This PDF file contains the front matter associated with SPIE Proceedings Volume 12876, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Two-photon polymerization (2PP) based 3D printing is a well-established technique. However, for the vast majority of its existence, 2PP was realized by applying general-purpose setups that were not tailored to any specific field. This resulted in limitations regarding how much 2PP can proliferate in any one particular area. Therefore, in this work, we will explore what can be achieved if a 2PP setup is built from the ground up for usage in one specific field - biomedical 3D printing. To achieve it a special femtosecond (fs) laser-based setup is assembled with integrated dynamic beam-shaping. Removal of zero order maximum in such an optical setup is demonstrated, and main related peculiarities are discussed. Then the beam-shaping is used to elongate voxels allowing to improve manufacturing throughput by more than two orders of magnitude. We then used the setup and developed voxel elongation methodology to produce biology-oriented structures, such as stents, grafts, and organoid scaffolds. We show excellent biocompatibility and cell growth on the later structures. Overall, the presented results show how focusing on 2PP system design to accommodate one particular field, in this case, biomedicine, helps to exploit the system’s capabilities beyond what general purpose 2PP setup could achieve.

Printing functional tissues and organs on demand is a major goal in biofabrication. However, replicating intricate structures resembling cellular arrangements and physical characteristics of human tissues and organs remains the greatest challenge. Up to date, several systems, such as extrusion and light-based bioprinting techniques, have been widely studied. Achieving desired realistic, high-resolution 3D features on multi-material and multi-layer complex structures while simultaneously incorporating cells and maintaining high cell viability is the holy grail of bioprinting and remains to be achieved. Addressing this limitation, we proposed, developed, and fully characterized a novel 3D-bioprinting technique called Photopolymerization of Orderly Extruded multi-Materials (POEM). The proposed technique operates by infusing temporarily viscous photo-cross-linkable bioinks layer-by-layer. It is subsequently followed by precise and high-resolution photopatterning of the layers to the desired shapes and configurations. The proposed POEM technique offers a single step photopolymerization that eliminates the requirement for multiple processing steps, interim cleaning processes, or material exchange throughout the multi-material/multi-layer printing procedure. This also eliminates cross-contamination and the loss of valuable cells and inks during the cleaning process. Herein, we demonstrate the utility of the POEM technique for rapid and high-resolution 3D printing of multi-material, multi-layer, and cell-laden structures. The printed configurations exhibit remarkable cell viability (approximately 80%) and metabolic activity for over five days. As proof of concept, we successfully fabricated and characterized a 3D structure representing the esophagus. The development of POEM represents a significant advancement in 3D-bioprinting technology, offering new possibilities for constructing physiologically relevant tissue constructs.

Two-Photon Polymerization (2PP) is a high-precision additive manufacturing technique enabling the creation of intricate three-dimensional structures with sub-100 nm resolution. By focusing an ultrashort laser pulse within a photosensitive material, the nonlinear process of two-photon absorption is initiated in the vicinity of the laser focus. This results in the curing of a small volume with a size below the diffraction limit. However, the widespread adoption of 2PP in research and industry has been hindered by its expensive experimental setup. The largest cost factor in the experimental setup is the laser source, as an ultrashort pulsed laser system is required. Conventionally, fiber lasers or titanium-doped sapphire lasers are used. In contrast, the use of a diode laser could significantly reduce the cost of the laser source. In this work, we report the first structures fabricated by 2PP using a newly developed monolithically mode-locked diode laser. The diode laser has a pulse width of 7 ps, a peak power of 34 W, a repetition rate of 6.6 GHz, and a center wavelength of 780 nm. The center wavelength of 780 nm is crucial for optimal absorption of the laser radiation by the photoresists commonly used in 2PP. As a result, single lines could be fabricated with 2PP in a single scan, enabling the fabrication of three-dimensional structures in a reasonable process time. The process and the laser parameters were optimized and compared with respect to the highest possible scan speed.

