737 research outputs found
Analysis of rheological behaviour of titanium feedstocks formulated with a water-soluble binder system for powder injection moulding
Binder selection and formulation are critical in powder injection moulding. Binders play a key role in controlling the rheological properties of a feedstock and influence whether the resulting feedstock can be successfully injection moulded, debound and sintered without defects. A four-step process was used to mix hydride-dehydride titanium alloy (processed) powder (Ti-6Al-4 V) with a polyethylene glycol (PEG) based water soluble binder system. The rheological properties, including flow behaviour index, flow activation energy, fluidity and melt flow index of the homogeneous feedstock, were determined with a capillary rheometer. All feedstock formulations exhibited shear thinning flow behaviour. The optimum feedstock consisting of 60 vol.% powder content, 32 vol.% PEG, 6 vol.% polyvinyl butyryl and 2 vol.% stearic acid was suitable for titanium injection moulding
Development and design of binder systems for titanium metal injection molding: An overview
Titanium metal injection molding (Ti-MIM) has been practiced since the late 1980s. Logically, the Ti-MIM practice follows the similar processes developed for the antecedent materials such as stainless steel and ceramics. Although Ti-MIM is a favorite research topic today, the issue of convincing the designers to use Ti injection-molded parts still exists. This is mainly because of the concern about contamination which seems unavoidable during the Ti-MIM process. Much information about the binder formulation, powder requirements, debinding, and sintering is available in the literature. There are several powder vendors and feedstock suppliers. However, most of the binders in the feedstock are proprietarily protected. The disclosed information on the binders used for formulating powder feedstock is very limited, which in turn discourages their adoption by engineering designers. This overview intends to discuss some of major binder systems for Ti-MIM available in the literature. It serves to provide a guideline for the Ti-MIM practitioners to choose a suitable powder feedstock
Some aspects of the injection moulding of alumina and other engineering ceramics
The literature concerning the injection moulding of engineering
ceramics has been reviewed. This indicated that a number of
claims had been made for the successful use of different organic
binders during moulding and their removal prior to sintering.
However, many of the claims were not supported by detailed/exact
eScperimental evidence as to powder-binder compositions, moulding
conditions, moulded properties, debinding times/cycles, or
details of the structure and properties of the solid ceramic
bodies produced. From the available information it was clear
that there were few systematic and scientific investigations
concerning the understanding of each stage of the injection
moulding process.
The present research programme has been carried out in two
phases as follows. The first phase was concerned with the reinvestigation
and re-evaluation of binder systems claimed to be
successful for the injection moulding of alumina ceramics.
The binders re-investigated included the thermoplastic-based
binders such as polystyrene, polyacetal and atactic
polypropylene and the water-based methylcellulose (Rivers)
binder system. Alumina was chosen as the main powder to be
investigated due to its simple handling and, highest applications
amongst ceramic materials and on the basis that there is
incomplete published work for almost every step of the injection
moulding process. During the first stage of this work the
optimum properties such as powder-binder compositions, mixing
and moulding conditions, debinding properties, green and
sintered densities provided by each binder system were
determined. The results of these investigations showed that all
the previous (re-evaluated) binder systems had major limitations
and disadvantages. These included low volume loading (64 %
maximum) of the alumina powder resulting in rather low sintered
densities (96 % maximum-of theoretical density) and very long
debinding times in the case of the thermoplastic-based binders.
it ry low alumina volume loading (55 % maximum resulting in a 94
% . sintered theoretical density) and long moulding cycle time (-
5 min) along with adhesion and distortion problems during
demoulding occurred in the case of the water-based
methylcellulose binder system. Further work did not appear
worthwhile. The newly developed binder systems have been used with a number
of other powders such as zirconia, silicon nitride, silicon
carbide, tungsten carbide-6 weight % cobalt and iron-2 weight %
nickel, to establish- whether injection moulding is feasible.
Optimum properties such as powder volume loadings, mixing,
moulding, demoulding, moulded densities, debinding and some
sintered density results showed that these new binder systems
can also be used successfully for the injection moulding of
other ceramic and metallic powders, although a fuller evaluation
of the properties such as optimum sintered densities and
mechanical properties is required
New Partially Water-Soluble Feedstocks for Additive Manufacturing of Ti6Al4V Parts by Material Extrusion
In this work, a process chain for the realization of dense Ti6Al4V parts via different material
extrusion methods will be introduced applying eco-friendly partially water-soluble binder systems.
In continuation of earlier research, polyethylene glycol (PEG) as a low molecular weight binder
component was combined either with poly(vinylbutyral) (PVB) or with poly(methylmethacrylat)
(PMMA) as a high molecular weight polymer and investigated with respect to their usability in FFF
and FFD. The additional investigation of different surfactantsā impact on the rheological behaviour
applying shear and oscillation rheology allowed for a final solid Ti6Al4V content of 60 vol%, which is
sufficient to achieve after printing, debinding and thermal densification parts with densities better
than 99% of the theoretical value. The requirements for usage in medical applications according to
ASTM F2885-17 can be fulfilled depending on the processing conditions
Development of a Polyethylene Glycol/Polymethyl Methacrylate-Based Binder System for a Borosilicate Glass Filler Suitable for Injection Molding
Powder injection molding is an established, cost effective and often near-net-shape mass
production process for metal or ceramic parts with complex geometries. This paper deals with
the extension of the powder injection molding process chain towards the usage of a commercially
available borosilicate glass and the realization of glass compounds with huge densities. The whole
process chain consists of the individual steps of compounding, molding, debinding, and sintering.
