In this paper we describe an application of arc sound for the detection of welding process. Arc sound has a good competence for the useful source of the information with high level of SPL and good S/N. The hole and step on the base metal, change in arc length, change in groove width, interruption of shielding gas, humping bead formation and burn-through were detected by the arc sound. And the value of its application was confirmed.
Crystalline materials in welding fumes of covered electrodes have been identified by X-ray diffraction method. Nine test electrodes have been prepared with covering. of single component material, MnO2, Fe2O3 or SiO2 using various binding agents. Five commercial electrodes including three types of non-lime electrodes and two types of lime electrodes have been used. The fume of tested electrode covered with MnO2 or Fe2O3 consisted mainly of MnFe2O4 or Fe3O4 respectively. Fe3O4 and amorphous materials are formed, in the fumes of tested electrode covered with SiO2. The fumes of. non-lime electrodes consisted mainly of Fe3O4. MnFe2O4 was also found in ilmenite type. Since these fumes contained about 20% SiO2 other elements seemed to form amorphous materials together with SiO2. The X-ray diffraction pattern of the fumes of lime type electrodes were so complicated that they were separated into water soluble, magnetic and non-magnetic materials. KCaF3, NaF, CaF2 and Fe3O4 were identified as the main crystalline materials in the fume of general lime type. NaF, CaF2, MgO and Fe3O4 were identified in the fume.of modified lime type. As soluble materials, K2CO3 or Na2CO3 was found in general type or modified type respectively. Both lime type fumes contained a little amount of chlorine as KCI.
The waveform analyzer containing minicomputer was developed. The computer system in this equipment is capable of sampling two channel simultaneously at rate up to a limit of 500 sampling per msec and storing 128, 000 data on each experiment. Waveform of arc voltage in short circuit transfer range of CO2 gas shielded arc welding was examined by this waveform analyzer. By setting up a certain threshold value, arc voltage wave was divided into two periods: short circuit period and arc period. In this study, the waveform in arc period was analyzed. The standard deviation of arc period (σ value) was related to arc stability. Arc stability decreased with the increase in σ value. σ value increased with higher arc voltage, higher welding current and longer wire extension, especially σ value was strongly influenced by the variation of arc voltage. Experimental formula for σ value, which evaluated the arc stability, was expressed by welding current, wire extension and arc voltage.
Pipeline installation requires the use of a welding equipment presenting high pipe-laying efficiency and therefore high welding speed. It has been attempted for this need to develop the latest automatic pipeline welding system. The first report has described the development of welding procedure by the automatic one side downhill welding method using high-current-density GMAW with regard to the girth welding of pipe. This report describes the development of these equipments and controlling system. Characteristics of this controlling system are summarized as follows. 1) All welding sequences and conditions are controlled by a microcomputer. 2) The position of welding carriage is controlled by ten thousand addresses around a pipe of any diameter. 3) Two welding carriages can detect starting point of arc automatically using the plate with two magnets. and can weld at the same time. 4) Beads of starting position and crater are overlapped automatically welding by Soft-Arc-Start condition, therefore weld is completed with no intergrinding.
The arc welding method, hereinafter referred as Switching TIG-MIG Welding Method, was carried out in the welding of thick plates of copper without preheating. This method is characterized by preventing the arc interaction between TIG and MIG electrodes by switching alternately the welding current to each electrodes. Furthermore, in this method, the polarity of the tungsten e!ectrodc of TIG is negative to eliminate its consumption and the polarity of the feeding wire of MIG is positive to increase its melting rate. In the welding for bead-on-plate runs with 10 mm thick copper plates, the deep penetration can be achieved by bringing each electrode closely and by increasing the TIG current in keeping the MIG current constant. Due to preheating by the leading TIG arc, the penetration in copper base metal incr as.s mor.: than a conv.ntional MIG. In those experiments, 10 mm thick copper plates are welded in one pass without any preheating. Therefore, this welding method was found effective in the welding of copper plates.
