LOW TEMPERATURE THERMAL DEBINDING BEHAVIOR OF WAX-BASED MULTI-COMPONENT BINDER FOR TUNGSTEN HEAVY ALLOY

１ＩＮＴＲＯＤＵＣＴＩＯＮＰｏｗｄｅｒｉｎｊｅｃｔｉｏｎｍｏｕｌｄｉｎｇ（ＰＩＭ）ｉｓａｎｅｗｐｒｏｃｅｓｓｆｏｒｍａｎｕｆａｃｔｕｒｉｎｇｎｅａｒｎｅｔｓｈａｐｅｐａｒｔｓｗｉｔｈａｄｖａｎｔａｇｅｓｏｆｌｏｗｃｏｓｔ，ｈｉｇｈｐｅｒｆｏｒｍａｎｃ...

Debinding of stainless steel foam precursor with 3-D open-cell network structure

The thermal debinding behavior of stainless steel foam precursor in vacuum was studied and compared with that in hydrogen.The formation cause of pore channel was analyzed.The experiment results show that the binder removal rate in vacuum is higher than that in hydrogen.In vacuum,the organic compounds can be removed effectively without change of pore size and the pore morphology for the sample.After pre-sintering,some sintering necks form and the sample has certain intensity.The initial surface pore forms with the temperature increasing at first,and then the internal melting binder is aspirated to form initial pore because of the capillary force and the metal powders re-arrange with the migration of binder at the same time.

Influence of the Compacts Homogeneity on the Incidence of Cracks during Thermal Debinding in Ceramic Injection Molding

During thermal debinding in ceramic injection molding, the inhomogeneity of green body is a key origin of cracks. In this study, the impact of low molecular weight binders on the homogeneity of the green body was investigated. Incidence of cracks during thermal debinding indicated that the volume ratio of wax to stearic acid should be out of high viscosity and incompletely wetting region. In these two formulation regions, typical inhomogeneous microstructures were observed. By mercury intrusion method, it was shown that pore size distribution of the debinded compacts was determined by thermal degradation of low molecular weight binders. A particle-rich region model was established to predict the nucleation of cracks caused by solid loading fluctuation. The criterion of cracks nucleation was that local capillary force from solid loading fluctuation was larger than the suction force from the surroundings.

DEBINDING MECHANISM AND KINETICS FOR PW IN PW－WC FEEDSTOCK UNDER AIR ATMOSPHERE

ＤＥＢＩＮＤＩＮＧＭＥＣＨＡＮＩＳＭＡＮＤＫＩＮＥＴＩＣＳＦＯＲＰＷＩＮＰＷ－ＷＣＦＥＥＤＳＴＯＣＫＵＮＤＥＲＡＩＲＡＴＭＯＳＰＨＥＲＥＬｉａｎｇＳｈｕｑｕａｎ；ＨｕａｎｇＢａｉｙｕｎ；ＱｕＸｕａｎｈｕｉ（ＮａｔｉｏｎａｌＬａｂｏｒａｔｏｒｙｆｏｒＰ...

Novel PEG-based binder system and its debinding properties for MIM

Binder system is critical to the success of metal injection molding(MIM). A novel PEG based binder for MIM was developed, which was made of high density polyethylene (HDPE), polyethylene glycol (PEG), polymer W, stearic acid(SA) and dioctyl phthalate (DOP). The components of binder have interactions with each other, so the binder have good compatibility. The thermal decomposition process of binder exhibits three stages during debinding. The binder could be debound by pyrolysis or solvent, and could easily be removed in a short time in ethanol without defects and evironmental concern. A lot of interconnected pores formed after solvent debinding, which is helpful to the escape of pyrolysis gases during subsequent thermal debinding or presintering. [

THERMAL DEBINDING MECHANISM OF METAL INJECTION MOLDING COMPACTS IN VACUUM

１ＩＮＴＲＯＤＵＣＴＩＯＮＤｕｒｉｎｇｔｈｅｐａｓｔｆｅｗｙｅａｒｓ，ｐｏｗｄｅｒｉｎｊｅｃｔｉｏｎｍｏｌｄｉｎｇ（ＰＩＭ）ｈａｄｅｍｅｒｇｅｄａｓａｎａｄｖａｎｃｅｄｍａｎｕｆａｃｔｕｒｉｎｇｔｅｃｈｎｏｌｏｇｙ［１］．Ｔｈｅｃｏｍｂｉｎａｔｉｏｎ...

