Dual-beam Laser Research Articles

Effect of welding parameters on porosity distribution of dual laser beam bilateral synchronous welding in 2219 aluminum alloy T-joint

The dual laser beam bilateral synchronous welding (DLBSW) for T-joint is limited to develop for the porosity defect in joint. In order to investigate the effect of porosity in T-joint, the DLBSW experiment of 2219 Aluminum Alloy T-joint is carried out. While, the distribution of porosity is scanned by X-ray non-destructive testing (NDT) and the size of porosity is measured by particle size analysis software Nano measurer 1.2. The morphology of pore in fracture and the elemental concentration around the pore are investigated by scanning electron microscopy (SEM) and energy spectrometer (EDS). Furthermore, the analysis results of porosity distribution show that the optimal parameter is 3700 W of laser power and 2.5 m/min of welding rate, under which the number of porosities reaches the minimum. The main factor, caused the fracture of weld seam, is the concentrated porosities in T-joint. In addition, technical porosity is mainly found in the center of the weld seam or at the bottom of the weld seam, and it can be eliminated by improving welding parameters. Metallurgical porosity mainly exists at the edge and the top of the weld seam, including hydrogen porosity and metal vapor porosity which formed by the burning of metal elements.

Dual-beam laser welding and seam accurately tracking control for 3D T-joint

The processing methods and quality of T-joint directly affect the performance of stiffened panels. In this paper, firstly, a ten-six axis dual-beam laser welding system is constituted to research the T-joint welding process. Then, the ten-six axis controller in laser welding system is designed to achieve the accurate controlling for position and attitude of welding head during 3D welding of T-joint. In addition, the real-time measurement on both sides of T-joint is adopted to enable deformation compensation and precise tracking for welding seam. Finally, the T-joint welding tests are carried out and the results show that the welding seam errors are within allowable range. Consequently, the dual-beam laser welding and seam tracking control technology presented in this study can meet the processing requirements for T-joint.

Dual-laser-actuated operation of small size objects at a liquid interface.

This work focuses on the use, for the first time to our knowledge, of dual laser beams in photothermal-effect-based propulsion of small size objects at liquid interfaces. Compared with the single-laser mode, dual-laser-actuated operation turns out to be much more controllable with high quality, efficiency, and anti-interference capacity, which can be achieved through automated programming instead of through manual operation. A series of experiments were carried out to verify the principle, with the effects of laser power, laser-spot distance, and movement speed discussed in detail. The findings of this work might provide some insights into the development of intelligent macro/micro-operation systems for manipulating objects at different scales, such as drug particles and cells at liquid interfaces in the future.

Research on the stripping performance during dual laser-beam bilateral synchronous welding of 2219 aluminum alloy T-joint for spacecraft

The promising dual laser-beam bilateral synchronous welding (DLBSW) technology was employed in the 2219 aluminum alloy T-joint which consisted of the skin and stringer components. The coherent weld seam (WS) is achieved under the heat affect of dual laser beam. The stripping experiment was carried out to test the stripping strength of DLBSW joint. With the purpose of discussing the relationship between the welding shape and stripping strength, H1 was measured to evaluate the shape of welded T-joint. The microstructure characteristics of T-joint were observed to discuss the crack location during striping experiment. Besides, the fracture morphology was observed by scanning electron microscope (SEM). The chemical element composition on the impure phase in the fracture was detected by energy dispersive spectrometer (EDS). The highest stripping strength is 317.46 MPa with the laser power of 5500 W and welding speed of 4.2 m/min. The stripping crack locations are mainly divided into three categories. The highest stripping strength is achieved under the second category of crack location which is taken place near the upper fusion line. It is indirectly found that the strength of WS in case 6 with the laser power of 5500 W is highest than the others. The degrading of stripping strength is mainly owing to the reducing of plasticity as well as the formation of internal defects such as pores, bonded structure and nubby impure phases. The nubby impure phase is mainly metal oxides (TiO2, Al2O3) which generally degrade the weld quality. It is notable that a new skin component accompanied with two bosses is firstly designed in the present study to replace the wire filler.