In electron beam welding of Al-5%Mg alloy casting (JISH5202, Class 7 AC7A), effects of factors such as welding conditions, base metal thickness (6, 16 mm), Ti addition (Ti free, 0.12%Ti) and etc. on welding phenomena, metallurgical and mechanical properties of weld zone have been investigated by microscopic observation, thermal cycle measurement, grain size measurement, fatigue test and etc. The results obtained are as follows: (1) In welding of AC7A with 6 mm thickness, arcing phenomena are reduced by proper welding condition and weld zone with sound mechanical properties are obtained. In welding AC7A (Ti) with 6 mm thickness, arcing phenomena are prevented by beam current at 5% down of filament current and weld zone with sound mechanical properties are obtained. (2) In welding of AC7A and AC7A(Ti) with 16 mm thickness, arcing phenomena are prevented by combined conditions such as low power density of beam (ab; 1.2), preheating (130°C) by EB passes and beam current at 5% down of filament current and weld zone with sound mechanical properties are obtained. (3) Intercrystallrne cracks in HAZ are observed with AMA, 16 mm thickness welded joints. Eutectic compositions (mainly Al3Mg2) with low melting point are recognized in intercrystalline cracks in HAZ. (4) Al-5%Mg alloy casting with 0.12%Ti addition shows good weldability owing to refined grain size of base metal and HAZ.
Possibility of controlling the reverse side bead formation during electron beam welding by detection and control of the eleccron beam current which pierces through the base plate (the piercing beam current) has been investigated. Three types of electron beam welding machines were used in this study. The first one is a 6 kW (150 kV×40 mA) high vacuum type, the second is a 15 kW (30 kV×500 mA) low vacuum type, and the third is a 42 kW (60 kV×700 mA) high vacuum type machine respectively. All welding were performed in the flat position. It was concluded from the study that, (1) It is possible to form smooth and stable reverse side bead by controlling the piercing beam current. (2) There is a large fluctuation in the wave form of the piercing beam current. When the piercing beam current signal is integrated by an integrator with appropriate time constant, the mean value of the signal can be adopted as the monitoring signal for the formation of appropriate reverse side beads. (3) A test controller of the piercing beam current was attached to the 15 kW (30 kV × 500 mA) EB welding machine, and bead-on-plate welding tests were performed on carbon steel pipe (SGP) of 15 mm in thickness. Smooth and stable reverse side beads are formed when the mean of the piercing beam current is 15 to 20 mA, the focus coil current is 2.94 A and welding speed is 400 to 500 nun/min.
Surface temperature of specimen at the central axis of the welding electrode was measured by a Pb. S optical pyrometer in resistance spot welding of mild steel. The measured value was related to process of nugget growth. The relationship between them was investigated under various welding conditions and with or without shunt current for various thickness specimens. The results of this study are as follows; (1) Temperature measuring technique with optical fiber and infrared detector is an effectual method for investigation of transient thermal phenomena in resistance welding, because it is less sensitive to electric noise. (2) The maximum surface temperature of specimen at the central axis of the electrode, the rate of temperature rise and the time when the rise in temperature is saturated are closely related to process of nugget growth qualitatively. (3) Surface temperature of specimen in welding is fluctuated at twice the frequency of the weld current. The delay angle of the phase of temperature fluctuation by the weld current increases with weld time in resistance spot welding of 1.2 mm thickness sheet.
