分流模挤压非对称断面铝型材有限元数值模拟分析

采用了一种基于Deform-3D结合Pro/Engineer的对分流模挤压过程中焊合面相互穿透网格进行重构的技术,并对空心型材分流模挤压过程中金属的流动行为、温度场及模芯受力情况进行了模拟分析。结果表明,网格重构技术对于空心型材挤压的数值模拟具有可行性,可实现焊合面与对称面不一致(非流动对称面)空心型材的分流、焊合及成形的挤压全过程的仿真,从而为研究挤压全过程(尤其是焊合过程)的金属流动行为、模具结构的合理性、变形体的温度场分布情况、焊合阶段模具的受力等提供了一种新的计算分析方法。     

三孔双芯模挤压方管型材的金属流动行为分析

为了分析双芯模挤压铝型材时造成的流动不均匀以及模具结构对该类型材焊合质量的影响,采用DEFORM-3D有限元分析软件,对三孔双芯模挤压6005A铝合金方管型材的金属流动行为进行了分析.模拟结果表明,分流孔面积分布不均易造成方管型材镰刀弯缺陷,当中间分流孔与一侧分流孔的面积比值为0.93～1.03时,型材出口流速均匀、焊缝居中.焊合室高度为13～16mm时焊合良好、成形质量好.挤压力在坯料与焊合室底面碰触后急速上升,在突破模孔时达到最高值.型材出口温度受分流孔面积和焊合室高度影响较小,当坯料温度为480℃时,型材出口温度为546～548℃.在650吨卧式挤压机上进行了挤压实验,实验结果与仿真结果吻合.     

Mg-3Zn-1Zr合金细径管材的挤压模具设计

基于Mg-3Zn-1Zr合金本构方程运用Defrom-3D软件对多种Mg-3Zn-1Zr合金细径管材的挤压模具参数的配合进行了有限元模拟分析。结果表明:挤压模入口圆角半径一定时,挤压模模角越大,挤压杆的载荷越小,挤压模圆锥段发生紊流现象越严重,挤压死区越大。挤压模入口圆角处的磨损最为严重,当挤压模模角为120°,挤压模入口圆角半径为2 mm时,模具磨损最小,挤压载荷和模具应力也较小。工作带长度超过4 mm时,随着工作带长度的增加,模具磨损深度显著增大,管材与模具易产生黏结,进而产生缺陷和变形不均匀。采用模拟优化的模具挤压出的Mg-3Zn-1Zr合金细径管材表面质量良好、尺寸精度高,说明基于Deform-3D有限元分析能够为实际模具设计与镁合金型材的生产提供可靠参考。     

挤压模具的数字化设计与数字化制造

介绍了基于数字仿真技术的挤压模具数字化设计、结构优化、产品质量预测的实现方法,以及挤压模具数字化制造的加工工艺.挤压模具数字化设计的目的是提供模具的几何、拓扑信息和挤压成形的工艺信息,其核心技术是数字化建模与数字化仿真.数字化仿真技术在挤压过程金属流动行为分析、模具结构优化、型材成形质量预测等方面已取得了良好的应用效果.采用基于仿真技术的虚拟试模方法,是实现挤压模具的“零试模”有效途径,也是形成新设计思路和设计方法的重要技术手段.大量采用CNC加工、热处理和表面处理系统是挤压模具数字化制造的主要特征.实现CAD、CAM和CAE的有效结合,提高复杂多孔空心型材挤压模具的制造技术水平,是我国挤压模具数字化制造的重要发展方向.     