Co-amplification: An efficient spectral beam combination approach for high power, closely separated dual wavelength dye laser systems

Characteristics of an efficient spectral beam combination of two dye laser beams with wavelength difference of less than 10 nm are presented. Two dye laser oscillator beams were spatially and temporally combined with reduced losses before their co-amplification in a common power amplifier. Yellow and green beams of 9 kHz (pulse repetition rate) copper vapour laser (CVL) Master Oscillator Power Amplifier (MOPA) Chain were utilised to pump Rh 101 dye laser oscillators and DCM dye common amplifier respectively. The characteristics of green beam pumped DCM dye common amplifier were studied at various pump power and input power ratios. Combination losses for this configuration were 40% relative to individually amplified configuration. Input–output characteristics of the common amplifier were determined at various input power ratios. Composite dual wavelength dye laser beam having total power of 7.35W at 38.4 W pump power with extraction efficiency 16.5% was demonstrated.

Experiment Study of Rapid Laser Polishing of Freeform Steel Surface by Dual-Beam

One of the challenges regarding widespread use of parts made from alloy steel is their time-consuming polishing process. A rough freeform surface of part has been often expected to be polished rapidly up to a smooth surface finish. The focus of this study is to develop a fast polishing method of freeform surface by using dual-beam lasers. The dual-beam laser system consists of continuous laser (CW) and pulsed laser based on a five-axis CNC device. In this study, a series of experiments of CW laser polishing present the effects of different spot irradiation on surface topography, then the combination trajectory of zigzag and square waveform of pulsed laser is explored to realize a “melting peak for filling into valley” (MPFV) method. The polishing experiment on a semisphere of S136H steel polished by dual-beam shows that a rough semisphere surface was rapidly polished from initial state value of Sa (=877 nm) to post-polished value of Sa (=142 nm), and the polishing efficiency is as high as 2890 cm2/H.

Interface characterization and mechanical properties of dual beam laser welding-brazing Al/steel dissimilar metals

The DP590 steel to AA7075 Al-alloy with lap configuration is successfully joined by dual beam laser welding-brazing without using filler metal. Through the introduction of the derived laser beam, the wetting angle, wetting distance and the thickness of intermetallic compound (IMC) layer are well improved and controlled. It is found that the wettability of liquid Al on steel improves with the increase of laser power, i.e. the wetting angle decreasing from 25.3° to 17.8° and the wetting distance increasing from 2.17 mm to 3.19 mm as the laser power increasing from 1.0 kW to 1.6 kW. Two kinds of IMC exist at brazing interface, one is η-phase (Fe2Al5) with flatten morphology closing to the steel side and the other is θ-phase (FeAl3) with needle-like morphology adjacent to the welding-brazing seam. The thickness of IMC layer increases from 8.37 μm to 12.12 μm with increasing laser power from 1.0 kW to 1.6 kW. Tensile test shows that both the wettability and the IMC thickness have influence on the welding-brazing joint strength. Poor wettability and too thick IMC layer will result in lower strength and fracture occurred in brazing interface. The optimal joint tensile strength of 123.7 MPa on average is achieved with the laser power of 1.4 kW.

Numerical Simulation Analysis of Dual-Beam Laser Welding of Tailored Blanks with Different Thicknesses

In order to meet the requirements of alignment capability, gap tolerance and welding track control, dual-beam laser welding has been put forward to weld tailored blanks with different thicknesses. The arrangement mode and power ratio of dual-beam laser determine the heat transfer and temperature field distribution, and then influence the weld profile and weld quality. In this study, based on consideration of the temperature dependence of material physical properties, convection and radiation heat transfer, and material latent heat, the finite element model was developed. The model validated was conducted to compare with experimental results and it showed good agreement. The arrangement mode and power ratio of dual-beam laser welding were compared and optimized based on the consideration of the weld width on top surface and gap tolerance. Finally, the temperature field characteristics with the preferable process were analyzed in detail according to the numerical simulation. The calculated results indicated the weld width is mainly controlled by the laser irradiation on the thin plate, and dual-beam laser welding of tailored blanks has great advantages on improving heat transfer, weld profile and gap tolerance, which helps to reduce welding defects and enhance welding quality.

