Bead Appearance Research Articles

Feedback and Ballooning Instabilities in the Magnetosphere‐Ionosphere Coupling

AbstractA unified model for the feedback and ballooning instabilities in the magnetosphere‐ionosphere (M‐I) coupling is developed by means of the reduced magnetohydrodynamic and two‐fluid equations, involving the local current closure and the ionospheric conductivity change in a scale of auroral fine structures, self‐consistently. In a low pressure gradient case, the Alfvén harmonics are destabilized through the feedback mechanism, while the ballooning instability appears if the magnetospheric pressure gradient exceeds a critical value. Transition of the dominant instability between the feedback and ballooning modes is brought by change of the normalized pressure gradient or the convection electric field in the magnetosphere. The obtained results imply a variety of appearance of auroral arcs and beads in the M‐I coupling system.

An Experimental Test and Optimization of Friction Stir Welding Process for AA6082 By using GRA

Friction stir welding (FSW) is a type of joining process, it uses solid state welding method, also it is widely used in same type and different types of welding like Al, Mg, Cu, Ti, and their alloys. In this study, friction stir welding of two aluminum alloys AA6082 is done with many sets of tool rotation speed, feed and axial force. In this experimental work FSW process was carried out for AA 6082 and optimization of that FSW process parameters were find out for maximum tensile strength values. Taguchi’s L4 orthogonal array was utilized for three parameters – tool rotational speed (TRS), traverse speed (TS), and axial force (AXF) with two levels. Several optimization was carried out with Taguchi method of grey relational tests. During the investigation obtained highest tensile strength value fourth sample 60.887 N/mm2 and lowest hardness strength value second sample 31HRB and bead appearance found very best surface occurred fourth test plates at the same time angle distortion observed very fine in the fourth test plate. The result was calculated for both ultimate tensile strength and hardness value. The expected grey relational grade was shifted from 0.704 to 0.792, it was the highest value received throughout this experimental results. It was mentioned that the multi-responses of FSW process was improved with this method.

Comparative study on the microstructures and properties of wire+arc additively manufactured 5356 aluminium alloy with argon and nitrogen as the shielding gas

This research explored the influences of shielding gases on the appearance of weld beads and the microstructures and mechanical properties of thin-wall samples using conventional gas metal arc welding as the heat source by using 5356 aluminium alloy welding wire as the raw materials and nitrogen (N2) and argon (Ar) as the shielding gases. The results showed that under the same parameters and after mono-layer single-bead welding was performed using N2 as the shielding gas, the bead height was higher, the bead width was narrower, and the penetration depth was shallower. The grain size of the thin-wall sample protected by N2 was 43.5–47.8 % smaller than that obtained under Ar protection. However, the sample protected by N2 contained many flaky nitrides, whose presence improved the microhardness but reduced the ultimate tensile strength (UTS) and plasticity. The average UTS of the thin-wall sample protected by N2 in the horizontal direction was 82.5 % of the UTS of the samples shielded using Ar. However, the average elongation in the horizontal direction of the samples protected by N2 was 18.6 % of that of the samples shielded by Ar. The mechanical properties of the sample protected by argon were more excellent.

Study of high-speed GMAW assisted by compound external magnetic field

A magnetic generating device was proposed to regulate the transverse and backward flow of weld pool for high-speed gas metal arc welding (GMAW). Compound external magnetic field (EMF) was simulated to verify the feasibility of designed magnetic generating device. The highest welding speed with good weld bead appearance was 1.7 m/min with the wire feed speed of 9.0 m/min when compound EMF was applied. The effect of the compound EMF on the arc and droplet motion was studied by image acquisition system. The suppression mechanism of the compound EMF on the undercut defect of high-speed GMAW was analyzed. The mechanism of the influence of the applied compound EMF on different welding speeds and welding currents was studied by the application of the compound EMF-assisted welding process, and low-cost, high-quality, and high-speed welding technology was realized.

