Diode Laser Welding Research Articles

Diode Laser Welding of Polyethylene

A high-power diode laser (HPDL) was used to weld high-density polyethylene (HDPE) sheets. Laser-welded joints were fabricated with different values of laser power and scan speed. Hot-tool welding was also employed to fabricate joints to make a comparison between this consolidated technology and HPDL welding. Initially, laser heating tests were carried out to study the laser–material interaction. Furthermore, welding tests were carried out and tensile mechanical tests were performed to characterize joints and sound specimens. A similar material behavior was recognized for all the specimens. While the laser process resulted in lower strength and ductility, in comparison to the tool-welding process, the aesthetics of the laser-welded joints were remarkable. The best values of the process parameters were individuated for the laser welding and were used to fabricate a closed structure having sharp edges. The same geometry cannot be obtained by any other welding technology.

Fusion Zone Microstructure Evolution of Al-Alloyed TRIP Steel in Diode Laser Welding

TRansformation Induced Plasticity (TRIP) steels are promising materials to achieve a better combination of formability and strength than conventional steels due to their unique microstructural makeup. Though welding is a vital part of auto body manufacturing, the weldability of TRIP steels has some complex and poorly understood features, which has served to retard the growth of its applications in the automotive industry. In this study, autogeneous welds were carried out on Al-alloyed TRIP steel using a 4 kW diode laser. Both fusion zone solidification behavior and subsequent austenite transformation products were investigated with optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. In terms of solidification behavior, fusion zones solidified with high temperature δ-ferrite as the primary phase. Fusion zone microstructure at room temperature was composed of ferrite with a skeletal morphology characteristic of solidification, and austenite decomposition products almost all having a lath morphology. Skeletal ferrite covered about 30% fusion zone area. Upper bainite laths separated by retained austenite films comprised most of the transformed microstructure, about 65% of the fused area. Lower bainite with carbide particles dispersed in an aligned way, chunk shaped retained austenite, lath martensite and twinned martensite were also occasionally observed. The Al content was considered to be for a dominant influence on fusion zone microstructure evolution.

Metallurgical and Mechanical Properties of Fusion Zones of TRIP Steels in Laser Welding

Transformation induced plasticity (TRIP) steels are a promising solution for the production of cars with low body mass because of the combination of high strength and high plastic strain capacity that they offer. Si and Al are two important alternatives for alloying of TRIP steels in order to suppress carbide precipitation in the bainite holding temperature range during steel manufacture. Weldability of TRIP steel is one of the key factors governing its application in auto industry. In this paper, Al-alloyed TRIP steel was investigated with the diode laser welding process in terms of fusion zone metallurgical and mechanical properties, with Si-alloyed TRIP steel also included for comparison. It was found that the fusion zone of the Al-alloyed steel has a multiphase microstructure, containing skeletal ferrite, bainitic ferrite, martensite and retained austenite of two different morphologies. In contrast, the Si-alloyed steel fusion zone consists almost entirely of martensite. The high martensite content results in low fusion zone ductility in the Si-alloyed steel, only providing half the tensile elongation of the Al-alloyed steel. The Si-alloyed steel shows a greater decrease of the strength‐ductility balance (ultimate tensile strength times elongation) due to welding, i.e., 62.9% compared to 45.2% for the Al-alloyed steel in quasi-static tensile testing. High strain rate tensile testing with a Hopkinson Bar apparatus shows no significant effect of strain rate on the fusion zone ductility for either steel. The fusion zone of the Al-alloyed steel does not exhibit a detectable TRIP effect probably due to the low carbon content in the retained austenite. Al and Si are both relevant as agents to suppress cementite precipitation, but they are found to exert very different influences on steel weldability.

Laser-assisted corneal welding in cataract surgery: Retrospective study

To evaluate the efficacy of laser welding to close corneal wounds in cataract surgery. Department of Ophthalmology, Hospital of Misericordia e Dolce, Prato, Italy. This retrospective nonrandomized interventional case series included 20 eyes of 20 patients. All eyes had cataract with visual acuity worse than 20/200. Ten patients had phacoemulsification surgery, and 10 had extracapsular cataract extraction (ECCE). Surgeries were followed by laser-assisted closure of the corneal wounds by diode laser welding of the stroma using a technique established in animal models. Preoperative and postoperative (1, 3, 7, 30, and 90 days) astigmatism, level of inflammation, Seidel testing, and endothelial cell counts were obtained. There were minor differences in preoperative and postoperative astigmatism except in 1 eye in the ECCE group. The Seidel test showed no wound leakage during the follow-up examinations, and endothelial cell loss was similar to that published for standard surgical cataract procedures. No collateral effects of the laser welding were detected, nor was postoperative inflammation. Astigmatism was slightly affected by the use of laser welding for corneal wound closure after phacoemulsification and ECCE. The laser-assisted corneal sealing procedure was rapid and safe and could serve as an alternative to corneal suturing, with significant potential applications for the closure of longer incisions, such as those used in penetrating keratoplasty.

