Extrusion process has been used for many decades as a transformation and shaping processes using in the plastic processing industries. In this study dies deformation was investigated in the plastic extrusion process by numerical modelling and compared with the experimental results. The dies with various thickness was fabricated with additive manufacturing (AM) stereolithography (SLA) method. Monitoring the performance of the insert in physical experiment is difficult or impossible, therefore COMSOL Multiphysics is applied as a supplementary method for the experiments. Hence in this work a Fluid-Structure Interaction (FSI) numerical model based on the finite element method has been developed. The FSI model solves full Navier-Stokes (N-S) equation for the insert flow, while its output serves as an applied distributed load, e.g. as a boundary condition, for the structural analysis of the extruder. Eventually, this model can enable one to identify the potential areas in the extrusion die where fractures might occur.