PhD Defence at DTU Mechanical Engineering

PhD Defence 16th August: Numerical Modelling of flow and compression of green sand

Tuesday 11 Jul 17


Emil Hovad
Data Scientist
DTU Compute

Emil Hovad from DTU Mechanical Engineering defends his PhD, "Numerical Modelling of flow and compression of green sand", Wednesday 16th August from 13:00 - 15:30. The defence takes place in Building 101, room S09, DTU Lyngby.

The focus of the industrial PhD project was on the production of the sand mold (green sand) which gives the cast component its final geometrical shape. In order to ensure a high quality of the cast component, it is important to control the manufacturing process of the mold itself so that it is homogeneous and stable. Therefore gaining a basic understanding of how the flow and deposition of green sand should be characterized and modelled was important, so that it could be used for simulation of the manufacturing process of the sand mold.

The green sand was characterized with a ring shear tester where a new way to define the flowability was suggested. A sand pile experiment was used to characterize the simple mechanical behaviour of green sand from the measured height. The Discrete Element Method (DEM) was chosen as the numerical model since the discrete nature of the method simulates the granular structure of the green sand with good agreement. The DEM model uses a rolling resistance model to emulate the non-spherical quartz sand particles' resistance to rolling and as well as a cohesive model to emulate the binding of the quartz sand particles from the bentonite.The ring shear tester was used to obtain the static friction coefficients for the DEM model. From the height of the sand pile the DEM model was also calibrated with respect to obtaining the values of the rolling resistance and obtaining the parameter in cohesive model.

The project dealt with the flow of the sand particles and the deposition of sand during the production of sand molds using the sand shot in the DISAMATIC process. The deposition of the green sand in the chamber was investigated with a special cavity design where air vents were placed inside the cavities. The air vents are used to transport the green sand with an airflow during the sand shot. By changing the air vents settings in the chamber and in the cavities it was possible to improve the filling in the narrow passages in the cavity design, thereby improving the final sand mold as well. The sand shot with the cavity design was simulated by the discrete element method (DEM) modelling the flow of the green sand combined with classical computational fluid dynamics (CFD) for modelling the airflow in the chamber and the airflow through the air vents. These experiments and simulations gave beneficial insights to the DISAMATIC process and how to improve it.

Hence, knowledge was acquired about the filling of the mold chamber with green sand in a special designed cavity geometry. The settings of the air vents together with the air pressure initially applied in the air tank gave valuable ideas for improving the filling in the cavities thereby improving the final mold. Furthermore, it was possible to apply the commercial software of STAR-CCM+ using the combined CFD-DEM model to simulate the process with a 3-D slice representation of the geometry successfully. This makes it more feasible to develop a stand-alone code in the future for simulating the DISAMATIC process.

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