Aesthetic Diode Laser Welding of Stainless Steel

In the present study the use of diode laser for stainless steel aesthetic welding is considered. In fact the surface smoothness of the weld bead, attributed to the mode stability of the laser system, suggests its application for aesthetic weld joint. The aims of this work were to: define a process map, based on an aesthetic criterion; mechanically characterize the weld joints (by Vickers micro-hardness and tensile test); analyse the surface of the specimens in terms of roughness. Moreover, gas tungsten-arc (TIG) weld joints were carried out and analogously tested to make a comparison with the diode laser results. Good aesthetic butt joints were obtained with diode laser welding. The same results were found working with constant power speed ratio (i.e. constant fluence). Comparison between TIG and Laser Beam Welding (LBW), showed no significant difference in roughness, while ultimate tensile load was higher for TIG welding. The differences in joint strength depend on the different cross-sectional area and on the extension and microstructure of the base metal, heat-affected zone and melted zone. However, diode laser technology allows to obtain smaller bead size.

Experimental and model analysis on the temperature dynamics during diode laser welding of the cornea

Corneal laser welding is a technique used clinically to induce the immediate sealing of corneal wounds. We present an experimental and model analysis of the temperature dynamics during diode laser-induced corneal welding, which is aimed at characterizing the mechanism of tissue fusion. Ex vivo tests were performed on porcine eyes in the typical irradiation conditions used for laser-induced suturing in cornea transplant. Three laser power densities (12.5 W/cm(2), 16.7 W/cm(2), 20.8 W/cm(2)) were tested. The superficial temperature of the cornea was measured by means of an infrared thermocamera. Experimental data were compared with the results of a three-dimensional (3D) model of a laser-welding process in the cornea, solved by the use of the Finite Element Method (FEM). The model solution and experimental results showed good agreement. The model was thus used to estimate the temperature enhancement inside the corneal wound and to calculate the thermal damage inside the tissue. The results indicated a selective, spatially confined heating effect that occurred at operative temperatures (59 to 66 degrees C) close to intermediate denaturation points of the stromal collagen, before its complete disorganization. No significant heat damage to the region of the laser-treated wound was evidenced in the operative irradiation conditions of corneal welding.

DIODE LASER-ASSISTED CAROTID BYPASS SURGERY

Conventional suturing methods of microvascular anastomosis are associated with various degrees of vascular wall damage that can lead to thrombosis and bypass occlusion. An experimental model of double end-to-side venous graft anastomosis on the common carotid artery was set up to compare conventional suturing methods with a low-power diode laser vascular welding technique. The experiments were performed on 40 rabbits that underwent implantation of a 15-mm segment of jugular vein on the common carotid artery. The proximal end-to-side suture was performed by eight interrupted stitches; the distal suture, which was done using a laser welding technique, was supported by four stay sutures. The animals were evaluated after 2 days (n = 15), 9 days (n = 15), and 30 days (n = 10). The vascular segments were excised and subjected to histological, immunohistochemical, and ultrastructural evaluation. The average clamping time to perform both anastomoses was 35 minutes. At the end of the follow-up period, one case of complete occlusion was observed after 9 days and one case was observed after 30 days. Surgical observations and pathological evaluation indicated that adoption of the laser welding technique reduced operative time and bleeding. Histologically, a reduction of thrombosis, inflammation, myointimal hyperplasia, and dystrophic calcification was observed in laser-assisted anastomoses. A better preservation of the endothelium was also evident in laser-treated anastomoses. The observed differences were deemed statistically significant (P < 0.05). Our study demonstrated the efficacy of diode laser welding in improving surgical techniques of high-flow bypass and in reducing the vascular wall damage observed with conventional methods.

