Powder Feeding Nozzle Research Articles

Investigating the effects of powder feeding rate on microstructure transformation in linear laser beam additive manufactured thick-walled structures

The coarse columnar crystals that grow through multiple layers are commonly observed in laser additive manufactured structures, with fractures tending to occur in regions where there are abrupt changes in grain morphology. This can lead to a degradation of the mechanical properties of the samples. In this study on laser additive manufacturing, thick-walled structures made of 304 stainless steel were created using a linear beam spot with a rectangular powder feeding nozzle. By adjusting the powder feeding rate to influence the thermal cycling characteristics during the laser additive manufacturing process, a hierarchical grain structure that combines coarse and fine equiaxed grains was achieved, enhancing the forming efficiency and overall mechanical performance of the structure. The results from the thermal cycling characteristics and microstructure analysis indicate that increasing the powder feeding rate during the additive manufacturing process can decrease the hierarchical cooling rate, temperature gradient, and heat accumulation effect. This reduction in turn decreases the grain size and facilitates the transformation of columnar crystals into equiaxed crystals. Furthermore, the transformation of low-angle grain boundaries into high-angle grain boundaries in the interlayer region helps to reduce stress concentration, weaken anisotropic tendencies, and mitigate intergranular fracture tendencies, ultimately improving the mechanical properties of the overall structure. In actual engineering applications, the powder flow can be adjusted to control the temperature gradient and cooling rate of the deposition layer, thereby altering the grain morphology and optimizing the mechanical properties of additive manufacturing parts.

Design and Numerical Analysis of an Inside-Beam Powder Feeding Nozzle for Wide-Band Laser Cladding.

Wide-band laser cladding technology has emerged as a solution to the limitations of traditional cladding techniques, which are small single-path dimensions and low processing efficiency. The existing wide-band cladding technology presents challenges related to the high precision required for the laser-powder coupling and the significant powder-divergence phenomenon. Based on the inside-beam powder-feeding technology, a wide-band powder-feeding nozzle was designed using the multi-channel powder flow shaping method. The size of the powder spot obtained at the processing location can reach 40 mm × 3 mm. A computational fluid dynamics analysis using the FLUENT software was conducted to investigate the impact of the nozzle's structural parameters on the powder distribution. It was determined that the optimal configuration was achieved when the powder-feeding channel was 8, and the transverse and longitudinal dimensions for the collimating gas outlet were 0.5 mm and 1 mm, respectively. Among the process parameters, an increase in the carrier gas flow rate was found to effectively enhance the stability of powder transportation. However, the powder feed rate had minimal impact on the powder concentration distribution, and the collimating gas flow rate appeared to have a minimal effect on the divergence angle of the powder stream. Wide-band laser cladding experiments were conducted using the designed powder-feeding nozzle, and a single-path cladding with a width of 39.96 mm was finally obtained.

Powder-flow behavior and process mechanism in laser directed energy deposition based on determined restitution coefficient from inverse modeling

In order to clarify the transportation mechanism of particles in continuous coaxial powder feeding (CCPF) process, a trial-and-matching method is developed to quantify the restitution coefficient which is used to describe the inelastic collision between the particle and the nozzle wall. The consistency of the outlet velocity and the spatial concentration distribution of particles between the experimental statistic and the numerical calculation shows that the restitution coefficient of 0.9 can be used to measure the inelastic collision behavior between particles and the nozzle wall. Employing the determined restitution coefficient, a semi-quantitative method based on optical diagnostic and quantitative analysis derived from numerical calculation are proposed to study the powder-gas flow transport characteristics from single-layer to multi-layer jet flow. It is found that the outer shielding gas flow (OSGF) has a great influence on the multi-layer jet flow field, and it is most conducive to powder focusing at the OSGF of 20 L/min. The velocity distribution of CGF determined by the inner structure of CCPFN and the inelastic collision between the particle and the wall are the two mutually coupled factors that determine the outlet velocity of particles. Frequent inelastic collisions and the decrease of the CGF velocity lead to velocity dispersion and trajectory fluctuation of particles. When the inlet velocity of particles is 1.33 m/s, the outlet velocity ranged from 0.4 m/s to 0.9 m/s. This paper aims to provide a general method to determine the restitution coefficient and offer a comprehensive understanding of transportation mechanism of power particles both inside continuous coaxial powder feeding nozzle (CCPFN) and multi-layer jet zone between substrate and the CCPFN outlet.

