The contradiction between manufacturing accuracy and manufacturing efficiency is discussed in this paper.In order to solve this problem,a novel droplet-targeting laser hybrid indirect arc for additive manufacturing te...The contradiction between manufacturing accuracy and manufacturing efficiency is discussed in this paper.In order to solve this problem,a novel droplet-targeting laser hybrid indirect arc for additive manufacturing technology is proposed in which a couple of wires are melted using the alternating current with interwire indirect arc to achieve high deposition rate.On the other hand,droplets actively target the laser beam and detach from wire tip under the recoil pressure subjected to pulsed laser irradiating at desired position and with controlled mass for a precise bead forming.The process of alternative droplet growing at desired position are mathematically analyzed and then preliminary verified by experiment.By precisely controlling the wire feed speed and current frequency,the melting process at desired position and mass of wire is successfully obtained which is the fundamental for next-step for the droplet actively targeting laser.展开更多
Additive manufacturing(AM)of metals often results in parts with unfavorable mechanical properties.Laser peening(LP)is a high strain rate mechanical surface treatment that hammers a workpiece and induces favorable mech...Additive manufacturing(AM)of metals often results in parts with unfavorable mechanical properties.Laser peening(LP)is a high strain rate mechanical surface treatment that hammers a workpiece and induces favorable mechanical properties.Peening strain hardens a surface and imparts compressive residual stresses improving the mechanical properties of a material.This work investigates the role of LP on layer-by-layer processing of 3D printed metals using finite element analysis.The objective is to understand temporal and spatial residual stress development after thermal and mechanical cancellation caused by cyclically coupling printing and peening.Results indicate layer peening frequency is a critical process parameter affecting residual stress redistribution and highly interdependent on the heat generated by the printing process.Optimum hybrid process conditions were found to exists that favorably enhance mechanical properties.With this study,hybrid-AM has ushered in the next evolutionary step in AM and has the potential to profoundly change the way high value metal goods are manufactured.展开更多
New materials and manufacturing technologies require applicable non-destructive techniques for quality assurance so as to achieve better performance.This study comprehensively investigated the effect of influencing fa...New materials and manufacturing technologies require applicable non-destructive techniques for quality assurance so as to achieve better performance.This study comprehensively investigated the effect of influencing factors includ-ing excitation frequency,lift-off distance,defect depth and size,residual heat,and surface roughness on the defect EC signals of an Inconel 738LC alloy produced by selective laser melting(SLM).The experimental investigations recorded the impedance amplitude and phase angle of EC signals for each defect to explore the feasibility of detecting sub-surface defects by merely analyzing these two key indicators.Overall,this study revealed preliminary qualitative and roughly quantitative relationships between influencing factors and corresponding EC signals,which provided a prac-tical reference on how to quantitively inspect subsurface defects using eddy current testing(ECT)on SLMed parts,and also made solid progress toward on-line ECT in additive/subtractive hybrid manufacturing(ASHM)for fabricating SLMed parts with enhanced quality and better performance.展开更多
Wire and arc additive manufacturing(WAAM) shows a great promise for fabricating fully dense metal parts by means of melting materials in layers using a welding heat source. However, due to a large layer height produce...Wire and arc additive manufacturing(WAAM) shows a great promise for fabricating fully dense metal parts by means of melting materials in layers using a welding heat source. However, due to a large layer height produced in WAAM, an unsatisfactory surface roughness of parts processed by this technology has been a key issue. A methodology based on laser vision sensing is proposed to quantitatively calculate the surface roughness of parts deposited by WAAM.Calibrations for a camera and a laser plane of the optical system are presented. The reconstruction precision of the laser vision system is verified by a standard workpiece. Additionally, this determination approach is utilized to calculate the surface roughness of a multi-layer single-pass thin-walled part. The results indicate that the optical measurement approach based on the laser vision sensing is a simple and effective way to characterize the surface roughness of parts deposited by WAAM. The maximum absolute error is less than 0.15 mm. The proposed research provides the foundation for surface roughness optimization with different process parameters.展开更多
This paper describes the process of repairing a damaged die for injection molding using a 5-axis Hybrid Milling Machine equipped with a Direct Laser Deposition(DLD)tool.A software developed by the authors—DUOADD—is ...This paper describes the process of repairing a damaged die for injection molding using a 5-axis Hybrid Milling Machine equipped with a Direct Laser Deposition(DLD)tool.A software developed by the authors—DUOADD—is adopted to detect the location of missing material and to create a solid model of the damaged spot.The resulting CAD file is used to calculate the paths of the DLD nozzle for filling the damage spot with new material.Finally,to restore the original shape of the mold,the surplus of added material is removed by a milling operation.The paper describes every step of the repair process:from 3D scanning of the damaged component to the finishing operation.This repair method can be applied to extend the life of a costly component and to restore the original shape of valuable objects—e.g.historical or artistic artifacts.The material used for the mold repair is stainless steel 316L,while the mold is made of hot-die-steel.In this paper the functionality of the repair process has been investigated by checking whether all the damaged spots are properly filled with new material.Moreover,this work investigates how to perform the milling operations that allow restoring the original shape of the object,minimizing mismatches between the machined surface and the original one.展开更多
