It is very valuable to develop a numerical model for various welding styles in order to understand the welding phenomena. The welding simulation models for a target work could be available for off-line robot programming or on-line robot control. The objective of this study is to develop a TIG welding simulation model for various works. Present model may apply to several work configurations with comparative ease. This paper discusses on a model for all position welding of plate and pipe, and the model applies to mild steel and aluminum and aluminum alloys. According to calculated results, it is made clear that homogenous weld is difficult to get for the fixed pipe welding due to the gravity effect, and that the weld bead shape on welding of plate and pipe is sensitive to changes in plate thickness. Accordingly, it is concluded that the model, proposed in this work, is useful for a simple simulation of TIG welding, and offers a powerful means for the estimation of optimum process parameters in the process.
Plasma transferred arc (PTA) surfacing process was proposed to produce in-situ intermetallic compound (IMC) surface layers. This process was quite capable of producing NiAl intermetallic composite surface layers on mild steel with physically mixed powder of nickel and aluminum. In the surface layer, the equiaxed and columnar structure of which grain size was 100-150 μm range were formed. The surface deposit was identified as NiAl and Fe3Al by a XRD analysis. The oxidation behavior of the surface deposits has been studied in air with isothermal conditions at 1173-1373 K up to 432 ks. The surface deposit with lower iron contents showed the formation of thin and uniform oxide film, whereas the surface deposit with higher iron contents showed coarse oxide film.
In order to improve wear resistance of titanium, fabrication of NiTi intermetallic compounds as a surface layer by plasma transferred arc surfacing process (PTA process) was investigated. Powder of unalloyed nickel was fed into the plasma during the PTA process and NiTi intermetallic layers were successfully synthesized. The surface layers have no cracks and blowholes with optimized conditions of the PTA process. The surface layers that largely consist of NiTi intermetallic phase could be achieved, while the microstructures of them were significantly influenced by the conditions such as the arc current. The NiTi layers exhibited high resistance to sliding wear under non-lubricated conditions and were much more resistant than titanium.
Laser welding is generally considered as a method to join parts with small distortion. However, demands for earth-friendly and high-precision processing automotive components such as fuel injectors with low volume of residual hydrocarbons in exhaust emissions become stronger than ever. For example, the circularity of cylindrical parts is designed to be less than one micrometer, and welding distortion become most critical. Not only a welding system but also a beam itself such as peak power, pulse width, beam profile and so on are dealt with in order to solve such a severe specification. In this paper, we treat an effect of a beam profile at a focal point on welding deformation so as to have understanding which profile is efficient to reduce welding deformation generating a deviation of the circularity. The beam with flattop profile has a high potential of distortion the deviation because of a high-efficiency melting. Furthermore, with the flattop profiled beam, process speed can be accelerated compared with the currently used gaussian-like profiled beam.
Through this series of investigation, safety against fracture on HT780 steel composed of martensite structure has been studied from various points of view comparing with ordinary ferrite steel. In this paper, property of ductile fracture initiation is evaluated on the relationship of equivalent plastic strain and stress triaxiality by analyzing damage amount quantitatively under repeated prestraining of tension and compression. Main results can be summarized as follows; 1) In case that ductile crack occurs from the center of the specimen, difference of the critical line of ductile crack initiation which is given on the relationship of equivalent plastic strain and stress triaxiality between HT780 (martensite) and ferrite steel, is small. But in case that ductile crack occurs from the surface of the specimen, this critical line of martensite steel shows worse than that of ferrite due to the difference of work hardenability. 2) Under repeated prestraining of tension and compression including Baushinger effect, property of the ductile crack initiation can be evaluated by effective damage concept in which the strain during showing Baushinger effect is not considered additionally as damage evolution of material. 3) Effective damage amount under repeated prestraining of tension and compression can be calculated by following back stress. In this report, the validity of this calculation was verified by positron annihilation lifetime spectrometry. Furthermore, it was suggested that in reverse loading process brought by dispersing of dislocations, the amount of damage decreased temporary.
