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1

The effect of welding fixtures on welding distortions

Vural M., Muzafferoglu H. F., Tapici U. C.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 20, nr 1-2

511-514

EN

Purpose: of this paper is to examine the effect of welding fixture used to prevent the distortions during cooling process utilizing a robot controlled gas metal arc welding method on cooling rate and distortions of welded structures. Design/methodology/approach: Using a specially designed welding fixture for a welded steel structure, six different types of AISI 1020 steel specimens are tested in three different welding speeds and two different cooling conditions either at fixture or without using fixture. Findings: designed fixture is reduced amount of distortions. The preheating effect of previous weld on the next weld has increased distortions on the other side of part. Increase in distortions is directly proportional to the increase in welding speed which affects the weld heat input. Research limitations/implications: the study can be repeated on more complex structures and fixtures. Practical implications: the study has shown that the fixture design has an important effect on cooling rate of the welded parts. Originality/value: most of papers in literature is about fixture design methodology, but this paper is an example of demonstration for a practically applied welding fixture.

2

On the friction stir welding of aluminium alloys EN AW 2024-0 and EN AW 5754-H22

Vural M., Ogur A., Cam G., Ozarpa C.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 1

49-54

EN

Purpose: Purpose of this paper is investigate the friction stir welding capability of the EN AW 2024-0 and EN AW 5754-H22 Al alloys are studied, because two aluminium alloys are widely used in the industry and friction stir welding is getting widened to be used to join the aluminium alloys. Design/methodology/approach: Friction stir welding (FSW) is a new solid fhase technique invented and patented for aluminium alloys. EN AW 2024-0 and EN AW 5754-H22 are aluminium alloys can be welded by fusion welding, but many welding problems arises from fusion welding. While the friction stir welding is a solid state welding process, some problems may be prevented. Findings: It is found in the course that these two aluminium alloys can be friction stir welded if fhe welding parameters are carefully selected. Hardness value in weld area for EN AW 2024-0, there is an increase about 10-40 Hv. Because of this is recrystalization and getting smaller grains. For EN AW 5754-H22 there is a decrease of hardness value because of recrystalization. Welding performance of EN AW 2024-0 is reached to 96.6 %. This value is 57 % for EN AW 5754-H22. It is possible to perform dissimilar welding using different aluminium alloys. Elding performance of dissimilar aluminium alloys EN AW 2024-0 and EN AW 5754-H22 is reached a value of 66.39%. Research limitations/implications: Research limitations are that the design of the welding probe which is used in the experiments is changed, the speed of the welding can be improved. The material of the welding probe can be changed. Originality/value: The aluminium alloys EN AW 2024-0 and EN AW 5754-H22 are widely used ones but the friction stir weldability is not investigated so far. It is found that if the welding parameters are carefully selected, these aluminium alloys can be friction stir welded succesfuly.

3

The ultrasonic testing of the spot welded different steel sheets

Vural M., Akkuş A.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 18, nr 1-2

247--250

EN

Purpose: Purpose of this paper is to investigate the applicability of spot welded different steel sheets to ultrasonic testing, because resistance spot welding of the steel sheets is widely used in the car bodies and transport fields and ultrasonic testing is a good way to evaluate the fatique life of the spot welds. Design/methodology/approach: Methodology of this paper is that two different steel sheets (AISI 304 type austenitic stainless steel sheet and Galvanized steel sheet ) were welded to each other by using resistance spot welding. Some pre-welding tests were made to obtain suitable and optimum weld nugget diameter; and the welding current vs. nugget diameter curve were obtained. By using this curve and kepting constant welding parameters such as current, electrode pressure, weld time, etch., fully identical four spot welded specimens having 5 mm (±0.2) nugget diameter were obtained. The specimens and nugget diameters were tested by using a special ultrasonic test apparatus which is designed for spot welded joints. Findings: Findings are that after the first ultrasonic tests, the four identical spot welded sheets which have AISI 304 - Galvanized steel sheet combination were subjected to the fatigue test in four different number of cycles. There is no any rupture or fracture in spot welded joints after fatigue tests. The spot welded specimens subjected to fatigue test were tested in ultrasonic test apparatus to observe the variation in the weld nugget and joint. The ultrasonic test results before fatigue and after fatigue were compared with each other; and the decreasing of the weld nugget diameter were observed while increasing the number of cycles. The results were shown in figures and discussed. Research limitations/implications: Spot welding of different steel sheets forms different microstructures which respond different values to ultrasonic testing. Evaluation of these responses are quiet difficult. Practical implications: Only a few spot welds can be evaluated among approximately 4 thousands of spot welds on a car body. Only selected spot welds can be ultrasonically tested. Originality/value: Resistance spot welding of AISI 304 and galvanized steel forms austenitic, martensitic and ferritic microstrucutre in the same weld region. Ultrasonic testing of austenitic microstructures is different than the other microstructures. In this study the response of different microstructures to ultrasonic waves are investigated.

4

The differences between the strengths of quality levels of weld imperfections given in ISO 5817

Vural M.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 15, nr 1-2

193--198

EN

Purpose: ISO 5817 “Arc-welded joints in steel-Guidence on quality levels for imperfections” is a widely used international standard for evaluating of the weld imperfections in arc welded joints. In this study, in order to see the differences between the quality levels given in ISO 5817, the welded joints of B, C and D levels are subjected to the same load and the differences of maximum stresses at the joints are analysed by FEM. Design/methodology/approach: The welded joints with the quality levels of the weld imperfections given in ISO 5817 are modeled by a Solidworks FEM program, and they are subjected to static loading in order to determine the maximum stresses at the cross-sections of the joints. Findings: The stress values at the welded joints generally increases from the quality level of “B” to “D”. Exceptions of this behavior are the imperfections defined as “fillet welds having the throat thickness greater than nominal value”, “excessive penetration” and “excessive asymmetry fillet weld”. In these imperfections, the cross-sections carrying the force increases from “B” to “D”. Because of static force, a greater cross-section forms a smaller stress value. Thus, it must be given in the ISO 5817 whether the welded joint is subjected to a static or dynamic load. Research limitations/implications: Three dimensional models can be investigated and the effect of 3D weld imperfections on the behavior of a more realistic model can be calculated. Practical implications: The results show that some imperfections like “excessive penetration” and “excessive asymmetry filet weld” have less importance compared to the others. Originality/value: ISO 5817 is a worldwide used Standard for evaluating the weld imperfections. The quality levels of weld imperfections are compared with each other with FEM. The Standard includes 57 different quality levels and this paper compared all these levels with each other.

5

Finite element analysis of some thermomechanical behaviours in resistance spot welding.

Vural M., Aydogan M.O.

Inżynieria Materiałowa

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1998

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R. XIX, nr 4

667-670

EN

In resistance spot welding, joining of the common contact surface of two sheet materials is quite complicated interaction of electrical, thermal, mechanical, metallurgical and surface phenomena. In this study, finite element analysis were employed to determine, the cooling times, the temperature distributions in both electrode and workpiece during cooling and the deformation behaviour of both tapered conical shaped electrode and workpiece during weld cycle.