Application of Computed Tomography in the analysis of the manufacture of eye beads technique

In the study of archaeological glass beads, the manufacturing process of eye beads is of great significance and value. This is a focused research investigation about eye beads. Based on previous research published 2019 [3], one of the eye beads unearthed in Shampula Cemetery was proved to be embedded manufacture. In this paper, several kinds of eye beads were studied and compared. With the results, a new manufacturing process for certain eye beads is discovered and compared by X-ray Computed Tomography (CT) technique. The shapes of air bubbles, the distribution of the air bubbles, and especially the direction of the eye part in the beads, were analyzed by CT. Two kinds of pattern of eyes were discovered based on the CT results and the appearance of specific eye beads. Thus, the manufacturing process of eye beads can be divided into two types. The difference between the two types is the placement direction of the eye parts. In addition, the manufacturing process of eyes produced either raised or embedded appearances of the eye beads. The squeezing direction was found to be perpendicular to the long axis of the elliptical bubbles in the bead body through the air bubble shape of the three samples producing raised eye beads and embedded eye beads which appear like human eyes. Analysis of the technological factors produced insights into the beads-making process within a historical context so as to provide better data for the origin of this particular batch of eye beads.

On the Role of Tool Tilt Angle on Friction Stir Welding of Aluminum Matrix Composites

The current study investigates the influence of tool tilt angle (TTA) on the mechanical strength of friction stir welded aluminum matrix composite (AMC). Aerospace-grade AA6092/ 17.5 SiCp- T6 plates of 6 mm thickness have been welded at different TTA of 1, 2 and 3 with fixed tool rotational speed of 1000 rpm and tool traverse speed of 1 mm/s. A conical pin-shaped tool of H13 tool steel having a hardness of 56 HRC has been used with a tool dimension of 16 mm shoulder dia., 6 mm pin root dia., and 4 mm tool tip dia. In order to study the microhardness, tensile strength, fracture toughness and fracture behavior of the joint the weld bead appearance, macrostructure and microstructure have been investigated. Results show that with an increase in TTA, the excessive flashing has been occurred in the weld bead and also affects the ratio of shoulder influenced region and pin influenced region in the macrostructure. The presence of detrimental Al2O3 has been found inside the weld at TTA of 3. It has found that the mechanical property of the joint increases as TTA increases from 1 to 2 and thereafter it decreases. The fractographic analysis shows a mixed-mode of failure for all the samples except for the TTA of 3 where it shows brittle failure. Overall the study suggests the implication of 1 to 2 TTA to get a sound weld of this particular type of AMC.

Halochromic Polystyrene Nanofibers Obtained by Solution Blow Spinning for Wine pH Sensing.

Colorimetric sensors developed by the solution blow spinning (SBS) technique have a rapid response to a variation in different physicochemical properties. In this study, polystyrene nanofibrous (PSNF) mats containing the bromothymol blue (BTB) indicator were obtained by SBS for the pH sensing of wine sample. The incorporation of the indicator did not promote changes in fiber diameter but led to the appearance of beads, allowing for the encapsulation of BTB. The halochromic property of BTB was retained in the PSNF material, and the migration tests showed that the indicator mats presented values below the maximum acceptable limit (10 mg dm−2) established by EU Commission Regulation No. 10/2011 for foods with an alcohol content up to 20%. The present study opens the possibility of applying nanostructured materials to innovative food packaging which, through nanosensory zones, change color as a function of the food pH.

Prediction of effects of process parameters and thermo-mechanical simulation of GMAW process for welding of AISI 430 steel

The present study is focused on welding of AISI 430 steel using AISI 309L wire rod using gas metal arc welding process. The welding voltage, welding speed, wire feed rate and gas flow rate are considered as input process parameters and their ranges are found out for good appearance of weld bead. The experiments are conducted using central composite design matrix and weld bead geometry parameters like bead height, bead width and bead penetration and mechanical properties like tensile strength and hardness are measured. The mathematical models for bead geometry parameters and mechanical properties are developed and the adequacy is checked using analysis of variance. The effects of process parameters on the bead geometry parameters, mechanical properties and microstructure are found out. The thermo-mechanical simulation is carried out using ANSYS simulation software to predict the temperature and stresses distribution in the weldment.