Investigation on solidification structure and temperature field with novel processing of synchronous powder-feeding underwater laser cladding

Synchronous powder-feeding underwater laser cladding(SULC) has a great application prospect in underwater in-situ manufacturing/remanufacturing due to its advantages of small heat input to the substrate and adjustable of additive materials. In this study, the iron-based planar coating with no phase transformation and dilution zone less than 8 μm was prepared on A32 deck steel by SULC using self-designed powder-feeding nozzle and optimizing process parameters. The powder-feeding gas flow rate directly determines the size and stability of the local dry region above the deposition point, and the laser power and powder-feeding rate are the key factors to compensate the laser energy dissipation. Due to the influence of local temperature gradient in SULC, the coating has obvious solidification structure distribution. Columnar grains are mainly distributed upon the trough of fusion line, while dendrites and equiaxed grains are distributed on both sides caused by the temperature gradient becomes smaller and the direction of heat flow changes due to the external environment. In the upper region of SULC coating the equiaxed grains tend to grow up with the increase of laser power. To gain better scientific understanding on differences between atmospheric laser cladding and SULC, the numerical simulation was used to reveal the temperature field changes and coating formation under SULC working parameters. The results show that under the same laser power, due to the forced cooling of larger gas flow and external water environment in SULC process, there is a larger temperature gradient at the deposition point, and the temperature drop rate of the coating and the substrate is greater. In the microstructure, it is shown as columnar grains has a greater directional growth trend. With the increase of laser power, this phenomenon becomes more obvious.

Optimal design of structure parameters of coaxial powder feeding nozzle for laser cladding

Aiming at the problems of large powder gathering diameter, low powder utilization rate, easy clogging of the nozzle, poor cooling water system effect and unstable powder feeding effect existing in the existing nozzles, an improved laser cladding coaxial powder feeding nozzle with external shielding gas structure is optimally designed. The response surface method and the BP neural network optimized by genetic algorithm are used to optimize the nozzle structure parameter combination. After the nozzle structure parameter combination is determined, the external shielding gas structure parameter range is determined according to the nozzle structure parameter combination. The unsupported laser cladding coaxial powder feeding nozzle is made of photosensitive resin material, and the powder feeding effect is verified. The optimized nozzle is measured for the powder converging point, powder converging diameter and powder utilization rate, which verifies the validity of the simulation results.

Analysis of the Agglomeration of Powder in a Coaxial Powder Feeding Nozzle Used for Laser Energy Deposition

Analysis of the Agglomeration of Powder in a Coaxial Powder Feeding Nozzle Used for Laser Energy Deposition

Simulation and experimental research based on carrier gas flow rate on the influence of four-channel coaxial nozzle flow field

This paper investigates the influence of carrier gas flow on the external flow field of coaxial powder feeding nozzle. FLUENT software was adopted to establish gas-solid two-phase flow. The simulation of powder stream field under different carrier gas flow was also carried out. Results show that the larger the flow of carrier gas is, the higher the gas flow field velocity at the nozzle outlet is. At the same time, the concentration at the convergence point is lower, and the convergent point is maintained at 0.015 m. Under the condition of 4 L/min, the powder flow convergence is good. When it exceeds 4 L/min, powder spot diameter increases. The experiment of powder aggregation and laser cladding forming were completed, which shows that the forming effect is the best one under the condition of 4 L/min. It is consistent with the simulation analysis results and has a high reference to the optimization of the process parameters of coaxial nozzle.

To study the laser cladding of ultra high strength AerMet-100 alloy powder on AISI-4340 steel for repair and refurbishment

