Automated finishing of free-formed steel moulds

Polishing is applied to manufacture steel surfaces with a low roughness and glossy shine up to a highly reflective mirror finish. As moulds and dies are mostly freeformed, no automated process is capable of polishing the surfaces so that the process is realised manually. Investigations are made to develop a robot polishing system and to elaborate robust process strategies. In this paper, the progress is shown by means of a mirror finish on a free-formed steel surface realised by automated polishing. The investigations of machining parameters (e.g. pressure, revolutions, feed rate) as well as path related parameters (e.g. trochoid radii, offsets) lead to an optimal process strategy. The free-form out of X38CrMoV5-l ESR was finished using six steps as illustrated in figure 2. Roughness values of Ra = 0.5 micrometer and Rt = 12 micrometer are common after fine milling. Grinding realises Ra = 0.3 micrometer and Rt = 4 micrometer. After lapping the matte surface exhibits Ra = 0.15 micrometer and Rt = 2 micrometer. The final surface quality is based on Ra = 5 nm and Rt = 55 nm revealing a defect-free mirror finish. Next steps will be the development of new strategies to finish other tool steels and the extension of available tools and paths to process more complex free-forms.