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QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY Vol. 38 (2020), No. 3

ISIJ International
belloff
ONLINE ISSN:
PRINT ISSN: 0288-4771
Publisher: JAPAN WELDING SOCIETY

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QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY Vol. 38 (2020), No. 3

Characteristics of Material Flow in Friction Stir Spot Welding Tools in Consideration of Cutting Tools

Akihiko IKUTA

pp. 125-133

DOI:

10.2207/qjjws.38.125

Abstract

This paper investigates the material flows in A5052/A6061 lap joints when friction stir spot welding tools with cutting edges and rake angles similar to a cutting tool are used. In this study, several kinds of modelling experiment were used to visualize the material flows during the friction stir spot welding. The majority of the material flows in A5052/A6061 lap joints was diagonally upward from the lower sheet, whether the rake angle of the probe with the cutting edge similar to a cutting tool was negative or positive. When the tool shoulder failed to contact the upper sheet surface, the stirring ability of the probe alone was to an extent high with a negative rake angle and very low with a rake angle of 0° and with positive rake angles. However, when the tool shoulder came into contact with the upper sheet surface and the chips generated by the probe were clogged, the stirring abilities of the tool with a rake angle of 0° and with positive rake angles were very high. In addition, in the tool with a rake angle of 0° and with positive rake angles where the discharge of chips was smooth, the lower sheet material moved upward as the chips were stirred and produced new material flows. From these results, when these tools are used, it is suggested that the generation, the discharge and the stirring of chips affect the material flow upwards, which is crucial, and also downwards, in A5052/A6061 friction stir spot lap joints.

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Characteristics of Material Flow in Friction Stir Spot Welding Tools in Consideration of Cutting Tools

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Numerical simulation and experiment on brittle fracture surface morphologies in steel

Shuji AIHARA, Tetsuya NAMEGAWA, Fuminori YANAGIMOTO, Tomoya KAWABATA

pp. 134-146

DOI:

10.2207/qjjws.38.134

Abstract

A numerical simulation model of brittle crack propagation was developed incorporating fracture surface irregularity, and small-scale crack arrest experiment of a steel plate was conducted to validate the model. Mechanisms of the formation of brittle fracture surface irregularities including chevron markings in the steel were discussed based on the model calculations and the experiment. Formation of the chevron markings was found to depend on applied stress intensity factor. The model calculations and the experiment showed that the chevron markings are nucleation and continuation of ridges, which are formed between two cleavage crack terraces with different height levels. The dependence of the extent of the chevron markings on applied stress intensity factor is understood as that a deep ridge reduces local stress intensity factor by shear stress acting on the ridge, and the deep ridge can develop only at high stress intensity factor level but only shallow ridges are possible if stress intensity factor level is low. This tendency agreed between the experiment and the calculation. Relationship between crack arrest toughness and fracture surface irregularities is discussed.

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Numerical simulation and experiment on brittle fracture surface morphologies in steel

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Study of burn-through prediction in MAG arc welding using molten pool monitoring technique

Takumi MATSUMURA, Kazufumi NOMURA, Satoru ASAI

pp. 147-156

DOI:

10.2207/qjjws.38.147

Abstract

In this paper, in order to predict the occurrence of excessive penetration and burn-through that occur in groove MAG welding, we observed the molten pool with cameras, and considered parameters correlating with the occurrence of the excessive penetration and burn-through. In the case of groove MAG welding using a robot, excessive penetration and burn-through that occur due to the effects of disturbances such as gap between base materials caused by heat distortion and member accuracy are obstacles to improvement of welding quality and production efficiency. So, we constructed a simultaneous observation system for the top and bottom side of the molten pool using two cameras. Molten pool width (W) and reduction of molten surface height (R) are extracted as feature quantities, and compared with the state of the bottom side of the molten pool. Although the decrease of W and R was confirmed, they alone were not enough to predict the occurrence of burn-through. Therefore, W+R was set as a new parameter (P) in consideration of the molten pool cross-sectional shape change. As a result, the decrease of P was confirmed before the occurrence of burn-through, and it was shown that P is an effective parameter for predicting the generation of burn-through.

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Study of burn-through prediction in MAG arc welding using molten pool monitoring technique

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Observation of Micro Fatigue Cracks at GMA Welded Joint of Thin Steel Sheet

Kazuki MATSUDA, Shinji KODAMA

pp. 157-163

DOI:

10.2207/qjjws.38.157

Abstract

Fatigue tests were performed on GMA welded joints using a prototype steel sheets with varying amounts of C. In addition, the origin of the fatigue cracks in the thin steel GMA welded joints were investigated through observation the micro cracks in the specimens that were judged to be not fractured by fatigue limit stress in the fatigue test. As a result of plane bending fatigue test of bead-on-plate welding sheet, fatigue limit of the welded specimen did not differ much between the steel sheets. Observing the specimens which were not fractured at the fatigue limit, micro cracks often occurred at the bottom of the ripples on the weld metal surface and in the ferrite structure. It was founded that fatigue cracks in thin steel sheet GMA welding using mixed gas occurred parallel along the bottom of the ripples and parallel cracks merged with the crack growth, resulting in a zigzag propagation path on the weld joint surface. The effect of ripple on the fatigue limit was predicted by comparing estimating the fatigue limit without considering the ripple with the fatigue limit obtained from experiment. Finally, the effect of ripple on the fatigue limit was more than 10% and less than 20%. And it was implied that higher the strength of the material, the greater the effect of ripple on the fatigue limit.

