A simple mathematical model for arc welding of thin plate is developed in this paper. The calculation model, used in this work, is divided into two phases. In the first phase, the heat flow in base metal is numerically analyzed in order to estimate the molten pool size. In the second, the surface tensional balance equation is numerically analyzed to obtain a theoretical configuration of molten pool and weld geometry. In the first part of this report, some typical phenomena in thin plate arc welding are simulated by the computational model and it is made clear that the computed results are quite satisfactory in a qualitative sense. In the second, the computed tolerance zone of process parameters, derived from the critical conditions of the lack of fusion and the burn-through, has been compared with the experimental one in thin plate TIG arc welding and a good correspondence has been obtained between the model analysis and the experiment. Consequently, it is concluded that the mathematical model, used in this work, is a useful guide to optimum process parameter in thin plate arc welding.
An investigation was carried out into bead formation characteristics of fused type SiO2-MnO fluxes with various angles of electrode inclination. Ripple marks on the bead surface were very rough and clear in low SiO2/MnO ratio, but it became indistinct with an increase in the ratio. And in case of very high ratio, the ripples was hardly able to find out. The roughness of ripples became heavy with an increase in the backward angle of the electrode, and in case of forward angle, the ripples was improved. And the improvement was more successful with flux of higher SiO2/MnO ratio probably due mainly to increase in the slag viscosity which suppress the pool motion. The change in the ripple appearance with the electrode inclination is considered to be a function of the efficiency of the arc force acting on the molten pool. So, if the electrode is inclined forward to strengthen the arc force, the more suppressed back and forth motion caused by pulsating gas pressure in the arc cavity would result in the calm ripplse. And the fact that the electrode angle is more effective at low SiO2/MnO ratio is considered due mainly to low slag viscocity. Besides, it was confirmed that Si and Mn content change in the weld metal hardly effect on the bead appearances.
A new hot wire TIG welding process has been developed to prevent magnetic interaction between TIG arc and hot wire current. In the new process, TIG arc current and hot wire current which are supplied from D.C power source are alternately switched by transistor switching circuit. Arc phenomena, wire heating and melting condition and upper limit of wire melting rate were investigated using this new process for stainless steel plate. The results obtained in this study are as follows. (1) Arc interaction at the time of TIG peak current was preventable and arc interaction at the time of TIG base current was slight when TIG base current was 50 A bellow. (2) Correlation of the hot wire feed rate and wire melting current was obtained in bead on plate deposition without TIG arc. (3) Relation between wire feed rate, deposition rate and wire current was obtained under bead on plate welding. Upper limit of wire melting rate was closely related to hot wire current.
The effect of welding parameters and wire compositions on the fume emission rate of CO2 arc welding by solid wire, has been examined. In addition, high-speed photographs of welding arcs have been observed to investigate fume generating phenomena. As welding current and arc voltage are raised, the fume emission rate increases, while it drops as tipplate distance is increased. The decrease of torch angle decreases the amount of fume. Increase of the argon content in CO2 shielding gas decreases the fume. The CO2 flow rate has almost no effect on the fume emission rate. The mechanism of the above phenomena can be generally explained by the fume formation mechanism previously proposed. Reduction of C and S content in the wire decreases the fume emission rate, while reduction of Mn, Si, Ti and Al content increases the rate. The influence of P content is almost none. These variation of fume generation can be mainly explained by the short circuit frequency of CO2 arc welding, on the basis of the fact that welding fumes are mostly generated immediately after the short circuit, which is observed by high-speed photographs.
Irregular variation of wire feeding rate in CO2 arc welding was investigated. Using a measuring apparatus, bearing a computer, for wire feeding rate, effects of welding conditions and wire characteristics on the feeding rate variation were studied. At the position of the feed roller, little variation was observed with and without arc generation. At the position of the welding torch, large variation was observed, especially when arc was generated. The effect of welding current was the most significant;the higher the current, the larger the variation. Therefore, the source of the variation was assumed to exist at or close to the welding roch. Wire curvature and copper coating also had significant effects.
Cooling efficiency of the plasma arc welding torch was investigated using visualization of water flow inside the nozzle cap. Cooling water in the heated nozzle is partially boiled and bubbles generate and extinguish repeatedly. Then water pressure vibration occurs by this phenomenon and it became clear that amplitude and frequency of this vibration correspond to changes in heat load and temperature of the nozzle. The thin-type torch was made as a trial and this torch can be inserted in the narrow gap (10 to 12 mm) joint. We used this torch for root pass welding in keyhole method in narrow gap joints and obtained satisfactory results.