Microstructure and Mechanical Properties of Aluminum Alloy/High Strength Steel Double Beam Laser Deep Penetration Welded Joint

A new dual beam laser deep penetration welding technology for lap joint of 1.5 mm thick aluminum alloy and high strength steel was explored in this paper, and the effects of three different beam energy ratios (RS=0.25,0.33,0.5) on weld formation, interface microstructure and mechanical properties were studied. The result shows that under certain conditions of other parameters, double beam laser deep penetration welding process can be applied to lap joint of aluminum alloy / high strength steel with good weld shape when RS=0.25,0.33,0.5. As RS increases from 0.25 to 0.5, the penetration of the weld reduces from 575 μm to 424.2μm, the thickness of intermetallic compound (IMC) layer at the interface between aluminum alloy and weld metal reduces from 3.4 μm to 2.5 μm, the average microhardness of the IMC layer decreases from 771.1 HV to 571.9 HV, the mechanical resistance of the joint raises from 95.7N/mm to 115.2N/mm. When RS=0.5, double beam laser deep penetration welding of aluminum alloy / high-strength steel joints has the highest mechanical resistance of joints, because of the relatively good plastic ductility of the joint.

Kinematics Analysis and Trajectory Planning of collaborative welding robot with multiple manipulators

According to the problem of trajectory planning for collaborative welding robot with multiple manipulators which is applied in dual-beam laser welding of aircraft double curved panel, the multi-manipulator kinematics model is constructed based on Devanit-Hartenberg (D-H) method, and the solution of inverse kinematics is deduced through the specific algebraic method. In addition, the motion law of each joint variable is obtained on the basis of the trajectory planning method for the continuous path. Finally, the correctness of inverse kinematics algorithm and the effectiveness of trajectory planning for the modified robot are verified by ADAMS simulation.

Fabrication of functionally-graded yttria-stabilized zirconia coatings by 355 nm picosecond dual-beam pulsed laser deposition

This article presents the design, fabrication, and characterization of functionally-graded yttria-stabilized zirconia (YSZ) coatings by using a novel dual-beam pulsed laser deposition method based on a 355 nm ps laser. Graded coatings were fabricated by mixing YSZ and the substrate material (stainless steel). The two materials were ablated and deposited on a substrate inside a vacuum chamber, in a way that the mixture composition gradually changes from stainless steel to YSZ, along the coating's growth direction, following a predesigned linear composition profile. The Rockwell indentation method was employed for the adhesion strength analysis based on the interfacial crack radius (c) and indentation load (P). When a load P is applied on the sample surface, a crack with a radius c will be formed. Hence, by using more than one loads and measuring the generated crack diameters, dP/dc can be estimated, which is considered as a critical parameter and is proportional to the coating's adhesion strength. The graded coating was found to provide improved adhesion strength (dP/dc = 9.41 N/μm) over pure YSZ coatings (dP/dc = 8.35 N/μm and 8.43 N/μm). In this study, the thermal barrier effects of the coatings were examined by measuring the thermal conductivity values of the coatings using a high-power multi-mode fiber laser as an impulsive heat source and an infrared camera, and the deposited YSZ coatings showed a low thermal conductivity (∼1.14 W/m·K).

Welding of Dissimilar Steel/Al Joints Using Dual-Beam Lasers with Side-by-Side Configuration

Welding of dissimilar steel/Al lapped joints of 1.5 mm in thickness was carried out by using dual-beam laser welding with side-by-side configuration. The effect of the major process parameters including the dual-beam power ratio of (Rs) and dual-beam distance (d1) on the steel/Al joint characteristics was investigated concerning the weld shape, interface microstructures, tensile resistance and fracture behavior. The results show that dual-beam laser welding with side-by-side configuration produces soundly welded steel/Al lapped joints free of welding defects. The processing parameters of Rs and d1 have a great influence on the weld appearance, the weld penetration in the Al alloy side (P2) and the welding defects. Variation in the depth of the P2 and the locations at the Al/weld interface cause heterogeneous microstructures in the morphology and the thickness of the intermetallic compound (IMC) layers. In addition, electron back scattered diffraction (EBSD) phase mapping reveals that the IMC layer microstructures formed at the Al/weld interface include the needle-like θ-Fe4Al13 phases and compact lath η-Fe2Al5 layers. Some very fine θ-Fe4Al13 and η-Fe2Al5 phases generated along the weld grain boundaries of the steel/Al joints are also confirmed. Finally, there is a matching relationship between the P2 and the tensile resistance of steel/Al joints, and the maximum tensile resistance of 109.2 N/mm is obtained by the steel/Al joints produced at the Rs of 1.50 during dual-beam laser welding with side-by-side configuration. Two fracture path modes have taken place depending on the P2, and relatively high resistance has been achieved for the steel/Al joints with an optimum P2.

