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Optical in-process height measurement system for process control of laser metal-wire deposition
摘要： We propose an in-process height measurement system for a weld bead and feedback control system for wire-feeding speed for high-quality laser deposition. Metal additive manufacturing, especially laser metal-wire deposition, is effective for complex shape fabrication and repair processing. However, we must control the gap between a weld bead and a feed wire in an optimal range for high-quality deposition. Conventionally, the Z-stage pitch for multi-layer deposition must be precisely adjusted by each deposition shape. In this paper, we design an in-process height measurement system that is integrated in a laser processing head, which measures the weld bead height by a line section method. We decreased the influence of the intense thermal radiation generated from a melt pool by inserting the band-pass filter of the line beam’s wavelength in the imaging system and optimizing its line laser power. Consequently, our system can measure the weld bead height near the melt pool, which is 4 mm in front of it. Next we show that our proposed system can measure the weld bead height during wire-laser metal deposition with 50-μm accuracy by comparing its value to the true value. Finally, we achieved a cylinder shape deposition of 50-mm height, regardless of the Z-stage pitch and the cylinder diameter of the multi-layer deposition, by controlling the wire-feeding speed based on the measured weld bead height.
关键词： Laser Metal Deposition,Light Section Method,Optical Sensing,Height Measurement,Process Monitoring,Additive Manufacturing
更新于2025-09-12 10:27:22
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Stress distribution in laser metal deposited multi-layer thick-walled parts of Ti-6Al-4V
摘要： The laser metal deposition is an additive manufacturing technology enabling the production of large scale complex parts without additional treatment like welding or machining. The study of the origin of the stress field during laser metal deposition is essential for solving a number of problems, including: the assessment of cold and hot cracking; prediction of the fatigue resistance, and the stress corrosion cracking. The quantitative study of transient and residual stresses in build parts is necessary for optimising the parameters of processing and post-production stress relieving heat treatment. Residual stress field in laser metal deposited 50-layer (4-pass per layer) wall of Ti-6Al-4V was analysed experimentally using neutron diffraction and numerically using finite element simulation. Long dwell time between passes and a rigid substrate was used in order to simulate conditions of large scale parts fabrication. An analysis of the calculated and experimentally measured residual stress field showed that near the edges of the buildup there is a region where all three components of stress field are tensile, and normal stress exceeds the yield stress by more than 25%. Moreover, normal plastic strain in this area are also tensile and reaches 2.5-3%. The longitudinal tensile stress closes to yield stress on almost the entire length of the several last layers near the top of the buildup. Residual stress field calculated using neutron diffraction data according to interplanar lattice distance obtained assuming plane stress approach has a satisfactory agreement with FE simulated results.
关键词： Neutron diffraction,Laser metal deposition,Simulation,Residual stress,Titanium alloy
更新于2025-09-12 10:27:22
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Processing Parameters Influence on Microhardness in Laser Metal Deposited Titanium Alloy using Design if Experiment
摘要： Laser Metal Deposition (LMD) is an additive manufacturing process for producing complex parts directly from the Computer Aided Design (CAD) model of the part and for repair of an existing worn out part. The LMD process is governed by processing parameters: laser power, gas flow rate, powder flow rate and scanning speed that influence the microhardness produced during the LMD process. In this study, statistical design of experiment to was employed to investigate the influence of processing parameters on the microhardness of laser metal deposited of Ti6Al4V powder on Ti6Al4V substrate. Full factorial design was used in this study because of its ability to capture the main effects and possible interaction effects of these processing parameters. Each processing parameters was set at low and high values and a total of sixteen (16) experiments was performed and the microhardness of each sample was measured and analyzed.
关键词： Laser Metal Deposition,Titanium alloy,Processing parameters,Microhardness,Full factorial design
更新于2025-09-12 10:27:22
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Microstructure by design: An approach of grain refinement and isotropy improvement in multi-layer wire-based laser metal deposition
摘要： The additive production of metallic components with high-throughput is usually associated with high process temperatures and slow cooling rates. This typically results in strongly oriented columnar grain growth along the building direction of the structure having exceedingly large grain sizes. As a result, such structures show typically low strength and anisotropic mechanical behaviour in as-deposited condition. Consequently, post-processing is commonly performed to homogenize and eventually increase the mechanical properties of the deposited structures. In this regard, precise control of the applied process energy allows a modification of the local temperature distribution and cooling conditions during the additive manufacturing process, which strongly influence the resulting solidification microstructure. The aim of the present study is the development of an approach that allows to influence the solidification conditions in wire-based laser metal deposition of an Al-Mg alloy through specific adjustments of the laser irradiation. It was found that significantly different solidification microstructures in as-deposited condition can be achieved by adjusting the laser beam irradiance within a range resulting in conduction mode welding conditions while keeping the heat input constant. The application of high laser beam irradiances, close to the transition to keyhole mode welding, results in structures with a homogeneous large-grained solidification microstructure exhibiting a degree of anisotropy of around 12% between building direction and the direction of deposition. In contrast, the use of low laser beam irradiances close to the lower limit of stable melting, results in structures with a significantly refined microstructure. Consequently, an increase of yield strength of up to 16% and microhardness of up to 13%, as compared to structures processed with high laser beam irradiance, could be obtained. Moreover, the anisotropy of the as-deposited structure was reduced to a degree lower than 2%.
关键词： Direct Energy Deposition,Aluminium Alloy,Laser Metal Deposition,Additive Manufacturing,Laser Irradiance,Grain Refinement
更新于2025-09-11 14:15:04
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Study of the porosity generated by the use of cutting fluid in hybrid processes combining machining and Laser Metal Deposition (LMD)
摘要： The use of hybrid manufacturing processes that combine additive and machining operations is on increase and an example of it is the fact that the most advanced machine tool manufacturers have developed hybrid machines solutions. Nevertheless, cutting fluid required for machining operations can present several problems for the Laser Metal Deposition (LMD) process. In order to solve this issue, the present work evaluates the influence of the coolants in the LMD process from the point of view of pore generation and clad quality. For this purpose, several tests are performed on a part impregnated with cutting fluid, both directly and after the elimination of the fluid by means of different alternatives.
关键词： additive manufacturing,cutting fluid,laser metal deposition,porosity,coolant,clad quality,lubricant,hybrid machines
更新于2025-09-11 14:15:04