Papers by Keyword: Debinding

Abstract: Impurity control remains to be a challenge to titanium metal injection moulding (Ti-MIM). Much attention has been paid to polyethylene glycol (PEG) based binder systems due to the eco-friendly and water-soluble feature of PEG. In this study, a new easy-to-debind PEG/polypropylene carbonate (PPC)-based binder system (76% PEG+17% PPC+3% polymethyl methacrylate (PMMA)+2% stearic acid (SA)+2% polyvinyl acetate (PVAc)) was developed. The rheological properties of the feedstocks prepared with the binder system in different proportions were assessed. Debinding behaviours of the moulded samples and impurity contents of oxygen (O), carbon (C), and nitrogen (N) of the thermal debound specimens were investigated as well.

Abstract: Sliding electrical contacts are traditionally produced by conventional compacting technologies. Employing the powder injection moulding process (PIM) as a new manufacturing method can offer several advantages such as the fabrication of complex net-shaped parts, cost-effectiveness and high volume productions. The PIM process route consists of the following steps: powder processing, compounding, injection molding, debinding and sintering. A two-stage process consisting of solvent debinding and thermal debinding is often used to remove the moulding binder. In the present paper, the suitability of the powder metallurgical processes: mechanical alloying and powder mixing for the preparation of bronze-graphite powder mixtures for the compounding and injection moulding of sliding contacts is discussed. The use of a suitable binder is of central importance for the preparation of injection-moldable feedstocks. For this purpose, two commercial ready-to-use binder systems were utilized and evaluated. The essential challenge of the process route is to optimize all parameters of the subprocesses to achieve a damage-free debinding and sintering of the injection-moulded parts. First results on the influence of the graphite content, the binder fraction, the debinding and sintering parameters are presented and discussed.

Abstract: The purpose of this work is to use the statistical methods including linear regression and statistical hypothesis test to study the dissolution behavior of polyethylene glycol (PEG), a water-soluble binder, during debinding step of the green specimens of mullite formed by powder injection molding (PIM). Two systems of composite binders were investigated including (A) 80 wt% polyethylene glycol (PEG) and 20 wt% polyvinyl butyral (PVB) and (B) 78 wt% PEG, 20 wt% PVB, and 2 wt% steric acid (SA)The lab-scale plunger type PIM machine was used to prepare the green specimens consisting of mullite powder and the composite binder. The possible solid loadings of the green specimens that could be prepared by this machine were 50, 52, and 54 vol% mullite (50, 48, and 46 vol% binder). The debinding was done by soaking the green specimens in the warm water at 40 or 60 oC to remove PEG. At level of significance 0.05 for statistical analysis, the dissolution behavior of PEG can be fitted with Avarami equation. In addition, from the Avarami equation obtained from each experimental condition, the dissolution rate of PEG was independent of the parameters used in this study including solid loading in the green specimens, water temperatures for debinding, and composite binder systems.

Abstract: The demand for components manufactured by Metal Injection Molding (MIM) has been increased due to a diverse range of applications on the high temperature mechanical properties and corrosion/oxidation resistance. Super alloy utilize the inherent physical properties of heat-resisting alloy based on iron-nickel, or cobalt specifically high purity and fine particle size distributions, which can enhance sintering and maximize the density of the final component. The development of super alloy Inconel 718 (IN718) using MIM is discussed. IN718 powder with binder formulation consists of polyethylene (PE) / palm stearin (PS) were mixed homogeneously and injected to produce green compacts. The binders then were removed through solvent extraction process from various heating temperature and duration of time. The binder removal was quantified by weight loss measurements and the evolution of pore structure for the debound specimens was observed using scanning electron microscope (SEM). Result shows that complete extraction of PS from the green parts can be concluded during 60 °C of heating and 6 hours of immersion in heptane.

Abstract: Metal Injection Moulding (MIM) has undergone development of various binder systems with the aims of shortening the overall debinding time duration. In the present work, binder system based on biopolymer has been utilised in injection moulding of hip stem CoCrMo alloy powder. The feedstock consisted of CoCrMo powder with mean diameter particle size of 16μm and binder system which comprised of major fraction of wax and minor fraction of polyethylene. The moulded part was immersed into n-heptane at 60°C in order to remove the paraffin wax and stearic acid, followed by sintering in a controlled vacuum atmosphere. Results showed that solvent extraction debinding technique allowed complete removal of paraffin wax and stearic acid from the injection moulded part within 5 hours without swelling or distortion of the debound part. Lower heating rate needed during thermal pyrolysis in order to retain the shape due to the thickness of the part.Keywords: CoCrMo, MIM, wax, debinding,

