装粉方式对钛粉压制成形影响的数值模拟

用MSC.Marc软件模拟了在3种不同装粉方式下钛粉压制成形过程中粉末的流动情况以及压坯的密度分布规律。研究结果表明:装粉方式对粉末压制过程及压坯密度具有较大的影响,与平式装粉方式相比,采用凸式装粉,试样的烧结坯密度提高6％,孔隙分布的均匀性得到相应的改善。     

压制参数对铁粉温压致密化过程的影响

本文研究了压制压力、压制温度、加压速度等压制参数对温压压坯密度的影响。实验结果表明 :随着压制温度升高 ,压坯密度并非连续增加 ,而是有一个最佳温度点 ,超过这一温度点 ,压坯密度反而下降 ;加压速度快可获得高压坯密度。文章还利用压制方程对粉末加热温度的作用进行了分析     

侧压系数及压坯高径比对温压有效性的影响

钢铁粉末温压技术的有效性不仅取决于粉末／模具加热温度、压制压力及润滑剂的特性，而且取决于所要生产的零件的特点，如几何形状。本文通过引入温压侧压系数（β）并运用唯象的温压压制方程着重分析了压坯高径比或高径差比对温压生坯密度的影响。理论分析表明，当β值超过某值时，温压生坯密度明显降低。不同β值的压坯温压实验表明，当β＝３～１０，温压生坯密度随粉末／模具温度变化有一最大值；而β≥２４时，无模壁润滑生坯密度随粉末温度升高而降低，而适当的模壁润滑却可保证得到６９０ＭＰａ下的７３８ｇ／ｃｍ３的高的温压生坯密度。     

用作温压基粉原料的Fe-Ni-Mo合金钢粉温压与烧结行为研究

与通常采用纯雾化铁粉和部分合金化铁粉作为温压基粉不同,作者对水雾化Fe-Ni-Mo合金钢粉作基粉的Fe-1.5Ni-0.5Mo-1.0Cu-xC(x=0.6,0.8,1.0)粉末进行了温压与烧结行为的研究.结果表明,通过设计新型聚合物润滑剂,高硬度的合金钢粉仍适用于温压工艺.当粉末和模具的加热温度分别为125和145℃时,Fe-1.5Ni-0.5Mo-1.0Cu-0.8C的温压密度较高,在735MPa的压力下进行压制,压坯密度达到7.35g/cm~3,比室温压制提高了0.19g/cm~3左右.并且,温压压坯的弹性后效比室温压制降低了40％,在1120℃烧结1h后的烧结密度为7.32g/cm~3.     

注重流动性、充填性的粉末冶金用预混合铁粉的开发

压制生产率是粉末冶金生产过程中的一个重要课题。控制压制生产率的生产作业有：（1）粉末从料仓中的排出;（2）将粉末充填于模具型腔中。为了评定粉末的排出特性,设计了简易的粉末排出装置,用来测定铁基预混合粉的临界流出径。已证明临界流出径和料仓中粉末的流动型式密切相关。在将粉末充填于模具型腔内的作业中,发现将空气从模具型腔内排出是一个重要现象。与常规装粉靴相比,可将空气加速从模具型腔中排出的“搅拌式装粉靴”,能够提高装粉速率和减小粉末压坯重量的波动。     

温压动态压制曲线及颗粒重排贡献率的探讨

通过对铁粉的动态压制曲线的研究认为粉末的温压成形过程可大致分为三个阶段。在第一阶段粉末颗粒重排起主导作用, 对温压致密化起了重要作用。温压成形过程颗粒重排的贡献率明显大于冷(室温)压。常规温压的颗粒重排占总压制行程的44%, 比冷压的颗粒重排份额提高了15%。而有模壁润滑温压的颗粒重排占总压制行程的50%, 比冷压的颗粒重排份额提高了31%。     

丰田压制法

丰田汽车中心研发室的研究人员利用温压、模壁润滑与高压制压力 ,使铁基粉末压坯近乎达到全密度。实验表明 ,最佳润滑剂是水中弥散分布着无污染硬脂酸锂 (10 μｍ)。这种润滑剂用于加热的模具上 ,可在压坯表面迅速形成 1μｍ厚均匀的化学吸附润滑膜 ,通过机械化学反应 ,可在很高的压力下压制。例如ＡＳＣ10 0 2 9铁粉 ,模壁润滑 ,压制压力为 1176ＭＰａ ,4 2 3Ｋ温压 ,生坯密度可达 7 74ｇ/ｃｍ3 ,弹性后效小于 0 1%。ＡＢＣ10 0 30铁粉 ,模壁润滑 ,压制压力为 1960ＭＰａ ,4 2 3Ｋ温压 ,生坯密度可达 7.85 ｇ/ｃｍ3 ,相对密度为 99 9%。…     