大型复杂薄壁铝合金空心型材挤压成形工艺

目的 解决大型复杂薄壁铝合金空心型材挤压过程中材料流速均匀性控制难,以及模具局部应力集中导致模具寿命低、挤压型材尺寸稳定性差的问题。方法 采用有限元模拟方法对此类典型型材挤压过程进行仿真分析,根据仿真结果中型材出口材料流速分布情况,通过调控不同部位材料流入量及材料流动阻力,并以型材出口流速差和流速均方差（SDV）作为衡量挤压过程中材料流速均匀性的指标,逐步迭代优化模具结构以提高材料流动均匀性;根据仿真结果中挤压模具应力分布情况,以模具最高应力作为衡量模具强度的指标,逐步迭代优化模具结构以减小模具应力。结果 通过迭代仿真依次优化模具工作带长度、分流孔尺寸、阻流块高度等参数,最终型材出口流速差由25.07 mm/s降至2.72 mm/s,流速均方差由9.84 mm/s降至0.72 mm/s;通过迭代仿真优化焊合角度,最终模具最高应力由945 MPa降至863 MPa。采用基于有限元仿真优化结构的挤压模具成功制备了合格的铝合金型材样件,挤压试验结果与数值模拟结果吻合。结论 通过优化模具工作带长度、分流孔尺寸及阻流块高度,调控不同部位材料流入量及材料流动阻力,能够有效解决大型复杂薄壁铝合金空心...     

常用空心铝挤压模具设计技术

铝合金挤压模具在型材挤压生产过程中起着重要作用，模具设计的质量对挤压成型过程影响很大。本文以生产过程中广泛使用的平面分流组合模为例，介绍了其结构设计要素及设计过程。     

光企9007铝型材挤压模具强度与刚度校核

采用材料力学模型,对自行设计的光企9007铝合金型材挤压模具进行了理论强度与刚度校核。计算结果表明,上模分流桥、下模悬臂等危险部位均满足强度要求,下模悬臂的刚度也同样满足使用要求,证明该模具的设计合理可行。     

扁形钛铜复合棒挤压模具设计与应用

对长宽比较大的扁形截面钛铜复合棒的挤压模具进行了设计研究。通过合理选材,并选择使挤压力最小的模具模腔轮廓曲线和半模角,改变模孔工作带的几何形状与尺寸,选择适当的挤压速度等,优化设计制备出扁形钛铜复合棒专用挤压模具。增加工作带长度可以增大摩擦阻力,使向该处流动的供应体的流动静压力增大,迫使金属向阻力小的方向流动,从而使型材整个断面上金属流量更加均匀。挤压实验结果表明,合理的模具设计对挤压材的挤压过程和挤压制品质量有重要影响,锥形模具更适合于扁形钛铜复合棒的挤压。解决了科研生产实际对大的长宽比扁型钛铜复合棒的需求。     

AZ31B镁合金挤压工艺研究

在油炉中熔炼AZ31B镁合金,用熔剂保护,石墨模铸造圆锭.铸锭经400℃×12h的均匀化处理后,进行热挤压,其挤压温度为400℃,挤压速度为1～2.5m/min,挤压比为10～45.共挤出了11种规格的棒材、管材、型材(工字型、槽型、角形、方形、T形等),挤压过程中均发生了动态再结晶,其抗拉强度σb在275～285MPa之间,屈服强度σ0.2 在220～225MPa之间,延伸率δ在15%～17%之间.所制订的工艺合理,挤压出的棒材、管材、型材有较好的力学性能.     

复杂截面型材力控制拉弯成形数值模拟分析

复杂截面挤压型材的高精度拉弯成形是制造框架式车身的关键技术.本文基于动态显式有限元软件PAM-STAMP,针对一种典型的框架武车身用复杂截面挤压型材,对其力控制方式的直进台面式拉弯成形进行了数值模拟研究,对比分析了两种截面形状的型材截面畸变和回弹随补拉力增大的变形规律,并得到了摩擦系数对成形精度的影响.数值模拟结果表明,增加型材截面的变形刚度,可以显著地减小截面畸变和回弹;增加补拉力,增大了截面畸变但减小了回弹;增大摩擦系数,截面畸变量减小而回弹增加.     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar-thermal applications

Spectrally selective Al_xO_y/Pt/Al_xO_y multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both Al_xO_y layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ? ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of Al_xO_y/Pt/Al_xO_y multilayer absorber indicated the Al_xO_y layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6-10 ± 0.2 nm respectively.     

Bulk crystalline BaPb34Bi14O3: A ceramic superconductor

The preparation conditions of the high T_C ceramic superconductor Ba(Pb,Bi)O₃ is correlated with the superconducting transition. Transition onsets of all materials are similar, but transition widths and transition completeness is strongly dependent on firing temperature. Only materials prepared over a narrow temperature range, resulting in a nearly ideal weight loss, have a complete and narrow transition.     

