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Hybrid structure between porous core and solid shell can combine lightweight open-cell structure of porous materials with good strength of solid shell. Laser welding is considered as an effective process to join porous metal with solid metallic shell. In this study, the evolution behavior of laser welding by a continuous wave (CW) disk laser welding between open-cell aluminum alloy (cast AC2A alloy) and aluminum sheet (wrought AA6063 alloy) was investigated. X-ray transmission system and a high-speed camera were performed during laser welding to investigate the dynamic keyhole, porosity formation, plasma plume, and spatter formation. Laser keyhole became unstable during entering and passing the vacancies of porous aluminum, which consequently resulted in bubble formation in the molten pool.

Despite the growing interest in using powder metallurgy shape memory alloys, there is limited research on their joining and welding aiming to expand their applications. In this research, we utilized a high-power, high-brightness disk laser welding process to join spark-plasma-sintered Ti-51 at.% Ni shape memory alloy and studied the primary factors that affect the strength and functionality of the created sound welds such as intermetallics and martensite (B19′) phase formation. The introduction of high-power laser could impede the formation of B19′ and undesirable intermetallics such as TiNi3 and Ti2Ni; however, the desired Ti3Ni4 would also be suppressed and post-weld heat treatment was necessary to induce them again. The microstructure of fusion zones was significantly altered, producing coarse columnar grains with centerline and equiaxed weld centers. Additionally, high-power laser welding of powder metallurgy Ti-Ni alloy triggered amorphous phase formation in the welds due to rapid cooling. It was found that a laser power of 3 kW and welding speed of 6 m/min are optimal welding parameters, since the produced weld solidified along favorable [001] direction of strain recovery in Ti-Ni shape memory alloys.

Laser welding of open-cell aluminum foam and solid shell was performed with the objective of fabricating promising hybrid metallic materials. In this study, a feasibility of laser welding of a solid A6063 aluminum sheet to an open-cell AC2A aluminum foam was investigated. The effects of various laser-welding parameters such as laser power, welding speed, and defocused distance in addition to the pore size of aluminum foam were evaluated in terms of the shear strengths of the welded joints between the aluminum solid sheet and porous plate. Increases in weld joint width (w) and penetration depth (d) were effective to an increase in the tensile shear strength of solid-porous material joint.

A real-time observation system for a longitudinal section of molten pool and temperature distribution was developed directly in real time by a combined system with the glass transmission method and two-color temperature analysis to clarify the mechanism of spatter generation during laser welding. A stainless-steel-type 304 (SS304) was employed in this study because of its application in many industries. The SS304 was set in a vacuum chamber and then a disk laser with an output power of 10 kW was irradiated and scanned on it to form a weld bead. At the same time, the behavior of the molten pool and keyhole was captured with the real-time temperature observation system and an x-ray transmission system, respectively. As a result, the temperature of the longitudinal section of the molten pool formed by laser irradiation under atmospheric pressure was about 1500 °C; however, at 10 Pa, it reached about 1700 °C, indicating that the temperature increases with a decrease in the ambient pressure. Furthermore, the fluctuation in the longitudinal sectional area of the keyhole and molten pool was evaluated. It was found that the average fluctuation in the longitudinal sectional area of the molten pool was 1.7% at 10 Pa and that of the molten pool was 18.8% under atmospheric pressure.

