管件电磁渐进胀形的数值模拟及成形均匀性

文章将渐进成形的思想融入到传统的管件电磁胀形工艺中,提出管件电磁渐进成形的新工艺,即采用小尺寸线圈,通过移动多次成形的方式成形长管件。提出了适合于管件电磁渐进胀形工艺的顺序耦合数值模拟方法,并与一次放电、两次放电、三次放电的实验结果进行对比,模拟结果与3组实验数据均吻合。采用数值模拟的方法,进一步研究重叠率和成形顺序对管件变形均匀性的影响,研究结果表明,重叠率为50%、成形顺序为b→c→a时,可获得最佳的成形均匀性。电磁渐进成形技术应用于管件胀形工艺中具有可行性,对实际生产具有指导意义。

7075-T6铝合金在电磁成形条件下的动态变形和断裂研究

针对传统冲压工艺下7075-T6铝合金成形极限低的问题,开展了铝合金的高速率动态变形研究。采用数值模拟仿真与实验手段,探讨了7075-T6铝合金板料的动态变形过程。发现在电磁力的直接作用下,板料在变形过程中出现了明显抖动现象,使零件顶部出现凹坑,变形均匀性差。采用纯铝板进行电磁驱动成形,提高了板料的变形均匀性。进行了拉伸试样的断裂模拟和实验研究。与准静态冲压成形相比,电磁成形条件下试样在断裂前需要更大的断裂能,导致零件出现多处延性断裂,并且达到更大的断裂应变。板料的动态变形和断裂模拟与实验结果一致,证明了有限元模拟的正确性。

圆柱体超声辅助分段镦粗准均匀变形

腰鼓形是圆柱体常规镦粗过程中常见的一种变形不均匀现象。为提高镦粗成形均匀性,以Φ4.08 mm×4.8 mm的6061铝合金圆柱体为实验对象,采用超声辅助分段镦粗工艺,即先进行超声辅助镦粗,然后继续进行无超声常规镦粗,分别得到细腰形中间体和最终的Φ5.4 mm×2.8 mm近圆柱体。实验和有限元仿真研究表明:超声辅助镦粗作用下形成的细腰形中间体可表现出近似椭圆形曲线或双曲线轮廓,同时细腰形轮廓的形成促进了圆柱形试样的端面径向变形。此外,超声辅助的分段镦粗可促进试样内等效塑性应变近似均匀地分布,从而改善腰鼓形不均匀变形。细腰形试样内部产生的切应变可与后段无超声常规镦粗形成的切应变产生抵消性矢量叠加,该切应变抵消机制促进了圆柱形试件整体的均匀变形。

Size effects on plastic deformation behavior in micro radial compression of pure copper

Micro radial compression tests were carried out on cylindrical specimens of pure copper polycrystals with different grain sizes. Experimental results indicated that phenomena of decreasing forming force, increasing scatter of forming force and more irregular surface topography occurred with the increase of grain size. A modified surface model based on dislocations pile-up in surface layer grains, and a flow stress scattering formulation based on standard deviation and grain size distribution were proposed to analyze size effects on forming force in micro compression. The inhomogeneous deformation of surface layer grains was discussed by the main deformation manner of rotation. A good agreement with the experimental results was achieved.

Finite element analysis and simulation for cold precision forging of a helical gear

To investigate the effects of billet geometry on the cold precision forging process of a helical gear, six different billet geometries were designed utilizing the relief-hole principle. And the influences of the billet geometry on the forming load and the deformation uniformity were analyzed by three-dimensional （3D） finite element method （FEM） under the commercial software DEFORM 3D. The billet geometry was optimized to meet lower forming load and better deformation uniformity requirement. Deformation mechanism was studied through the distribution of flow velocity field and effective strain field. The forging experiments of the helical gear were successfully performed using lead material as a model material under the same process conditions used in the FE simulations. The results show that the forming load decreases as the diameter of relief-hole do increases, but the effect of do on the deformation uniformity is very complicated. The forming load is lower and the deformation is more uniform when do is 10 mm.