Laser-based powder bed fusion of metallic materials (PBF-LB/M) is particularly suitable to produce complex components. The increasing demands regarding the performance of safety-related components and locally separated requirements within these are currently a major concern for manufacturing companies. Multimaterial powder bed-based Additive Manufacturing (MMAM) approaches are associated with cross-contamination and limited in-situ alloying due to a global material handling. This is accompanied by increased requirements for the facility systems for the deposition of various materials. A new machine concept combining the PBF-LB/M with a dispensing system has been developed to enable the production of graded and discrete intra- and inter-layer interfaces without joints in a single-stage process. Here, the combination of Inconel 718 (IN718) parts with locally applied copper (Cu) structures is reported, whereby discrete interlayer interfaces can be realized. The production of graded intra- and interlayer interfaces by simultaneously changing the proportions of IN718 and Cu is also investigated. In this work, we examined the influence of the process parameters of a dispensing unit for material application and a volumetric powder delivery device which is connected to the dispensing unit and allows in-situ-alloying. The influence of the subsequent fusion step on the structural properties of the interfaces was studied as well. Through this work, it is shown that the new machine concept enhances the design freedom of the PBF-LB/M process in the context of multimaterial processing. The production of discrete and graded intra- and interlayer interfaces is demonstrated using EDX measurement. Due to the different approach to material application, structures with differing properties are produced. Higher component densities can be achieved when copper is applied in a global IN718 powder bed (87% for the copper areas and 82% for IN718 areas). If the global material application is replaced by the dispensing system instead, a lower dimensional accuracy and a high error rate of 37 % can be observed.

Selective Laser Melting (SLM) technology has been widely used in various applications for aerospace, biomedical, molding and tooling, and automotive, etc. One of the key fundamental problems of the SLM is homogeneity of the manufactured structures, a roughness of their surface and precision of their sizes, which is strongly dependent on the material absorption coefficient that, in turn, depends on a wavelength of the laser radiation, and temperature, etc. Solution of this problem defines a success of SLM production in future its applications. Evidently, if a material under manufacturing, for example, consists of two different metals, then a temperature, stress and strain of these metals will differ because of strong dependence of the material’s absorptivity on a wavelength of laser radiation. As a result, after their solidification, one can expect an appearance of a crack or strain, at least. To avoid these disadvantages, we propose to irradiate the metals simultaneously by optical pulses with two different wavelengths. At corresponding choice of the laser pulses’ incident intensities, the temperature difference of the metals may decrease and heating (or stress, or displacement) of the metals will tend to more homogeneous one. To show this opportunity, we do a computer simulation of heating the 3D bimetallic plate, produced from Cu and a steel 316L, by irradiating the laser beams with wavelengths of 1060 nm and 515 nm separately and simultaneously. We account for the thermal conduction between Cu and 316L, and heat transfer to the substrate by copper and steel 316L respectively, the heat losses due to convection and radiation mechanisms from the metal domain to the environment as well as temperature-dependent thermophysical properties of the materials. Analyzing distributions of the temperature, stress, and displacement in the bimetallic plate, we analyze an efficiency of the dual-wavelength beams' action on improving the stress and deformation of the bimetallic plate under the SLM processing.

Laser powder bed fusion is at the forefront of manufacturing metallic objects, particularly those with complex geometries or those produced in limited quantities. However, this 3D printing method is susceptible to several printing defects due to the complexities of using a high-power laser with ultra-fast actuation. Accurate online print defect detection is therefore in high demand, and this defect detection must maintain a low computational profile to enable low-latency process intervention. In this work, we propose a low-latency LPBF defect detection algorithm based on fusion of images from high-speed cameras in the visible and Short-Wave Infrared (SWIR) spectrum ranges. First, we design an experiment to print an object while both imposing porosity defects on the print and recording the laser’s melt pool with the high-speed cameras. We then train variational autoencoders on images from both cameras to extract and fuse two sets of corresponding features. The melt pool recordings are then annotated with pore densities extracted from the printed object’s CT scan. These annotations are then used to train and evaluate the ability of a fast neural network model to predict the occurrence of porosity from the fused features. We compare the prediction performance of our sensor fused model with models trained on image features from each camera separately. We observe that the SWIR imaging is sensitive to keyhole porosity while the visible-range optical camera is sensitive to lack-of-fusion porosity. By fusing features from both cameras, we are able to accurately predict both pore types, thus outperforming both single camera systems.

