Process Selective Laser Research Articles

Direct powder bed selective laser processing of dense alumina-toughened zirconia parts

Direct powder bed selective laser processing of dense alumina-toughened zirconia parts

Ultrafast processing of zirconia ceramics by transient and selective laser absorption

Ultrashort-pulse lasers (USPLs) are used in the machining of zirconia ceramics (ZrO2) because of their extremely high peak intensities. However, highly efficient and high precision microprocessing of ZrO2 remains challenging. In this study, we applied a transient and selective laser (TSL) processing technique by combining a USPL and a continuous-wave (CW) laser to realize ultrafast drilling of opaque ZrO2. Ultra-high-efficiency TSL drilling of ZrO2 was achieved with a processing efficiency 1800 times higher than that of USPL drilling. The material removal mechanism, hole formation process, and parameter dependence of TSL drilling were revealed by direct observation of the internal processing phenomenon on a timescale of microseconds. The variations in the processed surface characteristics, including surface morphology, elemental composition, and phase composition, are also presented. Subsequently, the effect of different excited electron regions occurring in the picosecond timescale induced by the USPL on the TSL drilling performance is discussed. Finally, the repeatability and stability of the TSL processing were verified by fabricating microarrays of different sizes. This study will contribute to revealing the ultrafast processing mechanisms of TSL processing in ZrO2 microfabrication. Furthermore, this technique can significantly broaden the applications of ZrO2 in the advanced electronic industry by greatly improving the microprocessing efficiency.

Mechanism and performance evaluation of transient and selective laser processing of glass based on optical monitoring.

Femtosecond laser processing has been widely applied in glass processing owing to its ability to fabricate microscale components. To improve processing efficiency, a transient and selective laser (TSL) processing technique was previously developed, in which electron excitation was induced inside a transparent medium by a single pulse of femtosecond (fs) laser, and a single pulse of microsecond (µs) laser can be selectively absorbed in this excited region to heat and remove the material. However, because of its high speed removal process, the unclear mechanism and inefficient evaluation of its processing performance limit its further application. This study analyzes the transient spatiotemporal evolution of the induced plasma and the related material removal mechanism of the TSL processing using a side high-speed monitoring method. To achieve a rapid performance evaluation, a quantitative analysis of the optical plasma signals (on a microsecond timescale) generated in TSL processing was performed by employing a developed coaxial high-speed monitoring method using a photodetector. The variations in the shapes, intensity distribution, and dimensions of the plasma were quantitatively investigated. In addition, the relation between the plasma signal and drilling performance under different laser parameters, including hole depth, hole types, and cracks, was explored and quantitatively analyzed. The revealed mechanism is expected to contribute to the broadening of the application of TSL processing in microfabrication. Furthermore, the developed high-speed and precision monitoring technology can be utilized for high-speed evaluation and precision control of machining quality in real time during ultrahigh-speed laser machining, without time-consuming camera observations.

Nanowire-assisted freestanding liquid metal thin-film patterns for highly stretchable electrodes on 3D surfaces

Stretchable electronics is playing an integral role in fields such as wearable electronics and soft robots. Among soft conductive materials, liquid metal is drawing intense attention as an electrode material due to its liquid nature at room temperature. However, the merits of liquid metal conductor are limited by the presence of substrates or enclosed microchannels from physical disturbances by the underlying substrate when applying it to 3D surface and modifying complex circuit. To overcome this limitation, we develop freestanding patterned liquid metal thin-film conductor (FS-GaIn). FS-GaIn was achieved by introducing metal nanowires to liquid metal and subsequent sequential selective laser processing and etching of directly patterned traces. FS-GaIn can be applied directly to nonflat surface without substrates. When incorporated into electrical circuits, FS-GaIn shows high electrical conductivity, stretchability, and stability. The concept of freestanding liquid metal can open a functionality to the conventional liquid metal electronics.

Reactive laser synthesis of ultra-high-temperature ceramics HfC, ZrC, TiC, HfN, ZrN, and TiN for additive manufacturing

