Debinding Cycle Research Articles

Solvent debinding mechanism for alumina injection molded compacts with water-soluble binders

The solvent debinding process has been widely accepted in the ceramic injection molding (CIM) industry process due to its short debinding cycle. However, the organic solvents most adopted in solvent debinding now are flammable, carcinogenic and not environmentally acceptable. For eliminating the use of unsound solvents, water-soluble polyethylene glycol (PEG) is used in this study to modify the pattern of debinding in CIM. The purpose of the investigation was to examine the binder behavior during solvent debinding based on water extraction for a multi-component PEG binder system. Based on the in situ evaluation results of dimensional variations, mercury intrusion data and scanning electron microscope (SEM) observations, possible solvent debinding mechanism for alumina injection molded compacts with water-soluble binders is proposed.

Powder Injection Moulding to Recover Slate Wastes

This paper focuses on the use of new technologies of ceramic manufacturing for the recovery of wastes resulting from cutting and grinding of slates. Slates are commonly used for roof and floor tiles and billiard tables. Several tonnes/day of waste can be produced. After pressing and sintering, the physical, chemical, and mechanical product properties open new approaches for the recovery of these inorganic wastes. The particle size of slate wastes is suitable to injection moulding, for the production of large series of parts with complex shapes. In this study, a method for feedstocks preparation based on slate was optimised, and the influence of thickness of moulded parallelepiped bars on debinding cycle studied. Finally, the debinding and sintering treatments were performed to evaluate some physical and mechanical properties of the final product.

Recyclability of injection moulding feedstock

In this work we present the application to a T15 high speed steel of a modified metal injection moulding process based on the use of a thermosetting resin. This method has been successfully applied to produce 316L stainless steels and M2 HSS. The main characteristic of this manufacturing method is that the slurry (polymer and metal powder) is introduced into the mould at room temperature and afterward is heated at 90°C in order to polymerise the resin. We have optimised the powder-binder formulation and the best thermal debinding cycle by means of thermogravimetric analysis. Since the microstructure and properties of the HSS is very sensitive to the sintering temperature, its effect on the density, hardness, transverse rupture strength and microstructure was investigated. The mechanical properties obtained are in good agreement with other HSS parts manufactured by conventional MIM. During the sintering process it has been identified vanadium carbide (MC) and tungsten carbide (M6C) that are homogeneously distributed on the steel matrix.

Processing of P/M M2 high speed steels by mould casting using thermosetting binders

This communication presents a modified powder injection moulding (PIM) method for M2 tool steel powder using a new binder system based on a thermosetting resin. The moulding is carried out at room temperature by pouring directly the slurry (resin and tool steel previously mixed) in the mould. Afterwards, the mould is heated at the curing temperature of the resin. We have optimised the powder–binder formulations and the best thermal debinding cycle were determined by means of thermogravimetric analysis (TGA). The presence of carbon in the brown parts seems to be necessary in order to sinter the specimen. Moreover, the sintering temperature range can be extended to more than 100°C, being able to achieve very high density at 1100°C, by means of incomplete debinding. The microstructural study of sintered parts revealed the coarsening of the carbides with the temperature. Besides M 6C carbide that appears during all the temperature range studied, M 23C 6, M 2C and M 4C 3 carbides sequentially appear with the sintering temperature.

Processing of P/M T15 high speed steels by mould casting using thermosetting binders

Abstract In this work we present the application to a T15 high speed steel of a modified metal injection moulding process based on the use of a thermosetting resin. This method has been successfully applied to produce 316L stainless steels and M2 HSS. The main characteristic of this manufacturing method is that the slurry (polymer and metal powder) is introduced into the mould at room temperature and afterward is heated at 90°C in order to polymerise the resin. We have optimised the powder-binder formulation and the best thermal debinding cycle by means of thermogravimetric analysis. Since the microstructure and properties of the HSS is very sensitive to the sintering temperature, its effect on the density, hardness, transverse rupture strength and microstructure was investigated. The mechanical properties obtained are in good agreement with other HSS parts manufactured by conventional MIM. During the sintering process it has been identified vanadium carbide (MC) and tungsten carbide (M 6 C) that are homogeneously distributed on the steel matrix.

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

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.

