Effects of milling and active surfactants on rheological behavior of powder injection molding feedstock

ＩＮＴＲＯＤＵＣＴＩＯＮＰｏｗｄｅｒｉｎｊｅｃｔｉｏｎｍｏｌｄｉｎｇ (ＰＩＭ )ｆｉｔｓｅｓｐｅｃｉａｌｌｙｆｏｒｍａｎｕｆａｃｔｕｒｉｎｇｃｏｍｐｌｅｘｓｈａｐｅｄｐａｒｔｓｏｆｃｅｒｔａｉｎａｌ ｌｏｙｓｗｉｔｈｈｉｇｈｐｅｒｆｏｒｍａｎｃｅ[1 ] .Ｈｏｗｅｖｅｒ,ｄｕｅｔｏｔｈｅａｇｇｌｏｍｅｒａｔｅｄｉｒｒｅｇｕｌａｒｓｈａｐｅ,ｆｉｎｅｐａｒｔｉｃｌｅｓｉｚｅ,ｈｉｇｈｉｎｎｅｒｐｏｒｅｓａｎｄｓｐｅｃｉｆｉｃｓｕｒｆａｃｅａｒｅａｏｆｔｈｅｉｎｉｔｉａｌｔｕｎｇｓｔｅｎｐｏｗｄｅｒ,ｔｈｅ…     

Effects of surfactant on properties of MIM feedstock

Effects of the surfactant for improving the properties of MIM feedstock were investigated. Feedstocks were prepared by 17-4PH stainless steel(SS) powder and paraffin wax-based binder containing different contents of stearic acid(SA) as the surfactant. The viscosity of the feedstock decreases significantly when the SA is added. Besides, the wetting angle of the binder against the 17-4PH SS powder decreases greatly and the critical solid loading increases with the adding of the SA. Fourier transformation infrared spectroscopy(FTIR) analysis was used to prove the interaction between the SA and the 17-4PH SS powder. Chemical bonding is found on the surface of 17-4PH SS powder after mixing and it helps a lot to enhance the interacting force between the binder and the powder. Then an adsorbing model was adopted to estimate the least content of the surfactant that formed a monolayer adsorption on the mono-sized spherical powder (with smooth surface). The least content of the surfactant is calculated to be 0.19%. Whereas, the experiments indicate that about 5% is the optimal value to improve the properties of the feedstock. The reason may come from two aspects: firstly, the powders used in current experiment are not all mono-sized spheres and the coarse surface of the powder has a great effect on the adsorptive capacity of the powder; secondly, multilayer adsorption is likely to occur on the powder surface, which will also increase the adsorptive capacity.     

Rheological properties of metal injection molding feedstock

Viscosity of a polyethylene glycol-polymethyl methacrylate (PEG-PMMA) binder and PEG-PMMA/Fe-2Ni feedstock in powder injection molding was measured and calculated. A logarithmic additivity between viscosity of the binder and that of its constituents was found. Other factors, such as temperature, powder loads, content and type of surface-active agents and those of polymers, in relation to rheological properties of feedstock were discussed as well. The results showed that with increasing viscosity of surface-active agent, polymer melt index or temperature, the feedstock viscosity decreased while higher polymer content and powder loading would lead to additional feedstock viscosity. The relationship mentioned above is expressed and effectively explained why the change rate of feedstock viscosity will slow down with the increase of shear rate.     

表面活性剂添加对超细98W-1Ni-1Fe粉末注射成形喂料流变行为的影响(英文)

研究超细98W-1Ni-1Fe粉末的注射成形。系统研究球磨和硬脂酸(SA)添加对粉末特性以及喂料流变行为的影响。结果表明:球磨和SA添加均有效提高喂料的装载量。SA添加可以避免喂料制备过程中粉末与粘结剂间的表面反应,从而缩短混炼时间。SA添加可以降低喂料的粘度,但这种效果随温度升高而逐渐消失,在125℃以上时变为一种不利的效果。SA添加可以降低注射所需的温度。添加SA的粉末喂料在115℃时具有最低的粘度及剪切敏感性,而未加SA的粉末喂料在135℃时才具有最低的粘度及剪切敏感性。同时,添加SA的粉末喂料相比未添加SA的粉末喂料具有较低的温度敏感性及较佳的综合流变性能,因此,更适合于超细98W-1Ni-1Fe粉末的注射成形。     