Electron beam welding of conventional high manganese steels containing nitrogen or the like was difficult due to occurrence of blow holes and voids. In this report, tendency of defect occurrence (such as cracks and voids) and mechanical properties of electron beam welds of 14% Mn steel are described. A new type of high manganese steel (14% Mn, 0.6% C, 2% Cr, 2% Ni) without nitrogen addition which has been developed to prevent occurrence of blow holes and voids was used in this study. The steel plates used in the tests were 90 mm in thickness. A high vacuum type welding machine with maximum output of 42 kW (60 kV) was used throughout the tests. Test results indicated that weld defects occurred when bottle necked bead was formed and bead width was increased. The weld defects were voids and HAZ cracks. It was possible to prevent the defects by selecting a proper bead shapes and combining the bead width below 8 mm. HAZ cracks were explained in relation to the melting mechanism of electron beam welding and grainboundary liquation near the weld bond. Mechanical properties of electron beam welds were almost equal to those of the base metal.
The following results are obtained; 1) Focal point of Laser beam facility is determined by the minimum kerf width on tri-angle acrylic resin block. Focal point is constant and is not affected by changing Laser beam power. 2) Bead on mild steel plate experiment shows that the maximum penetration depth can be obtained by 125 mm focal length of lens which is focused at 2 mm under plate surface.
Real time measurement of the current path area of resistance spot welds is made at the middle and final periods of weld time on the foundation of physical information involved in the resistance between electrode tips, so as to construct new adaptive control systems for automatic quality assurance of spot welds in real time. Difference on physical meaning of the resistance and the voltage between electrode tips is shown theoretically and experimentally using R type and CF type electrode tips with different size in spot welding of thin mild steel sheet, that is, the resistance mainly involves information on current path area in spot weld and the voltage involves that on heat generation in unit volume at current path part and is not related to the current path area. Furthermore, the current path area of spot weld can be measured in real time at the middle and final period of weld time by the resistance between electrode tips, computed from the voltage between electrode tips and weld current in welding process.
Real-time measurement of the current ptah area in spot weld by the resistance between electrode tips can be applicable to the welds at the early period of weld time, introducing a new parameter of effective time-integral value of the voltage between electrode tips in the case of mild steel sheet of 0.8-3.2 mm thickness. The current path area in spot weld is related to the resistance between electrode tips, current path length and average resistivity, which is a function of material compositions and average temperature at the current path part in spot weld, based on Ohm's law. In above factors, the current path length is nearly constant in the case of no splashing, and furthermore, average temperature at current path part can be estimated from effective integral value of the voltage. So, average resistivity is determined only by effective integral value of the voltage. As the result, the current path area can be measured by both the resistance and the effective integral value of the voltage at any period of weld time under certain welding conditions with no splashing. Furthermore, the new real-time measurement of current path area by the resistance and the effective integral value of the voltage can be adapted to the spot welds with various thickness of 0.8-3.2 mm at any period of weld time under certain welding conditions of no splashing.
Effect of welding current direction on tensile shear strength (TSS) of joints has been studiedin the weld of aluminum alloy (0.8t 5052) to mild steel (0.8t SPCC). In this welding, uni-directional discharge current from capacitors is utilized as welding current. Therefore the polar effect, the difference of weldability caused by current direction relative to the position of dissimilar metals to be joined, has been investigated. It was found that higher TSS value was obtained using welding current with direction from SPCC to 5052 (refered this as SPCC (+) and the contrary as 5052 (+)). The difference of TSS was about 20 kg/spot with R-type electrode tips. It became more significant in the case of CF-type electrode tips; obtained TSS of the joint, by the use of welding current with peak value 45.6 kA and peak time 2.8 ms, was about 350 kg/spot under SPCC (+) and 150 kg/spot under 5052 (+) respectively. The shorter the duration of impulsive weld current, this tendency appeared more clearly. Measurement of the voltage between SPCC and 5052 revealed that the polar effect appeared in this faying interface at early stage of the welding process and vanished with metallic contact growth. It is concluded from the results that the polar effect is attributed to the semiconductor property of the surface film of the metal such as oxide film rather than the thermoelectric phenomena of the metals themselves.
Automation of welding process of nozzles, the part where trunk pipes and branch pipes join, has been very difficult due to the complex three-dimensional saddle-like shape of wedling lines. However, the authors have developed an industrial robot, controlled by a microcomputer, that can automatically perform multipass welding of such processes. This study is about the development of the algorithms and welding conditions that are suitable for nozzle multipass welds. This paper describes the basic concept of control methods for automating such welds utilizing industrial robots.
