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The 3D parts printed by the laser powder bed fusion (LPBF) process may have the disadvantages of residual stress, part deformation, and surface roughness. Post-processing is usually required to improve such part characteristics. This study investigated the effects of ultrasonic vibration-assisted compression (UAC) on stainless steel 316L parts fabricated by LPBF. The morphology of the molten pools, microstructure, and hardness by UAC and conventional compression (CC) were evaluated. It was found that UAC was more likely to refine the molten pools than CC. The number of sub-grain boundaries near the compressive surface was increased significantly by UAC. Compared with the CC sample, the UAC-processed specimens showed an increased hardness of 7%.

Selective laser melting (SLM) is one of the widely used metal additive manufacturing techniques. While SLM is able to produce high-quality products, the parameter selection process can be very complicated, especially for magnetic materials in that the iron loss and permeability properties must also be considered, which renders the parameter selecting process more complicated. This research explores the parameter selection process of magnetic material for SLM, which integrates machine and evolutionary algorithms to accurately predict magnetic characteristics, such as iron loss and permeability, and generates suggestions for the process parameters according to practical demands.

Distributed control is the most popular control strategy for controlling numerous slave devices. However, the performance of slave devices is hard to improve because the control algorithm is handled by the commercial slave devices. Therefore, this paper proposes a hybrid control structure that follows the concept of centralized control strategy and handles part of the control loop on the master computer in a distributed control system through EtherCAT fieldbus. In this study, different advanced control methods such as robust control and learning control were applied to handle the position control loop of a scanning mirror system in a selective laser melting (SLM) system with stringent demand of position error around 40 µm based on EtherCAT fieldbus. By designing a proper controller, the experiment results showed that the tracking performance was significantly improved. The tracking error dropped by about 80% after the proposed hybrid control structure was applied. By applying the proposed hybrid control structure, one can improve the high-performance-requirement devices, while reducing the calculation burden of the master computer for other low-performance-requirement devices by retaining the benefit of distributed control.

During green wavelength femtosecond laser ablation, d-band electrons are excited to become free and to participate in the absorption process. The increased electron temperature also induces the density of state shift and causes the gap between the d-band and the Fermi level to expand. The d-band electron transition effect during the laser ablation process causes nonlinear absorption, therefore, it should always be considered during simulations of laser-copper interaction.This study used a single femtosecond laser pulse with a wavelength of 515 nm and a pulse duration of 300 fs to ablate copper with fluence 0.7 - 63 J/cm2. The experimental results were compared with the theoretical results, where a modified Drude-critical point model was adopted to simulate the ablation depth. The modified model considered the electron transition effect and a two-temperature model that assumed both the linear and nonlinear absorption effect. Comparison of the experimental and simulated results revealed that the simulated ablation depth obtained using the nonlinear absorption model was consistent with the experimental results.

The laser powder bed fusion (LPBF) process can produce parts with complex internal geometries that cannot be easily manufactured using a material removal process. However, owing to the different heat transfer efficiencies of a laser melting process, the optimal process parameters are limited to a small range. This study used galvanometric scanner technology and a diffractive optical element (DOE) to build an experimental multi-spot LPBF system. Adjustable characteristics were the angle and the lateral distance between spots. An adjustable multi-spot method was used to modulate the temperature field on the powder bed and enhance the processing quality and throughput. The results from the synchronized three-spot method using different scanning strategies improved the layer surface roughness Ra by 3.2 μm. Moreover, the scanning time was decreased by 38.1% of the single-spot method.

This study compared the experimental and numerical results of femtosecond laser-induced periodic surface structures (LIPSS) produced on copper surface. The experiments were carried out using a fiber laser of duration 300 fs, wavelength 515 nm, and a repetition rate 100 kHz. The periods of LIPSS were obtained by 2D fast Fourier transform analysis of the SEM images, and the depths were measured with an Atomic force microscope. Numerical analysis was performed using a two-dimensional two-temperature model (TTM) along with a modified Drude-critical points model, periodic energy distribution, and the phase change and explosion models for material ablation. The simulation results are in fairly good agreement with the experimental measurements.

