液压冲孔数值模拟

采用DEFORM 2D有限元模拟软件研究液体压力、冲头直径以及管坯壁厚的变化对液压冲孔过程的影响,获得冲头推力、冲孔后纵向塌陷尺寸和塌陷区域面积在不同控制参数下的变化趋势,并进行工艺实验验证。结果表明:管内液体压力增加、冲头直径增加、材料壁厚增加都会使冲头推力增大;冲头直径和液体压力对塌陷影响较大,随着冲头直径的增加和内压的降低,塌陷深度尺寸和塌陷区域面积都明显加大,材料壁厚对塌陷尺寸的影响较小。     

管材性能对液压冲孔质量的影响(英文)

通过对3种不同材料的管材液压冲孔的实验研究,分析管材材料性能对液压冲孔质量的影响。研究表明:不同材料对塌陷形成的影响不同,材料的屈服强度越高,液压冲孔后的塌陷越大。塌陷尺寸随着内压的降低而增大,在同一内压下,沿管长方向塌陷变化较慢,沿垂直管长方向塌陷变化快。不同材料对断口质量的影响不同,材料屈服强度越高,断面质量越好,材料较软时,撕裂现象更明显。     

管材脉动液压成形时接触压强与液体压强关系的研究

采用商业有限元软件ABAQUS,建立了管材液压成形有限元模型,分别在非脉动和脉动液压加载下对管材液压成形过程进行了有限元仿真,并通过试验对有限元模型进行了验证。研究结果表明:在不同脉动液压振幅和频率加载下,接触压强均小于液体压强,而且随着管材的胀形,接触压强逐渐接近液体压强,当胀形结束时,接触压强与液体压强的差值为20%左右;脉动液压振幅越大及频率越高,则接触压强波动也越大;脉动液压振幅越大,接触压强越接近液体压强,但在脉动液压频率大小合适时,接触压强最接近液体压强。     

液压拉深工艺与模具

<正> 液压拉深工艺是利用充满液体的液压模腔代替刚性凹模,在拉深过程中,高压液体作用在金属板材上,所以金属板材不仅受凸模作用,而且还由于高压液体的反向压力,使板材紧贴凸模成形。其工作原理下面将详     

波节管液压成形过程的数值分析与实验研究

通过理论计算和有限元模拟的方法计算了液压成形波节管的成形压力,并进行实验验证。通过液压成形实验研究了波节管壁厚分布,并分析了适当提高成形压力对波节管尺寸精度的影响。通过爆破实验分析了液压成形波节管的内压爆破性能。结果显示:理论计算、数值模拟得到的成形压力与实验结果较为一致,提高成形压力不能明显的改善波节管的尺寸精度;成形后的波节管直管段管壁最厚,波峰处壁厚减薄量最大;波节管壁厚从波峰到直管段并不是单调增大,在过渡段边缘,壁厚局部减薄严重;经过液压成形得到的波节管内压爆破性能要优于原始光管。     

立式磨粉机液压系统关键参数研究

在分析了典型高压辊式立磨液压加压系统主要工作原理的基础上,对液压系统缓冲过程进行了理论研究,并在AMESim环境下建立了该液压系统的仿真模型。重点分析了蓄能器充气压力与液压系统保压能力和液压缸活塞杆运动位移之间的关系,以及不同的料层厚度变化量对液压系统保压压力和液压缸活塞杆运动位移的影响。结果表明:蓄能器总容积越大,液压缸压力变化幅值越小,当容积大到30 L以上时,缓冲效果即不再有明显改善;蓄能器连接油管直径越大,缓冲效果越好,内径在18 mm以上时效果比较好;蓄能器充气压力越大,系统保压能力越强,但过大的充气压力会引起缓冲过程中液压缸活塞杆振动过大;料层厚度变化量的增加会同时引起液压缸活塞杆振动幅值和液压缸压力峰值的增大。     

