Ultrasonic welding between SS400 mild steel sheet and aluminum alloy sheet containing magnesium (A5052) was conducted. In this study, authors investigated the influence of ultrasonic welding condition on the mechanical properties and the interface microstructure of a joint, and examined the effect of an insert metal to improve the joint strength. The main results obtained in this study are as follows. It was possible to ultrasonically weld SS400 mild steel sheet and A5052 sheet. When the clamping force was varied keeping the welding time constant for 1s, the joint strength showed the maximum at the clamping force of 588N and it decreased with the clamping force because the frictional action at the interface decreased with it. When the clamping force was kept constant at 588N and the welding time was varied, the joint strength reached the maximum at the welding time of 2.5s, and the strength of the joint welded for 3s decreased due to the formation of Fe2Al5 intermetallic compound at the interface. Using an insert metal of commercially pure aluminum successfully improved the joint strength and the strength of the joint welded at the welding time of 3s was about three times that of the joint without an insert metal.
The effect of carbon content on creep rupture strength and microstructural change in heat affected zone (HAZ) in high temperature service was investigated in order to alleviate the deterioration of creep rupture strength in HAZ of heat resistant ferritic steel. Simulated weld thermal cycle at 1273K was applied to test specimens machined from 10%Cr-3%Co-3%W-V, Nb ferritic steel plates with carbon content ranging from 0.005% to 0.1%. After heat treatment at 1013K for 1.8ks, simulating post weld heat treatment (PWHT), the creep rupture strength was evaluated at 823K, and the various microstructural examinations were carried out. By decrease of carbon content, the creep rupture time of simulated HAZ got longer and the deterioration of creep rupture strength in HAZ was alleviated. In HAZ with lower carbon content, the density of fine particles in diameter of less than 0.1μm, which were effective for dispersion strengthening, was higher after long term heating. Additionally, the growth rate of particles such as M23C6 type carbide and MX type carbo-nitride was slower in HAZ with low carbon content compared with in that with high carbon content. The growth of particle was roughly in accordance with the theoretical Ostwald ripening considering the proportion of growth of each particle. The mechanism to explain the effect of carbon content was considered as the following. The proportion of M23C6 and MX dominated by chromium diffusion, which has a higher growth rate than that of MX dominated by vanadium diffusion, contributing to Ostwald ripening of particles becomes lower by decrease of carbon content because of the decrease of partially-dissolved M23C6 during weld thermal cycle. As a result, the growth of particle is delayed during heating and the dispersion strengthening by fine particle is maintained for long term in HAZ with lower carbon content.
2 kW Fiber laser and 2.4 kW CO2 laser were used to investigate their welding characteristics of laser and laser-MAG hybrid welding processes. The effect of defocusing distance and welding speed on the weld bead and plasma interaction were investigated. Fiber laser can achieve deeper penetration weld bead than CO2 laser at the same welding speed and output power in laser welding. It is well known that the plasma produced by laser affects penetration and bead width in laser-MAG hybrid welding. The plasma produced during fiber laser-MAG hybrid welding is weak. On the contrary, the plasma produced during CO2 laser-MAG hybrid welding is very strong. The volume of plasma produced during hybrid is affected by laser-arc distance in laser-MAG hybrid welding. High energy density short wavelength fiber laser can couple with the arc completely than using long wavelength CO2 laser in laser-arc hybrid welding when the MAG power changed.
On the welding of the nodular graphite cast iron, many researches have been carried out until now. The shielded metal arc welding and TIG welding using the filler material with nickel, and oxy-acetylene welding have been recommended as a welding process of the nodular graphite cast iron. And, the execution of preheating, postheating, peening and interlayer thermal management is required in the welding procedure. But the expertise, experiences and high skills are needed to carrry out these executions. Thus, it is the fact that these executions are too complicated to be spread widely. In the research on the welding of the nodular graphite cast iron, there are many papers that heat input, interlayer thermal management, welding materials and welding conditions are examined and the results are discussed. However, it is hard to find a paper that compares the welding results by using several kinds of welding process and welding materials. In this study, 9 kinds of weld test pieces are produced by using 4 kinds of generally used welding process. And the welding of nodular graphite cast iron is examined not only on its hardness, tensile strength and bending strength, but also its workability, efficiency and cost. As we emphasized its practicability, we didn't consider preheating, postheating, peening and interlayer thermal management.
