齿形件精冲成形时的齿顶塌角分析及措施

针对精冲成形齿形件时的齿顶塌角问题,首先分析了齿形零件的几何特征及精冲成形特点,并分析了这些特征与齿形零件精冲时齿顶塌角的关系;将精冲变形区分为2个核心变形区和2个变形影响区,对核心变形区Ⅰ精冲塌角的形成过程进行了分析。然后,通过有限元模拟软件Deform-3D,找出齿顶塌角处材料在成形过程中的流动规律。结果表明:齿顶处A面轮廓附近的材料沿齿顶径向运动,一部分材料流向齿顶外侧;齿廓B、C侧附近的材料沿其轮廓线所指向的齿顶方向流动。再次,全面分析了影响精冲齿顶塌角大小的各种因素,找出压边力和反顶力对塌角大小的影响规律,得出反顶力比压边力对控制塌角的效果更显著。最后,提出了在齿形零件精冲成形过程中减小或消除齿顶塌角的具体措施对策。     

Evaluating drape shape in woven fabrics

A search of the scientific literature for the period 1950–2013 retrieved 36 different drape indicators. Despite the large number of indicators currently available, the drape ratio (%DR) continues to be the most widely used, even though it has proved inadequate to explain drape shape. In order to assess their actual performance, the 36 currently existing drape indicators were determined in a total of 37 commercial drapery, woolmaking, shirtmaking and lining woven fabrics spanning a wide range of composition, aerial weight and weave type using a digital Cusick drape meter. A correlation analysis between indicators, and subsequent suppression of duplicity and collinearity, revealed that seven were mutually correlated. A principal component analysis of the results revealed an underlying structure consisting of three common factors which allowed the indicators to be classified into three different groups according to drape intensity (a), severity (b) and shape symmetry and variability (c). Cluster analysis was additionally used to examine the results in graphical form and exposed three clusters coinciding with the three factors of the underlying structure. A criterion for distinguishing fabrics with an identical drape ratio in terms of drape shape based on sequential application of four of the seven initially selected indicators was developed and experimentally validated.     

超亲水多孔表面的小液滴发射行为及动力学特性

构建了4类不同的超亲水微/纳多孔结构,通过低速液滴撞击实验研究了多孔介质的结构参数如微/纳尺度特征、孔隙率以及表面粗糙度等对液滴行为和动力学特性的影响。结果表明：多孔表面液滴的早期扩散符合惯性扩散的幂函数规律,并且纳米级结构孔隙率的变化对幂函数关系无显著影响,微米级结构C和α的值随孔隙率增大而降低,粗糙度的提高能够导致C值增大。发现了两种新颖的小液滴发射模式,分别称为第1阶段断裂和第2阶段断裂。纳米级多孔结构发生第1阶段断裂的原因在于较快的惯性扩散速度和较长的惯性时间;第2阶段断裂发生于微米级多孔结构,原因在于渗透的强化导致液滴高度的快速下降以及惯性时间的缩短。     

Effects of lubricant and part geometry on the ejection characteristics during die compaction

The ejection of a part following die compaction is a critical step in manufacturing powder metal and ceramic parts as well as pharmaceutical tablets. In this paper, the ejection of die-compacted hollow cylinders of heights 0.5 and 1.2?cm from Fe–2%Cu–0.5%C powders mixed with various amounts of (0.2–0.8?wt-%) of ethylene-bis-stearamide (EBS) was studied to understand the effect of lubricant amount and part geometry on the ejection process. Additionally, the ejection data of gears of 0.5 and 1.2?cm die compacted from Fe–2%Cu–0.5%C powders with 0.8?wt-% EBS was analysed to understand the effect of geometry on the ejection process. Several ejection parameters were found to be sensitive to the amount of EBS as well as the size and shape of the parts. The results from the present study indicated that the major portion of the ejection cycle involved the movement of the part within the die.     

基于模块化设计的ACES-Ⅱ弹射座椅

ACES-Ⅱ弹射座椅进行模块化设计旨在减少维修工时和后勤保障费用。介绍了模块化设计的概念和模块划分原则,详细阐述了ACES-Ⅱ座椅模块的具体划分及其安装／拆卸,最后分析了座椅模块化设计及其维修性改进对我国军机弹射座椅设计具有的借鉴价值。     

手机面壳模内自动切浇口注射模设计

以某手机面壳为例,介绍注射模上一种实用的自动切浇口结构。通过设计2个顶出机构并控制注塑机上的参数设置,实现在模具上自动切断侧浇口,解决了侧浇口残留的问题,保证了制品外观质量要求,并因减少了手工去浇口的工序,从而降低生产成本,提高了生产效率。     

Continuous Boiling Phenomena of Sodium under Forced Convection by Direct Heating

The results of an experimental study on the continuous boiling behavior of sodium with upward forced convection loop are reported. The sodium was passed through a vertical tube of 14.9 mm I.D., where it was heated by d.c. power (~4V,~5,000 A) directly applied through the flowing sodium. The experiments were carried out in the following range of conditions:

Input power:6–12kW Pressure at the condenser: 0.9–1.1 kg/cm² Flow rate: 1.0–3.0 l/min Inlet temperature: 750°–830°C.

Under certain conditions, steady boiling occurred, but boiling generally had a tendency to become unstable, and flow patterns representing violently pulsating boiling were observed. These latter flow patterns were either of single bubble ejection type with expulsion and subsequent re-filling of sections of the tube mainly by liquid sodium falling back from above, or else of slug type with periodical expulsions, without fall-back of liquid. For these patterns of pulsating boiling, the frequencies of oscillation ranged from 0.5 to 1.0 Hz. The film thickness remaining on the channel wall was also measured.     

Modelling and a tabu search solution for the slab reallocation problem in the steel industry

This paper considers a slab reallocation problem arising from operations planning in the steel industry. The problem involves reallocating steel slabs to customer orders to improve the utilisation of slabs and the level of customer satisfaction. It can be viewed as an extension of a multiple knapsack problem. We firstly formulate the problem as an integer nonlinear programming (INLP) model. With variable replacement, the INLP model is then transformed into a mixed integer linear programming (MILP) model, which can be solved to optimality by MILP optimisers for very small instances. To obtain satisfactory solutions efficiently for practical-sized instances, a heuristic algorithm based on tabu search (TS) is proposed. The algorithm employs multiple neighbourhoods including swap, insertion and ejection chain in local search, and adopts solution space decomposition to speed up computation. In the ejection chain neighbourhood, a new and more effective search method is also proposed to take advantage of the structural properties of the problem. Computational experiments on real data from an advanced iron and steel company in China show that the algorithm generates very good results within a short time. Based on the model and solution approach, a decision support system has been developed and implemented in the company.     

"扣机式"二次顶出机构在模具中的应用

模具的顶出方式对制品的质量和生产效率有着重要的影响。列举实例介绍一种新型的"扣机式"二次顶出机构。该机构可解决一次顶出动作完成后注塑件难以完全脱模的问题,且使模具整体结构简单,使用安全可靠,同时可满足完全自动化的需求,适合于大批量生产的模具。     

北京地铁暗挖隧道注浆止水和加固技术分析

以北京地铁暗挖隧道施工为工程背景,结合当地地质条件,决定采取袖阀管深孔注浆和前进式注浆工艺相结合的施工方案对隧道周围土体进行加固,经数值分析可知加固效果较为显著,从而确保了隧道施工质量。