The clinical outcome of laparoscopic radical prostatectomy (LRP) was retrospectively investigated taking into consideration the surgeon's position during the procedure. The study cohort included 184 consecutive patients who had undergone LRP performed by a single surgeon from February 2013 to July 2018. During the study period,the surgeon stood alternately on either the left or right side of the patient. The D'Amico risk classification was low,intermediate and high in 26 (14.1%),45 (24.5%) and 113 (61.4%) patients,respectively. Mean surgical duration was 203.5 minutes and mean estimated blood loss was 437.6 ml. Nerve sparing (NS) was implemented in 82 (44. 6%) patients. The mean period of having an indwelling urethral catheter was 5. 0 days. Perioperative Clavien-Dindo degree ≥IIIa complications occurred in three (1.6%) patients. Except for cases with presurgical hormonal treatment,surgical margins were positive in 41 (22.3%) patients,among whom 23 (17.4%) had pT2 disease. The 5-year biochemical recurrence-free survival rate was 81.4%,and 84.8% of patients regained urinary continence at 12 months after surgery. Where the surgeon stood during LRP was not associated with significant differences in any parameter. However,the margin positive rate was higher on the side away from where the surgeon stood than the side closer to the surgeon (70.7% vs 29.3%). In conclusion,the position of the surgeon during LRP does not influence the outcome.

The objective of this research is to reveal relationship between melt flows and spatter reduction by angle of incidence and defocusing distance in partial penetration welding of an SUS304 stainless...

This study was undertaken in order to investigate the effect of reduced ambient pressure from an atmospheric pressure (101 kPa) to 0.1 kPa on one-pass full penetration welding of thick high-tensile...

Focused laser is one of the highest power density sources available to industries such as automotive industry, heavy industry, and nuclear power plant industry because thermal influence is narrow and it is excellent in local workability. However, laser welding causes defects of cracks and pores. In particular, the formation of keyholes, which are factors for forming these welding defects, and the mechanism of spatter generation have not been sufficiently investigated. In this study, an x-ray phase contrast imaging technique was employed to investigate the keyhole welding with laser in order to clarify the spatter generation mechanism and keyhole formation mechanism in vacuum. Furthermore, the amount of spatter generated by vacuum laser welding was quantitatively analyzed, and the factors that suppress the spatter under vacuum were clarified. As a result, it was found that the penetration depth was dependent on the keyhole aperture.

This research was performed with the objective of clarifying the effect of welding speed on melt flows during melt-run welding of SUS304 stainless steel plates with a 6-kW power laser beam on the basis of three-dimensional X-ray transmission in situ observation. As welding speed increased from 25 to 250 mm/s, three kinds of welds characterized by porosity formation and no defects or underfilling due to spatters were produced. The average and the maximum values of measured melt flow velocity were 3 and 10 times higher than the welding speed, respectively. Two kinds of circulation flows at the inlet or the tip of a keyhole were confirmed to control heat transfer in a molten pool. It was found that the circulation flows were so sensitive to the welding speed that bubbles resulting in porosity or spatters were often formed. According to X-ray observation of the formation of spatters with tungsten carbide (WC) tracers, as the melt flow rose along the keyhole wall, the velocity was accelerated from 0.24...

In laser cutting, industry practitioners have long demanded higher cutting speeds and better quality cuts. There is thus much interest in the elucidation of related processing phenomena. Cutting quality is known to be affected by ejection behavior of generated melt, which itself is thought to be influenced by the profile of the laser cutting front. It would thus be desirable to directly observe the cutting front in real time, but this is not easily done in practice, mainly because laser cutting speeds are relatively high and visible light generally cannot pass through workpieces. In this study, we used an X-ray transmission system to perform fluoroscopic observation of cutting fronts in real time during actual processing. Further, we discuss the effect of the cutting parameters (cutting speed, etc.) on cutting front profile and melt ejection. We find that both the profile of the cutting front and the ejected melt behavior were stable when a sound cut was produced. We directly confirmed that the cutting front profile changed along with cutting speed.

With the objective of reducing the operating costs, argon-rich shielding gas was replaced by 100% CO2 gas in hybrid laser-arc welding of shipbuilding steel. The welding parameters were optimized to obtain buried-arc transfer in order to mitigate spatter formation. Sound butt joints could be successfully produced for plates of 14 and 17 mm thickness in one welding pass. Subsequently, the welded joints were subjected to different tests to evaluate the influence of CO2 shielding gas on the mechanical properties of the welded joints. All tensile-tested specimens failed in the base material, indicating the higher strength of the welded joints. The impact toughness of the welded joints, measured at −20 °C, reached approximately 76% of that of the base material, which was well above the limit set by the relevant standard. The microstructure of the fusion zone consisted of grain boundary ferrite and acicular ferrite uniformly over the plate thickness except for the joint root where the microstructure was chiefly ferrite with an aligned second phase. This resulted in higher hardness in the root region compared with the top and middle parts of the fusion zone.