With the increasing demand for customized products, new requirements on production processes are set. Additive manufacturing with its tool-independent character shows great potential to replace conventional manufacturing processes. This also applies to power electronic assemblies, which are currently produced with a low variety of variants in large batches. However, high-quality processing of copper is a prerequisite for power electronics applications in order to achieve low power losses and long module lifetimes. Green high-power lasers show great potential to process pure copper powder by means of powder bed fusion using a laser-based system (PBF-LB/M) and open up new opportunities in power electronics production. PBF-LB/M not only facilitates the production of mono-material components such as load connectors or heat sinks but also provides multi-material capabilities, enabling 3D metallizations on ceramic substrates for use as power electronic circuit carriers. Therefore, parametric studies on the fabrication of copper metallizations via PBF-LB/M on alumina substrates using a 1 kW green laser have been conducted and are summarized in this paper. At first, the beam-matter interaction between preheated alumina substrates and parameterized laser radiation was analyzed. Based on the results, process parameters have been defined, which were then used for the production of copper metallizations. High temperature preheating of the ceramics was applied in order avoid delamination effects due to thermomechanical stresses during solidification. In parametric studies with respect to laser power, laser velocity and hatching distance on 500 °C preheated substrates, electrical conductivities of 30 MS/m and shear strengths of 69 MPa were obtained.

In powder bed fusion with laser beams (PBF-LB/M), the component's quality and mechanical properties are limited by restricted process parameter combinations and the geometry of the component. Combining PBF-LB/M with ultrashort laser ablation enables additional control of the heat flow to adjust local solidification. On the one hand it is possible to print heat-dissipating structures, which can be added and removed during the build process. On the other hand, ablated slits in the component can serve as a thermal barrier. To investigate the effect of slits and heat-dissipation structures on the local temperature field and solidification conditions, a numerical model was developed. Two different ablation strategies were investigated and compared to conventional PBF-LB. Numerical investigations of an additively manufactured AlSi10Mg component showed a larger melt pool, a lower temperature gradient, and a lower cooling rate if there are slits present next to the current PBF-LB track. This approach provides the potential to independently adjust microstructure and mechanical properties, exceeding limitations imposed by the component's geometry in conventional additive manufacturing.

Laser additive manufacturing of metallic materials may be improved by in-situ process monitoring. For example, determination of surface characteristics of the building layers and measurements of the temperature of the melting pool may be utilized in powder-bed selective laser melting systems. In this paper, we experimentally investigate the possibility of determining surface characteristics, specifically surface roughness, using a prototype setup comprising a fiber-based line-scan confocal optical system with a laser probe beam that operates at a low numerical aperture over at least 200 mm distance between its optical elements and the sample surface. A similar setup for thermal radiation, without the probe beam, was used to determine 2D thermal distributions at the melt pool and to demonstrate melt pool temperature stabilization.

