YAG Laser Welding Research Articles

An Investigation on the Effect of Pulsed Nd:YAG Laser Welding Parameters of Stainless Steel 1.4418

In the present study, a low average power pulsed Nd:YAG laser is used for bead-on-plate welding of low carbon steel plate. The effect of laser process parameters on the weld quality and weld bead profile, welding penetration (P), welding surface width (W) and welding pool area (A), is studied. Focal point position, welding speed, pulse duration, and energy are selected as the process variables. The formation of a keyhole and weld bead profile is found to be highly dependent on laser pulse parameters. Results show that the maximum penetration accurse when the focal point is above the surface, in pulse duration of 6 ms, welding speed of 2 mm/s and pulse energy of 16.67 J.

Deflection load characteristics of laser-welded orthodontic wires

To compare the deflection load characteristics of homogeneous and heterogeneous joints made by laser welding using various types of orthodontic wires. Four kinds of straight orthodontic rectangular wires (0.017 inch × 0.025 inch) were used: stainless-steel (SS), cobalt-chromium-nickel (Co-Cr-Ni), beta-titanium alloy (β-Ti), and nickel-titanium (Ni-Ti). Homogeneous and heterogeneous end-to-end joints (12 mm long each) were made by Nd:YAG laser welding. Two types of welding methods were used: two-point welding and four-point welding. Nonwelded wires were also used as a control. Deflection load (N) was measured by conducting the three-point bending test. The data (n = 5) were statistically analyzed using analysis of variance/Tukey test (P < .05). The deflection loads for control wires measured were as follows: SS: 21.7 ± 0.8 N; Co-Cr-Ni: 20.0 ± 0.3 N; β-Ti: 13.9 ± 1.3 N; and Ni-Ti: 6.6 ± 0.4 N. All of the homogeneously welded specimens showed lower deflection loads compared to corresponding control wires and exhibited higher deflection loads compared to heterogeneously welded combinations. For homogeneous combinations, Co-Cr-Ni/Co-Cr-Ni showed a significantly (P < .05) higher deflection load than those of the remaining homogeneously welded groups. In heterogeneous combinations, SS/Co-Cr-Ni and β-Ti/Ni-Ti showed higher deflection loads than those of the remaining heterogeneously welded combinations (significantly higher for SS/Co-Cr-Ni). Significance (P < .01) was shown for the interaction between the two factors (materials combination and welding method). However, no significant difference in deflection load was found between four-point and two-point welding in each homogeneous or heterogeneous combination. Heterogeneously laser-welded SS/Co-Cr-Ni and β-Ti/Ni-Ti wires provide a deflection load that is comparable to that of homogeneously welded orthodontic wires.

Effect of heat treatment on the properties of laser-beam welded rheo-cast F357 aluminum

Semi-solid metal rheo-cast F357 aluminum plates were joined by autogenous Nd:YAG laser welding and were welded in either the as-cast (F) condition, T4 temper or T6 temper condition. The weldability of this age-hardenable Al–7%Si–0.6%Mg casting alloy was characterized by assessment of the microstructure in the fusion and heat-affected zones and by measurement of the weld-plate tensile and hardness properties. The low heat input provided by the laser welding process resulted in high cooling rates (450–600 K/s) within the fusion and adjacent heat affected zones. This thermal cycle closely resembles quenching practice for standard solution treatments (500–700 K/s) and as a result the T4 condition was maintained during the welding process. Tensile properties equivalent to the parent metal T6 condition were obtained after exposing welded T4 plates to conventional artificial ageing treatment.

Investigation on Mechanical Properties of Pulsed Nd:YAG Laser Welding on AISI 304 Stainless Steel to AISI 1008 Steel

Product with low cost, lightweight and enhanced mechanical properties were the main reasons welding dissimilar materials thrived by most of the industries. The laser welding technique which has high-energy density beam was found suitable of carrying this task. This paper attempts to investigate welding of AISI 304 stainless steel to AISI 1008 steel through Nd:YAG pulse laser method. The main objective of this study was to find out the weldability of these materials and investigate the mechanical properties of the welded butt joints. Peak power, pulse duration and weld speed combinations were carefully selected with the aims of producing weld with a good tensile strength, minimum heat affected zone (HAZ) and acceptable welding profile. Response surface methodology (RSM) approach was adopted as statistical design technique for tensile strength optimization. Statistical based mathematical model was developed to describe effects of each process parameters on the weld tensile strength and for response prediction within the parameter ranges. The microstructure of the weld and heat affected zones were observed via optical microscope. The results indicate the developed model can predict the response within ±9% of error from the actual values.

