The authors have investigated on surfacing technique on aluminum alloys by using gas tungsten arc welding (GTAW) process. The used filler metals were composite cored wire of seamless tube type and 1.2 mm in diameter. They were of Al-Cu composition with varied copper contents of 60, 70 and 80%. Each wire consisted of a copper tube sheath and an aluminum solid wire enclosed. The authors investigated the effects of arc current and weld cooling rate on microstructure, hardness distribution and porosity formation. They studied through chemical analysis the oxide film that covered the surfacing weld metal. They also analyzed the gases evolved in vacuum from machine cut porosities. The hardness in cross section of Al-70%Cu surfacing weld metal decreased from 270 HV to 170 HV with an increase of surfacing current in the case of helium shielding. Helium shielding drastically reduced the porosities that existed in the case of argon shielding. The remaining porosities became smaller than 0.2 mm in diameter. Moreover, the dual shielding by argon-helium gases was found to eliminate perfectly the porosity formation in the surfacing weld metal. Chromatography analysis revealed that the gas in porosities was dominantly hydrogen. The thickness of oxide film on the argon shielded weld metal surface was found to be remarkably greater than that of helium shielded weld metal, and thereby it might have caused more porosities in the case of argon shielding.
The formation of an anodic spot on the molten pool is caused by a floating slag bit on the pool. The necessary conditions to change a slag bit into an anodic spot were discussed. The anodic spot current is a part of the whole arc current and the remaining current forms an anodic region dispersed within a certain range on the pool. The anodic spot exists within the region and is located in balance between the outward force of the plasma stream and the magnetic force between the spot current and the remaining current. Sometimes multiple anodic spots are formed around the circular molten pool in a stationary GTA on a steel plate. The anode configuration changes in shape with the passage of time. The formation mechanism of the multiple spots was clarified. The penetration profile is shaped as the pool is deeper around the periphery than at the center on the arc condition to form the multiple spots.
The purpose of the present report is to comprehend the property in the D.C. glow discharge under the conditions which is used for the actual plasma process. We observed the glow discharge morphologies, using the Langmuir probe method. We examined the influence of the metal (Al, Ag and Sn) vapor on the glow discharge phenomena. It was found that the morphologies of the glow discharge was classified into four types. Evaporation of Al into glow discharge increased the discharge current but decreased the discharge voltage. On the other hand, the introduction of Ag-vapor or Sn-vapor decreased the discharge current and increased the discharge voltage. These results suggest that there are the different states for metal vapor in glow discharge. It is concluded that these phenomena are mainly caused by the value of the ionization energy.
The change in arc sound with burn through in MAG welding was measured, being related with the welding current. Also, we observed the change in arc morphology with the burn through by a CCD camera. The welding current was 300 A and the welding speed was 5 mm/s, that is, the welding was carried out only in the spray transfer region. We made holes in the workpiece with diameters of 4-9 mm in advance of welding and intentionally produced the burn through. Two types of burn through were observed. One of them was the stagnation type in which molten metal temporally stands on the hole before the burn through. In the other, the molten metal does not stagnate. In the stagnation type, the arc sound instantly becomes low immediately before the burn through and increases suddenly at the same time when the burn through occurs.
An algorithm for the inverse heat conduction problem in welding on the quasi stationary state has been discussed in this paper. An optimization problem of the temperature field during welding has been proposed in order to estimate the distribution of heat inputs and/or the penetration shape. In the expression of the problem, the analytical solution of the heat flow equation are applied for the estimation of temperature field, and the objective function is defined as the difference between the calculated and the measured temperature. The convex programming method are applied to solve the optimization problem. As the result of this work, it is made clear that the proposed method is useful for the estimation of the efficiency of heat source and the temperature error at target point make it difficult to estimate the distribution of heat input accurately.
In this paper, the structure of bonding interface in wiring harnesses of automobiles is investigated depending on the experimental results, and described the new technology having suitable characteristics both electrically and mechanically by the use of hybrid method of crimp termination and welding with heat pressure
A new brazing method was investigated in order to improve the strength of insulated copper wires jointed by fusion technology. This process of the brazing method is composed of fusing and brazing for joining brass terminal and insulated copper wire. Shear tests of the joint were carried out at room temperature after each test, namely, 2000h exposure at 150°C or 250°C, 1000 thermal cycle test between -55°C and +150°C, and salt spray test at 35°C for 2000h. After durability test, We observed the joint interface and find Cu, Ag, P and a little Zn. In these tests, the fracture are observed at the base metal without damage at joint region. Moreover, the strength of the joint between a wire without insulating coat and a brass terminal was also evaluated, and equivalent strength is obtained as that given in case of the wire with insulating coat.
An example of application of neural network is introduced. The backpropagation (BP) model is applied to the weld bead visual inspection. The bead shape data are picked up from the actual weld bead and divided into three categories. The weight values of the connections which joint the units in the different layer of the neural network are formed through the learning process made by using these data for each category. As the result of the test, it is shown that the discrimination between the sound bead and the defect bead can be done properly if the selection of the network parameters and the learning process are made suitably.