Powder-based laser metal deposition (DED-LB/M) is often used to create coatings for rotationally symmetrical components. By creating a melting zone on a substrate with a laser beam and adding metal powder through a powder nozzle, a metallurgical bond results, and thus a robust coating is created. One of the parameters influencing the surface quality is the track overlap. When aiming for an optimized surface without post-processing expense, a high track overlap (around 50–60%) is needed to achieve less waviness for the coating. This leads to an extended processing time during the production of the coatings. In order to reduce the processing time, a low track overlap (around 10–20%) is needed, again leading to high waviness and an expanded post-processing time. In this paper, a new approach towards net-shaped DED-LB/M coatings is presented, leading to a significant reduction in the post-processing extent for various applications. The combination of supporting tracks, generated with a minimal spot size of 0.9 mm, and filling track, generated with a maximum spot size of 2.8 mm using stainless-steel (316L), is analyzed. In a first step, a parameter development for defect-free supporting tracks and filling tracks is performed by variating the laser power and powder mass flow. Using these parameters, the realization of a layer with reduced waviness is analyzed. Hereby, the track offset of both track types is set to 100%, leading to 0% overlap. Results show that the filling track parameter must be adapted to the height of the supporting tracks. A second parameter variation (laser power and powder mass flow) for the filling tracks is performed leading to a coating with reduced waviness. The manufactured layers with supporting tracks are showing a minimized waviness compared to standard layers that are generated without supporting tracks.

The production of safety class one blade integrated disks (blisks) traditionally involves costly and time-consuming methods, utilizing precision machining of a solid forged block of nickel-based alloy in compliance with DIN EN 9133. This conventional approach, while meeting stringent certification requirements for turbine components operating under extreme conditions (900-1400 °C), suffers from increased tool wear due to milling solid blocks, leading to design limitations impacting efficiency. In this context, layer-by-layer construction using Additive Manufacturing (AM) processes, such as laser-based powder bed fusion of metals (PBF-LB/M), enable a resource-efficient process with a high level of design freedom. Process-related support structures typical for the PBF-LB/M process must be subsequently separated using subtractive processes, whereby the synergy and implications of integrating additive and subtractive manufacturing on the certification process has been insufficiently researched. The component properties of PBF-LB/M components exhibit greater deviations compared to conventional manufacturing methods as a result of local remelting and the associated complex temperature fields, complex machine transferability and reproducibility. In this work, the integration of additive manufacturing into the existing process chain was investigated. Considering the aerospace certification of safety class one components, a holistic process chain from the digital component model to the finished part was developed, which consists of design definition, additive manufacturing, heat treatment, subtractive post-processing and referencing as well as quality assurance along the entire process chain. We investigated the interdependencies of the various work steps in the process chain and the transfer of certification requirements in accordance with the conventional production route. The divergence in input material (powder), data preparation methods (support structures), machine maintenance, manufacturing complexity (dimensional accuracy), and component properties (reproducibility) poses significant challenges in applying established standards. Additionally, the absence of regulatory guidelines within the aerospace sector and specific OEM directives for additive manufacturing complicates the comprehensive evaluation of the alternative approach proposed. A better understanding of the complex interplay of various factors impacting additive manufacturing is crucial to promote OEM acceptance. However, due to this complexity, a final validation requires the integration of OEMs and the official institutes such as DIN, ISO, ASTM and EN to assess and create alternative standards. The combination of additive manufacturing and subtractive manufacturing may change the nature of BLISK manufacturing for aerospace in the near future, ensuring high-performance and efficient aviation.

Laser-based powder bed fusion of metals faces limitations in accuracy, surface quality, and minimal structure size resulting from the inherent melting process. To address these challenges, a novel approach integrating additive and subtractive laser processes at the layer level has been developed. This quasi-simultaneous manufacturing process enables the fabrication of small structures with high aspect ratios, including narrow slits below 50 μm in width. The implications of this advancement are promising, particularly in the fields of electric drives and fuel cells, where accuracy and freedom of design are crucial. In this work, the latest results of the production of narrow, inclined slits in components made of pure iron will be shown. Characteristics like groove-to-groove distance and groove width were analyzed, achieving successful production of continuous slits with varying inclination angles of up to 30° within the manufactured components.

