This study has been performed on the heating form of the faying edges to be welded and the effect of the convergence-angle at the vee-shape which affect remarkably on the quality of weld in high-frequency-induction-welded aluminum-alloy tube with 20 mm outside-diameter. The results show that the heating form of the faying edges assumes a kind of flash near the apex of the vee-shape. This seems to be the part where the high-frequency current converges and short-circuits, and the faying edges are heated most intensively. It is necessary to supply power input enough to form the flash with sufficient brightness in order to melt the faying edges successfully. The flash form is significantly affected by the convergence angle. The angle narrower than 5° causes the unstalbe flash. It is recommended that the angle wider than 6°should be maintained to obtain the stable flash. On the other hand, the quality of the weld is, too, affected by the-angle. The reasons are the flash form mentioned above and resulting effect of welding-cycle time. The same recommendation is offered about the angle to produce the desirable quality. The angle recommended is wider than that in welded steel tubes. It appears that the high-frequency current does not so concentrate at the faying edges resulting from proximity effect in the wider angle. Therefore, it is extremely important to control the convergence-angle constantly.
The present study was carried out to examin the effect of mechanical heterogeneity on the static tensile properties of dissimilar metal welded joint. To prepare test pieces, steel plates (Yield strength: 29.1 kg/mm2, Ultimate strength: 35 kg/mm2) and Copper plates (Yield strength: 6.4 kg/mm2, Ultimate strength: 24.1 kg/mm2) were welded by electron beam welding. The results obtained are as follows: (1) When the angle between loading line and weld line becomes small, the tensile strength of test piece is lower than that of copper. (2) The large strain concentration appears at the neighborhood of weld line in copper when the angle between loading line and weld line is small. (3) Four types of fracture mode were obtained in the dissimilar metal welded joint.
The paper describes the method of solving differential equation of heat conduction for moving source under the boundary condition that the equiradial surface of fininite length around a heat source, i.e., semi-spherical surface for a point source and cylindrical surface for a linear one, is kept constant temperature, supposing to estimate thermal field in underwater welding by local cavity methods. Analyses are conducted for point and linear heat sources and rigorous solutions are obtained, and their results are compared in detail with Rosenthal's solutions. Furthermore, the average cooling rate at particular temperature range, which is practically useful for the prediction of hardness of welded part of steel plate, are analized using the obtained solutions and the effect of the radius of cooling terminal on the rate are clarified for various welding variables.
This paper describes the effect of focussing optics on the shape and dimensions of laser welded beads, and interaction between the focussed laser beam and material during welding with a 1 KW CO2 laser. Theresults obtained are summarized as follows: (1) In laser welding, a "bead transition" occurs, in which the shape and dimensions of the bead change significantly with a slight displacement of focal position relative to the workpiece surface, and is caused by a change in absorption rate of the beum energy depending on whethere or not a cavity is produced; the cavity is formed by the reaction force of evaporation depressing the molten metal surface. (2) Under optimized focussing conditions, the beam reflection loss during welding can be ignored in a wide range of welding speed, 1 to 40 in/min. (3) The bead width decreases with increasing welding speed; the width depends on the temperature of molten metal around the cavity at low speeds, and on the spot size at high speeds. (4) The focal length of lens is evaluated for the deepest penetration depth depending on welding speed at 1 KW power level; 127 mm for v<1 m/min and 64 mm for v>1 m/min are recommended. The distance between focal point and workpiece surface giving the deepest penetration depth is in proportion to the focal length, and decreases exponentially with welding speed. (5) The range of the focal position within which the penetration depth is deeper than 90 % of the maximum depth is determined. This range of the laser welding is extremely narrower than that of the electron beam welding, owing to the very high reflectivity of the laser beam at metal surface.
A series of researches has been conducted in order to establish the procedure of the Low Temperature Postweld Heat Treatment (LTPWHT) superseding the conventional intermediate stress relief annealing, by which the prevention of the transverse weld cracks induced in the thick 2-1/4Cr-1Mo steel weldments by submerged arc welding process can be made possible. First we found that this kind of crack could be prevented by only reducing hydrogen concentrations in the weld zone. Then, following this result, the relationship between hydrogen concentrations in the weld zone just after welding and the practical welding conditions was investigated, as was described in Report 2. Next, we proceeded to clarify the relation between the reduction of hydrogen concentrations through LTPWHT and its treating conditions in the previous paper. As the final step of this research, cracking tests were carried out to evaluate the critical hydrogen concentration under which the cracks did not occur at all, by comparing both results of the cracking tests and calculations on the distributions of the hydrogen concentrations obtained in the weld zone under the same conditions as the cracking tests. As a result, it was found that the highest hydrogen concentration had to be reduced to less than 3.3 cc/100 gr after LTPWHT in order to prevent the cracks. Adding this result to the results obtained previously made it possible to determine the appropriate conditions of the LTPWHT for preventing the cracks under a wide variety of the welding conditions, such as plate thickness, groove width, preheat and interpass temperature, and pass interval. An additional investigation clarified that a newly developed material of the low hydrogen flux had a large effect upon the mitigation of the LTPWHT conditions for preventing the cracks.
