Laser forming is an emerging manufacturing process capable of producing either uncomplicated and complicated shapes by employing a concentrated heating source. The heat source movement creates local softening, and a plastic strain will be induced during the rise of temperature and the subsequent cooling. This contactless forming process may be used for the simple bending of sheets and tubes or fabrication of doubly-curved parts. Different studies have been carried out over recent years to understand the mechanism of forming and predicting the bending angle. The analysis of process parameters and search for optimized manufacturing conditions are among the most discussed topics. This review describes the main recent findings in the laser forming of single and multilayer sheets, composite and fiber-metal laminate plates, force assisted laser bending, tube bending by laser beam, the optimization technique implemented for process parameters selection and control, doubly-curved parts, and the analytical solutions in laser bending. The main focus is set to the researches published since 2015.

Recent Advances in the Laser Forming Process: A Review

Laser bending is one of the thermal forming processes which in each pass of it, the temperature of sample increases at heat-affected zone during irradiation time considerably and then it cools to n...

Through-depth residual stress measurement of laser bent steel–titanium bimetal sheets:

Personal protective equipment, particularly facemasks, has an essential role in reducing the transmission risk of airborne infections from person to person. Thus, this study aimed to develop a hydrophobic facemask filter with antiviral and antibacterial effects to prevent the transmission of SARS-CoV-2 or other infectious pathogens that spread through the respiratory system. In this study, the melt-blown surface was modified with poly(acrylic acid) (PAA) by photoactivated graft polymerization and copper nanoparticles (CuNPs) were immobilized on the PAA-grafted melt-blown surface. The surface morphology and composition of the coated melt-blown surface were characterized by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, and Fourier transform infrared spectroscopy. CuNPs-coated melt-blown surfaces with hydrophobic nature showed inherent antiviral and antibiofilm formation activities against SARS-CoV-2 and Staphylococcus aureus and Escherichia coli, respectively. A more than 98% bacterial reduction and a significant decrease in the N and RdRp RNA titer were achieved following direct contact with the coated melt-blown surface. The standard sterilization processes, including autoclaving and UV irradiation, did not affect the antibacterial efficacy or the biocompatibility of the coated mask with dermal fibroblasts. The incorporation of CuNPs onto a melt-blown surface was not detrimental to the textile structure, although it caused a slight decrease in the air permeability, breathability, and tensile strength. The coated sample showed less than 4 ppm copper ion release during each of the 10 laundry cycles, and more than 50% of the initial copper content remained after the 10th laundry cycle, demonstrating the strong adhesion of CuNPs to the melt-blown surface. The facile processability of the CuNPs-coated hydrophobic mask filter with virus inactivation ability and reusability ensure its role in preventing the widespread transmission of viral infections through respiratory aerosols. 

Copper-Nanoparticle-Coated Melt-Blown Facemask Filter with Antibacterial and SARS-CoV-2 Antiviral Ability

In this study, electromagnetic-force-assisted laser bending and straightening process is proposed, in which the external force is applied by a controlled force generated by an electromagnet. The process was found suitable for laser assisted bending and straightening. The experiments as well as simulations indicated that a large bend angle can be obtained by controlling the electric current and air gap between electromagnet and workpiece. A good agreement between simulation and experimental results was obtained. Edge effect was very less in case of strips that got attached with the magnet during laser bending. The spring-back effect was very less at high laser power, low scan speed and high current. The laser irradiated region had higher micro-hardness than base material. The micro-hardness of laser irradiated region depended on laser power, scan speed and magnetic force of attraction. Straightening of mechanically bent strip was also carried out. Results indicate that use of an electromagnet with laser irradiation is an effective way to straighten bent strips.

Electromagnetic-Force-Assisted Bending and Straightening of AH36 Steel Strip by Laser Irradiation

Prediction of bending behavior for laser forming of lime coated plain carbon steel using finite element method

Laser forming is a comparatively recent technique which has been developed to shape metal components. It has also been applied to the forming of composite materials. In this process, thermal stresses are produced in the sheet metal by irradiating the surface of the sheet using a controlled defocused laser beam. This causes the sheet to bend, usually, towards the side of the sheet which is exposed to laser irradiation. The laser beam power, scan speed, beam size, and number of laser passes determine the shape of the final product. Laser forming is different when compared to the traditional forming techniques like bending, drawing, pressing, stamping, etc. in the sense that it is a non-contact technique. Hence, the advantage of the laser forming process for a small batch of components is its flexibility and reduction in cost and time. Research to-date on laser forming has been done theoretically, experimentally, and numerically. Effect of almost all the parameters—geometric, material and energy—affecting the shape of final product have been studied at length. Some experimental studies have been carried out using surface coating like graphite on the face of the sheet where the laser is passed. However, there are limited studies on the effect of different surface coatings on laser forming of sheets. Hence, the objective of the present work is to investigate the effect of different surface coatings on the laser forming of metal sheets. In the present work, mild steel is selected as the work material. Two different coatings, viz., commercial lime and cement are selected. First, the effect of the coatings is studied on simple line bending operation. The experiments are carried out at different values of laser power and laser scan speed for each coating. The results are compared with the results obtained from line bending of uncoated specimen. It is found that the cement coating performs better than the lime coating. Next, the effect of coatings is investigated on laser forming of complex shapes like dome and bowl shaped surfaces. For each coating the experiments are carried out at different values of laser power. It is found that the cement coated specimens can undergo more deformation than the lime coated specimens.