High Tensile Steels such as AISI-4340 is extensively used steel in various engineering sectors such as aerospace, defense, automotive, heavy engineering and power sectors for components such as pinion housing, gears, shafts, connecting rods, propeller shafts, & landing gears of aerospace vehicles etc. Such component faces extensive wear at the contact areas during operation resulting in loss of performance leading to replacement. Directed energy deposition or laser cladding for refurbishment of such components can reduce the cost of replacement and can also be advantageous in countering environmental concerns. In this study, feasibility of using AerMet-100 alloy powder for refurbishment of AISI4340 steel was explored using laser cladding process. A 6 kW diode laser with 6 + 2 axes robot was used for the experimentation where laser clads were generated by melting and depositing the powder that was fed through a powder-feeding nozzle. AerMet-100 clads were found to have good compatibility with the substrate and defect free clads were generated. In order to homogenize the microstructure at Heat Affected Zone, a post-clad heat treatment (PCHT) at 470 °C for 1hr was carried out. The as-cladded microstructure shows lath martensite with retain austenite, whereas post clad heat-treated sample shows slightly reduced retained austenite. Micro-hardness evaluation revealed increased in clad hardness after PCHT due to formation of fine carbides. Micro-tensile test of Post heat-treated clad showed max Tensile stress of 1752 MPa compared to substrate 1240 MPa. It can be concluded that AerMet-100 material can be a potential candidate for repair and refurbishment of AISI4340 steel.

Precise control of variable-height laser metal deposition using a height memory strategy

In respect of laser metal deposition (LMD) 3-D additive manufacturing technology, the method of non-parallel slicing is applied for the deposition of the overhanging and unequal-height parts and is capable of improving the deposition accuracy, stability and efficiency. Nevertheless, the produced uneven top surface derived from variable height deposition process has a possibility to result in instability and even failure of the deposition. In this study, the novel control strategies for the precise control of the unequal-height part were proposed. An inside-beam powder feeding nozzle was applied for the deposition with large overhanging angle. Based on a developed deposition height control system, multiple PI controllers were designed for varying desired deposition heights in an unequal-height layer. The actual heights of the uneven top surface in different positions were memorized by the deposition of a layer, and the process parameters for the next layer could be planned in advance to smooth this unevenness. Under the proposed control strategies, a geometrical stable and convergent process was made achievable when depositing a “fan-shaped” part and a “bent-pipe-shaped” part as the typical overhanging and unequal-height structures. The microstructures were observed to be uniform and compact, and the grain sizes and microhardness in different height positions were found to vary slightly.

激光金属增材制造同轴送粉喷嘴的研究进展

激光金属增材制造同轴送粉喷嘴的研究进展

Design optimization and experimental study of coaxial powder-feeding nozzle in the laser cladding process

To improve the powder convergence and cladding layer quality, the three-dimensional axisymmetrical powder flow through a coaxial feeding nozzle was simulated by the Eulerian-Eulerian two-fluid model. With the composite design via the response surface method, the significance between the main geometric dimensions of nozzle and fluidization characteristics of powder flow was analyzed and regression-fitted. Moreover, a mathematical model was constructed to optimize the nozzle structure, and the optimal nozzle was used in laser cladding experiments. The results show that appropriate powder flow can be obtained in the condition of the carrier gas more than 9 l/min, and the powder sending rate less than 7.5 g/min. The structural parameters of the optimized nozzle are as follows: nozzle angle of 62.94°, outlet width of 1.0mm, exit radius of 5.83mm, and flow separation angle of 3.00°. With the optimized nozzle, the waist diameter and focus depth of the original powder flow decreased by 39.4 and 46.4%, respectively, and the discrepancy between the experimental and simulation results was less than 9%. With the appropriate technological parameters, a layer with good geometry morphology and appropriate dilution rate can be prepared in the laser cladding process with a coaxial feeding nozzle.

Copper film formation on metal surfaces with 100 W blue direct diode laser system

In laser cladding, in the wavelength range of blue, light absorptivity of copper is much higher than that in the wavelength range of infrared. The authors developed the laser cladding system with the continuous wave blue direct diode laser (blue DDL). The system consists of a number of fiber-coupled blue DDLs with a maximum power of 20 W at a wavelength of 445 nm, a focusing lens, and a powder feeding nozzle. In this study, the authors investigated the fundamental characteristics of the multiple blue DDL system and formed copper film on 304 stainless steel plate using the system.

Closed-loop control of variable width deposition in laser metal deposition

In laser metal deposition (LMD) technology, multi-track overlapping is usually used for the deposition of the unequal width thin-walled part. In the present study, a single-track deposition with the variable width method was proposed to improve deposition accuracy and efficiency, and reduce repeated heating. The hollow laser beam internal powder feeding nozzle was applied to realize variable laser spot deposition. Based on the developed deposition height sensor, a closed-loop control system and PI controller were developed and tested. A segmented deposition height control method was developed. The unequal width thin-walled part was divided into several segments along the scanning direction, and each segment was matched with different laser spot sizes. The segments were controlled to have unequal widths, but with an equal height. A thin-walled part with a width range of 5.08–2.14 mm and a “blade-shaped” part with a width range of 6.18–2.64 mm were deposited. The control curves of most segments were stable and convergent. The microstructure and properties of the formed part varied with wall width. All width areas achieved the compact and small size of the grains, as well as high microhardness.

