This report is related to a case study on a new approach to technological forecasting of welding engineering. which seems to be one of the most appropriate methods, reviewing various methods for technological forecasting. In the modern age when the outputs of technological development have been applied and diffused in an exceedingly rapid rate, it would be next to impossible to establish more dynamic goals and development programs for the development of technology without predicting the possibility of technological development in terms of what, when and where. Under these circumstances, OECD reports that there are as many methods for technological forecasting as one hundred and dozens in kind. It is, however, true that most of the technological forecasting reported are nothing but concept and there are very few cases that the methods have been successfully applied. The case study reported here is to analyze the technoliglical forecasting in terms of its orientation, problems to be solved and a certain extent of its possibility, using so-called normative method and exploratory method, specifically about new segment of welding engineering which will stand for one of the major basic engineerings for production engineering in the future, and as a result we forecasted the future fifteen years later in terms of intuitive forecasting method (Delphi method). Consequently we have successfully, though not necessarily satisfyingly, made clear the possibility of 43 items range of newly developed welding engineering and its timing of realization as well as the conditions necessary for the forecasting and its realization. The purpose of this report is to review the technoligical forecasting methods and their procedures developed at the early stage.
Since plasma arc has been considered to be a suitable heat source for wet welding owing to the following factors, the feasibility of underwater welding by it is studied. (1) Plasma arc co-operating with plasma jet can be generated easily and kept in stable state in water, and is less sensitive to variations in torch-to-work spacing. (2) As energy transferred from plasma arc to work is highly concentrated, fusion efficiency of work is high. (3) Plasma arc is constricted by torch nozzle, so its directional property is excellent. (4) Plasma jet, kept operating all the diving time, acts as illuminating light source and makes it easy for the welder to work in water. As the first step to develop the process, preliminary experiments on some of the above-mentioned factors are made in simple welding environment, such as in city water and at water depth of 20 cm. And then butt welding and fillet lap welding under the conditions adopted according to information obtained in the preliminary experiments are done by using steel as base metal for a welded structure of 6 mm in thickness. Results of experiments show that underwater welding by plasma are (semi-transferred type plasma jet, i.e., plasma jet co-operates with plasma arc) can be done easily and stably and the weld has excellent properties in both tensile strength and notch toughness, though the weld metal includes blowholes to some extent. In conclusion, it is ascertained that this process can be put to practical use.
The welding process of solid phase welding was investigated using the tensile shear load and micro structure of cold pressure welds of copper, aluminum and iron followed by post heat treatment at various temperatures and for various times. The results are as follows. 1. The improvement process of the weld strength depends on post heat temperature, post heat time and welding deformation, and satisfies Arrenius' equation. 2. A rise in the weld strength is based on a relief of residual elastic stress due to recovery at the initial stage of post heat treatment, and an increase of welded areas which depend on thermally activated diffusion along the weld interface with the advance of post heat time. 3. The weld strength is determined by the combined effect of soundness of the weld interface and softening of the weld metal. The maximum weld strength is obtained at a certain time which depends on the base material, welding deformation and post heat temperature. 4. At elevated post heat temperature, the weld strength which has decreased due to softening of the weld metal, increases again owing to the elimination of voids at the weld interface, and welding deformation does not seem to affect the weld strength.
Recently, in design of structures, it is important that we have information on the correlation between load- and strain-cycling low-cycle fatigue. In this investigation, axial load- and strain-controlled fully reversed low-cycle fatigue tests were carried out on SM 50 steel, and especially characteristics of stress-strain hysteresis curves were studied. Behaviors of stress-strain hysteresis curves to failure can be discussed in terms of three stages-primary, stationary and final stage. Especially, authors clarified that stress-strain relationship in stationary stage, which occupies the most part of life to failure, depends upon plastic strain range rather than control method.
