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Characterization of polymeric binders for Metal Injection Molding (MIM) process.

机译：用于金属注射成型（MIM）工艺的聚合物粘合剂的表征。

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摘要

The Metal Injection Molding (MIM) process is an economically attractive method of producing large amounts of small and complex metallic parts. This is achieved by combining the productivity of injection molding with the versatility of sintering of metal particulates. In MIM, the powdered metal is blended with a plastic binder to obtain the feedstock. The binder imparts flowability to the blend at injection molding conditions and strength at ambient conditions. After molding, the binder is removed in a sequence of steps that usually involves solvent-extraction and polymer burn-out. Once the binder is removed, the metal particles are sintered.;In this research several topics of the MIM process were studied to understand how the polymeric binder, similar to the one used in the sponsoring company, works. This was done by examining the compounding and water debinding processes, the rheological and thermal properties, and the microstructure of the binder/metal composite at different processing stages. The factors studied included the metal contents, the composition of the binder and the processing conditions.;The three binders prepared during the course of this research were blends of a polyolefin, polyoxymethylene copolymer (POM) and a water-soluble polymer (WSP). The polyolefin resins included polypropylene (PP), high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE). The powdered metal in the feedstocks was 316 L stainless steel.;The compounding studies were completed in an internal mixer under different conditions of temperature, rotational speed and feedstock composition. It was found that the metal concentration was the most important factor in determining the torque evolution curves.;The observation of microstructure with Scanning Electron Microscope (SEM) at different stages during compounding revealed that the metal particles neither agglomerate nor touch each other.;The liquid extraction of the water-soluble polymer (WSP) from the molded parts (or water debinding) was investigated using two configurations of flow of water relative to the samples. Both permitted the reduction of the mass transfer resistance outside the parts, revealing information on the diffusion of the WSP inside the part exclusively.;The debinding studies showed that a single effective diffusivity could be used to model the extraction process of the binder from molded parts. This approach is more accurate when the debinding time is above 2 hours.;Steady shear and dynamic experiments were conducted on the binder and feedstocks samples containing LLDPE. The results of both experiments revealed that the feedstocks did not show yield stress even though the highest metal content was 64% by volume. Therefore, it was concluded that there were only hydrodynamic interactions between the metal particles.;The thermal characterization of binders, polymers and feedstocks included differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The DSC tests were performed after preheating and quenching of the samples. The heating rate was 20°C/min. The TGA scans were conducted from room temperature to 700°C at 20°C/min.;The DSC tests revealed that the melting point of the polymers