Optical and Electrical Characterization of Pure PMMA for Terahertz Wide-band Metamaterial Absorbers

The characteristics of relative permittivity and reflectance for poly (methyl methacrylate) (PMMA) films prepared by spin-coating were investigated and an excellent wideband terahertz (THz) metamaterial absorber (MA) had been fabricated by employing PMMA film as the dielectric layer. XRD and AFM indicated that all the PMMA films with thicknesses from 11 to 17 μm were amorphous and extremely smooth with roughness about 0.203 nm. Raman results demonstrated that vibration strength of the same covalent bonds tends to be consistent with an increase in film thickness. The dual beam laser interferometer (DBLI) was employed to study the influence of applied frequency and thickness on the relative permittivity, and the results exhibited dielectric constants increased from 2.88 to 4.04 with the thickness increasing from 9 to 14 μm. And the dielectric constants for PMMA films with a certain thickness (8 μm) gradually declined when the applied frequency increased from 100 to 105 Hz; besides, the dielectric constant in THz band was forecasted approximately 2.5. The terahertz time domain spectrometer (THz-TDS) results revealed that the THz reflectance was of gradual degradation from 80 to 58% at 3.2 THz, as the thickness increased from 11 to 17 μm. In addition, the UV-VIS spectrum showed that thickness had little effect on reflectance and transmittance in visible region, leading to the almost same Eg (energy gap) about 3.7 eV. At last, by employing PMMA film as the dielectric layer, a highly wideband metamaterial absorber with absorption > 80% from 4.1 to 7.4 THz was fabricated.

An optical trapping system for particle probes in plasma diagnostics.

We present one of the first experiments for optically trapping of single microparticles as probes for low temperature plasma diagnostics. Based on the dual laser beam, counter-propagating technique, SiO2 microparticles are optically trapped at very large distances in low-temperature, low-pressure rf plasma. External forces on the particle are measured by means of the displacement of the probe particle in the trap. Measurements can be performed during plasma operation as well as without plasma. The paper focuses on the optical setup and the verification of the system and its principle. Three examples for the particle behavior in the trapping system are presented: First, we measured the neutral gas damping as a verification of the technique. Second, an experiment without a plasma studies the changing particle charge by UV light radiation, and third, by moving the probe particle in the vertical direction into the sheath or into the plasma bulk, respectively, the acting forces on the probe particle are measured.

Enhancement of long wavelength preheating in dual-beam laser induced breakdown spectroscopy

Dual-beam laser induced breakdown spectroscopy (LIBS) is more sensitive than conventional single-pulse LIBS. A combined configuration of Nd:YAG and CW- CO2 lasers is used to improve the emission intensity of LIBS. The plasma of Al sample was observed under CW-CO2 laser and Nd:YAG laser excitation. The enhancement radiation was obtained from dual-beam LIBS rather than single LIBS, which indicated that IR preheating can cause significant enhancement of plasma. The effects of CO2 laser spot size, laser irradiation time and laser power on plasma emission intensity were investigated. And on this basis, the variation of electron temperature and electron density of plasma with delay time is obtained.

Toward sensitive determination of ammonium in field: A novel fluorescent probe, 4,5-dimethoxyphthalaldehyde along with a hand-held portable laser diode fluorometer

A new fluorescent reagent, 4,5-dimethoxyphthalaldehyde (M2OPA) is synthesized for the determination of ammonium in environmental waters. M2OPA has a similar molecular structure as o-phthalaldehyde (OPA), a commonly used fluorescent probe for ammonium, but M2OPA has two methoxy groups joining the benzene ring of OPA. Ammonium is reacted with M2OPA and sulfite to form a fluorescent derivative, which has a maximum of excitation (λex) and emission (λem) located at 380 and 485 nm, while the λex and λem of OPA reaction are 360 and 430 nm. The M2OPA assay has a rapid reaction and enhanced fluorescent intensity, compared with the OPA-based assay. To realize the ammonium detection in field, a hand-held portable laser diode (LD) fluorometer is developed as the detector for the M2OPA assay. Two LDs of 405 nm in parallel are used as the light source, allowing the detector to operate in single- and dual-laser beam modes. This allows for different linear ranges (0–5 and 0–2 μM, respectively). A photomultiplier tube is used for emission light detection. Limits of detection of 6.5 and 3.5 nM are obtained by using single- and dual-laser beam modes, respectively.

