Setup and Maintenance of Manufacturing Quality in CO2 Laser Cutting

Manufacturing of parts by laser cutting is widely accepted in industry. In the market there are systems which are highly focused on special applications such as robot based 3D cutting in the automotive industry but also all-round machines which cut a diverse set of sheet steels at a variety of thicknesses. Most of these machines use a melt based cutting process where the molten material is ejected by an assist gas. Quality of the laser cut part is determined by a dross free cut with minimal roughness on the cut face. To ensure this quality, several parameters of the cutting process have to be within their defined tolerances. Such parameters are the focal position, the distance of the cutting nozzle to the work piece and the beam quality to name only the most important ones. The paper reports about the approach to equip industrial laser cutting systems with sensors such that manufacturing quality comes to an advanced level. Prior work has shown that such technical systems can be enabled to determine their focal position autonomously. As a next step, active control of the laser focal position has been demonstrated keeping the process at its nominal operating point in this respect. The benefits for manufacture are discussed in relation to machine setup and sustainability. The reported system relies on expert knowledge about the system behaviour in order to reference the measurement signal to the focal position. As this behaviour is closely connected to the current state of all optical elements in the system, an inference from the current control signal to the status of the optical train of the system becomes possible. (C) 2014 Elsevier B.V.