Factors affecting the bonding strength of Si3N4-metals joints were discussed through examining the causes for improvement in tensile strength of Si3N4-molybdenum joints by controlling the reaction layer thickness using Cu-5%Cr, Cu-1%Nb and Cu-3%V insert metals. Microstructures of reaction layers being thinner than the optimum thickness were almost homogeneous and the interfaces between Si3N, and the reaction layers were still smooth. Defects such as porous zone and crack occurred in the reaction layers thickening than the optimum thickness, while the asperity of the interface became larger. The insufficient reactivity of insert metals against Si3N4 substrate provided the planar fracture at the interface between Si3N4 and the reaction layer and followed to diminish the bonding strength. The fracture in the reaction layer was due to the defects in the reaction layer and as a result, the bonding strength was deteriorated again.
A Mild steel was welded in pressurized Ar-O2 gas mixture atmospheres up to 2.0 MPa, using a 1.6 mm diameter solid wire. The effects of ambient gas pressure and gas composition on the arc welding phenomena and mechanical properties of weld metal were studied. The main results are as follows : The fluctuations of arc voltage and welding current are small and the arc stability is fairly good. The weld metals obtained in this experiments have no defects such as under-cutting, overlapping, blow holes. The Vickers hardness and tensile properties of weld metals were varied with the ambient gas composition, but did not depend on the ambient gas pressure. The Charpy V-notch toughness of weld metal was changed markedly with O2 partial pressure in atmosphere and showed a maximum at 0.02-0.05 MPa oxygen partial pressure which resulted in about 0.03 mass% oxygen content of weld metal having a fine ferrite structure. This suggests that toughness is strongly influenced by the oxygen content of weld metal.
Effect of two step aging and cold rolling treatment on the hardness of Ti-15V-3Cr-3Sn-3Al alloy and its welds. Two step aging treatment was made by a process aged at 673 K for various times and aged at 773 K for 86.4 ks after solution treatment. The cold rolling treatment was made by a process solution-treated, 20% or 50% cold rolled and aged at 673 K for various times. The two step aging treatment accelerated the precipitation of alpha phase, increased the volume fraction of alpha phase and increased the age hardening in both specimens solution-treated at 1573 K and 1073 K. As the aging time at first step 673 K was up to 100 ks, fine alpha phase was observed, the duplex microstructure consisting of fine alpha phase and corse alpha phase was observed above the time. The cold rolling treatment accelerated the precipitation of alpha phase in 1073 K solution treatment. The microstructure after aging showed fine spherical precipitates of alpha phase by cold rolling treatment. The two step aging treatment and the cold rolling treatment caused the hardness increase in not only the base metal but also the weld heat affected zone.
This paper deals with an effect of the load hysteresis on the fatigue life of single spot-welded joint specimen of tensile-shear type for mild steel (SPCC) and high strength steel (HT50) of 0.8 mm in thickness under 2-steps repeating load. Main results obtained are summarized as follows: (1) The fatigue life for SPCC is generally longer than one for HT50 under usual constant amplitude repeating load, but it is possible that the fatigue life for HT50 is very longer than one for SPCC under the specific repeating load condition. (2) It becomes clear that fatigue life is considerably influenced according to mechanical properties of spot welds, and fatigue damage due to each load of 2-steps repeating load is not independent each other and can not be discussed without considerations on the hysteresis effect of each load.
The objective of this work was to explain a relationship between a distribution of carbide particles in overlay composite alloys and the size of abrasive sand on abrasive wear. The overlay composite alloys were fabricated by plasma transfer arc powder welding. Reinforcing powders of Cr-carbide and Ti-carbide were mixed with Co-base alloy powder (stellite powder), respectively, and the mixing ratio of those powders were 80: 20, 60: 40 and 40: 60. The volume fraction of non-fused carbide particles and crystallized carbides increased with the increases of the mixing ratio. The average hardness of matrix including Cr-carbide powder increased with increase of the mixing ratio, while that of matrix including Ti-carbide did not depend on the mixing ratio. In order to assess the resistance to abrasive wear of the overlay composite alloys, a rubber wheel abrasion test was carried out on the surface using three size of abrasive sands, respectively. Weight loss caused by wearing decreased as the amound of carbide particles increases. Especially, the abrasive wear resistance of the composite alloys including Cr-carbide powder depended on the volume fraction of non-fused Cr-carbide particles including needle like carbide. On the distribution of carbide particles, distances between carbide particles have been measured to estimate a value of matrix mean free path (λm) from which the abrasive wear resistance can be appreciated. It is found that weight loss caused by wearing decreased when a value of λm/Ds (the size of abrasive sand) became less than 1. Within the value of λm/Ds below 1, the abrasive wear resistance of composite alloy including Cr-carbide was better than the composite alloy including Ti-carbide. The Ti-carbide particles were crushed by larger abrasive sands, and hence its resistance to abrasive wear decreased.
