粉末注射成形两相流动三维数值模拟及粉末与粘结剂的分离

分析齿轮零件粉末注射成形(PIM)实验成形坯密度分布以及成品容易出现飞边和塌陷的位置特点。根据粉末注射成形技术工艺过程的特点给出PIM的双流体模型及初边界条件,基于计算流体力学软件CFX对I型拉伸试样和齿轮零件的PIM两相流动过程进行三维数值模拟。根据数值模拟结果,对PIM充模流动过程中粉末和粘结剂两相速度的变化曲线进行对比分析,证实I型拉伸试样和齿轮零件的PIM充模过程中多个位置发生过不同程度的粉末与粘结剂两相分离现象。对模腔中多个不同结点处发生粉末与粘结剂两项分离的现象进行分析比较。结果表明:PIM充模过程中位于远离浇口狭窄模腔内的点容易产生两相分离现象,粉末与粘结剂两相分离现象只发生在相应位置被充填初期的一段时间内,且不同位置发生的两相分离持续时间也不同。     

PIM充模流动过程中粘度的变化与缺陷形成

通过对复杂几何形腔粉末注射成形(PIM)充模流动过程的数值模拟,给出了充模流动过程中模腔内粘度的变化和分布情况,分析了模腔内粘度的最终分布与PIM缺陷形成的关系.模拟结果表明,由于模腔接近充满时压力急剧升高构成无梯度压力场,导致模腔内粘度的最终分布复杂.在充模流动中心区域会形成较高粘度的小区域,分析了这些高粘度小区域的形成及其形状大小的变化过程.指出在流动中心区域形成的高粘度小区域可能使PIM充模流动过程产生粉末-粘结剂两相分离和成形坯件中粉末分布不均的现象.     

Effect of Zr, Mo and Y Adding on Microstructure, Mechanical and Electrical Properties of Au-Pd, Pt-Ir and Pd-Ru Systems

将金属粉末注射成形充模过程视为粉末、粘结剂和空气的三相流动过程,给出了金属粉末注射成形充模多相流动的控制方程。根据钳口复杂模腔的铁粉注射成形实际参数确定了充模多相流动控制方程的初边界条件,基于CFX计算流体力学软件对钳口铁粉注射成形充模多相流动过程实现了三维数值模拟。给出了钳口铁粉注射成形充模多相流动中固相粉末的速度流线图,分析了模腔中温度场和压力场分布的瞬态情况,以及模腔中不同位置的温度和压力随时间变化的曲线;分析了钳口铁粉注射成形充模多相流动过程中不同时刻粉末体积分数的分布情况。数值模拟结果可用于分析注射成形过程中产生粉末粘结剂两相分离和成形坯密度分布不均的原因,数值模拟为研究注射成形产品缺陷产生的原因提供了直观分析方法。     

复杂零件粉末注射成形多相流动过程三维数值模拟

将金属粉末注射成形充模过程视为粉末、粘结剂和空气的三相流动过程,给出了金属粉末注射成形充模多相流动的控制方程。根据钳口复杂模腔的铁粉注射成形实际参数确定了充模多相流动控制方程的初边界条件,基于CFX计算流体力学软件对钳口铁粉注射成形充模多相流动过程实现了三维数值模拟。给出了钳口铁粉注射成形充模多相流动中固相粉末的速度流线图,分析了模腔中温度场和压力场分布的瞬态情况,以及模腔中不同位置的温度和压力随时间变化的曲线;分析了钳口铁粉注射成形充模多相流动过程中不同时刻粉末体积分数的分布情况。数值模拟结果可用于分析注射成形过程中产生粉末粘结剂两相分离和成形坯密度分布不均的原因,数值模拟为研究注射成形产品缺陷产生的原因提供了直观分析方法。     

半固态铝-7石墨比重偏析控制的数值模拟

根据有限元体积法建立了流体方程组,并建立了固液两相双流体模型.利用流体模拟软件FLUENT对搅拌器中固液两相流的混合进行了数值模拟,得到了半固态铝-7石墨合金在600℃时机械搅拌情况下消除合金偏析时流体的流动特性和湍流动能分布,模拟出了三种温度下搅拌720 s后石墨分布的图形,同时确定600 ℃是所选的三个温度中石墨颗粒偏析程度最小的温度,也得出了时间与搅拌温度的关系.     