Ultra-high-temperature ceramics (UHTCs) are optimal structural materials for applications that require extreme high temperature resilience (Mp > 3000 °C), resistance to chemically aggressive environments, wear, and mechanical stress. Processing UHTCs with laser-based additive manufacturing (AM) has not been fully realized due to a variety of obstacles. In this work, selective laser reaction sintering techniques (SLRS) were investigated for the production near net-shape UHTC ceramics such as HfC, ZrC, TiC, HfN, ZrN, and TiN. Specifically, group IV transition metal and metal oxide precursor materials (<44 μm) were chemically converted and reaction-bonded into layers of UHTCs using single-step selective laser processing in 100 vol% CH4 or NH3 gas that might be compatible with prevailing powder bed fusion techniques. Conversion of either metals (Hf, Zr and Ti) or metal oxides (HfO2, ZrO2, and TiO2) particles was first investigated to examine reaction mechanisms and volume changes associated with SLRS of single-component precursor systems. SLRS processing of metal or metal oxide alone produced near stoichiometric UHTC phases and yields up to >99.9 wt% total for carbides and nitrides and during the rapid reactive in-situ processing scheme. However, for single-phase feedstocks, gas-solid reactivity induced volumetric changes (correlated with the stochiometry of the rocksalt-type UHTC carbide and nitride products) resulted in residual stresses and cracking in the model-AM product layer. To mitigate conversion-induced stresses of single-phase precursors, composite metal/metal oxide precursors were employed to compensate for the volume changes of either the metal (which expands during conversion) or the metal oxide precursor (which contracts). While conversion of the optimized composite materials produced HfC layers with as little as +0.9% volume change, results indicated interparticle adhesion must be optimized to obtain robust UHTC-AM layers. Computational models of carbon and nitrogen diffusion in host transition metal lattices corroborated experimental results where a progressive particle conversion might inhibit interparticle diffusion unless laser processing parameters are carefully optimized to favor reaction bonding over discrete particle conversion. While this method presents a host of processing considerations, we demonstrate how this reactive approach may be viable for the AM of numerous UHTC materials that are not readily produced using current methods.

Selective laser reaction synthesis of SiC, Si3N4 and HfC/SiC composites for additive manufacturing

Selective laser reaction sintering techniques (SLRS) techniques were investigated for the production of near net-shape non-oxide ceramics including SiC, Si3N4, and HfC/SiC composites that might be compatible with prevailing powder bed fusion additive manufacturing processes. Reaction bonded layers of covalent ceramics were produced using in-situ reactions that occur during selective laser processing and layer formation. During SLRS, precursor materials composed of metal and/or metal oxide powders were fashioned into powder beds for conversion to non-oxide ceramic layers. Laser-processing was used to initiate simultaneous chemical conversion and local interparticle bonding of precursor particles in 100 vol% CH4 or NH3 gases. Several factors related to the reaction synthesis process—precursor chemistry, gas-solid and gas-liquid synthesis mechanisms, precursor vapor pressures—were investigated in relation to resulting microstructures and non-oxide yields. Results indicated that the volumetric changes which occurred during in-situ conversion of single component precursors negatively impacted the surface layer microstructure. To circumvent the internal stresses and cracking that accompanied the conversion of Si or Hf (that expands upon conversion) or SiOx (that contracts during conversion), optimized ratios of the precursor constituents were used to produce near isovolumetric conversion to the product phase. Phase characterization indicated that precipitation of SiC from the Si/SiO2 melt formed continuous, crack-free, and dense layers of 93.7 wt% SiC that were approximately 35 µm thick, while sintered HfC/SiC composites (84.2 wt% yield) were produced from the laser-processing of Hf/SiO2 in CH4. By contrast, the SLRS of Si/SiOx precursor materials used to produce Si3N4 resulted in whisker formation and materials vaporization due to the high temperatures required for conversion. The results demonstrate that under appropriate processing conditions and precursor selection, the formation of near net-shape SiC and SiC composites might be achieved through single-step AM-compatible techniques.

Selective Laser Processing of B2O3 Coatings: Phase Evolution and Tribological Performance

Selective Laser Processing of B2O3 Coatings: Phase Evolution and Tribological Performance

Rehabilitation of Working Platforms for 3d Printing Device on Metal

AbstractThe 3D printing device on metal uses the technological process—selective laser melting, through which dental works with precision and speed can be printed. The dental works are printed on the surface of a metal platform, their attachment being with the help of supports. It is important that this study can rehabilitate the platforms on which the printing is done, by rectification, through several steps, namely: removal of residues (metal supports of dental work), smoothing the work platform with a device that has an abrasive material, washing them under a stream of hot water, so that the grease residues are removed, then keep them in a clean environment.

High-efficiency microdrilling of glass by parallel transient and selective laser processing with spatial light modulator

To use glass as the substrate material in next-generation large-scale integrations and biochips, the high-speed fabrication of high-aspect-ratio microholes is necessary. Transient and selective laser (TSL) processing significantly reduces the processing time per hole. To further improve the processing efficiency, parallel TSL processing using a spatial light modulator is proposed in this study. Two 100-µm depth holes are successfully machined in parallel, in 50 µs. Furthermore, the process control parameters are investigated through high-speed observation and the laser irradiation conditions required for processing are clarified. Parallel processing of three or more holes and depth control of each hole is expected to be realized in future.