An innovative hybrid laser-arc welding technique has been developed for one-pass welding of 25 mm thick steel plates. The parts to be welded were assembled into a butt joint configuration with a square groove and 2.5 mm air gap. A backing method was applied using ceramic strip or submerged arc welding flux. Cut-wire particles were inserted into the joint gap to protect the backing material from laser radiation and in the same time help to fill the gap. Laser power density was optimized to obtain full penetration joints without damaging the backing material. Defect-free joints with adequate fusion zone profiles and good mechanical properties were successfully produced. The technique was then applied to weld 50 mm thick plates in two welding passes. Using the same joint design, one welding pass was overlaid from one side of the joint and a second pass was deposited from the other side. In this case, a backing plate of any material could be used since the laser radiation does not reach the bottom side of the joint. Keywords: Hybrid laser-arc welding, Thick plate, Cut-wire, Ceramic backing, Flux backing

In this study, high-power disk laser–metal active gas arc hybrid welding was performed on thick plates of high-tensile-strength steel, HT780. The effect of shielding gas on the penetration, defects, and mechanical properties of the hybrid weld beads was investigated using either 80 %Ar–20 %CO2 or 100 %CO2 shielding gas. The results showed that the process window of laser powers for the production of sound welds was wider in 100 %CO2 gas, although more spatters occurred. Besides, the optimization of the arc parameters could reduce spattering significantly by controlling the globular transfer mode to form a buried arc. The Vickers hardness test was performed to identify the levels of hardening and softening in the bead and HAZ, respectively. The tensile test results showed that the tensile strengths of the joints hybrid-welded in either 80 %Ar–20 %CO2 or 100 %CO2 gas were much higher than those of the HT780 base material. The Charpy V-notch test results revealed that the values of the hybrid-welded joints in 80 %Ar–20 %CO2 gas were higher than those in 100 %CO2 gas. The reduction in toughness was attributed to the increase in the oxygen content and the consequent formation of a higher number of oxides in a weld bead made in 100 %CO2 gas.

A series of trials to fusion weld commercially pure titanium (CPTi) to stainless steel 304 (SS304) have been conducted using laser beam welding (LBW) and gas tungsten arc welding (GTAW). Neither technique produced adequate weld joints with LBW showing a more promising result, while GTAW yielded separation of the workpieces immediately after welding. Cracking and fracturing took place mainly on the SS304 side, which was explained by the differences in the materials&rsquo, thermal properties. Various intermetallic phases formed during welding that were identified using energy dispersive X-ray spectroscopy (EDS) and electron backscattered diffraction (EBSD) technique and were compared with an isothermal ternary phase diagram of Fe-Cr-Ti. Their corresponding hardness values are reported and correlated with alloy compositions.

This article briefly summarises previous reports as well as some recent results on welding of various titanium alloys. Titanium is available in a wide range, hence, their properties and characteristics (including welding characteristics) may also varied significantly. The alloys studied represented three major areas; they are (1): unalloyed or commercially pure titanium (CP Ti), (2): near α and α+β alloys, and (3): β alloys. From our preliminary results, it can be reported that the structure of fusion zone (FZ) and heat affected zone (HAZ) of alloys from area (1) may change but their hardness remained, arguably, the same as the as-received material. Alloys from area (2) showed an increase in hardness in the FZ and HAZ areas due to the formation of α-prime or martensite, while alloys from area (3) experienced a reduction in hardness associated with dissolution of α phase leaving only retained β in the FZ. Further investigations are required to confirm these findings. Such information are very useful so that appropriate post welding heat treatment (PWHT) can be applied to improve their properties and performance.

