Influence Of Laser Power Research Articles

Localized and efficient machining of germanium based on the auto-coupling between picosecond laser irradiation and electrochemical dissolution: Mechanism validation and surface characterization

The auto-coupling effect between picosecond (ps) laser irradiation and electrochemical dissolution is proposed to achieve localized and efficient dimpling of germanium (Ge), in which a highly localized electrical conduction channel is established via laser irradiation. Theoretical clarification and experimental validation are carried out to verify the proposed mechanism, and the machined surface is detailed characterized. It is found that the current increases rapidly to 3– 5 times higher level up to 225 mA once the defocused laser irradiates on top Ge surface, and a dimple with smooth surface and steep sidewall can be obtained on wafer bottom in neutral NaNO3 electrolyte. Meanwhile, the dimple centre precisely corresponds to the laser irradiating location, and micro oxide particles of about 1 μm in diameter have been observed attaching on the newly formed dimple surface. The influences of laser power, applied voltage and electrolyte jet velocity on the dimple shape and surface morphology are experimentally explored and amply discussed. The dimple entrance diameter can be controlled to around 1 mm with a flat copper cathode, while the depth can be easily up to about 480 μm within 200 s. Finally, the atomic removal mechanism of the localized and enhanced electrochemical dissolution is analysed.

Process Parameter Optimization on Selective Laser Melting of CuSn10 Powders Based on Response Surface Methodology

Abstract A shaping test of CuSn10 powders was carried out by using the selective laser melting (SLM) technology to study influences of process parameters of SLM on compactness of specimens. Meanwhile, process parameters were optimized based on the response surface methodology. Meanwhile, phase composition and microstructure of formed part were analyzed by XRD and OM. Results demonstrated that as the energy density of laser body increases from 146.7 J·mm-3 to 181.3 J·mm-3, pores of samples decrease and the compactness increases from 98.97% to about 99.7%. Subsequently, the compactness begins to decrease with the continuous increase of laser energy density. The incomplete melting of powder under low energy density and gasification of powders under high energy density are major factors that influence the compactness. Over low or high laser energy density is disadvantageous for the improvement of compactness. A mathematical model of interaction between three factors (laser power, laser scanning speed and scanning space) and response value (compactness) was built up by using the BBD principle design test of response surface methodology. The degree of fitting (R2) and correction coefficient (R2 adj) of the model were 0.9952 and 0.9866, which agree well with the fitting degree of experimental tests. Among three factors, influences of laser power and scanning speed on compactness are equivalent and more significant than scanning space. The optimal process parameters which were predicted by the model were laser power=331.471 W, scanning speed=648.045 mm·s-1, scanning space=69.9302 μm. Under this circumstance, the compactness of CuSn10 powders after SLM is 99.75%. According to experimental verification, the practical value of compactness is 99.74%, showing a very small relative error. This proves that the BBD model is reliable. The shaped part is mainly composed of α-Cu phase and metastable phase β’-Cu13.7Sn. Compared with the original powders, the content of metastable phase β’ increases significantly, while the δ-Cu41Sn11 phase disappears.

Study of weld formation characteristics in laser-arc hybrid welding

The laser-arc hybrid welding was carried out on the marine-use steel, and the effects of primary parameters on weld behavior were investigated. The results show that the weld penetration increased gradually with the increase of laser power. Meanwhile, superior weld formation, penetration and reinforcement were achieved when laser and wire distance was 2 mm. The weld width, penetration and reinforcement were increased with the increase of current, while they were decreased with the increase of welding speed. The influence of laser power on the generated microstructure was analyzed by the observation in junction of weld and heat affected zone (HAZ). The microstructure of HAZ coarsened with the increase of laser power, which is consistent with the hardness distribution trend in HAZ.

