Wire Arc Additive Manufacturing Process for Topologically Optimized Aeronautical Fixtures.

Additive manufacturing (AM) technologies in metallic materials have experienced significant growth over recent decades. Concepts such as design for additive manufacturing have gained great relevance, due to their flexibility and capacity to generate complex geometries with AM technologies. These new design paradigms make it possible to save on material costs oriented toward more sustainable and green manufacturing. On the one hand, the high deposition rates of wire arc additive manufacturing (WAAM) stand out among the AM technologies, but on the other hand, WAAM is not as flexible when it comes to generating complex geometries. A methodology is presented in this study for the topological optimization of an aeronautical part and its adaptation, by means of computer aided manufacturing, for WAAM manufacturing of aeronautical tooling with the objective of producing a lighter part in a more sustainable manner.

Sustainable Hybrid Manufacturing of AlSi5 Alloy Turbine Blade Prototype by Robotic Direct Energy Layered Deposition and Subsequent Milling: An Alternative to Selective Laser Melting?

Additive technologies enable the flexible production through scalable layer-by-layer fabrication of simple to intricate geometries. The existing 3D-printing technologies that use powders are often slow with controlling parameters that are difficult to optimize, restricted product sizes, and are relatively expensive (in terms of feedstock and processing). This paper presents the development of an alternative approach consisting of a CAD/CAM + combined wire arc additive-manufacturing (WAAM) hybrid process utilizing the robotic MIG-based weld surfacing and milling of the AlSi5 aluminum alloy, which achieves sustainably high productivity via structural alloys. The feasibility of this hybrid approach was analyzed on a representative turbine blade piece. SprutCAM suite was utilized to identify the hybrid-manufacturing parameters and virtually simulate the processes. This research provides comprehensive experimental data on the optimization of cold metal transfer (CMT)-WAAM parameters such as the welding speed, current/voltage, wire feed rate, wall thickness, torch inclination angle (shift/tilt comparison), and deposit height. The multi-axes tool orientation and robotic milling strategies, i.e., (a) the side surface from rotational one-way bottom-up and (b) the top surface in a rectangular orientation, were tested in virtual CAM environments and then adopted during the prototype fabrication to minimize the total fabrication time. The effect of several machining parameters and robotic stiffness (during WAAM + milling) were also investigated. The mean deviation for the test piece's tolerance between the virtual processing and experimental fabrication was -0.76 mm (approx.) at a standard deviation of 0.22 mm assessed by 3D scanning. The surface roughness definition Sa in the final WAAM pass corresponds to 36 µm, which was lowered to 14.3 µm after milling, thus demonstrating a 55% improvement through the robotic comminution. The tensile testing at 0° and 90° orientations reported fracture strengths of 159 and 161.3 MPa, respectively, while the yield stress and reduced longitudinal (0°) elongations implied marginally better toughness along the WAAM deposition axes. The process sustainability factors of hybrid production were compared with Selective Laser Melting (SLM) in terms of the part size freedom, processing costs, and fabrication time with respect to tight design tolerances. The results deduced that this alternative hybrid-processing approach enables an economically viable, resource/energy feasible, and time-efficient method for the production of complex parts in contrast to the conventional additive technologies, i.e., SLM.

Assessing Tetrahedral Lattice Parameters for Engineering Applications Through Finite Element Analysis.

Minimizing weight while maintaining strength in components is a continuous struggle within manufacturing industries, especially in aerospace. This study explores how controlling the dimensions of the geometric parameters of a lattice yields ideal mechanical properties for aerospace-related applications. A previously developed Bubble-mesh based computational method was used to generate a novel type of tetrahedral lattice that allows for the manipulation of three geometric parameters: cell size/density, strut diameter, and strut intersection rounding. Topology optimization and lattice generation within components are typical methods used to decrease weight while maintaining strength. Although these are robust optimization methods, each have their faults. Highly topology-optimized components may fail under unexpected loads, and lattice generation within commercial software is often limited in its ability to create ideal lattices with controlled geometric parameters, resulting in lattices with repeating unit cells. In this study, we used finite element methods (FEM)-based compression tests on latticed cubes with various parameter combinations to determine the best balance of lattice parameters. The results showed that strut diameter and strut intersection rounding were the best parameters to control to maintain strength and reduce weight. This understanding of the lattice structures was then applied to two aerospace components: a jet engine bracket and an airplane bearing bracket. By applying tetrahedral lattices with specified strut diameters and strut intersection rounding, the weight of the jet engine bracket was reduced by 51.8%, and the airplane bearing bracket was reduced by 20.5%.

PolyJet-Printed Bellows Actuators: Design, Structural Optimization, and Experimental Investigation.

Pneumatic bellows actuators are exceptionally suitable for Additive Manufacturing (AM) as the required geometrical complexity can easily be obtained and their functionality is not affected by rough surfaces and small dimensional accuracy. This paper is an extended version of a previously published contribution to the RoboSoft2018 conference in Livorno, Italy. The original paper (Dämmer et al., 2018) contains a simulation-driven design approach as well as experimental investigations of the structural and fatigue behavior of pneumatic multi-material PolyJet™ bellows actuators. This extended version is enhanced with investigations on the relaxation behavior of PolyJet bellows actuators. The presented results are useful for researchers and engineers considering the application of PolyJet bellows actuators for pneumatic robots.