金属粉浆浇注成型与烧结实验研究

金属粉浆浇注成型与烧结工艺,是基于快速原型的金属型腔模具快速制作中比较关键的工艺环节.文章以3种进口和国产树脂为粘结剂,分别使用平均粒径为44μm的较粗铁粉、平均粒径为4μm较细的羰基铁粉,以及两者按照一定比例组成的双形态混合铁粉为基体材料,分别在空气和真空下混浆、注浆,研究了粉浆浇注成型工艺中的若干关键技术问题.实验表明,采用真空下混浆、注浆,不但可以有效消除气泡,还可以同时提高浆体的流动性和密实性;另外,铁粉粒度的大小也直接影响着浆体的流动性.实验中同时发现,使用较细的羰基铁粉与相对较粗的铁粉,按照合理比例组成的双形态混合粉末,具有更好的流动性和充填性,而且从密度特征看,试样更具密实性.将注型坯试样在氢气保护下进行烧结,低温阶段将注型坯中的有机粘结剂成分进行脱除,高温阶段实现金属粉末烧结形成骨架状金属结构.实验结果表明,在合理的烧结规范下,选择合适的粘结剂,采用粗细两种铁粉组成的双形态混合粉浆,并且壁厚小于一定尺寸的试样,在烧结过程中更有利于试样形状的保持,且烧结后试样结构较为均匀.文章的实验研究为基于快速成型的金属基薄壁型腔模具的快速制作,提供了必要的工艺基础和技术支持.     

Ti-6Al-4V金属粉末注射成形喂料的制备与性能表征

通过Ti-6Al-4V粉末制备金属粉末注射成形喂料。利用转矩流变仪确定喂料的临界粉末装载量,观察喂料粘度的变化,判断喂料的均匀性。采用旋转流变仪对喂料进行流变实验。通过改变烧结温度确定合适的烧结工艺。结果表明,喂料的临界粉末装载量为51%,混炼2次能使喂料更均匀密实。喂料的粘度随剪切速率的增加而减小,喂料呈假塑性流体行为。当烧结温度为1280℃时,烧结坯密度为4.32 g·cm~(-3)、抗拉强度为987 MPa,此时拉伸断面具有较少的孔洞结构和较好的结构完整性。     

金属型腔模具粉浆浇注成型工艺的实验研究

以热固性环氧树脂为粘结剂，分别使用平均粒径为44μm的较粗铁粉、平均粒径为4μm较细的羰基铁粉，以及两者按照一定比例组成的双形态混合铁粉为基体材料，分别在空气和真空下混浆、注浆，探讨了铁粉粉浆浇注成型工艺中的若干问题。实验表明：采用真空下混浆、注浆，可以消除气泡，提高浆体的流动性和密实性；另外，铁粉粒度的大小也直接影响着浆体的流动性。实验中同时发现使用较细的羰基铁粉与相对较粗的铁粉按照合理比例组成的双形态混合粉末，具有更好的流动性和充填性，而且从密度特征看，试样更具密实性。     

微晶蜡对MIM多元蜡基粘结剂性能的影响

研究了微晶蜡MW的加入对PW-EVA-HDPE蜡基粘结剂、喂料的均匀性、流变特性的影响。对比实验发现MW加入不会明显改变粘结剂的粘度，加入20％MW(质量分数)的蜡基体强度提高了5倍，体积收缩率降低到6．44％，使多元蜡基粘结剂从粗大层片状(50μm-150μm)结晶细化为均匀的微细晶(5μm～8μm)；一定量的MW可以改善PW-EVA-HDPE三元蜡基粘结剂的组织均匀性和热稳定性，升高注射温度，能提高粉末装载量和粉末在粘结剂中分散的均匀性，从而提高产品的成品率和尺寸精度。     

316L不锈钢金属粉末注射成形喂料的流变性能研究

通过三种不同的316L不锈钢金属粉末制备了金属粉末注射成形喂料,利用RH2200型毛细管流变仪,研究了不同粒径不同形貌的316L不锈钢金属粉末对金属粉末注射成形喂料流变性能的影响。通过线性回归分析,计算该喂料的非牛顿指数n、粘流活化能E和综合流变学因子αSTV的大小。结果表明:喂料粘度随剪切速率的增大而减小,具有良好的充模性,呈假塑性流体;22μm球形316L不锈钢金属粉末制备的喂料具有较小的非牛顿指数和粘流活化能,综合流变性能最好。     

小功率激光烧结金属粉末直接成型工艺实验研究

在小功率（50W）激光快速成型机上，选择铁粉和石墨粉末按一定比例混合，在不添加粘结剂的情况下进行了金属粉末直接成型工艺实验，获得了典型的较为致密、形状和尺寸精度较高的金属烧结原型件。经二次高温烧结后显微组织表明，金属件由铁素体和珠光体组成。分析了主要工艺参数对成型的影响，研究了二次高温烧结工艺对烧结件微观组织的影响及存在的一些问题。     

