional oxide-mixed method. The phase structure, microstructure, and dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. The X-ray diffraction patterns showed that pure perovskite phase with rhombohedral structure can be obtained in all the ceramics. The grain size varied with x and y. The temperature dependence of dielectric constant and dielectric loss revealed there were two phase transitions which were from ferroelectric (tetragonal) to anti-ferroelectric (rhombohedral) and anti-ferroelectric to paraelectric (cubic). Either increasing x or y content can make T_m (the temperature at which dielectric constant _r reaches the maximum) increase. With the addition of Bi_0.5K_0.5TiO₃, the remanent polarization P_r increased but the coercive field E_c decreased. With the addition of Bi_0.5Li_0.5TiO₃, P_r increased obviously and E_c increased slightly. Due to the stronger ferroelectricity by modifying Bi_0.5K_0.5TiO₃ and Bi_0.5Li_0.5TiO₃, the piezoelectric properties were enhanced at x = 0.22 and y = 0.10, which were as follows: P_r = 31.92 μC/cm², E_c = 32.40 kV/cm, _r = 1118, tan δ = 0.041, d₃₃ = 203 pC/N and K_p = 0.31. The results show that the BNKLT-x/y ceramics are promising candidates for the lead-free materials.     

High-speed deposition of Y-Si-O films by laser chemical vapor deposition using Nd:YAG laser

Y-Si-O films were prepared by laser chemical vapor deposition (LCVD) with a Nd:YAG laser using TEOS (tetraethyl orthosilicate) and Y(dpm)₃ precursors. The effects of laser power (P_L), deposition temperature (T_dep) and total chamber pressure (P_tot) on the phase, microstructure and deposition rate of Y-Si-O films were investigated. At P_L < 102 W (T_dep < 1140 K), amorphous Y-Si-O films were obtained independent of P_tot. At P_tot = 0.6 kPa, mixture phase films of Y₂SiO₅ (the X1 phase) and Y₂Si₂O₇ (the α, β, δ and y phases) were obtained at P_L = 102 W (T_dep = 1210 K), while single phase X1-Y₂SiO₅ films were prepared at P_L > 139 W (T_dep > 1280 K). Y₂Si₂O₇ mixture phase films were obtained at P_tot = 3.5 kPa and Y₂Si₂O₇ and Y₂SiO₅ (the X2 phase) mixture phase films were obtained at P_tot = 7.5 kPa independent of T_dep. Amorphous Y-Si-O films showed a dense, glassy microstructure. Faceted columnar grains grew on the Y-Si-O films at P_tot = 0.6 kPa, whereas rounded cauliflower-like grains grew at P_tot = 7.5 kPa. The R_dep increased with increasing P_L and T_dep and reached a maximum of 430 μm h⁻¹ at P_tot = 0.6 kPa, P_L = 186 W and T_dep = 1310 K.     

Microwave dielectric properties and its compatibility with silver electrode of Li2MgTi3O8 ceramics

The effects of BaCu(B₂O₅) (BCB) additions on the sintering temperature and microwave dielectric properties of Li₂MgTi₃O₈ ceramic have been investigated. The pure Li₂MgTi₃O₈ ceramic shows a relative high sintering temperature (∼1000 °C) and good microwave dielectric properties as Q × f of 40,000 GHz, ?_r of 27.2, τ_f of 2.6 ppm/°C. It was found that the addition of a small amount of BCB can effectively lower the sintering temperature of Li₂MgTi₃O₈ ceramics from 1025 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 0.5 wt% BCB added Li₂MgTi₃O₈ ceramic sintered at 900 °C for 2 h exhibited good microwave dielectric properties of Q × f = 36,200 GHz (f = 7.31 GHz), ?_r = 26 and τ_f = −2 ppm/°C. Compatibility with Ag electrode indicates this material can be applied to low temperature-cofired ceramics (LTCC) devices.     

Temperature dependent admittance spectroscopy of GaAs/AlGaAs single-quantum-well laser diodes (SQWLDs)

In this study, the main electrical parameters, such as doping concentration (N_D), barrier height (Φ_CV), depletion layer width (W_D), series resistance (R_s) and Fermi energy level (E_F), of GaAs/Al_xGa_1−xAs single quantum well (SQW) laser diodes were investigated using the admittance spectroscopy (C-V and G/ω-V) method in the temperature range of 80-360 K. The reverse bias C⁻² vs. V plots gives a straight line in a wide voltage region, especially in weak inversion region. The values of Φ_CV at the absolute temperature (T = 0 K) and the temperature coefficient (α) of barrier height were found as 1.22 eV and −8.65 × 10⁻⁴ eV/K, respectively. This value of α is in a close agreement with α of GaAs band gap (−5.45 × 10⁻⁴ eV/K). Experimental results show that the capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the diode are affected by not only temperature but also R_s. The capacitance-voltage-temperature (C-V-T) and conductance-voltage-temperature (G/ω-V-T) characteristics confirmed that temperature and R_s of the diode have effects on the electronic parameters in SQW laser diodes.     

