A Comprehensive Model of the Transport Phenomena in Gas Metal Arc Welding

A comprehensive two-dimensional gas metal arc welding (GMAW) model was developed to take into account all the interactive events in the gas metal arc welding process, including the arc plasma, melting of the electrode, droplet formation, detachment, transfer, and impingement onto the workpiece, and the weld-pool dynamics and weld formation. The comprehensive GMAW model tracks the free surface using the volume of fluid method and directly modeled the coupling effects between the arc domain and the metal domain, thus eliminating the need to assign boundary conditions at the interface. A thorough investigation of the plasma arc characteristics was conducted to study its effects on the dynamic process of droplet formation, detachment, impingement, and weld-pool formation. It was found that the droplet transfer and the deformed electrode and weld-pool surfaces significantly influence the transient distributions of current density, arc temperature, and arc pressure, which in turn affect the droplet formation, droplet transfer, and weld-pool dynamics

Modeling of the Transport Phenomena in Metal Transfer and Weld Formation of GMAW under the Shielding of Ar-He Mixtures

A better understanding of the transport mechanism in the metal during a welding process is important for the improvements in the quality and productivity of welding. This project studied the influences of shielding gas compositions on the transport phenomena in the metal domain during gas metal arc welding (GMAW), which include the transient processes of electrode melting; the droplet formation, detachment, transfer and impingement onto the workpiece; and the weld pool dynamics and bead formation. The present study shows that electromagnetic force, which is affected by shielding gas compositions, plays the most significant role in determining the behaviors of metal transfer. For the same welding power input, the increase of He content in the mixture leads to the formation of larger droplets and the decrease of droplet detachment frequency. The predicted phenomena on metal transfer are consistent with the reported experimental observations

Modeling of the Transport Phenomena in GMAW Arc under the Shielding of Ar-He Mixtures

Gas metal arc welding (GMAW) is one of the most widely used method to assemble parts together in various industries. Argon and helium are the most common shielding gases used in GMAW to protect the molten metal from oxidization. The shielding gas composition is a critical parameter in the GMAW process, which affects the efficiency, quality, and overall performance of the welding operation. In this project, a numerical investigation was conducted to study the transport phenomena in the GMAW arc under the shielding environments of pure Ar and three Ar-He mixtures. The detailed description of the transient arc plasma generation and interactions with moving droplets and weld pool surface provides insights into how the thermal physical properties of the two shielding gases affect the arc characteristics

Effects of Shielding Gas Compositions on Arc Plasma and Metal Transfer in Gas Metal Arc Welding

This article presents the effects of shielding gas compositions on the transient transport phenomena, including the distributions of temperature, flow velocity, current density, and electromagnetic force in the arc and the metal, and arc pressure in gas metal arc welding of mild steel at a constant current input. The shielding gas considered includes pure argon, 75% Ar, 50% Ar, and 25% Ar with the balance of helium. It is found that the shielding gas composition has significant influences on the arc characteristics; droplet formation, detachment, transfer, and impingement onto the workpiece; and weld pool dynamics and weld bead profile. As helium increases in the shielding gas, the droplet size increases but the droplet detachment frequency decreases. For helium-rich gases, the current converges at the workpiece with a ring shape which produces non-Gaussian-like distributions of arc pressure and temperature along the workpiece surface. Detailed explanations to the physics of the very complex but interesting transport phenomena are given

3,6-Di-4-pyridyl-1,4-dihydro-1,2,4,5-tetra­zine

The mol­ecule of the title compound, C12H10N6, which is V-shaped due to the boat conformation of the dihydro­tetra­zine ring, has crystallographic C 2 symmetry. The dihedral angle between the planes of the two pyridine rings is 31.57 (3)°. Mol­ecules are linked by weak N—H⋯N and C—H⋯N hydrogen bonds, forming a two-dimensional polymeric structure

Study The Shielding Gas Effects On Transport Phenomena In GMAW Arc

This article presents a numerical investigation on the transient transport phenomena including the arc plasma generation and evolution; droplet formation, detachment, transfer and impingement onto the workpiece; weld pool dynamics and final weld bead shape for pure argon and three argon-helium mixtures (75% Ar + 25% He, 50% Ar + 50% He, and 25% Ar + 75% He) during the GMAW process. The results indicate that the arcs in different shielding gases behave very differently due to the significant differences in thermophysical properties, including the ionization potential and the electrical conductivity, thermal conductivity, specific heat, and viscosity at high temperatures. For the same welding power input, the increase of helium content in the mixture leads to a stronger convergence of electric current at the workpiece and a stronger upward electromagnetic force near the workpiece, resulting in a cone-like plasma arc, which is in contrast to a bell-like plasma arc for argon-rich mixtures

