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2 Journal of Achievements in Materials and Manufacturing Engineering

2 2006

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A study on variation of shielding gas in GTA welding using finite element method

Kim I. S., Son J. S., Kim H. J., Chin B. A.

Journal of Achievements in Materials and Manufacturing Engineering

2006

Vol. 17, nr 1-2

249--252

Purpose: Generally discrete alternate supply of shielding gas is a new technology which alternately supplies the different kinds of shielding gases in weld zone. In this study, welding characteristics under variation of alternate supply method of shielding gases in austenite stainless steel using a GTA welding process have been investigated and found the relationship between welding distortions and welding speed and different types of shielding gas and shielding gas supply. Design/methodology/approach: 2-D axisymmetric heat and fluid mathematical model about welding arc and weld pool has been developed for verifying the effect of alternate supply of shielding gas. The developed models were solved using a general thermofluid-mechanics computer program, PHOEINCS code, which is based on SIMPLE algorithm. Findings: The computed results showed that the developed computational models are very adequate to predict in the weld pool and bead geometry, and the technique of alternate supply of shielding gas should be useful to increase higher productivity, cost savings and better quality in arc welding. Research limitations/implications: The effect of alternate supply of shielding gas should be useful to apply for a narrow-gap welding process. Originality/value: The range of molten metal at the top of weld pool for supply of He shielding gas became wider than that for supply of Ar shielding gas. The developed computational models are very adequate to predict in the weld pool and bead geometry.

A study on electromagnetic transducers for the continuous casting process

Kim I. S., Son J. S., Kim H. J., Chin B. A.

Journal of Achievements in Materials and Manufacturing Engineering

2006

Vol. 17, nr 1-2

357--360

Purpose: One of the areas in the continuous casting process that has not been definitively instrumented is a method for reliably locating the part of a continuously cast strand that remains liquid for a period after the outer portion has solidified. Therefore, this paper is focused on the measurement of the solidification point made by a through transmission technique based on the relationship between ultrasonic speed and measured temperature using an EMAT sensor. Design/methodology/approach: An EMAT (Electro Magnetic Acoustic Transducer) has been designed and fabricated with an elongated spiral coil and a permanent magnetic core. Al75×75mm and 75×100mm simulators with 2, 4, 8, 16 and 32 mm holes were produced and demonstrated that the location of the final solidification point during the continuous casting process can be monitored using a 1.0 MHz frequency. Findings: The solidification point in a continuous casting bloom could be detected through a series of tests with the use of a fabricated probe and the amplitude extent of ultrasonic wave decreases as the hole diameter of the simulators increases. Furthermore, through a test of lift-off effect it was found that the extent of amplitude decreases as lift-off increases, thus one of the most important factors for a field application. Research limitations/implications: As cutting speed and cutting length can be predicted from a miniaturization of the sensor and construction of an on-line system for a field installation, a considerable amount of time and energy can be saved by reducing mistake ratio and curtailing unnecessary processes. Originality/value: The measured ultrasonic waves allow for prediction of the casting speed necessary to correctly locate the liquid core and thereby maximize the benefits of soft reduction and the productivity of the machine.