Effects of Injection Molding Parameters on the Production of Microstructures by Micropowder Injection Molding

Micropowder injection molding (μPIM) is a potential low-cost process for the mass production of metal or ceramic microstructures. In order to obtain good molded microstructures and to avoid molding defects, it is important to select suitable injection molding parameters. In this paper, the selection of injection molding conditions for the production of 316L stainless steel microstructures by μPIM is presented. Silicon mold inserts with 24 × 24 microcavities were injection molded on a conventional injection molding machine. The dimensions of each microcavity were Φ 100 μ m × depth 200 μm, giving an aspect ratio of 2. The distance between each microcavity was 200 μm. Five sets of experiments were conducted by varying one injection molding parameter at a time. The parameters included injection pressure, holding pressure, holding time, mold temperature, and melt temperature. Higher injection pressure and holding pressure were required during the injection molding process due to the small dimensions of the microcavities and the large number of microcavities (576 microcavities). High mold temperature was required for complete filling of the microcavities. Molded microstructures without visual defects were obtained using appropriate injection molding parameters. Catalytic debinding and sintering of the 316L stainless steel microstructures were successfully conducted.     

Thermal, Solvent, and Vacuum Debinding Mechanisms of PIM Compacts

The mechanisms of thermal, solvent, and vacuum debinding processes for powder injection molded (PIM) compacts were investigated. Mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) observations on PIM specimens showed that fine interconnected pores were developed in the early stages of debinding in all three processes. These pores were formed as a result of the decomposition of low temperature binders such as paraffin wax during thermal debinding or arise from the extraction of soluble binder components in solvent debinding. In the later stages of thermal and vacuum debinding, decomposed gases could be trapped in the center region and build up a pressure causing cracking or blistering defects. The solvent debinding process could alleviate these problems, but the penetration of solvent into the binder could still cause cracking or distortion due to swelling of the binder.

It was found that the pore structure evolution was influenced by the heating rate, temperature, pore size, and the amount of existing porosity. From the observed microstructure and mercury porosimetry data, debinding mechanisms were derived and the defects which were frequently seen during debinding were explained with these mechanisms.     

Influence of powder loading on densification and microstructure of injection molded Fe‐50Ni soft magnetic alloys

Metal injection molding (MIM) is a well‐known technique capable to produce micro size electromagnetic components with intricate shape features. Powder loading is a crucial parameter in the metal injection molding process which controls the densification and microstructure of the sintered parts. The lower powder loading leads to various defects and lower densification whereas higher loading results in failure of parts during injection molding. Therefore, it is important to engineer an appropriate powder loading to achieve defect‐free parts along with higher densification and improved microstructure. In this contest, three feedstocks of Fe‐50Ni alloys are prepared with powder loadings of 52 vol.%, 54 vol.% and 57 vol.% and injection molded. After debinding, the parts are sintered at 1325 °C for 2 h. The main objective of this study is to investigate the effect of powder loading on injection molding, densification, and microstructure. In addition, scanning electron microscopy and x‐ray diffraction analysis are performed during the study. The defect‐free green parts are produced successfully from the 52 % and 54 % loading. It has been found that the optimal powder loading of 54 % is the best from the perspective of enhanced densification and improved microstructure to assure the quality parts of Fe‐50Ni alloys via metal injection molding.     

钨合金正挤压棒坯溶剂脱脂缺陷的形成与控制

粉末挤压成形技术是制备大长径比钨基高比重合金棒材最有效的方法之一,而脱脂过程直接影响着样件缺陷控制及合金力学性能的改善效果.探讨了Φ12 mm和Φ15 mm钨基合金正挤压棒坯溶剂脱脂缺陷的形成及其控制,采用可控恒温仪调控溶剂脱脂速率,利用数码相机和扫描电镜分别对棒坯表面形貌和微观结构进行观察.结果表明：钨基合金正挤压棒...     