Process parameters investigation for direct powder bed selective laser processing of silicon carbide parts

Direct-powder bed selective laser processing (D-PBSLP) is a promising technique for the manufacturing of complex-shaped parts of Silicon Carbide (SiC) ceramic. In this work, a complex optimization of the process parameters was performed by numerical and experimental analysis. The numerical model was used to determine and optimize the effect of laser power, scanning speed and hatching distance at different layer thicknesses of 20, 30 and 40 µm. Regarding the experimental process parameters study, powder compaction was also studied and optimized. The optimization parameter criteria were to achieve reproducible and high relative density parts. Concerning the experimental manufacturing process, D-PBSLP of alpha-silicon carbide parts with a maximum relative density of 81% were manufactured. Moreover, the process viability can be confirmed with the manufacturing of SiC complex shapes in absence of any additives in the initial powder and without or post-treatment. The results from this study could be used as a guide for process parameters selection.

Multi-Layer Simulation of the Powder Bed Selective Laser Processing of Alumina for Residual Stress and Distortion Evaluation.

A numerical model was developed to simulate the real process of alumina powder bed selective laser processing (PBSLP) to thoroughly investigate the residual stress and distortion experienced in printed parts when multi-layer scanning with a CO2 laser source is considered. The model contains a user-defined function (UDF) for the laser source, temperature-dependent material properties, scanning strategies, and build orientations, and it is solved using ANSYS 2020R2. In addition, the model’s validation was confirmed with experimental results. The results revealed that a high scanning speed (up to 1200 mm/s) and low laser power are effective for the PBSLP of alumina, owing to alumina’s high absorptivity for CO2 lasers, and a high manufacturing rate can be achieved. During the multi-layer printing simulation, the accumulated heat inside the part increased gradually with an increased number of printed layers. Additionally, the calculated residual stress exceeded the yield limit for all the studied build orientations due to the printed part’s high-temperature difference. When preheating was applied, the residual stress decreased by 23% and the distortion decreased by 54%. For the successful PBSLP of ceramics, commercial printers cannot be used effectively. A particular printer equipped with a temperature controller and a preheating system is required for ceramics.

Personalized Artificial Tibia Bone Structure Design and Processing Based on Laser Powder Bed Fusion

Bone defects caused by bone diseases and bone trauma need to be implanted or replaced by surgery. Therefore, it is of great significance to design and prepare a tibial implant with good biocompatibility and excellent comprehensive mechanical properties. In this paper, with 316L stainless steel powder as the main material, a personalized artificial tibia design and processing method based on laser powder bed fusion is proposed. Firstly, the personalized model of the damaged part of the patient is reconstructed. Then, the porous structure of human tibia is manufactured by selective laser melting technology. To research the factors affecting the quality of selective laser melting porous structure, a laser heat source model, heat transfer model and molten pool model of laser powder bed fusion process were constructed; then, by changing the laser process parameters (laser power, laser beam diameter, scanning speed, powder layer thickness, etc.) to conduct multiple sets of simulation experiments, it is obtained that when the “laser power is 180 W, the laser scanning speed is 1000 mm/s, the laser beam diameter is 80 μm, the powder layer thickness is 50 μm”, the porous stainless steel parts with better quality can be obtained. Finally, the porous structure was fabricated by selective laser processing, and its properties were tested and analyzed. The experimental results show that the cell side length of cube is 1.2 mm, the elastic modulus of octahedral porous structure with pillar diameter of 0.35 mm is about 17.88 GPa, which match well with tibial bone tissue.

Powder bed selective laser process (sintering/melting) applied to tailored calcium phosphate-based powders

