Wednesday morning, 13 October

Chairmen:
Dr Animesh Bose,Trigon Advanced Materials
Professor José Torralba, University Carlos III Madrid

Oral

Rheological Behaviour of Powder Injection Moulding (PIM) Feedstocks Fabricated with a Thermoplastic Binder System Based on Polysaccharides
Torralba Castello, J M (Universidad Carlos III de Madrid, Madrid, Spain)

The present work is focused on the study of the rheological behaviour of novel feedstocks for powder injection moulding (PIM) based on polysaccharides derivative thermoplastic polymers. The introduction of this type of binder systems on industrial processes represents a natural alternative to conventional petroleum derivative polymers offering advantages as a fast and efficient elimination through catalytic debinding with different types of acid substances. Cellulose acetate butyrate (CAB) was used in combination with a low molecular weight polyethylene glycol (PEG) and glycerine to prepare binders with suitable properties to develop PIM feedstocks. The viscosity of powder-binder mixtures fabricated varying the solids loading were studied through torque and capillary rheometry and different rheological parameters such as flow index, yield stress and activation energy were calculated. These binders have shown a good rheological behaviour in the range of common process temperatures when applied to 316L stainless steel and T15 tool steel gas atomized powders.

Wall Slip Velocity as a Quantitative measure of Powder-Binder Separation During Powder Injection Moulding
Hausnerova, B (Tomas Bata University in Zlin, Zlin, Czech Republic)

A lot of effort has been paid to describe the onset of the powder-binder separation during the flow through the mould channels in the quantitative way. When a separation appears flow changes from a Poiseuille into a plug due to the fact that feedstock slips at the separated thin binder layer at the channel wall. The proper evaluation of the slip velocity can thus serve as a quantitative parameter directly connected to the separation phenomenon. In this paper the slip velocity will be evaluated not only as a function of processing parameters as temperature, pressure, and shear rate, but also as a function of the microscopic nature of the channel wall. For this purpose especially designed roughened rheometer with plates machined from the most often used mould-construction steel with different surface modifications (nitride, titanic nitride) and surface roughness (0.025 – 1.6) will be utilized to study breakdown of the feedstocks-mould interface.

Rheological Characterization of Powder and Micro-Powder Injection Moulding Feedstocks
Moinard-Checot, D (ECAM - Material Science Dept, Lyon, France)

Powder and Micro-Powder Injection Moulding, processes combining plastic injection and powder metallurgy, are widely used to manufacture small complex parts and parts presenting micrometer range details. These processes are based on injection moulding. Feedstock viscosities are crucial parameter to control the injection step having strong impact on the subsequent process steps, i.e. on final parts. Hence, feedstock rheological characteristics are very important, especially for complex parts having small structural details. Nevertheless, besides numerous studies on feedstocks, only a few works have addressed their rheological behaviour at shear rate close to those encountered in the injection moulding process.

In this contribution, we study commercial and 'self-made' feedstocks from rheological point of view. We focused on the influence of feedstocks components on rheological behaviour using wide shear rate range. The influences of binder composition and powder size, shape and nature on rheological characteristics are highlighted.

Development of Molybdenum Powder Injection Moulding Feedstock
Song, J (Xiamen Honglu Tungsten & Molybdenum Ind Co Ltd, Xiamen, China)

To fabricate the molybdenum powder injection molded products for high temperature applications, the as-received molybdenum powders have been treated by rod milling and jet milling respectively for the purpose of deagglomeration. The obtained powders from jet milling have better flow ability and particle shape suitable for injection molding, which is equivalent to the commercially available ready to mix molybdenum powders special for injection molding. Using the optimized wax-polymer binder, a feedstock with solid loading higher than 55 vol. % has been developed. The rheology properties for injection molding, debinding and sintering behaviors of this feedstock have been investigated. The application of this feedstock for producing a microwave part shows good dimensional accuracy and stability, mechanical properties and microstructures.

Poster

Comparative Study Using Different Suppliers With Water Debinding
Auzene, D (CRITT MDTS, Charleville Mezieres, France)

Within the framework of the European INTERREG IV network PRISTIMAT between the north of France and the Wallonie, the Collective Centre of the Belgian Technology Industry well known as SIRRIS and the French Regional Centre of Innovation and Technology Transfer specialized in Materials - Coatings and Surface Treatment named CRITT-MDTS are working together in order to develop the MIM technology.

