直齿轮精密塑性成形时齿面裂纹的产生机理及控制方法

本文通过对内齿轮缩挤成形工艺的有限元模拟 ,分析了直齿轮成形时齿面裂纹的产生机理 ,并从理论上进行了解释 ,进而提出了防止齿面裂纹产生的方法     

Formation and crystallization of bulk Pd_(82)Si_(18) amorphous alloys

1　INTRODUCTIONMetallicglassisregardedasastatethatisofdis orderunlikecrystalalloyswith periodicatomstruc ture.Soitshowsexcellentcapabilitiesofsoftmag netism ,mechanics ,corrosionresistance ,etc .How ever ,mostofamorphousalloyswereproducedbyus ingrapidsolidificationmethodssuchassplatquench ing ,meltspinning ,andsoon ,withcharacteristiccoolingratesof 10 4 10 6 K/s .Becauseamorphousal loysarepreparedwithsilk ,powderandribbon ,itisgreatlylimitedinengineeringapplication .Recently ,severalbulk…     

UBET-based numerical modeling of bulk deformation processes

The paper summarizes the development of numerical procedures for modeling bulk deformation process and preform designing techniques based on the upper bound elemental technique (UBET). UBET has a unique place where an approximate, but faster solution is needed for decision making. In designing and optimizing multistage forging and profile ring-rolling processes, an approximate solution can be used to identify the most influential process parameters. Once an optimum combination of process conditions are determined, computationally intensive, but more accurate finite element analysis can be used to verify and refine results. In this paper, UBET procedures for closed-die forging and profile ring rolling are high-lighted. Experimental investigations are used to validate the model predictions. Also, the UBET-based preform design tool is presented as a process and die design tool for multistage forging processes. Application of these techniques is presented with evidence of effective material usage and extended overall die-life.     

Observations of nodule growth during the oxidation of pure binary iron-aluminum alloys

Oxidation studies were carried out in oxygen at 800°C, on a series of pure binary iron-based alloys with between 1.9 and 9.8 wt. % aluminum. The results are presented in conjunction with the existing literature and these permit the development of a classification of scale morphologies based on alloy composition. Alloys with less than about 2.4 wt. % aluminum form bulky stratified scales composed of Fe₂O₃ and Fe₃O₄ with FeAl₂O₄ and Al₂O₃ at the scale-metal interface. Alloys with between 2.4 and 6.9 wt. % form an external Al₂O₃ scale but this is interspersed with iron oxide nodules that penetrate the alloy substrate. Only alloys with greater than 6.9 wt. % aluminum form completely protective Al₂O₃ scales. Models based on oxide nucleation are presented for the growth of bulky scales and also the iron oxide nodules.     

Examination of superplastic forming combined with diffusion bonding for titanium: Perspective from experience

Superplastic forming (SPF) combined with diffusion bonding (DB) has been used successfully for the fabrication of titanium aerospace hardware. Many of these applications have been for military aircraft, whereby a complex built-up structure has been replaced with monolithic parts. Several methods for applying the two- and four-sheet titanium SPF/DB processes have been devised, including the welding of sheets prior to forming and the use of silk-screened stop-off (yttria) to prevent bonding where it is undesirable. Very little progress has been made in the past few years toward understanding and modeling the SPF/DB process using constitutive equations and data by laboratory testing. Concerns that engineers face in designing for fatigue life, acceptable design loads, and damage tolerance are currently being studied, but the database is very limited. This is a summary of past work found in the literature and forms the foundation for additional research. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

Design of Bulk metallic glasses with high glass forming ability and enhancement of plasticity in metallic glass matrix composites: A review

To overcome some of the limits of existing metallic alloys, a new alloy design concept has been introduced recently in order to control the crystallinity, i.e. to utilize crystalline, quasicrystalline, and amorphous structures. In particular, bulk metallic glasses (BMGs) receive great attention because of their unique properties due to their different atomic configuration. Recently, significant progress in enhancing glass forming ability (GFA) has led to the fabrication of BMGs having potential for application as structural and functional materials. Moreover, successful design of BMG matrix composite microstructure suggests that the plasticity of BMGs can be controlled properly. In this review article, we introduce recent research results on the design of BMGs with high GFA and on the enhancement of plasticity in metallic glass matrix composites.     

固体颗粒介质成形新工艺及变形研究

固体颗粒介质成形新工艺,是采用固体颗粒代替刚性凸模(或弹性体、液体)的作用,对金属板料成形的工艺。固体颗粒介质成形新工艺,即可以解决流体介质、粘性介质的密封难题,又具有内压非均匀分布、便于控制成形、提高材料成形极限、降低投资成本、所得零件表面质量高、成品率高的优点,且固体颗粒无工业污染,可重复使用。该工艺为材料的加工制备提供了新的方法和手段。利用塑性增量理论,对自由变形区任意一点的应变进行了分析,得到了自由变形区任一点的应变及厚度计算公式。采用固体颗粒介质成形工艺,进行板料成形试验,成功试制出多种典型工件;对试验件壁厚分布的计算值和实测值进行了比较,证明理论正确。     

数控FWX2.4m旋压机微机控制系统的设计

针对数控FWX2.4m旋压机的微机控制系统进行了被控运动部分的分析,给出了微机系统的硬、软件配置和主要功能的基本设计理念。试验表明:该系统运行良好,可靠性高,响应迅速,抗干扰性强。     

塑性成形技术在金属复合管制备中的应用及展望

按金属界面间形成结合方式,机械结合和冶金结合,对目前国内外金属复合管的主要塑性成形制备技术进行了分类。对拉拔法、滚压法、旋压法、轧制法、抽真空法、液压胀形法和复合挤压法、爆炸成形法、多坯料挤压法、电磁成形法等各种塑性成形制备技术,进行了较详细的介绍和比较,指出各自的优缺点,并与离心技术法、消失模真空吸铸法、中频感应加热钎焊法等几种非塑性成形制备技术进行了比较,对其未来的发展趋势进行了展望。     

电磁辅助实体模快速成形技术

电磁辅助实体模快速成形技术是一种新型的板材加工技术.该技术利用磁场对磁性材料的作用和磁场的光顺性,使磁性材料粉末在磁场力的作用下,将离散单元体之间的凹坑填平,使单元体与磁性材料粉末在强磁场的作用下成为一体,即传统意义上的实体模.该技术有效地消除了多点成形中存在的压痕缺陷,提高了板材的成形质量.以一个成形零件为例,用ANSYS分析了其修形磁场,并用实验结果验证了电磁辅助修形技术的可行性.