Si-photonics based passive device packaging and module performance

We report a fully packaged silicon passive waveguide device designed for a tunable filter based on a ring-resonator. Polarization diversity circuits prevent polarization dependant issues in the silicon ring-resonator. For the device packaging, the YAG laser welding technique has been used for pigtailing both of the input and output fibers. Post welding misalignment was compensated by mechanical fine tuning using the seesaw effect via power monitoring. Packaging loss less than 1.5 dB with respect to chip measurement has been achieved using 10 µm-curvature radius lensed fibers. In addition, the packaging process and the module performance are presented.

Characteristics of the Keyhole and Energy Absorption during YAG Laser Welding of Al-Li Alloy

In this paper, the keyhole of YAG laser welding 5A90 Al-Li alloy was observed and measured through the high speed camera. The characteristics of the keyhole and the effects of welding parameters were studied. The characteristics of the absorption of laser energy and the susceptivity for heat input in welding 5A90 were given. The results show that in this welding condition, the keyhole of laser welding 5A90 is nearly a taper and the highest temperature area is in the bottom. There are clear effects of heat input on the characteristics, especially the surface radius of keyhole and plasma/vapor in keyhole. Another phenomena is observed that sometime plasma/vapor could disappear in 0.3ms welding time, and this feature will be more remarkable as decrease of heat input. It shows that the absorption of energy is unsteady. It is known that when this instability reaches a certain value, an unsteady weld will be formed.

The Research on YAG Laser Welding Porosity of Al-Li Alloy

The laser welding of Aluminum-Lithium alloy (Al-Li) alloy were conducted to investigate the weld porosity features in this paper. The results show that there are two kinds of weld porosity existing for laser welding Aluminum-Lithium alloy sheet. They are can be divided into metallurgical porosity and unstable keyhole porosity according to their different reason causing them. The mechanism of unstable keyhole porosity occurring was discussed according to the results of YAG laser welding processing. The methods how to reduce weld porosity for laser welding of Aluminum-Lithium alloy was also described.

Effects of Nd: YAG Laser Welding Parameters on the Microstructure of 21% Cr Ferritic Stainless Steel

21% Cr with Ti-Nb dual stabilized ferritic stainless was welded using Nd: YAG laser. The relationship between microstructure and parameters of laser welding was examined. The microstructure was investigated by using the optical microscope and scanning electron microscopes. The average grain size of the HAZ was increased with increasing heat input due to the slow cooling rate. Large precipitates as TiN, TiC and Nb(C,N) were dissolved in the HAZ. Fine precipitates which supposed to be TiC was formed uniformly distributed in the case of the fusion zones.

Advances in pulsed laser weld monitoring by the statistical analysis of reflected light

This paper describes two new techniques for monitoring the quality of laser welds by statistical analysis of the reflected light signal from the weld surface. The first technique involves an algorithm that analyses the variance of the peak values of the reflected signal as a measure of the stability of the surface during pulsed Nd:YAG laser welding in the heat conduction mode. Kalman filtering is used to separate a useful signal from the background noise. A good correlation between weld disruption and signal fluctuation has been identified. This technique could be used in tandem with the present practice of simply using the peak values of reflected (or emitted) light as an indicator of weld quality. The second technique investigated involves an assessment of the temporal shape of the power distribution of individual reflected pulses in comparison with an average of the results from a high quality weld. Once again a high correlation between a poor signal match and inferior quality welding was discovered, which may pave the way towards a new generation of optical weld monitoring devices.

Study on corrosion of welded steel for LBE-cooled fast reactors

Lead-bismuth eutectic (LBE) is a candidate coolant for fast reactors. Its physical, chemical and neutronic properties make it a prospect coolant for the reactors. However, corrosion of structure is the main problem of utilizing LBE as a coolant. Compatibility of welded structure with LBE at high temperature should be considered clearly for feasibility of lead-bismuth-cooled fast reactors. This study was preformed to investigate the mechanical properties and corrosion characteristics of the welded ferritic-martensitic (FM) steel, HCM12A, in LBE at 650 °C for 500 h. The welding methods were TIG welding (137 mm/min; 480 W), YAG laser welding (780 mm/min; 287 W) and electron beam welding (1000 mm/min; 60 kW). The oxygen concentration of test environment was maintained at 7 x 10 −7 wt% by injecting Ar–H2-steam gas mixture. Vickers hardness test and SEM/EDX analysis were conducted on the cross section of welded HCM12A. It was found that oxide layer was larger in the weld zones than base metal (BM). However, outer layer was detached on some areas.

