Dissertation project is focused on optimization of assembly subsystems, intended for fixing welding assemblies in prototype devices of ultrasonic welding machines as well as their use for automated ultrasonic cutters. There is a description of optimized devices stated in the project. Subsequently, a project is focused on the detailed analysis of the original assembling subsystems of welding assemblies. Based on analysis of the project there will be proposed a new optimized fixing of welding assemblies, suitable for incorporation into automated ultrasonic welding machines and cutters. The next step is a technical and economic comparison of original and optimized assembly knots. The end of the project is focused on database creation of design solutions of the proposed assembly knots.