The first part, namely, the search for a suitable feedstock composition with a very high solid load
and reliable molding properties, is mandatory for the successful manufacture of a dense glass part.
The most prominent feature is the binder composition and the related comprehensive rheological
characterization. In this work, a binder system consisting of polyethylene glycol and polymethylmethacrylate
with stearic acid as a surfactant was selected and its suitability for glass injection
molding was evaluated. The influence of all feedstock components on processing and of the process
steps on the final sintered part was investigated for sintered glass parts with densities around 99% of
the theoretical value
Printing of Zirconia Parts via Fused Filament Fabrication
In this work, a process chain for the fabrication of dense zirconia parts will be presented covering the individual steps feedstock compounding, 3D printing via Fused Filament Fabrication (FFF) and thermal postprocessing including debinding and sintering. A special focus was set on the comprehensive rheological characterization of the feedstock systems applying highāpressure capilālary and oscillation rheometry. The latter allowed the representation of the flow situation especially in the nozzle of the print head with the occurring lowāshear stress. Oscillation rheometry enabled the clarification of the surfactantās concentration, here stearic acid, or more general, the feedstocks composition influence on the resulting feedstock flow behavior. Finally, dense ceramic parts (best values around 99 % of theory) were realized with structural details smaller than 100 Ī¼m
New Feedstock System for Fused Filament Fabrication of Sintered Alumina Parts
Only a few 3D-printing techniques are able to process ceramic materials and exploit
successfully the capabilities of additive manufacturing of sintered ceramic parts. In this work, a new
two component binder system, consisting of polyethyleneglycol and polyvinylbutyral, as well stearic
acid as surfactant, was filled with submicron sized alumina up to 55 vol.% and used in fused filament
fabrication (FFF) for the first time. The whole process chain, as established in powder injection molding
of ceramic parts, starting with material selection, compounding, measurement of shear rate and
temperature dependent flow behavior, filament fabrication, as well as FFF printing. A combination of
solvent pre-debinding with thermal debinding and sintering at a reduced maximum temperature due
to the submicron sized alumina and the related enhanced sinter activity, enabled the realization of
alumina parts with complex shape and sinter densities around 98 % Th. Finally the overall shrinkage
of the printed parts were compared with similar ones obtained by micro ceramic injection molding
Fabrication and Characterization of Miniaturized Components Based on Extruded Ceramic-Filled Polymer Blends
The objective of this work is to develop an improved manufacturing process for microstructured ceramic components that is based on co-extrusion. Co-extrusion of structured feedrods holds promise for development of multi-layered, functionally graded and/or textured structures. However, it requires a polymer binder that is difficult to remove before structures can be sintered to full density. A two-step debinding is introduced to eliminate debinding defects that are commonly observed in thermal debinding (TD). Cracking is a major issue due to a lack of pore spaces for outgassing of pyrolysis products in traditional TD. In two-step debinding, a soluble binder is removed partially by solvent extraction (SE) which creates a porous network and allows gases to escape in subsequent TD of remaining binder components. The feasibility of solvent extraction (SE) is documented for the extrusion of solid ceramic rods and co-extrusion of tubes, where alumina powder was batched with polyethylene butyl acrylate (PEBA) as backbone polymer and polyethylene glycol (PEG) as water soluble binder. SE for specimens with varying PEBA:PEG ratios were tested in water at three different temperatures for various times. Experiments were also performed with different grades of PEBA and EVA to investigate the effect of thermoplastics on SE. The 1:1 mixture showed a PEG removal up to 80wt.% of the original PEG content after 6h extraction. After subsequent thermal debinding, rods and tubes were sintered successfully without defects, demonstrating the viability of the process. Scanning electron microscopy and optical analysis were performed to characterize the process. In order to illustrate potential applications, microfluidic devices were manufactured using extrusion followed by hot embossing. Ceramic microfabricated components have advantages over silicon, glass or polymer devices in terms of their ability to sustain high temperatures without compromising their functional capabilities. Flat tapes were extruded to create substrates, which were subsequently embossing micro patterns using a brass metal mold. To seal the microchanneled feature, a glass slide was attached to the chip by thermal bonding. Though a good bond was obtained, small portions were found where poor bonding was observed. To check leakage, colored water was forced to flow through the channel,and no leakage of water was found. A low temperature sintered ceramic material was fabricated as a potential alternative to the commercial low temperature co-fired ceramic (LTCC) tape. Overall, the study describes new possibilities for microstructure fabrication on ceramic based substrate and established the embossing process as a promising technique for fabrication
- ā¦