The Influence of the Powder Stream on High-Deposition-Rate Laser Metal Deposition with Inconel 718

For the purpose of improving the productivity of laser metal deposition (LMD), the focus of current research is set on increasing the deposition rate, in order to develop high-deposition-rate LMD (HDR-LMD). The presented work studies the effects of the powder stream on HDR-LMD with Inconel 718. Experiments have been designed and conducted by using different powder feeding nozzles—a three-jet and a coaxial powder feeding nozzle—since the powder stream is mainly determined by the geometry of the powder feeding nozzle. After the deposition trials, metallographic analysis of the samples has been performed. The laser intensity distribution (LID) and the powder stream intensity distribution (PID) have been characterized, based on which the processes have been simulated. Finally, for verifying and correcting the used models for the simulation, the simulated results have been compared with the experimental results. Through the conducted work, suitable boundary conditions for simulating the process with different powder streams has been determined, and the effects of the powder stream on the process have also been determined. For a LMD process with a three-jet nozzle a substantial part of the powder particles that hit the melt pool surface are rebounded; for a LMD process with a coaxial nozzle almost all the particles are caught in the melt pool. This is due to the different particle velocities achieved with the two different nozzles. Moreover, the powder stream affects the heat exchange between the heated particles and the melt pool: a surface boundary condition applies for a powder stream with lower particle velocities, in the experiment provided by a three-jet nozzle, and a volumetric boundary condition applies for a powder stream with higher particle velocities, provided by a coaxial nozzle.

Thermo-mechanical model for simulating laser cladding induced residual stresses with single and multiple clad beads

A three dimensional finite element (FE) model was developed to simulate residual stress induced for laser cladding of AISI 4340 steel powder onto a similar substrate material. A laser power attenuation model was proposed for the laser-powder-interaction zone under the coaxial powder feeding nozzle. The thermal analysis integrated the deposition of clad beads with laser heating. This was performed using user-defined subroutines to thermally activate clad element conductivity and surface heat transfer film conditions simultaneously with the translating attenuated laser heat flux. The FE model investigated three case studies: (i) laser heating without powder feeding, (ii) deposition of single clad bead and (iii) deposition of double adjacent clad beads. The numerical results of the thermal field were compared with thermocouple measurements and heat affected zone (HAZ) sizes from experimental specimens cross-sectioning. X-ray diffraction (XRD) stress measurements were performed to validate the modeled residual stress in case (ii). The FE model was subsequently applied to simulate cladding 10 clad beads over an area to study the effects of depositing multiple successive clad beads on residual stress field.

Microstructure and Mechanical Properties of Laser Clad and Post-cladding Tempered AISI H13 Tool Steel

This study reports a detailed investigation of the microstructure and mechanical properties (wear resistance and tensile strength) of hardened and tempered AISI H13 tool steel substrate following laser cladding with AISI H13 tool steel powder in as-clad and after post-cladding conventional bulk isothermal tempering [at 823 K (550 °C) for 2 hours] heat treatment. Laser cladding was carried out on AISI H13 tool steel substrate using a 6 kW continuous wave diode laser coupled with fiber delivering an energy density of 133 J/mm2 and equipped with a co-axial powder feeding nozzle capable of feeding powder at the rate of 13.3 × 10−3 g/mm2. Laser clad zone comprises martensite, retained austenite, and carbides, and measures an average hardness of 600 to 650 VHN. Subsequent isothermal tempering converted the microstructure into one with tempered martensite and uniform dispersion of carbides with a hardness of 550 to 650 VHN. Interestingly, laser cladding introduced residual compressive stress of 670 ± 15 MPa, which reduces to 580 ± 20 MPa following isothermal tempering. Micro-tensile testing with specimens machined from the clad zone across or transverse to cladding direction showed high strength but failure in brittle mode. On the other hand, similar testing with samples sectioned from the clad zone parallel or longitudinal to the direction of laser cladding prior to and after post-cladding tempering recorded lower strength but ductile failure with 4.7 and 8 pct elongation, respectively. Wear resistance of the laser surface clad and post-cladding tempered samples (evaluated by fretting wear testing) registered superior performance as compared to that of conventional hardened and tempered AISI H13 tool steel.

