用于常规粉末冶金工艺的生坯切削加工

生坯切削加工的好处已众所周知，如切削刀具的寿命较长，能够用可烧结硬化粉末制作形状复杂的零件等。零件生坯强度高可防止在运送过程中生坯开裂与损坏。但是，用常规粉末冶金工艺不易达到所要求的高生坯强度(约大于20MPa)。因此，生坯切削加工尚未得到广泛应用。用魁北克金属粉末公司(QMP)新开发的高生坯强度(high green strength，简称HGS)聚合物润滑剂。正在消除使用生坯切削加工的限制。这种润滑剂的一个杰出特性是其对温度的敏感性。在压制温度55℃下整个坯件就能获得高生坯强度，这用冷压很容易达到。若将零件生坯压制到密度6．8g／cm^3，随后经固化处理。甚至可将生坯强度增高到48MPa左右。这样高的生坯强度使得用常规粉末冶金工艺制造的零件都能进行生坯切削加工。本文介绍了用正时链轮进行生坯切削加工试验的一些结果。使用的材料是由QMP ATOMET 4601与HGS润滑剂组成的可烧结硬化的粉末混合料。先用冷压将链轮压制到密度约6．8g／cm^3，再对用压制的生坯与经固化处理的生坯进行切削加工(在齿的中间车槽)。结果表明，HGS润滑剂，特别是固化处理后，可赋予生坯足够高的强度，以进行装卡与切削加工作业。切削加工表面光滑且棱边完好。由可烧结硬化粉末制作的可生坯切削加工的链轮，能省掉热处理，大大延长刀具寿命以及改善尺寸公差。     

粉末冶金零件需要的高性能润滑剂

目前粉末冶金零件产业要解决的主要问题是:在合理降低成本的情况下生产高密度零件。生产高密度零件的工艺方法有很多种,其中包括零件的成形工艺和烧结技术。特别是,像温压与模壁润滑之类的一次压制工艺。这种工艺依据粉末的组成,生坯密度可达到的范围为7.2~7.5 g·cm-3。尽管如此,和传统压制工艺相比,这些压制工艺一般都需要严密控制,费用也相对较高,还有可能减小生产率。为了能让冷压制或控制温度的阴模压制达到较高的生坯密度,最近开发了一些新的高性能润滑剂。本文介绍了这些新开发的高性能润滑剂在试验室与大量生产中得出的生坯与烧结件特性。特别对这些新润滑剂和其他常规润滑剂的压制与脱出特性进行了对比。     

温压工艺的研究进展

温压工艺在制造低成本、高密度、高强度、高精度异形复杂的粉末冶金零件方面具有巨大的优势。因而，详细介绍了该工艺所具有的诸如压坯密度大、强度高，烧结密度高、密度分布均匀，脱模压力低，制造成本低等技术与经济特点；分析了其关键技术，如温压用粉末制备、新型润滑剂和温压系统；总结了其致密化机理，即颗粒重排和塑性变形，并概括了其应用状况。最后指出发展我国温压工艺的意义。     

粉末冶金零件生坯切削加工性能研究进展

综述了粉末冶金生坯切削加工技术的进展,指出其关键在于提高生坯强度以达到可加工的要求;分析了切削参数控制与刀具磨损和零件质量的关系,以及对生坯样品加工性能、烧结性能等的影响。通过预烧结、温压等工艺提高了钨基合金粉末冶金生坯的强度,并对其进行了切削加工试验。结果表明,经预烧结或温压的生坯均可进行装夹与切削加工,而预烧结生坯的加工性能更好,其加工表面光滑且棱边完好;采用生坯切削加工技术,可延长粉末冶金零件生产中的刀具寿命,节约成本,提高效率。     

高密度铁基粉末冶金零件制备技术

介绍了东睦新材料集团股份有限公司已经使用的高密度铁基粉末冶金产品制造技术,包括温压成形、温模压制、复压复烧等,并讨论了这些技术的优缺点。所述高密度铁基粉末冶金零件制备技术虽可以提升粉末冶金零件的密度,强度也达到较高的水平,但是零件的精度及粗糙度等尚不能满足高端应用的要求,仍需进一步机加工。未来仍需提升粉末冶金模具的制造精度、粉末特性和工艺稳定性,开发低成本、高精度、高强度的烧结铁基零件制备技术。     

粉末冶金温压技术的进展

1994年,国际上出现了高密度粉末冶金铁基零件的生产新技术———温压技术。该技术通过一次压制,一次烧结的较低成本工艺使零件的密度提高0.15～0.25g/cm3。这个密度的提高给我们的提示,温压技术对粉末冶金铁基结构零件的发展前景,经过6年的实践,国际上的新进展,我们对温压技术要有一个怎样的认识,温压技术的控制因素—温压技术的"瓶颈"问题,产业化的困难,具有操作性的对策等,这些都需要认真思考。本文将就上述问题,特别是对技术的理解—温压技术系统工程,包括:零件设计基础、铁粉、润滑剂、模具与模壁润滑、烧结、热处理等环节;市场经济条件下的团队合作几个方面,提出一些初步的意见。     

