비만아 부모의 돌봄 경험: q 방법론

Three types of laser beam oscillating welding were applied on 5A06 aluminum alloy sheets. The microstructure and mechanical properties of the welded joints were characterized. The formation and elimination mechanisms of welding pores during laser beam oscillating welding was investigated. The results showed that laser beam oscillating welding using linear, circular and infinity paths allow to reduce the porosity of the welded joint when compared to the joint produced without beam without oscillation. Among the three oscillating paths, the infinity mode was the best in terms of decreasing the porosity in the weld and increasing the tensile strength. The decrease in porosity of the fusion zone was associated with the weld shape and the decrease of the depth-to-width ratio of the weld due to the oscillation of the heat source. Laser beam oscillating welding applied to aluminum alloys can be of significant interest to industry to decrease porosity problems typically encountered during laser welding of these materials.

Laser beam oscillating welding of 5A06 aluminum alloys: Microstructure, porosity and mechanical properties

The surface integrity of machined metal components is critical to their in-service functionality, longevity and overall performance. Surface defects induced by machining operations vary from the nano to macro scale, which cause microstructural, mechanical and chemical effects. Hence, they require advanced evaluation and post processing techniques. While surface integrity varies significantly across the range of machining processes, this paper explores the state-of-the-art of surface integrity research with an emphasis on their governing mechanisms and emerging evaluation approaches. In this review, removal mechanisms are grouped by their primary energy transfer mechanisms; mechanical, thermal and chemical based. Accordingly, the resultant multi-scale phenomena associated with metal machining are analyzed. The contribution of these material removal mechanisms to the workpiece surfaces/subsurface characteristics is reviewed. Post-processing options for the mitigation of induced surface defects are also discussed.

Surface integrity in metal machining - Part I: Fundamentals of surface characteristics and formation mechanisms

Laser ablation in liquid (LAL), one of the promising pathways to produce nanoparticles, is used herein for the modification of the abundant biowaste, calcium lignosulfonate (CLS), adorning it with palladium nanoparticles (Pd NPs). The ensuing Pd/CLS nanocomposite, fabricated via a simple stirring method, is deployed for hydrogen storage and environmental cleanup studies; a hydrogen storage capacity of about 5.8 C g-1 confirmed that Pd NPs serve as active sites for the adsorption of hydrogen. Additionally, the novel, sustainable, and reusable nanocomposite also exhibits superior catalytic activity toward the reduction of hexavalent chromium [Cr(VI)], 4-nitrophenol (4-NP), and methylene blue (MB) in an aqueous solution in a short time; the synthesized nanocatalyst could be reused for at least eight successive runs.

Upgraded Valorization of Biowaste: Laser-Assisted Synthesis of Pd/Calcium Lignosulfonate Nanocomposite for Hydrogen Storage and Environmental Remediation.

This paper presents a numerical framework of keyhole-induced porosity formation and methods to suppress porosity in laser beam oscillating welding. Circular and infinity oscillating paths with amplitude of 2 mm and frequencies of 100 Hz and 200 Hz were used. A numerical model for multiple phases, including solid metal, liquid metal and shielding gas is presented using the commercial software FLUENT. An adaptive rotated Gaussian volumetric heat source was developed for analysis of the heat input and temperature distribution during laser oscillating welding. The mechanism of porosity formation caused by keyhole collapse is studied by means of numerical analysis and experiments, and compared to conventional laser welding without oscillation. The numerical simulations were in good agreement with the experimental results. It can be concluded that upon the use of oscillation during welding, porosity decreased and was fully inhibited when using infinity-oscillating path with a frequency of 200 Hz. The developed multi-physics model aids in understanding the dynamics characteristics and keyhole-induced porosity formation during laser beam oscillating welding of 5A06 aluminum alloy.

Modeling and numerical study of keyhole-induced porosity formation in laser beam oscillating welding of 5A06 aluminum alloy

Numerical analysis of heat transfer and fluid flow in swing arc narrow gap GMA welding

Without any presupposed mechanism, a unified three-dimensional model is developed to predict the formation of humping bead in high speed gas metal arc welding, which considers the three phase coupling of solid, liquid and gas and the effect of shear stress exerting on weld pool surface caused by arc plasma. A strong backward fluid flow in weld pool is identified as the major factor for bead hump formation. The generation of thin liquid transition zone and its premature solidification are two conditions responsible for the occurrence of humped weld. In case of low inner contact angle between the liquid metal and workpiece surface, the bead hump is still generated. With increasing welding current, the bead hump can be suppressed.

Modelling of bead hump formation in high speed gas metal arc welding

An infrared visual sensing detection approach for swing arc narrow gap weld deviation

A 3-D finite element model is developed to predict the temperature field and thermally induced residual stress and distortion in laser+GMAW hybrid welding of 6061-T6 aluminum alloy T-joint. And the characteristics of residual stress distribution and deformation are numerically investigated. In the simulation, the heat source model takes into account the effect of joint geometric shape and welding torch slant on the heat flux distribution and a sequentially coupled thermo-mechanical method is used. The calculated results show that higher residual stress is distributed in and surround the weld zone. Its peak value is very close to the yield strength of base metal. Besides, a large deformation appears in the middle and rear part of the weldment.

Numerical Analysis of Welding Residual Stress and Distortion in Laser+GMAW Hybrid Welding of Aluminum Alloy T-Joint

The ultrasonic vibration-assisted laser drilling is a recently emerging/growing new technique, especially in laser drilling. Differently from the previous work reported, this paper proposed to use the ultrasonic vibration (25 kHz) for assisting the millisecond pulsed Nd:YAG laser percussion drilling process to improve the drilling performance. Through comparing the drilled microholes without/using ultrasonic assistance, the influence of ultrasonic vibration on the drilled blind hole morphology/geometry, the hole wall surface roughness, the recast layer microstructure, and the hardness distribution of the heat affected zone for the drilled microhole was analyzed by altering laser pulse energy and/or laser pulse number. It was shown that the ultrasonic vibration incorporated into the laser drilling process might enhance the drilling efficiency in terms of the increase of hole depth and width. However, the drilled hole taper might be decreased via using ultrasonic assistance. Moreover, the ultrasonic vibration might clean the inner hole wall surface, and the microhole morphology/geometry could be improved through using ultrasonic assistance, resulting in a relatively clean and better-profiled hole wall with less defects and smaller taper due to the contribution of ultrasonic assistance. In addition, it was indicated that ultrasonic vibration might also improve the microhole heat affected zone hardness and reduce the inner hole wall surface roughness.

Guoxiang Xu

Papers

Numerical analysis of heat transfer and fluid flow in swing arc narrow gap GMA welding

Modelling of bead hump formation in high speed gas metal arc welding

An infrared visual sensing detection approach for swing arc narrow gap weld deviation

Numerical Analysis of Welding Residual Stress and Distortion in Laser+GMAW Hybrid Welding of Aluminum Alloy T-Joint

Influence of ultrasonic vibration on percussion drilling performance for millisecond pulsed Nd:YAG laser