The motivation for the presented approach results from the absence of an integrated method of supporting the designing of injection molded parts. Thereby, the focus lies on the rheological optimization, which is ensured by knowledge transfer from the production engineer to the designer. I. e. the mentioned aim is achieved by creating a knowledge base including the expert knowledge. This method is based on an integrated product simulation containing the interconnection of CAD and CAE-systems. The first step in the process is a filling simulation done by a standard injection molding process simulation software. The gate location is considered as fixed and optimal. Nevertheless, it is still possible that a uniform mold filling is not reached. To determine an uneven mold filling the results of the simulation are exported as scalar values to a post processing software tool. Thus, a knowledge based analysis of the results using user defined parameters based on flow length, pressure distribution, etc. is enabled. To enhance the filling the original part design is modified by adding flow aids or barriers. Their positioning is calculated by the post processing software tool and this result is returned to the CAD-system. There the preliminary design is done by an analytical approach. By iterations of the mentioned method the geometry of the flow aids or barriers and thus the mold filling are improved. The presented approach is illustrated exemplarily by an injection molded part. As a result the designer is supported methodically in designing injection molded parts by implementing and using expert knowledge. So the number of iterations and the development time (costs) are reduced.