B. Levenfeld

Development of new feedstock formulation based on high density polyethylene for MIM of M2 high speed steels

Abstract A new feedstock formulation for metal injection moulding (MIM) of M2 high speed steels has been developed. The binder is a multicomponent system based on high density polyethylene (HDPE) and paraffin wax (PW). The compatibility between binder constituents has been studied by dynamomechanical thermal analysis (DMTA) showing a partial miscibility between both components. Viscosity measurements of the different binder mixtures at different shear rates showed that the optimum formulation for MIM was 50 vol.-% HDPE. With this optimised binder, several mixtures were prepared with different powder loadings of M2 grade high speed steel. Torque measurements of the mixtures indicated that the maximum amount of metal to be used was 70 vol.-%. The wide distribution of the metal powder was homogeneously distributed into the polymer matrix. The polymeric part was driven off by thermal debinding using a thermal cycle designed on the basis of a thermogravimetric study of the binder. Finally the vacuum sintering of the parts allow high quality parts to be obtained.

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.

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

Abstract 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 6 C carbide that appears during all the temperature range studied, M 23 C 6 , M 2 C and M 4 C 3 carbides sequentially appear with the sintering temperature.

Influence of Binders on the Structure and Properties of High Speed-Steel HS6-5-2 Type Fabricated Using Pressureless Forming and PIM Methods

Based on the comparison of structures and properties of the HS6-5-2 high speed steels made with the powder injection moulding method, pressureless forming, compacting and sintering, and commercial steels made with the ASEA-STORA method, fine carbides spread evenly in the steel matrix were found in the structure of all tested high-speed steels in the sintered state. The use of a nitrogen atmosphere in the sintering process, causes the formation of fine, spherical MX type carbonitrides, stable in high sintering and austenitizing temperatures. The steels made with the pressureless forming method are characteristic of the lowest sintering temperature and the highest density, resulting from the high carbon concentration coming from the binding agent degradation. Moreover, the higher carbon concentration causes an increase in the retained austenite portion and a lower hardness after quenching and tempering. The heat-treated injection moulded steel attains hardness comparable to the commercial ASP23 type one, demonstrating the well-founded reasons for using the powder-injection moulding method for manufacturing the high-speed steel. The powder-injection moulding makes manufacturing tools possible with their final shape, i.e., leaving out the plastic forming and machining which is necessary for instance in case of the ASP 23 type steel. Furthermore, the degradation and sintering process time of the injection moulded steels is approximately 10h shorter than for steels made with pressureless moulding, which is due to the use of a two-component binding agent.

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.

Metal injection moulding of bronze using thermoplastic binder based on HDPE

Abstract In the present work, the injection moulding process of a Cu–10Sn bronze has been studied. Different formulations of binders based on high density polyethylene, paraffin wax and polyethylene glycol have been used. The optimisation of the metallic load is based on torque measurements and rheological studies. The optimum powder loading was 60 vol.-%. The moulding parameters are selected to obtain homogeneous specimens with three different geometries and without distortions. The green parts have an adequate strength for handling. The organic binder was eliminated by thermal debinding under N2/10%H2 atmosphere. The debinding process has been designed by means of thermogravimetrical analysis of binder and feedstock and considering the maximum heating rates at which the samples do not present cracks. The specimens were sintered at temperatures between 875 and 950°C in the same reducing atmosphere.

Effect of residual carbon on the microstructure evolution during the sintering of M2 HSS parts shaping by metal injection moulding process

In this present investigation, Metal Injection Moulding (MIM) of M2 High Speed Steel (HSS) parts using a wax-High Density Polyethylene (HDPE) binder is shown. This work is focused on the examination of the sintering densification and microstructure evolution of the parts. The injection molding process of the feedstock has been optimized to obtain high quality green parts. The elimination of organic binder was carried out by thermal debinding under inert atmosphere. In order to keep carbon in the sample that could improve the sintering process, incomplete debinding was performed between 450 and 600 °C. The specimens were sintered at temperatures between 1210 and 1280oC in high vacuum atmosphere, obtaining the 98% of the theoretical density. A homogeneous distribution of fine M6C carbides was obtained as well as V-rich carbides (MX) during sintering which reinforced the HSS and hence increasing the mechanical properties of the parts. In the samples with higher residual carbon content, the sintering window was extended up to 20 degrees and the optimum temperature was lower.

Coarse and cheap may beat fine and expensive

One of the basic realities of powder metallurgy is that you pay more for finer powders than for coarser grades. Spanish researchers looking for ways to strike at the comparatively high cost of gas-atomised MIM powders experimented with mixtures of gas- and water-atomised bronze powders…