KEYWORDS: Particles, Laser processing, High speed photography, Signal attenuation, Laser range finders, Clouds, Cladding, Materials processing, Laser applications, Process modeling
With deep studying on the process of laser rapid forming (LRF) the researchers gradually meet the knowledge that it is very important to understand the mechanism of interaction between the laser and the powder particles since it is the key point to realize the effective control of the LRF process. The high-speed photography has been employed to realize in situ observation on the delivery process of powdered materials for the first time. A group of parameters -- delivery parameters of powder is put forward to characterize the delivery process in quantitative by dealing with the digital images obtained. On the basis of quantitative description of the powder delivery, an analytical model is presented to study the attenuation of the laser power caused by the cloud of the power particles. Another analytical model is also presented to study the temperature rise of the particle irradiated by the laser. It can be found that the attenuation ratio is determined together by the powder specifications, the powder feeding parameters and the powder delivery parameters. With the off axial powder nozzle being employed in the paper, the diameter of the powder steam was always bigger than the diameter of laser spot, thus the laser processing parameters have no effect on the laser attenuation. The temperature rise of the particle is determined by the powder specifications and the powder delivery parameters too. Meanwhile the laser processing parameters also affects the temperature rise of the particle. With the decreasing of the particle radius, the irradiation heating effect increases remarkably.
The Laser Rapid Forming (LRF) has been used to build up default free and nonoxidation Ti- 6Al- 4V samples in atmosphere controlled LRF equipment. The microstructure and mechanical properties of as-deposited and heat-treatment are analyzed. It has been found that the macrostructure of as-deposited Ti- 6Al- 4V alloys takes the shape of huge columnar prior beta grains (PβG) with continuous boundary and epitaxial growth along the vertical direction (Z) of the laser scanning. Between cladding layers there are bands of coarse structures resulting from the reheating by laser beam when the prior cladding layers forming. The substructure in prior beta grains is mainly of the fine acicular α and basketweave matrix of α+β. After high temperature annealing treatment, little basketweave matrix of α+β remains and the acicular α changes into α laths with clear β outlines. After quenching-aging treatment, the substructures are mainly of the α laths and basketweave matrix of α+β. Multi-quenching -aging heat treatments produce bi-modal structure. The physical property test shows that the tensile strength and plasticity at the vertical direction (Z) of the laser scanning are higher than those at the direction of parallel (X). After high temperature-annealing treatment, the Ti-6Al-4V alloy has lower level of tensile strength and plasticity while quenching-aging treatment decreases tensile strength and increases plastic slightly.
Laser rapid forming (LRF) is a new and advanced manufacturing technology that has been developed on the basis of combining high power laser cladding technology with rapid prototyping (RP) to realize net shape forming of high performance dense metal components without dies. Recently we have developed a set of LRF equipment. LRF experiments were carried out on the equipment to investigate the influences of processing parameters on forming characterizations systematically with the cladding powder materials as titanium alloys, superalloys, stainless steel, and copper alloys. The microstructure of laser formed components is made up of columnar grains or columnar dendrites which grow epitaxially from the substrate since the solid components were prepared layer by layer additionally. The result of mechanical testing proved that the mechanical properties of laser formed samples are similar to or even over that of forging and much better than that of casting. It is shown in this paper that LRF technology is providing a new solution for some difficult processing problems in the high tech field of aviation, spaceflight and automobile industries.
Design and fabrication of a weld protection drag-cover has been discussed in the paper as using high-power CO2 laser to weld Ti6A14V in various thickness. Argon was used to protect the weld and its nearby region from contamination from hydrogen, oxygen and nitrogen as their temperature were higher than 300 degrees Celsius. The protection effect has been proven to be good, since the weld surface was smooth, the obverse side appeared silvery white, and the reverse side appeared light-yellow.
This paper describes Ti-6Al-4V plae 1.3 mm thick welded by CO2 laser beam. The orthogonal test of 3-level and 3- factor is adopted and technological parameters are optimized. The shielding case full of Helium is put behind the pool This experiment indicates that the tensile strength of the weld can reach up to that of parent metal, when the weld joint is regular. Moreover the joint structure is analyzed also.
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