Selective Laser Welding Research Articles

Selective laser welding in liquid: A strategy for preparation of high-antibacterial activity nanozyme against Staphylococcus aureus

Nanozyme was considered as one of the most promising substitutes for antibiotics, due to the selective catalysis for pathogens. In this work, a high-antibacterial activity SOD-like nanozyme based on hybrid Ag/CeO2 nanocomposite was facilely prepared by using an innovative approach of selective laser welding in liquid. This prepared nanozyme displayed a high antimicrobial effect against Staphylococcus aureus under visible light illumination, the sterilization rate as high as 82.4%, which was 2.93 and 2.99 times higher than those of pure Ag and pure CeO2, respectively. The enhanced antibacterial activity was attributed to the anchoring of Ag nanospheres on the surface of CeO2 nanosheets, which induced the reduction of CeO2 bandgap and boosted the visible light harvesting. Therefore, the charge carriers can be effectively stimulated to produce abundant reactive oxygen species on the Ag/CeO2 nanocomposite via a SOD-like route. This work demonstrated a facile strategy for the preparation of high-antibacterial activity nanozyme, giving it great potential for scalable application in the biomedical and pharmaceutical industry.

An experimental investigation of oil-water flow in a serpentine channel

The co-current oil-water flow in a horizontal serpentine channel is studied experimentally by high-speed imaging. Due to the channel geometry, the flow exhibits curved streamlines, which can induce secondary flows and alter the flow pattern transition boundaries in comparison with those observed in straight channels. This can have important applications in the development of microfluidic mixing devices. The serpentine channel was cut out in a black polypropylene sheet sandwiched between two transparent polypropylene sheets and bonded by selective laser welding. Different flow patterns were generated by changing independently the superficial velocities of the two fluids using a dual-drive syringe pump. Results enable the construction of a flow pattern map, which shows significant differences with the equivalent map obtained for straight microchannels.

Engineered composite polymer sheets with enhanced thermal conductivity

An innovative type of engineered composite polymer sheet with enhanced thermal conductivity is described and tested. The concept is to sandwich a closed-loop serpentine channel, cut out in a polypropylene sheet and containing a self-propelled liquid-vapour mixture, between two sheets of the same material bonded by selective laser welding. Polymer materials are widely used to replace metals in different applications, however sometimes this is not possible because of their poor thermal conductivity. Thin, flexible and low-weight polymer sheets can be advantageous in various aerospace, aircraft and portable electronic applications where the device weight and its mechanical flexibility are crucial. The transient and steady-state thermal response of a prototype engineered polymer sheet was characterised for different heat power levels and spatial orientations. The equivalent thermal conductance, calculated from the surface temperatures at opposite ends of the sheet, increases four to six times in comparison with a composite polypropylene sheet without working fluid.

Thermal Performance of Pulsating Heat Stripes Built With Plastic Materials

A low-cost, flexible pulsating heat pipe (PHP) was built in a composite polypropylene sheet consisting of three layers joint together by selective laser welding, to address the demand of heat transfer devices characterized by low weight, small unit thickness, low cost, and high mechanical flexibility. A thin, flexible, and lightweight heat pipe is advantageous for various aerospace, aircraft, and portable electronic applications where the device weight, and its mechanical flexibility are essential. The concept is to sandwich a serpentine channel, cut out in a polypropylene sheet and containing a self-propelled mixture of a working fluid with its vapor, between two transparent sheets of the same material; this results into a thin, flat enclosure with parallel channels hence the name “pulsating heat stripes” (PHS). The transient and steady-state thermal response of the device was characterized for different heat input levels and different configurations, either straight or bent at different angles. The equivalent thermal resistance was estimated by measuring the wall temperatures at both the evaporator and the condenser, showing a multifold increase of the equivalent thermal conductance with respect to solid polypropylene.