用温压制造汽车变速器输出轴毂

汽车中应用的铁基粉末冶金零件在不断增加,这主要是由于密度的增高和动态性能的改进。粉末冶金零件的新应用还必须通过不断采用新工艺的最终形成形能力及减少制造工序,降低生产成本。用于制造某些新零件的生产工艺,还必须能生产出几何形状复杂的薄壁零件。采用温压工艺(ANCORDENSETM),用一次压制可达到较高密度水平。这种工艺还能增高生坯强度与减小脱模力。汽车变速器输出轴毂在20世纪90年代以前,是用二次压制/二次烧结工艺大量生产的一个重要粉末冶金零件。1995年前后,用温压工艺进行了制造这种零件的试验,并和用二次压制/二次烧结工艺生产的零件进行了对比。     

关于用不同工艺制作的高密度铁基粉末冶金材料性能的研究

可能有几种方法可使铁基粉末冶金零件达到较高密度。二次压制/二次烧结可使密度大于7.3g/cm3,但受到成本与几何形状条件的限制。对一种新方法进行了评价,用这种方法可一次压制得到高使用性能材料,并将其和其他生产工艺进行了比较。比较是利用Ancorsteel 85HP与Distaloy 4800A基本材料进行的。对各种生坯与烧结件性能进行了评价,其中包括:生坯强度,横向断裂强度,拉伸性能及冲击值。数据清楚地证明,拥有专利的[1]ANCORDENSETM工艺(温压)提供的使用性能可与二次压制/二次烧结制作的相比拟。用一次压制达到了生坯密度值的无孔隙密度极限的98.5%。     

为生坯加工用强化生坯强度的润滑系统的开发

粉末冶金零件烧结后往往面要切削加工，以达到压制时无法成形的设计特征或窄小的尺寸公差。可是，随着高性能材料出现，鉴于这些材料烧结后表观硬度与强度高，采用生坯切削加工可减低切削加工费用与增强竞争性，因此，是一种很有吸引力的生产工艺。现在，采用新润滑系统可使零件在烧结前进行切削加工，这些新润滑系统和常用润滑剂相比，都是一些能大大增高零件生坯强度的聚合物润滑剂。在切削加工时，较高的生坯强度可减低生坯开裂和／或棱边剥落的危险。这篇论文对由新聚合物润滑系统或常用EBS蜡润滑剂压制的烧结硬化材料FLC-4608的脱模特性与生坯特性进行了比较。这种比较是用实验室与生产规模压机压制成形的密度为6．7～7．1g／cm^3的横向断裂试样和油泵齿轮进行的。还报告了油泵齿轮烧结后的性能和零件间性能的均一性。     

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。     

润滑剂含量对钛粉高速压制性能的影响

采用高速冲击压机压制钛粉,研究润滑剂含量对压坯性能的影响.结果表明:加入适量的润滑剂可以提高钛粉成形时的质量能量密度,从而获得更高密度的压坯.当润滑剂加入量为0.3%(质量分数)时,钛粉成形的最大质量能量密度为0.192 KJ/g,压坯密度为4.38 g/cm3,相对密度为97.4%.此外,适量的润滑剂能提高钛粉压制过...     

Bearing Materials by Powder Metallurgy

Abstract

The dependence of green strength on green density and on compacting pressure was investigated for the bidirectional die pressed and isostatically pressed Cu powder compacts. The breaking strength of the pressed Cu compact was found to increase with green density and also with compacting pressure. The green strength seemed to be directly proportional to the contact area between powder particles. A theoretical equation for the relationship between green density and contact area was derived from a geometrical consideration, and agreed well with experimental findings. PM/0272     

Improving iron compact green strength using powder surface modification

Abstract

In powder metallurgy, green strength has important consequences for part production rates and product end quality. Mechanical interlocking and interparticle cold welding are the main mechanisms responsible for green strength. These mechanisms are affected by compaction pressure, temperature, amount of lubricant and additives admixed to the powder, and surface characteristics of the powder. The present paper describes the effect of iron powder surface modification on the green strength of compacted specimens. The green properties of compacts fabricated from iron powder treated with diluted sulphuric acid and coated with copper by a non-catalytic displacement plating method are presented. The results indicate that surface modifications strongly influence the green strength of the compacts.     