High sintering resistance of a novel thermal barrier coating

Sintering resistance of a novel thermal barrier coating Nd_xZr_1 − xO_y with Z dissolved in, where 0 < x < 0.5, 1.75 < y < 2 and Z is an oxide of a metal selected from Y, Mg, Ca, Hf and mixtures thereof, was studied. The coatings of Nd_xZr_1 − xO_y and typical 7YSZ were deposited by electron beam physical vapor deposition (EB-PVD) and air plasma spray (APS). The samples with the coating system of EB-PVD Nd_xZr_1 − xO_y or 7YSZ overlaid onto a MCrAlY bond coat were cyclically sintered at 1107 °C for 706 hours. The freestanding coatings of EB-PVD Nd_xZr_1 − xO_y and 7YSZ were isothermally sintered at 1371 °C for 500 hours. The microstructure of EB-PVD Nd_xZr_1 − xO_y before and after the sintering was evaluated and compared with EB-PVD 7YSZ. The sintering resistance of freestanding APS Nd_xZr_1 − xO_y coating was also investigated after isothermal sintering at 1200 °C for 50 and 100 hours. The results demonstrated that the new coatings of Nd_xZr_1 − xO_y applied with both EB-PVD and APS have higher sintering resistance than EB-PVD and APS 7YSZ, respectively.     

Mg-substituted ZnNb2O6-TiO2 composite ceramics for RF/microwaves ceramic capacitors

Microstructure and microwave dielectric properties of Mg-substituted ZnNb₂O₆-TiO₂ microwave ceramics were investigated. Mg acted as a grain refining reagent and columbite phase stabilization reagent. With an increasing Mg content, the amount of ixiolite (Zn, Mg) TiNb₂O₈ decreased, and the amount of (Zn_0.9Mg_0.1)_0.17Nb_0.33Ti_0.5O₂ and columbite increased. ZnO-Nb₂O₅-1.75TiO₂-5 mol.%MgO exhibited excellent dielectric properties (at 950 °C): ?_r = 35.6, Q × f = 16,000 GHz (at 5.6 GHz) and τ_f = −10 ppm/°C. The material was applied successfully to make RF/microwaves ceramic capacitor, whose self-resonance frequency was 19 GHz at low capacitance of 0.13 pF.     

Corrosion behavior of select MAX phases in NaOH, HCl and H2SO4

In this paper we report on the electrochemical corrosion of select MAX phases, namely Ti₂AlC, (Ti,Nb)₂AlC, V₂AlC, V₂GeC, Cr₂AlC, Ti₂AlN, Ti₄AlN₃, Ti₃SiC₂ and Ti₃GeC₂ in 1 M NaOH, 1 M HCl and 1 M H₂SO₄ solutions. Polarization characteristics recorded in 1 M NaOH show that V₂AlC, V₂GeC and Cr₂AlC undergo active dissolution at potentials more positive than the corrosion potential, while Ti₂AlC, (Ti,Nb)₂AlC, Ti₃SiC₂ and Ti₃GeC₂ passivate. In the 1 M HCl solutions, Ti₂AlC, V₂AlC and V₂GeC actively dissolve; Ti₃SiC₂ and Ti₃GeC₂ passivate. Depending on potential, (Ti,Nb)₂AlC and Cr₂AlC showed trans-passive behavior. In 1 M H₂SO₄ solutions, Ti₂AlC, (Ti,Nb)₂AlC, Ti₃SiC₂ and Ti₃GeC₂ passivate, V₂AlC and V₂GeC show active dissolution, while Cr₂AlC exhibits trans-passive behavior. Ti₂AlN and Ti₄AlN₃ were passive in all solutions except in 1 M HCl, where Ti₂AlN showed trans-passive behavior. Given that the corrosion behavior of (Ti,Nb)₂AlC is unlike either Ti or Nb, the behavior of the former cannot be predicted from that of the latter.     

Microstructure, ferroelectric, and piezoelectric properties of (1 − x − y)Bi0.5Na0.5TiO3-xBaTiO3-yBi0.5Ag0.5TiO3 lead-free ceramics

Lead-free (1 − x − y)Bi_0.5Na_0.5TiO₃-xBaTiO₃-yBi_0.5Ag_0.5TiO₃ (BNT-BT-BAT-x/y, x = 0-0.10, y = 0-0.075) piezoelectric ceramics were synthesized by conventional oxide-mixed method. The microstructure, ferroelectric, and piezoelectric properties of the ceramics were investigated. Results show that a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases of BNT-BT-BAT-x/0.04 ceramics is formed at x = 0.06-0.08. The addition of BAT has no obvious change on the crystal structure of BNT-BT ceramics while it causes the grain size of the ceramics to become more homogenous. Near the MPB, the ceramics with x = 0.06 and y = 0.05-0.06 possess optimum electrical properties: P_r ∼ 42.5 μC/cm², E_c ∼ 32.0 kV/cm, d₃₃ ∼ 172 pC/N, k_p ∼ 32.6%, and k_t ∼ 52.6%. The temperature dependences of k_p and polarization versus electric hysteresis loops reveal that the depolarization temperature (T_d) of BNT-BT-BAT-0.06/y ceramics decreases with increasing y. In addition, the polar and non-polar phases may coexist in the BNT-BT-BAT-x/y ceramics above T_d.