The fine shot material, which is about 1.7 times in hardness and about 1.9 times in specific gravity compared with the conventional one, has been newly developed. And an improvement is investigated in the fatigue strength of the aluminum alloy A-5083-PO welding coupling in the peening treatment performing with this new shot material. The results are summarized as follows. (1) The fatigue strength of welding coupling is improved very well even in low projection air pressure 0.2–0.3MPa when the peening treatment is performed with the new developed shot material of the high hardness and specific gravity in particle size 150μm. (2) This shot material is effective for the improvement of fatigue strength of a soft welding coupling such as aluminum alloy. (3) The improvement using this shot material is more effective than that of conventional stainless steel shot material even if low projection air pressure is applied. (4) This improvement of the fatigue strength is caused by not only that of hardness by peening treatment but also an addition of the residual stress. (5) Under this conditions, it became clear that the fatigue strength is efected by hardness and compressive residual stress mostly, not by surface roughness.
A paste comprising fine alumina particles was applied on surfaces of steel plate specimens and welded joint specimens, and the effects of the paste on restraint and visual detection of fatigue crack growth were experimentally investigated by performing fatigue tests with in situ observations by a CCD microscope and through various kinds of fractographic observations and elemental analyses using a SEM (Scanning Electron Microscope) and an EPMA (Electron Probe Microanalyser). As a result, the crack growth rate in the plate specimen was drastically retarded by the wedge effect of the alumina particles, and 344% increase in failure life was produced. Similar crack growth restraint effects were also observed on the welded joint specimens, producing 117-175% increase in failure life. In the fatigue tests of the specimens on which the alumina paste was applied, remarkable black color developed in the white alumina paste along the paths of crack propagation, exceedingly facilitating the visual detection of the cracks. An analysis using an X-ray diffractometer showed that the black matter in the paste consists of fine debris derived from the base metal and the alumina particles.
Residual stress in an E-Sialon/SKS3 joint with a brazed metal larger of BAg8 was analyzed by using an elasto-plastic-creep FEM model. The joint was brazed at 1113K and cooled under different cooling conditions to room temperature. Before the analysis, creep deformation characteristics of SKS3 and BAg8 were examined by means of tensile test at high temperatures. It was found that creep deformation occurs in SKS3 at above 673K and BAg8 at above 473K. These creep data were adopted for the analysis of residual stress in the E-Sialon/SKS3 joint bonded under different cooling conditions. Based on the analysis, cooling process for reducing the residual stress in the joint was discussed. In a cooling rate of 10K/s – 0.001K/s, it was found that the residual stress after cooling decreases as the cooling rate decreases. This means that a stress relaxation occurs during cooling due to the creep deformation of SKS3 and BAg8, in which the creep deformation of BAg8 was estimated to be especially large. Moreover, effect of maintaining at a constant temperature in the cooling process was discussed for reducing the residual stress. It was found that the maintaining for 3600s at 523K is quite effective for reducing the residual stress in the joint cooled to room temperature.
Hot dip metal plating is considered to be effective for increasing corrosion resistance in steel structures. The planting makes possible to reduce the residual stress in the welded portion due to annealing effect, and stress concentration at the weld toe is reduced by the plating if a part of stress is transmitted in the aluminum layer. Therefore, it is considered that fatigue strength can be improved by hot dip aluminum coating. These facts mean that the hot dip aluminum coating is one of useful countermeasure against the fatigue and corrosion, which are regarded as weaknesses of steel structures. However, it has not been clear how the planting influences the fatigue strength of a welded joint. This study aims at clarifying fatigue strength of welded joints coated with aluminum. For this purpose, out-of-plane gusset welded joints specimens were made of SM400 and were plated on two conditions of hot dip aluminum coating, then fatigue tests were carried out on these specimens. Furthermore, microstructures on the plating layer and fatigue crack origin were closely observed.
Load-carrying fillet welded joints in welded steel structures are extensively used for connecting the structural members. Typical fatigue cracks have been observed at the welded joints such as secondary structural members of steel bridges. The object of this research is to clarify the influence of the difference in plate thickness on the fatigue behavior of load-carrying fillet welded cruciform joints. Fatigue tests were carried out on the joints with plate of different thickness. The main plate thickness was 9, 14 or 25 mm and the cross plate thickness was 6 or 14 mm. Fatigue crack propagation and strength analyses using fracture mechanics were also performed on the joints with various plate thickness. The tested specimens indicates that the fatigue cracks are initiated and propagated almost along extended line of non-penetration weld line regardless of the main plate and the cross plate thickness. The experimental and the analytical results show that the larger the difference of thickness in each main plate is, the lower the fatigue strength is, when the cross plate thickness is smaller than that of the main plate.
