Optimisation of eco-friendly binary binder system for powder injection moulding

Abstract

In recent years, many efforts have been made to obtain more environmentally acceptable powder injection moulding processes. In this sense, the purpose of this study is to optimise an eco-binder based on polyethylene glycol (PEG) as a water soluble component and cellulose acetate butyrate (CAB) as a natural backbone polymer derived from cellulose for powder injection moulding of zirconium silicate powders until a solvent debinding stage. Four different feedstocks have been investigated. As well as, a volume fraction of PEG and CAB 70/30 (vol.-%) and a solid loading of 57·5 (vol.-%) were maintained, molecular weights of polymers were combined in order to minimize distortion during binder solvent extraction. Water solvent debinding was carried out at three temperatures stepwise during 5 h. As a result, efficient removal of the PEG as well as free defects samples were obtained after solvent debinding for binder systems based on low molecular weight of PEG.     

Influence of multisteps thermal control in metal powder injection moulding process

Abstract

In metal injection moulding, the quality of the products depends highly on an effective and suitable debinding process. The improvement of the debinding process thus becomes one of the most important topics in metal injection moulding research. To increase the binder debinding rate and decrease the defects of the products, it is essential to understand the influence of thermal control on the debinding process. The present paper aims to investigate the effect of multisteps thermal control on the debinding rate through experiments. Different from previous researches in which single binder is usually adopted, multicomponents binder is used to reflect the real manufacturing situations in industry. The relationship among viscous force, capillary force and pressure force for different working conditions is discussed in details. Experimental results show that the debinding rate and the final debinding fraction are dominated by particle size in the compact rather than that in the wick. For thick compact with low porosity, the shape of green compact is well maintained and the defect of neck shrinkage is reduced by multisteps thermal control. The neck shrinkage situation can further be improved by using the two component binder.     

Dilatometric analysis of thermal debinding of injection moulded iron compacts

Abstract

The less than desired tolerance control of powder injection moulded compacts is a result of inconsistent dimensional changes in the compacts accumulated during moulding, debinding, and sintering. This study investigated the in situ length changes and their causes during thermal debinding on compacts which have been solvent debound. The dilatometric analysis showed that the specimen shrank in the early stage between 250 and 370°C, not because of sintering, but through the loss of N, C, and O in the carbonyl iron powder. At temperatures between 370 and 450°C, the specimen expanded owing to the carburisation of the iron powder. The length change was also influenced by the heating rate, debinding atmosphere, and the amount of the backbone binder. These dilatometric results are helpful in establishing the guidelines in designing binder compositions and debinding schedules.     

Sintering parameters and mechanical properties of injection moulded aluminium powder

Abstract

This paper describes the microstructural and mechanical properties of injection moulded aluminium powder. Gas atomised aluminium powder was injection moulded with wax based binder. The critical powder loading for injection moulding was 62·5 vol.-% for feedstock. Binder debinding was performed in solvent and thermal method. After debinding, the samples were sintered at different temperatures and times in high purity N₂. Metallographic studies were conducted to determine the extent of densification and the corresponding microstructural changes. The results show that gas atomised aluminium powder could be sintered to a maximum 96·2% of theoretical density. Maximum density, tensile strength and hardness were obtained when sintered at 650°C for 60 min.     

New trends in powder injection moulding

Powder injection moulding (PIM) is a rapidly growing technology for producing complex geometry, net shaped components from ceramics, metals, hard metals, and intermetallics. The shaping of ceramic powders using injection moulding has a highly creative aspect with regard to the complexity of the structural parts. This permits the most near-net shaping possible. Therefore, costly finishing of the sintered components can be reduced to a minimum or totally eliminated. This potential for ceramic injection moulding (CIM) has led in the recent past to intensified international research and development activities. A number of new binder systems have been developed, i.e., polyacetate based, PEG-polymer based, acrylic-polymer based, agarose-based, etc. The development in the area of new binder composition was in parallel assisted by a significant improvement in debinding processes. New debinding systems have been developed, i.e., computer assisted thermal debinding, extraction debinding, catalytic debinding, or even freeze drying or microwave assisted drying, which significantly shortened the debinding time from days to hours and lowered the emission of undesirable volatile organic by-products to a minimum. The formation of defects during the debinding process was also practically eliminated. Nitherlands Enegy Research Foundation ECN. Published in Poroshkovaya Metallurgiya, Nos. 3–4(406), pp. 16–23, March–April, 1999.     