Microstructure and Mechanical Properties of Nd:YAG Laser Welded Invar 36 Alloy

Invar 36 alloy is increasingly used as a structural material for manufacture of liquefied natural gas (LNG) transporters and storage tanks. However, the conventional arc welding of Invar 36 alloy has high susceptibility of hot-cracking. As a high-energy-beam welding process, laser welding could be effective for producing defect-free Invar 36 weld. In the present study, defect-free Invar 36 weld was successfully produced by Nd:YAG laser welding. The microstructure and mechanical properties of weld were also tested.

Image processing of weld pool and keyhole in Nd:YAG laser welding of stainless steel based on visual sensing

In order to obtain good welding quality, it is necessary to apply quality control because there are many influencing factors in laser welding process. The key to realize welding quality control is to obtain the quality information. Abundant weld quality information is contained in weld pool and keyhole. Aiming at Nd:YAG laser welding of stainless steel, a coaxial visual sensing system was constructed. The images of weld pool and keyhole were obtained. Based on the gray character of weld pool and keyhole in images, an image processing algorithm was designed. The search start point and search criteria of weld pool and keyhole edge were determined respectively.

Nd:YAG Laser Welding of Stainless Steel 304 for Photonics Device Packaging

Although pulsed Nd:YAG laser welding has been widely used in microelectronics and photonics packaging industry, a full understanding of various phenomena involved is still a matter of trials and speculations. In this research, an ultra compact pulsed Nd:YAG laser with wavelength of 1.064μm has been used to produce a spot weld on stainless steel 304. The principal objective of this research is to examine the effects of laser welding parameters such as laser beam peak powers, pulse durations, incident angles, focus point positions and number of shots on the weld dimensions: penetration depth and bead width. The ratio of the penetration depth to the bead width is considered as one of the most critical parameters to determine the weld quality. It is found that the penetration depth and bead width increase when the laser beam peak power, pulse duration and number of shot increase. In contrast, the penetration depth decreases when the laser beam defocus position and incident angle increase. This is due to the reduction of the laser beam intensity causing by the widening of the laser spot size. These experimental results provide a reference on an optimal laser welding operations for a reliable photonics device packaging. The results obtained shows that stainless steel 304 is suitable to be used as a base material for photonics device packaging employing Nd:YAG laser welding technique.

Process Control of Stainless Steel Laser Welding using an Optical Spectroscopic Sensor

The in-process monitoring and real-time control of the penetration depth during laser welding is evaluated. An optical collimator collects the optical emission for measurement with a fast spectrometer. The sensor data are used to calculate the electron temperature and subsequently to determine the weld quality of overlap welds in AISI 304 stainless steel sheets performed both with CW Nd:YAG and CO2 lasers. A PI-controller adjusts the laser power aiming at a constant penetration depth and has been tested for Nd:YAG laser welding. Optical inspection of the weld verifies the results obtained with the proposed closed-loop system of spectroscopic sensor and controller.

A Reliable Nd:YAG Laser Welded Stainless Steel 304 for Photonics Device Packaging Application

An ultra compact pulsed Nd:YAG laser with laser beam peak power of 3.5kW and 6.5ms pulse duration is employed to produce a butt joint and lap joint for both spot and seam welding on a stainless steel 304 specimen. The strength test of the weld joints is conducted by pulling the joint materials using INSTRON Series IX/s Automated Materials Tester System. From the experimental results, it is found that a butt joint produces much stronger attachment than a lap joint. The stronger attachment is contributed by a larger volume of welded stainless steel 304 at the joint interfaces. However, the strength of a lap joint can be increased by producing a deeper weld penetration depth. It is done by controlling the laser beam parameters such as laser peak power and pulse duration. It is inferred that the commercial welding material, InvarTM, provides more robust joint than stainless steel 304. It is also concluded that the welded stainless steel 304 cannot attain the strength and elastic modulus of the stainless steel 304 itself. However, the stainless steel 304 is a good welding material for photonics device packaging by using pulsed Nd:YAG laser welding technique.

