Laser-Based Manufacturing II

Laser-based manufacturing technologies have consolidated their key position among competitor manufacturing technologies thanks to the elevated level of accuracy, productivity, consistency, and flexibility provided by the advances in laser technology (e.g., widespread utilization of high-brightness laser sources, diode lasers with improved beam quality, efficient ultrafast lasers, etc.). Using lasers, most of the traditional manufacturing processes (cutting, welding, drilling, marking, forming, hardening, etc.) have been replicated and expanded in terms of productivity. On the other hand, laser technology has also made the development of new manufacturing technologies a reality, such as additive manufacturing, where most of the processes are laser-based [1]. These technologies have revolutionized the potential parts to be constructed and manufactured in novel materials, enabling new functionalities [2]. Laser technology has made possible the mass production of complex geometries [3,4,5], enhancing the material and/or surface properties, and the production of new materials [6], among others.

The current Special Issue, titled Laser-Based Manufacturing II, covers a collection of research articles that explore the latest developments in laser-based manufacturing techniques, including additive manufacturing, laser cutting, or laser surface modification. These studies highlight the interplay between processing parameters, material properties, and final product performance, offering valuable insights for both academic researchers and industrial practitioners.

Traditional laser processes, well-known in industry, include laser cutting, drilling, welding or marking. These processes are characterized by high accuracy and excellent surface quality and productivity [7,8]. Current research in these fields is mainly focused on the optimization of processing parameters (using, e.g., statistically planned experiments, or by machine learning or artificial intelligence (AI) methods) or in the processing of new materials. In this way, Kechagias et al. [9] has addressed the optimization of laser cutting parameters to predict and optimize the kerf geometry and surface roughness in processed fused filament fabrication (FFF) plates. This study also highlights the potential of machine learning techniques to improve process efficiency and quality, avoiding the lengthy traditional experimentation based on trial-and-error.

Laser technology has revolutionized surface engineering, where functional surfaces are routinely and accurately produced in many traditional and novel materials for advanced applications [10]. For example, Ioffe et al. [11] explored the formation of bubble-like structures on coated glass surfaces using picosecond laser pulses. This work demonstrates the unique advantages of picosecond laser pulses, over femtosecond and nanosecond, for efficient bump formation. It also provides a roadmap for scaling up this technology for industrial use in optoelectronic devices. Jamaatisomarin et al. [12] have reviewed the state of the art on the application of laser scribing to reduce the photocurrent and resistance losses in photovoltaic solar thin films and to boost their efficiency. The impact of processing parameters used to achieve efficient ablation has been discussed, with the pulse duration and beam quality being some of the most relevant. The potential impact of large processing speeds has been indicated to be attractive for industrial production.

The advantages of laser surface engineering are also relevant in other industrial fields but especially in medicine and electronics, as these processes can be performed avoiding any type of contact or contamination and reducing the impact on the bulk material. In this last field, Petillon et al. [13] investigated the application of laser direct structuring on thermoplastic substrates (LCP Vectra E840i LDS) and the subsequent electroless metallization (with Cu/Ni/Au) to produce conductor tracks with different structures and compositions. Moreover, the structures were subjected to flexural tests to evaluate the lifetime of the conductor tracks.

The development of additive manufacturing technologies has come hand in hand with laser technology. First, commercial additive manufacturing technology relied on the application of a UV laser to photopolymerize a liquid polymer [14]. Since then, many laser-based additive manufacturing processes have been developed, e.g., powder-bed methods (such as selective laser sintering (SLS) or selective laser melting (SLM)) or directed energy methods (such as laser-directed energy deposition (LDED), using powders or a wire). Currently, additive manufacturing is one of the most active research areas in laser-based manufacturing. Some of the research efforts have been directed to optimize the processing parameters to obtain parts with a desired microstructure and surface characteristics in well-known metallic alloys. In this sense, Barrionuevo et al. [15] studied the effect of processing parameters over the resulting mechanical properties during SLM of AISI 316L stainless steel powders. The effect of the laser power, scanning speed, and hatch spacing on the relative density, microhardness, and microstructure was assessed using statistically planned experiments. A direct relation between scanning speed and porosity was obtained. Parts with a densification larger than 99% were confirmed, reaching levels comparable to conventional processes (>99%). Other researchers have studied laser-based additive manufacturing processes to obtain parts made of novel materials or with specific microstructures. In this way, Cui et [16] studied different blends of austenitic stainless steel (X2CrNiMo17-12-2) powder and super duplex stainless steel (X2CrNiMoN25-7-4) powder to achieve duplex microstructures in the as-built condition during SLM. It was observed that desired duplex microstructures (roughly 50/50 austenite/ferrite) could be found after optimizing processing parameters. An increase in the amount of austenite was found after increasing the level of the laser input in the process. Wilms et al. [17] successfully incorporated yttrium oxide nanoparticles into Cu-Cr-Nb alloys to stabilize the microstructure. This represents a breakthrough in the additive manufacturing of high-performance materials, as a high-strength, high-temperature-resistant, and highly conductive copper alloy was developed.

Postprocessing of AM parts (produced or not by a laser) is also an active research field. Different authors have investigated the utilization of lasers to improve surface finishing, for example, by laser polishing the final parts [18]. Dolly Clement et al. [19] studied the effect of the heat treatment on the microstructure of AlSi10Mg parts produced by SLM to obtain better control of the microstructural and mechanical properties of the manufactured parts. It was demonstrated that the heat-treated specimens exhibit a homogenized microstructure; however, it was impossible to eliminate all the precipitates. Boschetto et al. [20] used areal analysis to characterize the surface quality of the parts produced by selective laser melting. The effect of the building orientation and barrel finishing postprocessing was analyzed. The results revealed significant variability and anisotropy as compared to traditional measurement methods (2D roughness analysis).

In summary, the publications in this Special Issue provide valuable insights into research developments in laser-based manufacturing, offering a comprehensive overview of the current research field and future prospects. Laser technology holds great promise for advancing the sustainable and reliable manufacturing of high-quality, high-precision products in the current and future industry.