喷射成形多孔材料的致密化工艺综述

介绍了6种常用的喷射成形多孔材料致密化工艺,即热挤压、轧制、锻造、热等静压、楔形压制和陶粒压制工艺,重点介绍了各种工艺的原理、特点、优缺点以及针对某些缺点而采取的一些改进措施.发现热挤压、轧制、锻造、热等静压和陶粒压制工艺能单次使喷射成形多孔材料整体成形致密化,而楔形压制是一种通过局部小变形累积以实现整体成形致密化的工艺;楔形压制在致密化喷射成形大尺寸材料方面具有独到的优势.最后,探讨和展望了今后的发展方向.     

铜基电触头材料温压成型工艺的研究

研究了铜基电触头材料的温压行为,通过温压试样性能分析得出了最佳的温压工艺参数,并与冷压压制试样的性能进行了比较.结果表明,在相同压力下,温压试样的电阻率、硬度和抗氧化性明显比冷压试样的好;压制温度的最佳值是130℃,润滑剂的最佳添加量为0.7%(质量分数).     

金属粉末压制成形机理及影响因素模拟分析

利用MSC.MARC有限元分析软件对金属粉末致密化成形过程进行了模拟分析。采用基于更新拉格朗日方法描述的大位移弹塑性分析,研究了不同工艺(压制方式、摩擦条件)对不同侧压系数(K=4、6、8)压坯中金属粉末致密化成形行为的影响规律。结果表明,双向压制工艺相比单向压制工艺可改善压坯应力和密度均匀性;摩擦条件的改善有利于增大金属粉末移动,减少应力集中,降低粉末压制力,提高压坯密度均匀性;而相同压制工艺下,压坯高径比小时,密度分布更均匀。     

原位化学法制备纳米ZrO2/Cu复合材料的研究

为了提高铜基复合材料的强度和电导率,采用具有良好机械性能和热物理性能的ZrO2(3%(摩尔分数)Y2O3)作为增强相,原位化学法制备了ZrO2纳米颗粒增强铜基复合材料,其主要制备工艺包括前驱复合粉体CuO、ZrO2的制备,经氢气还原得到ZrO2/Cu复合粉,再经过压制,真空烧结,复压等工序制得最后的样品.研究了制备工艺包括初压压力,烧结温度、时间对材料性能的影响;结果表明,在初压压力为550MPa,975℃烧结1.5h时,可得到最佳性能复合材料.透射电镜观察表明,在ZrO2/Cu纳米复合粉中,氧化锆纳米颗粒形状为圆形和四方形,平均尺寸约为20nm左右.纳米ZrO2在基体中分布均匀,细化了晶粒,提高材料硬度,使复合材料具有良好的综合性能.随着ZrO2含量的提高,密度、电导率降低,硬度升高.     

数控车床加工切屑的控制

数车加工对切屑是有严格要求的。要实现理想车削,就要解决断屑的问题。切屑是否容易折断,与切屑的变形有直接联系。合理利用材料变形进行断屑、利用工艺手段进行断屑、利用数控机床特有的数控编程功能进行断屑,提高车削稳定性。     

粉末冶金温压工艺的技术特点及其新发展

本文概述了温压工艺的特点及其最新的发展,如流动温压、热模压制等,重点讨论了热模压制工艺的技术特点与应用,并指出以AncorMax D为代表的热模压制工艺由于工序比常规温压工艺更简单,压制温度更低,因此在将来很有可能取代常规温压工艺,成为高密度粉末冶金零件的一种非常有应用前景的方法.     

SiC 颗粒增强铝合金基梯度复合材料的制备与压缩性能研究

把梯度功能材料(FGM ) 的设计思想用于金属基复合材料(MMCs) 的开发之中, 成功地制备出了SiC 颗粒增强铝合金基梯度复合材料。对该材料的组织结构和高温压缩性能进行了实验研究。结果表明: 采用复压烧结粉末冶金工艺能提高材料致密度, 消除梯度层间界面; 高温下材料的真实应力-应变曲线可分为初始硬化和逐渐软化两个阶段, 材料强度主要由基体决定; 高温下变形时, 材料梯度层间界面无相对滑动, 变形情况与梯度分布方式有关。      

大尺寸重力铸造A356铝硅合金管坯楔压致密化

为了消除铸造铝硅合金中的孔洞、疏松等缺陷,提高合金性能,采用基于多道次局部小变形累积整体成型的楔压成型工艺,压制出力学性能良好,整体致密化,外形圆整的A356管坯。通过金相组织、室温拉伸、布氏硬度和SEM等手段,对楔形压制致密化的规律及其合金的微观组织和力学性能进行研究。试验结果表明:楔形压制工艺能显著压合甚至消除重力铸造产生的孔洞,力学性能得到显著提高,抗拉强度和延伸率分别从楔压前的148MPa,2.5%提高到224MPa,7.3%。     