Influence of lustrous carbon defects on the fatigue life of ductile iron castings using lost foam process

Ductile cast irons are technologically important materials and are used extensively in automotive industry. Defects produced during casting process often play a dominant role in limiting mechanical properties and fatigue life under cyclic loading in cast alloy components. In order to investigate the effects of process induced defects on the fatigue behavior, in this paper two batches of ductile iron specimens cast using green sand and lost foam molding processes were studied. The ductile irons produced by lost foam molding generally were characterized to have lustrous carbon defects which left from the foam material. To evaluate the effect of lustrous carbon defects on fatigue performance of lost foam molded specimens, experimental fatigue tests were conducted on the both batches of ductile cast iron specimens to obtain S–N data. These data were used to compare fatigue performance of two batches of specimens. The lost foam molded specimens obviously exhibit lower fatigue life i.e. lower S–N curve than green sand molded specimens. Also, the fatigue life of lost foam molded specimens were predicted using AFGROW software, which works based on linear elastic fracture mechanics (LEFM), by assuming lustrous carbon defects as cracks in which they grow until final fracture under cyclic load. The predicted fatigue lives were compared with the experimental ones.     

Influence of Tool Geometry in Friction Stir Welding

In this article we highlight the results of a recent study undertaken to understand the influence of tool geometry on friction stir welding (FSW) of an aluminum alloy with specific reference to microstructural development, defect formation, and mechanical response. The welding trials were made on 4.4 mm thick sheets using tools made of die steel and having different diameters of the shoulder and the pin, and the profile of the pin. Throughout the welding operation, the rotational speed, traverse speed, and tool axial tilt were held constant at 1400 rpm, 80 mm/minute, and 0 degrees, respectively. For a shoulder diameter of 20 mm and a pin diameter of 6 mm, the severity of defects in the weld was found to be the least and the resultant tensile strength of the weld was high. For the welds that were made using a tool having a shoulder diameter of 10 mm and a pin diameter of 3 mm the tensile strength of the weld was the least since the degree of defects observed were higher.     

Effects of Polymer Decomposition Behavior on Thermal Debinding Process in Metal Injection Molding

The thermal degradation mechanism of several polymers was studied for the metal injection molding (MIM) process. The depolymerization type polymers (polybutyl-methacrylate (PBMA) and polyacetal (POM)) had fast thermal degradation speed. On the other hand, the thermal degradation of the random type polymers (polypropylene (PP) and ethylene-vinyl acetate (EVA)) was influenced by the type of debinding atmosphere (air and nitrogen). In the thermal debinding process, it was clear that the thermal degradation speed of the feedstocks that contained more than 35.3 vol.% of depolymerization type polymers was faster than that of the feedstocks which contained more than 8.5 vol.% of random type polymers. For the feedstocks that contained more than 35.3 vol.% of POM and PBMA, the sintered test pieces had less than 30 ppm of carbon and the sintering relative density of the sintered parts was in the range of 95.5 to 96.5%. The debinding ratio of the test pieces decreased with an increase in the PP content. However, the thermal degradation gases of POM and PBMA (without any PP) caused some cracks and holes when a heating rate greater than 30°C hr^-1 was used to heat the specimen to the 270-300°C temperature range.     

Metal injection molding of pure molybdenum

In this work the processing steps for producing molybdenum parts by means of metal injection molding technique, including milling, mixing, debinding and sintering, were investigated in detail. Different feedstocks were prepared from received and milled molybdenum powder and a thermoplastic binder based on paraffin wax. The feedstock including 50% by volume of milled molybdenum powder had better rheological property and was injected successfully at low pressure. The molded specimens were debinded by two different processes, direct thermal debinding and solvent–thermal debinding. The content of carbon and oxygen were respectively less than 0.060% and 0.0042% after the parts were sintered under hydrogen atmosphere. The parts sintered at 1850 °C for 120 min exhibited a highest density of 9.70 g/cm³,meanwhile the tensile strength and hardness was 229 MPa and 193 HV10, respectively.     

Thermolysis of Plastically Formed Ceramics: Modeling and Computer Simulation

Several polymer processing techniques, such as extrusion, injection molding, vacuum forming, blow molding and film blowing can be used to mass produce complex shape components from engineering ceramic powders with a high degree of dimensional accuracy and good process control. In these processes the ceramic powder is dispersed in one or several additive(s), usually polymeric. These additives are only useful as the vehicle of the forming process and therefore have to be removed subsequently whilst retaining the architecture of the ceramic particle assembly which is densified by the conventional process of sintering. The removal of the additives, usually referred to as the debinding stage, is carried out usually by slow heating (thermolysis) to about 400°C. This is a crucial and a difficult stage as many unforgiving strength-limiting defects could appear during thermolysis. Defects which occur during thermolysis are difficult to prevent because these can be caused by several factors. Several variables, e.g. the section thickness, the geometry of the body, process control parameters such as the heating rate, development of porosity and numerous material properties (both of the additives and the ceramic powder) affect the process and influence the creation of defects. Therefore, trial and error experiments do not help in developing general criteria for the avoidance of defects which appear during debinding and there is no alternative but to model the process. Modeling combined with computer simulation seeks the variables which affect the creation of these defects. This leads to the identification of the critical variables which can be optimized and used in the design of additives and ceramic powders more suited for plastic forming.     