Mechanical properties of Laser Powder Bed Fusion (LPBF) processed components are sensitively affected by the inferior surface quality, typical for this additive manufacturing technique for metal parts. Using a promising hybrid additive manufacturing approach, combining LPBF and in-situ high-speed milling, the surface quality can be strongly improved within a single process cycle. The milling process is directly integrated into the additive manufacturing chamber, machining the 3D-built surfaces while interrupting the LPBF-process. As a result, surface defects and surface near porosities are greatly reduced. Even though Inconel 718 is difficult to machine, as well as the milling process within the powder bed poses different challenges on this promising approach, a surface roughness of Ra ⪅ 1μm is generally achievable, using this particular hybrid additive manufacturing approach. We present a comparative study of the mechanical properties of conventional LPBF- and hybrid-build components with particular focus on the static and dynamic load behavior, in turn allowing to evaluate the effects of finished surfaces on these mechanical properties. In addition, the influence of different heat treatments on the static load behavior as well as the fatigue behavior is investigated. Different heat-treatments are performed, improving the density of the components, and leading to a higher maximum load behavior. Furthermore, the fatigue behavior is modified, as the material properties can be changed by virtue of the development of different material phases during the heat treatment processes. Comparing the sole LPBF- and hybrid-built components for the as-built and the different heat-treated states, an improvement of the maximum load capacity as well as of the dynamic load behavior can be observed for the hybrid-built specimens.

With direct laser writing, we show that laser scan rate can control the elemental ratio of two metals in the deposited structure. This occurs when one deposition process is triggered by photoexcitation while the other is a secondary dependent reaction. Energy Dispersive Spectroscopy (EDS) is used to find the atomic ratio of the metals. The ratio of copper to silver can be tuned from over 90:1 to below 1:1 and the trend follows an inverse relationship with scan speed.

Additive manufacturing enables direct prototyping of complex 3D-objects that are difficult to manufacture using conventional methods. It is widely used to fabricate cost-efficient prototypes and portrays as a bridging technology to connect different scientific and industrial fields, e.g. Engineering, Medicine, etc. Consequently, additive manufacturing finds its applications in the production of patient-specific orthoses. This paper discusses the application of the stereolithography apparatus process to develop a pressure sensor based on an optical waveguide principle to embed into a below-knee orthosis. For Orthopaedic patients, the below-knee orthosis must be adjusted to the lower leg at regular intervals due to anthropometric changes in patient’s body to achieve proper mobility and correct load. Currently, this alteration relies on the patient’s estimation of support load and is only sub-optimal. Hence, the concept of developing an intelligent orthosis with a novel embedded optical system to monitor the exact support load at the neuralgic is proposed.

In recent years, additive manufacturing has witnessed remarkable advancements, revolutionizing traditional manufacturing processes. Additive manufacturing has recently also moved into the field of glass processing using photopolymer-based resin containing fused silica nanoparticles. The optical losses of silica parts made from such nanocomposites were previously only quantified in sample lengths ⪅1 cm. Here, we significantly increase the accuracy of the optical loss measurement by fabricating optical fibers several meters long. The fibers were designed to consist of a silica core surrounded by a ring of six air-holes. The cores were either 3D-printed or cast from a fused silica nanocomposite. The materials used in this work are photocurable fused silica nanocomposites which can be either cast or processed with a DLP 3D-printer, and then cured by a UV-light source. Vitrification of the manufactured parts is achieved by subsequent debinding and vacuum sintering. The spectral loss was measured and compared with a fiber made entirely from ultra-high purity synthetic fused silica glass (Heraeus F300). We demonstrate that the fibers made using the nanocomposite show a loss below 4 dB/m in the whole Vis-NIR region (400-1700 nm), except for an OH-related peak at 1380 nm.

