Pressing and sintering processes

Numerical simulation of the pressing and sintering processes

When using powder technology for the forming and shaping of components, die compaction has been established for many materials (ceramics, hard metals, sintered steel, magnetic materials, pharmaceutical powders). Complex components place high demands on the pressing technology: typical problems are the warpage caused by the green density gradients as well as cracks caused when extracting the component from the die or by temperature gradients during the sintering process. The simulation methods developed by the scientists at the Fraunhofer IWM allow for quantitative predictions of the green density distributions as well as the resulting sintering distortion. This supports the optimization of tool shapes and pressing schedules in the preliminary stages of the tool manufacturing process and recommendations to be made for improvements in the finished parts.

• Kraft, T.; Optimizing Press Tool Shapes by Numerical Simulation of Compaction and Sintering – Application to a Hard Metal Cutting Insert, Modelling and simulation in materials science engineering 11/3 (2003) 381-400 Link
• Kraft, T.; Riedel, H.; Rosenfelder, O.; Compaction and Sintering of a Ceramic Seal: Modeling and Experimental Response, Int. J. Powder Metall 39/6 (2003) 27-34 Link
• Kraft, T.; Riedel, H.; Numerical Simulation of Die Compaction and Sintering, Powder Metallurgy 45/3 (2002) 227-232 Link
• Kraft, T.; Riedel, H.; Stingl, P.; Wittig, F.; Finite Element Simulation of Die Pressing and Sintering, Adv. Eng. Mater. 1 (1999) 107-109 Link

Pressing

Many industrial applications aspire to a homogenous density distribution in pressed green products. Scientists at the Fraunhofer IWM have developed a continuum mechanics material model which has been implemented in the finite element (FE) program ABAQUS®, that aids in anticipating the varying density distributions during the pressing stage as well as making complex 3D component predictions. Additionally, the model supports simulations of powder layers in order to conduct detailed analysis of individual mechanisms such as anisotropic yield points or crack formation and use this information to continuously improve the continuum mechanics characterization.

• Schmidt, I.; Trondl, A.; Kraft, T., Yielding and failure of an assembly of frictional elasto-plastic particles: A computational RVE study, Journal of the Mechanics and Physics of Solids 154 (2021) Art. 104496, 15 Seiten Link
• Schmidt, I.; Trondl, A.; Kraft, T.; Wonisch, A.; Simulation of the Material Behaviour of Metal Powders during Compaction, J. Process Mech. Eng. 224 (2010) 187-194 Link
• Coube, O.; Riedel, H.; Numerical Simulation of Metal Powder Die Compaction with Special Consideration of Cracking, Powder Metallurgy 43/2 (2000) 123-131Link

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Calculations of drying and sintering distortion in large scale ceramic components

In order to produce large-scale ceramic components by means of slurry or pressure die casting, for example commodity or sanitary ceramics, the effects of gravity often cause undesirable deformations to occur during the drying process. Drying tension poses an additional problem, which can lead to crack formation in critical areas. During the subsequent sintering process further distortions are often inevitable, the source of which may stem from additional factors beyond pure gravity, such as friction with the support structures. Drying and sintering models developed at the Fraunhofer IWM enable calculations of this warping in advance of the construction of the casting mold and allow for appropriate adjustments to be recognized and implemented.

• Kraft, T.; Riedel, H.; Numerical Simulation of Solid State Sintering – Model and Application, Journal of the European Ceramic Society 24/2 (2004) 345-361 Link

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Simulation of sintering under heavy external loading

During hot isostatic pressing or sinter forming processes, the ceramic or metallic green bodies become additionally compressed because of external pressure. A special simulation model developed at the Fraunhofer IWM can calculate this process in detail, for example predicting capsule deformations when hot isostatic pressing. This allows unwanted warpage in the capsule design to be compensated for in advance.

• Reiterer, M.; Kraft, T.; Riedel, H.; Application of a microstructure-based model for sintering and creep; Ceramic Transactions 157, Characterization and Modeling to Control Sintered Ceramic Microstructures and Properties: Proceedings of the 106th Annual Meeting of The American Ceramic Society; DiAntonio (Ed.);  John Wiley & Sons, Inc., (2006) 49-58 Link
• Reiterer, M.; Kraft, T.; Riedel, H.; Manufacturing of a Gear Wheel Made from Reaction Bonded Alumina - Numerical Simulation of the Sinterforming Process, Journal of the European Ceramic Society 24 (2004) 239-246 Link

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