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- 저자 : Stefan Dimov (검색결과 3 건)
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Nasrollahi, Vahid,Penchev, Pavel,Jwad, Tahseen,Dimov, Stefan,Kim, Kyunghan,Im, Changmin Elsevier 2018 Optics and lasers in engineering Vol.110 No.-
<P><B>Abstract</B></P> <P>Micro drilling employing ultra-short pulsed lasers is a promising manufacturing technology for producing high aspect ratio holes, particularly on ceramic substrates due to the growing range of application in electronic industry. Controlling the morphology and quality of the holes is an important factor in fulfilling the requirements of such applications. In this research, the effects of a wide fluence spectrum associated with the use of femto-second lasers on achievable aspect ratios were investigated by employing lenses with different focal distances. The holes’ morphology and quality were analysed utilising a high resolution X-ray tomography (XCT). It was demonstrated that the achievable aspect ratio can be increased from 3 to 25 just by varying the lenses focal distances. In addition, the quality of produced holes in terms of taper angle and cylindricity was investigated and the results showed that the quality would be improved by increasing the fluence and/or decreasing the focal distance. At the same time, the limitations of drilling holes with low focal distance lenses were discussed, i.e. sensitivity to defocusing and increased risks of recast formations inside the holes and bending effects, that should be considered in designing processes for high aspect ratio percussion drilling.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effects of different focal distance lenses and fluence on achievable holes’ aspect ratio in percussion drilling with femto-second lasers are investigated. </LI> <LI> The achievable holes’ aspect ratio can be increased significantly by employing lower focal distance lenses. </LI> <LI> Holes’ morphologies, cylindricity and taper angle improve by employing smaller focal distance lenses. </LI> <LI> The use of high fluence and high pulse energy in percussion drilling leads to a high penetration depth. </LI> <LI> Key limitations in using lenses with smaller focal distances are a higher sensitivity to defocusing, risks of recast formations and bending effects. </LI> </UL> </P>
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Nozzle Designs in Powder-Based Direct Laser Deposition: A Review
Ahmet Guner,Prveen Bidare,Amaia Jiménez,Stefan Dimov,Khamis Essa 한국정밀공학회 2022 International Journal of Precision Engineering and Vol.23 No.9
Laser-based Direct Energy Deposition (L-DED) is one of the most commonly employed metal additive manufacturing technologies. In L-DED, a laser beam is employed as a heat source to melt the metal powder that is deposited on a substrate layer by layer for the generation of a desired component. The powder is commonly fed through a nozzle into the molten pool by means of a carrier gas and therefore, a nozzle design that ensures optimal deposition of the material is of critical importance. Additionally, its design also affects the powder and gas flows that arise in the nozzle and during the deposition. This, in turn will affect the characteristics of the generated clad and the performance of the whole deposition. Therefore, an optimization of deposition nozzle geometry can be as important as the controlling of deposition process parameters in order to obtain best component qualities. In this context, the present review work is aimed at analysing the different nozzle designs employed in powder-based L-DED processes and the influence of different geometrical features and configurations on the resulting powder and gas flows. Concretely, the main characteristics of each design, their advantages and their possible shortcomings are analysed in detail. Additionally, a review of most relevant numerical models employed during the development of new and optimised nozzle designs are also addressed.
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