https://www.springer.com/cda/content/document/cda_downloaddocument/9788132223511-c2.pdf?SGWID=0-0-45-1501768-p177302083

Laser Forming of Mild Steel Sheets Using Different Surface Coatings

The present study focuses on the component transfer from one liquid phase to another liquid phase, commonly known as the extraction process, performed in a microchannel in the presence of spontaneous interfacial convection, driven by either an interfacial tension gradient or an applied external electric field. Marangoni instability occurs as a result of a lateral gradient of interfacial tension existing along the interface of the two fluids. Nonequilibrium phenomena associated with factors such as temperature imbalance, a nonuniform distribution of surface-active components at the interface, evaporation, etc. can lead to the interfacial Marangoni instability. In the present study, first, we have explored temperature gradient driven Marangoni instability, which deforms the interface with significant acceleration and induces local convective mass transfer along with the conventional diffusion mode. Next, we have explored the same phenomenon in the presence of an external electric field, which can also deform the liquid-liquid interface almost instantaneously to a considerable extent. The relative strength of the mass transfer rate for different cases, such as temperature driven instability, in the presence of uniform and nonuniform electric fields has been reported in detail. It has also been observed that, due to the larger mass transfer area, the annular flow offers an enhanced rate of mass transfer compared to the stratified flow. Additionally, this article reports that the nonuniform electric field could influence the process of interfacial instability more strongly compared to the uniform electric field. The effect of the nonuniform electric field with different spatial periodicity on the extraction process has been studied in detail.

Efficient microextraction process exploiting spontaneous interfacial convection driven by Marangoni and electric field induced instability: A computational fluid dynamics study

The advent of COVID-19 pandemic has made it necessary to wear masks across populations. While the N95 mask offers great performance against airborne infections, its multilayered sealed design makes it difficult to breathe for a longer duration of use. The option of using highly breathable cloth or silk masks especially for a large populace is fraught with the danger of infection. As a normal cloth or silk mask absorbs airborne liquid, it can be a source of plausible infection. We demonstrate the chemical modification of one such mask, Eri silk, to make it hydrophobic (contact angle of water is 143.7°), which reduces the liquid absorption capacity without reducing the breathability of the mask significantly. The breathability reduces only 22% for hydrophobic Eri silk compared to the pristine Eri silk, whereas N95 shows a 59% reduction of breathability. The modified hydrophobic silk can repel the incoming aqueous liquid droplets without wetting the surface. The results indicate that a multilayered modified silk mask to make it hydrophobic can be an affordable and breathable alternative to the N95 mask. © 2021 American Chemical Society.

Nanometer-Thick Superhydrophobic Coating Renders Cloth Mask Potentially Effective against Aerosol-Driven Infections

In the present work, the effect of different surface coatings, namely lime and cement, on laser forming of mild steel sheets is studied. The performance of the coatings is evaluated at different values of laser power and scan speed. It is found that the cement coating leads to higher deformation. This means that in case of line heating of sheets cement coating leads to higher bend angles. For other complex shapes for e.g. bowl or dome it leads to higher heights.

/pdf/effect-of-different-surface-coatings-on-laser-forming-of-1ofvegi8ip.pdf

Effect of different surface coatings on laser forming of mild steel sheets

Nonlinear solid friction between the gel matrix and DNA molecules inhibits the motion of DNA during electrophoresis. We report enhanced mobility of the DNA using external noise to alleviate the effect of solid friction. In presence of noise, the mobility of 1 kbp DNA increases ~ 86% compared to the conventional gel electrophoresis, whereas the increment is more than ~113 % for 6 kbp DNA. At low power of the noise, super Arrhenius kinetics suggest the collective behavior of the activated motion of DNA molecules. Stochastic simulation following modified Langevin equation with the asymmetric pore size distribution of the agarose gel successfully predicts the mobility of DNA molecules and estimates the huge frictional force at the DNA-gel matrix interface.

Noise Activated DNA Translocation for Faster Screening

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