There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Additive manufacturing of metallic components – Process, structure and properties

Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting....

Polymers for 3D Printing and Customized Additive Manufacturing

In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).

Laser Material Processing

Monitoring of greenhouse gases is essential to understand the present state and predict the future behavior of greenhouse gas emissions. Carbon dioxide (CO2) is the greenhouse gas of most immediate concern, because of its high atmospheric concentration and long lifetime. A fiber-optic Mach–Zehnder interferometer (MZI) is proposed and demonstrated for the laboratory-scale monitoring of carbon dioxide concentration. The interferometric sensor was constructed using a small stub of hollow-core photonic crystal fiber between a lead-in and lead-out standard single mode fiber, with air-gaps at both interfaces. At room temperature and atmospheric pressure, the sensor shows the sensitivity of 4.3 pm/% CO2. The device was packaged to demonstrate the laboratory-scale leakage detection and measurement of CO2 concentration in both subsurface and aqueous environments. The experimental study of this work reveals the great potential of the fiber-optic approach for environmental monitoring of CO2.

https://www.mdpi.com/1424-8220/19/15/3357/pdf

Monitoring of Carbon Dioxide Using Hollow-Core Photonic Crystal Fiber Mach-Zehnder Interferometer.

Additive manufacturing (AM) has changed the entire manufacturing enterprise by offering unique features for the fabrication of complex-shapes with superior mechanical properties. In the last decades, through an exponential advancement, AM has been promoted from a prototyping to a series and mass production platform. Like all conventional techniques, quality assurance procedures/tools are of the utmost importance in aiding manufacturers in quality management and certification. For this purpose, in-line melt pool monitoring devices, installed in laser-based AM systems, provide vital real-time information about process characteristics, implicitly or explicitly leading toward understanding the quality of printed parts. This research aims to develop a defect-detection platform using in-situ monitoring of light intensity emitted from the melt pool of laser powder bed fusion (LPBF) to detect pores initiated from the lack of fusion phenomenon. This platform is driven by correlating disturbances in the light intensity emitted from the melt pool to actual pores identified through a post-processing micro-computed tomography (CT) scanning. Two sets of experiments were devised: one with embedded micro-voids to purposefully mimic the lack of fusion in printed parts composed on Hastelloy X to assess the sensor response and develop the analysis algorithm. The second set was included printed parts with stochastic/randomized distributions of pores to evaluate the proposed approach. The recorded data were extracted from an Absolute Limits algorithm and were analyzed offline through image processing. Next, the printed samples were CT scanned, and the data from both steps were analyzed by the segmentation method and confusion matrix to examine the correlation. The results of the intentionally seeded defects demonstrated that voids larger than 120 µm were detectable through the collected photo-diodes signals. The evaluation matrices to validate stochastic/randomized distributions of pores also showed that for two sets of process parameters with a high laser power of 200 W, hatching distance of 150 and 90 µm, and process speed of 1000 and 1500 mm/s, the sensor prediction from randomized defects is about 70.14 ± 2.24% and 72.82 ± 1.39%, respectively. However, for the low laser power cases with laser power of 100 W, hatching distance of 90 µm, and process speed of 1000 mm/s, the correlation was less than 30%.

Development of a defect-detection platform using photodiode signals collected from the melt pool of laser powder-bed fusion

This article addresses experimental-based modeling of the powder injection laser cladding process. An accurate model for the process is essential for controller design and process automation. There are few dynamic and static models for the process, however, due to the limitations and intensive numerical calculations, their application to real-time process control are not practical. Two model structures, the Hammerstein–Wiener model and Elman recurrent neural network are implemented to identify the laser cladding dynamic model. The type of experiments and collected data are explained, and model predictions for different and unseen data are compared with experimental results. It is shown that the Hammerstein–Wiener approach can more accurately describe the transient response of the process. Results are promising and show that experimental-based models can effectively be used in laser cladding processes.

Application of experimental-based modeling to laser cladding

A novel and compact interferometric refractive index (RI) point sensor is developed using hollow-core photonic crystal fiber (HC-PCF) and experimentally demonstrated for high sensitivity detection and measurement of pure gases. To construct the device, the sensing element fiber (HC-PCF) was placed between two single-mode fibers with airgaps at each side. Great measurement repeatability was shown in the cyclic test for the detection of various gases. The RI sensitivity of 4629 nm/RIU was demonstrated in the RI range of 1.0000347–1.000436 for the sensor with an HC-PCF length of 3.3 mm. The sensitivity of the proposed Mach–Zehnder interferometer (MZI) sensor increases when the length of the sensing element decreases. It is shown that response and recovery times of the proposed sensor inversely change with the length of HC-PCF. Besides, spatial frequency analysis for a wide range of air-gaps revealed information on the number and power distribution of modes. It is shown that the power is mainly carried by two dominant modes in the proposed structure. The proposed sensors have the potential to improve current technology’s ability to detect and quantify pure gases.

Hollow-Core Photonic Crystal Fiber Mach–Zehnder Interferometer for Gas Sensing

In this article, a laser processing protocol for heat treatment of micro-scale printed graphene patterns is developed, and the results are compared with the counterpart results obtained by the conventional heat treatment process carried out in a furnace. A continuous-wave Erbium fiber laser is used to enhance electrical properties of the aerosol-jet printed graphene patterns through removing solvents and a stabilizer polymer. The laser power and the process speed are optimized to effectively treat the printed patterns without compromising the quality of the graphene flakes. Furthermore, a heat transfer model is developed and its results are utilized to optimize the laser treatment process. It is found that the laser heat treatment process with a laser speed of 0.03 mm s −1 , a laser beam diameter ~50 μm, and a laser power of 10 W results in pure graphene patterns with no excessive components. The ratio of D to G bands ( ) II / DG in Raman graph of the laser treated pure graphene, which is an indicator of the level of the active defects in graphene structures, is 0.52. The laser treated pure graphene structures also have a C/O ratio and an electrical resistivity of ~4.5 and 0.022 Ω cm, respectively. These values are fairly comparable with the results of samples treated in a furnace. The results suggest that the laser processing has the capability of removing stabilizer polymers and solvents through a localized moving heat source, which is preferable for flexible electronics with low working temperature substrates.

http://iopscience.iop.org/article/10.1088/0022-3727/48/37/375503/pdf

Ehsan Toyserkani

Papers

Monitoring of Carbon Dioxide Using Hollow-Core Photonic Crystal Fiber Mach-Zehnder Interferometer.

Development of a defect-detection platform using photodiode signals collected from the melt pool of laser powder-bed fusion

Application of experimental-based modeling to laser cladding

Hollow-Core Photonic Crystal Fiber Mach–Zehnder Interferometer for Gas Sensing

Laser heat treatment of aerosol-jet additive manufactured graphene patterns