Production of titanium grade 4 components by powder injection moulding of titanium hydride

Abstract

Recent developments are presented on powder injection moulding of titanium from metal hydride powders and binders composed of polyethylene, paraffin wax and stearic acid. The feasibility of using this route to process fit for purpose, complex parts is assessed. Titanium hydride offers a low cost solution compared with pure titanium powders. Feedstocks for powder injection moulding were prepared in a sigma mixer. Tensile test specimens and demonstration parts were injection moulded. Solvent debinding in heptane was followed by thermal debinding and dehydrogenation under argon. Titanium parts were sintered at 1200°C under argon. Sintered parts exhibit a linear shrinkage of about 20%, good shape preservation and reproducibility. The yield strength (519 MPa), ultimate tensile strength (666 MPa), elongation to fracture (15%) and interstitial content measured by quantitative analysis meet the requirements for titanium grade 4.     

Modified metal injection moulding process of 316L stainless steel powders using thermosetting binder

Abstract

A modified metal injection moulding (MIM) process of 316L stainless steels powders using an acrylic thermosetting resin has been developed. Gas and water atomised 316L powders were used. In order to optimise the mixing and moulding steps, different volume fractions of the two components were investigated. Mixing of metal powder and binder was carried out at room temperature and immediately moulding was performed by pouring the slurry in the moulds. It was then heated at 90°C to permit the polymerisation and cross linking of the resin. Different heating cycles, rates, and atmospheres were studied by means of thermogravimetrical analysis. The data obtained were used to establish the best debinding cycle. The debound samples were sintered at different temperatures and high densities (98% of theoretical) were obtained. Materials in as moulded (green part), debound (brown part), and sintered conditions were examined by means of SEM.     

YG8硬质合金注射成形脱脂工艺的研究

采用传统蜡基和(油+蜡)基改进型两种粘结剂,对粒度为1.97μm的WC-8Co混合粉末注射成形,研究了两种喂料的热脱脂、溶剂脱脂+热脱脂工艺,确定了热脱脂、溶剂脱脂+热脱脂的优化工艺路线。从脱脂速度和脱脂时间、脱脂缺陷和脱脂工艺控制的难易程度等方面比较了两种粘结剂的热脱脂和溶剂脱脂效果。研究了热脱脂温度、时间、不同脱脂方式以及粘结剂组成对脱脂坯碳含量的影响。结果表明,以氢气为脱脂气氛,在450℃以下进行热脱脂可以将有机聚合物完全脱除而且不产生脱碳,溶剂脱脂后再进行热脱脂更有利于控碳和减少脱脂缺陷,而且大大缩短脱脂时间。(油+蜡)基改进型粘结剂在热脱脂和溶剂脱脂时具有更好的脱脂特性。     

WC-10Co-1TaC硬质合金异形刀片注射成形与合金性能的研究

采用粉末注射成形工艺制备了合金成分为WC-10Co-1TaC的硬质合金抗弯试样和可转位异形刀片。采用电子扫描显微镜、光学显微镜、万能电子力学试验机、钴磁测量仪等对样品的形貌、组织以及力学性能进行研究分析。研究结果表明:采用溶剂脱脂+热脱脂的脱脂方式,可以很好地控制脱脂过程产生的开裂、变形;理想的溶剂脱脂温度为40℃,溶剂体积与样品体积比为7∶1,脱脂时间为6h,脱脂率为50%;理想的热脱脂工艺为:以2℃/min的升温速率从室温升到420℃并保温45min。烧结样品的抗弯强度为2200MPa,硬度(HV30)为1350MPa,矫顽磁力(Hc)为10.7kA/m,钴磁(Com)为9.4,达到制品的性能要求。     

Processing of Mn–Zn ferrites using mould casting with acrylic thermosetting binder

Abstract

In this paper, a simple manufacturing process for Mn–Zn ferrite powder is described, which can be considered as a modified powder injection moulding process. This method uses acrylic thermosetting resin as the binder. The moulding is carried out at room temperature by directly pouring the slurry (resin and ferrite) in the mould. The mixture is heated at the curing temperature (70°C) of resin to permit polymerisation and cross linking of the polymer. In order to optimise the moulding step, different volume fractions of powder with resin were mixed. The optimal powder load was 50 vol.-%. The best thermal debinding cycle was determined by means of thermo-gravimetric analysis. Sintering was performed according to oxygen partial pressure equilibrium curves at 1330°C for 3 h. Magnetic properties were compared with those obtained by uniaxial compacted parts.     

