粉末冶金多台阶复杂结构件自动成形工艺与装备

介绍了粉末冶金多台阶复杂结构件自动成形的工艺过程 ;介绍了国际先进的可控模冲接合器和相应的电脑数控粉末成形压机的主要功能与特性 ;指出了压机技术发展的方向。本文对提高粉末冶金多台阶复杂结构件的生产技术与装备的改进 ,有指导意义     

空调压缩机法兰阀口成形裂纹的研究

用粉末冶金方法生产空调压缩机法兰可以使用二上二下、一上三下的模具结构.对于法兰小板部位厚度比较薄的产品只能采用一上三下的模具形式.这种形式的二下模冲侧面单向受粉末压力,并且存在着一、二下模冲之间的配合间隙.试验表明,在粉末侧压力的作用下,二下模冲的偏移是否会造成阀口芯棒的弯曲变形,是阀口裂纹是否产生的关键.其中芯棒变形的程度决定了裂纹的形态和严重程度.消除裂纹的方式,可以通过提高一、二下模冲的配合精度和在阀口芯棒增加拔模斜度来解决.     

视点 他山石

日本获奖产品游丝夹具ＭｉｔｓｕｂｉｓｈＭａｔｅｒｉａｌｓＣｏｒｐ(Ｔｏｋｙｏ)生产的游丝夹具获得了日本粉末冶金协会 (ＪＰＭＡ) 2 0 0 0年设计奖 ,该游丝用于汽车测速计上。夹具由两部分零件组成 ,每个零件的法兰盘上有六个形状复杂的支架 ,这些零件因形状复杂使得机加工的费用很高 ,该公司用粉末冶金近终形技术开发了这些零件。为了保证模腔强度和尽量减少压坯中的裂纹 ,该公司用带台阶模具生产支架 ,而不是冲压成形。除此之外 ,还对模冲长度及厚度进行有限元分析 ,以减少生坯中由于弯曲而产生的裂纹。用粉末冶金方法代替机械加工方…     

粉末冶金台阶件的压制成形

介绍了粉末冶金台阶件的压制成形方法及成形方式,分析了模具结构对改善制品密度均匀性的作用。     

模壁润滑剂对氢化钛粉末冷压成型的影响

以海绵钛通过氢化脱氢法(HDH)制取的氢化钛TiH2粉体为原料,分别选择硬脂酸锌(ZnSt)、硬脂酸(SA)和聚乙二醇(PEG-6000)作为模壁润滑剂进行冷压成形,并真空烧结得到最终制件。对比不同模壁润滑剂对生坯和烧结件的性能及质量的影响,研究分析对钛及钛合金粉末冶金冷压成型最适宜的模壁润滑剂。研究结果表明,模壁润滑剂的使用不仅能提高生坯的密度和强度,还能有效改善掉边和裂纹现象,延长模具寿命。同时,模壁润滑剂还有一定的提高烧结密度的能力,并有利于孔洞的减少和优化,对制件的增氧影响也较为有限。这些实验结果说明模壁润滑剂是适合钛及钛合金粉末冶金的。而相比于其他两种模壁润滑剂,硬脂酸无论是在成形生坯件还是烧结件上都具有明显的优势,是较为适宜的钛及钛合金粉末冶金成型的模壁润滑剂选择之一。     

铁基粉末冶金液压马达阀板的研究与制备

阀板是液压马达的关键零件,具有多台阶异形复杂结构和力学性能要求高等特点。本文采用粉末冶金技术替代原铸造工艺,通过精选材料配方,合理进行成形模具模架设计,控制烧结熔渗过程,优化热处理工艺参数,制造出了高质量铁基粉末冶金阀板零件,完全满足液压马达的应用要求,可代替铸造阀板件。     

7A60铝合金杯形件等温压扭关键工艺参数分析

以7A60铝合金杯形件为研究对象,通过工艺实验和有限元模拟研究了杯形件在等温压扭成形过程中关键工艺参数对其成形性能的影响。结果表明:坯料高径比对累积变形量的影响主要在镦粗变形阶段,下模扭转速度增大,成形载荷降低,扭矩增加;但当下模转速太大时,压扭件盘面过渡圆角区域损伤值将大于1,边缘易于产生破裂缺陷;成形温度的变化对成形载荷和扭矩的影响较为显著;成形过程中对压扭件施加小于1圈的扭转剪切变形,合金的连续性不会遭到破坏,且合金强度相比传统挤压件有所提高。     

一种粉末冶金外台阶件的成形模架

一种粉末冶金外台阶件的成形模架陈强蔡一湘（广州有色金属研究院,广东５１０６４０）１问题的提出目前在粉末冶金生产中采用的国产全自动粉末专用压机,多装有拉下式脱模模架。该模架结构简单,效率也较高。但是,当压制外台阶类零件时,采用弹簧浮动压套,使得模具制作...     