Linear regression analyses were made to show the effect of alloying elements and welding conditions on mechanical properties of submerged-arc weld heat-affected zone quantitatively. Alloying elements which decrease weld softening and are highly significant are carbon, chromium, molybdenum, and vanadium. Cooling rate of weld bond is also highly significant and the increase of cooling rate decreases weld softening. Factors which improve notch toughness of weld bond and are highly significant are increase of weld bond cooling rate and addition of vanadium. Silicon, nickel and molybdenum are effective in improving notch toughness of weld bond, they are little significant. Alloying elements which deteriorate notch toughness of weld bond are carbon, manganese, chromium, aluminium and boron, and carbon and manganese are highly significant, but addition of manganese and chromium seems to be necessary to have bainitic structures in weld bond. And carbon equivalents for notch toughness of weld heat-affected zone and softened zone strength are presented fcr quenched and tempered high tensile steel. The effect of alloying elements on notch toughness of middle heat-affected zone and quenched and tempered plate is not always consistent with that of weld bond.
A test was conducted at low temperature using notched tension plate specimens in order to investigate the influence of notch geometry and plate thickness on fracture stress and critical crack opening displacement. The following results were obtained. 1) Fracture stress and critical COD of welded specimens are lower than, those of base metal specimens. 2) Fracture stress clearly comes under the effect of plate thickness in region below transient temperature and critical COD also comes clearly under the effect of plate thickness except notch type C. 3) Fracture stress and critical COD of notch type B are lowest and so it is proposed that notch geometry of standard specimen of DEEP NOTCH TEST be substituted by notch type B.
Aluminum and aluminum alloys are usually welded by TIG or MIG welding, and the former may generally give less blowholes in deposited metal than the latter. But TIG welding has slow deposition rate, which causes a wider softened zone, and may lead to insufficient mechanical properties of welded joint. MIG welding gives higher welding speed and deeper penetration, but it is likely to form blowholes. This experiment was carried out to compare the static and dynamic mechanical properties of TIG and MIG welded joints. The following results are obtained; 1) Tensile strength and ductility of MIG butt-and double-tee joints, which were welded with lower heat input than TIG welding, were superior to those of TIG joints. 2) Fatigue strength at 107 cycles were : 9.1 Kg/mm2 for base metal, 8.0 Kg/mm2 for MIG butt-welded joint (reinforcement removed), 7.1 Kg/mm2 for TIG butt-welded joint (reinforcement removed), 5.5 Kg/mm2 for TIG double-tee joint, and 4.5 Kg/mm2 MIG double-tee joint. But the toe angle of fillet welds seemed to more affect the fatigue strength, because the higher fatigue strength was obtained by MIG double-tee joints with round-worked toe than by TIG joints. 3) According to X-ray radiographs MIG deposited metal had more blowholes than TIG deposited metal, but microscopically many blowholes were observed in a boundary zone of passes by TIG deposited metal. Especially interdendritic cavities were also found in MIG deposited metal.
Root cracking due to residual hydrogen has been investigated in 80 and 100 kg/mm2 high tensile steels by various loading fracture tests. The results indicate that (1) the fracture strength of root of welded joint decreases with time under constant loading condition, (2) delayed cracking may not occur when the residual hydrogen within weld metal is dischareged by post-heat treatment, (3) the activation energy determined by the effect of post-heat treatment on the cracking is in good agreement with the published values for the diffusion of hydrogen, (4) the residual stress and the applied stress have the same influence on the delayed cracking, and (5) the specimens preloaded prior to the final tests are less sensitive to the delayed cracking. From thermodynamical considerations, (1) the drift velocity of the solute hydrogen resulting from the stress filed of the notch root increases proportionally to stress intensity factor, (2) the hydrogen concentration near the root is proportional to dilatational stress, and (3) the energy balacne concept satisfies crack initiation condition.
Underwater welding was experimentally carried out in a water box by coated electrodes and semiautomatic CO2 welding. And It was investigated the occurrence of blowhole was affected by various welding parameters. The following results were obtained: 1) Sound deposited metal and welded joints were obtained under flat, horizontal and vertical positions from every coated electrode except the low hydrogen type one. Kinds of power sources and water proofing coatings of electrodes had no special effect on appearance and soundness of bead. 2) Welded joints by coated electrodes were superior in tensile strength but inferior in ductility to the mild steel base metal. 3) It was difficult to get a sound weld metal by low hydrogen type electrode under water. Blowholes in weld metal were remarkable in all welding current and arc voltage ranges. 4) It was also considerably difficult to obtain a weld metal quite free from blowholes by underwater semiautomatic CO2 welding.