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

The removal of the binder from the powder compacts (debinding) can be a slow step and a source of problems. To improve the debinding process of powder injection molding operation, it’s necessary to understand the thermal and mechanical properties of powder injection molding feedstocks and to find the major causes responsible for molding difficulties and compacts shape retention during debinding process. The effects of thermo mechanical properties of the PIM feedstock on the compacts shape retention during debinding process were discussed and explained from practical point of view. The results indicate that the heat of fusion affects the cooling time. The binder component with high heat of fusion and high decomposed temperature is more effective as the second binder component for the compact to retain its shape during debinding.

Injection molding and debinding of micro gears fabricated by micro powder injection molding

Micro powder injection molding （μPIM） was investigated for possible mass production of micro-components at rela- tively low cost. However, scaling down to such a level produces challenges in injection molding and debinding. Micro gears were fabricated by μPIM from in-house feedstock. The effect of injection speed and injection pressure on the replication of the micro gear cavity was investigated. Solvent debinding and thermal debinding processes were discussed. The results show that micro gears can be successfully fabricated under the injection pressure of 70 MPa and the 60% injection speed. Either too low or too high injection speed can cause incomplete filling of micro gears. The same is the case with too low injection pressure. Too high injection pressure can bring cracks. Solvent debinding of micro gears was performed in a mixture of petroleum ether and ethanol. Subsequently, micro gears were successfully debound by a multistep heating schedule.

Thermal debinding dynamics of novel binder system

The thermal debinding dynamics of newly developed binders for cemented carbides extrusion molding was studied. It is shown that the thermal debinding processes can be divided into two stages: low temperature region, in which the low molecular mass components (LMMCs) are removed; and high temperature region, in which the polymer components are removed. The rate of thermal debinding is controlled by diffusion mechanism. The thermal debinding activation energies were solved out by differential method and integral method. The results show that the addition of other components acted as a catalyzer can effectively decrease the activation energy of thermal debinding processes.

Binder composition and debinding process in PIM of AlN

The thermal degradation behaviors of AlN green specimens were studied by thermogravimetry analysis during the ceramic powder injection molding debinding process. The optimum binder composition and the debinding cycle were demonstrated by observing the TGA and DTA plots of AlN green specimens and analyzing the microstructure at different temperatures. By adding HDPE into the PW EVA binder used in powder injection molding AlN can effectively reduce the mass lose rate in debinding process and improve the shape retention ability. At last, aluminum nitride ceramic with high room temperature thermal conductivity of 162.5?W·m -1 ·K -1 was produced. [

Comparison between the Requirements of Flowability and Moldability and the Shape Retention of PIM Compacts during Debinding Process

To successfully employ powder injection molding (PIM) as a manufacturing technique, the function of the component, design of the part, material and process should be optimized for overall processing ability of the PIM process. A comparison between the requirements of flowability and moldability and the compacts shape retention has been made in this work. There is often a contradiction between the requirements of flowability and the compacts shape retention. Many works have been done to attain good molding conditions. However, they fail to take into account the effect of some factors that satisfies good molding conditions on the compacts shape retention during debinding. This paper studies the effect of the powder-binder mixture characteristics and the molding conditions on the flowability and moldability and the shape retention of PIM compacts during debinding process so as to attain the benefits of each.

