Particle-based Process Modeling
Fraunhofer Institute for Mechanics of Materials IWM
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Process Optimization through Particle Simulation
- Fluidization of cohesive powder; predictions of density distribution during die filling and compaction; description of anisotropy properties during tape casting; prediction of deposit patterns during drying processes; prevention of crack formation during sintering
- Targeted abrasive surface processing and edge rounding
- Avoidance of erosive abrasion
- Efficiency improvements and minimization of kerf loss during wire sawing
- Reduction of track widths during print processes
- Maximization of torque transmission in magnetorheological clutches
- Optimization of the cleaning capacity of toothpaste
- Development of application specific material models and force laws
Measuring the morphology of granules when spray drying powders
In the ceramics industry spray drying is an important process for converting fine primary powders into bigger granules with better transport properties. To achieve a high quality end product requires good attributes, specifically in reference to the handling and compaction of the granulate. For this reason, the granules should preferably be spherical and possess a homogeneous density. At the Fraunhofer IWM, material models are linked using the discrete element method (DEM) and numerical flow simulations to investigate granule formation. This enables us to simulate the evolution of granular materials through drying individual droplets. As a result, the correlation between parameters such as the droplet’s surface tension or the surface energy of the primary powders and the shape of the resulting granules are available for process optimization.
Maximizing torque transmission in magnetorheological clutches
Magnetorheological fluids (MRF) consist of magnetizable solid particles in carrier fluid. When applying an external magnetic field the particles become magnetized and form chains along the field lines. As a result, the MRF changes within milliseconds from a liquid to a solid state. This is very useful for targeted industrial applications, for example, clutches, shock absorbers and brakes. At the Fraunhofer IWM, MRF are modeled under real-life operating conditions at the particle level. In this way, a detailed and in-depth understanding of the MRF mechanisms at work is achieved, which allows the properties of the particles to be specifically optimized, in essence tailoring them to the desired application.
- Lagger, H.; Breinlinger, T.; Di Renzo, A.; Di Maio, F. P.; Korvink, J.; Moseler, M.; Bierwisch, C.; Influence of hydrodynamic drag model on shear stress in the simulation of magnetorheological fluids; Journal of Non-Newtonian Fluid Mechanics 218 (2015) 16-26
Minimizing kerf loss during wire sawing of silicon wafers
Industrially, multi-wire saws are used for the separation of silicon ingots. A steel wire is drawn over pulleys whose indentations guarantee a constant spacing of the wires. The sawing process is achieved by pressing the silicon ingot against the wire mesh, which is moistened with abrasive slurry. The slurry typically consists of polyethylene glycol and angular SiC grains. The challenge is to simultaneously minimize silicon kerf loss while maximizing sawing efficiency. At the Fraunhofer IWM, particle based simulations have been implemented for the sawing process which is difficult to access experimentally; these provide insights into interactions within the carrier fluid, abrasive grains and silicon surfaces and show optimization options for both sawing waste and sawing efficiency.
- Bierwisch, C.; Kübler, R.; Kleer, G.; Moseler, M.; Modelling of contact regimes in wire sawing with dissipative particle dynamics, Philosophical Transactions of the Royal Society A 369/1945 (2011) 2422-2430 Full Text
Reducing structural widths for screen printing of ceramic multi-layer circuits
Ceramic multi-layer circuit carriers are found in microwave circuits, pacemakers, sensors and WLAN units, as well as in several other industrial applications. The fine conductive tracks are applied to the circuit boards via screen printing. A metal paste containing fine aluminum or silver particles is printed through a template corresponding to the desired form on the surface and afterwards sintered together with the ceramic foil using relatively low temperatures. At the Fraunhofer IWM, simulation models have been developed and are in use that provide full descriptions of the paste’s flow behavior during the screen printing process. Detailed studies show that hydrophobic coatings on the underside of the screen greatly improve paste detachment while a separate coating of the top side of the screen is not required. This facilitates the development of appropriately coated screens and adapted, matching pastes by the industrial partner, leading to a reduction of structure widths from approx. 80 µm to 20 µm.
- Schwanke, D.; Pohlner, J.; Wonisch, A.; Kraft, T.; Geng, J.; Enhancement of fine line print resolution due to coating of screen fabrics, Journal of Microelectronics and Electronic Packaging 6(1) (2009) 13-19 Full Text