Research and Development of a Novel TIG Welding Torch for Joining Thin Sheets

This paper aims to develop a novel tungsten inner gas (TIG) welding torch in order to join thin sheets efficiently. Using a narrowing nozzle (constricted nozzle) inside a conventional TIG torch can critically improve the position accuracy of the tungsten electrode and also the arc plasma characteristics and heat input density. In order to evaluate the efficiency of this new torch, weld bead appearance and cross-section images were examined by an optical microscope, scanning electron microscope (SEM), and electron back scatter diffraction patterns (EBSD). The results showed that in all cases, the weld bead profile was stable without undercut and burn-through. Full penetration weld was seen. The width of weld bead on the bottom surface was increased much in comparison to conventional TIG welding. However, the results from SEM and EBSD images indicated that in the case of low welding current, the blowholes were found out on the side of the thinner material (SS400). The penetration of SUS430 material to SS400 material was not good. It seems that no fusion of SUS430 material to SS400 at the bottom surface can be seen. Meanwhile, no blowholes were seen in the case of high welding current. The penetration was better, and the fusion was reached on the bottom surface.

Superhydrophobic membrane by hierarchically structured PDMS-POSS electrospray coating with cauliflower-shaped beads for enhanced MD performance

The construction of superhydrophobic surfaces for improving the anti-wetting performance of membrane distillation (MD) is still an on-going challenge. In this study, we fabricated a hierarchically structured electrospray coating with cauliflower-shaped beads by adjusting polymer chain entanglement. A series of poly(dimethylsiloxane)-polyhedral oligomeric silsesquioxane (PDMS-POSS) nanocomposites were synthesised by the chemical incorporation of rigid V-POSS into a flexible PDMS matrix. With the optimal incorporation content, we successfully obtained a homogeneous molecular-level dispersion of V-POSS into PDMS matrix, forming a more branched yet looser network, leading to the appearance of cauliflower-shaped beads when electrosprayed with polyvinylidene fluoride (PVDF). Moreover, the integrated V-POSS and its self-crosslinked clusters contributed to the formation of convexities and protrusion on the beads. This optimal coated membrane with PVDF as substrate exhibited superhydrophobicity, as evidenced by a water contact angle of ~166°; which resulted from the rough surface with well-defined ridges and valleys, composed of irregular beads. Once applied in direct contact MD (DCMD) processes, it demonstrated stable performance and high salt rejection (>99.9%) during the 200 h treatment of synthetic seawater containing 0.1 mM sodium dodecyl sulfate (SDS), along with great robustness under harsh feed condition containing 0.3 mM SDS, showing good applicability for preventing wetting.

Court Beads: Manchu Rank Symbols in the Náprstek Museum

Abstract Court beads worn with formal dress represented one of the symbols of social standing of the Qing dynasty aristocracy and officialdom. The appearance of court beads and material used for their production were prescribed in the 18th century encyclopaedic work The Illustrated Regulations for Ceremonial Paraphernalia of the Imperial Court. Nowadays, court beads are found in antiquities markets and in museum collections. The Náprstek Museum in Prague also keeps a small collection distinguished from the several tens of pieces of Qing dynasty formal dress, dress accessories, and other signs of social rank, the number of these items are surprisingly few. In order to answer the question about the scarcity of the objects, the origin of the collection has been studied.

A Study to Improve GMAW-MIG High-Speed Weldability

The poor arc stability of stainless steel GMAW-MIG welding makes high speed welding impossible. In this study, TiO2 powder with low ionization potential was applied in advance to carbon steel and STS based materials, and as welding progressed, good arc stability and excellent bead appearance was observed, even for 120cpm high speed welding. Analysis of the welding waveform showed that as the output welding current increased, the output welding voltage did not change, and the welding resistance decreased. Analysis of the cross section of the weld showed that the height of the bead decreased, and the bead width and penetration depth increased. Photographs of the arc indicated the length of the arc increased and the stability of the arc improved. Chemical component analysis of the weld metal determined that the Ti content increased by 0.004% and the other components were similar to conventional levels. The tensile strength and impact toughness of the weld metal remained at the same level as before. Key words: GMAW-MIG, 100%Ar, High-speed welding, Active flux, TiO2, Stainless steels

Optimization techniques used in gas tungsten arc welding process – A review

Optimization techniques are widely used tools in the engineering sector and suitable to all the fields of mechanical engineering. Welding is an important manufacturing process and its parameter optimization is highly focused on getting optimal results. Gas Tungsten Arc Welding (GTAW) is the suitable arc welding process joining variety of the engineering materials. This process has various parameters like welding current, speed, arc length, shielding gas and gas type etc. A lot of attempts were made by the researchers to get an optimal outcome like the appearance of the weld bead and tensile strength etc… In this article, various optimization techniques used in GTAW process are discussed. The widely used optimization methods, GTAW parameters and the outcomes are discussed from the literature. These result will help the researchers to avoid selecting same techniques and parameters. This paper will give guidelines to the researchers to focus on new studies.