Arc additive manufacturing is a high-productivity and low-cost technology for directly fabricating fully dense metallic components.However,this technology with high deposit rate would cause degradation of dimensional ...Arc additive manufacturing is a high-productivity and low-cost technology for directly fabricating fully dense metallic components.However,this technology with high deposit rate would cause degradation of dimensional accuracy and surface quality of the metallic component.A novel hybrid additive manufacturing technology by combining the benefit of directed energy deposition and laser remelting is developed.This hybrid technology is successfully utilized to fabricate 316L component with excellent surface quality.Results show that laser remelting can largely increase the amount ofδphases and eliminateσphases in additive manufacturing 316L component surface due to the rapid cooling.This leads to the formation of remelting layer with higher microhardness and excellent corrosion resistance when compared to the steel made by directed energy deposition only.Increasing laser remelting power can improve surface quality as well as corrosion resistance,but degrade microhardness of remelting layer owing to the decrease inδphases.展开更多
Additive manufacturing(AM)is gaining traction in the manufacturing industry for the fabrication of components with complex geometries using a variety of materials.Selective laser melting(SLM)is a common AM technique t...Additive manufacturing(AM)is gaining traction in the manufacturing industry for the fabrication of components with complex geometries using a variety of materials.Selective laser melting(SLM)is a common AM technique that is based on powder-bed fusion(PBF)to process metals;however,it is currently focused only on the fabrication of macroscale and mesoscale components.This paper reviews the state of the art of the SLM of metallic materials at the microscale level.In comparison with the direct writing techniques that are commonly used for micro AM,micro SLM is attractive due to a number of factors,including a faster cycle time,process simplicity,and material versatility.A comprehensive evaluation of various research works and commercial systems for the fabrication of microscale parts using SLM and selective laser sintering(SLS)is conducted.In addition to identifying existing issues with SLM at the microscale,which include powder recoating,laser optics,and powder particle size,this paper details potential future directions.A detailed review of existing recoating methods in powder-bed techniques is conducted,along with a description of emerging efforts to implement dry powder dispensing methods in the AM domain.A number of secondary finishing techniques for AM components are reviewed,with a focus on implementation for microscale features and integration with micro SLM systems.展开更多
基金supported by National Natural Science Foundation of China(51475009)National Natural Science Funded Youth Projects(51505009)+1 种基金Natural Science Foundation of Beijing Projects(3162004)China Postdoctoral Science Foundation Program(2015M570021)。
文摘The contradiction between manufacturing accuracy and manufacturing efficiency is discussed in this paper.In order to solve this problem,a novel droplet-targeting laser hybrid indirect arc for additive manufacturing technology is proposed in which a couple of wires are melted using the alternating current with interwire indirect arc to achieve high deposition rate.On the other hand,droplets actively target the laser beam and detach from wire tip under the recoil pressure subjected to pulsed laser irradiating at desired position and with controlled mass for a precise bead forming.The process of alternative droplet growing at desired position are mathematically analyzed and then preliminary verified by experiment.By precisely controlling the wire feed speed and current frequency,the melting process at desired position and mass of wire is successfully obtained which is the fundamental for next-step for the droplet actively targeting laser.
基金supported by in part by the National Science Foundation through the awards CAREER #1846478 and STTR #1521188
文摘Additive manufacturing(AM)of metals often results in parts with unfavorable mechanical properties.Laser peening(LP)is a high strain rate mechanical surface treatment that hammers a workpiece and induces favorable mechanical properties.Peening strain hardens a surface and imparts compressive residual stresses improving the mechanical properties of a material.This work investigates the role of LP on layer-by-layer processing of 3D printed metals using finite element analysis.The objective is to understand temporal and spatial residual stress development after thermal and mechanical cancellation caused by cyclically coupling printing and peening.Results indicate layer peening frequency is a critical process parameter affecting residual stress redistribution and highly interdependent on the heat generated by the printing process.Optimum hybrid process conditions were found to exists that favorably enhance mechanical properties.With this study,hybrid-AM has ushered in the next evolutionary step in AM and has the potential to profoundly change the way high value metal goods are manufactured.
基金Supported by Basic Research Project of Science and Technology Plan of Shenzhen(Grant No.JCYJ20170817111811303).