Experimental Investigation of Laser Welding Process in Overlap Joint Configuration

This paper presents an experimental investigation of laser overlap welding of low carbon galvanized steel. Based on a structured experimental design using the Taguchi method, the investigation is focused on the evaluation of various laser welding parameters effects on the welds quality. Welding experiments are conducted using a 3 kW Nd:YAG laser source. The selected laser welding parameters (laser power, welding speed, laser fiber diameter, gap between sheets and sheets thickness) are combined and used to evaluate the variation of three geometrical characteristics of the weld (penetration depth, bead width at the surface and bead width at the interface). Various improved statistical tools are used to analyze the effects of welding parameters on the variation of the weld quality and to identify the possible relationship between these parameters and the geometrical characteristics of the weld. The results reveal that the reached hardness values are similar for all the experimental tests and all welding parameters are relevant to the weld quality with a relative predominance of laser power and welding speed. The effect of the gap is relatively limited. The investigation results reveal also that there are many options to consider for building an efficient welds quality prediction model. Results achieved using an artificial neural network based simplified model provide an indication of the prediction model performances.

Selective laser fiber welding on woven polymer fabrics for biomedical applications

Localized cartilage damage is a common problem for younger patients. This can heal, but often results in a painful condition that requires intervention. A welded-woven three-dimensional polymer fabric has been suggested as a suitable cartilage replacement because such materials closely match the mechanical properties of cartilage. However, such materials fare poorly when evaluated with respect to wear. A microscopic investigation of wear mechanisms showed that it is critical that the fibers not deflect laterally under a normal load. This observation led to the use of a new process for selective laser welding of the surface layers of three-dimensional fabrics in order to improve their wear resistance. Experimental evaluations were made in a pin-on-disc arrangement with a biomimetic loading. All materials used in the studies have previously been used in orthopedic devices or meet the requirements for United States Pharmacopeial Convention (USP) Class VI biocompatibility approval. The wear rates were significantly reduced and the lifespan of the fabrics was markedly improved due to surface welding, making this a viable option for cartilage replacement in vivo.

The influence of pre-heat treatment on laser welding of T-joints of workpieces made of selective laser melting steel and cold rolled stainless steel

The details produced by additive manufacturing have limitations in sizes, if you produce large details then there are large residual stresses. It is also economically advantageous to produce complexly configured details by additive manufacturing and then weld them to rolled or wrought cheaper details. The aim of this study is to investigate the influence of pre-heat treatment on laser beam weldability of Selective Laser Welding (SLM) stainless steel to Cold Rolled (CR) stainless steel. The results of metallographic studies and mechanical tests of produced welds are presented. The results showed that the pre-heat treatment of SLM workpieces affects the welded joint strength. The laser welding mode, keyhole or conduction, affected the microstructure and microhardness of the welds.

МОДЕЛЬ ПРОЦЕССА КРИСТАЛЛИЗАЦИИ С УЧЕТОМ СМЕНЫ ФАЗ ПРИ ФОРМИРОВАНИИ МЕТАЛЛИЧЕСКОГО МАТЕРИАЛА МЕТОДОМ ЛАЗЕРНОГО СПЛАВЛЕНИЯ

Theoretical principles of models of crystallizing bodies being developed are now applied to model the technological process of selective laser welding regarding the description of interaction between “melt - solid body” and determining a body’s buckling owing to emergence of residual stresses in a cooling down work piece. At the same time one of the relevant problems of the research is creating the defining relations which make it possible to describe the interaction between “melt - solid body”. This work considers the application of the known defining relations of the viscoelastic growing body for the hardening metal alloy. The crystallization process takes place in a wide temperature range and is followed by structural changes. A crystallization process is a transition of metal material from a liquid state into the hard one. Within the research, the general statement of the boundary problem of mechanics of the crystallizing body is considered. Realization of the defining relations describing the crystallization process is executed using two problems, i.e. the problem related to the nonuniform controllable cooling of the rod and plate’s cooling from the temperature that is higher than the melting point of the studied material. Thus, numerical models of crystallization of isotropic bodies taking into account phase transfers for linear and two-dimensional statements based on the finite element method have been obtained. The results of applying the finite element method based on the new defining relations do not contradict the physics of the crystallization process and can be applied, when modeling the selective laser welding of metal materials taking into account phase transfer. Images of stress-strain states of the structure have been obtained for each model problem: fields of distribution, stresses and strains. Also, the analysis of the numerical solution convergence is performed, the fulfillment of the natural boundary conditions is analyzed, the temperature fields and the degree of crystallization are obtained within the framework of the study.