This paper focuses on the tailoring of calcium phosphate powders for their use as powder bed selective laser process feedstock. Hydroxyapatite and chlorapatite were used as starting powders for the preparation of different blends through the addition of graphite as a laser absorptance additive. A methodical study was conducted to compare the processing windows of the blends containing different amounts of graphite through the laser patterning of circular samples. It was found that the addition of graphite increases the process window of the powder blends being the powder without additive non processable. Hydroxyapatite showed a clear phase transition (decreased when using higher volumetric energy density) into other calcium phosphate phases while chlorapatite was demonstrated to be thermally stable during the whole process (examined through X-ray diffraction and vibrational spectroscopies). In parallel, the study evaluating the powder blend composed of hydroxyapatite and graphite for the production of solid and complex parts was carried out although it required long printing times. The productivity of the process was improved by modification of printing parameters. Then, a series of solid samples were produced for the analysis of the microstructure and mechanical properties. High interconnected porosity was observed in the samples which could improve the bioactivity of the bioceramic scaffolds. A post-treatment of the parts increased their proportion in the hydroxyapatite phase and their mechanical properties. These results are expected to contribute to the application of powder bed selective laser processing of calcium phosphates powders toward bone tissue engineering. • Graphite as absorption additive improves the laser-material interaction enlarging the process window. • Laser parameters directly influence the hydroxyapatite phase transition into other calcium phosphate phases. • Chlorapatite did not undergo phase transition during the process due to its inherent higher thermal stability. • Solid parts containing a majority of HA phase in the structure were obtained although with low mechanical properties.

Laser Welding of Metal-Polymer-Metal Sandwich Panels

In the production of metal-polymer multilayer composite parts, e.g., for automotive applications, the possibilities of thermal joining are limited due to the instability of the polymer core at elevated temperatures. Accordingly, such materials require a special approach to their welding. The three-layered metal-polymer-metal samples were made of DPK 30/50+ZE dual-phase steel as cover sheets that were electrolytic galvanized, and a polypropylene-polyethylene foil as core material, with thicknesses of 0.48/0.3/0.48 mm. The samples were welded on both sides using a 1.06 µm Nd:YAG ROFIN StarWeld Manual Performance laser. Significant improvements of the welding conditions are achieved by machining the edges of materials to be welded. The parameters of laser welding were chosen in such a way that the polymer structure remained almost unchanged. The weld thickness was about 40% of the thickness of each steel layer. It was established that within the selected laser processing parameters the melting occurred uniformly, while the polymer layer practically did not change its structure. Therefore, it can be stated that two-sided joint welding of metal-polymer-metal composite sandwich panels, without significant degradation of the polymer core layer, is feasible.

Scanning Strategy Investigation for Direct Powder Bed Selective Laser Processing of Silicon Carbide Ceramic

Direct-Powder Bed Selective Laser Processing (D-PBSLP) is considered a promising technique for the Additive Manufacturing (AM) of Silicon Carbide (SiC). For the successful D-PBSLP of SiC, it is necessary to understand the effects of process parameters. The process parameters are the laser power, scanning speed, hatching distance, and scanning strategies. This study investigates the effect of scanning strategies on the D-PBSLP of SiC and ensures that other process parameters are appropriately selected to achieve this. A numerical model was developed to obtain the proper process parameters for the investigation of scanning strategies in this work. Different scanning strategies available in the commercial Phoenix 3D printer manufactured by 3D Systems, such as concentric in–out, linear, inclined zigzag, and hexagonal, have been investigated. It was concluded that the zigzag strategy is the best scanning strategy, as it was seen that SiC samples could be printed at a high relative density of above 80% without a characteristic pattern on the layer’s top surface. SiC samples were successfully printed using different laser powers and scanning speeds obtained from the numerical model and zigzag strategy. Additionally, complex geometry in the form of triple periodic minimum surface (gyroid) was also successfully printed.

Powder Bed Selective Laser Processing of Alumina: Scanning Strategies Investigation

Powder Bed Selective Laser Processing (PBSLP) is a promising technique for the additive manufacturing of alumina. For the method’s success, PBSLP process parameters such as laser power, scanning speed, hatching distance, and scanning strategies need to be investigated. This paper focuses on studying the scanning strategies’ effects on the PBSLP of alumina numerically and experimentally. Scanning strategies such as linear with different orientation, concentric, and islands were investigated. A numerical model was developed in which the PBSLP parameters, scanning strategy effects, and interpreting the experimental results could be observed. The numerical model proved its ability to reach the proper process parameters instead of using experimental trails which are time and cost consuming. For relative density, the island strategy succeeded to print alumina samples with a high relative density reaching 87.8%. However, there are round passages formed inside the samples that remain a barrier for the island strategy to be effectively used in PBSLP of alumina. Both linear and concentric strategies achieved a relative density of 75% and 67%, respectively. Considering the top surface roughness, samples printed with linear strategies gave low top surface roughness compared to the island and concentric strategies. Linear-45° is considered the effective strategy among the studied strategies as it achieved good relative density and low roughness at top and side surfaces. For PBSLP of alumina, new scanning strategies should be considered, and this study presents a new scanning strategy that is mainly based on space filling mathematical curves and should be studied in future work.