A new starch-based binder for metal injection molding

A composition of starch and linear low-density polyethylene (LLDPE) was prepared as the binder and a mixture of this binder with 316L stainless steel powder was used to achieve a feedstock with 57% vol. powder loading. Rheological specifications of the binder and the feedstock were observed by means of capillary rheometery. Pseudo-plastic behavior of the binder and feedstock was investigated as a necessity in metal injection molding (MIM) process by proper flow characterization tests and their viscosity as the most significant flow characteristic was obtained in acceptable ranges. Thermogravimetric analysis (TGA) was carried out on feedstock in order to understand decomposition behavior of the binder components. In the next step, injection molding of the components was successfully conducted. Mechanical properties of compacts were then investigated through the triple point flexure test and the results showed that mechanical strength of specimens are very close to established ranges. The density of green parts was measured to assess the compaction of feedstock and it was achieved within the expected range for ferrous-based feedstocks. Debinding process was accomplished on compacted articles at three different temperature ranges including 70, 80 and 90 °C. Sintering process also was successfully accomplished on samples. For observing microstructures, the surface and cross section of specimens were compared before and after debinding as well as after sintering using scanning electron macrograph (SEM). Generally, this newly developed binder demonstrated a good potential for being utilized in MIM process.     

Determination of critical and optimal powder loadings for 316L fine stainless steel feedstocks for micro-powder injection molding

Adapted from powder injection molding (PIM), the micro-PIM technology satisfies the increasing demands for functionalization and miniaturization of micro-parts. Research works in this area have been carried out through micro injection molding tests issued from mixtures consisting in 316L stainless steel fine powders with D₅₀ = 3.4 μm and different thermoplastic polymeric binders. The well appropriate polymer–powder formulations are composed with different binders. The binders have been adapted to micro-injection and tested to find out an optimum feedstock. The rheological characterization of the elaborated feedstock has been carried out according to the selected stainless steel powders and polymers. The critical powder volume loading has been determinated and fixed in the range of 68–70%, and the optimal powder volume loading has been chosen around 66% for 316L stainless steel feedstock (D₅₀ = 3.4 μm). This choice has been confirmed by processing of the micro-components with the retained feedstock loaded up to 66%.     

Rapid debinding of 316L stainless steel injection moulded component

Wax-based binder system is widely used but they suffer from long debinding time and a tendency to slump or distort during debinding. This has been a major obstacle for the economic process for metal injection moulding (MIM). For improving the debinding process, two-step debinding process has been introduced. Gas-atomised 316L stainless steel powder was injection moulded using two types of multi-component binder system comprising (1) a major fraction of paraffin wax and a minor fraction of polyethylene (PE) and stearic acid (SA) as a lubricant, (2) a major fraction of polyethylene glycol (PEG) and a minor fraction of polymethyl methacrylate (PMMA) binder system. Debinding was carried out in two steps; first, the moulded part is immersed in heptane or distilled water at 60 °C to remove the major component of the binder and then heated to remove the remaining binder. The results show that no swelling or distortion was observed on the moulded specimens on both binder systems. Furthermore, the specimens had an adequate strength for handling even after solvent extraction. Large pore were formed from the surface to the interior of the debound part during solvent extraction, allowed easy escape of pyrolysis gases during thermal debinding. Thermal debinding with ramp heating at rates from 3 to 15 °C/min was found to be successful.     