This report is concerned with the weldability, especially the characteristic of the nugget formation in the spot welding of metal plated steel. The factors which determine the characteristic of the nugget formation are as follows, i) the melting point of plated material, ii) the surface condition of plated material and base material. In case of one side plated steel, the influence of the melting point of plated material on the characteristic of the nugget formation depends upon the combination of the plated film; that is, the plated sides face to face or the plated sides face with electrodes. For instance, in case of the plated sides face with electrodes, the plated film with 800°C melting point doesn't melt during welding because electrode is cooled by water. In case of the plated sides face to face, the same film melts because interface is the nugget formation area. As a result, the current density during welding depends upon the combination of the plated film. In case of the both side plated steel, the nugget formation is more difficult than that in one side plated steel. In addition, nugget formation is also influenced by the surface condition of the plated material. In case of the base material, the same tendency is obtained. This surface condition means the amount of oxides on the surface of the plated material or the base material. For instance, the increasing of the amount of oxides means the increase of the resistivity, and thus current path is restricted. As a result, the nugget is easily formed.
This report deals with the effect of faying face condition on welding phenomena and mechanical properties of the welded joint in continuous drive type friction welding. The base metals used were pure aluminium and 0.25% carbon steel. Conditions of faying faces are labelled as, A: Clean face degreased with benzine B: Greased face C: Face covered with oxide film D: Face with a drilled hole of 1 mm in diameter and 3 mm in depth. Main results are as follows; (1) There is no problem to make the joint, which has good qualities in tensile test and bending test, in case of A. (2) In case of B, the weld, which is made by using lower friction and upsetting pressures, is broken in the aluminium zone adjacent to weld interface in tensile test and has small cracking angle in bending test. These phenomena are caused by pores owing to grease itself and steel particles, which are kneaded into the aluminium base metal in width of 0.1 mm from the rubbing interface. (3) In case of C, the weld has low tensile strength and poor bending ductility, which are attributed to the oxide film remained at the weld interface. (4) In case of D, the centre hole of faying face does not affect strength and bending ductility of the weld, unless the ratio of area of the hole to that of faying face is not so large.
Titanium-steel is a combination of dissimilar materials, which are difficult to weld in general, owing to inevitable formation of the brittle intermetallic compounds. A prominent feature of friction welding process is being able to weld dissimilar materials in many kinds of combinations. This report deals with friction weldability of pure titanium and S25C steel with a diameter of 12 mm. Main results are summarized as follows; (1) A suitable welding condition to obtain sound weld, which has over 100% joint efficiency, is Rotational speed N: 2440 rpm, Friction pressure P1 : 20 kgf/mm2, Upsetting pressure P2: 24 kgf/mm2, Friction time T1: 2.5-5.0s. (2) Bond condition at central part of weld interface has a great influence on tensile strength of joint. (3) The welded joints fracture at titanium base metal in rotary bending fatigue test. It shows that fatigue limit of the weld must be over that of base metal, 24 kgf/mm2. (4) The joint, made under even the suitable welding condition, has poor bending ductility.and impact value. (5) The decarbulized layer is formed in S25C steel along the weld interface and thin intermetallic compounds arc formed at the weld interface excepting central part. (6) Tensile fracture takes place in the heat affected zone of S25C steel at central part of weld. However, the intermetallic compounds at peripheral and middle parts cause brittle fracture of weld.
The influence of mixing of helium into argon on some characteristics of plasma jet, spraying phenomena and properties of coatings are investigated. Spraying conditions are; Operating gas: Ar (100%), Ar (75%) +He (25%), Ar (50%) +He (50%), Flow rate (total) : 40 l/min Electrical output: 21, 28, 35, 42 kW, Spraying distance: 100 mm, Spray powder: Ni-Cr alloy Main results arc summarized as follows. (1) Arc voltage becomes higher with the increase of helium into argon. (2) Thermal efficiency of plasma jet spray torch decreases with the increase of mixing ratio of helium into argon. (3) Mixture of helium makes plasma jet angle smaller. Therefore in such a case higher temperature of the jet is kept to a wide range. (4) Plasma jet, which is operated by argon mixed with helium, has higher heating effect to the object in front of torch. (5) Flying velocity of particles decreases with the addition of helium into argon. (6) The structure of Ni-Cr alloy coating becomes finer and adhesive strength of coating is improved considerably by addition of helium into argon.
