The stress and motion state of droplet in MIG welding with alternating longitudinal magnetic field were analyzed, and the impact of alternating longitudinal magnetic field on the droplet transfer were studied by high-speed video camera. The results show that the droplet is spherical approximately and transfer to molten pool along the welding wire axis without external longitudinal magnetic field. When alternating longitudinal magnetic field was introduced into welding process, the droplet rotate around the welding wire clockwise and counter-clockwise alternately. Shape of droplet became flat and direction of transfer deviated from the welding wire axis under the action of magnetic field. As the exciting current increased, extent of deviation from the wire axis increases. When the exciting current is too large (I >20A), extent of deviation is too large and droplet are disintegrated into several small droplet during the transition. So droplet can not transfer into molten pool successfully and the bead can’t be formed.
In order to optimize the MIG welding procedure of aluminum alloy with longitudinal magnetic field and improve the mechanical property, effect of longitudinal magnetic field frequency on microstructure and properties of surfacing layer were investigated. The results show that when the additional longitudinal magnetic field was introduced into welding process, grain was refined, the wear resistance and tensile strength of the surfacing layer were improved as longitudinal magnetic field frequency increased. When frequency of magnetic field is 20 Hz and exciting current is 15 A, effect of grain refining is the best and the mechanical property is the highest. But when exciting current continue to increase, grain became coarse and the mechanical property decreased. So it is concluded that grain was refined and the mechanical property of the surfacing layer were improved under longitudinal magnetic field. But magnetic field frequency has an optimal value; otherwise grain refining and the mechanical property can’t achieve the best effect.
Currently, there are no harmonized guidelines which govern skin banking in the Asia Pacific region. Therefore, skin banks are either unregulated or rely on their nation’s legislation or international accreditation to uphold their quality standards. A new set of skin banking guidelines was developed through a comprehensive review and collation of best international practices for the Asia Pacific Burn Association (APBA) members, from donor screening and testing, to skin recovery, processing, storage and distribution, and quality assurance. National regulatory requirements reviewed include the European directives, Australia’s Therapeutic Goods Administration and Singapore’s tissue banking standards. Further technical and quality management recommendations are referenced from the American Association of Tissue Banks (AATB), the United States Food and Drug Administration standards and guidance documents, various relevant European guides, Japanese Society of Tissue Transplantation guidelines and the Asia Pacific Association of Surgical Tissue Banking. Adapted mainly from the AATB standards, the new Asia Pacific Burn Association Guidelines for Skin Banking in Therapeutic Applications offer a comprehensive manual, addressing: governance and contracts; staff responsibilities; quality management; facilities, equipment and supplies management; donor consent and testing; and recommendations of good practices pertaining to skin recovery, processing, storage and distribution. Besides complementing current generic regulations, they provide technical specifications of major aspects unaddressed in most legislations. This inaugural set of new regional skin banking guidelines would be a start for regional members of the APBA to adopt, and will hopefully culminate in a set of standards so that, in the long run, skin allografts from this region can be of similar quality, which can simplify import process and facilitate the exchange of allografts between members.
In the study, thermal efficiency in MIG welding of aluminum alloy with longitudinal magnetic field was analyzed, as well as softening behavior of heat-affected zone (HAZ) and base metal were investigated. The results showed that welding current decreased and resultingly total heat input reduced as the exciting current increased, meanwhile arc thermal efficiency increased and melting efficiency decreased. As a result of action of the magnetic field, the trend of grain growth of HAZ slowed down and the influence on base metal of heat input decreased. When the exciting current was 20A, microhardness of HAZ and base metal improved evidently. However, as the exciting current continued to increase, the effect of magnetic field on softening behavior did not change significantly.
In the study three dimensions finite element mathematical model of MIG welding with longitudinal magnetic field was established. By ANSYS FEA software the temperature and other physical characteristics of the arc were obtained including the distributions of current density and arc pressure on the anode surface. The simulated results show that when the additional longitudinal magnetic field was introduced into welding process, the temperature of arc decreased remarkably and peak value of temperature changed from 16 950K to 13 700K at a welding current of 120A. Under the action of longitudinal magnetic field, on the one hand, heat flux density and current density at the anode surface decrease in the arc core and rise at the edge of arc, on the other hand, arc pressure decrease and arc potential increase. Keywords: Numerical simulation; MIG welding arc; magnetic field
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