Evaluation of Binder Burnout by Thermal Analysis

A three component binder system composed of polypropylene, paraffin wax and stearin was chosen in order to investigate the weight loss and phase transformations during thermal debinding cycles. Carbonyl iron powder served as metallic material. After debinding samples were sintered, and the shrinkage and microstructures were evaluated. Shrinkage started at 600 °C, and a linear shrinkage of 10% was observed at 1300 °C. Three variables were studied: debinding atmosphere; heating rate during debinding step; and heating rate during sintering step. A strong effect of the atmosphere, comparing air and argon, was observed. Three different regions of weight loss were determined, and one of them (between 410 °C and 610 °C) was related to the iron powder weight loss. Thermogravimetry and calorimetry were carried out simultaneously. A discussion about the mechanisms of binder removal, based on isothermal treatments, is also presented. The controlling debinding step, considering the discussed system, is the diffusion through polypropylene to pore surfaces.

Metal and ceramic powders for injection moulding: P.Minuth et al. (H.C.Starck GmbH, AG, Germany.)

A high temperature batch furnace has been constructed for real-time analysis of sample weight, compact temperature profile and evolved gas composition using various gas analysis methods. The furnace has digital mass flow controllers for atmosphere composition control. A separate precision dilatometer is used to provide dimensional change data. These analytical capabilities are controlled by a microprocessor coupled to a control computer which records the output from the various sensors. The long range goal is to develop an expert systems software to fully govern the thermal and atmosphere cycle in a closed-loop feedback mode. This will allow optimization of the sintering pathway for any material, processing objectives, and component geometry. In addition, the equipment will be used to investigate the debinding cycle of powder injection moulded (PIM) parts. By varying the heating rate, time at temperature, and atmosphere during the debinding cycle, the debinding mechanisms and rate controlling parameters can be identified. The goal of these experiments is to significantly lower the debinding time while maintaining compact integrity. A model for optimized processing is being developed in parallel with these experiments.

Nanophase and superfine cemented carbides processed by powder injection molding

Two commercial superfine and one innovative nanophase cemented carbide powders were used in this study. They cover straight and complex grades of cemented carbides. The nanophase cemented carbides are characterized by a combination of high hardness and strength. However, the nanophase cemented carbides do not have a favorable moldability. The as-received nanophase particles are agglomerated hollow balls. Therefore, milling was used on the as-received nanophase powder to form a particle suitable for injection molding. Even so, manufacture of nanophase cemented carbides via powder injection molding (PIM) is highly challenging. Several processing parameters affect the success, including powder moldability, binder chemistry, mixture homogeneity, molding parameters, debinding cycle, and sintering densification level. Binder-related factors were the focus of this study, including binder chemistry, binder-powder compatibility, feedstock preparation, molding conditions, and binder removal after molding.

Comparative study of pore structure evolution during solvent and thermal debinding of powder injection molded parts

The solvent debinding process has been widely accepted in the powder injection molding (PIM) industry due to its short debinding cycle. In the current study, specimens were immersed in a heptane bath for different lengths of time, and the pore structure evolvement in the compact was analyzed. Mercury porosimetry analyses and scanning electron micrographs showed that the binder extraction started from the surface and progressed toward the center of the compacts. As the debinding contin-ued, the pores grew and were widely distributed in size. This pore structure evolvement was different from that of straight thermal debinding in which the pore size distribution was quite narrow and the mean pore diameter shifted toward smaller sizes as debinding time increased. After the soluble binders were extracted, parts were subjected to a subsequent thermal debinding during which these pores served as conduits for decomposed gas to escape. Concurrently, the remaining binder became fluidlike and was redistributed within the compact due to capillarity. This pore structure, as observed from the mercury intrusion curves, showed a sharp increase in the pore volume at the 0.8-µm size, followed by a series of fine pores, which is different from the pore structure of straight thermal debinding. The difference in the pore structure evolvement between solvent and thermal debinding and its effect on the debinding rate are discussed.

Controlled sintering for optimized debinding in powder injection moulding

A high temperature batch furnace has been constructed for real-time analysis of sample weight, compact temperature profile and evolved gas composition using various gas analysis methods. The furnace has digital mass flow controllers for atmosphere composition control. A separate precision dilatometer is used to provide dimensional change data. These analytical capabilities are controlled by a microprocessor coupled to a control computer which records the output from the various sensors. The long range goal is to develop an expert systems software to fully govern the thermal and atmosphere cycle in a closed-loop feedback mode. This will allow optimization of the sintering pathway for any material, processing objectives, and component geometry. In addition, the equipment will be used to investigate the debinding cycle of powder injection moulded (PIM) parts. By varying the heating rate, time at temperature, and atmosphere during the debinding cycle, the debinding mechanisms and rate controlling parameters can be identified. The goal of these experiments is to significantly lower the debinding time while maintaining compact integrity. A model for optimized processing is being developed in parallel with these experiments.