Influence of paraffin wax characteristics on the formulation of wax-based binders and their debinding from green molded parts using two comparative techniques

The influence of paraffin wax characteristics on the formulation of wax-based binders has been examined. Four paraffin waxes (PW₁, PW₂, PW₃ and PW₄) were physically and molecularly evaluated and four binder systems 1–4 were formulated by mixing the major binder consisting of the paraffin wax with stearic acid (SA) and the minor binder; poly (ethylene-co-vinyl acetate) (EVA). Differential scanning calorimetric (DSC) and thermo gravimetric analysis (TGA) were used to evaluate the thermal characteristics of the pure binder components and the formulated binder systems. Also, the rheological properties of the formulated binder systems and feedstock were studied to measure their viscosities. Data indicated that the binder system no. 4 consisted of 35 wt.% EVA (containing vinyl acetate content of 9 wt.%), 62 wt.% of PW₄ and 3 wt.% of SA is the preferable binder for powder compression or injection molding. Also, in order to compare between the two debinding techniques (solvent evaporation–condensation and solvent immersion techniques) to extract the soluble binder components (paraffin wax and SA) completely from the green molded parts, powder compression molded parts were prepared and subjected to both techniques. It can be concluded that solvent immersion is a preferable technique as it saves the amount of solvent used as compared with the evaporation–condensation technique. Consequently, the solvent immersion technique using cyclohexane solvent at extraction temperature of 40 °C and after extraction time of 5 h are the most suitable conditions for extracting the major binder and SA constituents completely from the binder mixture in the green molded part.     

大长径比超细WC-Co圆棒PIM充模过程的数值模拟

基于计算流体动力学的粉末-粘结剂双流体模型,采用CFX商业软件对大长径比超细WC/10Co粉末注射成形(PIM)充模过程进行数值模拟。结果表明:数值模拟结果与实际充模过程相一致,其假设条件和参数设置具有合理性,双流体模型具有可行性;粉末与粘结剂的温度分布一致,喂料熔体最低温度(≥330K)高于粘结剂的玻璃化温度,不发生凝固现象;粉末的粘度为50.0～379.4Pa·s,粘结剂的粘度为2.9～9.2Pa·s,粘度差是造成偏析现象的主要原因;从浇口处到模壁处,粉末与粘结剂的相对速度差从0.2%增加到1.8%,从浇口处到远端,相对速度差从0.1%增大到1.6%,相对速度差是引起偏析现象的主要原因。     

Effects of cooling rate on mechanical properties and corrosion resistance of vacuum sintered powder injection molded 316L stainless steel

This study presents the results of corrosion behavior of powder injection molded 316L stainless steel parts sintered in vacuum. The feedstocks of metal powder and plastic binder were prepared and their viscosity was measured. Green samples were injection molded and binder was removed from the green parts. Brown test parts were sintered at 1325 °C with heating rate of 5 °C/min and 10 °C/min for 2 h followed by the same cooling rate. Corrosion response of the sintered test samples was measured by weight loss method in Ringer's Solution of pH 7.4 for 15 days. The test samples using cooling rate 10 °C/min showed higher mechanical properties and improved corrosion resistance compared to those sintered at low heating and cooling rate. High cooling rate reduced the evaporation of Cr and developed passive chromium oxide layer on the test samples resulting improved corrosion resistance.     

Effect of thermo-mechanical properties of PIM feedstock on compacts shape retention during debinding process

1　ＩＮＴＲＯＤＵＣＴＩＯＮＡｍｏｎｇｃｒｉｔｉｃａｌｉｓｓｕｅｓｉｎｔｈｅｐｏｗｄｅｒｉｎｊｅｃｔｉｏｎ ｍｏｌｄｉｎｇｐｒｏｃｅｓｓｔｈｅｒｅａｒｅｔｈｅｃｏｎｔｒｏｌａｎｄａｖｏｉｄａｎｃｅｏｆｄｉｓｔｏｒｔｉｏｎｄｕｒｉｎｇｔｈｅｒｍａｌｄｅｂｉｎｄｉｎｇａｎｄｔｈｅｍｉｎｉ ｍｉｚａｔｉｏｎｏｆｓｔｒｅｓｓｅｓｉｎｔｈｅｃｏｍｐａｃｔａｆｔｅｒｄｉｅｆｉｌｌｉｎｇ[1] .Ａｆｔｅｒｍｏｌｄｉｎｇｔｈｅｓｔｒｅｎｇｔｈｏｆｔｈｅｃｏｍｐａｃｔｓｉｓｄｅｐｅｎ ｄｅｎｔｏｎｔｈｅｐａｒｔｉｃｌｅ…     