Injection moulding of 316L stainless steels reinforced with nanosize alumina particles

Abstract

This study aims to compare the effect of Al₂O₃ nanoparticle additions on the densification and mechanical properties of the injection moulded 316L stainless steels. The 316L stainless steel and Al₂O₃ nanoparticles were dry mixed and moulded using a wax based binder. The critical powder loading for injection moulding were 60 vol.-% for all samples. Debinding process was performed in solvent using thermal method. After the debinding process, the samples were sintered at 1405°C for 60 and 120 min under vacuum. Metallographic examination was conducted to determine the extend of densification and the corresponding microstructural changes. The sintered samples were characterised by measuring tensile strength, hardness and wear behaviour. Wear loss was determined for all the samples after wear testing. All the powders, fracture surfaces of moulded and sintered samples were examined using scanning electron microscope. The sintered density of straight as well as Al₂O₃ nanoparticles reinforced injection moulded 316L stainless steels increases with the increase in sintering time. The additions of Al₂O₃ nanoparticles improve the hardness and wear resistance with the increase of sintering time.     

Water debinding behaviour of water soluble Ti-MIM feedstock

Abstract

A water soluble polyethylene glycol (PEG) based binder system was used to formulate three feedstocks containing prealloyed Ti–6Al–4V, NiTi and blended elemental Ni/Ti powders respectively. The selection of these metal powders was to investigate the effect of powder characteristics such as particle size and particle shape. Various solid loadings were investigated in these feedstocks. The water debinding behaviours were systematically studied in terms of debinding temperature, time, sample thickness, powder characteristics and solid loading. Corresponding debinding rate was calculated from the measurements using a shrinking core reaction kinetic model.     

Effect of residual carbon on the sintering process of M2 high speed steel parts obtained by a modified metal injection molding process

In this article, we present the evolution of the microstructure during sintering of M2 high speed steel (HSS) parts obtained by a modified powder injection molding (PIM) process, which uses a new binder system based on a thermosetting resin. The most important characteristics of this process is that molding is carried out at room temperature by pouring the slurry (resin and tool steel previously mixed) directly into the mold. The mold is then heated to the curing temperature of the resin. The best mixture of polymer and steel powders was 60 pct volume of metal powder. The resin was removed by thermal debinding. The sintering process was carried out under vacuum atmosphere. We tested different debinding temperatures in order to retain residual carbon in the samples coming from the thermal degradation of the polymer. The best results were obtained at low debinding temperature (300 °C). In this case, residual carbon had a beneficial effect, extending the sintering temperature range by 100 deg, making it possible to reach very high density at temperatures as low as 1100 °C. The mechanism of this densification seems to be via supersolidus liquid phase (SPLS). The microstructural study of sintered parts revealed a homogeneous distribution of carbides that change their morphology with increasing temperature. Besides spherical M₆C carbides, which appear in all the temperature ranges studied, a new rodlike M₂C carbide appears.     

Microstructural and mechanical properties of injection moulded gas and water atomised 17-4 PH stainless steel powder

Abstract

This paper describes the microstructural and mechanical properties of injection moulded 17-4 PH stainless steel gas and water atomised powder. Gas and water atomised stainless steel powders were injection moulded with wax based binder. The critical powder loading for injection moulding were 62·5 and 55 vol.-% for gas and water atomised powders respectively. Binder debinding was performed using solvent and thermal method. After dedinding the samples were sintered at different temperatures for 1 h in pure H₂. Metallographic studies were conducted to determine to extend densification and the corresponding microstructural changes. The results show that gas atomised powder could be sintered to a maximum (98·7%) of theoretical density, and water atomised powder could be sintered to a maximum (97·08%) of theoretical density. Maximum tensile strength was obtained for gas atomised powder sintered at 1350°C. The tensile strength of the water atomised powder sintered at the same temperature was lower owing to higher porosity. Finally, mechanical tests show that the water atomised powder has lower mechanical properties than gas atomised powder.     