Additive manufacturing of micro-optics using Two-Photon-Lithography (2PL) has been a rapidly advancing field of technology. Striving for ever more sophisticated optical systems prerequisites the access to appropriately fast and accurate wave-optical simulation methods to predict their optical performance. A simulation routine, which has been proven well suited for simulation of a vast range of 3D-printed micro-optical systems, is the Wave Propagation Method (WPM). Nevertheless, limitations in applicability remain due to the restriction on scalar electromagnetic fields, which prohibits e.g. consideration of polarization and thereby also the calculation of backwards reflection at optical interfaces. Capabilities for design and analyses are therefore impaired for 3D-printed optical systems using those properties as key features in their design. As a first step to overcome those limitations, we presented new simulation methods based on the WPM in previous publications, extending its applicability towards simulation of vector electric fields, while maintaining short simulation runtime. In the present manuscript, we focus on elaborating the practical application and integration of the previously presented simulation methods in the design of complex 3D-printed optical systems. With it, we demonstrate the consideration of polarization and backward reflections in simulations far beyond paraxial and thin element approximations.

CO2 laser additive manufacturing of multi-layer heterogeneous transparent films using anatase-TiO2 and SiO2 nanoparticles (NPs) is reported. The preparation of these films was carried out in two steps; corresponding to (i) evaporation of liquid, and (ii) sintering NPs to form transparent thin films on the quartz substrate. A heat transfer theoretical model was developed to select the proper laser processing parameters. Based on the anti-reflection coating (ARC) model, a 55 nm thickness of each layer; i.e., TiO2 and SiO2, was chosen to minimize the reflectance. The microstructural properties were determined using SEM and XRD analysis. UV/Vis/NIR spectrophotometry measurements show that the sintered films are highly transparent, with an average transmittance above 85% in some wavelength ranges. The effects of the sequence of the TiO2 and SiO2 layer deposition on the optical properties of films were investigated. The porosity, transmittance, and reflectance data were utilized to determine the optical constants, refraction index, and absorption index of the TiO2/SiO2 coatings. Our results provide a comprehensive understanding of the ARC properties of the TiO2/SiO2 coatings.

Additive manufacturing of micro-optics enables new possibilities for optical system design. The high degree of freedom regarding surface shape allows for the miniaturization of complex systems. We present a miniaturized 3D-printed holographic optical tweezer for micromanipulation. Different systems were manufactured and analyzed regarding focal distance and intensity ratio between the two foci. Furthermore, we present the concept for parallelization and microfluidic integration of our system.

We present a flexible catheter endoscope using a 3D printed miniature side-viewing reflective lens for OCT imaging. A reflective lens with a depth of field (DOF) of 3mm and a maximum spot size of 80 microns was first designed and optimized in OpticStudio (ZEMAX). The structure of the lens and the fiber mating part of the optic was then constructed using 2-photon polymerization technique, and a gold reflective coating was added as the final step for the reflective lens. The reflective lens was then glued to cleaved optical fiber, and the assembly was covered by a torque coil to allow rotation of the catheter endoscope. This endoscope was used with a fiber-optic rotary joint and custom-built Mach-Zehnder interferometer to acquire OCT images.

Hybrid additive manufacturing techniques capitalise the advantages of additive manufacturing, while, at the same time, circumvent its disadvantages by using in-situ combined subtractive processes. A particularly promising hybrid additive manufacturing approach unites Laser Powder Bed Fusion (LPBF) with in-situ high-speed milling. Here, the advantages of LPBF such as, e.g., design of freedom and choice of a variety of qualified metal powders can be used, shaping complex as well as custom-designed 3D metal parts. The in-situ high-speed milling process, in turn, yields finished surfaces with superior surface roughness and guarantees high geometrical accuracy without the need of any further post processing. While the typical process sequence of this hybrid approach interrupts the LPBF process every 3-10 layers by milling the accessible surface regions of interest, different challenges arise, as this milling process is directly integrated into the powder bed of the LPBF chamber. Wear characteristics of the milling tools increase as a consequence of the surrounding powder, getting reinforced by the elevated temperatures of the thus far printed parts. As being a super-alloy, Inconel 718 is a promising and well-studied candidate for LPBF additive manufacturing, exhibiting high strength and good mechanical properties. However, it is also well known to be a difficult to machine material. This contribution evaluates the process parameters of this innovative hybrid combination with particular focus on optimizing the surface quality. By varying the high-speed milling process parameters infeed, z-pitch, feed rate and rotational velocity of the milling cutter, smooth surfaces with a roughness of R_a ⪅1μm are accomplished. In addition, the wear characteristics of the milling cutter are investigated, characterizing the flank wear as well as the abrasion of the cutters coating. As the flank wear gets increased by the surrounding powder during the milling process, a specific milling path suction is installed, extracting the powder at the surfaces of the components ahead of the milling path. Advantages of this approach are quantified in a comparative study by the analysis of the milling cutters lifetime.