Abstract: Debinding involves long and delicate processing periods of removing binder components from a green body after injection moulding; failure to completely remove the binder components results in distortion, cracking, blisters and contamination at elevated temperatures. This study focuses on optimising thermal debinding process parameters on the basis of obtaining a defect-free part after sintering and also determining a sintering time that gives high sintering density. Thermal debinding was conducted after solvent debinding. The feedstock used to produce green compacts composed of Ti6Al4V powder and a wax-based binder. The binder’s backbone component is a low density polyethylene (LDPE). Careful selection of thermal debinding parameters was guided by thermo-gravimetric analysis (TGA) results. The Taguchi method was used to determine an optimum debinding process. Thermally debound compacts were analysed for residual binder using a TGA. Archimedes’ principle and optical microscopy were done to analyse the sintering density and microstructure of the sintered product, respectively. Optimum debinding and sintering conditions were identified. The study demonstrated that heating rate during debinding was the most influential factor that contributes to minimum residual binder followed by debinding dwell time and temperature. Longer sintering time of 4 h favoured higher density of 91.6 ±1.55%. A typical radial shrinkage level of 11.1 ±0.0816% was determined.

Abstract: Metal injection moulding (MIM) is a well-established, cost-effective method of fabricating small-to-moderate size near net-shape metal components. MIM is increasingly being employed as a process for fabricating orthopaedic and dental products with complicated shapes. In this study, commercially pure titanium (CP-Ti) powder has been used to fabricate dental implants via MIM. The CP-Ti powder was mixed with binders containing Polyethylene glycol (PEG), High Density Polyethylene (HDPE) and stearic acid (SA) to form the MIM feedstock. Commercially available feedstock was also used to fabricate MIM implants. The MIM compacts were then subjected to debinding and sintering, and then the mechanical and chemical properties of the compacts were investigated for their suitability for dental implantology. The effect of the MIM processing variables on the surface roughness of CP-Ti was also investigated and studies for biocompatibility were carried out using in-vitro cell culture. The results showed that the mechanical and chemical properties of the sintered components were within ASTM Grade MIM 2 and Grade MIM 3 (ASTM F2989 − 13) specifications for titanium. The results also showed that the implants produced by MIM appeared to meet basic biocompatibility requirements. It was concluded that dental implant prototypes may be fabricated successfully using MIM and this approach offers greater opportunities for future manufacturing.

Abstract: Debinding is one of the most critical and time consuming stage in metal injection moulding (MIM). German and Bose (1997) reported that early debinding practice relied on thermal binder degradation, requiring up to 300 hours for complete binder removal. Today multi-stage debinding techniques are introduced cutting down the debinding time to as little as 2 hours. This work investigates solvent debinding variables prior to thermal debinding. Solvent debinding is carried out in n-heptane. Wax and stearic acid are the target binder components being leached out from the green bodies, with wax as the major constituent in the binder formulation. Debinding is conducted at 50, 55, 60 and 65°C for 1-4 hours at each temperature. Weight loss measurements were done. For porosity and surface appearance, scanning electron microscope (SEM) analysis and visual inspection were done. Samples de-bound at 65°C showed an appreciable amount of mass loss; however, surface cracks and warping were observed. A 60°C temperature and time of 4 hours demonstrated best results i.e. a satisfactory mass loss, absence of surface cracks and no warping. Mass loss is directly proportional to temperature and time. SEM results are discussed in the paper.

Abstract: The aim of this paper is to propose the approach for applying statistical methods (linear regression and statistical hypothesis testing) to study the behavior of binder during binder removing (debinding) step in powder injection molding (PIM) and also the parameters that affect the binder removing rate. In this work, the binder system under the investigation is the composite binder of 85wt% polyethylene glycol (PEG) and 15 wt% poly (methyl methacrylate) (PMMA) where PEG can be removed from the green product by using warm water while PMMA is removed later during sintering. At 0.05 level of significance, the linear regression method and the statistical hypothesis test prove that the dissolution behavior of PEG can be described using Avarami equation. Furthermore, the dissolution rates of PEG were independent of all parameters used in this study including binder contents in the green products, temperatures, and powder sizes.

Abstract: This work investigated the influence of specimen dimensions and temperature on the debinding behavior of alumina feedstock for powder injection process. Polyethylene glycol (PEG) was used as a based binder. It is soluble in water therefore the use of wax-based binder system can be avoided. PEGs with a molecular weight of 1500 and 4000 were mixed with polyvinyl butyral (PVB) a minor component. Stearic acid was added during feedstock preparation to act as a lubricant. Debinding process was carried out using a water leaching test at 30 and 70 °C to study for PEG removal rate. Specimens retained their shapes after leaching of the binders. In general, the rate of binder removal increased at initial stage then slowed down at longer leaching times. A faster debinding rate was achieved at 70 °C when compared to 30 °C. In addition, samples with a higher surface area to volume ratio (As/V) led to an increase in the %PEG removal rate. This study also showed the relationship between %PEG removal as a function of different surface area to volume ratio (As/V) which can be helpful in predicting %PEG removal for any other samples having cylindrical shape.