Influence of laser power on microstructure and mechanical properties of laser welded TWIP steel butted joint

The twinning-induced plasticity (TWIP) steel is a newly developed which possesses fantastic mechanical properties and high potential for anti-crash weight-optimized structural applications. In this study, the weldability of 2 mm thick TWIP steel plate by laser welding method was investigated. The welded joint exhibited fully austenitic structure, and the weld seam consisted three types of solidification structures: columnar dendrite, cellular crystal and equiaxed dendrite. The microsegregation of C and Mn elements occurred in the interdendritic regions during the solidification of the weld seam. The toughness of the heat-affected zone (HAZ) was higher than that of the weld seam. The microhardness diagram of cross-section of welded joints presented V-shaped under different laser power. The microhardness of equiaxed dendrite zone was higher than that of the weld seam and coarse grain heat affected zone (CGHAZ). The average strain and tensile strength increased first and then decreased with the rising of laser power. Further study demonstrated that the fracture of the laser welding TWIP steel joints during tensile test presented ductile mode characteristics. The results show that the appearance and performance of the welded joint are optimal with laser power of 1800 W in present study, and the tensile strength and total elongation are 915 MPa and 48%, respectively.

Fabrication of PDMS chips by laser engraving for protein enrichments

Abstract PDMS (Polydimethylsiloxane) chips are increasingly important for the application of fluorescence measurements due to their auto-fluorescence free, excellent transparency, and biocompatibility. However, the design of PDMS microfluidic chips requires to fabricate plenty of molds for structure optimization, resulting in high cost. In the present, PDMS chips with nafion membrane were fabricated by simple and low-cost method for bull serum albumin (BSA) enrichment. To optimize the laser cutting and bonding parameters, simulation models were established using Bilinear Kinematic and Mooney-Rivlin models, respectively. The influence of laser power and cutting speed on the width and depth of the micro-channels was investigated. And the effect of bonding pressure on the deformation of PDMS micro-channel and stress distribution near the micro-channels was also analyzed. The leakage test and BSA enrichment demonstrated the practicability and feasibility of the present fabrication method in this work.

Microstructure and mechanical properties of TC4/6061 and TC4/2024 dissimilar joints by autogenous laser welding-brazing

In this work, titanium alloy (TC4) and aluminum alloys (2024 and 6061) were joined by autogenous laser welding-brazing, and the influence of laser power on weld appearance, microstructure and mechanical properties of Ti/Al dissimilar joints was investigated. As the laser power increased, the amount of TiAl3 intermetallic compounds in the weld zone gradually increased, and the granular intermetallic compound changed to fine needles and long strips. With an increase in laser power from 1500 W to 1800 W, the average microhardness of the TC4/2024 and TC4/6061 weld zone increased from 103 HV0.3 to 110 HV0.3 and 77 HV0.3 to 96 HV0.3, respectively. When the laser power was 1700 W, the average tensile strength of the TC4/2024 and TC4/6061 dissimilar joints reached 298 MPa and 220 MPa, respectively. Thermodynamic analysis of the interfacial reaction showed that Cu element increased the Gibbs free energy of the alloy system, thereby reducing the driving force for the formation of intermetallic compound, while Si element reduced the Gibbs free energy of the system, making the interface reaction of TC4/6061 more likely to occur than that of TC4/2024. With the increase of Ti content, the chemical potential gradient of Si element was larger than that of Al element, which caused the segregation of Si atoms at the interface of TC4/6061 joint.

Influence of laser welding power on steel/CFRP lap joint fracture behaviors

Dual-phase steel DP590 and carbon fibre reinforced polymer (CFRP) were successfully joined by laser welding. Experiments and numerical simulations were performed to clarify the influence of laser power on the joint characteristic, bonding mechanism and fracture behavior. The results indicate that the melting width and depth of CFRP increased with the enhancement of laser power. With relatively low laser power, un-bonded steel/CFRP interface was formed due to the insufficient melting of resin matrix and interfacial residual stress resulted from thermal expansion mismatch between steel and CFRP. Compact-bonding was produced with the laser power range of 400–700 W. Decomposition of CFRP at the interface occurred with the further increase of laser power to 800 W due to excessively high peak temperature. The highest tensile-shear peak load of 3855 N was produced at 700 W laser power. Three different fracture modes were found in the joints with different laser powers, i.e., interfacial fracture (IF) at 300 W and 400 W, cohesion fracture (CF) in CFRP at 500 W and 600 W, and interface fracture at inner region together with cohesion fracture at outer region of the bonding interface (IF + CF) at 700 W and 800 W. X-ray photoelectron spectroscopy results showed that C-M and O-M chemical bonds were formed at the interface due to the reaction between resin matrix and DP590. Stronger O-M and C-M chemical bonds produced at higher laser power were beneficial for the improvement of fracture load.