The automation of the multi-pass welding of nozzles is very difficult because of the complex shape of the weld line. However, the authors have developed an industrial robot controlled by a microcomputer that can automatically perform the multi-pass welding. The parameters of MAG welding process such as torch position, torch direction, welding velocity, etc. were first obtained, then the welding algorithm was established and confirmed experimentally. The objective of this study is to select the welding conditions to input to microcomputer. It has been confirmed that the prameters of welding condition were enalbe to give suitable bead shape and bead appearance.
Arc phenomenon and wire fusion in the arc spraying of aluminium and stainless steel are ovserved by a high speed camera. Arc voltage and arc curernt are measured by an oscilloscope. The whole arc spraying process from the wire fusing stage to the particle adhesion is investigated. Main results of the experiments are summarized as follow; (1) The arc fluctuates periodically with the period of 0.6-1.2 ms long in this study. (2) The fused metal flies in the band like shape at relatively low speed in the arc flame. (3) Arc voltage fluctuates within 50% of its average value corresponding to the motion of the arc under the normal spraying condition, however, the short circuit does not occur. (4) The fluctuation of arc voltage depends on the spraying condition and material, and it is closely related with the adhesion strength of sprayed coatings.
A welding heat conduction simulator to analyze melting, solidifying and cooling processes in arc welding has been developed using an interactive personal computer (CPU: Z80). The system is characterized in procedures as follows: 1) Basic routine for the determination of welding conditions by interaction between an engineer and a computer: In the first step, desirable or expecting welding parameters are input by an engincer. Next, the computer checks whether these conditions are reasonable or not, and displays the results. Finally, if the results are not satisfied, the flow is returned to the first step and the conditions are corrected by the engineer. With repetition of the above trial, practicable and reasonable conditions can be found out. 2) A method for presetting three dimensional weighted distribution as a simulation of arc heat source in each welding process: Geometrical heat elements, such as line, disk, half-elliptical plane or -ellipsoid composed of point heat sources are prepared. Then, each dimension and distribution of each element are set, and each direction and combination of the elements are input according to display on the CRT. 3) A method for deciding position of heat source and its extent in a given groove: The first approximation of deposited and molten regions in the groove is carried out using the estimating value of melting efficiency, wire melting rate and mean bead width. The heat source can be set on the CRT on the basis of the result. 4) A procedure for determining optimum welding conditions: Three routines, that is, approximation of deposited and molten regions, computation of a weld thermal cycle and shapes of penetration and HAZ boundary, and estimation of hardness and microstructural constituents with memorized SH-CCT diagrams, are utilized to determine optimum welding conditions.
Mo and W, which have excellent high temperature properties, are often brazed to Fe for extended use. However, the direct brazing of Fe to Mo or W tends to cause the exfoliation of the brazed joint in service. In order to eliminate this defect, the Ni plating on the Fe base metal prior to brazing has been practiced in industry. This paper clarifies the effect of Ni plating on Cu brazing of low C steel to Mo or W. It also examines the shear strength of the brazed joints. In the case of no plating, the low C steel base mteal dissolves into molten Cu filler metal and, simultaneously, the dissolved low C iron deposits as a plate-like Fe-Mo-Cu or Fe-W-Cu alloy phase from the Mo or W base metal at a constant brazing temperature—that is, a "dissolution and deposit of base metal" takes place. Since Fe of the deposited phase penetrates into the Mo or W base metal, an intermetallic compound phase Fe7Mo6 or Fe7W6, which is inherently brittle, is formed at that base metal boundary. The Ni plating of 1.1 to 4.3μm thickness on the low C steel base metal to be joined restrains the dissolution and deposit of base metal; it also improves the mechanical properties of both deposited and intermetallic compound phases by alloying with Ni. The shear strength of the brazed joint is thereby improved.
The effect of additional elements of silver filler alloys on the corrosion resistance of brazed stainless steel joints have been investigated in relations to the microstructure of filler alloys and brazed interface. Corrosion tests were made in 0.4 mol/l NaCl +0.005 mol/l CuCl2·2H2O at 25°C. Addition of Mn enhanced the corrosion of filler alloy itself by yielding β phase. Additions of Si, Sn, Sb and Ni improved the corrosion resistance, above all Ni addition appreciably improved the interfacial corrosion resistance. The mechanism of improvement of corrosion resistance at brazed interface by Ni addition were thoght to be as follows. Ni depleted zone was formed at brazed interface of stainless steel side in the case that the stainless steel was brazed with Ni free filler alloys. The Ni depleted zone was changed into ferrite phase during brazing and was less corrosion resistant compared with stainless steel matrix, whereas the zone was not formed in the case that brazed with Ni bearing filler alloy. Therefore, Ni addition into filler alloy maintained the relatively good interfacial corrosion resistance by preventing the formation of less corrosion resistant Ni depleted zone.
