Antonino Squillace

This study presents a measurement framework for the evaluation and online quality estimation of the Wire Arc Additive Manufacturing process based on Cold Metal Transfer (WAAM–CMT). Although several monitoring approaches have been proposed for WAAM, the identification of reliable non-invasive indicators capable of capturing process stability in real time remains challenging due to the highly non-stationary nature of arc current signals. A non-invasive monitoring strategy based on electrical current acquisition was implemented, using a clamp-type sensor to acquire the electrical current signal during the welding process. The acquired current signals were analyzed in both the time and frequency domains. To address the inherent variability of the current waveform, a wavelet coherence (WC) approach was adopted, enabling localized time–frequency correlation analysis between the measured current and a reference waveform. From this representation, a Mean Global Wavelet Coherence (MGWC) index was derived as a quantitative indicator of process stability. The proposed methodology showed effectiveness in distinguishing between stable and unstable deposition regimes, linking signal irregularities to the geometric quality of the deposited tracks. In addition, measurement uncertainty was explicitly evaluated by combining probability density functions derived from instrument specifications with Monte Carlo propagation, enabling the estimation of the confidence level associated with the monitoring indicator. The resulting framework integrates electrical current sensing, time–frequency signal analysis, and uncertainty quantification, providing a scalable and non-invasive solution for real-time monitoring and quality assessment in WAAM–CMT processes.

Additive layer manufacturing is changing the industrial landscape worldwide, particularly in high-end technology sectors, including aerospace applications. In mechanical engineering, and particularly in the aerospace industry, it is essential for quality certification that components are produced using qualified and robust manufacturing processes that guarantee high product repeatability. Unfortunately, nowadays, too few standards are available for the qualification of products manufactured by additive technologies for the aerospace sector. The aim of this work is to qualify a metallic space component, manufactured by additive technology, according to ESA ECSS standards: in particular, the qualification of a non-conventional configuration of the interfacing flanges used to connect two adjacent space launcher’s stages, manufactured by Electron Beam-Powder Bed Fusion (EB-PBF) additive technology, is presented in the present work.

This work introduces an initial finite element (FE) framework for modelling particle-substrate interaction during fluidized bed surface finishing of Laser Powder Bed Fusion (L-PBF) components. Due to the complexity of as-built surface morphology and the difficulty of experimentally observing high-speed particle impacts, the mechanisms governing material removal remain poorly understood. The proposed 3D explicit FE model simulates the impact of stainless-steel particles on representative AlSi10Mg asperities using Johnson-Cook plasticity model and damage formulations. Results show that erosion occurs mainly through localized brittle-like detachment rather than extensive plastic deformation. Sequential impacts and oblique trajectories significantly increase internal energy absorption, enhancing asperity fragmentation and the surface smoothing level. The framework provides a foundation for future optimization of Fluidized Bed Finishing (FBF) parameters for improved finishing of additively manufactured metal parts.

Additive manufacturing (AM) offers greater advantages in building intricate geometry and customised functional parts with flexible designs. However, the inferior quality of as-built AM parts is one obstacle that fails to meet the functional industry requirements. To overcome the inferior quality, as-built AM components, including thin-walled structures, must undergo one or more forms of post-processing treatments. The post-processing is an essential step in the AM process that ensures the AM part quality meets the necessary specifications of industrial standards. Hot-isostatic pressing, shot peening, chemical and electrochemical polishing, continuous wave laser hardening, etc., are the popular mainstream and advanced post-processing techniques applied to improve the final part quality of complex as-built AM parts. The industrially recognised HIPing helps to increase the part density while reducing the number of porosities and refining the microstructure. The chemical surface finishing and similar treatments are applied to enhance the final part quality of complex as-built AM parts, like thin-walled structures. Shot peening, mechanical polishing, and hybrid methods are used to significantly improve the surface quality of as-built AM parts. Overall, the mainstream and advanced post-processing treatments help to improve the dimensional tolerance and the holistic final part quality of as-built AM parts.

Additive manufacturing (AM) offers greater advantages of building intricate geometry and thin-walled structures, with comparable mechanical properties of the feedstock materials, at reduced lead times and material wastage. Utilising the promising feasibility benefits of AM has immensely helped to fabricate thin-walled structures used in aerospace, biomedical, automotive, energy absorption, and other functional applications. However, more benefits present more challenges. The complex thermodynamic phenomena of the AM processes comprise non-uniform phase transitions resulting in thermal residual stresses. Achieving process stability by optimising thermal stresses and other design considerations poses an even bigger challenge due to the presence of a wide array of AM process parameters. Although AM has shown signs of promise to overcome these critical issues associated with fabricating mainstream AM components, the real challenges persist while fabricating thin-walled structures: (i) the most common challenges encountered are the occurrence of inevitable metallurgical defects, anisotropic microstructures, poor surface quality and substandard mechanical properties, especially under dynamic loading conditions, and (ii) the stability challenges associated with AM thin-walled structures are buckling behaviour, inadequate load resistance, and load-sensitive fracture mechanisms. A sincere effort has been made to briefly present the existing challenges, and the applications of AM thin-walled structures have been discussed and summarised.

Laser-directed energy deposition (L-DED) is a highly versatile additive manufacturing technology that supports both the fabrication of near-net-shape components and the repair of critical parts, thereby extending service life, enhancing material utilization, and reducing overall production costs. These advantages are particularly significant in die and mold applications, which demand materials capable of withstanding severe thermal and mechanical loads. In this context, AISI H13 hot-work tool steel is among the most widely adopted materials due to its superior hardness, wear resistance, and thermal stability, making it an ideal candidate for L-DED technology. The present study aims to comprehensively investigate the influence of deposition strategy, overlap distance, and two sets of laser power, powder-feed rate, and scanning speed on the quality of L-DED H13 single-layer depositions. A systematic evaluation of surface waviness, microhardness, microstructure, and defects was carried out. The findings indicate that an overlap of 60% results in the least waviness, while the implementation of a unidirectional scanning approach enhances surface uniformity by approximately 25% compared to a bidirectional strategy. Microhardness values up to 720 HV were achieved, exceeding those of conventionally manufactured H13. The findings highlight process windows that enable defect-free depositions without substrate preheating, providing practical guidelines for optimizing L-DED of H13 tool steel components.