Influence of Laser Power on Droplet Transfer Behavior and Spatter in Laser-MIG Hybrid Welding of Aluminum Alloy

Influence of Laser Power on Droplet Transfer Behavior and Spatter in Laser-MIG Hybrid Welding of Aluminum Alloy

Influence of laser power in nanosecond laser texturing for a hydrophobic state on SS316L

The use of lasers in surface engineering has recently made significant progress. The hydrophobic surface is commonly studied because of the application in various fields, including vehicles, aerospace, biomedicine, etc. Since these laser methods require many combination parameters, such as laser power (P), frequency (ƒ), scan speed (ʋ) and laser beam diameter (D), the effect of the parameters must therefore be investigated to produce the hydrophobic condition. This research tries to relate the laser power with the morphological properties and contact angle of the SS316L surfaces. Samples are subjected to laser texturing with different laser power settings. The surface is then characterised by surface roughness, and the contact angle is measured according to a specific time interval. The laser power output and energy density function on the surface and contact angle were investigated in these contexts experimentally. Surface roughness was defined and validated to show that the laser parameters' effect is effective and controllable. This study shows that the laser output intensity significantly contributes to regulating surface roughness and the substrate's wetting activity. The 18W and 24W laser outputs produce a spiked surface with various peaks that cause the surface to become hydrophobic over time because of the air-trap that happens in the valley.

Fabrication of Microgrooves by Synchronous Hybrid Laser and Shaped Tube Electrochemical Milling.

The fabrication of deep microgrooves has become an issue that needs to be addressed with the introduction of difficult-to-cut materials and ever-increasing stringent quality requirements. However, both laser machining and electrochemical machining could not fulfill the requirements of high machining efficiency and precision with good surface quality. In this paper, laser and shaped tube electrochemical milling (Laser-STEM) were initially employed to fabricate microgrooves. The mechanisms of the Laser-STEM process were studied theoretically and experimentally. With the developed experimental setup, the influences of laser power and voltage on the width, depth and bottom surface roughness of the fabricated microgrooves were studied. Results have shown a laser power of less than 6 W could enhance the electrochemical machining rate without forming a deep kerf at the bottom during Laser-STEM. The machining accuracy or localization of electrochemicals could be improved with laser assistance, whilst the laser with a high-power density would deteriorate the surface roughness of the bottom machining area. Experimental results have proved that both the machining efficiency and the machining precision can be enhanced by synchronous laser-assisted STEM, compared with that of pure electrochemical milling. The machining side gap was decreased by 62.5% while using a laser power of 6 W in Laser-STEM. The laser-assistance effects were beneficial to reduce the surface roughness of the microgrooves machined by Laser-STEM, with the proper voltage. A laser power of 3 W was preferred to obtain the smallest surface roughness value. Additionally, the machining efficiency of layer-by-layer Laser-STEM can be improved utilizing a constant layer thickness (CLT) mode, while fabricating microgrooves with a high aspect ratio. Finally, microgrooves with a width of 1.79 mm, a depth of 6.49 mm and a surface roughness of 2.5 μm were successfully fabricated.

Comparative ex vivo Investigations on the Cutting Quality of the CO2 Laser and the Diode Pumped Er:YAG Laser.