液压导管疲劳破裂与液体压力关系的研究

在分析液压导管破裂类型的基础上,重点分析了液体压力作用与液压导管破裂的关系。结果表明：导管内液体压力在弯管处产生与导管轴线垂直的横向载荷,在椭圆截面导管周向产生拉伸和弯曲载荷;横向载荷、拉伸载荷、弯曲载荷与液体压力成正比;因液体压力脉动形成的作用于液压导管的交变载荷是造成液压导管疲劳破裂的主要因素之一。     

SS304微型管件的液压胀形

微型管件液压成形技术是金属微管在高压液体的作用下产生塑性变形后贴合模具,从而成形出截面形状复杂的微型管件的技术。通过拉伸试验和胀形试验分别研究了SS304微管的材料性能的尺寸效应和微管壁厚、晶粒尺寸对微管成形性能的影响,结果发现,SS304微管随着壁厚的减小,表现出"越薄越强"和"越薄越脆"的尺寸效应;SS304微管的胀破压力和抗拉强度的比值与宏观尺度下的管件的胀破压力和抗拉强度的比值偏离较大,导致这种偏差的主要原因与SS304微管材料性能的尺寸效应有关。     

新型管材冲击液压成形装置的设计

针对常规的管材液压成形技术需要昂贵的专用设备及模具、生产效率低等不足,开发了一种简单实用、可在冲床或压力机上使用的管材冲击液压成形装置,可用于薄壁金属管材的自然胀形、轴压胀形和异形截面中空件的冲击液压成形。该装置无需外部高压供给系统和专用液压成形设备,通过撞击轴压头挤压容腔中液体的方式来为管材提供液压力和轴压力。通过设计轴压头的行程和调节溢流阀的溢流压力值等来实现最大液压力和轴向进给量的合理匹配,并以304不锈钢毛细管和H65黄铜毛细管为试验管材做了相关试验。研究结果表明:该装置结构简单、操作方便;可实现最大液压力与轴向进给量的协调控制;合理的载荷匹配能显著地提高管材冲击液压成形的成形性能;H65黄铜毛细管破裂时所需的液压力小于304不锈钢毛细管破裂时所需的液压力。     

大采高液压支架立柱系统动态特性研究

大采高液压支架供液管路的工作压力为23～32.5 MPa、通流直径为38～60 mm、管路长度为1 000～1 500 m,供液管路具有明显压力、流量响应滞后效应,导致立柱缸液压系统的速度、位移动态特性较差。对液压支架大通径高压供液管路进行水锤试验,试验结果为:在流量为182.7、351.2和521.5 L/min时,压力波速分别为715、979和1 065 m/s。建立了AMESim管路模型和液压支架系统模型,分析管路长度、管路通径和初始压力对液压支架立柱动态特性影响规律。仿真结果表明:管路长度越大,管路通径越大,管路初始压力越小,立柱响应时间越长,升柱和降柱过程平稳性高,所用时间增长。     

异形截面管充液成形工艺及过程优化

异形截面管件广泛应用于汽车底盘结构件领域,它不仅可以充分利用材料的强度和刚度,而且是实现结构轻量化的重要措施之一。对汽车底盘变截面管件进行研究,利用有限元软件Dynaform建立了QSTE340低碳钢管材充液成形的有限元模型。研究了充液成形过程中管材预制坯形状、初始屈服压力、整形压力及推头轴向进给量对成形结果的影响,并通过试验验证了仿真分析的准确性。研究结果表明:在异形截面管零件成形过程中,管材预制坯各截面周长与最终零件各截面周长相近时,可以提高成形质量;当初始屈服压力为70 MPa、整形压力为200 MPa、轴向补料量为25 mm时,可以成形出合格零件。     

Axial crush of hollow cylindrical structures with various polygonal cross-sections: Numerical simulation and experiment

