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Sintered gears manufactured through powder metallurgy technology contain residual porosity that can make them inadequate for high power supply. Crack propagation is significantly enhanced by both residual porosity and cyclical stresses involving the teeth. The use of densification processes can highly improve their performances, permitting the reduction of the residual porosity. Among the densification processes, the rolling assumes a key-role. The process permits the densification of the tooth flanks, the most stressed parts of the wheel. However, the performances of the rolled wheel depend on several process parameters, whose setup phase requires several efforts and many experiments. Finite element (FE) model can be a helpful tool, allowing a faster estimation of the process parameters, reducing waste and costs linked to the experimental tests. In this sense, FE modelling techniques discussed in literature only cover the simulation of spur gears densification process, since they consist of in-plane 2D finite elements. In this paper, different numerical modelling techniques, based on 2D finite elements, are proposed to simulate the densification process of spur gears and used to perform a tendency analysis to explore the effects of wheelbase reduction between the forming rollers on the material densification. Material densification appeared higher for reduced wheelbases, but an increasing cavity was observed at the tooth root as the wheelbases decreases. Moreover, a FE model based on 3D finite elements is proposed to reproduce numerically the rolling process of a helical gear. The accuracy of the 3D FE model was measured against the results provided by some experimental tests, herein discussed too. A good agreement between numerical and experimental results was observed. [ABSTRACT FROM AUTHOR]

The advent of additive manufacturing technologies significantly encouraged the development and usage of lattice structures. This paper aims to experimentally investigate the influence of dimension, building position, and orientation on the mechanical properties of Ti6Al4V trusses, manufactured by electron beam melting process, to be used in lattice cells. Specimens were manufactured considering the following parameters: truss diameter (1, 1.5, 2 mm), growth orientation (0°, 45°, 90°), and specimen position inside the building chamber. Trusses with diameter of 1 mm showed inconsistent mechanical properties caused by the poor manufacturing quality. Specimen position was found to influence the analyzed mechanical properties. Unmelted powders were observed to affect the outer surfaces of all specimens and the whole cross-sections of specimens manufactured at 0°. Specimens manufactured at 45° with diameter of 2 mm demonstrated the best performances, whereas specimens manufactured at 90° with diameter of 2 mm displayed the highest elongation at fracture. [ABSTRACT FROM AUTHOR]

Ti-6Al-4V is an alloy increasingly used in aeronautics due to its high mechanical properties coupled with lightness. An effective technology used to manufacture titanium components with a reduced buy-to-fly ratio is laser beam welding. Previous studies showed that the key factor that rules the mechanical properties and the fatigue life of the joint is its morphology. The aims of this paper were to investigate the influence of the geometrical features of the joints (height of the top and root reinforcement, depth and radius of the underfill, and the valley-valley underfill distance) on their mechanical properties and also to conduct a finite element (FE) analysis on the real geometry of the welded joints. Ti-6Al-4V rolled sheets 3.2 mm thick were welded in butt joint configuration using a laser source and their performance was studied in terms of weld morphology, microstructure, Vickers microhardness and fatigue life. A full factorial plan, designed varying the welding speed and laser power, was carried out. The real geometry and then the joint morphology were studied through an innovative approach: for each specimen, both the total weld face and the total root surface were acquired using a confocal microscope. Finally, through these acquisitions, the clouds of points of the scanned surfaces were used in order to carry out a FE analysis capable of providing a stress concentration factor, K , value for each detected joint. The main results are the realization of a reliable FE model by an experimental agreement and the relationship found amongst the fatigue performances and some noticeable metallurgical and geometrical features, such as the underfill depth and the aspect ratio defined as the ratio between the maximum height of the joint and the valley-valley underfill distance. [ABSTRACT FROM AUTHOR]