Many reactor pressure vessels for chemical, oil refining and coal conversion process have been successfully operated at elevated temperatures under high pressure hydrogen. At present, it is well recognized that appropriate cares shall be taken in the design, fabrication and operation for the safety of these reactors, since hydrogen-induced material degradations have been observed in existent hydro-desulfurizing reactors for oil refining. It has been pointed out that one of the key problem is the disbonding or cracking at the transition zone of overlay and base metal interface. This report summarizes and discusses about; a) Fundamental study on the effect of welding parameters of strip overlay welding process on the sensitivity to hydrogen-induced disbonding. b) Discussions for reducing disbonding susceptibility. c) Experimental results carried out on above concepts. The main results obtained in this investigation are as follows; 1) With respect to the susceptibility to hydrogen induced disbonding, there observed no significant effects of strip overlay welding conditions. 2) The stainless steel overlay weld metal of austenitic-martensitic duplex structure exhibited satisfactory resistance to the disbonding than that of austenite plus several percents ferrite structure. 3) The overlay metal of austenitic-martensitic duplex structure can be deposited by controlling welding current and travel speed to the extent considerably higher than convensional range.
Type of inclusions in ESW metal and the relation between the existence ratios of these inclusions and CaF2 content in slag were investigated by scanning electron microscope observation and energy dispersive X-ray analysis. Existence ratio of oxide-type inclusion shows a minimum at the content of 8-19 mol% CaF2 in slag. The observation of the minimum can be attributed to the beginning of the formation of Ca-F bond at the content of 7-10 mol% CaF2 which is clarified by various spectroscopic methods such as X-ray photoelectron and emission X-ray spectroscopies. Refining effect of manganosilicate slags containing more than about 10 mol%. CaF2 on oxide inclusions decreases by the formation of Ca-F bond in the slags. Further, it is suggested that relations between existence ratios of oxide, oxysulfide and sulfide inclusions can be discussed in connection with sulfide capacity in slag.
Using an arc atmosphere controlling chamber, effects of the welding condition and atmosphere on the nitrogen content of the iron weld metal were investigated by gas tungsten arc welding. The results are as follows: (1) The nitrogen content decreases with increasing the welding current. (2) The nitrogen content hardly depends on the arc length and the travel speed. (3) The nitrogen content is anomalously high at low arc atmospheric pressure region and constant above 0.2 atm of the nitrogen pressure in N2 gas atmosphere (PN2≤1 atm). (4) The nitrogen content increases with increasing the nitrogen partial pressure and is constant above 0.1 atm of the nitrogen partial pressure in the N2-Ar and N2-He gas mixture atmospheres (PN2+PAr=1atm, PN2+PHe=1 atm). (5) The nitrogen content gradually increases with increasing the nitrogen partial pressure in the N2-H2 gas mixture atmosphere (PN2+PH2=1 atm). (6) The nitrogen absorption into weld metal was discussed with equilibrium data.
At present, it is very difficult to make clear solidification processing of weld metal, because it includes various problems which are difficult to solve theoretically and experimentally. This experiments, as a fundamental stage to make clear the solidification processing, were performed on high pure Al, in which solidification processing is comparatively simple, by TIG arc spot welding, which needs no filler metal. Measurement of temperature was carefully carried out by very slender thermocouple, and also dynamic observation of sloid-liquid interface in whole solidification processing was performed by high speed camera. The experimental results were analized from the following points such as behavior of solid-liquid interface, solidification rate, temperature distribution, cooling rate, temperature gradient, undercooling, and the relation between points mentioned above and welding conditions. As the analized results, it was found that the transitional measurements were considerably different from calculated values based on theory of heat conduction, because it was based on mean value in solidification processing.