Investigation on the mass transfer control, process stability and welding quality during underwater pulse current FCAW for Q235

Pulse current technology is employed to adjust the mass transfer and improve the welding quality, and effects of the pulse frequency (f), load duty cycle (D) and peak current (Ip) on the droplet were analyzed based on Taguchi method during underwater flux-cored arc welding (FCAW). In underwater wet pulse FCAW (FCAW-P), the mass transfer process is observed and the interaction mechanism of the pulse current on the droplet is investigated using in-situ X-ray imaging method. Within one pulse period, the decreasing repulsive force and the increasing gravitational assist the droplets detach from the wire or touch with the welding pool at the end of the peak pulse duration and reduce the droplet detachment angle, improving the mass transfer stability and thus increasing the arc stability and ameliorating the bead appearance. The stable mass transfer process and welding arc increase the effective heat input, and thus decreases the acicular ferrite and increases the pro-eutectoid ferrite in the bead. The hardness distribution and the tensile strength of the beads deposited in conventional and pulse current underwater wet FCAW are identical basically, demonstrating the application of pulse current technology does not deteriorate the mechanical properties.

Effect of shielding gas composition and welding speed on autogenous welds of unalloyed tungsten plates

Tungsten usually exhibits poor weldability and marked brittleness at room temperature. This causes tungsten welds to be affected by the evolution of cracks along the weld bead, which can be eliminated by using a pre-heating step to reduce thermal straining. In this study, based on the tungsten inert gas welding process, a working envelope, focussed on varying welding speed and five different shielding gas mixtures of argon and helium, has been defined with the view of producing crack-free autogenous welds. The bead appearance and the microstructure of the different welds were correlated to the welding parameters, whose main effects have been analysed. Welding defects such as humping occurred when using gas mixtures with relatively low content of helium, and when using relatively high welding speeds. Crack-free autogenous welds have been produced without pre-heating when using a high content of helium and relatively low welding speeds. Thus, this study has demonstrated that a helium-rich shielding gas is required for welding thick tungsten plates. Moreover, the low thermal shock induced by the process, coupled with the purity of the tungsten plates used, strongly contributed to avoid the occurrence of any crack.

Experimentation and weld parameter optimisation using grey fuzzy analysis

The most popular steel grade material highly used in the fabrication of industrial pressure vessels and boilers is SA516 grade 70. Submerged Arc Welding is a metal joining technique widely used in heavy fabrication industries for its high quality, reliability, attaining deeper penetration and a smooth appearance of weld bead. In this paper, Taguchi's L27 orthogonal array is used to perform welding of SA 516 grade 70 steel plates. To improve the weld quality, the optimal combination of welding parameters is chosen using grey relational analysis. Grey fuzzy optimisation of welding parameters is based on four different output performance characteristics, namely, bead reinforcement, bead width, bead penetration and dilution. From analysis of variance it is evident that electrode stick out is the most influential factor in submerged arc welding process parameters. Mechanical and metallurgical studies are performed to confirm the effectiveness of the approach.

