Kiyoshi Terai

Studies on Prevention of End Cracking in One Side Automatic Welding (2nd Report)

Recently one sided automatic welding has widely been prevailed in the assemble stage of Japanese shipyards. As one of the problems of welding procedure, as well as any other welding techniques, cracking which sometimes occurs near the end of weld, has become an important problem.The authors have proposed the calculation technique in the seam welding. The most significant feature of the method differing from the ordinary welding thermal stress analysis is that the conditions of calculation are simulated to be those of more realistic welding procedures.Then, the following assumptions are imposed in order to calculate stress and strain during welding.(1) Before welding, specimens are connected by tack welds and prepared edges are free boundaries.(2) Molten region containing arc tip is free from stress.(3) After the arc passed by, the plates are connected by solidifying of the molten pool, that is, free prepared edge changes to supported one as temperature is cooled down.(4) When the arc passed through a tack weld, it should be melted away and free from stress.In order to calculate the thermal stress analysis during welding, firstly we solved un-stationary heat conduction problems and obtained temperature distribution during welding. Based on the calculated temperature distribution, we analysed uncoupled thermal stress problems by using the finite element method, and conclusively showed that one of the main causes of end cracking is the transient tensile stresses generated near the end part of weldment when the stress re-distribution is taken place due to the melting of the last tack weld.To endorse the numerical calculation by the proposed method, experiments are carried out and it is confirmed that the method could be applicable to this kind of transient welding stress-strain state with time depending varying boundary conditions.

Recent Developments in Electron Beam Welding in France

フランス原子力庁サ クレー原子 力 研究センターの溶 接 研究所で は,い まか ら約15年 まえにすで に電子 ビー ム溶 接 装置 を 完成 し,こ れを ウラン燃料棒のキ ャンニ ング (canning)に 実用化 している. 当時 この報告 はIIWの 年次総会をは じめとす る2,3 の会議で報告 され たが,そ の結 果あ る場合には これ は特殊 な小型 部品 に対す る溶接法にす ぎぬと して黙殺 同 様の扱 いを受け,ま たあ る場 合にはその将来性 に大 きな 期待 を寄せ られ ることに もな った.す なわち前者 の場合 電子 ビー ム溶接は 真空 チ ャンバーを 利 用 せねば な らな ず,こ の チ ャンベーサ イズによ って 被溶接物 の大 きさが 制限 され単 に搬入 可能な部品の溶接 のみにとどまり,と てもアーク溶接と同様には使 用できるもので はない.な どの理 由によ り主に構造 物製作関係者 を して黙殺同様の 扱 いを受け たが,い っぽ うこれ ら制約 のなかか らも,な お従来 の溶接法では溶 接不 可能とされ ていた活性金属, 高融点金属 ならびに異種金属の溶接 などの 可能性をたて に原子力および航空機方面 の関係者か らはその将来性に 大 きな期待がよせ られた. しか しいま これ らを総合 して両者 の立場か ら電子 ビー ム溶接法が構造 物の溶接 において将来性を にな う有力な 溶接法であ ることを認め研究開発を 促進 して いるフラン ス原子力庁を中心と したひとつ グル ープが ある. そ こで ここでは,こ の グループにお いて数年来研究が な され,最 近構造 物の電子 ビーム溶接法 と して開発 され た局所真空型電子 ビーム溶接法 の概略をのべ るとと もに その開発および実用 化状 況について ふれてみ たい とお も う. 2.局 所真空型電子 ピー厶溶 接とは

ECONOMIC ASPECTS OF AUTOMATION OF WELDING IN SHIPBUILDING

This treatise discusses economic effects of various methods for promoting automation of welding in shipbuilding by calculating welding arcing time for ship construction. From the viewpoint of economy, the automation of welding is one of the most imperative requirements now imposed on the shipbuilding industry. In most of the cases so far, the automatic welding has found its application only in the fabrication work on the assembly ground of flat panels contained in the cargo part of a ship. A ship, however, inevitably must take a streamlined shape since it travels in the water, a fluid. Hence, there exists curved part at the bow and stern of it. Further, the welding work on the building berth as a whole amounts to about 40 percent of the total welding work with respect to the required man-hour. In view of the above, the authors discuss here, (1) automatic welding of the curved shell plate as well as of the flat panel on the ground, (2) actual measures of automation of welding on the berth and (3) the economic effects to be achieved thereby.

