In the "Squish" project, the Fraunhofer IPT, together with industrial partners, developed two new tool concepts as an alternative to conventional post-processing of milled component surfaces. On the one hand, a diamond spinning tool and on the other hand a carbide ball head tool with a strongly rounded cutting edge were developed and tested. The aim of both tool concepts is to reduce the surface roughness after milling by an additional machining step in such a way that the duration of the subsequent polishing process is significantly reduced. In addition, residual compressive stresses are introduced into the surface edge zone of the component by the spinning process, thus increasing the wear resistance of the tool form in use.
The contact of the tools with the component surface levels out the roughness peaks that occur during milling. With the diamond spinning tool, a diamond ball presses on the surface of the component. Similar tool systems are already in use for rotationally symmetrical machining. With the carbide ball nose tool, the large rounding of the cutting edge acts like a spinning bar. Due to the large cutting edge radius, the contact between tool and workpiece does not produce any chip removal. Instead, the rounded cutting edge presses on the workpiece surface and levels the roughness peaks.
Both tool concepts can be used automatically on conventional 3- or 5-axis machining centers without additional machine units. The tool paths correspond as far as possible to those of milling. Therefore, no separate programming is required and only minor additional work is required for work preparation.
Investigations at the Fraunhofer IPT showed that the surface roughness can be reduced by more than 50 percent with the two tools, both in the feed direction and transverse to the feed direction, compared to milling. The task of the Fraunhofer IPT was now to identify the optimal process parameters for the application of the innovative tool concepts. Besides the geometric process parameters, the focus was on possible feed and cutting speeds. Thus, it was necessary to determine maximum path distances in order to both reduce the machining time for upstream milling and to shorten the duration of surface finishing. Based on the investigations, the Fraunhofer IPT was able to provide end users in the research project with an optimal process parameter window for the respective tool concept.
Finally, various coatings were tested in order to achieve possible increases in tool life.
The two new tool concepts significantly reduce the polishing effort that was previously required. Future process chains in tool and mould making will be able to use one of the two new tool concepts after finishing milling on the same machining centre. To do this, only the path distance and the axial infeed must be adapted in the existing CAM path planning. The additional effort involved is very low - especially compared to the savings that result from shorter polishing and set-up times and lower upfront investment costs.
The research project is funded by the Federal Ministry of Education and Research (BMBF).
Projektträger Karlsruhe (PTKA)