The crush behaviors of hollow cylindrical structures with various regular polygonal cross-sections are numerically investigated under axial compression using the FEM program code of the public domain version of DYNA3D. The effects of wall thickness and plastic hardening rate of material on the crush behavior are also investigated. Crush strength increases as the number of corners of the cross-section increases, though it almost saturates for the number of corners beyond 11. Cross-sectional shape with less than six corners should be avoided to take a regulated collapse pattern. The effect of number of polygonal corners on enhancement in crush strength becomes more prominent as the initial wall thickness decreases. Higher plastic hardening rate stabilizes the collapse pattern, where it is a symmetric accordion mode in circular cross-section, otherwise asymmetric diamond one occurs. Further, for hollow cylindrical structures with circular or square cross-section which are aluminum alloy extrusions, quasi-static and impact axial compression tests and the corresponding computations are carried out. As for the circular cross-section, the number of corners induced during collapse increases as the initial wall thickness decreases both in the experiment and the numerical simulation. Crush strength is lower for square cross-section than that for circular one. This tendency agrees with the computational result.     

焊接工艺参数对锆合金薄板YAG激光焊接气孔形成的影响及控制机理分析

以Zr-4和N18为研究对象,采用YAG激光焊接设备,通过抛切焊缝断面统计气孔数量,并观察焊缝中气孔位置和形貌,研究了非熔透性焊接过程中激光脉冲电流、脉冲宽度、离焦量等工艺参数以及脉冲激光调制对锆合金密集焊缝激光焊接气孔形成规律的影响。结果表明:在锆合金YAG激光非溶透性焊接过程中,气孔的形成主要源于焊接过程中匙孔的不稳定塌陷所形成的工艺型气孔,在熔池中气泡逸出熔池的速率低于熔池金属凝固速率的情况下会产生气孔。在满足焊缝熔深1.0 mm的情况下,随着激光脉冲电流、脉冲宽度的增加,气孔出现的几率逐步增加;随着离焦量的增加,气孔出现的几率逐渐减小;相比未分段编程模式,采用分段编程、电流缓降、降低焊接速度的方式,使焊缝气孔率明显降低,气孔尺寸有效控制在0.5 mm以下。     

热挤压法生产紫铜电脑散热片的研究

分析了电脑散热片产品的截面形状特点和该产品在挤压过程中的模具工况，从模具的强度出发，优化设计了一套分流挤压模具，用高温挤压成形技术进行电脑散热片实心型材成形实验。研究结果表明：通过减小悬臂承受的压力和受力面积以及转化悬臂的受力形式等结构优化设计，可以使悬臂的受力和变形减小，保证和加强了模具的强度，分流挤压模具没有出现任何失效形式，并保证了挤压制品的质量。利用SEM技术对产品焊合部位组织进行分析，产品的分流焊合部位和非分流焊合部位的组织都很致密，焊合质量较好。     

氧化锆陶瓷微孔钻削加工工艺试验研究

针对氧化锆陶瓷钻削微孔过程中出现的轴向力大和出口崩边严重的问题，使用直径为0.2 mm的金刚石涂层钻头钻削完全烧结的氧化锆陶瓷微孔，通过单因素试验方法，研究主轴转速、进给速度和步进距离对轴向力的影响，在此基础上开展啄钻工艺对比试验，探索变进给啄钻工艺对出口崩边尺寸的影响。结果表明：轴向力大小随着进给速度和步进距离的增加而增大，随着主轴转速的增加先降低后增大；采用变进给啄钻可以有效提高孔出口加工质量。     

基于数值模拟的厚板精冲挤压过程分析

针对厚板精密冲裁过程存在的缺陷(塌角与毛刺等),基于Deformed2D分析了10mm厚钢板精密冲裁过程中双齿V形压料板对冲裁质量的影响.采用V形压料板可在一定程度上减小塌角的高度,但不能完全消除.随后采用精冲挤压方法对这一厚板的成形过程进行了分析,结果表明:采用精冲挤压成形工艺后,厚板零件表面塌角得到了完全消除,零件...     