A method is proposed for the fabrication of Ag patterns on plastic substrates by printing Ag conductive inks, followed by selective laser sintering (SLS). The printing and sintering processes were realized by a motion control system with a real-time non-uniform rational basis spline (NURBS) curve interpolator. The proposed approach achieves a constant laser scanning speed along the curve path. Ag patterns fabricated by a NURBS curve interpolator and compared to those produced using a linear interpolator. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License .

The selective laser melting (SLM) process, a kind of metal additive manufacturing method, can produce parts with complex geometries that cannot be easily manufactured using material removal processes. With increasing industrial applications, there are still issues such as part quality and productivity that need to be resolved. In this study, maraging steel parts fabricated by synchronized three-spot scanning strategies, i.e., lateral spatial (LS) and spatial inline (SiL), are firstly presented. The LS and SiL represent the three-spot offset direction is perpendicular and parallel to the scanning direction, respectively. A laboratory SLM machine equipped with a fiber laser and three-spot module is used to fabricate the maraging steel parts with two scanning strategies, i.e., LS and SiL. The influence of these scanning strategies on the surface roughness, relative density, hardness, molten pool shapes, and microstructures are investigated. The relative density (~99.02%) and surface hardness (~34.0 HRC) are experimentally found to be higher than the SiL by the LS scanning strategy.

Recent clinical trials showed that short aspirin duration (1 or 3 months) in dual antiplatelet therapy (DAPT) followed by P2Y12 inhibitor monotherapy reduced the risk of bleeding and did not increase the ischemic risk compared to 12-month DAPT in acute coronary syndrome (ACS) patients undergoing percutaneous coronary intervention (PCI). However, it is unclear about the optimal duration of aspirin in P2Y12 inhibitor monotherapy. The purpose of this study was to evaluate the influence of aspirin treatment duration on clinical outcomes in a cohort of ACS patients with early aspirin interruption and received P2Y12 inhibitor monotherapy. From January 1, 2014 to December 31, 2018, we included 498 ACS patients (age 70.18 ± 12.84 years, 71.3% men) with aspirin stopped for various reasons before 6 months after PCI and received P2Y12 inhibitor monotherapy. The clinical outcomes between those with aspirin treatment ≤ 1 month and > 1 month were compared in 12-month follow up after PCI. Inverse probability of treatment weighting was used to balance the covariates between groups. The mean duration of aspirin treatment was 7.52 ± 8.10 days vs. 98.05 ± 56.70 days in the 2 groups (p 1 month. Our results indicated that ≤ 1-month aspirin may be enough in P2Y12 inhibitor monotherapy strategy for ACS patients undergoing PCI.

Laser-induced periodic surface structures (LIPSS) are used for the precision surface treatment of 3D components. However, with LIPSS, the non-normal incident angle between the irradiated laser beam and the specimen surface occurs. This study investigated LIPSS on four different metals (SUS 304, Ti, Al, and Cu), processed on a tilted surface by an s-polarized femtosecond fiber laser. A rotated low spatial frequency LIPSS (LSFL) was obtained on SUS 304 and Ti materials by the line scanning process. However, LSFL on Cu and Al materials was still perpendicular to the laser polarization. The reason for the rotated and un-rotated LSFL on tilted metal surfaces was presented. The electron-phonon coupling factor and thermal conductivity properties might induce rotational LSFL on tilted SUS 304 and Ti surfaces. When fabricating LSFL on an inclined plane, a calibration model between the LSFL orientation and inclined plane angle must be established. Hence, the laser polarization direction must be controlled to obtain suitable LSFL characteristics on a 3D surface.

Neodymium iron boron (NdFeB) magnet that is manufactured using laser powder bed fusion (LPBF) machines has attracted attention since the complex magnetic parts can be directly manufactured. This study used LPBF systems with single and three-beam lasers to fabricate NdFeB components, and the effects of different process parameters (pulsed or continuous wave laser, powder layer thickness, laser power, and scanning velocity) on the magnetic characteristics were investigated. The results from the synchronized three-beam method using the two-zone scanning strategy improved the maximum magnetic energy product by 33.42 kJ/m3, and the processing time was decreased by 38% compared to the single-beam method.