Effect of nickel boride and boron additions on sintering characteristics of injection moulded 316L powder using water soluble binder system

Abstract

A new metal injection moulding system for 316L stainless steels has successfully been derived and tested. A mixture of small water atomised powder (average size 15 µm), larger gas atomised powder (average size 75 µm), and sintering additives has been coupled with a new water soluble binder system for economical powder injection moulding. The details for each process step and the effect of sintering additives are described. The binder system consists of poly (2-ethyl-2-oxazoline) as the leachable polymer, polyethylene as the backbone, and stearic acid as a surfactant and plasticiser. This binder system provides satisfactory mixture stability, excellent mouldability, and reasonably fast water leaching and thermal debinding rates. The optimum powder/binder compositions were determined using torque and capillary rheometry. Densification was by persistent liquid phase sintering through additives, such as nickel boride and boron. This 316L powder system was sintered to 7·9 g cm ^-3 (98·75% of theoretical) at 1285°C using nickel boride addition and at 1245°using boron addition. nickel boride additions are particularly effective at increasing the tensile strength and ductility. In contrast, the boron additions only increase the tensile strength and decrease ductility. Based on microstructure evaluations, this effect is traced to a continuous boride phase on the grain boundaries of the boron doped samples and a discontinuous boride phase on the grain boundaries of the nickel boride samples.     

Hot micro-embossing: effect of pressure on 316L metal parts

Abstract

The use of replicative processes has become strategic and critical in industry to produce precise, microscopically detailed metallic parts and devices via low cost manufacturing routes. Metal powder hot embossing is an emerging process that brings some advantages associated with the reduction of production costs relative to powder injection moulding (PIM). The technology involves four distinct steps: preparation of the selected feedstock material (powder and binder); hot embossing; debinding; and sintering. The effect of continuous pressure during the hot embossing step as a means of replicating microdetails in 316L stainless steel parts is examined. Dimensional accuracy, microstructure and mechanical properties of the parts produced were evaluated. For the configuration tested, the most promising results were achieved when processing at 180°C for 30 min at a pressure of 14 MPa.     

Finite element investigation of backbone binder removal from MIM copper compact

Abstract

Finite element (FE) model based on kinetic analysis was developed to describe the thermal debinding process of previously solvent debinded metal injection moulded (MIM) copper compacts. Thermophysical properties (specific heat, density, thermal diffusivity and thermal conductivity as a function of temperature) of MIM copper compact were measured using differential scanning calorimeter, laser flash analyser, thermogravimetry analyser and pushrod dilatometer. The proposed model is solved numerically to study binder removal and binder distribution during thermal debinding. The investigations included the analysis of residual (backbone) binder content for cylindrical MIM copper compacts at different temperatures and positions. The FE calculations are strongly based on measured thermophysical data and kinetic analysis of copper system. The FE simulated and experimental results were compared to validate the underlying FE model based on FE temperature field calculations. Drawing the real furnace temperature conditions in finite calculation can result in obtaining more accurate data.     

Experimental investigation and numerical simulation analysis of sintered micro-fluidic devices

ABSTRACT

This study investigates the use of numerical simulations to describe the solid-state diffusion of a sintering stage during a metal injection moulding process for micro-fluidic components with 316L stainless steel powders. Finite element (FE) analysis based on a thermo-elasto-viscoplastic model was conducted to describe the densification process of a stainless steel porous component during solid-state sintering. The numerical analyses, which were performed on a 3D micro-structured component with various powder volume loadings to take into account the thermal debinding effect to propose a full debinding sintering simulation, demonstrated that the FE simulation results are in agreement with the experimental ones.     

Powder extrusion moulding of 430L stainless steel thin tubes for porous metal supported SOFCs

Abstract

Thin and thick walled tubes made of 430L stainless steel for porous metal supported solid oxide fuel cells (SOFCs) were prepared by powder extrusion moulding (PEM). A gas atomised metal powder and a binder composed by 50?vol.‐% high density polyethylene and 50?vol.‐% paraffin wax were chosen. The most suitable powder loading for feedstock (68?vol.‐%) was determined by means of torque experiments and rheological measurements. Mixing temperature was selected taking into account the results from differential scanning calorimetry. The extrusion of tubes was carried out in a single screw extruder and two kinds of tubes with two different wall thicknesses were obtained. In order to investigate the homogeneity of feedstock, microstructure of green tubes was evaluated by SEM. Thermal debinding was performed on the basis of thermogravimetric analysis results. After sintering, tubes with good dimensional stability and without defects were obtained. Different wall thicknesses extruded were 150 and 500?μm.