新型金属注射成形催化脱脂型粘结剂的催化快速分解研究

催化脱脂是目前MIM技术领域新的发展方向,研究了新型金属注射成型催化脱脂型粘结剂的催化快速分解,研究结果表明,该催化脱脂型粘结剂在以HNO3为催化剂进行催化脱脂时,注射成形坯经3－4h催化脱脂后,脱脂坯内部已形成大量的连通孔道,脱脂时间,脱脂温度以及 不同粘结剂组成影响催化脱脂效果。     

Effect of processing method on migration of antioxidant from HDPE packaging into a fatty food simulant in terms of crystallinity

Migration of additives from plastic packaging into food products is generally considered to be affected by polymer crystallinity. In the present work, migration of Irganox 1010 from high density polyethylene into a fatty food simulant (ethanol 95%) was studied for samples prepared with different percent crystallinities. For this purpose, 2 different processing techniques, injection and compression molding, were used, and the preparation conditions were changed to obtain high density polyethylene samples with crystallinities in the range of 50 to 70%. Migration analysis was carried out at 121°C for 2 hours, and then at 40°C for 238 hours using high performance liquid chromatography. In general, the injection molded specimens had lower crystallinity and higher overall migration than the compression molded ones. A similar trend for both injection and compression molded samples was observed indicating that the overall migration was a function of crystallinity degree. However, the specific migration rates of Irganox 1010 especially before 50 hours were found to be different for the 2 processing methods because of dissimilar morphologies. Theoretical modeling based on Fickian diffusion was applied to give more insights into the involved processes during specific migration. The interaction of the food simulant with the polymer was taken into account considering the food sorption into the polymer. By fitting the model on experimental data, it was possible to obtain the model parameters such as partition coefficients (K) and the swelling constant (B) as a function of sample crystallinity.     

Structure and thermal conductivity of powder injection molded AlN ceramic

AlN powders doped with Y₂O₃ (5 wt.%) were compacted by employing powder injection molding (PIM) technique. The binder consisted of paraffin wax (PW, 60 wt.%), polypropylene (PP, 35 wt.%) and stearic acid (SA, 5 wt.%). The feedstock was prepared with a solid loading of 62 vol.%. The binder was removed through debinding process in two steps, solvent debinding followed by thermal debinding. At last, the debound samples were sintered in flowing nitrogen gas at atmospheric pressure. The result reveals that thermal debinding atmosphere has significant effect on the thermal conductivity and structure of AlN ceramics. The thermal conductivity of injection molded AlN ceramics thermal debound in flowing nitrogen gas is 231 W m^?1 K^?1.     

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.     

CF/PA12 composite femoral stems: Manufacturing and properties

The fabrication process for a novel carbon fiber-reinforced polymer (polyamide 12) composite femoral stem using inflatable bladder molding was studied. Effect of processing temperature, holding time and applied internal pressure on the consolidation quality of the composite was investigated. Consolidation quality was evaluated by density and void content measurements and scanning electron microscope analysis. As expected, void content (porosities) and presence of large resin pockets were found to increase for lower processing temperature, holding time and applied pressure. Crystallinity as well as melting temperatures measured using differential scanning calorimetry could be related to molding conditions. A progressive reduction of the previous thermal history (crystalline peak of neat composite) and an increase in crystallinity were obtained for higher molding temperature. Static compression testing with void content analysis of molded specimens was used to determine optimal molding conditions. The composite structure molded showed compressive modulus close to cortical bone’s. Compression load at failure of composites molded in optimal conditions were found to be three times higher than those of femoral bone for jumping on one leg or 10 times those for normal gait. The molded composite structure appears to be an excellent candidate for femoral stems used in total hip arthroplasty.     

