Additive manufacturing regarding 3D-Printing of metallic material can be considered a primary shaping process. In contradiction to other primary shaping processes like casting, additive manufacturing does not require molding tools. This makes the process very interesting for economic lot size 1 production. Furthermore, additive manufacturing has additional advantages with respect to subtractive manufacturing like milling. Therefore, it is considered for industrial part production already with high potential of further growth.
Hybrid manufacturing in the context of metallic 3D-printing means the integrative combination of additive and subtractive manufacturing processes, both with respect to information technology and manufacturing systems. The technical approach shall complement the advantages of both processes and at the same time compensate for particular disadvantages on both sides.
Typical representatives of additive manufacturing processes are powder bed processes like Selective Laser Melting (SLM) or build-up welding based processes like Direct Energy Deposition (DED). In powder bed based processes, thin layers of evenly distributed metallic powder are applied and melted with a mirror controlled laser beam at each position of the layer where material has to be added. With the DED process, the material feed can take the form of metal powder or wire. A multi-axes driven application head that brings the material to the application area where it will be melted with a heat source. This could be performed either by laser beam or by an electric arc.
Additive manufacturing as foundation for hybrid solutions
Advantage of those additive manufacturing processes is a considerably extended freedom of geometrical shaping. This would allow for part shaping to better comply with the functional part requirements. One example is multi-functional integration which reduces the number of parts in an assembly. Especially in the field of aerospace, additive manufacturing processes allow the realization of light weight concepts that follow bionic principals.
Although the mentioned processes are capable of performing near-net-shape part geometry, it is not possible to meet quality and accuracy requirements for functional surfaces or fittings. Hence, a subsequent processing with more precise subtractive processes like milling is necessary. Furthermore, additive manufacturing could require additional support structures in order to secure areas with overhang, to transfer heat or to avoid heat indicated distortions. Those support structures have to be removed after the 3D-printing process by means of another cutting procedure.
Higher requirements towards process planning
Meanwhile, hybrid manufacturing systems exist already. They are capable of combining additive and subtractive processes in one setup without additional part handling which reduces material usage and processing time.
Planning of those hybrid manufacturing processes leads to extended requirements for process planning and NC-programming. For optimization of path planning for a DED process, it has to be taken into account that collision critical interference contours only appear during the additive process. This has to be considered for subsequent moves of the application head.
Unfortunately, it is not sufficient for NC-programming of DED processes to invert corresponding milling tool paths. Usually, it is not relevant for the milling process whether the cutter passes an area multiple times. In additive processes, however, this would lead to scrapping of the surface.
Data quality is key
Beside this, further requirements exists with respect to data integration along the value chain of hybrid manufacturing. In the area of data preparation for additive manufacturing, the STL-format is still widely used, although it produces discontinuities in the information chain. This is due to the fact that a lot of information that is generated through the design process and represented in a 3D-CAD model gets lost. One reason is the approximated geometry representation of triangular facets which leads to reduction of geometrical accuracy and, thus, does not qualify for the generation of accurate cutting tool paths, e.g. for removal of support structures. Due to extended capabilities of the modern additive manufacturing process, the disadvantages of the STL format become more and more apparent since the increase of geometrical accuracy on a facet model leads to unproportioned increase of data amount without substantial increase of information content. Hence, an optimized data integration approach has to make use of the exact geometry data representation of a 3D-Cad model directly.
Today’s 3D-CAD Systems are not only able to represent geometries with high accuracy, they would also allow the representation of manufacturing relevant topology features like holes, ribs, pockets, etc., as well as the representation of manufacturing relevant technology information like tolerances and surface quality. An integrated data management system for this information is a prerequisite for an optimized planning of complex hybrid manufacturing processes.
Guiding research projects
In order to address the aforementioned requirements, CENIT is participating in two research projects in the area of hybrid manufacturing. The EU funded project Bionic Aircraft explores a holistic view of the whole lifecycle of additively produced light weight parts in the aerospace industry, from the design down to recycling. For the research project PR0F1T, funded by the German government, CENIT is investigating the data integration along the value chain of hybrid manufacturing processes which is based on exact 3D-CAD data. The heterogeneous tool chain used in the hybrid manufacturing process for structure analysis, topology optimization, design, and manufacturing data preparation, both for additive and subtractive processes, as well as for quality data management leads to extended demand for data integration. Up to date, has not been sufficiently satisfied.
The gained knowledge from this research activities will be considered for future developments of the digital factory solution FASTSUITE EDITION 2 as well as for the extension of consulting capabilities in the promising area of hybrid manufacturing.