Resistivity in Formation and Decomposition of Natural Gas Hydrate in Porous Medium

A new one-dimensional system for resistivity measurement for natural gas hydrate(NGH)exploitation is designed,which is used to study the formation and decomposition processes of NGH.The experimental results verify the feasibility of the measurement method,especially in monitoring the nucleation and growth of the NGH. Isovolumetric formation experiment of NGH is performed at 2°C and 7.8 MPa.Before the NGH formation,the initial resistivity is measured to be 4-7Ω·m,which declines to the minimum value of 2-3Ω·m when NGH begins to nucleate after the pressure is reduced to 3.3 MPa.As the NGH grows,the resistivity increases to a great extent,and finally it keeps at 11-13Ω·m,indicating the completion of the formation process.The NGH decomposition experiment is then performed.When the outlet pressure decreases,NGH begins to decompose,accordingly,the resistivity declines gradually,and is at 5-9Ω·m when the decomposition process ends,which is slightly higher than the resistivity value before the formation of NGH.The occurrence and distribution uniformity of NGH are determined by the distribution and magnitude of the resistivity measured on an one-dimensional sand-packed model.This study tackles the accurate estimation for the distribution of NGH in porous medium,and provides an experimental basis for further study on NGH exploitation in the future.

Effect of key factors on cold orbital forging of a spur bevel gear

Cold orbital forging is an advanced spur bevel gear forming technology. Generally, the spur bevel gear in the cold orbital forging process is formed by two steps: the preforming step and the final step. Due to the great importance of the final step to gear forming and its complication with interactive factors, this work aims at examining the influence of key factors on the final step in cold orbital forging of a spur bevel gear. Using the finite element(FE) method and control variate method, the influence rules of four key factors, rotation velocity of the upper tool, n, feeding velocity of the lower tool, v, tilted angle of the upper tool, γ, friction factor between the tools and the billet, m, on the geometry and the deformation inhomogeneity of the cold orbital forged gear are thoroughly clarified. The research results show that the flash becomes more homogeneous with increasing v, increasing m, decreasing n or decreasing γ. And the deformation of the gear becomes more homogeneous with increasing v, decreasing n or decreasing γ. Finally, a corresponding experiment is conducted, which verifies the accuracy of FE simulation conclusions.

基于数值仿真的油箱外壳拉延成形缺陷分析及成形参数优化设计

针对摩托车油箱外壳成形缺陷,采用Dynaform软件对油箱外壳双片组合成形(Double-Cover Forming,DCF)过程进行了数值仿真分析,仿真结果表明侧壁起皱和局部破裂是主要缺陷。利用数值模拟与正交试验设计(Orthogonal Experimental Design,OED)相结合的方法分析和优化了拉延筋高度和压边力参数,分析表明适当增大拉延筋高度和压边力可有效抑制起皱缺陷。采用优化后的参数进行制件压延成形试验,结果表明制件成形均匀性有了较大改善,成形质量得到提高。

多缝隙集磁器的磁脉冲管件缩径成形及连接

磁脉冲管件缩径是金属管件与金属或者非金属管件、杆件连接时使用的一种高速成形工艺。集磁器能显著提高磁脉冲的焊接效率。传统集磁器中通常存在一个缝隙,用于改变感应电流流向,进而调控磁力分布。缝隙的存在使得电磁力在周向上分布不均,靠近缝隙处的区域难以焊接,这种缺陷降低了磁脉冲管件缩径的周向均匀性。为了提高磁脉冲管件缩径的均匀性,提出了一种多缝隙集磁器结构,并研究了缝隙数目N对磁脉冲管件缩径性能的影响,最终通过电磁力分布与成形结果确定了N=4为较好的工艺参数。结果表明,带有多缝隙集磁器的磁脉冲管件缩径系统能够显著提高管件自由缩径与磁脉冲焊接周向成形的均匀性。

基于克里金模型和遗传算法的铝合金高筋薄壁锻件多目标优化

以数值模拟和智能算法为手段,以某高筋、薄壁、带有纵横内筋的铝合金锻件为研究对象,将其成形过程中的坯料高宽比、坯料温度、成形速度以及摩擦系数作为设计变量,将填充性能、组织流线、成形均匀性作为优化目标,利用克里金模型构建坯料高宽比、坯料温度、成形速度、摩擦系数与填充性能、组织流线、成形均匀性之间的高度非线性关系。利用多目标遗传算法(NSGA-Ⅱ),对克里金模型进行寻优得到Pareto解集,均衡考虑实际工艺条件,选取了一组比较均衡的最优解进行工艺试制。结果表明:优化结果能够显著地提升应变均匀性和填充性能,并改善流线分布。

A laser beam shaper for homogeneous rectangular illumination based on freeform micro lens array

An effective design method of freeform micro lens array is presented for shaping varied laser beams into prescribed rectangular illumination. The variable separation mapping is applied to design concave freeform surfaces for constructing a freeform lens array. Several dedicated examples show that the designed freeform optical lens array can achieve a prescribed rectangular illumination pattern, especially without considering the initial states of incident laser beams. Both high collection efficiency and good spatial uniformity can be available simultaneously. Tolerance analysis is also performed to demonstrate that this optical device can well avoid fabricating difficulty in actual applications.