Concerning electron beam welding of nodular cast iron, effects of factors as pretreatment of base metal, heat input and number of passes on behavior of graphite in welds by bead welding and insert type welding (insert metal; SUS304, 0.5 mm thickness) have been investigated by microscopic observation, electron probe microanalysis, thermal cycle measurement, tensile test, etc. The results obtained are as follows: (1) Microstructures of fusion zone by bead welding are almost eutectic structures. Carbon contents of fusion zone by insert type welding (4.5 kJ/cm) are in the range of 0.51 to 1.63% according to penetration ratio and microstructure of fusion zone (as cast, 1 pass) by low penetration ratio shows almost austenitic structures and microstructures of fusion zone by other conditions (as cast; 2 passes, annealed; 1, 2 passes) show austenitic plus martensitic structures. (2) Carbon contents of melted zone surrounding graphte in bond are in the range of 4.3 to 5.0% (hypereutectic structures). Carbon contents of acicular martensite outside of melted zone are in the range of 1.2 to 1.8%. Carbon contents of these zones and diffusion distance of carbon from graphite show tendency to increase as heat input and number of passes increase. As cast material has tendency to show higher carbon contents of these zones than annealed material. (3) In tensile tests of welded joints by insert type welding, fractures have tendency to initiate from hyper eutectic zones in bond and propagate through these brittle zones. Lowering of joint efficiency are influenced by these brittle zones.
Relationships among the solidification variables and the primary structures which significantly affect the mechanical properties of Weld metals have been investigated using 25Cr-20Ni austenitic submerged arc welds composed of one-directionally solidified structures. Over the tested range of heat input grain growth in the heat affected zone of as-casted plates occurred to a lesser extent than solid-solution treated plates. Width of columnar grains was agree with the base plate austenite grain size at the fusion boundary, and increased toward the weld center. Quantitative correlation among columnar grain width and the solidification variables, however, was not observed. Coarsening and the morphological change of dendritic structures took place in the same manner as casting, and the primary dendrite arm spacings are in reciprocal proportion to the square root of cooling rate in the liquid-solid region. Coarsening process of cell structures can be also explained by variations in cooling rate like dendritic structures. In a elliptical shaped weld puddle solidifying with dendritic structures, cooling rate in the solid increased with an increase in the distance from the fusion boundary, whereas cooling rate in the liquid-solid region varied inversely.
A study has been performed to examine the influence of nitrogen and oxygen pick-up on the weld toughness of the commercial high purity 19Cr-2Mo steel using the mixed gas of argon and various percent of nitrogen, oxygen and air as the shielding gas. The effect of REM on the weld toughness was also investigated with the intention of improving it. The toughness of the weld metal was evaluated using subsize Charpy V-notch specimens. With addition of small amount of air to the shielding gas, the toughness of the weld metal drastically deteriorates due to the pick-up of nitrogen and oxygen. The increases of nitrogen and oxygen in the weld metal cause the precipitation of fine intragranular chromium nitrides and spherical oxide inclusions of more than l μm diameter, respectively, which induce the embrittlement of the weld metal. The weld toughness is found to be significantly improved by REM addition. Effective REM content ranges 100 ppm to 400 ppm when the amount of air in the shielding gas being less than 1%. The absorption rate of nitrogen and oxygen in the REM bearing weld metal seems to decrease due to the formation of the REM oxide film or the REM-absorbed layer on the surface of the molten pool. Consequently, the amounts of nitrogen and oxygen picked-up in the weld metal decrease, whichi result in improving the weld toughness.