Performance Evaluation of Arc Welding Process Using Weld Data Analysis

Shielded metal arc welding (SMAW) and metal inert gas (GMAW) welding process are the two most widely used welding processes. These processes are widely used for the construction and fabrication purpose in almost all type of industries. Some of the important factors which govern the weld quality in these welding processes are welding power sources, role of shielding gas (for GMAW process), welding consumables and skill of the welders. Currently, effects of these factors are evaluated by examining the quality of the weld produced and not by monitoring how welding process is affected by change in these factors. This is an indirect method because actual contribution made by individual parameter in physical process is effectively ignored. Further, this is expensive and time-consuming as the assessment can be carried out only after the weld is completed. Hence, a procedure to assess the quality of welding process using the data acquired while welding is in progress is preferred to testing of the weld for this purpose. In both SMAW and GMAW processes, welding speed, voltage and current are important parameters that affect the quality of the welds. Among these, monitoring of welding speed is relatively easy; but monitoring voltage and current is not. This is because, welding is a stochastic process in which wide variation in voltage and current occurs and duration of these variations is so short that they are not observed in the voltage and current displayed in the power source. However, with the help of a high-speed data acquisition system, voltage and current variations during actual welding process can be recorded and subsequently analysed to reveal very useful information on the welding process, and subsequently quality analysis of individual welding parameters can also be done. In the present study, the voltage and current signals acquired using a digital storage oscilloscope have been used to study SMAW and GMAW processes. Data was acquired for duration of 20 s at a sampling rate of 100,000 samples/s while welding is in progress. In the case of SMAW process, welding data was acquired for welds made using different welding power sources, but with same welder and same type of electrode. In the case of GMAW process, welds were made using same wire and same welder but with different gases for shielding and at different set currents. Dynamic variation in the voltage and current signals were carefully studied using time domain and statistical analyses. Results showed that differences in the characteristics of the different power sources used for SMAW process and effect of shielding gases and arc current on GMAW process could be easily revealed by such analysis. For SMAW process, results obtained could also be correlated with the appearance of the weld beads. Hence, a procedure involving high-speed data acquisition of voltage and current signal while welding is in progress and the statistical analysis of the acquired data have been proposed for monitoring of these two arc welding processes.

The Effects of Low Frequency on the Microstructure and Mechanical Properties of High-Strength Al-Mg Aluminum Alloys by Wire and Double-Pulsed Arc Additive Manufacturing

An innovative and high deposition efficiency process, the double-pulsed arc additive manufacturing process, is used to produce high-strength Al-Mg wall components. This dissertation investigates the electrical parameter acquisition, bead appearance, porosity morphology, microstructure and mechanical properties of additively manufactured high-strength Al-Mg wall components and how these are affected by the low frequency of the double-pulsed arc additive manufacturing process. Then, using this process at different low frequencies of 0, 1, 3, 5, 7 and 9 Hz, multilayer deposition experiments were performed. It can be observed that the deposit porosity is obviously eliminated compared with cold metal transfer (CMT) process. The bead appearance of the deposited aluminum wall varies clearly with low frequencies, and at a low frequency of 3 Hz, its appearance is the best of all. The optical observation of microstructure proves that the average grain size varies significantly with low frequency, and at a low frequency of 1 Hz, it is the smallest. In addition, the deposited wall showed maximum mean microhardness and maximum ultimate tensile strength at a low frequency of 3 Hz. Considering the deposited porosity and mechanical priorities, double-pulsed arc additive manufacturing with a frequency of 3 Hz is more suitable for making high-strength Al-Mg wall components than at other low frequencies.

Bead formation characteristics in laser welding of high-strength steel under subatmospheric pressures

A series of laser welding experiments were carried out on low-alloy high-strength steel specimens under subatmospheric pressure. The welding penetration and weld bead formation characteristics were evaluated by performing metallographic examination on weld bead cross sections. The effects of technological parameters such as ambient pressure, laser power, and welding speed on weld bead formation were investigated. A multi-factor regression prediction model of welding penetration was established on the basis of the above experimental investigation to evaluate the welding penetration in accordance with the adopted welding parameters under certain ambient pressures. To have more insights into the effect of dynamic behavior of molten pool on the bead formation, the laser welding on “glass-metal” composite samples was performed under varied ambient pressures, and a high-speed digital camera was employed to observe the keyhole profile and the molten pool surface during welding process. A correlation between the welding penetration and the ambient pressure for laser welding of high-strength steel was found that in the range of 101–3 kPa, the decrease of ambient pressure leads to the raise of welding penetration and a smoother weld bead appearance.

Influence of Welding Current on Formation of Weld Bead in TIG Welding for Joining Thin Plates

In this paper, a new (novel) welding technology has been applied to join 0.1 mm thin plates. An initial study on the influence of welding current on the welding properties for stainless steel SUS304 plates is discussed in this paper. The weld bead appearance on both top surface and bottom surface was observed by microscope to indicate the change of weld bead size and welding defects. The results showed that by utilizing a constricted nozzle, a good weld bead is found out when the arc length is too short (0.3 mm), welding speed is very high (3000 mm min-1) and base metal is very thin (0.1 mm) with suitable welding conditions.