In this paper, a method of predicting welding residual stress in a T-joint using inherent strain (the source of residual stress) is verified by experiments. The measured inherent strains are compared with the results of thermal elastoplastic analysis and the simplified formulae proposed by some of the authers. Released strains along the welding direction of T-joints were measured by strain gages, and inherent strains were calculated from the released strains. The stress equilibrium across the cutting plane during releasing strains is necessary for determining the inherent strains accurately. Measured inherent strains in T-joints agree well with the results of thermal elastoplastic analysis and also with the simplified formulae which are presented within the scatter of the inherent strain rlictrihntinn The proposed method of predicting welding residual stresses using the inherent strains is experimentaly validated.
The establishment of analytic condition of tearing instability of structural component containing weld defects is required. However, because of the mechanical heterogeneity in welds, it is complex to evaluate the resistance of crack extension and tearing instability in the welded joints. In this paper, the applicability of various tearing instability criteria to welded joints was experimentally investigated. The results obtained are as follows ; (1) Tearing instability criterion described by fracture mechanical parameter should be applied to homogeneous material like base metal in principle. (2) However, the prediction of instability on the even-matched weld joints was not almost affected by the estimation error on fracture mechanics parameter caused by the heterogeneity. (3) Tearing instability criteria without fracture mechanical parameter were suitable for the prediction of instability on the welded joints. But the application criterion should be selected by the aim of instability assessment. (4) Behavior of tearing instability was affected by CM, (=material compliance) as well as CMZ (= loading compliance). It was clear that material having large CM1 value was not easy to instabilize.
Research and Development of Si3N4 turbo-viscous vacuum pump rotor were conducted. It is difficult to fabricate this type of the rotor by machining of monoblock Si3N4 because it's shape is complex. So, bonded construction in which disks and axle were located by the connection of projection and bore was applied to fabrication after disks and axle were separately sintered and machined. Main results obtained are as follows. (1) 80wt%Cu-20wt%Ti brazing was chosen for bonding method because joint strength properties at room temperature -773 K were excellent. (2) It was predicted by calculation of stress that high stress generated in bonding joint near the connection of projection and bore at high speed rotating. From this calculation result, restriction of bonding area which was not brazed this high stress area was applied so that reliability of rotating characteristic could be raised. (3) Si3N4 turbo-viscous vacuum pump rotor fabricated with above mentioned method rotated by peripheral speed 196 m/s at spin test. From this spin test result, it was confirmed that ceramic vacuum pump rotor could be alterable for metal vacuum pump rotor.
New microsoldering process has been researched and developed by inserteing Sn/In and Sn plating layers at the bonding interface preliminary without both additional solder and flux. This paper clarified In roles is improvement of bonding strength and ductility of Sn-In diffusion reaction layers at the bonds. The bondability is improved as supply of In plating layers of thickness of 1 to 3μm on the Sn plated Cu alloy lead of thickness of 2 to 10μm, and also it makes possible bonding such as low heating temperature which is tip temperature of 500 to 650 K. Furthermore, this paper showed experimentally to the optimal thickness of plating layers and the possibility of fine pitch, multi-lead mounting in bonding process. The good reliability of the bond is clarified by both high temperature storage and whisker test.
The authors had investigated the kerf formation phenomena in an argon plasma cutting and in a nitrogen one in the previous report. Then, it was clarified that the optimal value of cutting speed for minimum bevel angle condition is different from that for minimum dross adhesion one. This fact suggests that the plasma arc behavior generated within the copper nozzle due to constricting the arc remarkably influences the kerf formation phenomena in the plasma arc cutting. However, it is not easy to examine the plasma arc behavior by experimental methods. Especially, the behavior within nozzle cannot be observed by the experimental method. So, the authors tried to make a numerical simulator to estimate the flow behavior of plasma arc within and out of nozzle. Then, governing factors of the plasma behavior were examined with the new simulator. Consequently, it was concluded that the dissociation phenomena of working gases influence on the radial temperature and velocity distribution of plasma arc. Then, the mixing phenomena of surrounding gas into plasma arc flow govern the spreading phenomena of arc diameter out of the nozzle. Moreover, the influences of arc current and working gas flow rate on the radial temperature and velocity distributions are clarified in the present study.
The method of butt welding of very thin 0.3 mm thick aluminum sheets at very high welding speed (6000 mm/min) using ordinary TIG welder were newly developed. The process are as follows. Polarity is DCEN. The aluminum sheets were put in between 30 mm thick copper plates. By this method the aluminum sheets were butt welded up to 0.2 mm and bead welded up to 0.1 mm thick by bead on plate successfully. At comparatively low welding speed (500 mm/min), pushing roller had better to be added. Generally, welding heat input at high welding speeds are smaller than those of low welding speed. The appearance of successful welding are shown in photgraphs.
New bonding method and adequate joint structure for residual thermal stress relief at bonding Al2O3 tube to metal flange were investigated. Main results obtained are as follows. (1) Ag-Cu-Ti brazing after Cu2O+Cu plating on A12O3 tube and sandwich joint structure using assisted A12O3 tube snipped thin Kovar flange were established. (2) It was confirmed that cavity coupler, ion accelerater tube brazed by the above mentioned method had excellent leak tight property (<1×10-9 Torr⋅l/s) and this vacuum brazing method could replace Mo-Mn process.