The joining of continuous fibre-reinforced thermoplastic composites (TPC) by means of plastic deformation often results in a complex material structure in the forming zone. Especially process- and material-related parameters have high influence on the local deformation behaviour and therefore on the properties of the joint. In this paper, the focus is on mechanical joining processes based on the principle of moulding holes by a tapered pin. For the investigations, a simplified test is used in which the pin is pushed through a heated TPC plate in the thickness direction. By the pin movement the fibres and molten matrix are displaced radially and along the tool motion direction. Detailed investigations of the resultant material structure by computed tomography and numerical simulations are performed with varying pin tool geometries with bidirectional TPC material. For numerical analysis, the Arbitrary-Lagrangian-Eulerian method combined with a multi-filament approach is used. The result show that the tool geometry has a strong influence on the piercing force, the resultant material structure, and the occurring phenomena. It could be shown, that the simulation is capable to predict the resultant material structure.