Experimental Investigation of Laser Welding Process in Butt-Joint Configurations

This paper presents an experimental investigation of laser welding low carbon galvanized steel in butt-joint configurations. The experimental work is focused on the effects of various laser welding parameters on the welds quality. The investigations are based on a structured experimental design using the Taguchi method. Welding experiments are conducted using a 3 kW Nd:YAG laser source. The selected laser welding parameters (laser power, welding speed, laser fiber diameter, gap between sheets and sheet thickness) are combined and used to evaluate the variation of four weld quality attributes (bead width, penetration depth, underfill and hardness) and to identify the possible relationship between welding parameters and weld physical and geometrical attributes. The effects of these parameters are studied using ANOVA to find their contributions to the variation of different weld characteristics. Plots of the main effects and the interaction effects are also used to understand the influence of the welding parameters. The results reveal that all welding parameters are relevant to bead width (BDW) and depth of penetration (DOP) with a relative predominance of laser power and welding speed. The effect of laser fiber diameter on penetration depth is insignificant. Typical gap-dependent weld shapes show that a small gap results in a narrower and deeper weld. Due to the standard sheared edge, an underfill between 5% and 10% occurs for no-gap experiments. The resulting hardness values are relatively similar for all the experimental tests.

Modeling and optimization of tensile shear strength of Titanium/Aluminum dissimilar welded component

Titanium was successfully welded to Aluminum using laser welding. Laser welding parameters ranges combinations were experimentally determined using Taguchi approach with the objective of producing welded joint with acceptable welding profile and maximizing the tensile shear strength. Tensile shear strength of dissimilar Al/Ti was evaluated as a response function of the selected laser welding parameters and statistical model was developed to describe it. The result indicates that the developed model can predict the responses satisfactorily. Tensile strength of the joints was found to be same as Al base metal. Furthermore the microstructure and microhardness of the joint have been studied.

Application of Taguchi method to optimise dissimilar laser welded components

In this study CO2 Laser Beam Welding (LBW) process was successfully applied and optimised for joining a dissimilar AISI 316 stainless steel and AISI 1008 low carbon steel plates. Laser power, welding speed and defocusing distance combinations were carefully selected with the objective of producing welded joint with complete penetration, minimum fusion zone size and acceptable welding profile. Fusion zone area of dissimilar austenitic stainless steel with ferritic low carbon steel was evaluated as a function of the selected laser welding parameters. Taguchi approach was used as statistical Design of Experiment (DOE) technique for optimising the selected welding parameters in terms of minimising the fusion zone. A mathematical model was developed to describe the influence of the selected parameters on the fusion zone area and to predict its value within the limits of the variables being studied. The result indicates that the developed model can predict the welded bead area satisfactorily.

Using Taguchi method to optimize welding pool of dissimilar laser-welded components

In the present work, CO 2 continuous laser welding process was successfully applied and optimized for joining a dissimilar AISI 316 stainless-steel and AISI 1009 low carbon steel plates. Laser power, welding speed and defocusing distance combinations were carefully selected with the objective of producing welded joint with complete penetration, minimum fusion zone size and acceptable welding profile. Fusion zone area and shape of dissimilar austenitic stainless-steel with ferritic low carbon steel were evaluated as a function of the selected laser welding parameters. Taguchi approach was used as statistical design of experiment (DOE) technique for optimizing the selected welding parameters in terms of minimizing the fusion zone. Mathematical models were developed to describe the influence of the selected parameters on the fusion zone area and shape, to predict its value within the limits of the variables being studied. The result indicates that the developed models can predict the responses satisfactorily.