This study, which pertains to the butt welding of 590 MPa high strength steel plates with a high power laser over gaps, was conducted to investigate weld penetration characteristics, to clarify welding phenomena, and to develop procedures for obtaining high quality joints. Butt welding was performed on 12 mm thick plates with a 16 kW high power disc laser together with a hot wire. In this way, welding defects are suppressed and weld metal oxygen content is controlled, thereby producing sound, fully penetrated welds. Penetrations were stable over a range of gaps from 0 to 0·4 mm, owing to an ejection of excess melt through a keyhole outlet at the bottom of the molten weld pool by a strong plume. Here, the use of a hot wire together with a laser of sufficient power to produce a fully penetrated keyhole was effective in improving the gap tolerance and suppressing oxygen inclusion within the butt weld.

Laser-arc hybrid welding is considered to be an efficient, practical welding process because its deposited metal from welding wire can increase gap-bridging ability and prevent welding defects such as undercutting or underfilling. The deposition rate from welding wire, however, cannot be adjusted independently on the welding current under the stable welding conditions because it is necessary to maintain a constant arc voltage. Although the combination of a higher deposition rate and a lower welding current is sometimes needed, for example during the welding of a thin sheet, a high deposition rate generally accompanies with a high welding current in the conventional laser-arc hybrid welding. In order to solve the above-mentioned problems, the authors have proposed a novel method, a filler-added laser-arc hybrid welding (FLA welding) process, to increase a deposition rate without increasing the welding current itself in the welding of aluminium alloy. As a result, gap-bridging ability can be increased in th...

It is well known in welding of die-cast magnesium alloys that porosity is easily formed and degrades the performance of the welded joints. The porosity produced inevitably during laser deep-penetration welding has been studied through metallographic observation, gas content analyses and a high-speed X-ray transmission real-time imaging system. Porosity formation was chiefly attributed to the phenomena that the gases in the pre-existing pores in the base material were swelled to form bubbles during welding and these bubbles had few chances to escape from the weld molten pool because of the vigorous melt flows and the rapid solidification associated with high welding speeds. It was also observed that keyhole instability contributed to porosity formation by generating bubbles from a keyhole tip or a bulged keyhole. Moreover, the insertion of an extruded porosity-free alloy sheet between the die-cast alloy parts resulted in 50% reduction in the weld metal porosity.

This paper deals with a newly developed pretreatment for TIG arc welding to improve weld penetration. As a pre-treatment, a small oxidized region was produced on the surface of stainless steel plates by laser irradiation using oxygen gas prior to travelling TIG arc. The effect of the pre-treatment (especially named LA pre-treatment) on the TIG weld penetration was evaluated. It was found that the pre-treated region extremely smaller than the weld could make the TIG weld penetration deeper at lower welding speeds.

This paper describes a variety of fundamental research results of laser welding which the authors have recently performed. The behavior and characteristics of a laser-induced plume were elucidated. Especially, in remote welding with a fiber laser, the effect of a tall plume leading to shallow weld was interpreted by considering the interaction of an incident laser beam against the zone of a low refractive index from the Mickelson interferometer results. The laser absorption in the plate was higher in the case of a smaller focused beam of fiber laser, lower welding speed and higher power, and the reason was interpreted by considering the size and location of a keyhole inlet and a beam spot. High power tandem laser beams could produce deep penetration, and laser welding in vacuum was developed for production of deeply penetrated welds. Laser direct joining was also developed for joining of metal to plastic or CFRP.

A lot of welding fumes are generated due to the evaporation of magnesium during welding aluminium alloys using Al–Mg welding wires. Fume formation is mainly evaluated by two methods. An average formation rate can be calculated by collecting the fumes formed during a constant welding period. The other one is carried out by observing the droplet with a high speed video. However, these two methods become invalid in quantitatively evaluating the evaporation rate of magnesium in peak or background period during pulsed metal inert gas arc welding. In this paper, a novel method was developed to evaluate the evaporation rate and flux of magnesium in the peak period. First, a robot welding system was used to produce a series of droplets by shutting down the peak current at different times in the peak period. Second, the magnesium contents of these droplets were analysed. Finally, the evaporation rate and flux of magnesium in the peak period were calculated.