Fatigue strength obtained from cruciform welded joint specimens may be different from that of actual joints such as welded connections of lateral girder flange to main girder web or vertical stiffener to main girder flange, because main girder web is mush wider than lateral girder flange or vertical stiffener is narrower than main girder flange. For the purpose of examining the influence of specimen configuration on the fatigue strength, fatigue tests and stress analyses have been performed using model specimens on the connections of lateral girder flanges and usual cruciform welded joint specimens. Fatigue test results suggest that fatigue strength of the model specimens has been nearly equal to that of cruciform welded joint specimens. This fact has been also confirmed from the stress analyses considering weld shape at the corner of main plate.
In The Japan Welding Engineering Society standard WES 2805-1997, a fracture mechanics parameter, crack tip opening displacement (CTOD), relative to the flaw located in highly stressed region surrounded by clastic stress field is estimated using the CTOD design curve from the flaw size and the applied local strain considering strain concentration in the components. In this report, finite element analyses using three-dimensional solid elements and tensile tests were performed to evaluate an accuracy of CTOD estimated by the design curve for a continuous circumferential surface crack which was present at the corner boxing toe. It was found that a CTOD estimated by the design curve in WES 2805 had to allow for a great margin of safety. It was possible to estimate a CTOD accurately using te applied local strain calculated from the correction function of the stress intensity factor Mk for the design curve.
This paper deals with "Joint Design Supporting System" that aims to support activities of welding design and joint design comprehensively. The following concepts are introduced into our system in order to deal with both the welding design and joint design explicitly: (1) Design information on both joint and welding is clearly and explicitly defined as product data. (2) The phase of joint design is different from the phase of welding design, and these two phases start from the division of the full structure into parts and end in determining values of detailed data to execute welding operations. (3) Joint and welding data is decomposed into some data, and appropriate design procedures depend on the decomposed data. (4) "Determining optimal joint data" is converted into "selecting the optimal plan from a lot of feasible design plans". That is to say, a lot of feasible plans in every design stages are created semi-automatically and evaluations of each plan are calculated automatically by our system. As a result, optimal design plans are selected and the design stage moves to the next. (5) The design processes that are explicitly described are utilized in our system. In order to implement our system, two design process models of both welding and joint are discussed in this report: one model is "Vertical Flow Model" and the other is "Horizontal Flow Model". The "Vertical Flow Model" indicates the design process among design stages, on the other hand, the "Horizontal Flow Model" indicates the value determination activities in each design stage. Some examples of both welding design and joint design by using our system are shown in this paper.
Authors proposed "Joint Design Supporting System" in the previous paper. In our system, both data of welding and joint is clearly and explicitly defined as product data, and a lot of feasible plans are created semi-automatically in every design stages and evaluations of each plan are calculated automatically by the computer system. Because of managing a lot of data involved, our system needs not only data processing functions but also total framework to integrate and handling data. In this paper, therefore, the implementation of "Joint Design Supporting System" is discussed from viewpoints of followings: (1) Data models for welding and joint. (2) Data processing functions to generate and evaluate data models for welding and joint. (3) Data processing functions to generate a lot of design plans based on the designer's intents. (4) Frameworks to describe and reuse generation flow and evaluation flow of joint design and welding design. (5) Frameworks to manage and utilize design plans and evaluation results. Based on these discussions, two "Joint Design Supporting Systems" which are intended for different products are developed, and validities of the proposed implementation method are shown.
So-called "baby-boom generation", who was born just after the World War II, will retire soon, starting at March 2007 in many manufacturing industries, and the young successors who have less experience will not follow them to the fullest extent. Since the transmission of the work skill is greatly doubted, this is the hot topic at present in Japan as so-called "2007 problem" as an issue to be solved urgently. There will be two approaches for the solution: One is to introduce the education and training system by effective and systematic supporting tools using IT fully subject to approving the present skill as it is. The other is to study the ambiguity (tacit knowledge) of present skill systematically, and replace it to the explicit knowledge by finding the rule and principle, and then create the new system. The latter is called technologization of the skill. This paper took up the digital manufacturing as the latter example, and one application was introduced for the pipe unit fabrication. Next, it was explained that the skilled workers judged the work procedure heuristically like a combinatorial optimization. The simulation example using "reinforcement learning method", one of the heuristic combinatorial optimization technique, was introduced for the welding sequence of the ship hull block.