摩托车右曲轴箱多向挤压铸造模具设计

以摩托车右曲轴箱为研究对象,采用ProCAST软件,对其进行了凝固过程数值模拟,确定了补缩位置.模具采用镶块结构、组合式单分型面、增加内浇口厚度的浇注系统设计,选取合理的工艺参数(浇注温度为670～690℃,上模温度为200℃,下模温度为160℃,充型速度为5 m/s),解决了复杂壁薄铸件的挤压铸造成形问题.     

基于数值模拟的复杂铸件粉末注射成形问题研究

采用流体力学计算软件CFX对钳口铸件注射成形工艺的充模过程进行了三维模拟分析,得到了充模过程中各位置的瞬时温度场分布和瞬时压力场分布,并分析了充模过程中不同时刻模腔中各位置的压力和温度变化。通过研究铸件钳口熔体充模流动过程中不同时刻流体粉末的体积分数变化,指出数值模拟过程中固体粉末的体积分数变化和分布,可以得到成形精致坯的密度分布,以分析成形精致坯出现密度分布不均以及成形坯缺陷的原因,寻找控制成形缺陷和零件质量的方法。     

水雾化Inconel713C喂料流变性能的研究

以水雾化法制备的Inconel713C合金粉末为原料,利用ZRZ1452型熔体流动速率仪,研究了三种塑基粘结剂体系和Inconel713C合金粉末混合制备的喂料的流变性能。通过线性回归分析,计算出非牛顿指数n和τ_w-γ_w近似关系式。结果表明:在52%装载量下,三种组分喂料的粘度均随温度的升高以及剪切速率的增大而减小。粘结剂组成为85%POM+5%HDPE+10%其他助剂的喂料(D1)具有最好的充模性,呈假塑性流体。喂料D1的粘度与温度关系更好地符合Arrhenius定律,随剪切速率的增加,粘流活化能降低,而指前因子增大。     

水辅助注射成型充模过程的数值模拟研究

基于Hele-Shaw流动模型,采用广义牛顿流体本构方程,建立了三维薄壁塑件的水辅助注射成型充模过程数学模型,采用有限元/有限差分/控制体积法数值求解。对薄壁平板塑件的水辅助注射成型充模过程进行了模拟,模拟得到的熔体前沿位置与前人实验结果吻合较好,浇口处压力变化、水的厚度分布及平均温度分布合理,验证了所建立的模型和采用的数值模拟方法的有效性。     

基于Projection VOF方法的熔模铸造蜡模充型过程数值模拟

针对熔模铸造蜡模充型过程数值模拟软件自主开发，建立了流动场和温度场数学模型，采用Cross-WLF粘度模型描述蜡料的流变性能，基于Projection VOF方法进行蜡料流动过程速度场、压力场以及自由表面的求解。通过试验测量获取了K512型蜡料的热物理性能和流变性能的相关数据，拟合得到粘度模型参数。分别在蜡料常粘度和变粘度模型两种条件下对扳机铸件蜡模充型过程进行模拟，结果表明，所建立蜡模充型过程数学模型能较好地描述蜡料的动态流变特性和传热行为。     

Thermo-physical characterization of binder and feedstock for single and multiphase flow of PIM 316L feedstock

A thorough knowledge of the material properties of the feedstock and binder system is essential for successful powder injection moulding (PIM) as well as for numerical simulation. In view of the above, characterization of a developed binder system and feedstock has been reported in this paper for processing of 316L stainless steel powder through PIM route. The binder system consists of paraffin wax, stearic acid and low-density polyethylene. The feedstock comprises of 316L stainless steel powder and the above binder system. The thermal, physical and rheological characteristics of the binder system and feedstock have been investigated separately along with binder removal technique from the injection-moulded green compact. The thermal characterization revealed the semi-crystalline nature having distinct melting and solidification range for both the binder and feedstock. Data from DSC and TGA show that injection of the feedstock should be carried out above 102 °C (i.e. the upper melting temperature) but below 154 °C as beyond which the binder components paraffin wax and stearic acid start degrading and mould temperature should be below 57 °C. The binder and feedstock are found as shear-thinning fluid as viscosity decreases with the increase in shear strain rate and temperature. However, the viscosity of the binder is more sensitive to shear strain rate and temperature compared to that of the feedstock.     

