Emerging solid-state additive manufacturing (AM) technologies have recently garnered significant interest because they can prevent the defects that other metal AM processes may have due to sintering or melting. Additive friction stir deposition (AFSD), also known as MELD, is a solid-state AM technology that utilises bar feedstocks as the input material and frictional–deformational heat as the energy source. AFSD offers high deposition rates and is a promising technique for achieving defect-free material properties like wrought aluminium, magnesium, steel, and titanium alloys. While it offers benefits in terms of productivity and material properties, its low technology readiness level prevents widespread adoption. Academics and engineers are conducting research across various subfields to better understand the process parameters, material properties, process monitoring, and modelling of the AFSD technology. Yet, it is also crucial to compile and compare the research findings from past studies on this new technology to gain a comprehensive understanding and pinpoint future research paths. This paper aims to present a comprehensive review of AFSD focusing on process parameters, material properties, monitoring, and modelling. In addition to examining data from existing studies, this paper identifies areas where research is lacking and suggests paths for future research efforts.

Additive friction stir deposition (AFSD) is a solid-state AM method that feeds, plasticizes, and deposits solid bars using frictional heat. Although the AFSD is a promising method, its limited technology readiness level precludes its wider use. The use of optimum process parameters is critical for achieving successful results, and closed-loop control of process parameters can improve quality even further by reacting to and resolving any unanticipated issues that arise during the process. This article investigates the utilization of a process monitoring setup including various sensors to examine temperatures, forces, vibrations, and sound during the AFSD of the Al6061 aluminum alloy. Furthermore, it benchmarks the outcomes of the same process’ parameter set with or without utilizing a proportional–integral–derivative (PID). Large thermal gradients were observed at various locations of the deposit. Significant fluctuations in temperature and force were demonstrated for the initial layers until stability was reached as the height of the deposit increased. It has been shown that the change in the process parameters may lead to undesired results and can alter the deposit shape. Finally, residual stresses were investigated using the contour measurement technique, which revealed compressive stresses at the core of the part and tensile stresses in the outer regions.

With the growing acceptance of additive manufacturing (AM) across various sectors, laser-based powder bed fusion (PBF-LB) has widely been utilized to create intricately shaped parts from a range of metals alloys. The factors contributing to this reception are limited not only to the achievable geometrical complexity but also enhanced product functionality. Prominent sectors such as aerospace, defense, and biomedical have begun to leverage PBF-LB for a wide range of applications; its use in other industries, such as cutting tool manufacturing, remains more limited. Therefore, to address the potential of LPBF for higher performance in cutting tool applications, this study examines topology optimization and the laser powder bed fusion of face mills with experimental modal characteristics and cutting performance. The objectives in topology optimizations were to decrease the vibration magnitudes of face mills while keeping them stiff against deformation due to cutting forces. Three distinct designs were benchmarked, each with different weight reduction targets, and were fabricated using PBF-LB with M300 maraging steel. The optimized face mills demonstrated better performance with diminished vibration magnitudes and less tool wear patterns.

Additive manufacturing (AM) enables the consolidation of components and the integration of new functionalities in metallic parts, but layered fabrication often results in poor surface quality and geometric deviations. Among various surface treatment techniques, machining is often favoured for its capability to enhance not only surface finish but also critical geometric tolerances such as flatness and circularity, in addition to dimensional accuracy. However, machining AM components, particularly thin-walled structures, poses challenges related to unconventional material properties, complex fixturing, and heightened susceptibility to chatter. This study investigates the vibrational behaviour of thin-walled Ti6Al4V components produced via laser powder bed fusion, using a jet-engine compressor blade demonstrator. Four stock envelope designs were evaluated: constant, tapered, and two topologically optimised variants. After fabrication by Laser Powder Bed Fusion, the blades underwent tap testing and subsequent machining to assess changes in modal characteristics. The results show that optimised geometries can enhance modal performance without increasing the volume of the stock material. However, these designs exhibit more pronounced in situ modal changes during machining, due to greater variability in material removal and chip load, which amplifies vibration sensitivity compared to constant or tapered stock designs.