Metals and plastics have been widely used in several industrial applications such as automobiles, aircrafts and electronic devices. Joining of a metal and a plastic is important and necessary from a fundamental viewpoint of manufacturing. The joining has been performed using adhesion bonds (glues) or mechanical tools such as rivets. However, it has some problems in terms of environment, preserved conditions and mass production. It is thus expected that a noble innovative method should be developed for direct joining of metals and plastics. Therefore, we have newly developed a noble Laser-Assisted Metal and Plastic (LAMP) joining method. The LAMP joining method could produce a strong joint between a Type 304 stainless steel plate and an amorphous polyamide plastic sheet. The tensile shear test samples of 30 mm width and 2 mm thickness possessed the tensile shear loads of over 1,560 N. Moreover, the tensile shear load of 3,390 N was achieved for a wide LAMP joint including sub-millimeter-sized bubbles, which were formed from rapid heating and quenching due to the heat input of a line-beam-shaped diode laser. It was found that the joint strengths depended upon not only the area of a joint part but also bubbles formation and size. The SEM images of the LAMP joints demonstrated that the stainless steel and the polyamide plastic were closely bonded in micro size.
Nowadays, amorphous state of metallic material can be obtained in many alloys by rapid quenching from the melt condition at a quenching rate more than 106K/s. However, in the normal rapid quenching method, amorphous alloys can be formed not as a bulk shape but only as a ribbon or powder shape. On the other hand, in some kind of alloys, amorphous state can be easily given even at a much lower quenching rate like 1–100K/s, and it is possible to fabricate bulk shape materials in these alloys. These amorphous alloys are called as a metallic glass. There are several kinds of manufacturing processes to fabricate the bulk metallic glasses such as an arc melting mixture, copper mold casting and so on. However, especially in an application of metallic glass to the high performance corrosion resistance coating, these processes are hard to apply to real large area coatings on already existing object surface. Thermal spraying has the advantage of low cost and in-situ formation ability for such large area coatings. Recently, many metallic glasses were developed such as Zr-, Fe- or Ni-based alloy systems. Among these alloy systems, one of the most important alloys can be regarded as Fe-based alloys exhibiting good corrosion resistance. Especially, Fe43Cr16Mo16C15B10 alloy are known to have very high corrosion resistance. In this study, Fe43Cr16Mo16C15B10 metallic glass coatings were fabricated by gas flame spraying. Metallic glass coatings were successfully obtained by gas flame spraying by using a reducing flame and water atomized powders. The oxide films which had existed on the feedstock powder surfaces might prevent the oxidation of the powders during spraying. It was indicated that the gas flame sprayed particles were once heated over its melting point, and the particles became amorphous state by rapid quenching after the deposition onto the substrate.
Recent progress in high power laser resonator has been extending the welding application to the heavy section plate structures in a variety of industries. One of the major problems in the deep penetration welding is formation of some weld defects such as porosity and hot cracking. A final goal of a series of our investigations is to develop defect free laser welding process with the depth of more than 20mm. In the present paper, pulse modulation of the laser power has been attempted to suppress the porosity. Dynamic keyhole behaviour was observed by a micro-focused X ray transmission imaging system at the framing rate of 1000 s-1. Keyhole stability was evaluated by variation of keyhole diameter with time. The porosity formation significantly depends on the modulation frequency. If the eigenfrequency of the keyhole radial oscillation is selected as the modulation frequency, the keyhole is perturbed more significantly than the CW welding, resulting in forming a lot of large porosity. On the other hand, the porosity is effectively suppressed at the eigenfrequency of the molten pool oscillation. This is attributed to stabilizing the keyhole by controlling the laser / molten metal interaction periodically.
The characteristics of thermal pinch effect of arc in welding process are studied to clarify its mechanism. A simplified model based on energy balance between ohmic heating and conduction loss in an idealized cylindrical arc is useful for discussing the behavior of thermal pinch effect of welding arc. Furthermore, two-dimensional numerical simulations of gas tungsten arc in two imaginary shielding gases, namely, an argon except for the specific heat and an argon except for the thermal conductivity are presented for clarifying the mechanism of the thermal pinch effect. The numerical simulations show the results that the greater specific heat of shielding gas leads to the greater arc constriction but the greater thermal conductivity leads to the arc expansion. It is concluded that the thermal pinch effect is an arc constriction in a consequence of the greater specific heat of shielding gas which is generally given in molecular gas, for example, CO2.