Deformation behavior and strength evolution of MIM compacts during thermal debinding

Effects of the debinding atmosphere,powder characteristic,solid loading and heating rate on the compact deformation were investigated.The compact strength after thermal debinding was measured by bending mode.The experimental results indicate that the vacuum atmosphere is beneficial to improving the deformation resistance compared with nitrogen atmosphere.Small particle size,irregular particle shape and high solid loading are suitable for decreasing the deformation defects.Besides,too fast heating rate may induce deformation defects.It is also indicated that effect of the factors for the deformation defects is different in different debinding stages.The strength evolution of the compacts during thermal debinding was also discussed.

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

Pore opening and binder flow during the initial stage of thermal debinding in metal injection molded parts was investigated. Scaning electron microscopy(SEM) pictures of 316 L stainless steel parts using wax based binder show that small particles will move to the surface with the process of debinding. SEM pictures of different mass loss rate specimens indicate that initial pores will emerge when as little as 4% binder removes. During the initial stage of thermal debinding, vapor tension varies in different place due to the difference of curvature. Thus more binders will be removed in places with smaller cavity between metal powders, and in these places small openings emerge.

Debinding and sintering of warm compacted and binder-treated complex iron-base part

Regular elemental powders were used in warm flow compaction instead of the expensive micron-sized powders to fabricate cross-shaped parts. Debinding behaviors,sintering properties and shape consistency of the sintered parts were studied. Binder removal was accomplished by heating green compacts at intermediate temperatures with optimal heating rates until the debinding temperature was reached. Results show that by controlling debinding process,complex parts with good shape consistence can be obtained by warm compaction of binder-treated powder. Fine and shiny surface was obtained and no surface defect can be observed for sintered parts debinded at 2 ℃/min,while defect can be observed in sintered parts debinded at 4 ℃/min.

Microstructure and properties of 3D-printed alumina ceramics with different heating rates in vacuum debinding

The effect of heating rates during vacuum debinding on the microstructure and mechanical properties of alumina ceramics are discussed in this paper.The threedimensional(3D)-printed alumina ceramics examined in this study were found to have a layered structure,and interlayer spacing increased as the heating rate increased The pore diameter,shrinkage,flexural strength and hardness were found to decrease as the heating rate increased due to weak interfacial bonding between alumina particles Shrinkage was found to be much larger along the Z direction than along the X or Y directions due to the layer-bylayer forming mode during 3D printing.0.5°C·min-1is considered the optimum heating rate,yielding ceramics with interlayer spacing of 0.65 lm,shrinkage of 2.6%2.3%and 4.0%along the X,Y and Z directions,respectively,flexural strength of 27.5 MPa,hardness of29.8 GPa,Vickers hardness of HV 266.5,pore diameter of356.8 nm,bulk density of 2.5 g·cm-3,and open porosity of38.4%.The debinding procedure used in this study could be used to produce a high-quality ceramic which can be used for fabricating alumina ceramic cores.

金属粉末增塑成形用聚甲醛基黏结剂发展现状及改性研究进展

金属粉末增塑成形结合了有机黏结剂的增塑流动特性,辅助混合喂料可快速成形复杂坯件,是不锈钢、合金钢及钛、镍、钨等有色金属及其复合材料的重要近净成形方法。新型聚甲醛(POM)基黏结剂因具有高的成形坯件强度、优异的脱脂保形性、高效率、低碳残留等优点,已成为金属粉末注射成型的主流黏结剂体系,是极具发展潜力的粉末增塑成形用黏结剂。本文总结近年来粉体增塑成形的技术进展,概述POM基黏结剂的物理特性与粉末注射成型用组分设计,探究POM基黏结剂的流变性能及其影响因素,分析催化脱脂的工艺反应过程与关键因素,综述POM基黏结剂在有色金属构件中的典型应用,并展望POM基黏结剂存在的问题与未来研究方向,为推动POM基黏结剂在粉体增塑成形中的应用提供参考。