depressed when blended in the binders and feedstocks. The depression was more intense for POM and the water-soluble polymer than for the polyolefins. Therefore, it was concluded that the melting point depression of POM and the water-soluble polymer was caused by their entrapment in the polyolefin matrix and in between the metal particles.;The TGA scans showed that the feedstocks with higher metal concentration had higher final decomposition temperature, but similar onset temperature. The reason was that the higher the metal concentration the more difficult the diffusion of the products of the decomposition of the binder out of the samples.;The morphological studies revealed that the binders were heterogeneous showing domains of the polar resins, embedded in a continuous phase composed of polyolefin. This distribution of phases was the result of the immiscibility between the polymeric components, and of the higher concentration (>70 vol%) of the polyolefin with respect to the polar components (polyoxymethylene and water-soluble polymer).;The deformation during steady shear testing and compounding of the binder with the metal modified the size of the dispersed domains. The steady shearing increased the size of the dispersed domains by coalescence of the particles. On the other hand, the presence of powdered metal during compounding forced a redistribution of the dispersed phases. Apparently, a thin heterogeneous layer of binder surrounded the metal particles while most of the polyolefin occupied the space between the coated metal particles. The SEM study on samples obtained after water debinding revealed that the water-soluble polymer did not distribute uniformly on the surface of the molded disk of feedstock used for water debinding tests.
机译：金属注射成型（MIM）工艺是生产大量小型复杂金属零件的经济上有吸引力的方法。这是通过将注塑成型的生产率与金属微粒烧结的多功能性相结合来实现的。在MIM中，金属粉末与塑料粘合剂混合以获得原料。粘合剂在注塑条件下赋予混合物共混物流动性，而在环境条件下赋予强度。模制后，按通常包括溶剂萃取和聚合物烧尽的一系列步骤除去粘合剂。一旦除去粘合剂，金属颗粒就被烧结。在本研究中，研究了MIM工艺的几个主题，以了解聚合物粘合剂如何与赞助公司中使用的粘合剂类似地工作。通过检查复合和水脱脂过程，流变学和热学性质以及在不同加工阶段的粘合剂/金属复合材料的微观结构来完成此操作。研究的因素包括金属含量，粘合剂的组成和加工条件。在本研究过程中制备的三种粘合剂是聚烯烃，聚甲醛共聚物（POM）和水溶性聚合物（WSP）的混合物。聚烯烃树脂包括聚丙烯（PP），高密度聚乙烯（HDPE）和线性低密度聚乙烯（LLDPE）。原料中的金属粉末是316 L不锈钢。在不同的温度，转速和原料组成条件下，在内部混合器中完成混合研究。发现金属浓度是决定扭矩变化曲线的最重要因素。;在混合过程中不同阶段用扫描电子显微镜（SEM）观察的微观结构表明，金属颗粒既不凝聚也不相互接触。使用相对于样品的水流的两种配置，研究了从模制件中提取水溶性聚合物（WSP）的液体（或水脱脂）。两者都允许降低零件外部的传质阻力，仅显示有关WSP在零件内部扩散的信息。;脱脂研究表明，可以使用单个有效扩散率来模拟从成型零件中提取粘合剂的过程。当脱脂时间超过2小时时，此方法更为精确。对含LLDPE的粘合剂和原料样品进行了稳定的剪切和动态实验。两个实验的结果表明，即使最高的金属含量为64体积％，原料也没有表现出屈服应力。因此，可以得出结论，金属颗粒之间仅存在流体动力学相互作用。粘合剂，聚合物和原料的热表征包括差示扫描量热法（DSC）和热重分析（TGA）。在样品预热和淬火之后进行DSC测试。加热速度为20℃/分钟。 TGA扫描是在室温至700°C下以20°C / min的速度进行的； DSC测试表明，将聚合物与粘合剂和原料共混时，其熔点会降低。与聚烯烃相比，POM和水溶性聚合物的凹陷更强烈。因此，可以得出结论，POM和水溶性聚合物的熔点降低是由于它们在聚烯烃基体中和金属颗粒之间的截留所引起的； TGA扫描表明，金属浓度较高的原料的最终分解较高。温度，但起始温度相似。原因是金属浓度越高，粘合剂分解产物从样品中扩散出来的难度就越大。形态学研究表明，粘合剂是不均匀的，显示出极性树脂的域，它们嵌入连续相中由聚烯烃组成。相的这种分布是聚合物组分之间不溶混的结果，也是聚烯烃相对于极性组分（聚甲醛和水溶性聚合物）的更高浓度（> 70％（体积））的结果。粘合剂与金属的测试和复合改变了分散域的大小。稳定剪切通过粒子的聚结增加了分散域的尺寸。另一方面，在混合过程中金属粉末的存在迫使分散相重新分布。显然地，一薄层不均匀的粘合剂层包围了金属颗粒，而大多数聚烯烃占据了被覆金属颗粒之间的空间。对水脱脂后获得的样品进行的SEM研究表明，水溶性聚合物在用于水脱脂测试的原料成型盘表面上分布不均匀。

著录项

  • 作者

    Adames, Juan M.;

  • 作者单位

    The University of Akron.;

  • 授予单位 The University of Akron.;
  • 学科 Engineering Materials Science.;Plastics Technology.
  • 学位 Ph.D.
  • 年度 2007
  • 页码 237 p.
  • 总页数 237
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;整形外科学（修复外科学）;
  • 关键词

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