The contact face of materials to be joined recieves compression and shearing force under ultrasonic vibration, with becomes hot by friction, and then both the metallic faces are exposed, metallic atoms appreaching mutually; in this way ultrasonic welding is done through mutual attactive force and diffusion of metallic atoms. In this joining method, the joined state sometimes becomes crescent-or ring-shaped, but in order to get perfect (the whole area) joining, it is necessary for to chose the conditions so as to give enough compression and shearing force. There are many factors that influence heat generation at the contact face of materials to be joined, of which particularly effective conditions are described below. 1. Ultrasonic power: The greater it is, the higher is temperature rise. 2. Tip pressure: The lower it is, the higher becomes temperature rise. But under the same ultraso nic power, tip pressure for the highest temperature at the contact face of materials has some limit, which increases with increase of ultrasonic power. 3. Joining time: Temperature immediately rises within 1 to 2 sec., but thereafter becomes almost constant. 4. Materials to be joined and sheet thickness: The harder the material is (of cource enough compression and shearing force must be given) and the thinner the sheet is, the higher is temperature rise. 5. As the contact face of differently thick materials, the temperature is higher under the condition when a thinner sheet is placed on the tip side than when a thicker sheet is done, and the thinner is the sheet on the tip side, the higher is the temperature rise. Therefors joinability (workability) by ultrasonic welding is almost dependent on materials and their sheet thickness to be placed on the tip side. In this study, we observed a temperature rise over 700°C. The relationship between joining strength and conditions is proportional to the relationship between temperature rise at the contact face of materials to be joined and ultrasonic vibrating conditions which elevate the temperature, and All of 0.08 mm titanium, aluminum and copper were fractured in the base metal around nugget of joining part. The effects of joining conditions on joining properties are as follows: 1. Ultrasonic power: The greater it is, the higher is joining strength. But tip or anvil and material to be ioined are often ioined. 2. Joining time: Within the limits in which the material to be joined is not joined with tip or anvil, the longer the better. 3. Tip pressure: When the joining strength is proportional to the joining area, tip pressure had better be high to the effect that nugget diameter is enlarged. 4. Surface condition of the material to be joined: The cleaner the surface, the higher is the joining strength, especially electrolytically polished material is excellent. In joining titanium to titanium or titanium to stainless steel, tip pressure (50 to 60%), ultrasonic power (40 to 70%) and joining time (over 100%) should be increased in comparison with the joining condition of same thickness aluminum sheet. And using of convex anvil is efficient. Joinability (workability) and joining strength by ultrasonic welding were improved by means of electrolytically polishing the material to be joined and using suitably insert.
The most essential fact in arc welding is that the mother drop is always confined within the surface of penetration. Putting a focus on this point, the author discussed in this paper on a growing liquid drop model which is considered to reproduce essential features of arc welding phenomena. It was concluded as follows. (1) The pulling force due to the surface tension acting upon an arbitrary contact line of a liquid drop was calculated, and the nature of the pulling force, which is acting on the contact line of a liquid drop confined within a flat surface of solid and counteracting pushing force of gas jet, was, discussed. And the mechanism of oscillation of a liquid drop blasted by gas jet explained. (2) A model which is constituted of a growing liquid drop, which is constantly added with liquid through a moving pipe at a constant rate, and led by an accompanying gas jet. with cleathe ping action upon the flat surface of a solid covered by an unwettable film, was shown to behave in quite simillar way to arc welding. (3) Especially the self-regulating effect of welding process, by which the welded bead is kept normal in some range of welding conditions, was proved to be the result of interaction between the interfacial tension of mother drop and the pushing force of arc. The phenomenon of undercut or overlap was explained as the phenomenon deyond range of the above-mentioned effect. (4) The similarity between the action of common gas jet against a liquid drop and that of arc force against a mother drop has become clear.