Objectives: A sufficient histological evaluation is a key pillar in oncological treatment, especially in situations of cancer of unknown primary. CO2 laser technology is used in clinical routine of soft tissue surgery because of its cutting quality and availability. Diode pumped solid state Er(bium):YAG laser systems promise a higher cutting efficiency and minor thermal damages. The aim of this study was to compare both laser systems with respect to their suitability for cutting soft tissue.Methods: A setup was realized which enables comparable experiments with the clinical CO2 laser (AcuPulse 40ST DUO, Lumenis) and the Er:YAG laser system (DPM 40, Pantec Biosolutions AG). Fresh mucosal samples of porcine tongues were used to determine the influence of laser power and sample velocity on cutting depth and thermal damage width for both lasers. In addition, for the Er:YAG laser, the influence of the pulse repetition rate was examined additionally. For analysis, images of histological sections were taken.Results: In all experiments, the Er:YAG laser shows a significantly higher cutting depth (P < 0.0001) and less thermal damage width (P < 0.0001) than the CO2 laser. For example, at an average power of 7.7 W and a sample velocity of 5 mm/s the Er:YAG laser shows a mean cutting depth of 1.1 mm compared to the CO2 laser with 500 μm. While the Er:YAG laser shows a mean thermal damage width of 70 μm compared to 120 μm. Furthermore, the Er:YAG enables the adjustment of the cutting depth and thermal damage width by varying the irradiation parameters. A decrease of the repetition rate leads to a reduction of thermal damage. For example, a repetition rate of 100 Hz results in a thermal damage width of 46 μm compared to 87 μm at 800 Hz at an average power of 7.7 W and a cutting velocity = 5 mm/s while a homogenous cutting quality can be achieved.Conclusions: In conclusion, the results of these ex vivo experiments demonstrate significant advantages of the diode pumped Er:YAG laser system for soft tissue ablation compared to the CO2 laser, in particular regarding cutting efficiency and thermal damage width.

Dissimilar laser spot welding of aluminum alloy to steel in keyhole mode

Laser spot welding was used for the dissimilar joining of aluminum alloy to steel in the keyhole mode. The results showed that the defocusing amount and laser power had significant influence on the weld formation. The aluminum alloy was prone to the formation of welding defects, such as porosity and cracks in the fusion zone, which resulted in an extremely instable welding process and poor joint strength. In order to improve the weld quality, a copper heat sink was placed under the aluminum alloy, which effectively absorbed the heat of the aluminum alloy and reduced the previous reported welding defects. The influence of laser power, defocusing amount, welding time, and shielding gas on the joint characteristics was also investigated. The microstructure analysis showed that a conelike fusion zone and sparsely distributed Fe-Al intermetallic compounds were formed. Hence, a combination of metallurgical bonding and mechanical interlocking was achieved in the laser keyhole spot welds, enhancing the joint mechanical properties. The joint strength of the laser keyhole spot welds reached 620 N/mm, which was comparable to that obtained in resistance spot welds.

Selective Laser Melting of Pre-Alloyed NiTi Powder: Single-Track Study and FE Modeling with Heat Source Calibration.

Unique functional properties such as the low stiffness, superelasticity, and biocompatibility of nickel–titanium shape-memory alloys provide many applications for such materials. Selective laser melting of NiTi enables low-cost customization of devices and the manufacturing of highly complex geometries without subsequent machining. However, the technology requires optimization of process parameters in order to guarantee high mass density and to avoid deterioration of functional properties. In this work, the melt pool geometry, surface morphology, formation mode, and thermal behavior were studied. Multiple combinations of laser power and scanning speed were used for single-track preparation from pre-alloyed NiTi powder on a nitinol substrate. The experimental results show the influence of laser power and scanning speed on the depth, width, and depth-to-width aspect ratio. Additionally, a transient 3D FE model was employed to predict thermal behavior in the melt pool for different regimes. In this paper, the coefficients for a volumetric double-ellipsoid heat source were calibrated with bound optimization by a quadratic approximation algorithm, the design of experiments technique, and experimentally obtained data. The results of the simulation reveal the necessary conditions of transition from conduction to keyhole mode welding. Finally, by combining experimental and FE modeling results, the optimal SLM process parameters were evaluated as P = 77 W, V = 400 mm/s, h = 70 μm, and t = 50 μm, without printing of 3D samples.