To achieve the latest stringent requirements for the mechanical properties and the bead shape of submerged arc welds (SAW) such as the longitudinal welds of large diameter pipe, the solidification process has been fundamentally studied using 25Cr-20Ni welds obtained by the one-sided SAW process at two heat input levels. The basic solidification variables have been measured by immersing W·3Re-W·25Re thermocouples and the correlation with weld puddle shapes has been discussed in relation to welding heat transfer. In the liquid-solid region of tear-drop shaped weld puddles observed commonly in SAW process, cooling rate and temperature gradient decreased toward the weld center and consequently the length of liquid-solid region increased. These results are similar to those in casting. Solidification rate, however, showed a maximum value at the inflection point of hammer decanted weld puddle contour, which was approximately agree with the measured isotherm of liquidus temperature. Formation of the tear-drop shaped weld puddle can be explained by considering a substantial decrease in heat flow dimension in the vicinity of inflection point. This proposed mechanism provides interpretations that the shape transit of weld puddle from the ellipse to the tear-drop occurs with increasing in heat input or welding velocity and the solidification process of the latter is significantly influenced by the latent heat of fusion.
The authors proposed the simple approximate equations for estimating thermal cycle of bond of Tjoint considering the change of heat flow and law of similitude in geometrically similer specimen. These approximate equations have terms of plate thickness-ratio and heat input. Unbalance of heat input and heat-exchange between veritcal and horizontal plate have not so much effect on the thermal cycle of bond. Therefore, these equations are able to use for practical case. Estimated values from these equations nearly corresponded to the experimental values obtained from arc welding with coated electrode.
The initiation and propagation of root cracks in steel have been investigated with oblique y, straight Y and 45° single bevel grooves of the TRC test in the underwater wet welding process with covered electrode. Welding experiments are carried out by using HT 60 steel and D5003 covered electrode. The following results are obtained: (1) The diffusible hydrogen quantity reaches to the constant volume in about 2.4 x 104 min. (about 408 hrs.), where in air, it is about 30 cc/ 100 g Fe, and in underwater, about 70 cc/100 g Fe, i.e., the more root cracks occur in underwater welding. (2) The maximum hardness of the heat-affected zone is about Hv 350 in air, and Hv 440 in underwater, thus the crack sensitivity is higher in underwater welding. (3) In the TRC test, the lower critical stress of straight Y groove is higher than that of 45° single bevel groove in both air and underwater welding. (4) As for no-fracture specimens in the TRC test in underwater welding, there are many microfissure at the martensitic structure in the coarse grained zone near the bond. (5) The fracture surface shows predominantly the dimple pattern in air welding, while in underwater welding, the quasi-cleavage of hydrogen embrittlement pattern is widely observed there and near the root it shows many intergranular patterns.
Authors have already reported that fatigue strength of structural steel welded joint was improved by rapid cooling from below A1 temperature, and that this improvement depended mainly on quench aging of interstitially disolved atoms. But the amount of them may be decreased by such heat-treatment when as-received steel has more disolved atoms than solid solution limit at heat-treatment temperature. Therefore, in this study, the effect of interstitially disolved atoms on fatigue strength improvement of welded joint by such heat-treatment for some steels and the amount of interstitially disolved atoms in as-received SS-41 steel were investigated by fatigue test and internal friction measurement. Results obtained were as follows; 1) Fatigue strength of welded joint of SS-41, SM-41, and SM-50 steels were remarkably improved by rapid cooling from 700°C. 2) By succeeding aging at 50°C, fatigue strength of SS-41 steel welded joint had much disolved atoms were improved, but that of SM-50 steel welded joint had fewer disolved atoms were not improved. 3) The amount of interstitially disolved atoms in as-received SS-41 steel was almost equivalent to solid solution limit at room temperature.