Copper is expected to have many applications due to its virus inactivation property, high thermal conductivity, high electrical conductivity and so on. The market demand for processing of copper is increasing as electric car expand more prevalent. Besides the copper is expected to be used for handrails, doorknobs etc., which touched by many people to prevent from infectious diseases because of having the excellent properties such as an antibacterial property and a virus inactivation property. Thus, a multi-beam blue diode laser installed laser metal deposition (B-LMD) system was newly developed with a laser intensity of 4.7×105 W/cm², which is improved about five times higher than that of previous systems. There is, however, a problem that the surface is discolored due to the oxidation of copper in the air. Thus, Cu-Zn alloy was developed and tried to coat on the substrate surface with B-LMD system. As a result, Cu-Zn alloy layer was formed on the stainless-steel-plate with no pores at the output power of 40 W. It was found that the cross-sectional-area of layer was increased with increase the output power of laser in the Cu-Zn alloy coating. The addition of zinc to copper improves the energy efficiency for layer formation, and zinc concentration is found to be a factor that increases the energy efficiency. So, in this study, the copper layer was formed using different weight % Cu-Zn powder and investigate of threshold for copper layer formation. And the effect of zinc concentration on the threshold value for copper layer formation was examined. The copper layer was formed on SUS304 stainless steel substrate using pure copper or copper alloy. The effect of copper layer formation due to the difference in the amount of zinc was investigated, using (a) pure copper, (b) 80% Cu-20% Zn, and (c) 70% Zn-30Zn powder. In order to form a pure copper layer, an output equivalent to the threshold, which the substrate start to melt, was required. It was possible to form a copper layer with an output power lower below the threshold by adding zinc. On the other hand, when the amount of zinc added was increased, it became possible to form a copper layer at an even lower output power. It is thought that the absorption rate increases by adding zinc, and heat is transferred to the substrate through the Cu-Zn layer. As the amount of zinc added increases, the absorption rate increases further, and it is thought that a copper layer can be formed at a lower output. So, it is thought that even at power below the threshold, the substrate melted slightly and formed copper layer. It was possible to form a copper layer with low output power by adding zinc. It is thought that processing at low output can contribute to energy savings and carbon neutrality.

SLA (Stereolithography) printing technology can achieve high precision and accuracy compared to other 3D printing methods. However, the single laser movement mechanism has the disadvantage of increasing processing time during the printing process and causing problems such as incomplete curing and premature gelation. In this study, we address these challenges by using Acoustic Emission (AE)-based detection of curing defects during the printing process in SLA, which utilizes UV-curable resin as its primary material. PVDF (Polyvinylidene Fluoride) sensors are used to detect AE during resin curing. Signals were analyzed based on the presence or absence of specific events to avoid signal ambiguity caused by internal voids during resin curing. Several AE parameters were evaluated experimentally. The most suitable parameters were identified for the detection of thermal cure signals. Among these parameters, AE RMS and AE Count showed the most significant variations in response to thermal curing signals. The proposed method can be used for smart monitoring in SLA printing to detect defects, such as incomplete curing, early in the process, contributing to precision manufacturing.