316L不锈钢粗粉注射成形喂料的流变行为

制备了平均粒度为30μm的316L不锈钢粗粉注射成形喂料,研究了剪切速率、温度对喂料流变行为的影响,应用毛细管粘度计测量了3种喂料在不同温度下的粘度值,比较了3种不同成分喂料的应变敏感性因子的大小。结果表明:粉末装载量为58%、粘结剂成分为65%PW+30%LDPE+5%SA的喂料应变敏感性因子较小,较适合316L不锈钢粗粉的注射成形。     

Relationship between binder contents and mechanical properties of 17-4 ph stainless steel fabricated by PIM process and sintering

Mechanical properties and microstructures of 17-4 ph stainless steel parts produced using different binder contents (powder loading) of powder injection molding (PIM) feedstock have been studied. The tensile and wear properties have been evaluated. Wear tests were conducted by a pin-on-disk tribometer, without lubricant, at different loads and sliding distance. SEM examination of the fracture sufaces revealed good particle bonding and a high ductile fracture surface for high powder loading. The surface fractures of the bars with higher powder loading show a closed porosity. High performance properties such as fully dense, ultimate tensile strength, hardness and wear resistance are obtained with high powder loading.     

Fabrication of cemented tungsten carbide components by micro-powder injection moulding

Micro-powder injection moulding (micro-PIM) is an advanced net-shaping process for the fabrication of metal and ceramic complex micro-components. Cemented tungsten carbide (WC–Co) hardmetal is known for its high hardness and wear resistance in various applications. Micro-PIM is a new alternative manufacturing technique for hardmetal micro-parts. In this work, the fabrication of WC–Co components via a micro-PIM process was studied. A fine WC–10Co–0.8VC (wt.%) powder was mixed with a binder system consisting of paraffin wax, low density polyethylene and stearic acid. A micro-component was injected at low pressure using a semi-automatic injection moulding machine. The injection temperature was determined from the rheological investigation of the feedstock. The binder extraction was carried out in solvent and thermal debinding methods under an argon atmosphere. Thermal gravimetric analysis was used to confirm the removal of the soluble binder from the green part. The sintering process has been performed within a temperature range of 1330–1450 °C under vacuum. After sintering, a density of 94.5% theoretical density was obtained, which is a reasonable value. The micro-components showed length shrinkage between 16 and 22% and good surface quality and hardness values when compared with conventional powder metallurgy. This research shows that micro-PIM is able to produce small WC–Co components with properties comparable to conventional powder metallurgy.     

W—Ni—Fe纳米晶粉末的流变特性

研究了W-Ni-Fe纳米晶粉末的注射成形（MIM）。纳米晶粉末采用机械合金化（MA）的方法制备,然后将这种纳米晶粉末与蜡基粘剂混合以制备出喂料。讨论了MA球磨时间、纳米粉末的体积装载量和实验温度以喂流料流变行为的影响。结果表明,随球磨时间增加,喂料粘度降低,粘度对剪切速率的敏感性也降低,因此,随球磨时间增加,喂料的流动性和成形性变好,随粉末装载量增加,喂料粘度呈非线性增加,喂料粘度与粉末装载量的关系为:η=η0A[1-（ΦΦm）]∧-n,其中n=0.68,粉末经球磨后,粘度变化随温度和剪切速率的变化不大。因此,注射温度和注射速度的变化对MTM产品的质量影响不大。     