压制工艺及压坯高径比对金属粉末致密化成形影响的模拟

利用MSC.MARC有限元分析软件对金属粉末压制成形过程进行了模拟,采用基于更新拉格朗日法描述的大位移弹塑性分析,研究压制方式、摩擦条件对不同侧压系数(K=2,K=4,K=8)圆管压坯性能的影响.结果表明,双向压制工艺相比单向压制工艺可提高压坯应力和密度分布均匀性;压坯高径比大时,两种压制工艺下压坯应力和密度不均现象加剧;摩擦条件的改善有利于增大金属粉末移动,减少应力集中,降低压制力,提高压坯密度均匀性.     

注射成型用氧化锆粉体的表面改性研究

陶瓷粉体在高分子粘结剂中的分散性以及注射喂料的流动性是陶瓷粉末注射成型的关键因素.由于高分子的分子结构和物理形态与陶瓷粉体不同,导致两者相容性差.并且陶瓷粉体表面自由能较高,与高分子粘结剂混合过程中会有团聚的倾向.本研究采用硬脂酸对氧化锆粉进行表面改性,降低了粉体的表面自由能,提高了喂料的均匀性.改性后的陶瓷粉体表面由亲水性变为亲油性,提高了粉体与粘结剂的相容性,降低了喂料体系的粘度.     

成型方法对高性能钡钨阴极基体孔结构的影响

采用全自动压汞仪对传统的模压成型和等静压成型的钨坯和钨基孔结构分布进行了研究。结果表明:模压成型的钨坯平均孔径为1.02μm,钨基平均孔径1.41μm,孔径分布不均匀,钨基中小孔径与大孔径的量较多;等静压成型的钨坯平均孔径为1.18μm,孔径分布范围窄,钨基平均孔径为1.55μm,1.00～2.20μm的孔径占总孔径的68.15%。     

WC-Co硬质合金刀片注射成型参数优化研究

采用石蜡基多聚合物粘结剂体系,通过注射成型制备了WC-10％Co硬质合金的ZTKD型号切断切槽刀片试样。通过脱察该月片注射坯及断口形貌,分析注射坯的缺陷情况和质量变化等,研究了温度、压力、保雎时间等参数对WC-10％Co硬质合金注射成型性能的影响,确定了优化值,该注射成型刀片最佳参数为注射温度110℃、注射压力150MPa,保压压力为120MPa,保压时间为2．5-3．08。结果发现,注射温度、注射压力对注射结果影响最大;注射温度太低,喂料流动性不足,温度太高,将容易产生粉末与粘结剂两相分离;随着注射压力加大,注射坯密度也增大,并趋向一最大值,但压力过大,残余应力也大,产品容易变形、裂纹等,脱模也困难;为有效释放注射坯内应力,保压压力应低于注射压力,保压开始阶段,注射坯密度增加明显,随着保压时间的延长,保压压力与注射坯浇口处反作用力达到平衡,密度不再增加。     

不同热塑性蜡基粘接剂对316L注射成型件性能的影响

用金属注射成型方法研究三种热塑性蜡基粘接剂(高密度聚乙烯、高密度聚乙烯/聚丙烯、聚丙烯)对316L不锈钢尺寸稳定性及其机械性能的影响,对三种热塑性蜡基粘接剂溶剂脱脂过程进行了分析。实验结果表明用高密度聚乙烯/聚丙烯热塑性蜡基粘接剂得到的316L不锈钢注射成型件尺寸稳定性及机械性能较好,溶剂脱脂时间较短、效果较好,其长、宽、高三维尺寸稳定性比聚丙烯热塑性蜡基粘接剂得到的注射成型件分别高46 %,40 %,20 %,密度、硬度和拉伸强度分别为7.28 g/cm₃、72.3 HRB和579MPa。     

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.     

超声辅助激光熔覆SiC/316L温度场和应力场分析

建立了激光熔覆SiC/316L复合涂层有限元分析模型,采用超声振动热效应转化和施加动态边界条件相结合的方法对超声振动边界条件作近似处理,对超声辅助激光熔覆SiC/316L复合涂层的温度分布和残余应力进行分析,并分析了超声振幅和扫描速度对温度场和应力场的影响.结果表明,随着超声振幅增大和扫描速度减小,涂层表面温度升高;超声作用下涂层残余应力有所降低,且随着超声振幅和扫描速度增大,残余应力值先减小后增大.采用优化工艺参数进行超声熔覆试验,超声作用使涂层中各区域组织得到细化且均匀分布,有利于降低涂层中残余应力.     