Laser-induced periodic surface structures (LIPSS) is the sub-wavelength periodic nanostructure, which is generally generated by the femtosecond laser. There are two kinds of LIPSS, low spatial frequency LIPSS (LSFL) and high spatial LIPSS (HSFL), and the period size is close and less than half of the laser wavelength, respectively. Fabrication of two-dimensional (2D) LSFL and HSFL on a titanium surface with a linear-polarized femtosecond green laser beam (wavelength 515 nm) and cross-scanning strategies is demonstrated in this study. Four types of LIPSS structures are obtained by controlling the laser fluence, irradiated pulses, and cross-scanning strategies: 1D-LSFL perpendicular to laser polarization with a period of 300&ndash, 360 nm, 1D-HSFL parallel to laser polarization with a period of 55&ndash, 75 nm, 2D-LSFL dot-like structures with a period ~200 nm, and 2D-HSFL net-like structures with a period of 50&ndash, 100 nm.

The ablation of copper, using a 10 GHz burst ultrafast laser with a wavelength of 1030 nm, a pulse duration of 1 ps, a variable total laser fluence, and a number of sub-pulses per burst, is investigated theoretically. A two-temperature model with an extended Lorentz–Drude model for dynamic optical properties is used to simulate the melting and ablation process. Due to the heat accumulation from the preceding pulses, multipulse laser ablation could be advantageous over a single pulse. Moreover, the ablation performance can be maximized by properly selecting the pulse number, separation time, and energy in a laser burst. The numerical result shows that the present prediction is in fairly agreement with existing experimental result. Under the same total laser fluence of 32 J/cm2, a 10 GHz burst laser with an optimized 128 sub-pulse can significantly enhance the ablation depth, 4.2 times that a single pulse does. It is found that the optimized ablation depth is a linear function of the total fluence of ultrafast laser bursts.

Background: P2Y12 inhibitor monotherapy is an alternative antiplatelet strategy in patients undergoing percutaneous coronary intervention (PCI). However, the ideal P2Y12 inhibitor for monotherapy is unclear. Methods and Results: We performed a multicenter, retrospective, observational study to compare the efficacy and safety of monotherapy with clopidogrel versus ticagrelor in patients with acute coronary syndrome (ACS) undergoing PCI. From 1 January 2014 to 31 December 2018, 610 patients with ACS who received P2Y12 monotherapy with either clopidogrel (n = 369) or ticagrelor (n = 241) after aspirin was discontinued prematurely were included. Inverse probability of treatment weighting was used to balance covariates between the groups. The primary endpoint was the composite of all-cause mortality, recurrent ACS or unplanned revascularization, and stroke within 12 months after discharge. Overall, 84 patients reached the primary endpoint, with 57 (15.5%) in the clopidogrel group and 27 (11.2%) in the ticagrelor group. Multivariate adjustment in Cox proportional-hazards models revealed a lower risk of the primary endpoint with ticagrelor than with clopidogrel (adjusted hazard ratio (aHR): 0.67, 95% confidence interval (CI): 0.49&ndash, 0.93). Ticagrelor significantly reduced the risk of recurrent ACS or unplanned revascularization (aHR: 0.46, 95% CI: 0.28&ndash, 0.75). No significant difference in all-cause mortality and major bleeding events was observed between the 2 groups. Conclusions: Among patients with ACS undergoing PCI who cannot complete course of dual antiplatelet therapy, a significantly lower risk of cardiovascular events was associated with ticagrelor monotherapy than with clopidogrel monotherapy. The major bleeding risk was similar in both the groups.

In this study, novel annular microstructures on metal surfaces were fabricated with a femtosecond laser beam propagating through a microhole and irradiating on the surface of stainless steel SUS 304. The results showed that, with the use of a linearly polarized femtosecond laser beam (800 nm, 120 fs) irradiating through a microhole of diameter 80~100 μm and depth 800 μm, annular microstructures with a period of 4~8 μm were formed. Differing from the laser induced periodic surface structure (LIPSS), the formed annular microstructures are independent of laser polarization. This study speculates that this formation mechanism is due to the interference between the incident laser beam and the reflected beams from the microhole walls.