Effect of process parameters on bead properties of A359/SiC MMCs welded by laser

Metal matrix composites are well known materials that present several positive features, mainly in terms of mechanical strength to weight ratio. On the other side, MMC's are extremely difficult to machine (in particular by chip removal processes) and this difficulty has limited a wider diffusion. Welding, together with other joining technologies, could be a solution to limit the chip removal processes in the production of a MMC part, but this is not a problem-free process. This paper presents an experimental study on the laser welding of MMCs using both a CO 2 and a diode laser source. The CO 2 welding is performed in keyhole conditions (deep penetration), whereas the diode laser performs a conduction welding. Results show that the CO 2 welding is greatly affected by the formation of Al 4 C 3 , that compromises the toughness of the bead. The content of Al 4 C 3 can be reduced by acting on the process parameters, but cannot be completely eliminated. Instead, diode laser welding generates a sound bead, with negligible Al 4 C 3 formation and of superior quality. Considering also the other positive features of this kind of sources (high efficiency and radiation wavelength, that is, highly absorbed by MMCs), diode laser welding seems to be highly recommendable for MMCs laser welding.

Closure of skin incisions by 980-nm diode laser welding

A 980-nm diode laser is proposed to be an alternative welding laser in dermatology due to its optimal penetration in tissue. An in vivo predosimetry study was done to estimate the optimal laser energy delivery conditions (6 W, 400 ms). Next, in vivo experiments were comparatively performed to examine healing of wounds closed either with suture or laser welding. One-centimeter-long, full-thickness incisions were done on the dorsal side of Wistar rats. Wounds were surgically removed at 1, 4, 7, 14, and 21 days postoperatively. Macroscopic examinations showed that welding had minimal scarring and a fine quality healing. According to histological (hematoxylin and eosin staining) results, change of epidermal thickness and granulation tissue formation through 21 days of healing period showed similarities in both methods. Epidermal thickness of welded wounds decreased from 62.46+/-6.87 microm (first day) to 36.49+/-0.92 microm (21st day) and that of sutured wounds decreased from 62.94+/-13.53 microm (first day) to 37.88+/-7.41 microm (21st day). At day 14, epidermal thickness of sutured wounds (61.20+/-6.60 microm) were higher than welded wounds (49.69+/-6.31 microm) (p<0.05). Besides, granulation values were greater for the sutured wounds but the difference was statistically significant (p<0.05) only for the seventh day (197,190.29+/-.89,554.96 microm(2) for sutured wounds, 138,433.1+/-51,077.17 microm(2) for welded wounds). Those differences indicate a faster recovery with laser welding. It is concluded that tissue welding with a 980-nm diode laser can be a good candidate for tissue welding applications with accelerated and improved healing, but further investigations are in progress for clinical use.

CMAC-based modelling for HPDDL welding process control

A Cerebellar Model Articulation Controller- (CMAC-) based modelling method and closed-loop control system were developed to estimate and control the weld fusion for measuring the topside and backside bead widths of the weld pool in High Power Direct Diode Laser (HPDDL) welding. Because of the difficulty in using backside sensor, a topside weld pool geometry is measured using a topside vision sensor and is also used to measure the backside bead width. The drive current of the laser and the welding speed are taken as the control variables. The basic function of CMAC-based steady-state models, which are more easily obtained than dynamic ones, of the non-linear controlled process can predict the control variables with satisfactory accuracy to shorten output response transient time, and two simple Proportional and Integral (PI) controllers are included in the control system to adjust the control variables to maintain outputs at the desired levels. The results of closed-loop control simulations of laser welding process demonstrate that the developed control system is effective and robust to fluctuations or variations that lead to the changing parameters of the non-linear model.

Investigation on Ti6Al4V laser welding using statistical and Taguchi approaches

Ti6Al4V is presently one of the most widely used titanium alloys, accounting for more than 50% of all titanium tonnage in the world, and to date no other titanium alloy has been a threat to its dominant position. Laser welding of Ti6Al4V is a major issue in the automotive and aerospace industries. In this paper, both CO 2 and diode laser welding processes were investigated for Ti6Al4V alloy sheet joining using either lap or butt configurations. Artificial neural networks (ANN) processed the data coming from the experimental trials. The aim was to interpolate the database in order to form a suitable database for the analysis of the variance (ANOVA) and the Taguchi analysis of the means. The ANOVA has the merit of being able to be validated on a statistical basis while the Taguchi engineering approach has the ability of maximizing the information coming from a small database of data. Therefore, reliable and valuable information over the ranges of the processes investigated was individuated from a limited number of trials.