Mesoscopic simulation of overlapping behavior in laser powder bed additive manufacturing

The prediction of the flow behavior of Metal micro-molten pool is prerequisite for high-quality Laser Powder Bed Fusion (L-PBF). In this study, mesoscopic scale numerical simulation modelling for L-PBF process was used to help understand the melting process of pure copper micro-melt pool. In this study, the orthogonal test was designed to study the influence of laser power, laser scanning velocity, hatching space on the flow behavior of molten pool and the overlapping rate of adjacent molten tracks. The results shows that laser scanning speed has the greatest influence on both the size and overlapping rate of the molten pool, and the overall trend was that the size of molten pool continues to increase as the volume energy density increases, and the maximum molten pool size was 243.6 um × 110 um with volume energy density 370.037 J mm−3, overlapping rate of adjacent molten tracks was 48.84% with volume energy density 285.71 J/mm3. The optimized pure copper laser process parameters were obtained: laser power 300 KW, laser scanning speed 500 mm/s, hatching space 0.07 mm, overlapping rate 48.84%.

Monitoring of high-speed laser welding process based on vapor plume

The increase of welding speed can improve the productivity of laser welding. The behavior of vapor plume is an important indicator reflecting the state of the laser welding process. However, the behavior of vapor plume in high-speed laser welding (whose welding speed is higher than 10 m/min) has not been studied adequately. In this research, images of the vapor plume in high-speed laser welding of SUS304 austenitic stainless steel are captured through high-speed imaging for the monitoring of the welding process. Characteristics of the vapor plume are extracted with image processing, and the influences of laser power and welding speed on these characteristics are analyzed. The relationships between the behavior of vapor plume and melt pool are discussed, and three ejection regimes of the vapor plume are proposed. In order to predict the occurrence of humping, which is a typical defect in high-speed laser welding, samples are built by applying a time sliding window and then a classification model is built with the random forest. In addition, the importance of features in the classification is analyzed. The test results show that the proposed method can predict the humping defect in high-speed laser welding accurately.

Effect of Tb3+ ion concentration on the up-conversion and down-conversion luminescence properties of the Yb3+/Ho3+/Tb3+ tri-doped SiO2–Al2O3–Y2O3–NaF–CaF2 glasses

Yb 3+ -Ho 3+ -Tb 3+ co-doped SiO 2 –Al 2 O 3 –Y 2 O 3 –NaF–CaF 2 glasses were prepared. The XRD of the glass was obtained, which proved the amorphous state of the glass. The crystallization temperature of glass was measured by differential scanning calorimetry, and the crystallization activation energy was obtained. The absorption spectrum of glass was investigated. The network structure of glass was studied. The up-conversion and down-conversion spectra of the glass were obtained under 980 nm and 369 nm excitation, respectively, and the fluorescence decay lifetime of Tb 3+ : 5 D 4 was measured. The influence of laser power on up-conversion luminescence intensity was investigated by changing the laser power. The energy transfer relationship among Yb 3+ , Ho 3+ , and Tb 3+ was researched. The CIE chromaticity coordinate was calculated according to the emission spectrum. It shows that this series of glasses have possible applications in the field of the green light display. • Yb 3+ -Ho 3+ -Tb 3+ tri-doped SiO 2 –Al 2 O 3 –Y 2 O 3 –NaF–CaF 2 glass was prepared. • Intensity of the up-conversion and down-conversion emission peaks was dominated by Tb 3+ ions. • Energy level transitions and energy transfer modes between Yb 3+ -Ho 3+ -Tb 3+ ions were discussed. • This series of glass has potential applications in the field of green light display elements.

Thermal imaging of high power ultrashort pulse laser ablation of alumina towards temperature optimized micro machining strategies

The application of pulsed laser systems with pulse durations in the pico- and femtosecond regime for material processing is commonly associated with a cold ablation. Due to the minimized interaction-time between the ultrashort laser pulses and the material, this statement is almost valid as long as no heat accumulation effect appears. With the increasing demand of high productivity processes, the average power of ultrashort pulsed laser systems increases above 100 W, which leads, however, to increased thermal effects during laser processing. This is especially important for laser processing of technical ceramics like alumina. Large temperatures gradients, which locally occur during laser processing using high average power could lead to thermal modifications and cracks in the material. In this study, we present a process-optimization method for high power laser ablation of alumina based on thermal imaging. The use of a 2D IR camera enables the estimation of the temperature distribution during the laser processing. We investigate the influence of laser power up to 80 W, pulse duration between 900 fs and 10 ps and processing duration on the resulting material temperature. Beside the material temperature we evaluate the material removal rate and the resulting surface quality.

