PIERCING PHASE SIMULATION OF FLOW DRILL SCREWDRIVING® (FDS®) FOR SHEET METAL JOINING

In this thesis research, the piercing phase of Flow Drill Screwdriving® (FDS®) for joining sheet metal is investigated. Starting from their main characteristics, as well as the process phases for their installation, the author describes the Screws in their main parameters, then focuses on the steps required to correctly install them. Lately, the process parameters are analyzed, mainly axial force applied, torque and rotational speed, followed by the main defects. Consequently, the common applications are described, including the tests needed for reliability assessment. In the next section, the main physics behind these screws is reported, including a state of the art based on available documentation on precedent research and experiments, as well as the experimental set-up adopted for joint mechanical characterization and data on the workpiece material, AW6082-T6. Next, the 2D geometrical Axisymmetric model is defined within MSC® Simufact® Forming 2020 for the DP600 and AW6082-T6 piercing phase. Due to the drilling procedure, a careful description of the heat generation and flow is included into the FE model. These allow for the Scaling Factors choice to consider the temperature effect on the material properties. Subsequently a Factorial analysis is developed to optimize all the most relevant factors both for the simulation and for the joint manufacturing process. In particular for what concerns the simulation factors, such as Coulomb friction coefficient, Interface shear factor and screw rotational speed, variations on workpiece material, thickness and width, as well as on lower sheet-screw contact condition and FDS® rotational speed, simulations are performed to observe the implied changes and, possibly, compare them with experimental evidence.