粉末注射成形热塑-热固粘结剂的开发研制

介绍了硬质合金粉末注射成形用热塑 -热固性粘结剂RG1- 2、RG2 - 3的开发研制过程。结果表明 :在注射完成之前 ,粘结剂和喂料完全表现为热塑性 ,该粘结剂可直接应用于热塑性注射机。喂料的低温流变性能好 ,粉末临界装载量达到 5 9%。RG1- 2、RG2 - 3注射生坯强度分别达到 5 .8MPa和 7.8MPa ,固化后成形坯强度分别达到 17.6MPa和 19.1MPa。采用该粘结剂及相应的注射成形工艺制备的YG8、YT5硬质合金强度分别达到 2 480MPa和 2 10 0MPa ,硬度分别达到HRA89.7和HRA90 .4,制品最小尺寸偏差达到± 0 .0 2mm ,尺寸精度及保形性优于传统蜡基粘结剂。     

A novel binder and binder extraction method for powder injection molding of tungsten cemented carbide

1　INTRODUCTIONPowderinjectionmolding (PIM ) ,whichisde rivedfromplasticinjectionmolding ,isakindofnet shapepowdermetallurgyformingprocess[13] .Com bininghigh partcomplexitywithhigh productionquantities ,itsupplementstheestablishedprocesseslikediecompaction ,machiningandinvestmentcasting[4 6 ] .Comparingtoconventionalpressing/sinteringprocess,thePIMhasgreattechniqueandcostadvantagesforthepro ductionofcementedcarbidecomponentswithcomplexshapes[7,8] .Sincehydraulicpressureisappliedduringi…     

铌合金注射成形脱脂工艺研究

设计了一种适合于铌合金注射成形的低残碳粘结剂体系,为68％PW-5％LDPE-22％PMMA-5％SA（质量分数）,并研究其脱脂工艺。结果表明：脱脂时间、温度及样品厚度对溶剂脱脂率影响显著。采用三氯乙烯为溶剂,在脱脂温度为40℃,溶剂脱脂6h,即可使粘结剂脱除率达到52．8％,使后继热脱脂时间缩短至7．5h。以粘结剂的DSC差热分析结果为指导,可快速制定合理的热脱脂工艺,在真空热脱脂气氛条件下可使脱脂坯残余碳、氧含量得到有效控制,分别为0．18％．0．25％．     

Enhanced sintering, microstructure evolution and mechanical properties of 316L stainless steel with MoSi2 addition

Sintering 316L stainless steel to near full density with an appropriate sintering additive can ensure high mechanical properties and corrosion resistance. We present here a sintering approach which exploits the dissociation of ceramics in steels at high temperatures to activate sintering densification to achieve near full dense 316L stainless steel materials. MoSi₂ ceramic powder was used as a sintering additive for pre-alloyed 316L stainless steel powder. Sintering behavior and microstructure evolution were investigated at various sintering temperatures and content of MoSi₂ as sintering additive. The results showed that the sintering densification was enhanced with temperature and MoSi₂ content. The distribution of MoSi₂ was characterized by XMAPs. It was found that MoSi₂ dissociated during sintering and Mo and Si segregated at the grain boundaries. Excess Mo and Si were appeared as separate phases in the microstructure. Above 98% of theoretical density was achieved when the specimens were sintered at 1300 °C for 60 min with 5 wt.% MoSi₂ content. The stainless steel sintered with 5 wt.% MoSi₂ exhibited very attractive mechanical properties.     

表面活性剂对金属粉末注射成形喂料性能的影响

研究了表面活性剂对聚乙二醇-聚甲基丙烯酸甲酯/Fe-2Ni粉末注射成形喂料性能的影响。首先用单分子层吸附模型计算出形成单分子层吸附所需表面活性剂的理论值,然后分别将硬脂酸、司班-20、司班-80、吐温-60等不同表面活性剂加入粘结剂中,发现表面活性剂可通过降低粘结剂对粉末的润湿角、降低粘结剂-粉末喂料的粘度而提高最大粉末装载量,在超过单分子层吸附的量之后,继续增加表面活性剂、仍能进一步发挥其有益作用。不同表面活性剂对喂料性能影响的程度有所不同,通过选择合适的表面活性剂,该聚乙二醇-聚甲基丙烯酸甲酯粘结剂对Fe-2Ni羰基粉末装载量达55%（体积分数）。