CNC压机不同移粉状态的数值模拟北大核心

CNC粉末成形液压机能够实现无预压粉末移动,即压制前粉末可在轴向上移动到任意位置而不会产生粉末横向移动或受压变形,该功能可保证成形多台阶复杂零件的密度均匀性。本文运用有限元Deform软件对VVT正时皮带轮在不同移粉状态下的压坯密度进行模拟分析。通过模拟数据对移粉位置研究,优化压制参数,提高压坯密度分布的均匀性,实现VVT正时带轮采用粉末冶金近净成形的先进方法制造,并满足其对精度、密度、性能的要求。     

喷油器压板自动成形模的设计

用手动模成形喷油器压板的毛坯时,生产效率低,压制时下模冲容易开裂,脱模时毛坯的槽子出现裂纹。通过调查和理论分析,介绍了自动成形模的结构设计、主要零件的设计及成形调试。使用自动成形模,解决了生产效率、效益及质量的问题。     

Mechanics of Composite Solids

The mechanical properties of composite, elastic solids are determined using the method of volume averaging. Volume-averaged forms of Hooke’s law and Cauchy’s equation are developed for each phase. When the condition of local displacement equilibrium is valid, the volume-averaged displacement vectors are essentially equal and the spatially smoothed equations for each phase can be added to obtain a one-equation model of a two-phase system. This one-equation model contains area integrals of the spatial deviation displacement vector, and a closure problem is developed to determine this vector. The closed form for the stress-deformation relation contains effective coefficients to be determined by the solution of the closure problem.     

Microstructure Strain Localization during Sheet Metal Hydroforming Processes

This investigation deals with the interdependence between microstructure constituents and local material flow under stress in regard to deep drawing of cold rolled steel sheets. The studies of the local flow and phase deformation of DP, TRIP and ULC steels included hydraulic bulge testing, stretch‐forming with a semicircular punch and tensile testing. Changes in the microstructure distribution and orientation of the constituents were determined metallographically by optical and scanning electron microscopes (SEM), by in situ tensile tests as well as by determining texture by electron back‐scattered diffraction (EBSD) and X‐ray diffraction methods. A quantitative microstructure examination of phase deformation was carried out and used for the analysis of strain localization under uniaxial and biaxial tension. In the examined forming processes the different microstructure constituents showed different local deformations; this phenomenon can be described by the coefficient of heterogeneity deformation (CHD). As expected, there is a correlation between the CHD, texture and the disappearance of the material's plastic reserve during deformation. Variations in the material flow are due to changes in microstructure constituents during the forming processes. These variations and changes can be expressed by the coefficient of macro heterogeneity. For the examined cold deformation processes three characteristic ranges of inhomogeneity development were found in each case, which are based on the corresponding changes in microstructure. The CHD‐formation can be used in combination with a forming limit diagram to evaluate the suitability of a material to a forming process.     

非同轴坯件的成形方法

介绍了一种按常规模压方法几乎不能成形的非同轴坯件的模压成形方法,着重介绍了模具结构设计、力学计算、结构特征及模具的动作原理。结果表明,当沿着与具有特殊形状的下冲头轴线方向成θ角的方向施压时,可完成非同轴坯件的成形。     

Role of yield criteria and hardening laws in the prediction of forming limit diagrams

Forming limit diagrams (FLDs) are calculated based on an extension of previous analyses by Jones and Gillis,^[1] Choi et. al. ^[2] and Pishbin and Gillis.^[3] They considered the plastic behavior of sheet metals in three deformation phases using a generalized flow law and using the commonly used power hardening law to describe the stress-strain behavior. In the present study, however, the yield criterion proposed by Hosford is used in conjunction with both power-law and Voce material constitutive equations to develop a model. This model is capable of predicting the forming limit strains achievable during sheet metal forming operations for sheets having planar isotropy. The predictions from Voce and power-law equations have been compared with the experimental forming limits determined by hemispherical punch stretching of gridded blanks of AA3105 and AA8011 aluminum alloys. The results indicate good prediction of limit strains for the two alloys when the Voce equation is applied.     

