In the present degree paper a process where we optimized fitting rubber and plastic intermediate product is presented. In the theorethical part of the degree, a Poka-Yoke method is presented, which we also use later in the task. The experimental part shows a complete proccess of optimization. We present the procedure and analysis of a current state, in which the duration of mounting of rubber and plastic parts according to duration of the whole project is too long. The solution for reducing the mounting duration is in developement of a new mounting device. The limits and ideas for designing the device, the procedure of building a new machine including the calculated costs, constructing procedures and elimination of the errors are shown. The optimization of the procces is succesfully carried out with the half-automatic mounting device, which works in the wake of Poka-Yoke method. With it, we save more than 4.500 hours in the process of the project.