Microstructure and mechanical properties of Ti-22Al-25Nb/TA15 dissimilar joint fabricated by dual-beam laser welding

Ti-22Al-25Nb and TA15 alloys were welded by using continuous dual-beam laser welding. The effects of laser spot spacing and laser power ratio (lead/lag beam) on the appearance, microstructure, and properties of the weld joint were explored. The results showed that with an increase in laser spot spacing and laser power ratio, the width of the weld root decreases, and even the weld is lack of penetration. In addition, the content and sizes of O phases increase in the fusion zone due to the prolongation of time of B2 phase transforming into O phase and O phase growing up. The microhardness at the weld joint changed rapidly and the fusion zone showed the lowest microhardness value. A dimple fracture morphology appeared in all tensile samples. The tensile strength increased from 1001 MPa to 1011 MPa upon increasing the laser spot spacing from 0.18 mm to 0.36 mm, and the tensile strength increased from 1016 MPa to 1206 MPa with an increase in the laser power ratio from 30:70 to 40:60, except the material could not be penetrated when using a laser spot spacing of 0.54 mm or a power ratio of 50:50.

Bubble dimer dynamics induced by dual laser beam ablation in liquid

An approach based on dual laser beam ablation in liquid is presented for the preparation of bimetal hydroxide. The dynamics of a dual laser-induced bubble dimer is studied by the combination of an inviscid Rayleigh-Plesset model, an ultrafast camera, and time-resolved shadowgraphy experiments. It indicates that the dual laser-induced bubble pair will rapidly merge into a dimer and then undergo evolution as a single bubble, which can promote the agglomeration of two kinds of metal particles in this thermodynamic environment. Moreover, the atomic ratio of bimetal hydroxide with high crystallinity can be precisely adjusted by the dual laser energy ratio without any additives.

Analysis of the Differences of Overlap Function of Dual Laser Beams in SO2/NO2 DIAL System

Geometric Form Factor(GFF) or overlap function in transition range is an important factor of a lidar system, especially in a SO2 and NO2 DIAL system. An unstable overlap function will seriously affect measurements of gas concentration and degrade its retrieval accuracy in transition range. In technique of SO2 and NO2 DIAL, retrieval of gas concentration is directly related with ratio between two return signals of emitting laser beam. Construct stability of overlap between two laser beam and receiver can be estimated using the ratio between two return signals. In this paper data acquired from SO2/NO2 DIAL measurements was analyzed. Relative standard deviation of ratio between two return signals in transition range is less than 1%. It shows that Construct stability of overlap between two laser beam and receiver, and quality of laser beam are very good.

Investigations on dual laser beam welding of aluminum high pressure die castings at reduced ambient pressure

During the manufacture of aluminum high pressure die castings, the aluminum alloy is in a liquid phase during the majority of process steps. Due to the high solubility of hydrogen in liquid aluminum, the die casted part likely has an increased hydrogen content, which affects the weldability negatively. When welding these materials, hydrides dissociate and hydrogen is liberated and forms porosity during solidification. To avoid the described formation of porosity, friction stir welding below the melting point and electron beam welding with high frequency beam oscillation were investigated in prior research. Other studies reported that the formation of porosity during laser beam welding of pure aluminum was prevented by the application of dual beam configurations. However, it is well known that laser beam welding under vacuum condition has several advantages, such as the increase in penetration depth, the enhanced degasification, or the overall calming effect on the melt pool when welding ferrous metals. Aiming to combine these advantages, the current work consequently focuses on the occurrence of porosity during dual laser beam welding of aluminum die castings under vacuum (100–0.1 hPa) and atmospheric conditions. All results are based on the outcome of x-ray computed tomography or tensile testing.