Electrostriction in Pb (Zn13Nb23)O3

The electrostriction in $\text{Pb (Zn}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ crystals has been investigated using a strain gauge method. In the ferroelectric phase below 140 C, the strain vs the electric field shows a hysteresis, which is ascribed to the effect of ferroelectric domains. A quadratic relation holds between the strain x and the electric polarization P as x = QP² above about 170 C in the paraelectric phase. Values of the electrostrictive Q coefficients are determined from the measurements near 190 C, as Q₁₁ = 1.6·10^?2m⁴/C², Q₁₂ = ?0.86·10^?2m⁴/C², and Q₄₄ = 0.85·10^?2m⁴/C².     

Magnetic,electrical and thermal studies on the V1−xMox02

The monoclinic-to-tetragonal structure transition of oxides V_1?xMo_x0₂ with $\text{0≤}\text{x}\text{≤0.20}$ has been studied by means of DTA, X-ray diffraction, magnetic susceptibility (powder samples) and electrical conductivity (single crystals) measurements within the temperature region 80 K to 400 K. A linear decrease of the transition temperature of 11 K per atom % Mo was observed. The magnetic susceptibility of the low temperature phase was found to be temperature independent paramagnetic for all preparations. Electrical conductivity measurements on the same phase showed crystals with $\text{x}\text{? 0.04}$ to be semiconducting, while a metallic behavior was observed in the region $\text{0.10 ?}\text{x}\text{? 0.14}$.     

n-PbTep+−Pb1−xSnxTe heterojunctions prepared by a modified hot wall technique

$\text{n-PbTe}\text{p}{}^{\mathrm{+}}\text{?}\text{Pb}{}_{\mathrm{1?x}}\text{Sn}{}_{\mathrm{x}}\text{Te}$ heterojunctions with a long wavelength spectral cutoff (λ_c ≈ 6 μm) were prepared using the double-channel hot wall technique. The electrical and photoelectrical properties of the heterojunctions at 77, 197 and 300 K were investigated. Detectors with R_oA equal to 170 Ω cm² and a quantum efficiency of 25–40% were obtained. Reasons for the shift of the long wavelength spectral cutoff of the heterojunctions towards shorter wavelengths are given.     

Core-current-enhanced domain-wall pinning in nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 15.5/B/sub 7/ ribbon

We have studied the influence of surface fields H/sub p/ (generated by either direct or alternating core current) on soft magnetic properties of amorphous and nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 15.5/B/sub 7/ ribbon. While in an amorphous ribbon the coercive field H/sub c/ decreases with H/sub p/, in the same optimally annealed ribbon (H/sub c/=1.3 A/m, M/sub m//spl ap/M/sub s/) H/sub c/ increases with H/sub p/ for all the explored types of H/sub p/ (static and dynamic with different phases with respect to that of the magnetizing field H). The unexpected increase of H/sub c/ in nanocrystalline ribbon is associated with the influence of H/sub p/ on the surface and main (inner) domain structure. Here, we develop a model that takes into account this influence and explains the experimental results.     

Reactive plasma deposited SixCyHz films

Si_xC_yH_z films have been prepared at 200°C by reactive plasma deposition from SiH₄ and CH₄ diluted in helium in a tubular reactor. These films have a ratio s (equal to $\text{Si}\text{(}\text{Si+C}\text{))}$ ranging from 0.2 to 0.8, a refractive index ranging from 1.96 to 2.6 and an optical energy band gap in the range 2.7-2.2 eV. The total quantity of hydrogen in the film is 40% when s=0.5. Infrared analysis shows that these films have large fractions of homonuclear bonds and that this material is best described as a polymer. Mass spectrometric measurements of the gaseous products formed in the SiH₄-CH₄-He plasma have been performed and the results are related to the composition of the deposited layers.     

Interfacial microstructure of NiSix/HfO2/SiOx/Si gate stacks

Integration of NiSi_x based fully silicided metal gates with HfO₂ high-k gate dielectrics offers promise for further scaling of complementary metal-oxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi_x film. Ni content varies near the NiSi/HfO_x interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSi_x/HfO₂ interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSi_x/HfO_x was found higher than that of poly-Si/HfO₂, likely due to compositional non-uniformity of NiSi_x. No intermixing between Hf, Ni and Si beyond interfacial roughness was observed.