A particular projection welding was carried out for welding dissimilar metals as the way previously reported. Two pairs of dissimilar metals, namely, carbon steel (C steel) disc with ring projection and pure titanium block, low alloy steel (LA steel) disc wirh ring projection and cast iron block, are welded respectively. Main results of this study are as follows; (1) In C steel-titanium weld joint, the welding strength depens more loosely on the projection sharpness than in C steel-cast aluminum alloy weld joint previously reported. The low thermal conductivity of titanium causes the temperature of the projection to decay monotonously from the top to the bottom during welding, therefore projection does not collapse in its middle portion differenig from C steel-cast aluminum alloy weld joint. (2) In C steel-titanium weld joint, the shorter welding time leads to the higher weld strength because of its smoller heat input. Large heat input causes the formation of intermetalliccompounds in cooling process after welding. (3) C steel-titanium weld joint having the tensile strength equivalent to that of titanium base metal (36 kg/mm2) can be gotten, using next welding factors. The ring projection diameter is 22 mm, its corsssection is isosceles-trapezoid, height 2 mm, top width 0.5 mm, bottom isotropic angle 80°, and the welding current is 60KA, weld time 0.5 cycle (8.3 msec), electrode force 2.2 ton. (4) In LA steel-grey cast iron joint, the weld strength remains at most the half of grey cast iron base metal strength (23 kg/mm2) because of the disposition of flaky graphite parallel to weld surface. But in LA steel-nodular cast iron joint, the weld strength rises as high as 90 % of base metal tensile strength (41 kg/ mm2), using next welding factors: The ring projection diameter is 30 mm, its crossection is isosceles-trapezoid, height 2 mm, top width 0.5 mm, bottom isotropic angle 70°, and the welding current is 69 KA, welding time 3 cycles (50 msec), electrode force 1.6 ton. (5) According to the estimations of the temperature distribution in weld joints by calculation, the differences of the plastic flow caused by the projection sharpness are explained qualitatively, and the various characteristics of plastic flow in C steel-cast aluminum alloy, C steel-titanium, LA steel-cast iron weld joints can be explained. (6) Practically to weld dissimilar metals using this method, condenser welder is better than any, other welders for its stability and efficiency, and spring-attached electrode is indispensable.
This paper deals with the effect of welding conditions and a restraint pitch on changes of root gap during welding in case of butt weld joints with restraint. The calculations. of changes of root gap during welding are carried out under. various conditions of heat input and restraint pitch. In this case it is assumed that the rigidity of restraint is infinite. The main conclusions obtained in this report are summarized as follows: (1) In case of butt weld joints with restraint under the condition of relative small restraint pitch, a root gap closes in any welding condition. (2) The root gap closes largest between the weld start position and the first restraint position during welding. (3) When the moving distance of heat source become large, the displacement at heat source uH pulsates with a constant amplitude. In this case the, maximum closing displacement uH occures when the heat source passes the restraint position. The maximum closing displacement uH in this quasi-stationary state is constant even if the restraint pitch is changed. The maximum closing displacement uH is approximately expressed by the following equation. -uH=4.5(q/h⋅√v)-1/2 [uH] : mm [q/h] :cal/sec⋅cm [v] :cm/sec (4) The maximum closing displacement between the weld start position and the first restraint position is expressed by the following equation. |uH|+(ΔuH)s (ΔuH)s=Bs(q/h⋅√v)-1/2 Bs=1.1(1p=600) Bs=4.2(1p=1200) Bs=5.3(1p=2100) (5) It is sufficient to make the restraint pitch short only in the neighborhood of weld start position in order to decrease the maximum closing displacement during welding.
In the plasma welding, the welding conditions, that is nozzle diameter, composition and flow rate of plasma gas and cover shield gas, welding current and travelling speed, must be selected according to material and thickness of the work. In the plasma arc welding of stainless steel, we discovered that the range of proper welding condition is remarkably affected by the quality of the back. shield gas. To study the effect of the composition of back shield gases on the forming of back beads, we examined plasma arc welding of 304 stainless steel (t=9 mm), with various back shield gases of Ar, N2, CO2, Ar mixed CO2, Ar mixed O2, N2 mixed CO2, and N2 mixed O2. A summary of the results is shown below. (1) When O2 or CO2 is mixed to inert gas as back shield gas, the length of back plasma flame is shorter than in the case of pure inert gas. There is a tendency of the flame be coming shorter according to the amount of O2 or CO2 mixed to inert gas. (2) When we used inert gas that is Ar or N2 as back shield gas, the range of proper welding condition is very narrow. Therefore welding work is very difficult. But the range of proper welding condition is remarkably expanded by mixing of oxidizing gas that is O2 or CO2 to inert gas. (3) By mixing of 10% O2 or 30% CO2 with Ar, the range of proper welding condition becomes maximum. With mixing of over 50% O2, the back bead is severely oxidized, spatter increase, undercut and concave occur at the back bead. (4) Indifferently to the composition of back shield gas, the cross section of welded metal appeared wine cup. And microstructure, hardness and corrosion resistibility of the welded metal were not affected by the composition of back shield gas.