Direct, Mold-less Production Systems
||Design, extension, operation and integration of highly flexible direct manufacturing
systems into one-piece-flow production systems in order to produce individualized
products, fulfilling customer needs
|(1) Development of a reference architecture for direct, mold-less production
systems applied on Laser Powder Bed Fusion (L-PBF) production systems
(2) Implementation and validation of a L-PBF production system as a representative
one-piece-flow production system with high product diversity
Additive Manufacturing (AM) technologies such as Laser Powder Bed Fusion (L-PBF) can contribute to the manufacture of individualized products to costs comparable to mass production. The manufacturing principle of the L-PBF process is based on a layerwise build-up of products from metallic powders. The parts exhibit a density of nearly 100 % and show mechanical properties comparable to conventional processes such as die casting. The main advantage of the L-PBF process is the capability to economically manufacture individual products. No tools or molds are needed. Moreover products with outstanding functionalities can be manufactured due to a lower amount of geometrical restrictions.
To qualify the L-PBF process for series production, an increase of productivity is needed. There are two ways to increase the productivity of the process. First, the application of higher laser powers up to 2 kW (High Power L-PBF) can boost the build-up rate. To handle the high amount of energy input in the powder bed at laser powers of up to 2 kW, the hull-core principle was developed. Second, the parallelization of multiple laser spots in one L-PBF-machine can increase the productivity of the L-PBF process by reducing the main process time of melting the powder. Laser powers up to 2 kW were already applied to boost the build-up rate for the tool steel material 1.2709. A specific heat treatment for 1.2709 was developed to achieve mechanical properties comparable to the conventional L-PBF process with lower laser powers. To demonstrate the feasibility of using laser powers of up to 2 kW, a profile extrusion tool was manufactured. In a field test it was shown that plastic profiles with high quality can be produced with the L-PBF-built profile extrusion tool. The post-processing of the exit zone of the extrusion tool is sufficient to guarantee a constant quality of the plastic profiles. In a next step a heating will be integrated into the profile extrusion tool to substitute the conventional heater band. This will further improve cycle times and the quality of the plastic profiles.
Moreover the profile extrusion tool will be optimized by topology optimization to reduce the amount of melted material. To boost the productivity of the L-PBF process by the parallelization of multiple laser spots, two different prototype machines were developed. The first machine is based on a modular principle and is equipped with two laser scanners with overlapping scan fields. Current working points are the integration of the two laser sources in the machine concept and the development of a controlling software to handle the overlapping areas. A second L-PBF-machine based on a multi-diode array, which is placed on moveable axes, has been developed and was officially presented at Euromold 2014 in Frankfurt. The overall feedback was very positive and currently ways for commercialization of the L-PBF-machine concept are investigated. Moreover a L-PBF-specific cost model is developed to allow the estimation of part costs depending on the SLM-machine configuration that is used for the build-up. The L-PBF-specific cost model contributes to the development of a production theory and allows the systematic development of L-PBF-machines regarding specific requirements.
Beside the development of new machine concepts to increase the productivity of the L-PBF process, the design for Additive Manufacturing is a strong research focus of the sub-project. The qualification of lattice structures manufactured by L-PBF is the key to exploit the geometric freedom offered by L-PBF. Various mechanical tests are carried out to gather mechanical properties of such light-weight structures. These investigations play a key role to functionally optimize parts by integrating different types of lattice structures. Moreover the influence of different scan strategies on the mechanical properties of small sized struts (<1 mm) and lattice structures was investigated. It could be concluded that the contour-hatch scan strategy shows better results regarding the mechanical properties of struts and lattice structured compared to the point-like scan strategy. Additionally, a new type of lattice structures (hollow sphere structure) was developed based on topology optimization that shows high isotropy. Based on the known mechanical properties of lattice structures a rim-support for a stub axle was designed and successfully tested in several formula student races. The rim-support demonstrates the light-weight potential of L-PBF parts and the opportunities to design and manufacture functional integrated products with extended functionalities.
To guarantee the transfer of the research results to our industrial partners, the new BMBF research campus Digital Photonic Production (DPP) was launched in January 2015. This research campus on the RWTH Aachen University campus features a signaling effect demonstrating a new way of conjoint research activities between industry and research facilities under one roof. The main objective of the research campus is the investigation and further development of photonic technologies. The further development of the SLM process is focused on in the subproject “Direct” within the research campus. Moreover a Design Center for Additive Manufacturing (DCAM) was founded to strengthen the research activities in this field. Various services such as design workshops or the redesign of parts will be offered to industrial partners to ensure a successful application of the SLM process in industry.