CO 2 and diode laser welding of AZ31 magnesium alloy

Magnesium alloys are being increasingly used in automotive and aerospace structures. Laser welding is an important joining method in such applications. There are several kinds of industrial lasers available at present, including the conventional CO 2 and Nd:YAG lasers as well as recently available high power diode lasers. A 1.5 kW diode laser and a 2 kW CO 2 laser are used in the present study for the welding of AZ31 alloys. It is found that different welding modes exist, i.e., keyhole welding with the CO 2 laser and conduction welding with both the CO 2 and the diode lasers. This paper characterizes welds in both welding modes. The effect of beam spot size on the weld quality is analyzed. The laser processing parameters are optimized to obtain welds with minimum defects.

Development of Space DL Welding Process for Construction and Repair of Space Structures in Space

An ultra-high vacuum diode laser welding system capable of performing a diode laser (DL) welding experiment at the International Space Station orbital pressure of 10−5 Pa was developed for investigating the effect of environmental pressure on DL welding phenomena. A DL welding experiment with a power density of about 100 kW/cm2 was conducted on 304 stainless steel at pressure levels between 105 Pa and 10−5 Pa. Although a laser-induced plasma plume was observed during welding at environmental pressures, 105 Pa and 103 Pa, no laser-induced plasma plume was found in the pressure range from 10 Pa to 10−5 Pa. The mode of the melting process (weld pool shape) under these experimental conditions was a keyhole-type melting mode or a transition-type melting mode at environmental pressures of 105 Pa and 103 Pa. However, the melting mode at pressures lower than 10 Pa changed to a heat-conduction-type melting mode. Although the penetration depth decreased when the environmental pressure was dropped to 103 Pa, it did not change at pressures lower than 10 Pa. We also determined that the prevention technology of metal vapor deposition on optical devices needs to be developed for DL welding technologies used in space.

宇宙半導体レーザ溶接法による各種環境圧力でのステンレス鋼の溶接現象

The authors develop the space Gas Hollow Tungsten Arc (GHTA) welding which can be performed in a vacuum, since 1993. In order to establish the space welding technologies necessary for the space development, we are also developing the space Diode Laser (DL) welding process in which the welding principle is completely different from the space GHTA welding. The paper describes the welding results by the perpendicular irradiation and oblique irradiation of the laser light in a vacuum. The DL welding experiments using the stainless steel clarified the melting characteristics and the evaporating phenomena in molten metal. And also, it has been clarified that the mass of the metal vapor during welding increases with the reduction of the environmental pressure and the radiation distribution of evaporation metal follows the cosine law.

Development of a High Power Diode Laser Welding System and Usability for Tailored Blank Processing

We developed new high power diode lasers and welding system applied to automobile industry. This paper describes the developed machine concept and the possibility of replacement to high power diode laser welding for tailored blank processing which has been performed by CO2 lasers or YAG lasers.

宇宙空間での宇宙構造物の建造・修理を対象にした宇宙レーザー溶接法の開発

An ultra high vacuum diode laser welding(UHVDLW) system in which a diode laser(DL) welding can be performed in the ISS orbital pressure 10-5Pa was developed for investigating the effect of an environmental pressure on a DL welding phenomenon. The DL welding experiments with power density around 100kW/cm2 were conducted on 304 stainless steel in pressure levels between 105Pa and 10-5Pa. Although a laser-induced plasma plume is observed during welding in the environmental pressure 105Pa and 103Pa, no laser-induced plasma plume is found in the pressure ranging 10Pa to 10-5Pa. A formation of melting process(weld pool shape) with this experimental condition is a keyhole melting type or a transition melting type in the environmental pressure 105Pa and 103Pa. But, a melting process in the pressure lower than 10Pa changes to a heat conduction melting type. The penetration depth showed a decrease with the environmental pressure down to 103Pa and then appears to no change in a pressure lower than 10Pa. Establishment of space DL welding technology needs to develop a suppression technology of a metal vapor deposition to an optical device.