Tailoring hydroxyapatite microspheres by spray-drying for powder bed fusion feedstock

The present work deals with a study on the physical characteristics of stoichiometric hydroxyapatite microspheres produced by spray-drying process through different operating conditions. Obtained hydroxyapatite microspheres are intended to be used as powder feedstock in powder bed selective laser processing additive manufacturing technologies where the flowability and the particle size distribution of the powder feedstock are of special importance. The powders produced at different spray-drying operating parameters were evaluated by analysing the particle size, shape, moisture, and agglomerates strength. Spray air pressure (0.25–2 bars) and the solid content of the slurries (10–50% wt.) were the most influent parameters to control the final particle size distribution, whereas the higher process recovery rate (79%) was obtained at specific values of inlet temperature (250 °C), spray air pressure (2 bar), and feed rate (4.9 kg.h−1). A 5 wt% of polyvinyl alcohol as an organic binder to the ceramic part was found to increase the strength of the granules. The flowability of the produced hydroxyapatite microspheres (x50 = 64 μm; span = 1.77) was found to fulfil the defined feedstock requirements (e.g., Hausner ratio < 1.25), without alteration of the physico-chemical properties of the material. These promising results confirm the use of a spray dryer as an efficient method for the production of hydroxyapatite microspheres for powder bed selective laser processing.

Powder bed selective laser processing (sintering / melting) of Yttrium Stabilized Zirconia using carbon-based material (TiC) as absorbance enhancer

This study aimed to process 8 mol.% yttrium stabilized zirconia by powder bed selective laser processing, as well known as selective laser sintering / melting. Titanium carbide was used as absorbance enhancer to a Nd:YAG laser. Titanium carbide was chosen for having the lowest weight / absorbance ratio among four additive options: silicon carbide, carbon black, graphite, and titanium carbide. Several trials were performed using 0,25 wt.% of titanium carbide as absorbance enhancer of 8 mol.% yttrium stabilized zirconia, testing different laser powers, laser speeds, laser strategies, hatch distances and designs. A window of optimized parameters was identified within the study conditions, capable of manufacturing parts with high relative density. In addition, challenges and technical aspects are discussed by analyzing the observed phenomena.

Design and 3D Printing of Interbody Fusion Cage Based on TPMS Porous Structure

To solve the mismatch between the comprehensive mechanical properties of the spinal fusion cage and body, a fusion cage inner hole design method based on controllable TPMS-P to characterize the inner hole structure is proposed to solve the related problems. Firstly, the method of TPMS-P parameterization was used to construct the bionic porous structure model, which was designed as the linear gradual internal porous structure model. Then, we optimized the topology of the obtained porous structure implants to achieve precise control of the overall comprehensive mechanical properties of the fusion cage structure and obtain an optimized model that matched the mechanical properties of the fusion cage. To verify whether the method met the requirements, its simulation model was established. The porous structure was fabricated by selective laser processing, and its properties were tested and analyzed. The results show that its yield strength is 79.83 MPa, which match well with spinal bone tissue.

Comparison of Selective Laser Melted Commercially Pure Titanium Sheet‐Based Triply Periodic Minimal Surfaces and Trabecular‐Like Strut‐Based Scaffolds for Tissue Engineering

This systematic comparison between sheet‐based triply periodic minimal surfaces (TPMS) and strut‐based ordered and disordered lattice topologies offers insights into parametric designs for tissue engineering scaffolds intended as implants. The study explores the effect of topology on compressive properties and in vitro osteoblastogenesis. TPMS‐sheet gyroid and IWP, Voronoi tessellation with different sharpness, and cubic orthogonal lattices are studied. Disparities between the design intent and the as‐manufactured scaffolds, intrinsic to selective laser processing, are considered to ensure that actual porosity and surface area per unit volume, two important factors in tissue engineering, are consistent across the set. Surface analysis reports the presence of microporosity created by partly sintered titanium particles. The TPMS topologies display a stretching‐dominated deformation and the strut‐based disordered ones a bending‐dominated double‐shear failure. Although the trabecular‐like structures exhibit an enhanced compressive behavior when the designed topology is smoothed, they are more prone to printing imperfections with sharper finishes. The in vitro studies reveal that the trabecular sharp topology displays a faster proliferation rate, explained by concavity‐driven cellular growth, but its smooth counterpart promotes a larger differentiation extent, outperforming TPMS, as it is aided by larger pore throats lined with microporosity at the scale of osteoblastic geometric features.