Recognition of specific ubiquitin conjugates is important for the proteolytic functions of the ubiquitin-associated domain proteins Dsk2 and Rad23

Ubiquitin (Ub) regulates important cellular processes through covalent attachment to its substrates. The fate of a substrate depends on the number of ubiquitin moieties conjugated, as well as the lysine linkage of Ub-Ub conjugation. The major function of Ub is to regulate the in vivo half-life of its substrates. Once a multi-Ub chain is attached to a substrate, it must be shielded from deubiquitylating enzymes for the 26 S proteasome to recognize it. Molecular mechanisms of the postubiquitylation processes are poorly understood. Here, we have characterized a family of proteins that preferentially binds ubiquitylated substrates and multi-Ub chains through a motif termed the ubiquitin-associated domain (UBA). Our in vivo genetic analysis demonstrates that such interactions require specific lysine residues of Ub that are important for Ub chain formation. We show that Saccharomyces cerevisiae cells lacking two of these UBA proteins, Dsk2 and Rad23, are deficient in protein degradation mediated by the UFD pathway and that the intact UBA motif of Dsk2 is essential for its function in proteolysis. Dsk2 and Rad23 can form a complex(es), suggesting that they cooperate to recognize a subset of multi-Ub chains and deliver the Ub-tagged substrates to the proteasome. Our results suggest a molecular mechanism for differentiation of substrate fates, depending on the precise nature of the mono-Ub or multi-Ub lysine linkage, and provide a foundation to further investigate postubiquitylation events

A genome-wide synthetic dosage lethality screen reveals multiple pathways that require the functioning of ubiquitin-binding proteins Rad23 and Dsk2

<p>Abstract</p> <p>Background</p> <p>Ubiquitin regulates a myriad of important cellular processes through covalent attachment to its substrates. A classic role for ubiquitin is to flag proteins for destruction by the proteasome. Recent studies indicate that ubiquitin-binding proteins (e.g. Rad23, Dsk2, Rpn10) play a pivotal role in transferring ubiquitylated proteins to the proteasome. However, the specific role of these ubiquitin receptors remains poorly defined. A key to unraveling the functions of these ubiquitin receptors is to identify their cellular substrates and biological circuits they are involved in. Although many strategies have been developed for substrate isolation, the identification of physiological targets of proteolytic pathways has proven to be quite challenging.</p> <p>Results</p> <p>Using a genome-wide functional screen, we have identified 11 yeast genes that cause slower growth upon their overexpression in cells lacking two ubiquitin-binding proteins Rad23 and Dsk2. Our results suggest that proper functioning of Rad23 and Dsk2 is required for efficient pheromone response, transcription, amino acid metabolism, and DNA damage response. Two proteins identified by the screen are shown to be proteolytic substrates of Dsk2, validating the large scale synthetic dosage lethality screen as a new strategy for identifying substrates of a specific degradation pathway.</p> <p>Conclusion</p> <p>In conclusion, as proof-of-concept, we show that a synthetic dosage lethality screen, which is based on the toxicity induced by gene overexpression, offers an effective, complementary method to elucidating biological functions of proteolytic pathways.</p

Three-Dimensional Modeling of Transport Phenomena and their Effect on the Formation of Ripples in Gas Metal Arc Welding

Distinct, periodic arc-shaped ripples are observed on the surface of the weld bead in almost any welded components which have a significant effect on weld quality. This article presents the complex transport phenomena and their effect on the formation of ripples in three-dimensional moving gas metal arc welding. The transient distributions of the melt flow velocity and temperature in the weld pool, weld pool shape and dynamics, and solidified weld bead are calculated. It is found that the surface ripples are formed by the interplay between the up-and-down weld pool dynamics, caused mainly by the periodic droplet impingements, and the rate of weld pool solidification. The effects of various welding parameters, including the welding current, droplet size, droplet frequency, droplet impinging velocity, and travel speed on the pitch (distance between two ripples) and height of the ripple are investigated. This study provides fundamental understanding to the underlying physics that cause the formation of ripples with different pitches and heights