Comparative Study on Failure Prediction in Warm Forming Processes of Mg Alloy Sheet by the FEM and Ductile Fracture Criteria

An important concern in metal forming is whether the desired deformation can be accomplished without any failure of the material, even at elevated temperatures. This paper describes the utilization of ductile fracture criteria in conjunction with the finite element (FE) method for predicting the onset of fracture in warm metal working processes of magnesium alloy sheets. The uniaxial tensile tests of AZ31 alloy sheets with a thickness of 3 mm and FE simulations were performed to calculate the critical damage values for three kinds of ductile fracture criteria. The critical damage values for each criterion were expressed as the function of strain rate at various temperatures. In order to find out the best criterion for failure prediction, Erichsen cupping tests under isothermal conditions were carried out at various temperatures and punch velocities. Based on the plastic deformation histories obtained from FE analysis of the Erichsen cupping tests and the critical damage value curves, the initiation time and location of fracture were predicted under bi-axial tensile conditions. As a result, Cockcroft–Latham’s criterion showed good agreement with the experiments.     

An Improved Model for the Longitudinal Peak Strain in the Flange of a Roll Formed U‐Channel developed by FE‐Analyses

Today one can find cold roll forming (CRF) products in many applications, for example vehicles, furniture and in the building industry. Though CRF is a well known sheet metal process, it is still not entirely understood due to the geometrically complex forming. There are several computer aided engineering (CAE) programs on the market that can assist the tool maker when designing a new CRF machine. However, they are often based on simple formulas when predicting the stress and the strain in the strip. The main objective of this study is to improve formulas for the longitudinal peak membrane strain and the deformation length when a U‐channel is formed. These are important since they can be used to determine the number of forming steps and the distance between them. A two‐level factorial design is done using the finite element analysis to investigate which parameters affect the peak strain and the deformation length. The parameters are then used to build models for the peak strain and the deformation length.     

新型粉末高温合金多火次等温锻造过程中晶粒细化机制

为探索多火次等温锻造对新型粉末高温合金晶粒细化的影响, 本文对实验合金进行了每火次变形量40%左右的三火次等温锻造, 采用商用有限元软件DEFORM 2D模拟锻造过程中的等效应变分布图, 采用电子背散射衍射技术对各火次后的锻坯进行显微组织观察和分析.研究表明: 等温锻造过程中, 锻坯轴向剖面大致分为三个区域, 位于上、下两端面附近的Ⅰ区变形量最小, 位于两侧附近的Ⅱ区次之, 位于剖面中心的Ⅲ区变形程度最大.经过三火次等温锻造后, 锻坯Ⅱ、Ⅲ区再结晶充分, 获得等轴细晶组织, 平均晶粒尺寸2~3 μm.然而Ⅰ区形成再结晶不完全的"项链"组织, 在变形晶粒周围分布大量细小的再结晶晶粒, 变形晶粒内小角度晶界含量较多, 位错密度较高.通过对三火次后的锻坯进行合适的热处理, Ⅰ区"项链"组织得到细化, Ⅱ、Ⅲ区组织发生晶粒长大, 整个盘坯为较均匀的细晶组织, 平均晶粒尺寸为6~8 μm.      

铁基多孔烧结材料锻造镦粗成形致密的特性研究

通过对铁基多孔预成形坯粉末锻造成形致密实验,研究了在不同初始相对密度、不同高径比、不同摩擦条件下的粉末锻造成形致密规律,得到了粉末锻造成形断裂极限应变迹线和成形极限工艺参数,为预成形坯和模具的优化设计提供了大量实验数据.     

Discussion of Theoretical Methods to Predict Scale Thickness in Hot Rolling of Steel Strips

Oxidation of iron during hot rolling is inevitable and scale layers are formed on the strip. There are different rate laws of oxidation of iron to predict the scale thickness, in which parabolic rate law and mixed rate law are usually used in hot rolling of strips. As the strip passes through the roll gap, the scale layer can plastically be deformed. Due to limited plasticity of the oxide, cracks through the scale layer can be formed in every roll gap. They open and form new free metallic surfaces which are then oxidized in the interstand. By means of numerical simulations different rate laws of oxidation are compared and the scale deformation with different cases is taken into account. Sensitivity of some rolling parameters to prediction of the scale thickness is discussed in the present paper. Numerical results show that the parabolic rate law overestimates the scale thickness as compared with the mixed rate law and the mixed rate law is not sensitive to the deformation extent of scale.     

双辊铸轧704不锈钢薄带的冷轧实验

对双辊铸轧704不锈钢薄带进行了冷轧处理,分析了冷轧前后薄带的表面质量及显微组织.结果表明:在冷轧过程中,因动态再结晶和动态回复,使薄带的晶粒进一步得到细化.变形量过大时,冷轧薄带内部出现微观晶界裂纹,并随着变形量的增加最终发展成宏观裂纹.笔者还应用金属学、结晶热力学对晶界裂纹的产生机理进行了分析,认为当冷轧变形量达到一定程度后必须对薄带进行固溶处理,以避免裂纹出现.另外,结合冷轧过程中薄带板形的变化,对704不锈钢铸轧薄带给出了合理的冷轧变形量.