以旋转阴模双向压制薄壁套制品

介绍了在工业条件下长薄壁粉末铁套的双向压制结果。研究了带旋转阴模的工业压制模具的设计。对双向压制工艺和脱模工艺进行了摩擦学析。讨论了双向压制摩擦系统部分的及全部的平衡条件。给出了平均密度和沿压坯高度方向密度分布的结果。与传统的压制方法相比,在最佳阴模圆周速度V=0.79mm/s(n=1r/min)时,沿压坯高度方向的密度差约降低5倍,压坯平均密度约提高10%(单位压制压力p=600MPa)。     

压制方式对电解Cu粉高速压制成形特征的影响

采用HYP35-2型高速冲击压机对电解Cu粉(150μm)分别进行单次和2次压制成形,测定压坯的密度、最大冲击力与脱模力,研究压制方式对成形过程的影响。结果表明,在总冲击能量相同的情况下,单次压制的压坯密度高于2次压制的密度;而2次压制时,第1次压制能量较小时获得的压坯密度高于第1次能量较大时的压坯密度。压制方式对最大冲击力的影响与其对压坯密度的影响相似。采用单次压制和2次压制的高速压制方式,脱模力均较低且稳定,压坯密度与最大压力之间的关系符合黄培云压制方程。此外,对比研究了单次压制和2次压制的应力波曲线。     

以不同压制方法和烧结温度制备的高强度粉末冶金材料的性能

Astaloy CrM(含3%Cr和0·5%Mo)和Astaloy Mo+2%Ni(含1·5%Mo)经普通方法压制,在网带炉1 120℃烧结后,抗拉强度为650~1 000 MPa。若在1 200℃以上温度烧结,抗拉强度的值会增加。如果采用温压处理或高速压制结合高温烧结,上述材料抗拉强度的值会进一步提高。本次实验选用Astaloy Crm、Astaloy Mo和Astaloy Mo+2%Ni,分别采用普通压制、温压工艺、高速压制方法制成样品,温压时粉末的温度是130℃,模具的温度是150℃。实验采用两种烧结:1 120℃烧结30 min,烧结气氛为90/10 N2/H2,冷却速度为0·8~1·0℃/s;1 250℃烧结30 min,烧结气氛为90/…     

On the compressibility of metal powders

A new equation relating the porosity of green compacts and the applied external pressure during the cold die compaction of metal powders is proposed. All of the parameters in the model have a clear physical meaning. These parameters are those related to the plastic behaviour of the material, as well as to the ‘structural resistance’ of the powder mass. Also the friction between the powders and die walls is considered, as a kind of constraint that diminishes the local pressure borne by the fully dense material. The model includes, as a key parameter, the tap porosity of the powders (an extremely useful property that contains the morphometric information of the powder). The proposed model has been experimentally checked with the compressibility curves obtained with five metal powders of different types. The agreement between the model and experimental data is reasonable over the tested pressure range.     

不同类型金属粉末的温压行为

研究了铝粉、铜粉、钨粉的温压压制行为,并与铁粉的温压过程进行了对比。实验发现,温压无论对塑性粉末还是脆性粉末均有效果。温压压制可提高粉末压坯密度,降低压坯脱模压力和弹性后效     

用温压制造高密度材料的关键参数

温压技术是由在加热的阴模中压制预热的粉末组成[1],已知温压有助于零件密实,从而改进烧结件的性能[2,3]。温压需要在适合温压的温度范围内进行。特别是,粉末混合粉应具有好的流动性,同时对阴模模壁有良好润滑性,以减小脱模力。在试验室和工业生产中都研究了用粘结剂处理的和未经粘剂处理的用温压技术制造的材料的性状与性能。为了确定和定量各种关键生产参数,诸如压制压力,粉末温度与阴模温度,生产速率及零件大小对生坯和烧结件特性和零件脱模力的影响,进行了专门的试验研究。依照粉末流动性与松装密度的稳定性,压制压力与温度以及压制零件的重量与密度讨论了温压的工艺性。     

A densification equation derived from the stress-deformation analysis of uniaxial cold compaction of metal powder mixes

A new densification equation for uniaxial cold compaction of four low alloy steel powders was determined from the deformation vs. mean axial stress correlation. Both deformation and stress are averaged along the height of the powder column. A power law relation, with two parameters representing the plasticity and the inverse of the resistance to deformation (densification) of the powder mix, respectively, fits the curves that are divided in two steps, distinguished by the prevailingdeformation/densification mechanism (rearrangement or plastic deformation).