Sheet forming of flax reinforced polypropylene composites using vacuum assisted oven consolidation (VAOC)

Fibre reinforced plastics are widely used in different industry sectors since the past half century. Considerable research has been carried out on natural fibres as reinforcements because of their light weight, good mechanical properties, biodegradability, sustainability and higher stiffness per unit mass compared to glass fibres. This paper develops a knowledge base for the manufacture of vacuum assisted fibre reinforced thermoplastic composites inside a simple oven from sheets of the fibre and the thermoplastic. The compaction behaviour of the reinforcements used was investigated and used to target a range of achievable fibre volume fractions to manufacture the composites. The reinforcements were also characterized on the basis of their transverse permeability to quantify the ease of polymer flow through the reinforcements. An experimental setup was designed to measure the relevant processing parameters during the experiment. Thickness, pressure and temperature of the composites were monitored with applied vacuum pressure and oven temperature during the experiments. The mould temperature inside the oven was first increased to the melting temperature of the thermoplastic, held at that temperature for a certain time period and then cooled subsequently. The application of compaction pressure and the holding time was varied to study its effect on consolidation quality. The achieved fibre volume fraction of the manufactured composites was calculated by first using the average thickness of the composites and then using the density of the composite. The cross-section of the laminates was examined under an optimal microscope to evaluate the quality of consolidation. Tensile and short beam shear tests were performed to assess structural integrity, strength and stiffness of the composites. The results show that this manufacturing technique can produce composites at expected fibre volume fractions under vacuum. The cooling rate, applied temperature, pressure and sheet layup were found to have considerable effects on the fibre volume fraction. It was also found that the mechanical properties of natural fibre reinforced thermoplastic composites (NFRTS) do not change appreciably even after modifying the process so as to reduce the manufacturing time.     

内压对薄壁铝合金管材充液压弯过程的影响

采用实验和数值模拟研究5A02铝合金薄壁管材充液压弯成形过程中内压对缺陷的影响规律,分析内压对弯曲内侧起皱、截面畸变及壁厚分布的影响,获得壁厚变化规律;通过数值模拟给出的应力状态,揭示缺陷形成机制。结果表明:提高内压能降低轴向压应力的绝对值,减小失稳起皱趋势,当内压超过一个临界值时,皱纹完全消除。对于直径为63 mm、壁厚为1 mm的5A02-O铝合金管材,其内压临界值为2.8 MPa。充液有效地减小截面畸变程度,随内压的增大,截面畸变程度逐渐减小。弯曲后,壁厚最大减薄点位于弯曲外侧点,且随内压的增大,轴向和环向拉应力均呈增大趋势,弯曲外侧壁厚度减薄的趋势也增大。     

Effect of interface wetting on flattening of freely fallen metal droplet onto flat substrate surface

A free-falling experiment was conducted as a simulation of a thermal spray process. The flattening behavior of the freely fallen metal droplet impinged onto a flat substrate surface was investigated in a fundamental way. The substrates were kept at various temperatures, and the substrates were coated with gold by physical vapor deposition (PVD) and were prepared in order to investigate the effect of wetting at the splat-substrate interface on the flattening behavior of the droplet. A falling atmosphere was created with atmospheric pressure of nitrogen to prevent the oxidation of the melted droplet. Experiments under low-pressure conditions also were conducted. The different types of splat morphology were recognized in experiments conducted under a nitrogen atmosphere with atmospheric pressure. The splat morphology on a substrate at room temperature was of the splash type, whereas that on a substrate at high temperature was of the disk type. The microstructure observed on a cross-section of the splat obtained on the substrate at room temperature was an isotropic coarse grain, whereas that on the substrate at high temperature was a fine columnar grain. The grain size changed transitionally with increasing substrate temperature. The temperature of the transition on the gold-coated substrate was higher than that on the naked substrate. The microstructure of the cross-section of the splat obtained under low pressure was finely columnar even on the substrate at room temperature. The results indicate that the metal droplet wets better under the low-pressure condition than under the atmospheric pressure nitrogen condition and that wetting has a significant role in the flattening of the droplet.