THERMAL DEBINDING MECHANISM OF METAL INJECTION MOLDING COMPACTS IN VACUUM

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Effect of backbone polymer on properties of 316L stainless steel MIM compact

This study compares the effects of three backbone polymers, LDPE, HDPE and LDPE/HDPE, on the dimensions and mechanical properties of 316L stainless steel MIM compact. MIM parts of optimal quality can be produced using properly formulated binders. A spiral flow test is performed firstly to elucidate the flow behaviors of MIM feedstocks. Secondly, the injection molding of tensile bars is tested to examine the dimensional stability and the mechanical strength of sintered parts against variation in the binder formula. Among the three backbone polymers considered herein, HDPE performs best in terms of both the stability of flow and the MIM compact quality; LDPE performs the worst. HDPE has significantly better length, width, density, and hardness by up to 24%, 27%, 30%, and 64%, respectively. In summary, this work has demonstrated that a backbone polymer strongly affects the dimensions and the mechanical properties of the sintered part. The proper selection of a backbone polymer, such as HDPE, is required to increase the dimensional accuracy and quality of 316L sintered parts.     

Optimization of Binder Jetting Using Taguchi Method

Among several additive manufacturing (AM) methods, binder-jetting has undergone a recent advancement in its ability to process metal powders through selective deposition of binders on a powder bed followed by curing, sintering, and infiltration. This study analyzes the impact of various process parameters in binder jetting on mechanical properties of sintered AM metal parts. The Taguchi optimization method has been employed to determine the optimum AM parameters to improve transverse rupture strength (TRS), specifically: binder saturation, layer thickness, roll speed, and feed-to-powder ratio. The effects of the selected process parameters on the TRS performance of sintered SS 316L samples are studied with the American Society of Testing Materials (ASTM) standard test method. It was found that binder saturation and feed-to-powder ratio were the most critical parameters, which reflects the strong influence of binder powder interaction and density of powder bed on resulting mechanical properties. This article serves as an aid in understanding the optimum process parameters for binder jetting of SS 316L.     

体能量密度对SLM成形316L不锈钢耐腐蚀性的影响

为了探究不同体能量密度对SLM成形316L不锈钢耐腐蚀性的影响,采用正交试验法制备不同激光功率、扫描间距和扫描速度下的SLM 316L不锈钢成形件,利用扫描电镜和电化学试验对其微观组织和自腐蚀电位进行观察和测量。结果表明,体能量密度过大或过小时,成形件表面的气孔和孔洞等缺陷较多,自腐蚀电位减小,耐腐蚀性变差。体能量密度为44.64 J/mm^-3时,SLM 316L不锈钢成形件的自腐蚀电位最高,组织表面的气孔等缺陷相对较少,耐腐蚀性最好。激光功率、扫描间距和扫描速度对SLM 316L不锈钢成形件的耐腐蚀性影响的次序为:激光功率＞扫描间距和扫描速度,最佳的工艺参数组合为激光功率250 W,扫描间距0.14 mm,扫描速度800 mm/s。     

球铁件铁丸真空实型铸造工艺的研究

球铁件铁丸真空实型铸造时,造型材料采用粒径分别为φ0.3 mm、φ0.5 mm、φ0.8 mm的空气雾化铁丸,按比例混合,混后其紧实堆装密度宜为4.78 g/cm3。造型时振动频率为50 Hz,振幅在0.5~1.5 mm之间,振动时间5 min左右。浇注时铸型真空度根据铸件的尺寸和质量控制在-0.038~-0.068 MPa之间。力学性能检测结果为(QT500-7):бb(铁丸)≥568 MPa,бb(干砂)≥514 MPa,比干砂铸造提高约10%;δ(铁丸)均=9.2%,δ(干砂)均=8.8%,基本无变化。     

单钢轮振动压路机振动液压系统动态特性联合仿真

为研究实际压实工况下钢轮振动、振动液压系统压力和驱动扭矩随压实度变化的动态特性,利用ANSYS APDL建立柔性体路面模型,在Adams中进行钢轮-路面刚柔耦合动力学建模,通过AMESim与Adams建立单钢轮振动压路机振动液压系统联合仿真模型,进行不同压实度时的压实仿真。结果表明：仿真模型准确,随着压实度的增大,钢轮振动容易出现二倍频,发生跳振,振动液压系统平稳压力减小,起振时间缩短,驱动扭矩减小。     

Pore opening and binder flow during initial stage of thermal debinding in MIM

1　INTRODUCTIONMetalinjectionmolding(MIM )isanet shapingtechnology ,whichhasthecharacteristicsoftheplas ticinjectionmoldingandconventionalpowdermetal lurgy(PM ) .MIMenablestheproductionofproductswithgreatershapecomplexity ,andwithbetterper formances.This processconsistsofthefollowingsteps :certainamountofbinderisblendedwithprop erpowders ,inorderforpreparingsuitablefeed stockstoinjection ;afterinjectionmolding ,partsarede boundandthensinteredandinthiswayfinalproductsareformed[1,2 ] .Th…