Comparison of high power diode laser and Nd:YAG laser microwelding of k-type thermocouples

k-Type thermocouple (NiCr–NiAl) joints are currently manufactured by argon arc welding. One of the weaknesses of this joining method is that the weld bead diameters are about three times of the thermocouple wires. This slows the response time of these thermocouples. Furthermore, porosity exists in the joints affecting the conductivity and repeatability for temperature measurement. In this paper, the feasibility and the characteristics of welding 0.2 and 0.5 mm diameter k-type thermocouples using a 120 W diode laser and a 400 W Nd:YAG laser are reported. The energy density requirement and the effects of shroud gas are described and analysed quantitatively. The performances of the laser welded thermocouples are evaluated against the commercial ones. Reductions of 35 and 15% in response time have been achieved compared to the commercial and the Nd:YAG laser welded 0.2 mm diameter thermocouples, respectively, whereas for the 0.5 mm diameter thermocouples, the HPDL welded ones performed 5% better and the Nd:YAG welded ones performed 9% better. The tensile strength of the diode laser welded thermocouples was found to be around 1620 N mm −2 at 0.2 mm diameter and 480 N mm −2 at 0.5 mm diameter. This is well above the industrial standard of 400 N mm −2. The work shows that diode laser welding can generate beadless and porosity-free butt joints in the thermocouples superior to the ones produced by argon arc welding.

Laser Welded Vesicourethral Anastomosis in an In Vivo Canine Model: A Pilot Study

We evaluated laser welding as an alternative method of forming the vesicourethral anastomosis. Eight dogs underwent open total prostatectomy, including 4 in which the vesicourethral anastomosis was formed by 830 nm. diode laser welding using a chromophore doped albumin solder and 3 or 4 support sutures. The remaining 4 anastomoses were conventionally formed using 8 interrupted sutures. Acute leakage was tested intraoperatively. The anastomosis of 1 animal per group was assessed on postoperative days 3, 5, 7 and 14 by radiography before sacrifice. Each anastomotic specimen was then tested for leak pressure and examined histologically. There were no leaks during intraoperative testing of laser welded or sutured anastomoses. On radiography there were no leaks in the laser welded group. In 1 control there was slight localized leakage. All anastomoses achieved physiological leak pressures of 70 mm. Hg or greater with 3 of the 4 in the laser welded group recording supraphysiological pressures of greater than 200 mm. Hg. While 3 of the 4 laser welded specimens showed evidence of muscle necrosis, there were no other differences in healing in the 2 groups. These short-term results suggest that diode laser welded vesicourethral anastomosis is feasible. This technique has the potential to simplify anastomotic formation in laparoscopic radical prostatectomy, shortening operative time. Diode laser welding in this small cohort created an immediate and ongoing watertight anastomosis and, therefore, it may also be an alternative in open radical prostatectomy cases. Further study is needed to assess long-term effects on healing.

Characterization of CO2 and diode laser welding of high carbon steels

Deep penetration welding with a high power CO2 and diode laser may offer an attractive means to join metal for certain applications, for instance: welding car drive shafts and gear plant. The rapid cooling rate of laser welding results in high hardness discontinuities across the welded joint; however, this leads to brittle weld and fatigue failure. To avoid this critical problem, it is useful to optimize the laser operating parameters in order to improve the mechanical properties of the weld. In this study, an experimental analysis was used to predict the significant effect of the weld quality using CO2 and high power diode laser (HPDL) laser welding, operating at 10.6 μm and 810 nm, respectively. Investigations into the weld quality were done to quantify the effect of different welding velocities by examining the hardness profiles, tensile strength, aspect, weld volume formation rate, and microstructure formation. In all cases, the results showed that for the HPDL weld configurations, cracking was observed in the fusion zone, whereas, for a CO2 laser weld, a greater weld strength and wider weld width were observed. For HPDL welding, center-line cracking was found along the fusion zone at higher welding velocities.

Quantitative changes in collagen levels following 830‐nm diode laser welding

Background and Objective The actual mechanism by which laser irradiation welds tissue is presently unknown; however, collagen is a major constituent of tissue welded by laser irradiation. Study Design/Materials and Methods: Collagen was extracted from the abdominal aorta of Wistar rats by acetic acid extraction and repeated pepsin digestion after tissue welding (254 W/cm2) by using an 830-nm diode laser. The collagen levels were determined by using the Sircol Collagen Assay (Biocolor, Northern Ireland). Results Compared with untreated aorta, the collagen content of the treated vessel was obvious decreased (P < 0.001) immediately after laser irradiation. Levels then increased by day 3, with a peak at day 10 (P < 0.002). The collagen content returned to normal levels on day 30 and remained at this level throughout the rest of the experimental period. Conclusion These results suggest that a proportion of the collagen molecules in the vessel are denatured by the heat of the laser. Collagen synthesis is stimulated during the healing process after laser welding with the parameters used in the present study. Lasers Surg. Med. 22:207–211, 1998. © 1998 Wiley-Liss, Inc.