3D打印陶瓷坯体热脱脂机理与工艺研究进展

采用3D打印成型技术制备先进陶瓷往往需要添加大量有机粘结剂,陶瓷坯体中的有机粘结剂主要通过热脱脂工艺排出,故热脱脂工艺对3D打印的素坯质量具有重要影响,是实现高质量先进陶瓷制备和应用的关键。本文综述了具有代表性的3D打印陶瓷坯体中热脱脂的理论和实践问题。从有机粘结剂的组成和作用出发,比较了不同分子量有机粘结剂的受热排除方式;讨论了有机粘结剂与陶瓷颗粒表面间的相互作用及脱脂气氛对有机粘结剂热裂解的影响;描述了热脱脂过程的三个阶段及坯体结构的变化;分析了热脱脂过程中三种主要的传质途径:液相在毛细管力作用下的迁移,气相在液相中的扩散和气相在气孔中的扩散或渗透;归纳了在热脱脂过程及此前的工艺步骤中可能导致开裂或变形等缺陷的原因,并提出了相应的控制措施。

后处理工艺对粘结剂喷射3D打印316L不锈钢显微组织及力学性能的影响

粘结剂喷射3D打印(Binder jet 3D printing,BJP)作为一种增材制造技术,由于能够以高效率和低成本获得复杂结构材料而具有独特的应用价值。然而,实现高致密、高强度金属材料是BJP的一个难题。通过热重分析、金相组织观察、显微硬度测试、致密度和体积收缩率计算、拉伸曲线测试等手段,探究了后处理工艺对粘结剂喷射3D打印316L不锈钢显微组织及力学性能的影响。结果表明,在脱脂阶段,当脱脂温度为600℃、保温时间为120 min时,不同高度的样品脱脂率均保持在4.5%~5.0%之间。在烧结阶段,晶粒尺寸随着烧结温度的升高逐渐增大。在1350℃下烧结,其平均晶粒尺寸为47.27μm。当烧结温度升高到1400℃时,晶粒尺寸增大到51.26μm,且随着烧结保温时间从1 h延长到3 h,晶粒尺寸增大到69.78μm。相应地,316L不锈钢烧结后的致密度从92.20%提高到98.39%,但烧结时间的延长并未提高样品的致密度,这归因于烧结气氛氩气在316L不锈钢中不溶解,当它被困在孔隙中时,压力的增加限制了致密化过程。烧结温度越高,样品强度越高,当样品在1400℃下烧结1 h时,其力学性能最好,此时抗拉强度为536.85 MPa,延伸率为73.74%,继续延长保温时间会由于晶粒尺寸增大以及第二相的增加而使得力学性能降低。

金属注射成形技术进展

分析了影响金属注射成形（ＭＩＭ）产业化进程的两个主要技术因素，即适合ＭＩＭ要求的原料粉末的生产方法和ＭＩＭ生产工艺，并概述了目前ＭＩＭ技术的发展状况。

硬质合金注射成形脱脂过程中的碳含量控制

研究了不同脱脂气氛 (不同比例N2 与H2 的混合气体 )和脱脂方法 (热脱脂、溶剂脱脂 +热脱脂、冷凝蒸汽脱脂 +热脱脂 )对PIM硬质合金脱脂坯及合金碳含量的影响。结果表明 :N2 热脱脂粘结剂容易以炭黑的形式残留在脱脂坯中 ,造成合金增碳 ;H2 热脱脂导致合金脱碳 ;75 %N2 +2 5 %H2 (体积分数 )混合气体热脱脂既能有效地脱除粘结剂 ,又能保证合金碳含量相对稳定 ;溶剂脱脂和冷凝溶剂脱脂能显著缩短脱脂时间 ,而且由于高温保持时间短 ,在后续热脱脂过程中采用H2 作保护气也可获得满意的碳含量 ,说明该方法对工艺条件的适应性强。通过调整热脱脂高温保持时间 ,可在一定范围内对脱脂坯的碳含量进行调整 ,说明过程的可调控性好。与溶剂脱脂相比 ,冷凝蒸气脱脂粘结剂脱除率更高 ,脱脂坯有较高的强度 ,有效地防止了脱脂坯软化变形的现象。