The market demands a wide range of products with competitive prices which means cost reduction in every part of the production system. An analysis of the total costs by many companies found that an increasing proportion of assembly costs can be reduced using many modern strategies. With the use of Group Technology, products are divided into logical groups that can simultaneously travel through the assembly line. Part families can be created in several ways, but it's important to create those which bring the greatest cost reduction whilst keeping high productivity. In this case, part families based on the similarity of the used parts were created. Simulation software allowed for an iterative process of the assembly system designing which changed many characteristics from preliminary to the final model, such as the number of assembly stations, number of workers, and working shifts. The final assembly system has a high degree of efficiency with good blocking resistance and is in constant operation. Such an iterative approach successfully synchronized operation of all subsystems and the entire system achieves the set goals in form of productivity, efficiency, and annual product rates.