Assuming that the contact angle of mother drop upon the surface of penetration is a constant value θ0, the pulling force acting on the contact line of the mother drop was calculated, by which the oscillation of the mother drop was caused. It was concluded as follows. (1) Defining the X-and Y-component of pulling force due to the interfacial tension acting upon ds part along the depressed contact line of the mother drop within the surface of penetration as dFX and dFY dFS=γS⋅dY, dFY=γY⋅dX, γX=γ(cosθ0 cos θg+sinθ0 sin θg/cos α) γY=γ cos θ0/cos θg where θg; angle of inclination of the surface of penetration at point P α; angle between the contact line and equi-depth contour line at point P (2) Using the above equation, there is found a strong pulling force acting upon the contact line near the point where it starts to deviate from the melting line of the surface of penetration, which tends to pull back the drop to the melting line. (3) If the depressed contact line of mother drop starts to displace itself, the movement is accelerated by the digging action of arc upon the bare surface of mother plate. (4) The interaction between these forces and the digging action of arc brings about an oscillation of the mother drop and a displacement of exposed surface of mother plate, which results in uniform penetration. The shape of penetration depends on the strength of arc force or size of depressed part of mother drop.
Effects of transverse restraining force on root cracking of high strength steel welds were studied with NRIM TRC tester, that is, Tensile Restraint Cracking Tester which was developed by the National Research Institute for Metals. In the TRC test, two pieces of a butt welded specimen is tensile-loaded transverse to the weld line and kept at an arbitrary constant value until cracking occurs. In the present tester, two pieces, 210×120 mm, test welded as long as 120 mm, can be loaded up to a maximum of 20 tons. Since the root cracking in this investigation was exclusively of cold cracking, type, the tensile loading was done 3 minutes after the finish of test welding in a Y-groove joint. The results obtained with high strength steel welds of tensile strength level of 60 to 80 kg/mm2 are as follows : (1) The root cracking of high strength steel welds in this study was of cold cracking and delayed failure type. Effect of hydrogen embrittlement in welds was obvious. (2) A cold cracking was generally initiated after a certain incubation period and finished after an additional period. The incubation period was the smaller, the greater the tensile restraining stress which is defined as the mean stress in weld metal, that is, the load divided by the longitudinal sectional area transverse to the direction of loading. (3) There was a critical stress below which root cracking did not occur. The value of the critical stress seems to depend on ductility of weld metal, hydrogen content in weld zone and welding condition. The critical stress was increased by raising the preheating temperature until the value reached the yield stress of the weld metal at a critical value of preheating temperature. With thecr itical preheating, it was observed that no root cracking occurred in modified Lehigh Restraint Cracking Specimen tested with the same welding condition. (4) For a T-1 steel weld, welded at room temperature and kept tensile stress free in the TRC tester for 20 minutes and more after welding, both the critical tensile stress and the incubation period were considerably increased, which seems to show that the amount of diffusible hydrogen in weld metal is an essential factor in root cracking of high strength steel welds. (5) The latest theory of hydrogen embrittlement in steels which had been proposed by Troiano and others seems to be valuable in explaining the mechanism of root cracking in high strength steel welds.
One of the most conspicuous merits of projection welding is the application of multiple projection welding, whereas prevailing conditions are mostly for single projection welding. In practice, the application of single projection welding is rather rare. In the case of multiple projection welding, if we multiply the welding condition (current, electrode force) based on the single projection welding by the number of projections, an enormous capacity is required and it is not feasible in practice. So, welding current and electrode force have come to be reduced and accordingly the size of projection should be minimized. In case we apply the multiple projection welding with minimized zize of projection, projection nuggest is inclined to move and the weld strength lowers sometimes.It is the purpose of our experiments to scrutinize the cause and mechanism of movement and to obtain the specific index for welding design and procedure. The following experiments were done with the pneumatic pressure fixed to zero and only with the dead weight of upper movable part. i) Series projection welding ii) Moving condition in various welding currents. In the next experiments, the welding machine was set horizontally and carried out varying the following points : i) mass of movable part. ii) size of projection. iii) thickness of mating plate. iv) distance between projections. v) stainless steel. vi) welding current. vii) electrode force. we could find the cause of movement as follows : a) in case the projection fuses, and the mating plate does not melt at the moment. b) no sufficient electrode force which is necessary for the welding part at the moment. c) strong electro-magnetic force by welding current.