Welding research
Welding research is a continuous requirement for development.
Welding Technology has come to this stage due to continuous research and development done in several countries in the last 60 years. Paton welding institute , welding institute UK (TWI)
http://www.twi-global.com , Edison welding institute (EWI)http://www.ewi.org , American welding societyhttp://www.aws.org ,german welding society , japan welding research institute , welding institute aachen , French welding institute , welding technology association Australia , welding institute (Halle) , welding research institute ( Czechoslovakia) , welding research institute (India) , are some of the institutes where extensive research on various aspects of welding is going on.
Some organizations are providing patent search in the internet. Literature support is given to many by search engines in the internet.http://www.uspto.gov
Many professional bodies are providing opportunities for learning and disseminating knowledge through seminars , workshops and conferences on a regular basis. Some of the journals are main source of current literature.http://www.iiwindia.com.
Many educational institutions are also engaged in research and contributing for continuous development.
Research in automotive sector
“Intelligent SpotTM welding” is a technology in which stable nuggets are formed by changing the electrode force and welding current during welding. Three thickness lap joints are welded successfully.
Indirect type single-side spot welding method is used to solve single side welding applications. In this method, it is necessary to optimize the position of the grounding electrode depending on the component, but in addition to this, the electrode force and current are also controlled during weld ing. Taking advantage of this feature, this is a welding technology with excellent robustness which makes it possible to suppress instability.
As a welding technology which accesses the weld
from one side, laser welding is also emerging as an important technology. Recently, a high efficiency welding technology called remote laser welding was developed due to progress in laser oscillators and peripheral hardware such as optical systems, and the technology has been applied widely, both in Japan and other countries.
DEVELOPMENT IN SUBMERGED ARC WELDING
A lot of development has taken place in the submerged arc welding process since it was used by the fabrication industries. Some of them are discussed below.
1. hot wire submerged arc welding
In addition to the main welding wire , another wire is fed to the weld pool. The second wire is heated by electrical resistance heating method by using separate AC transformer. The hot wire fed to the weld pool does not ‘arc’ on the base material butt is just fed in a red hot condition. It melts by using the heat available from the main arc. The deposition rate can be increased by 30 to 40%. This process is well suited for pipe welding.
2.Strip cladding
Stainless steel and high alloy steel deposits can be deposited over carbon steels and low alloy steels for corrosion resistance in chemical vessels and nuclear applications.Instead of an electrode wire, a strip is used in the strip cladding process. A strip of 0.5mm thickness and 60 mm width or more is used. A wide , shallow penetration overlapping beads can be deposited in this process.
3.Narrow gap submerged arc welding
When thick plates are welded , a large amount of weld metal need to be deposited.The gap between the edges is kept at 18-20mm. A special wire aligning system is used to weld in deep grooves. A special flux is required for easy slag removal and smooth bead formation in deep grooves. Normally two passes per layer are laid in narrow gap submerged arc welding
Rail Welding Technologies
Rail welding consists of three welding operations, namely, primary welding, in which short rails are made up in the shop into long rails with lengths of 100–200 m, secondary welding, in which the length of the rails is extended to approximately 1 km in the field, and tertiary welding, in which final laying or rail exchange is per- formed at the site. Primary welding is performed by flash welding, and secondary welding is done by gas pressure welding. The main techniques for tertiary weld- ing are enclosed arc welding and thermit welding. Flash butt welding gives high welding efficiency, with a flash welding time of about 1.5–4 minutes, which is shorter than that by other joining methods, and is also excellent in terms of quality stability and welding management.
This machine is a light- weight, portable machine designed for use at field . This technology supported the rapid pitch of field work of 30 or more rails.
Welding of stainless steels
Stainless steel welding alloys have been designed with a view to minimising the distortion due to residual stresses that develop during the cooling of a welded assembly. The alloy design procedures have ensured solidification as delta ferrite, then transform almost completely into austenite and finally into martensite. The remnants of delta ferrite do not form continuous networks in the final microstructure, leading to good toughness. Further- more, the martensite start temperature has been suppressed to about 220 deg C, a feature essential in order to ensure the accumulation of thermal contraction stresses following the exhaustion of the austenite. The transformation plasticity associated with the formation of martensite under the influence of the stresses that develop when a weld cools, has been shown experimentally to be capable of reducing the distortion in the final weld.