In order to manufacture I section of bridge, the fillet welding of the both sides for the web is conducted simultaneously, or conducted one side sequentially. The angular distortion will occur in the case of simultaneous welding, the leaning deformation on the flange to the first welding side will occur in the case of sequential welding for the thick plate. Compared with the angular distortion, it is difficult to correct the leaning deformation on the flange. If we can estimate the amount of the leaning deformation on the flange to first welding side, we will be able to set the flange lean to the second welding side before welding and keep the flange right angle to the web without correcting the deformation after welding. We conducted some cases of experiment and thermal elastic-plastic analysis for I section with sequential fillet welding. From the results, we developed the program for estimating the leaning deformation on the flange with tandem submerged arc welding method sequentially, and we applied to the actual bridge manufacturing. Consequently, we reduce the correcting work drastically, and achieve the cost reduction in production.
This paper proposes laser pressure welding technology for joining dissimilar metals. Laser pressure welding of aluminum alloy A6061 and low carbon steel SPCC sheets was carried out by changing the roller pressure. And a YAG laser beam was irradiated on different locations into the wedge of two sheets by a f:θ lens and scanned at various frequencies and patterns using two dimensional scanning mirrors. The tensile shear strength and peel strength of welded joints were measured. The tensile shear and peel test specimens made in Ar gas flows fractured in the A6061 base metal and along welded dissimilar metal interface, respectively. The highest tensile strength and peel strength were obtained at the laser power of 1.8 kW, the laser scanning speed of 30 Hz, the laser irradiation position of centerline, the roller pressured of more than 245 MPa and the welding speed of 0.5 m/min in Ar atmosphere. The interfaces of the joints were analyzed by using SEM and EDX, and the formation phases on the peeled surfaces were analyzed with XRD. It was revealed to be important for the production of a sound joint with high mechanical properties to prevent a welding high temperature part from oxidation.
Experiment was accomplished on the diffusion bonding of TiAl intermetallic compound to Ti-6Al-4V alloy and pure titanium and comparison was made on the tensile strength and the microstructure of the joints. The common aspects between these two types of bonding are as follows: (1) The reaction layer of Ti3Al was formed at the bonding interface. (2) The tensile strength of the joint decreased with increasing the width of the reaction layer. (3) The scatter in the tensile strength was substantially large, which is mainly due to the properties and the shapes of the reaction layer of Ti3Al. The points of difference between two bondings are as follows: (1) The optimal bonding temperature for the TiAl/Ti-6Al-4V was lower than that of the TiAl/Ti joint when the other conditions were kept identical. It is explained by the diffusion speed of Al atom to Ti alloy or pure Ti, which depends on the crystal system of Ti(α) and Ti-6Al-4V(α+β). (2) Kirkendall voids were observed at the bonding interface of the TiAl side on TiAl/Ti joints at 1223K, whereas no such voids were observed on TiAl/Ti-6Al-4V joints.
Ultrasonic wave of 19.5 kHz frequency oscillated with an ultrasonic transducer and amplified with a step type of horn was irradiated on metal surface in water to introduce compressive residual stress. Slight plastic deformation occurred at the surface region of pure metal such as Cu and compressive residual stress was introduced. It seemed that the plastically deformed depth from the surface corresponded approximately to the region where the compressive residual stress is extended from the surface. The higher compressive residual stress could be introduced into the surface of Cu-Zn brass and SUS304 stainless steel because work-hardening was simultaneously induced to those alloys. Furthermore, since martensitic transformation was induced by the plastic deformation in the case of SUS304, the lager compressive residual stress could be introduced more deeply into the surface region. The residual stress of SUS304 surface reached to the maximum value of 574 MPa by irradiating for 5 min and the stress extended to the depth of about 170μm from the surface.