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针对含硼中碳钢铸坯角部裂纹问题,通过检测保护渣凝固液渣层硼含量发现钢中硼的质量分数为0.001 3%时,进入渣中B2O3的质量分数为0.74%,并测得原渣样和液渣样粘度分别为0.122、0.12Pa·s(1 300℃),认为钢中硼含量对保护渣性能影响较小,无需针对含硼钢设计特殊保护渣。对原中碳钢保护渣性能进行了优化,碱度(R)从1.23增加到1.27;1 300℃下粘度从0.165Pa·s降低到0.123Pa·s;1 350℃下熔速从22kg/h增加到27kg/h;熔点从1 085℃增加到1 155℃,铸坯角部裂纹得到了明显的控制。     

粘结剂组成对粘结剂和喂料热性能的影响

研究制备了PW，BO，OP3大系列10种组成的粘结剂及相应10种W-Ni-Fe粉末与粘结剂的混合料。并采用热失重-差热分析(TGA-DTA)分析了粘结剂和喂料的热性能。研究结果表明，粘结剂组成对粘结剂和喂料的热性能如熔点、热分解温度和热分解曲线有很大的影响。通过此变化可以更为准确地确定不同粘结剂组成的喂料中的粘结剂脱除工艺和脱除方式。     

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.     

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.     

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。     

两种形状Nd-Fe-B粉末的混炼

采用快淬法和雾化法制得的2种不同形貌的NdFeB磁粉，以尼龙12作粘结剂，研究了注射成形粘结磁体的混炼过程。结果表明：混合料的均匀度与混合时间的关系近似符合Boltzmann方程，磁通热损失率近似符合指数函数，混合料的流变符合假塑性流体的特征；平均粒度相当的粉末、雾化粉的临界充填率、初始均匀度和充分混合后的均匀度都高于快淬粉；相同剪切速率下，雾化粉的粘度远比快淬粉低。     

硬质合金增塑粉末螺杆挤压成形

探讨了用于硬质合金粉末螺杆挤压成形技术的新粘结剂制备及挤压棒的组织形貌。新粘结剂由几种低分子量组元与1种热塑性弹性体高分子组元构成。采用溶剂溶解与加热熔融相结合的办法制备粘结剂。室温下，用合适的剪切力搅拌，能很快将粘结剂与YG8粉末混合均匀，制得组成均一的料浆式挤压用喂料。用扫描电子显微镜观察了挤压毛坯的微观组织及脱脂试样的组织结构与缺陷。用热重(TG)与微分热重(DTG)方法研究了热脱脂机理与动力学，发现了三维扩散控制热脱脂的速率。在脱脂的第1阶段，低分子量组元被脱除掉，挤压毛坯内形成了连通毛细孔。在脱脂的第2阶段，剩下的高分子量组元被完全脱除；第2阶段的热脱脂能以较快的升温速率进行。制备出了φ20mm的硬质合金挤压棒。     

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）。     

Binder jet printed WC infiltrated with pre-made melt of WC and Co

WC-Co was made via binder jet additive manufacturing of tungsten carbide followed by melt infiltration with a Co-WC infiltrant. The goal of the study was to achieve fully densified parts in near-net shape with minimal shrinkage while keeping the Co content low. The exact amount of infiltrant was determined in order to fully densify with minimum shrinkage based on the actual volume taken up by WC powder in the preform based on theoretical density, the bounding volume of prints after shrinkage, and the volume from the infiltrant. The eutectic nature of the infiltrant enabled melting at much lower temperature compared to the melting temperature of pure Co. The density, microstructure, grain size, hardness, and fracture toughness were characterized. The shrinkage and net shaping were assessed with light scans. A detailed look at the fracture mechanics was assessed. This approach achieved highly dense WC-Co parts in net-shape with Co vol% of near 29 (Co wt% ~19), density of 96.2% theoretical, hardness of 8.34 GPa, grain size of 7.7 μm, magnetic saturation of 0.5 T, room temperature thermal conductivity of 125 W/mK, and fracture toughness of 24.7 MPa·m^1/2.