Notch Toughness of Heat Affected Zone in Welded High Tensile Steels

The heat affected zones (HAZ) of three kinds of high tensile steels were reproduced with a synthetic thermal cycle apparatus, and their notch toughness was evaluated by fracture stress curve test and Double Blow test in respect to the initiation of brittle fracture.As the results of the experiments it was found that the synthetic HAZs were in general remarkably notch sensitive, and the results of both tests had the same relation as previoulsly reported on many other base plates.The transition temperatures of synthetic HAZ were compared with the ones of bead welded specimen in the first report. It was revealed that Trα5 in Kinzel test and (TrEi) 2 in the synthetic HAZ varied almost in similar way with the increace in the hardness. On the other hand, a close corelation was not found between (TrEi) 2 in the synthetic HAZ and Tr15 in the bead welded specimen.Finally, the behavior of brittle fracturing of bead welded specimen was schematically discussed, and it was concluded that the existence of thin and brittle layer as seen in HAZ would obviouly have adverse influence on the notch toughness of the specimen, for the range of the temperature lower than TrS of the base plate.

New Production System based on Statistical Quality Control

A revolutionary change was brought after the world war II into the production engineering of shipbuilding industry through the remarkable development of welding techniques. Following such technological innovation, the efforts for the modernization have continously been made and have recently been exerted actively in the mechanization and automation of manual operation mainly in welding, the introduction of electronic computer into production control, as well as the rationalization of production process by the adoption of conveyor system.In spite of these technical developments, more efforts have to be done in the solution of problem of the labour-intensive shipbuilding industry, which is suffering at present from the “prospertity without profit”.To cope with this difficulty of shipbuilding industry, the authors conducted the study on the characteristics of shipbuilding industry in comparison with the other modern industries. This study has revealed that the standardized production process can be settled on the basis of the steadiness of quality by the introduction of statistical quality control, and further that such work system with high productivity as is in general called “continuous flow production system” can be also adopted in the shipbuilding industry. Moreover, the authors have proved this fact by applying it actually to the hull construction works and have made a success of such modernization as is shown in the automation and specialization of welding in their company.Thus, it has been made clear that only on the basis of substantial improvement of production system through the application of mass prduction method, a series of modernization measures such as mechanization of manual labour, adoption of conveyor system and production control with use of electronic computer, will be realized on a full scale.

Study on the Notch Toughness of Structural Steels (2 nd Report)

In the previous report, it was revealed that the effects of high temperature prestraining on the retained ductility and notch toughness of various structural high tension steels were generally slighter than those for mild steels.In this paper, the characteristics of fracture stress curves were investigated on five high tension steels whose tensile strengths were ranging from about 50 to 80 kg/mm2, and also on two special structural steels for low temperature use, and compared with the results of previous report2) 12) for mild steels.Concerning the natures of both fracture stress curves, cleavage and fibrous, important informations were clarified as follows : (1) The shapes of both fracture stress curves were practically similar in each steel. Also those shapes were approximately same for every steel tested. The height of fibrous fracture stress curve was nearly proportional to the nominal tensile strength.(2) A good relationship was found as shown in Fig. 22 between the height of both fracture stress curves and transition temperature in V-Charpy test, using a reasonable parameter in Eq. (7).(3) An excellent notch toughness of quenched and tempered steel was chiefly attributable to the rise in fracture stress curve by this heat treatment observed remarkably for cleavage type one. Such behavior in stress curves should be favorable to the notch toughness judging from the above relationship.