The purpose of this study is to investigate the fundamental phenomenon of fatigue strength of brazed joint. Torsional fatigue strength of brazed butt joint was measured, and some presumptions as follows for the fatigue strength of brazed joint were discussed. 1) Filler metal which does not have a fatigue limit in a form of bulk has fatigue limit in a brazed gap when the strength of base metal is higher than that of filler metal. 2) The fatigue strength of brazed joint does not have the direct relation with the static strength. 3) The effects of base metal strength and joint gap on fatigue strength of brazed joint should be discussed as the relation between joint geometry and small scale plastic deformation at crack tip in filler
The purpose of this study is to clarify the effect of welding residual stresses on fatigue crack propagation rate. Materials used are steel of 800 MPa in tensile strength. Specimens are center cracked plate and consist of four kinds: base metal, welded joint with a longitudinal bead on center of specimen, this welded joint done post heat treatment and welded joint with longitudinal beads on both sides of specimen. Results obtained are summarized as follows: (1) Tensile residual stresses increase fatigue crack propagation rate and compressive one decrease it. (2) The effect of residual stresses on fatigue crack propagation rate (da/dN) is more remarkable when stress intensity factor range (ΔK) is small and stress-ratio is low. (3) When tensile residual stresses are large and ΔK is small, da/dN-ΔK relation is unique and independent of stress-ratio. (4) Above results are closely related with fatigue crack closure phenomena.
One of the most fruitful areas for application of the AE technique lies in monitoring defects of weld part. AE monitoring system was designed to apply AE technique to the continuous detection of weld defects and classification of noise during welding process by using synchroscope and spectrum analyzer. The system applied to a simulation welding experiment where several simulating AE were generated at the simulated weld line on the test specimen like as travelling weld arc and weld defects in weld bead, if occurred, and received at the various location of different distance from the signal source of the simulated weld line. Both reproducibility of simulated AE source and directivity of transducer have of good performance to detect the weld defects and noise. Further the system will be successfully applied to monitor and analyze the signal from weld defects and noise by the AE signal shape and frequency spectra.
AE of hot cracking has been monitored and quantitatively correlated with crack length for SUS 310S stainless steel on TIG welding. It was found that there exists a linear relationship between length of hot cracking and the total summation of AE counts, and the total summation of AE energy also. AE signal from weld specimen can be classified three types of AE signal from theirs shape and frequency spectra by using the AE monitoring system. The frequency spectra of their AE signals were distinguished, especially, the different distribution of frequency band from DC to 400 kHz. It is considered that the source of A type AE signal was generated at hot cracking, the type B one was generated from sound of friction between weld specimen and jig, and the type C was generated from arc noise only during welding. These classification of AE signals could be useful for the practical application of acoustic emission monitoring to welding situations.
In previous work, the detected shapes and frequency spectra of AE signals were distinguished from AE signal of hot cracking and arc noise in the frequency band of DC to 400 kHz. This work was carried out to distinguish the all of these AE signals from hot cracking test during TIC welding for SUS 310S stainless steel with the AE monitoring system added data recorder and analyzed fully the AE signals in the frequency band from 290 Hz to 320 kHz. The shape of AE signal from hot cracking had a larger amplitude than the sound of friction and the one of arc noise, and its frequency spectra had the A type shape which had 2 or 3 peaks in the frequency band from 290 Hz to 320 kHz. Fracture surface of hot cracking consist of dendritic boundaries and divided into two region of liquidus phase and solidus phase in just welding. The fractographic observation confirmed that the histogram of the A type of AE signal correspond closely to the area of solidus phase region. Therefore, the A type of AE signal generated at hot cracking. The shape of AE signal generated from friction had smaller amplitude and its frequency spectra consist of same level in a continuous freouencv bands between 290 Hz and 320 kHz. The shape of AE signal from arc noise was recognized small amplitude like as a sine curve and its frequency spectra had single frequency component at about 150 kHz. Further the system added data recorder will be successfully applied to classify the AE signal from weld sounds including hot cracking and arc noise by AE signal and frequence spectra and monitored the hot cracking for welding process.