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Observation of Micro Fatigue Cracks at GMA Welded Joint of Thin Steel Sheet

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High-Efficiency and Low-Heat-Input CO2 Arc-Welding Technology for Butt Joint of Thick Steel Plate Using Hot Wire

Somchai WONTHAISONG, Shinichiro SHINOHARA, Kenji SHINOZAKI, Rittichai PHAONIAM, Motomichi YAMAMOTO

pp. 164-170

DOI:

10.2207/qjjws.38.164

Abstract

The purpose of this study was to develop a high-efficiency and low-heat-input CO2 arc-welding process using hot-wire feeding. The optimization of welding conditions using only two welding passes on the butt joint of 20-mm thickness steel plates was investigated using several combinations of hot-wire feeding speed and welding current. Stable welding phenomena, such as molten pool formation and hot-wire feeding during welding, were observed for all tested conditions. A sound joint without any defects could be obtained in only two welding passes using the optimized conditions. The proposed hot-wire CO2 arc-welding process has potential to simultaneously achieve both high efficiency and low heat input. Use of a higher hot-wire feeding speed with a lower welding current enabled a lower dilution ratio, narrower width of the heat-affected zone, and higher weld metal hardness owing to the resultant lower molten pool temperature and higher cooling speed. The proposed hot-wire CO2 arc-welding process also achieved about 50% reductions in the power consumption and arc time compared with those of the conventional CO2 arc-welding process on the butt joint of 20-mm thickness steel plates.

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High-Efficiency and Low-Heat-Input CO2 Arc-Welding Technology for Butt Joint of Thick Steel Plate Using Hot Wire

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Observation of welding phenomena with blowholes for detection of welding defects

Kazuki KASANO, Yosuke OGINO, Satoshi FUKUMOTO, Satoru ASAI, Tomokazu SANO

pp. 173-182

DOI:

10.2207/qjjws.38.173

Abstract

Arc welding is important technology for manufacturing that is directly linked to quality and productivity. Especially GMAW with Ar or CO2 shielding gas is widely used in various industries because of its high productivity. To achieve high quality and productivity, in-process welding quality control technology will be required. In this study, the authors observe welding phenomena with Blowholes(BH) by using high speed cameras to develop in-process welding defects detection technology with image sensing methods. By observing welding phenomena with BH bubbling phenomena are observed just under the arc and on the surface of moltenpool. It was found that the bubble generation on the surface of the molten pool is correlated with the pinhole generation, and the bubble generation just under the arc is correlated with the blowhole generation.

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Observation of welding phenomena with blowholes for detection of welding defects

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Influence of Thickness Reduction in Base Plate on Elastic Stress State of Patch Plate Joint by Combination of Welding and Bonding

Mikihito HIROHATA, Naoki FUJIMURA

pp. 183-192

DOI:

10.2207/qjjws.38.183

Abstract

For investigating influence of thickness reduction in base plate on elastic stress state of patch plate joint by combination of welding and bonding, a series of experiment and analysis were conducted. A static tensile loading experiment was carried out. The thickness reductions of 2.5mm were applied to the both top and bottom surfaces of base plate with a thickness of 12mm. The thickness-reduced parts of base plate were covered by the patch plates with a thickness of 6mm. The joining methods of patch plates were only fillet welding, only bonding and the combination of welding and bonding. The load-carrying effect at the center of joint was improved by the combination of welding and bonding compared to the case with only welding. However, the stress reduction effect around the welded part could not be clearly confirmed from the experimental result. 2D elastic analysis was performed for simulating the experiment and examining the stress reduction effect around the welded part in detail. Furthermore, the influence of degree of thickness reduction in base plate on the stress state around the welded part was investigated. The results indicated that the stress reduction effect by the combination of welding and bonding was larger around the weld root rather than the weld toe.

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Influence of Thickness Reduction in Base Plate on Elastic Stress State of Patch Plate Joint by Combination of Welding and Bonding

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Proposal and applicability of a method to evaluate surface tension of liquid using large volume sessile drop in gravity

Kunio TAKAHASHI, Yoji IGUCHI, Keiichiro HAMADA, HEMTHAVY Pasomphone, Shigeki SAITO

pp. 193-198

DOI:

10.2207/qjjws.38.193

Abstract

Based on a theory of sessile drop in gravity, a method to evaluate surface tension is proposed, and its applicability is discussed. All of parameters are theoretically normalized. Although it is impossible to obtain analytic solution of the surface profile of the sessile drop, it is possible in an extreme condition of large volume. A universal parameter which determine the volume of liquid is derived in a normalized form. The large volume condition is theoretically defined using the parameter. Under the large volume approximation, an equation is derived which gives the surface tension from a height and an angle of the drop surface. In order to discuss applicability of the approximation, numerical calculation is carried out. It is found that the surface tension can be obtained with a tolerance less than 16%, if we measure the height of the sessile drop and the contact angle, under the large volume approximation. This method proposed in the present study is beneficial for the estimation of wettability of liquid using sessile drop.

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Proposal and applicability of a method to evaluate surface tension of liquid using large volume sessile drop in gravity

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