Procedia CIRP最新文献

Beam shaping of lasers is a topic that has received relatively less attention in the context of metal additive manufacturing (MAM) processes. This technique allows for modulation or spatial alternation of the intensity profile of the laser. As the bulk of the work within MAM primarily revolves around Gaussian beam profiles, the precise impact and potential of other beam shapes is still an unanswered question. In this work a multiphysics numerical model of the laser powder bed fusion (LPBF) process of Ti6Al4V without powder is developed and the model can predict thermo-fluid-microstructural conditions. The model predictions are compared with experimental data from single-track specimens, and the comparison shows a very good agreement. It is shown that the ring spot beam profile (RSBP) results in substantially wider melt pools as compared to the ones forming using the Gaussian beam profile (GBP). The microstructural predictions show that for GBP the grains converge to the center line of the melt pool, while for ring beam profile (RBP), the grains tend to converge to a single point. Finally, the impact of different ring radii for RBP is studied and the results show that at larger ring radii, a noticeable bulge of liquid metal forms right beneath the laser beam.

Temporal power modulation bears an enormous potential for high power laser beam welding of round bars since all its specific challenges are faced. They can be summarised as deviating welding conditions towards the round bar‘s centre. Accordingly, a tailored amount of energy would be provided to that area. The investigations are conducted on 30 mm diameter bars of 1.4301 stainless steel with the use of a 16 kW disk laser. The modulation parameters comprise 6/12/50/100/200 Hz modulation frequency and 0.30/0.47/0.73 modulation depth or power modulation ratio. Post analysis focuses on metallographic longitudinal sections and calculations. The modulation‘s outstanding capability is creating deeper and narrower weld seams due to higher peak power and more intense evaporation of protrusions along the keyhole front wall. Therefore, more laser power is provided to the weld root and despite applying lower average power, the same weld depth is achieved. Finally, more ecological and economical welding as well as welding of more temperature sensitive materials is enabled.

Welding of high-alloy steels results in spatter formation addressing high welding speeds above 8 m/min, i.e., the seam quality is significantly reduced due to material losses and adhering spatter. A reduction of spatter can be addressed by using concentric intensity distributions consisting of core and ring, by affecting melt and metal vapor flow. In this paper, the understanding of spatter formation on sheet top and bottom side is significantly enhanced for full penetration welds of AISI 304. Therefore, different concentric intensities and tophat distributions were systematically studied and compared. Fundamental interactions between concentric intensity distributions and spatter formation during full penetration welding were determined and summarized in model concepts. In particular, spatter formation can be reduced on both sheet sides using a concentric intensity distribution due to a smaller keyhole geometry with a smaller angle of inclination of the keyhole front.

Laser Metal Deposition (LMD) allows the fabrication of complex shapes onto non-planar surfaces. This manuscript presents a 3D-scanning strategy for the dimensional inspection of LMD-manufactured gear teeth onto cylindrical substrates. The standard registration (alignment) methods are ineffective in the context of LMD because they minimize the global distance between the reference model and the 3D-scanning point cloud. This global minimization wrongfully biases the alignment. In response to this limitation, this manuscript discusses a registration procedure that avoids global distance minimization by sequentially aligning the datums (gear root cylinder and planar faces) of both datasets. This datum-alignment procedure fixes 5 out of 6 Degrees of Freedom (DOF). The final DOF is determined by finding the optimal rotation angle that minimizes the distance between the gear teeth of both datasets. The strategy is validated with actual LMD-manufactured spur and helical gear teeth onto cylindrical substrates. This strategy would also save time during the grinding process.

Laser-based powder bed (PBF-LB) fusion of polymers has emerged as a versatile technique for additive manufacturing (AM), offering laynew processing freedom through promising beam-shaping techniques. This study explores a novel approach to overcome the NIR absorption limitations of the market-dominant standard material polyamide 12 (PA12) by increasing the sensitivity for effective diode laser processing through surface modification with NIR-absorbing nanoparticles (NPs). The investigation encompasses nano sensitization strategies and theoretical analysis of energy input to the polymer, alongside comparisons with volume-modified polymer feedstocks, demonstrating that diode laser printing of surface-modified (s-mod) PA12 is possible with a macroscopic quality comparable to a commercially available volume-modified (v-mod) feedstock.

Today, complex structural components for lightweight applications are frequently manufactured by laser powder bed fusion (PBF-LB), often using aluminum alloys such as AlSi10Mg. However, the application of cyclic load cases can be challenging as PBF-LB produced AlSi10Mg parts typically have low ductility and corresponding brittle failure behavior in the as-built condition.

Therefore, this paper presents investigations on the feasibility of a laser heat treatment of PBF-LB produced AlSi10Mg parts to locally increase the ductility and decrease the hardness in critical areas. Potential heat treatment process parameters were derived theoretically based on the temperature fields in the material calculated assuming three-dimensional heat conduction and a moving heat source. PBF-LB produced specimens were then laser heat treated at varying laser power and scan speed. Hardness measurements on metallographic cross sections showed hardness reductions of over 35 % without inducing hydrogen pore growth.

The numerous advantages of Additive manufacturing (AM) are being utilized to print multi-material components for different applications. Although the AM method of laser powder bed fusion (LPBF) can print more complex and dimensionally accurate parts than the directed energy deposition (DED) method, printing multi-material components is challenging for LPBF. This study demonstrates an attempt at bimetallic 3D printing of stainless steel 316L and Inconel 718 by multi-material laser powder bed fusion and its characterization. A continuous wave (CW) fiber laser was used for the LPBF process and laser parameters for the bimetallic components were optimized. Microstructural studies were carried out with optical microscopy and scanning electron microscope (SEM) to investigate the interfacial characteristics for different numbers of interlayers. The thickness of the interfacial region was around 50-100 μm. Vickers microhardness (HV) and nanoindentation were performed at various locations around the fusion zone resulting in an average micro and nano hardness of 303 HV and 4.622 GPa respectively.

In laser-based powder bed fusion of metals (PBF-LB/M), the atmospheric residual oxygen plays a key role, particularly for highly reactive materials like Ti-6Al-4V. Oxygen concentrations present in commercial machines are still too high to effectively prevent oxidation of the powder and oxygen take-up into built parts deteriorating the part quality and mechanical properties. In this work, to reduce the residual oxygen content to a range adequate to an extreme high vacuum (XHV) while maintaining normal pressure, a silane-doped argon atmosphere (< 0.001 vol.-% silane in argon) is introduced. Ti-6Al-4V powder was processed both under a conventional argon atmosphere (< 0.01 vol.-% oxygen) and argon-silane atmosphere (< 10^-20 vol.-% oxygen). The influence on the resulting porosity was investigated using a central composite design. Additionally, the tensile properties were analyzed. High tensile strengths > 1290 MPa and low porosities < 0.02 %, but no significant influence of the atmosphere was found.