The joining capability of metal cellular structures fabricated using the additive manufacturing (selective laser melting (SLM)) method is investigated herein. The metal cellular structures are composed of sub-millimeter holes and internal pores. The direct joining of 3D-printed ABS-M30i thermoplastic parts to metal cellular structures by ultrasonic welding is demonstrated. The SLM-fabricated structures comprised of partially melted powders provide micro-scale roughness, which enhances the micro-mechanical interlocking between joining parts. A shear strength 17.7 MPa and normal tensile strength of 15.2 MPa were obtained, up to 55 and 48% of ABS-M30i ultimate tensile strength, respectively. Moreover, normal tensile plastic strength up to 86% of the shear strength was obtained.

Summary: The proportion of people whose age exceeds 65 years is growing rapidly throughout the world and the prevalence of metabolic syndrome (MetS) is increasing among older adults. MetS had a two-fold increased risk for cardiovascular (CV) disease. Most patients with MetS exhibit atherogenic dyslipidemia, which includes elevated triglycerides (TG) and reduced high-density lipoprotein cholesterol (HDL-C). Therefore, physicians are advised to recognize the presence of dyslipidemia in elderly patients with MetS and provide appropriate therapy to reduce CV risk. Lifestyle modification is the initial step for treating dyslipidemia. For older adults with MetS who cannot attain treatment goals by lifestyle modification, pharmacological intervention is usually considered. Treating dyslipidemia in older adults with MetS requires knowledge of the benefits and adverse effects of various pharmacologic agents in the presence of possible multiple comorbidities. The purpose of this article is to review the evidence for recognition and management of atherogenic dyslipidemia in elderly individuals with MetS. Keywords: dyslipidemia, metabolic syndrome, older adults

This study investigated laser-induced periodic surface structures (LIPSS) produced on a tilted stainless steel surface with a p- and s-polarized laser beam. Different types of LIPSS on the tilted surface were compared, and the direct fabrication of one-dimensional rotational low spatial frequency LIPSS (LSFL) on a tilted surface using a stationary s-polarized laser beam was demonstrated. In addition, by changing the laser scanning strategy, an area pattern covered with lightning-like structures and even the two-dimensional structures fabricated on the tilted surface we demonstrated. The evolution of LSFL at different line scanning regions was obtained, and the possible reason for the rotation of LSFL on tilted surfaces was presented.

This study proposes an approach for determining the lateral displacement distance between adjacent scanning paths for femtosecond laser ablation of a uniform crater profile on stainless steel with a controllable ablation depth. The first step performs the ablation experiment and measures the ablation depth. The second step calculates the laser intensity accumulation factor according to different lateral displacement distances. The required lateral displacement distance needed to achieve the design ablation depth can be obtained based on the experimental data.

Thermal ablation of a copper foil surface by a single femtosecond laser pulse of duration 120 fs and wavelength 800 nm was investigated herein both theoretically and experimentally. A 1D two-temperature model with temperature-dependent material properties was considered, including the extended Drude model for dynamic optical properties. The rapid phase change and phase explosion models were incorporated to simulate the material ablation process. The simulated ablation depths agree well with the experimental measurements for the high laser fluence regime ranging from 6.1 to 63.4 J/cm2.

Ultrafast laser-induced melting of silver nanoparticles (NPs) using a femtosecond laser pulse is investigated both theoretically and experimentally. The sintered Ag structure fabricated from printed Ag NP ink using femtosecond laser (1064 nm, 300 fs) irradiation is experimentally studied. A two-temperature model with dynamic optical properties and particle size effects on the melting temperature of Ag NPs is considered. The rapid phase change model is incorporated to simulate the Ag NPs’ ultrafast laser-induced melting process, and a multi-shot melting threshold fluence predicted from the simulated single-shot melting threshold is developed.

The femtosecond laser-induced periodic surface structure (FLIPSS) is a one-step process for fast fabrication of periodic-like nanostructures on different materials and enables a new range of functionalized surface processing [1]. In our pervious study, ablation of a copper foil surface by femtosecond laser pulse (800 nm, 120 fs) was investigated theoretically and experimentally [2]. The simulated ablation depths agree well with the experimental measurements.