On the multipass welds in heavy plates of high tensile strength steels, various types of cracks occur, namely, root cracks, toe cracks and underbead cracks at the heat affected zone and transverse cracks in the weld metals. Extensive studies have been devoted to the factors causing these cracks and the methods of preventing them. Recently, a new type of cracking has been detected. These cracks occur transverse to the welds in segregated areas of the beat affected zone. So it is considered that the factors and counterplans have to be newly developed. In this paper, testing methods which simulate actual welding conditions were used. And a U-groove restraint test specimen, which was partially dipped into water, was used as a standard test condition. From this severe condition, the required postheating time and temperature were investigated. Various types of steels were tested with these conditions. The main results are as follows; 1. The transverse crack at the heat affected zone initiates at segregated regions in the heat affected hardened layer and propagates in the hardened layer of one pass of the multipass weld by hydrogen and residual stress. 2. The occurrence of the cracks is related to the carbon equivalents of the plates, including segregation. The crack occurred in plates over 0.45-0.50% in carbon equivalent, when preheating at about 100°C. 3. Where the plate is 100 mm in thickness and 0.57-0.58% in carbon equivalent, and the heat input is 45 KJ/cm by submerged arc weld, the preheating of 125-150°C and the postheating of 250°C×4h is required to prevent the crack.
The carbon equivalent of heavy thick plate of high strength steel is usually high in order to obtain sufficient strength, and the effect of the segregation is notable due to a small reduction ratio. Moreover, there are two disadvantages in heavy thick plate; firstly, high three dimensional residual stresses develop during welding; secondly, hydrogen accumulates due to the difficulty of its emission. So the precautions against various kinds of cracking during welding are required. The same factors exist when practising gas cutting for edge preparation before welding. Therefore, it is probable that the edge crack due to gas cutting occurs in heavy thick plate of 50 kgf/mm2 class high strength steel. In this paper, the features and the factors affecting edge cracks during edge preparation by gas cutting were studied in the case of heavy thick plate of 50 kgf/mm2 class high strength steel. The main results are as follows; 1. Hydrogen gets into the heat affected zone from environment during gas cutting. Reducing the cutting speed or increasing the hydrogen atomic ratio of the cutting gas enables more hydrogen to enter the heat affected zone and this increases the risk of cracking. 2. The tempered martensite embrittleness due to heat cycle by bevel cutting assists hydrogen induced edge cracking. 3. In case of the steel of 0.45% carbon equivalent and 145 mm thickness, the crack occurred at the segregated portions in plate caused by both hydrogen and tempered martensite embrittleness.
To make clear the effect of inclusion-shape and distribution on the lamellar taering macro-pattern of fracture surface and direction of crack-propagation have been investigated. As the results, several modified cranfield type cracking test methods have been pi oposed. These cranfield tests have several built-up direction of weld beads against the rolling direction of steels. For comparison, some slow bend tests with same materials are used for the study. Following results were obtained. (1) In the cranfield test, the steels with many elonged inclusions have characteristic striped pattern in their fracture surfaces. Typical terrace-and-wall is obsreved in the cross section along the stripes. (2) Crack-behavior in the cranfield tests shows several different types, it depends on the built-up direction and inclusion-length or width. (3) Slow bend tests have same tendency of crack-behavior in cranfield tests.
13 Cr cast steels, which are martensitic stainless steels, have been shown that the sensitivity of weld cracking was remarkable. However, their properties of residual stress distributions are not made clear. From the standpoint of confirmation of welding conditions and strength assessment for weldments, it is required to investigate the distributions of welding residual stresses. Therefore, transient thermal stresses of weld heat-affected zone about 13 Cr cast steels, SCS5 are investigated by a round bar which both ends are fixed and subjected to a thermal cycle simulating weld heat. The results indicate that the effect of transformation expansion on residual stress distribution are remarkable in comparison with carbon steels, SM41B. The residual stress in a region heated above Ac1 transformation point become compressive stress of about -100 MPa and yet the peak residual stress become about 400 MPa in a region out of the HAZ. And also, one-dimensional analysis method to conveniently evaluate residual stresses is presented. The effects of preheat temperature on residual stresses are discussed and the estimated residual stresses by the convenient method showe good agreement with the experimental results of butt welded joints.
Gusset welded joint is known as having the lowest fatigue strength among other types of welded joints. In order to improve the fatigue strength of gusset welded joints, the effect of the shape of weld ends on fatigue strength was investigated for three types of gusset welded joints using mild steel (SS41). Non-load carrying and load carrying gusset welded joints were examined, which were boxing fillet welding (type A and A'), side fillet welding (type B and B') and lengthened side fillet welding (type C and C') types. The test result indicates that the fatigue strength increases in the following order, type A and A'<type B and B'<type C and C' and that type C and C' are about 22% stronger than type A and A' at N=2×106. This result can be discussed in terms of difference in notch effect at the weld ends and in crack propagation process. The effect of residual stress may be insignificant. The effect of toe grinding was also investigated. Toe grinding increased fatigue strength of type A' and did not increase that of type C' while it changed location and appearance of the fracture.