Quantitative analysis and experimental study of the influence of process parameters on the evolution of laser cladding

To avoid and eliminate cracks on the surface of a workpiece, it is very important to quantitatively analyse the temperature field, stress field, and flow field during the laser cladding process. This paper uses the finite element method to establish a multiphysics coupling model based on the laser cladding process of a disc laser. The thermophysical parameters of the base material ASTM 1045 and the powder material Fe60 are calculated by the CALPHAD method. In the modelling, the mutual influence between the light powder is considered but also the influence of the surface tension and buoyancy of the liquid metal in the molten pool on the flow of the molten pool and the dynamic change of the cladding layer morphology are considered. In the laser cladding process, the distribution and change law of the temperature field, flow field, and stress field are obtained. An infrared thermometer was used to measure the temperature during the cladding process, and a Zeiss-ƩIGMA HD scanning electron microscope was used to observe the outline of the cladding layer, which verified the accuracy of the mathematical model. The response surface model was established by the CCD method, and the influence law of the process parameters on the cladding layer was determined. The influence of laser power, beam radius, and scanning speed process parameters on the changes of temperature field, flow field, and stress field in the cladding process was analysed, providing an effective way to reduce residual stress.

Laser additive remanufacturing parameters optimization and experimental study of heavy-duty sprocket

Experimental research on laser additive remanufacturing technology of heavy-duty sprocket was carried out. The influences of laser power, scanning speed, and powder feeding rate on cladding height, cladding area, melting area, and dilution rate were compared and analyzed. The prediction models of the combination of process parameters with the geometric characteristics of cladding layer and dilution were established. A multi-objective process parameter optimization model with the maximum cladding height and cladding area, the minimum melting area, and dilution rate as objective functions was established, and the model was optimized and solved based on MOPSO algorithm. The laser additive remanufacturing repairing experiment of damaged sprocket was carried out by using the optimal parameter combination, and the microstructure and mechanical properties of the repaired region were analyzed. The results show that the scanning speed and powder feeding rate are the main factors influencing the geometric characteristics and dilution of the cladding area, and the models have good prediction accuracy. The optimal process parameters (1150 W, 950 mm/min, 3.8 rad/min) obtained by MOPSO algorithm are adopted to repair the damaged sprocket. The repaired area without cracks and pores and the cladding layer show good metallurgical bonding with the substrate, and the microhardness is twice that of the substrate. The experimental results prove that the laser additive remanufacturing technology is feasible to repair the damaged heavy-duty sprocket and has a strong engineering application prospect.

Influence of laser power on precipitate formation and multiple step transformation kinetics in NiTi shape memory alloy weld joints

NiTi shape memory alloys are considered to be one of the fastest-growing materials with vast potential. However, the broader applications in intricately designed components are limited due to difficulties faced during welding processes such as degradation of functional and mechanical properties, precipitate formation, and selective vaporization of elements. In this study, the effect of laser power on precipitates formation and subsequent transformation temperatures on NiTi shape memory alloy was investigated by testing 0.8 kW, 1.0 kW and 1.2 kW welded specimens. The microstructures revealed the formation of Ni4Ti3 precipitates in the fusion zone and energy dispersive X-ray spectroscopy assessment exhibited preferential Ni evaporation. Differential scanning calorimetry analysis revealed the evolution of multiple step transformations (3-step / 3-step) after laser welding. Furthermore, enthalpy change in peak transformations was evaluated and increasing order of enthalpy change was recorded for weld joints with increasing laser power. The kinetics of martensite transformation was evaluated by placing emphasis on average activation energy. High laser power welded joints showed easy martensitic transformation compared to low laser power welded joints. X-ray diffraction assessment also validated the existence of Ni4Ti3 precipitates and martensitic phase in NiTi alloy after laser welding. The electron backscattered diffraction maps of welded joints revealed the grain growth in the fusion zone and heat affected zone, and the unindexed black region emphasized the formation of distorted interphase of austenite/martensite and additional martensite phase at the fusion zone/heat affected zone interface.