曲面薄壁钛合金铸件变形工艺控制研究

目的 研究曲面薄壁钛合金铸件变形规律及发生的阶段,提出防止变形的工艺措施。方法 通过对出气管铸件成形过程进行计算机模拟仿真,对蜡模、浇注成形后的铸件、热等静压后的铸件进行扫描拟合,分析了出气管在蜡模压制、铸造成形、热等静压过程中的变形,提出了控制蜡模变形和铸件热等静压过程变形的工艺措施,并进行了试验验证。结果 出气管蜡模在压制和放置过程中,远端浇口连接处发生翘曲变形,变形量约0.5 mm;铸件在无约束的热等静压过程中,发生扭曲变形,变形量约0.5 mm,蜡模变形和热等静压过程变形叠加,导致铸件变形约1 mm。结论 计算机模拟仿真可以有效缩短铸件研制过程,获得优质铸件;增加蜡模胎膜和约束下铸件热等静压,可以有效控制铸件变形,获得合格铸件。     

模具钢斜面切屑形成过程的实验研究

本文钢斜面切屑为对象，通过仿真实验研究了不同走刀方式及斜面倾角条件下的切屑形态。并对切屑与未变形切屑及实际切屑之间进行对比，结果表明不同的刀具前角、走刀方式及切屑用量所带来的切屑变形差异较大，轮廓铣削与斜坡铣削相比，切屑卷曲更为明显，同时也发现在切屑顶端由于有效切削速度较大而产生大量切削热，形成了熔融后凝固的球状颗粒。     

蒸汽爆破预处理白芦笋下脚料多糖提取工艺

目的研究蒸汽爆破预处理白芦笋下脚料多糖提取的最佳工艺,分析蒸汽爆破预处理对多糖得率的影响。方法以白芦笋加工下脚料为原料,采用蒸汽爆破预处理提取多糖,探讨物料粒径、汽爆压力、维压时间、料腔比(物料与料腔体积的比值)对多糖得率的影响,利用响应面优化设计筛选白芦笋下脚料多糖的最佳提取工艺。结果汽爆压力对白芦笋下脚料多糖得率的影响最大,其次为物料粒径、维压时间、料腔比。得到了响应面优化蒸汽爆破预处理的最佳提取条件,物料粒径为30目,维压时间为128 s,汽爆压力为1.50 MPa,在此条件下多糖得率的实测值达到8.86%,较直接热水浸提法的多糖得率增加了22.88%。结论蒸汽爆破预处理对提升多糖得率具有一定的促进作用。     

Experimental Investigation on Sialon Ceramic Inserts for Ultra-high-speed Milling of Inconel 718

A series of milling aerospace material Inconel 718 experiments were conducted with a sialon ceramic tool to investigate chip evolution, cutting force, and tool wear at different cutting speeds. Round inserts were used at ultra-high-speeds under dry cutting conditions. A scanning electron microscopy and an optical microscope were used to observe the worn surfaces and to reveal the wear mechanisms of the inserts. The experiment results showed that the macroscopic shape of the chips was small scraps and fan-shaped. With the increase in the cutting speed, the plastic deformation of the chips was increasingly serious. The minimal average cutting forces were obtained at v_c = 700 m/min. The rise of cutting temperature was resulted from the increase in cutting deformation work and friction work with cutting speed. The combined effect of thermal stress and mechanical stress contributed to the tool chipping, flaking, microcrack propagation, abrasion, and adhesion which were the primary reasons of the sialon ceramic tool wear.     

Cutting performance and failure mechanisms of a pure WC cutting tool in dry cutting of Cr12Mn5Ni4Mo3Al stainless steels and HT200 grey cast iron

A pure WC cutting tool material was fabricated by hot pressed sintering and treated by hot isostatic pressing (HIP). The cutting performance, failure modes and mechanisms of the pure WC cutting tools were investigated via dry cutting Cr12Mn5Ni4Mo3Al stainless steels and HT200 grey cast iron in comparison with those of YW2 cemented carbide tools. General view of the worn tool face was observed by light optical microscopy. Worn and fractured surfaces of the cutting tools were observed by scanning electron microscopy (SEM) and chemical analysis by energy-dispersive X-ray spectroscopy (EDS). The results of cutting process revealed that the wear mechanisms and failure modes of the pure WC cutting tool in cutting various workpiece materials were totally different due to the discrepant adhesion tendency of the workpiece materials to the pure WC material. The different wear behaviors of the pure WC cutting tools in cutting Cr12Mn5Ni4Mo3Al stainless steels and HT200 grey cast iron result in the completely opposite cutting performance and tool life.     