润滑剂对Fe基粉末冶金材料温压工艺的影响

通过扫描电子显微镜观察和性能测试研究了硬脂酸锌、乙烯基双硬脂酰胺(ethylene bis stearamide,EBS)、复合润滑剂以及压制温度对Fe基粉末冶金材料温压工艺的影响规律。结果表明:当润滑剂加入量(质量分数)超过0.4%后,Fe基粉末的流动性和松装密度均随润滑剂加入量的增加而降低,其中加入单一EBS润滑剂的影响更大。添加润滑剂后增加了Fe基粉末冶金生坯的致密度,其中添加硬脂酸锌和复合润滑剂的Fe基粉末冶金生坯断口颗粒间结合更为紧密。润滑剂对提高Fe基粉末冶金试样生坯密度、烧结密度及抗弯强度的作用顺序为复合润滑剂硬脂酸锌EBS,Fe基粉末冶金材料的密度和力学性能均随温压温度的升高而增加。在最佳润滑剂加入量0.4%时,120℃温压Fe基粉末冶金试样密度比室温压制Fe基粉末冶金试样的密度提高了0.14~0.21 g/cm~3,硬度和抗弯强度提高了40%~65%。     

用先进的温模压制工艺生产高密度汽车零件

高密度压制工艺(温模压制)扩大了粉末冶金零件的应用范围。鉴于一次压制/一次烧结(1P/1S)所达到的密度已超过了7.3 g/cm~3,这种成本可行的零件生产方法,往往是最新高密度汽车零件应用采用的方法。达到较高零件密度的关键的第一步是改进润滑剂与预混合工艺,以将润滑剂的含量减小到预混合粉重量的0.25%。本文详述了新润滑剂系统,能够使润滑剂含量减低到预混合粉重量的0.25%,并使生坯密度高达7.5 g/cm~3左右。除了生坯密度高外,生坯强度也达到了30 MPa左右;并能将压制与生坯零件后续处理时开裂的可能性减小到最小程度。虽然还不能用于所有类型的零件,但在Cloyes Gear已证明,这种新的粉末预混合粉,对于生产汽车的气门机构零件是成功的。将详述开发工作的情况和得到的生产体验,并讨论其优点与局限性。     

Relationship between physical structure and machinability of green compacts

Abstract

The dependence of green machinability on compact density and strength was investigated for room temperature and warm compacted steel powder compacts containing two different types of lubricant. Brazilian disc compression tests were employed to determine green strength, while machinability was assessed in terms of response to drilling.

For the room temperature compacted materials, it was found that high compact densities and strength were not, in most cases, associated with improvements in machinability. Furthermore, it was shown that lubrication (both type and quantity) and compaction pressure plays a critical role in determining the level of breakouts observed. In contrast, the use of warm compaction, in conjunction with specially designed lubricants, has been shown to be a suitable method of producing high density, high strength compacts while retaining good green machining characteristics. Mechanisms responsible for the observed behaviours of both the room temperature and warm compacted specimens have been forwarded in the present paper.     

Measurement of green strength of warm pressed Distaloy PM compacts: influence of specimen geometry and test method

Abstract

It is important that the green strength properties of powder compacts be accurately determined if advanced manufacturing techniques, such as green machining, are to be exploited successfully. In this study, the green strength of Distaloy AE Densmix, a powder mix designed for such applications, was measured using several test methods. Fracture statistics were correlated with compact density and test method employed, and the Weibull modulus calculated for each case. It was found that Weibull analysis accurately predicted the green strength dependence on the test configuration utilised.     

Influence of Lubricants on Dimensional Changes and Mechanical Properties of Sintered Ferrous Compacts

Abstract

The influence of admixed zinc stéarate on the shrinkage of uniaxially pressed iron powder compacts has been studied. For pressing conditions which caused inhibition of compaction the removal of the stéarate during sintering produced an increase in shrinkage parallel to the pressing axis and in direct proportion to lubricant content. Additions of stearic acid (varying particle size), zinc stearate, lithium stearate, stearamide, and Cosmic 64 wax were used to investigate the influence of lubricant on mechanical properties of green and sintered iron powder compacts. Green strength was reduced relative to unlubricated material only by lubricants whose physical and chemical properties enabled them to produce and maintain extensive interparticle films during pressing. Vapour from the rapid initial decomposition of lubricants which reduced green strength could have a deleterious physical influence on the tensile strength of dewaxed or sintered Fe compacts. Decomposing lubricants also produced undesirable chemical effects. These arose from reactions between lubricant decomposition products and the matrix or by these products interfering with reactions between matrix and sintering atmosphere.     

Pressing behavior of atomized iron powders

Conclusions The optimum zinc stearate content, ensuring the greatest compressibility of a powder at a given pressing pressure, is determined mainly by the volume of interparticle pores. The higher the density of a compact and the smaller the size of its pores, the smaller is the amount of zinc stearate it can hold. The weakening action of zinc stearate, which manifests itself in stress relief at interparticle contacts during pressing, substantially increases the density of compacts and at the same time decreases their strength. This phenomenon is particularly pronounced with compacts from powders of poor compactibility. After pressing at any given pressure, the strength of a compact with zinc stearate will be higher than that of a compact without a lubricant when the decrease of the contact surface brought about by the elastic aftereffect in the stearate is counterbalanced by the increase of this surface resulting from better compressibility of the powder. The addition of an optimum amount of zinc stearate to an iron powder is always more effective than lubrication of the die walls. A new mechanism of densification of iron powder with zinc stearate is proposed, in which the key factor is an intensification of stress relief at interparticle contacts by the solid lubricant.Translated from Poroshkovaya Metallurgiya, No. 5(221), pp. 16–22, May, 1981.