大尺寸ZrO2注射成型坯体热脱脂缺陷成因探究

采用蜡基ZrO2粉末喂料注射成型获得大尺寸ZrO2陶瓷粉末注射产品（坯体）,并根据喂料热分析曲线的变化特点,系统研究了大尺寸ZrO2坯体的热脱脂过程及规律。通过对热脱脂前后坯体的重量损失、尺寸收缩、外观缺陷和微观组织形貌的分析评估,着重探讨了大尺寸ZrO2坯体热脱脂过程中存在的主要缺陷和成因。研究表明,流蜡、鼓泡和开裂等热脱脂缺陷主要发生在低温脱脂阶段,其主要原因是液态石蜡扩散及分解过程的失衡。为此,结合“失重率控制”的思路和喂料的热失重规律,对热脱脂工艺进行了优化,在不延长总脱脂时间的前提下,显著提高了大尺寸ZrO2坯体的脱脂合格率。     

改性PET的微孔注塑成型

采用均苯四甲酸二酐(PMDA)扩链增粘改性后的聚对苯二甲酸乙二醇酯(PET)(M-PET)进行Mucell微孔注塑成型实验。扫描电镜(SEM)结果表明,M-PET具备了维持良好泡孔形态所需的熔体强度,其微孔注塑制品分为皮层、中间层与芯层三部分。通过正交实验和信噪比(S/N)分析法,考察了M-PET在微孔注塑成型过程中各重要操作参数对制品拉伸强度的影响。研究结果表明,高的熔胶量,适中的发泡剂含量和熔体温度,以及较低的射胶速率和模具温度有利于提高制品的拉伸强度,在各操作参数中,熔胶量对制品拉伸强度影响最大。获得了发泡样条力学性能与减质量之间的关系。     

CIM中最新脱脂工艺的进展

陶瓷注射成型是一种近净尺寸可塑成型方法 ,可高效率成型形状复杂的陶瓷部件。脱脂是陶瓷注射成型中最复杂、最重要的环节 ,本文介绍了陶瓷注射成型最新脱脂工艺进展 ,详细介绍了催化脱脂和水基萃取脱脂的脱脂原理 ,并对各种脱脂工艺的优缺点进行了比较。     

Thermal debinding of Fe3Al-X metal powder compacts

The process of removing a multicomponent binder from a metal powder compact has been investigated. Model experiments of debinding were performed on compounds consisting of less than 40 vol% binders (low molecular weight polyethylene, paraffin and Carnauba waxes) and more than 60 vol% metal content. As typical representatives for injection moulding morphology and meeting all other requirements for optimal powder characteristics, elemental powders of the Fe-Al system were used. Viscosity results over a wide range of shear rates for various plastisols are presented as functions of binder system composition and metal powder content. Based on the rheological response, an optimization of plastisol formulation was performed. Results are reported on three series of debinding modes using heat and fluid wicking in air and in nitrogen. The time dependence of fractional debinding, x(t), during wicking has been estimated using a model. Direct observation by SEM of binder distribution and pore structure evolution at different stages of the debinding process was made. Wick-assisted thermal debinding in nitrogen proved to be an effective debinding method in terms of shape preservation and the absence of defects in the studied material.     

Effects of debinding parameters on powder injection molded Ti-6Al-4V/HA composite parts

Titanium alloy-hydroxyapatite(Ti-6Al-4V/HA) composite powders produced by a ceramic slurry were mixed with a multi-component binder system in the powder injection molding process. The binder system comprises mainly of natural wax, fatty acid wax, stearic acid, poly-oxialkyen-etherand olefln-hydrocarbons. After molding, the binder system was removed by conventional thermal debinding. The effects of heating rate and gas flow rate on the quality of the debound part in terms of defects, mass of binder removed and residual carbon level were discussed. A slow heating rate (20° C/h) at the beginning stage of the debinding step and a higher gas flow rate (250 cm³ /min) were required for the production of defect-freeparts with minimal carbon level.     

陶瓷注射成形中脱脂工艺及其新进展

陶瓷注射成形是先进的陶瓷近净成形技术,可高效成形形状复杂的陶瓷部件.而脱脂是陶瓷注射成形中最复杂和重要的环节.详细介绍了陶瓷注射成形各种脱脂工艺的脱脂原理,并对各种脱脂工艺的优缺点进行了比较.