Thanks to the writing of a roadmap about this industrial process, two main topics are emerging: bi-material injection and environment friendly debinding. This second subject will be develop and is aimed at comparing different feedstock’s suppliers. We would like to study the influence of following parameters: temperature, ultrasound’s using, pressure, partial pressure, vapour or liquid water, water cycling, etc. … in order to give an industrial point of view about productivity, return and environmental impact.

Rheological and Thermal Behaviour of Powder Injection Moulding (PIM) Fedstocks Fabricated with Binder Systems Based on Waxes
Torralba Castello, J M (Universidad Carlos III de Madrid, Madrid, Spain)

This work is focused on the study of the rheological and thermal behaviour of feedstocks based on waxes for their application in powder injection moulding (PIM). Wax materials present thermoplastic behaviour and good rheological properties, reason why they are frequently used in the formulation of binder systems for PIM. Besides that, waxes can be easily removed by solvent debinding or thermal evaporation at low temperatures leading to lower carbon and oxygen contents in comparison with others thermoplastic binders. In this study, the rheological and thermal behaviour of low alloy steel 4140 powder-binder mixtures fabricated with different types of waxes were studied through capillary rheometry and thermal techniques as thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). These binder systems have shown very low viscosities along low impurities contents after thermal debinding which make them appropriate for the fabrication of reactive mate rials such as titanium.

Defects in PIM Components and Their Relevance to Binder Redistribution during Thermal Debinding
Fan, Y-L (National Taiwan University, Taiepei, Taiwan)

Our previous study of solvent debinding showed that when 62% of the soluble binder is removed from powder injection molded compacts, interconnected pores can be established at the center of the specimen. It was thought that these interconnected pore channels allowed the decomposed gas to escape to the ambient during the subsequent thermal debinding. However, it was observed that these interconnected pores closed again during the early stage of thermal debinding and that binder-rich areas were formed. As a result, blistering and cracking occurred when a heating rate of 5Ž/min was employed. This study re-establishes the required minimum level of soluble binder removal, above which defect-free components can be produced after thermal debinding and sintering. The binder distribution phenomenon and its relevance to the binder amount and defect formation are discussed.

Metal Injection Moulding of Iron Based Syntactic Foams
Salk, N (Fraunhofer Institut - IFAM, Bremen, Germany)

Metal foams based on aluminium have already been implemented in industry as light weight construction or crash absorbing components. However, their compression strength of 5-30 MPa is not sufficient for a lot of applications. Therefore, new approaches are needed to obtain syntactic foams based on iron or steel materials. In this paper the development of new iron based syntactic foams by applying the metal injection moulding technology is presented. In this process Fe powder is mixed with microscopic glass hollow spheres. The mixture is then homogenised with a special binder system. The resulting feedstock is injection moulded on conventional moulding machines. The binder is removed in the Fe foam is sintered at 900°C.

With this technology tensile test specimens were manufactured in series for foams containing up to 13 wt% hollow spheres in the iron matrix. Material properties of the respective materials were measured and as a result compression strengths of up to 300 MPa were obtained.

Mould Filling Behaviour Of Alumina Feedstock For Micropowder Injection Moulding
Thomas, P (Universidad Carlos III de Madrid, Madrid, Spain)

One of the main challenges in micropowder injection moulding is the dimensional accuracy since parts can have structural details of less than 100 µm. In this experimental work alumina feedstock was used to produce dental brackets by micropowder injection moulding. Process stages including mixing, injection moulding, debinding and sintering were optimized. Final parts reached high densities and exhibited good surface finish and shape retention. However a slight dimensional scatter was detected on the retention zone of the bracket. Mould flow simulation was performed to establish a possible correlation between the mould filling behaviour and this dimensional scatter of the sintered part. It was seen that rib and channels tend to fill towards the end of the moulding stage when the feedstock is at the lowest temperature and is subjected to the highest shear being a possible cause for good shape retention in the moulding stage but dimensional scatter in the sintered stage.

Related features for download:

• Powders, binders and feedstocks for powder injection moulding
• Feedstock for Powder Injection Moulding: production and commercial suppliers
• Quantitative study of powder binder separation of feedstocks
• Mixing simulation for powder injection moulding feedstock: Quantification by the mixing entropy
• Characterisation of alumina feedstock with polyacetal and wax-polymer binder systems for micro powder injection moulding
• Study of the rheological properties of a new bronze 90/10 feedstock based on irregular powder particles for application in powder injection moulding (PIM)
• Moulding properties and causes of deterioration of recycled Metal Injection Moulding feedstock
• BASF, a leader in the supply of ready-to-mould feedstock for metal and ceramic injection moulded components
• Preventative quality assurance for PIM producers: A new batch-to-batch feedstock testing method