Papers by Keyword: Laser Rapid Forming

Abstract: Based on the technology of laser cladding manufacturing process with coaxial inside-beam powder feeding, screwy thin-walled part is accumulated on the substrate of 45# steel by controlling the angle of inclination, scanning paths, Z axis incremental and power. Through the inclined wall accumulation model and a large number of tests, limiting angle of the cladding accumulation is obtained. According to the forming process of screwy thin-walled part, two scanning paths are designed, which include continuous laser scanning between each layer and intermittent laser scanning between each layer, the better scanning path is gained by analyzing each path. A good forming part is obtained by controlling Z axis incremental and power simultaneously. The forming part is higher with smooth appearance and lower roughness, and wall thickness is uniformed.

Abstract: In order to study the residual stress distribution in the titanium alloy laser rapid forming parts, the incremental-step hole drilling method is improved. Choose a calibration sample which has the same material as the test sample to conduct internal residual stress measurement by incremental-step hole drilling method. Conduct stress-release heat treatment (insulation 4 hours in 750 centigrade, furnace cooling) to the calibration sample before the measurement to uniform the internal stress. Calculate calibration compensation coefficient according to the calibration sample stress measurement result, and use the compensation coefficient to compensate the stress measurement result of the laser rapid forming sample. This method improves the reliability of internal residual stress measurement by incremental-step hole drilling method. Then use this method to measure the stress of laser rapid forming sample. The result shows that both the residual stress in the X direction and the Y direction is larger when the depth ranges from 1 mm to 3 mm. When the depth is greater than 3 mm, the residual stress decreases gradually with the hole depth increasing. The maximum value in the X direction is 147.13 MPa, and the maximum value in the Y direction is 236.32 MPa.

Abstract: TA15 titanium alloy thick-wall parts have been deposited by Laser rapid forming (LRF) process. In this paper, a new overlap method between two adjacent laser tracks has been used to deposit the thick-wall titanium part. Results showed that the LRFed thick-wall titanium part was good in shape by using the new overlap method. The microstructure of the LRFed titanium alloy primarily consists of columnar prior-beta grain, which is perpendicular to the substrate resulting from directionally solidification. It also could be observed that the size of alpha phase increased with increasing laser power and decreasing scanning velocity. Tensile properties of LRFed titanium was slightly lower than that of the wrought annealed TA15 titanium alloy, after the heat-treatment of 940°C/1h/AC, the heat-treated titanium alloy showed good tensile properties which were equivalent to that of the wrought annealed TA15 titanium alloy.

Abstract: In the process of metal powder laser rapid forming, various defects may be caused in forming parts on account of technical parameters, equipment performance, material characteristics and other factors. While dimensional accuracy error and surface sticky powder caused by powder factor are the two major defects of forming parts. The experimental analysis finds that less or over accumulation resulting from powder feed delay is the main reason for affecting the dimensional accuracy of cladding and the main reason which affects the appearance of surface sticky powder is specific energy.

Abstract: Laser rapid forming is a kind of new developed technology combining laser surface modification and rapid prototyping technology. It provides a powerful tool for the manufacturing and repairing of metal components. Laser rapid forming repairing experiments of 45 and 2Cr12 steel have been carried out with 316L stainless steel powder. Microstructure and properties of the repaired components are analyzed and tested with optical microscopy (OM), scanning electron microscopy (SEM) and electronic tensile experimental machine etc. Repaired components of different materials have been metallurgically bonded with the deposited layers, with fine microstructure, better mechanical properties and free of defects.

Abstract: Laser rapid forming (LRF) is introduced as a novel fabrication process for Ni-based superalloy Rene88DT. The effect of heat treatment parameters of quenching rate and aging time on size and distribution of γ′ precipitation was investigated. The heat treatment parameters were first determined by DSC, and then optimized based on the examination of the microstructure and mechanical properties of heat treated LRF Rene88DT. The experimental results show that, the precipitation of γ′ is inhomogeneously distributed as a result of uneven heat-cycle during LRF in as-deposited Rene88DT, resulting in low mechanical properties. After being heat treated at 1165°C, 2h/AC + 760°C,28h/AC, γ ′ precipitation are homogeneously distributed with the size of 40~60nm, and the tensile strength of heat treated sample shows an increase of 400MPa as compared to that for as-deposited. The yield strength is close to that of the PM+HIP standard.

Abstract: Ti-Ni based functionally graded alloy is a kind of the promising material, which has potential to be used in aero engines. Using laser rapid forming, a Ti-Ni graded alloy with a continuous compositional gradient from pure Ti to Ti-50wt.%Ni were fabricated. On comparison with the graded alloy, a series of homogenous deposits with the typical composition between pure Ti to Ti-50wt.%Ni were also laser rapid formed. The phase evolution along the compositional gradient direction in the graded alloy is: α+β→β+Ti2Ni →(TiNi +Ti2Ni)+ TiNi; and the phase evolution in the corresponding compositional homogeneous deposit is: α+β→ β+(β+Ti2Ni)→ β+Ti2Ni+(β+Ti2Ni)→ (TiNi+Ti2Ni)+TiNi. The phase transformation and microstructural evolution along the compositional gradient were analyzed by using the microstructure selection map.

Abstract: Laser Rapid Forming (LRF) is a new and advanced manufacture technology to accomplish near net shape metal components with high performance for use in the aerospace, defense and chemical processing industries. In this paper the close-range continuous photography is used to take side views on the cladding zone in order to disclose inherent characteristic of the laser rapid forming process. The vivid molten pool shape is obtained by adopting image partition technology since the not molten area is eliminated from the photos. It is found that the molten pool size depended essentially on the LRF process parameters. With introducing the metal powders into the focus spot of the laser beam, the molten pool retains a segment arc raised outward and the molten pool free surface inclines to the axis of laser beam. Further results show that the molten pool inclination plays an important role on the microstructure of the LRF components.