This paper describes the mechanical properties of square section bar welded joint that was made by a center insert drive friction welding method. A center insert drive friction welding method was proposed by authors, which was carried out by the center drive friction welding machine with the center drive gear system. The joint was made up by using a flat disk insert specimen of 10mm or short thickness, and that was inserted to a center gear supported by the drive gears. The material joined was a low carbon steel (same materials) with the weld faying surface shape of 8.9mm square section, and the effect of the friction welding condition on joining phenomena and the joint mechanical properties were investigated. The following conclusions are provided. (1) Friction torque curve had wear and seizure stages until the initial torque, when the base metals were welded at high friction speed and low friction pressure, i.e. 27.5s-1 and 36MPa. On the other hand, when the base metals were welded under high friction speed and high friction pressure conditions, i.e. 27.5s-1 and 90MPa, almost no wear existed until the initial torque was reached. The friction torque rapidly increased and reached the initial peak immediately after the weld faying surfaces contacted each other. (2) The joint that was made by using the disk insert specimen under a friction pressure of 36MPa and a friction time of 1.6s, or a friction pressure of 90MPa and a friction time of 0.6 to 1.5s, had the same tensile strength as the base metal, and fractured in the base metal. Those joints had a notch defect at the corner part in the adjacent region of the welded interfaces although the joints had also 90 degrees bend ductility. (3) When the joint was made by using the disk insert specimen under a friction pressure of 36MPa, a friction time of 1.6s and a forge pressure of 90MPa, it had a notch defect at the corner part in the adjacent region of the welded interfaces. Also, when the joint was made under a friction pressure of 36MPa, a friction time of 1.6s and a forge pressure of 36MPa with by using the convex type insert specimen, it had a notch defect. However, a notch defect of those joints were less in comparison with the joint, it was made under a friction pressure of 36MPa and a friction time of 1.6s with a flat disk insert specimen. (4) The friction welded joint with less notch defect at the corner part in the adjacent region of the welded interfaces was able to make with using a convex type insert specimen and adding forge pressure of 180MPa. The adjacent region of the welded interfaces will be able to make with using a convex type insert specimen and adding higher forge pressure.
This paper describes about the autocompleting friction welding method that was developed by the authors. The autocompleting friction welding method was produced by using a center insert drive friction welding machine, and it was carried out with a circumferential share fracture at the disk type insert specimen by the friction torque generated during friction process. The material joined was low carbon steel (same material) with the weld faying surface diameter of 10mm, and the effect of an insert thickness of a disk type specimen (insert thickness) on joining phenomena were investigated. The following conclusions are provided. (1) When an insert thickness was 3.2mm at a friction pressure of 36MPa with a friction speed of 27.5s-1, the peripheral portion of an insert specimen at the welded interfaces had provided circumferential share fracture by the initial torque that was produced during friction process. The joint had a crack at the adjacent region of the welded interfaces although it had the same tensile strength as the base metal. (2) The joint made by using a disk type insert specimen that had the groove on the peripheral portion had the same tensile strength as the base metal and it fractured at the base metal. This joint had also 90 degrees bend ductility with no crack. In this case, the optimum groove thickness was 1.2mm at a groove inner diameter of 11mm with the insert thickness of 4.0mm at a friction pressure of 36MPa with a friction speed of 27.5s-1. (3) The joint was automatically welded by using the disk type insert specimen, that insert thickness and the groove thickness was determined with the material, the diameter of the weld faying surface, and the friction welding condition. That is, the sound friction welded joint was made by the autocompleting friction welding method.
The thermal elastic-plastic analysis for the welding transient and residual stresses and deformations needs the huge computation time to obtain the accurate results. The main cause is that the increment of temperature has to be small enough to calculate accurately. In this study, the thermal elastic constitutive equation and the thermal elastic-plastic constitutive equation are refined so that the very large increment of temperature can be used. Moreover, in the latter, the definition of differential coefficient of the yield stress for change of temperature is modified to be ingenious. The new constitutive equations are introduced to the FEM program. Simple typical problem of thermal elastic-plastic analysis was calculated to confirm the reliability and the accuracy of the above theory. Then, some complex welding problems were analyzed. The welding residual stresses and deformations were compared with the accurate results obtained using small temperature increment. As a result, it was confirmed that the computation time is very largely shortened, compared with the usual incremental method using small temperature increment, keeping the high accuracy.