Densification of the four powder mixes is greatly affected by the starting density in the die cavity, while the chemical composition of the base iron powder has a less significant effect.     

Densification and deformation during uniaxial cold compaction of stainless steel powder with different particle size

The behaviour of austenitic stainless steel powder column during uniaxial cold compaction was investigated in this work. Powders with different particle size were compacted to the same green density in a hydraulic press, also providing different H/D ratios in order to account for the influence of geometry. The analysis of the data continuously recorded by the press allowed distinguishing the contribution of the reversible phenomena (elastic deformation of powders and tools) and of the irreversible phenomena (rearrangement and plastic deformation of the powders). An analytical model for densification was proposed, considering both density and increase in density versus the applied pressure. The trend of reversible and permanent deformations versus the applied pressure was evaluated, also proposing an analytical model. The comparison between the densification curves and the curves of permanent deformation allowed highlighting the physical meaning of the model describing the increase in density for the different particle size.     

几种润滑剂对温压工艺的影响

温压工艺的技术关键之一是润滑剂 ,其主要作用是减小压制过程中粉末颗粒与模壁之间及粉末颗粒之间的摩擦 ,增大有效压力 ,从而使压坯密度相对于传统压制工艺明显提高。不同润滑剂的润滑效果不同 ,最佳压制温度也有差异。本文选用 3种不同的润滑剂 ,在不同温度、压力条件下采用温压技术制备铁基粉末冶金材料 ,研究了压坯密度的变化规律和它的力学性能 ,探讨了润滑剂对温压工艺的影响     

Investigation of warm compaction and sintering behaviour of aluminium alloys

Abstract

The effects of warm compaction on the green density and sintering behaviour of aluminium alloys were investigated. Particular attention is paid to prealloyed powders, i.e. eutectic and hypereutectic Al-Si alloys, regarding their potential applications in the automotive industry. The effects of chemical composition, alloying method, compacting temperature and the amount of powder lubricant were studied. The compaction behaviour was examined by an instrumented die enabling simultaneous measurement of density, die wall friction coefficient, the triaxial stresses acting on the powder during the course of compaction and ejection pressure. The sintering behaviour was studied via dilatometeric analysis as well as normal batch sintering. The results show that warm compaction could be a promising way to increase the green density of aluminium alloys, especially prealloyed powders, and to decreased imensional instability during sintering. Moreover, it reduces the sliding friction coefficient and the ejection force during the powder shaping process. This paper presents the significant advantages and drawbacks of using the warm compaction process for commercial PM aluminium alloys.     

铁粉特性对温压生坯密度的影响

从铁粉类型、粒度组成、化学成分和粉末显微硬度等因素对温压生坯密度的影响情况进行了系统试验,结果表明,通过控制粉末形状、粒度分布、化学成分等因素,温压可获得高压坯密度,在本试验中,经过处理的国产粉温压压制密度最高可达7.30g/cm3,接近国外粉末压制密度。     

Mechanical properties of green compacts. II. Effect of powder relative bulk density on the strength of compacts with different forming temperature conditions

Mechanisms of strength for green compacts made from powders of iron, nickel and its alloys, copper, tin, and zinc are analyzed. The strength of green compacts prepared from metal powders of medium fineness with a relative bulk density (RBD) from 0.119 to 0.568 by two-way compaction in rigid dies with homologous temperatures from 0.15 to 0.59 (pressure from 200 to 800 MPa, powder deformation rate 10^?2–10^?3 m/sec) is studied. Compact strength is determined by diametric compression of cylindrical compacts. The dependence of strength on compact porosity is studied by the Bal’shin equation. The possibility is demonstrated of using this relationship in order to describe hot compaction and formally describe cold compaction of powders with RBD up to 0.40. The effect of homologous temperature and powder RBD on compact strength is determined. The homologous temperature for transition from warm to hot compaction and the effect of compact density (degree of deformation) on this temperature is studied. It is shown that linear approximation is possible for the dependence of compact strength on powder RBD according to the equation σ _f.c = 87–217?RBD.