Additive manufacturing of metallic components – Process, structure and properties

Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

Additive manufacturing of metals

Consolidation phenomena in laser and powder-bed based layered manufacturing

Welding Metallurgy of

In this paper the innovative arc-fiber laser welding process (hybrid welding) was investigated on steel parts built by the Selective Laser Melting (SLM) process.SLM is probably the most rapidly growing technique in Additive Manufacturing (AM) technologies. This success results mainly from the possibility to create metal parts with complex shape, intrinsic engineered features and mechanical properties comparable with those of components produced with traditional processes.A preliminary study was performed on the possibility of welding SLM parts. The choice of the hybrid arc-fiber laser welding was justified by the possibility of this process to avoid air inclusions and fill gaps along the seam due to the relevant roughness of SLM parts. The hybrid joints were characterized in terms of micro-hardness, microstructure and shape of the transverse cross section. Comparisons between wrought, sintered and dissimilar welds were performed.In this paper the innovative arc-fiber laser welding process (hybrid welding) was investigated on steel parts built by the Selective Laser Melting (SLM) process.SLM is probably the most rapidly growing technique in Additive Manufacturing (AM) technologies. This success results mainly from the possibility to create metal parts with complex shape, intrinsic engineered features and mechanical properties comparable with those of components produced with traditional processes.A preliminary study was performed on the possibility of welding SLM parts. The choice of the hybrid arc-fiber laser welding was justified by the possibility of this process to avoid air inclusions and fill gaps along the seam due to the relevant roughness of SLM parts. The hybrid joints were characterized in terms of micro-hardness, microstructure and shape of the transverse cross section. Comparisons between wrought, sintered and dissimilar welds were performed.

Preliminary investigation on hybrid welding of selective laser molten parts

In this paper we consider to merge the stability problem for bilateral teleoperators and the contact force control problem for manipulators during constrained motion, tackling them jointly. In particular we evaluate the effects of the presence of a slave local force loop in a force reflecting master slave equipment with time delay in the communication channels. The study keeps into account the digital synthesis of the controller, which usually represents the most critical and undervalued aspect of the problem. Simulative and experimental results are given, in particular showing that the local integral force control can be tuned to the delay in the communication channel in order to guarantee stability, and, up to certain extent, a favourable transient behaviour.

The local force control loop approach in bilateral control of master-slave systems

In this work, the control framework of the DexROV Horizon 2020 project is presented. The framework is based on the task priority concept, extended by the authors to allow the activation and deactivation of tasks. The general concepts of control objectives, task and actions are given. The execution of a pipeline's weld inspection is used as study case to test the proposed framework in a simulation setting.

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DexROV project: Control framework for underwater interaction tasks

This paper presents the control framework developed within the Horizon 2020 ROBUST project aimed at building an autonomous system for exploring deep sea mining sites. First, the Autonomous Underwater Vehicle analyzes the initial zone of interest with the aim of finding a sub area with the highest probability to contain a manganese nodule field. When such an area is found, a low altitude survey is performed. When a possible nodule is detected, the vehicle lands on the seafloor, allowing a dedicated sensor mounted on the manipulator’s end-effector to perform the nodule analysis.This work presents the ROBUST control framework and the task priority based kinematic used for its implementation. In addition, software in the loop simulation, dry and pool test results are shown to validate the control framework addressed.

Autonomous Deep Sea Mining Exploration: The EU ROBUST Project Control Framework

This paper explores the effects of laser scarfing on a CFRP tape consisting of unidirectional carbon fiber with a layup of [(45/0/-45/90)4] sym with a total laminate dimension of 5.952 mm. The laser system used in the experimental investigations consisted of a nanosecond Nd: YAG laser source with an average maximum power of 20 W in a pulsed mode. The material was a with a total laminate of 5.952 mm. The laser process aims to investigate the surface modification by laser ablation. In more details, the effects of scanning speed (550 ÷ 650 mm/s) and frequency (23 ÷ 27 kHz) for three different scanning strategies on the scarfing depth, specimen dimensions (in x and y direction) and surface conditions were studied by full factorial experimental plan. By scarfing, the fibers were either oxidized, partially stripped, stripped and excessively stripped. After the statistical analysis, the best results in terms of surface conditions were achieved with the x-parallel laser scanning strategy, where the presence of excessively stripped fibers was not noticed. The mixed-hatching (MH) mode was the strategy that produced the worst results for the scarfing depth, which can negatively affect the ablation rate, even if it turns out to be the most stable strategy. The best results in terms of scarfing depth and x-y dimensions were achieved with MH mode, and with a scanning speed of 600 mm/s and a frequency of 27 kHz.

Giuseppe Casalino

Papers

Preliminary investigation on hybrid welding of selective laser molten parts

The local force control loop approach in bilateral control of master-slave systems

DexROV project: Control framework for underwater interaction tasks

Autonomous Deep Sea Mining Exploration: The EU ROBUST Project Control Framework

Statistical modelling and optimization of nanosecond Nd:YAG Q-switched laser scarfing of carbon fiber reinforced polymer