High-power and high-brightness lasers such as fiber laser or disk laser are promising as desirable heat sources for deeply-penetrated welds, owing to their superior power density. However, their tightly-focused beam spots have low gap tolerance in butt welding. The objectives of this research are to investigate penetration characteristics, to clarify welding phenomena and to develop high quality welding procedures in butt welding with several gaps of zero to 0.4 mm for 590 MPa-high-strength steel plates with a 10 kW fiber laser or a 16 kW disk laser. The butt welding was performed on 12 mm-thick plates under several welding conditions including using a cold wire or a hot wire. In the case of 0.4 mm gap, underfilling and burn-through welds were obtained by the conventional 10 kW fiber welding and with using a cold wire. On the other hand, welding defects were greatly reduced with a hot wire. Moreover, a 16 kW high power disk laser with a hot wire could produce sound fully-penetrated welds to suppress not only the welding defects but also oxygen content in the weld fusion zone. The weld penetrations were stable in spite of several gaps from zero to 0.4 mm, owing to removal of excessive melt depending on the gap size from bottom keyhole inlet in the molten pool by a strong laser-induced plume.Consequently, it was revealed that laser power sufficient to produce a full-penetrated keyhole using a hot wire was effective to the improvement of gap tolerance and suppression of oxygen content in the weld fusion zone in butt welding of thick high-strength steel plates with a high-power and high-brightness laser.

High power fiber lasers of high beam quality have been developed, and remote welding with a high-power fiber laser has been expected to be one of new high-speed welding procedures in automobile industries. In particular a long-focal-distance focusing optics is beneficial to the welding of a wide area. However, features and effects of a laser-induced plume in such welding process are not fully understood. Therefore, the study was undertaken to investigate weld penetration characteristics with or without removal of a laser-induced plume, to clarify welding phenomena and to develop a stable welding procedure in 4 kW high-power fiber laser welding of a 1.5 mm-thick zinc-coated steel sheet using the focusing optics with a lens of 1,250 mm in focal length. The welds obtained at the focal position without removal of the plume were so unstable that the full penetrations were changed to partial penetrations during laser welding. To fundamentally understand the remote welding phenomena, refractive-index distribution above the laser-irradiated area was visualized by the Michelson interference method. The observation results of fringe patters through a high-speed video camera demonstrated that the incident laser beam was defocused and refracted by a wide formation range and complicated behavior of small refractive-index values derived from the high-temperature metal vapor of the plume, leading to the formation of an unstable penetration weld. It was also confirmed that the removal of the laser-induced plume and the corresponding widespread field of low refractive-index values by using a fan was essential to the stable production of fully-penetrated welds in the high-power fiber laser remote welding with the long-focal-distance focusing optics.

To confirm the process potential and limitations of laser welding of magnesium alloys, a newly developed disc laser of 16 kW in maximum power was used to weld thin plates of AZ31B and AZ61A alloys. Melting characteristics and weld metal properties were studied under different process parameters. The very high power density of the applied beam caused the keyhole and the molten pool to be unstable. Underfill was the main welding defect limiting the process window and its formation was closely related to the keyhole instability. A process diagram indicating areas of sound and defected welds could be constructed. Sound welded joints could be obtained for AZ31B alloy with similar mechanical properties as that of the base material. The brittle intermetallics network present along the grain boundaries in AZ61A weld metals required a higher energy input to alleviate its detrimental effect on the mechanical properties of the welded joints.

Laser-arc hybrid welding (LAHW) is a promising technique for joining sheets due to fast processing speeds and small gap bridgeability. Prior to welding, the edges are often prepared using laser cut ...