3245 Effect of Continuous Diode Laser on Crack Generation in Pulsed Nd:YAG Laser Welding of Aluminum Alloy

3245 Effect of Continuous Diode Laser on Crack Generation in Pulsed Nd:YAG Laser Welding of Aluminum Alloy

The Connection of Welded Seam Three Dimensional Appearance with Performance for Joints of Stainless Steel Plate Laser Welding

It has been carried out the test and research to the stainless steel plate laser welding welded seam, by two-dimensional, three-dimensional appearance observation and tensile methods. Its result is: The YAG laser welding, is welding speed, frequency, pulse width and so on technological parameter influences to be big. In the power limit, raising the power or reducing welding speed; or increasing the frequency, or increasing the pulse width in critical value range, it be possible to increasing joints strength, however, when the pulse width surpasses critical value range its joints strength instead fall. In this study, the parameter that the appearance and the quality are all good of welded seam for welds speed 60mm/min, frequency 10Hz, pulse width 3ms, defocusing amount -1mm, the tensile strength of joints may reach 390MPa. The joints that the performance is good, its keyhole's microscopic appearance is also more complete good, but the joints that the macroscopic appearance is good, it has fine mechanical properties certain by no means. The three-dimensional observation of keyhole appearance is relatively feasible to be appraisal laser welding welded seam newest method，it is worthy discussing and carrying out.

Texture evolution in Nd:YAG-laser welds of AZ31 magnesium alloy hot rolled sheets and its influence on mechanical properties

AZ31 hot rolled magnesium alloy presents a strong basal texture. Using laser beam welding (LBW) as a joining process induces high temperature gradients leading to major texture changes. Electron back scattered diffraction (EBSD) was used to study the texture evolution, and tensile tests coupled with speckle interferometry were performed to understand its influence on mechanical properties. The random texture obtained in the LBW fusion zone is mainly responsible for the yield strength reduction.

Effect of laser and laser hybrid welding on the corrosion performance of a lean duplex stainless steel

The use of duplex stainless steel increases steadily worldwide and the fluctuations in nickel price the recent years have contributed to further growth. The lean duplex grade Outokumpu LDX 2101® (EN 1.4162, UNS S32101) has a low nickel content and is alloyed with nitrogen and manganese to give a balanced microstructure. It means that good austenite formation is obtained even when laser welding autogenously (without filler). This is in contrast to most other duplex grades, for which laser welding is normally associated with high ferrite fractions, known to reduce the ductility and corrosion performance. Nd:YAG, CO2 and fiber laser welding of LDX 2101® has been performed with and without filler wire and as laser hybrid welding with gas tungsten arc (GTA) and gas metal arc (GMA). The microstructure was evaluated and related to the corrosion performance, and the mechanical properties are presented. The austenite formation in autogenously laser welded LDX 2101® is not sufficient to completely avoid chromium nitride precipitation and the weld metal pitting resistance is consequently affected. This is particularly seen when fiber laser welding. The mechanical properties of all welds were on a similar level with those of the base metal, while the corrosion performance and ductility were marginally to significantly lower. Use of filler wire when Nd:YAG laser welding and Nd:YAG laser-GTA hybrid welding with and without filler wire, and nitrogen additions to the GTA shielding gas improved the austenite formation and hence the pitting resistance. CO2 laser and CO2 laser-GMA hybrid welding proved to result in most austenite and generally showed the highest pitting resistance of all laser welds.

Study on YAG Laser Welding Process of Fe-Mn-Si Shape Memory Alloy

In this study, 1mm thick Fe-Mn-Si shape memory alloy was welded by both sides using YAG laser welding. In a certain range of parameters, the optimal processing parameters for the maximum tensile strength are current 100 A, pulse frequency 3 Hz and pulse width 15 ms by orthogonal experiment. With the optimal processing parameters, the tensile strength of the welded joint can achieve 94% of base material,and the fracture appears in the center of welding seam and the surface morphology of welding seam is good. The influence of processing parameters on tensile strength of weld joint is directly embodied in cross-section of the welding seam morphology. In the laser welding, the tensile strength of nonpenetration in seam and hourglass shape welded joint is generally poor, and the perfect welded joint has conditions such as wide welding seam, deep penetration, weld pool filling and “non-hollow”. Most importantly, the central area in cross-section of the welding seam is the widest.