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Investigation of the track width-dependent melt pool characteristics during laser-sintering of polyamide 12 in correlation to various focus diameters
摘要： Factors such as not only costs, production time, reproducibility, but also the quality of the components are decisive factors in assessing the economic efficiency of a manufacturing process. With additive manufacturing processes, component production is made possible directly from a 3D CAD model. This means that small series and prototypes can already be produced economically today. In this area, the laser-sintering process, in particular, offers great potential for series production due to its high strength values and ductility. With laser-sintering systems that allow an optical widening of the laser focus, a faster exposure of the component and thus a shortening of the building time is possible. We developed a laser-sintering system whose laser focus diameter is adjustable in its cross-sectional area from 0.47 to 2 mm. The goal for the future is to produce large-area components significantly faster by widening the focus diameter, thus making laser-sintering more productive. In this paper, the focus-dependent melt pool formation is examined in correlation to different hatch distances during the laser-sintering of polyamide 12. For this purpose, a test specimen was developed which can display single tracks as well as a multitude of different track widths for all feasible focus level variations. This knowledge is required to determine and investigate the track width-dependent melt pool formation as a function of the focal diameter of the component cross sections.
关键词： Laser-sintering,Focus diameter,Single track,Polyamide 12
更新于2025-09-23 15:21:01
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Single track scanning experiment in laser powder bed fusion process
摘要： Laser powder bed fusion (LPBF) process utilizes laser source to melt the powder particles. As a result, melt pool is formed which develops along the scan track. In this study, single track scanning with Ti-6Al-4V alloy is performed in alternate layers over the supporting base pad. Multiple single scan tracks with scanning speeds of 200mm/s, 400 mm/s and 600 mm/s are defined and thermal responses are captured using infrared camera. The thermal images record the apparent temperature measurements; therefore, derivate method is used to find the liquidus-solidus transition region which is required to estimate the melt pool length and width. Based on the estimation, the average melt pool width of the single track decreased with increasing speed while the average melt pool length for 200 mm/s scanning speed was 438.62 μm, for 400 mm/s was 432.27 μm and for 600 mm/s was 451.2 μm. Besides, cylindrical powder container samples with enclosed single tracks were designed to investigate internal features using computed tomography (CT). The CT images showed that the scanning speed of 200 mm/s and 400 mm/s resulted in formation of significant number of pores due to keyhole formation which may contribute to variation in melt pool length.
关键词： Thermal image,Single track,Infrared Camera,Porosity,Melt pool
更新于2025-09-12 10:27:22
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Effect of process parameters on the formation of single track in pulsed laser powder bed fusion
摘要： There has been increasing interest in Laser Powder Bed Fusion (L-PBF) of metallic materials as a promising manufacturing technology. Although most L-PBF systems utilize laser beams with continuous wave emission (L-PBF(CW)), the possibility of using pulsed lasers (L-PBF(P)) has become available in some industrial L-PBF machines over the past few years. Previous studies suggest that the use of pulsed lasers could enable larger control of heat input and melt pool formation during the process, and could thus enable improvement of spatial resolution and feature sizes in L-PBF. In this study, the experiments were implemented using a pulsed laser in combination with continuous scanning movement instead of the ‘point-and-shoot’ method typically used by industrial L-PBF(P) machines of today. The experiments were executed using a trial L-PBF system (IPG ytterbium fiber laser, wavelength 1075 nm) for gas-atomized stainless steel 316L powder on compositionally similar substrates. Single tracks were melted with three different pulse lengths (50, 100, and 200 μs) by using a constant layer thickness of 50 μm, while varying pulse repetition rate, scanning speed and laser power based on six preset values of volume energy density (VED) of 36-120 J/mm3. In order to allow a comparison to be made, additional samples were manufactured by using the CW emission of the same laser. It was observed that the L-PBF(P) samples yielded narrower tracks in comparison to the samples manufactured using CW emission. In addition, the results of the experiments show that, while maintaining constant VED values, decreasing the pulse length or scanning speed decreased the widths of the tracks and their penetration into the substrate. Consequently, it was noticed that shorter pulse lengths require more overlap between consecutive pulses in order to produce continuous tracks. Pulsed emission shows potential for improving the spatial resolution of the L-PBF process.
关键词： Laser powder bed fusion,Single track,Pulsed emission,AISI 316L,Additive manufacturing
更新于2025-09-12 10:27:22
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On the formation features, structure, microhardness and tribological behavior of single tracks and coating layers formed by laser cladding of Al-Fe powder bronze
摘要： In this paper, the effect of the gas flow and pressure on the powder flow, as well as the effect of the conditions of laser cladding on the microstructure, phase composition, microhardness and tribological behavior of an Al-Fe powder bronze coating, is studied. The features of single tracks, single- and double-layer coatings are described. The speed of a laser beam, the pitch of the single track and the distance between the nozzle and the coated surface affect the microstructure and microhardness of the coating. These parameters are more stable for double-layer coatings because a denser coating with better fusing along the grain boundaries is formed as a result of secondary melting. Under dry friction conditions, with deposition speeds less than 140–160 mm/min, the coefficient of the friction is stable and significantly lower compared with cast aluminium bronzes. In such conditions, the wear resistance of the coating increases with the increase in deposition speed. With further speed increases, a substantial rise in the friction coefficient in time and a substantial seizure of friction surfaces are observed. Under lubricated friction conditions, when the load increases from 120 N to 360 N, that is, where the pressure on the contact surface increases from 1.75 to 5.3 MPa, a sharp increase in the wear rate occurs with a deposition speed of 120 mm/min almost 130-fold and for a speed of 140 mm/min ~9-fold.
关键词： Al-Fe bronze,Powder flow,Single- and double-layer coating features,Laser cladding,Tribological behavior,Single track features
更新于2025-09-09 09:28:46