The paper deals with a real manufacturing system improving through simulation models creation. The aim of the paper is to present the possibilities of simulations models as a tool for optimization and quantification of proposals to improve production lines in engineering production. The research is carried out as a case study of a production plant in a Slovak machine-building company dealing with the components for the automotive sector production. The paper presents the creation of simulation models of the original line as well as the simulation model of improved line where robotic arms were used for material handling. Output statistics comparing the performance of the original line and its improved variant are part of the paper. We expect that in the coming years there will be an increased demand for creation of simulation models of manufacturing systems by modern enterprises that will try to implement the Industry 4.0 strategy and thus increase its competitiveness.