文摘New materials and manufacturing technologies require applicable non-destructive techniques for quality assurance so as to achieve better performance.This study comprehensively investigated the effect of influencing factors includ-ing excitation frequency,lift-off distance,defect depth and size,residual heat,and surface roughness on the defect EC signals of an Inconel 738LC alloy produced by selective laser melting(SLM).The experimental investigations recorded the impedance amplitude and phase angle of EC signals for each defect to explore the feasibility of detecting sub-surface defects by merely analyzing these two key indicators.Overall,this study revealed preliminary qualitative and roughly quantitative relationships between influencing factors and corresponding EC signals,which provided a prac-tical reference on how to quantitively inspect subsurface defects using eddy current testing(ECT)on SLMed parts,and also made solid progress toward on-line ECT in additive/subtractive hybrid manufacturing(ASHM)for fabricating SLMed parts with enhanced quality and better performance.
基金Supported by National Natural Science Foundation of China(Grant Nos.51505394,61573293)Key Technologies R&D Program of Sichuan Province of China(Grant No.2015GZ0305)
文摘Wire and arc additive manufacturing(WAAM) shows a great promise for fabricating fully dense metal parts by means of melting materials in layers using a welding heat source. However, due to a large layer height produced in WAAM, an unsatisfactory surface roughness of parts processed by this technology has been a key issue. A methodology based on laser vision sensing is proposed to quantitatively calculate the surface roughness of parts deposited by WAAM.Calibrations for a camera and a laser plane of the optical system are presented. The reconstruction precision of the laser vision system is verified by a standard workpiece. Additionally, this determination approach is utilized to calculate the surface roughness of a multi-layer single-pass thin-walled part. The results indicate that the optical measurement approach based on the laser vision sensing is a simple and effective way to characterize the surface roughness of parts deposited by WAAM. The maximum absolute error is less than 0.15 mm. The proposed research provides the foundation for surface roughness optimization with different process parameters.
文摘This paper describes the process of repairing a damaged die for injection molding using a 5-axis Hybrid Milling Machine equipped with a Direct Laser Deposition(DLD)tool.A software developed by the authors—DUOADD—is adopted to detect the location of missing material and to create a solid model of the damaged spot.The resulting CAD file is used to calculate the paths of the DLD nozzle for filling the damage spot with new material.Finally,to restore the original shape of the mold,the surplus of added material is removed by a milling operation.The paper describes every step of the repair process:from 3D scanning of the damaged component to the finishing operation.This repair method can be applied to extend the life of a costly component and to restore the original shape of valuable objects—e.g.historical or artistic artifacts.The material used for the mold repair is stainless steel 316L,while the mold is made of hot-die-steel.In this paper the functionality of the repair process has been investigated by checking whether all the damaged spots are properly filled with new material.Moreover,this work investigates how to perform the milling operations that allow restoring the original shape of the object,minimizing mismatches between the machined surface and the original one.
基金This work was supported by Beijing Municipal Science&Technology Program(Grant No.Z181100003318001).
文摘Arc additive manufacturing is a high-productivity and low-cost technology for directly fabricating fully dense metallic components.However,this technology with high deposit rate would cause degradation of dimensional accuracy and surface quality of the metallic component.A novel hybrid additive manufacturing technology by combining the benefit of directed energy deposition and laser remelting is developed.This hybrid technology is successfully utilized to fabricate 316L component with excellent surface quality.Results show that laser remelting can largely increase the amount ofδphases and eliminateσphases in additive manufacturing 316L component surface due to the rapid cooling.This leads to the formation of remelting layer with higher microhardness and excellent corrosion resistance when compared to the steel made by directed energy deposition only.Increasing laser remelting power can improve surface quality as well as corrosion resistance,but degrade microhardness of remelting layer owing to the decrease inδphases.
基金financial support from the Science and Engineering Research Council,Agency for Science,Technology and Research(A*STAR),Singapore(142 68 00088)
文摘Additive manufacturing(AM)is gaining traction in the manufacturing industry for the fabrication of components with complex geometries using a variety of materials.Selective laser melting(SLM)is a common AM technique that is based on powder-bed fusion(PBF)to process metals;however,it is currently focused only on the fabrication of macroscale and mesoscale components.This paper reviews the state of the art of the SLM of metallic materials at the microscale level.In comparison with the direct writing techniques that are commonly used for micro AM,micro SLM is attractive due to a number of factors,including a faster cycle time,process simplicity,and material versatility.A comprehensive evaluation of various research works and commercial systems for the fabrication of microscale parts using SLM and selective laser sintering(SLS)is conducted.In addition to identifying existing issues with SLM at the microscale,which include powder recoating,laser optics,and powder particle size,this paper details potential future directions.A detailed review of existing recoating methods in powder-bed techniques is conducted,along with a description of emerging efforts to implement dry powder dispensing methods in the AM domain.A number of secondary finishing techniques for AM components are reviewed,with a focus on implementation for microscale features and integration with micro SLM systems.