One Example of Retrenchment in Man-Hours of Welding of Hull Construction (3) : Some Calculations Applied for Estimation of Economies Obtained by Technical Improvements of Welding

結果な らびに諸経験 にもとついてその建 造方式に も徹底 的な検討の メスを加 えて おり,そ れぞれ各社の周囲条件 に合致 した合理的な方式を確立 し,か つ実 行す る段階 に 落ち着いて きてい る.し たが って この現状 か ら考えて今 後の国際的な価格競争の波を乗 りこえて い くには,建 造 方式の根本的な改変あ るいは設備面 の大 巾な拡充 とい っ た件 もさるこ と な が ら,む し ろ各 工 場 で 分割 された stage,あ るいはさ らにこれを細分化 したbayの 諸点 で の各単位作業の細かい作業分析,な らび にこれに もとつ く諸工程の工数節誠に頼 らざるを得 ない時点に きてい る とい ってよいであろ う.こ こに述べ る自動溶接 付随作業 の改善 も上述0)ご とき現状 に直面 して得 られた結果の1 例であ るが,特 に 自動溶接 とい うものが部外 者の 目に も めだつ ものであ ることか らもおおか たの関心が もたれ る もの と考え,し たが って これにつ いて各造船所の現場で 考え られかつ行なわれていることに,筆 者 らの資料 も若 干加筆 して参考までにまとめてみ たもので ある.

Fracture of Notched Bar Tension Specimen

In order to investigate the characteristics of fracture stress curve of steel by notched bar tension specimen, we must clarify first the range of notch shapes which would cause an initial crack not at the contour, but at the center of notched section. Authors carried out extensive experiments and obtained some results, which are summarized as follows:(1) Initiation of center crack of fibrous type could be observed after sectioning longitudinally the specimens which were strained and unloaded just before their fracture by means of very careful and minute adjustment of load, using a rigid and small tension testing machine of screw type (capacity, 5tons) (cf. Photos. 1-4).(2) It was proved that “rim effect” could be recognized conspicuously on the flow stress curve of the specimen in which the center crack was initiated. By observing this rim effect, the range of notch shapes that would produce center crack was determined in detail as shown in Fig. 3.(3) It was also proved that no contour crack was found in the case where center crack would initiate and that this phenomenon might also be observed in the reverse way. Moreover, we observed that contour crack grew slowly in comparatively a long period and was quite stable, and that, on the contrary, center crack was very unstable and accordingly the specimen broke just after its initiation. The fracture mode was shear at the contour in almost all specimens and fibrous at the center.(4) It was presumed that micro metallurgical defects of steel might influence strongly on the initiation of ductile crack.

Observation about the Application of Arc-Air Gouging Process in Shipyard

It is a well recognized fact that the arc-air gouging process is more advantageous than the pneumatic chipping method in point of economy. In carring out the gouging in Japanese shipyards there arises an important problem because their electric source is of alternating current whereas the arc-air gouging should be of direct current.Considering this special situation of Japanese shipyards, authors have made different types of carbon electrodes for arc-air gouging in order to investigate their applicabilities and ascertained the usefulness of carbon electrode for use with alternating current in shipyards.

Kommerell Bead Bend Test for High Tensile Steels

To save the weight of structure, it is general tendency to adopt the low high-tensile-strength steel to the large structures instead of heavy section of mild steel plates.But it is quite difficult to weld such low alloy steels without causing cracks, because of their hardenability as compared to mild steels.The authors have studied the weldability of these steels and prepared this report to summarize our present knowledge of the effect of electrode types and preheat temperatures on weldment.As a result, conclusions have been obtained as follows :(1) In Kommerell bead bend test, comparison of transition temperature at 45°bending angle to maximum load (ductility transition temperature) or of bending angle to maximum load at temperature -20°C shows the difference between ductile and brittle behaviour of weldments for high tensile steels, while comparison of transition temperature at 90°maximum bending angle (fracture transition temperature) or of maximum banding angle at tmperature 20°C shows little significant effect of electrode type. (See Fig. 9)(2) Measuring above-mentioned ductility transition temperature, the weldments of low hydrogen type electrods shows sufficient ductility as compared to these of ilmenite or cellulose type electrods, (See Fig. 9)(3) Little difference has been obtained between the toughnesses of both weldments with ilmenite type electrodes when preheated at temperature 50°C, and with low hydrogen type electrodes without preheating. (See Fig. 14)(4) In any cases preheating over 250°C is needless. (See Fig. 13)(5) In general, higher hardness levels in heat affected zone of specimen exhibit lower bending angle to maximum load at temperature -20°C. In this case, hardness over 350 V.H.N. is unfavourable from the standpoint of behaviour of ductility transition in Kommerell test. (See Fig. 17)