热挤压AZ91D镁合金边角料组织和性能的研究

采用热挤压工艺直接热挤出AZ91D镁合金边角料,研究挤压温度对挤压成形镁合金组织和性能的影响,并讨论其断裂行为.结果表明:在450℃热挤压时,晶粒尺寸均匀,组织中已不存在原始边角料之间未打碎的结合面,边角料之间结合较好;在350～450℃之间热挤出时,AZ91D镁合金随挤压温度的升高,抗拉强度和延伸率均增加,当挤压温度...     

Design of Compound Die for Production of Cutting Blades for Nonactive Rotary Paddy Weeder

Press working is a chip-less manufacturing process on sheet metal through the application of immense force with the help of press tools for short interval and hence results in shearing or deformation of the work material. It is a chip-less manufacturing process by which various components are made from sheet metal. A compound die is one that is used for cutting operations only, and the operation is completed by a single-press stroke. In this article, a die was designed to serve the purpose of cutting down the blades for paddy weeder and clearances to be provided in the die were calculated so as to reduce the material consumption with reduction in production cycle time. The die thus designed served for the purpose with 73% reduction in production time, with enhanced quality and helped in enabling mass production by eliminating several processes such as marking, cutting done with the help of a cutter, shaping, and so on.     

高性能Ag-SnO_2材料的制备及其电寿命研究

研究了Ag-SnO2电接触材料的制备工艺,通过采用掺杂和表面改性地方法改善了氧化物和银的浸润性,从而提高了触头材料的导电性、加工性能和使用寿命。该材料经过大变形量热变性和冷变形后,性能可达到国际先进水平。     

B1500HS材料热成形后冷冲切试验

目的研究热冲压零件冷冲切刀块易磨损寿命低的问题。方法设计开发一套多功能冷冲切试验模具,对热成形后B1500HS材料进行连续冲切试验,并对3组模具间隙、4种典型模具钢材质对应的冲切试样进行断面质量检测及统计,以此分析热冲压高强钢冷冲切合理模具间隙和典型冷冲切模具钢的冷冲切特性。结果 8%~10%料厚模具间隙在冲切初期毛刺较小,且在连续冲切过程中毛刺高度比较稳定,为合理的模具间隙范围;4种典型模具钢中,ASP60冲头耐磨性性能最优,SKD11冲头耐磨损性最差,SKH-9和CALDIE介于两则之间。结论热冲压钢的冷冲切稳定性及刀块寿命相对常规高强钢还存在较大差距,针对其冲切特性有必要开发更高寿命、高性价比的模具钢及热处理方法,以提高刀块寿命和生产效率,降低零件制造成本。     

发泡石头纸的制备和性能检测

在石头纸粒料中分别加入质量分数为0.1%,0.4%和0.7%的AC发泡剂,经过高速冷混、熔融混合后,从挤出机挤出预发泡纸膜,再经过热压使纸膜发泡,冷切后分别制得了厚度增加倍率为0.4,0.2和0.8的发泡石头纸。通过扫描电镜对发泡石头纸表面结构和横截面结构进行了观察,发现石头纸表面有微孔结构,石头纸内部的微孔结构规整,其孔壁在发泡产生的气体压力下被拉伸,随着发泡剂量的增加这种拉伸现象越明显。研究表明:发泡石头纸的密度比普通未发泡石头纸减小了16%～30%;石头纸中AC发泡剂质量分数为0.1%时,发泡石头纸的物理性能增强,质量分数为0.4%和0.7%时,其物理性能有所下降。     

Optimization of Positioning of an Acoustic Emission Sensor for Monitoring Hot Forging

Optimization of a sensor location for effective characterization of a hot forging process using acoustic emission (AE) signals is discussed in this paper. Acoustic emission signals generated during forging operations on an aluminium alloy were recorded using three sensors simultaneously by mounting them on the top bolster, bottom bolster, and bottom die of the press. The AE signals with maximum sensitivity could be detected with a sensor attached to the bottom die in preference to the other positions. Using AE parameters, the forging process could be differentiated into three regions, i.e., 1) yielding of the workpiece material, 2) intermediate deformation region, and 3) filling of the die. The results show that the optimum position of the AE sensor for monitoring hot forging is found to be the bottom die of the forging press.     

导热型高性能树脂微电子封装材料之一:封装材料的制备

微电子行业迫切需要新一代优异性能的封装材料。采用聚酰亚胺／氮化铝复合材料作为封装材料，可以组合聚酰亚胺和氮化铝的优点，具有高导热、低热胀、低介电、电绝缘等优异的性能，应用于现代微电子领域前景良好。文章讨论了这种封装材料的制各，首先将单体反应物反应得到聚酰亚胺预聚体，然后将预聚体与氮化铝高能球磨混合，最后热压成型。成功制各出一系列聚酰亚胺／氮化铝复合导热型高性能塑料微电子封装材料。