Computational Simulation on a Coaxial Substream Powder Feeding Laval Nozzle of Cold Spraying

In this paper, a substream coaxial powder feeding nozzle was investigated for use in cold spraying. The relationship between nozzle structure and gas flow, the acceleration behavior of copper particles were examined by computational simulation method. Also, one of the nozzle was used to spray copper coating on steel substrate. The simulation results indicate that: the velocity of gas at the center of the nozzle is lower than that of the conventional nozzle. Powders are well restrained near the central line of the nozzle, no collision occurred between the nozzle wall and the powders. This type of nozzle with expansion 3.25 can successfully deposit copper coating on steel substrate, the copper coating has low porosity about 3.1 % – 3.8 % and high bonding strength about 23.5 MPa – 26.8 MPa. DOI: http://dx.doi.org/10.5755/j01.ms.20.3.4244

Optimal Conditions of Electrostatic Spray Deposition (ESD) for Composite Biomaterials Coating for Biomedical Applications

Various types of metals and alloys are used for medical implants due to their excellent mechanical properties and corrosion resistance; however, their lacks of osteoinductive properties bring about the introduction of biomaterials which can help enhancing the bioactivity between the bones and the implants. Hydroxyapatite (Ca10(PO4)6(OH)2, or HA) which is one of the calcium phosphates that has similar mineral constituents of human bone, has been used as coating material to the metals/alloys substrate. Coating HA usually involves high-temperature such as the plasma spraying coating, which can alter the crystal structure of the HA partially become amorphous. The amorphous nature of HA lessen the benefits of coating with the biomaterial HA. Electrostatic spray deposition (ESD) was used in this research due to the fact that this process is simple, economical, and room-temperature operated. The preliminary results showed a promising thickness layer of about 40 μm; however, the adhesion of the coated layer to the stainless steel 316L was improved by mixing the HA powder with phosphate bioglass and cured in the vacuum furnace at 700oC. Taguchi experimental design technique was used for screening several ESD process parameters: powder feed rate, voltage, current, air volume, distances, time, and nozzle types to significant factors to the coated thickness of the ESD process. The results showed that feed rate, air volume, and time were the significant factors and then Full factorial analysis and response surface method was used for obtaining optimal conditions for the coating, as well as the predicted equation for determine the thickness coated layer with significant factors.

激光熔覆同轴送粉喷嘴研制

激光熔覆同轴送粉喷嘴研制

Erosion wear behavior of laser clad surfaces of low carbon austenitic steel

Austenitic steel surfaces are laser cladded using a 4 kW continuous wave CO 2 laser with coaxial powder feeding nozzle to investigate the improvement in slurry erosion characteristics. Colmonoy-6 and Inconel-625 are cladded on AISI 316L steel and AISI 304L steel, respectively by laser cladding. Initially, single-pass clad track is overlaid to optimize the laser processing parameters, namely scanning speed and powder feed rate to obtained a sound clad. Minimum cracks, porosity and distortion were found at scanning speed of 0.1 m/min and powder feed rate of 12 g/min. For these parameters, the dilution was 17.33% for Colmonoy-6 and 40% for Inconel-625. To clad large surface area, the optimized laser processing parameters were used to deposit the clad tracks with 60% overlap. Maximum surface hardness of 746 VHN is obtained in case of Colmonoy-6 clad on AISI 316L steel and is 352 VHN in case of Inconel-625 clad on AISI 304L steel. EDAX analysis shows higher degree of mixing of substrate material in the clad pool of Inconel-625 than Colmonoy-6. The results of slurry erosion test of Colmonoy-6 clad surface have shown improvement in erosion resistance of the order of 1.75–4.5 times of the substrate AISI 316L steel at all impact angles and the maximum wear angle has also increased which can be attributed to the increase in the surface hardness. However, Inconel-625 laser clad surface has shown little improvement in erosion resistance of the substrate AISI 304L steel at shallow impact angles with no significant improvement at normal impact condition. The SEM micrographs of worn out Colmonoy-6 clad surfaces at shallow impact angles show that the material is removed mainly by micro-cutting which increases with increase in the impact angle.