The authors proposed the switch back welding method to make the stable back beads in the first layer weld during one side multilayer welding. In the proposed welding method, the torch motion is important to control the weld pool, i.e., the welding torch is moved backward and forward like switch back. It is important to investigate the behavior of the weld pool to get the optimum welding parameters such as the traveling speed, the forward distance, the backward distance, the welding current and so on. There are many welding parameters. In order to find the optimum welding parameters, the numerical simulations are useful method instead of the welding experiments. Since the deposited metal is considered in the numerical models of the welding in the thick plates, the numerical analysis becomes complicated. In order to simplify the analysis, the authors discussed the numerical simulations of the welding in the thin metal plates because the effect of the deposited metal can be minimized. First, the fundamental welding experiments were carried out in MIG welding. By using the experimental results, the numerical models in the switch back welding are determined. Next, the behaviors of the temperature are investigated under the change of the traveling speed and the backward distance. If the traveling speed is constant in the switch back welding, the weld pool size may sometimes become big. In this case, the burn trough may take place due to the flow in the weld pool. When the traveling speed of the forward movement is faster than backward movement, the weld pool length becomes shorter than the case of the constant traveling speed. Moreover, if the backward distance is longer than half of the forward distance of the switch back welding, the authors can obtain continuous back bead regardless of the disturbance such as the variation of the arc length, i.e., the stability of the weld pool is increased. The switch back welding method is useful to make the stable back bead in the MIG welding.
Effects of base metal hardness on improvement of fatigue strength by shot peening treatment are investigated using various carbon steels for machine construction. Furthermore, an effect of shot peening treatment on improvement of fatigue strength of friction welding is investigated. The results are summarized as follows. 1) The improvement of fatigue strength by shot peening treatment is effective in the case of harder material on using the high carbon steel. 2) Fatigue strength of a friction welded joint becomes higher than the base metal although the flash does not be removed if shot peening treatment is applied. 3) The fatigue strength increases in proportion to the raise in hardness near the surface in the both cases of base material and the one with shot peening treatment.
This paper describes a butt-welding of AZ31B magnesium alloy plate to commercially pure titanium (CPTi) plate by the solid state welding using a rotating probe with a thread. The effect of the right-hand and left-hand thread on the tensile strength and microstructure was investigated. The following results were obtained in this study. The probe with a thread increased the tensile strength of a joint by about 79% or less compared with without a thread. There were little differences in the maximum tensile strength of the joints made by the right-hand thread and the left-hand thread. Using the probe without a thread, the fragments of CPTi were produced in a continuous form, but using the probe with a thread, the fine fragments of CPTi tended to scatter in Mg alloy matrix. The increase in the tensile strength of the joints using the probe with a thread was considered to be due to the sufficient plastic flow of Mg alloy caused by the fine fragments of CPTi scattered in Mg alloy matrix. However, the tensile strength of the joint was lower than that of the parent material and the fracture path occurred around the interface. X-ray diffraction analysis revealed a deformation texture with the (002) basal plane near the interface of the magnesium side. It seems that both of the decrease in Al concentration in the Mg alloy and the formation of the deformation texture with the (002) basal plane caused the tensile strength lower, compared with parent material.
WES 2805, a Japanese fitness-for-service procedure, proposes a crack tip opening displacement (CTOD) design curve for the brittle fracture assessment of welded joints, where the local strain acting on the cracked region, ε, is calculated using the stress concentration factor, Kt, and ε is converted to CTOD. However, in WES 2805, Kt, is shown as a few constants that depend on the ratio of crack depth, α, to the welded joint thickness, t, and the constants can be excessively conservative. In this study, the relation between Kt and the stress intensity magnification factor, Mk, was theoretically indicated, and the utility of Mk in the design curve was investigated for three kinds of welded joints. In addition, the local average strain by area was calculated by finite element analysis, and was used for the design curve instead of ε. It was demonstrated that constant Kt was sometimes excessively high and Mk was helpful in modifying Kt. Moreover, the local average strain by area contributes to good CTOD estimation, especially for a toe crack in a load-carrying fillet welded cruciform joint.