Procedia CIRP最新文献

Laser Glass Deposition is an additive manufacturing method to produce individualized structural components out of glass. A CO₂ laser is utilized as a heat source to melt fused silica filaments and transform them into a formable viscous state. The fiber filament is fed laterally under a defined angle into the process zone. The viscous filament is deposited layer-by-layer using a 3-axis linear system with an integrated rotational axis. To investigate the surface and volume quality of the additively manufactured fused silica components, fully dense test specimens are analyzed in this paper. Quality characteristics such as surface roughness, formation of boundary layers and optical transparency constitute the focus of the investigations. Consequently, fully dense glass components with homogeneous volume structures without pores and boundary layers and a surface roughness of less than 30 nm were printed successfully.

Copper alloys´ high thermal conductivity combined with the freeform capabilities of the additive manufacturing technologies, offer new opportunities in the design of aerospace components, such as thrust nozzles. However, the high reflectivity of copper alloys at the 1.076 µm wavelength range makes their manufacturing with conventional fibre lasers difficult. Therefore, an effective methodology for manufacturing CuNiSiCr-alloys with conventional fibre lasers is required.

For this purpose, the laser-based Directed Energy Deposition (DED-LB) process for depositing a CuNiSiCr-alloy is parametrized to ensure a defect-free operation of the final part. Through a design of experiments process, the optimum parameters are obtained and they are validated through the manufacturing of single clads and more complex geometries. During the tests, the melt-pool temperature and dimensions are monitored to increase the control over the manufacturing process and ensure process stability. Results show a high metallurgical integrity, which justifies the viability of fibre lasers to manufacture CuNiSiCr-alloys.

Duplex stainless steels (DSS) employ a bi-modal microstructure consisting of equal parts ferrite and austenite. However, when processed via laser-based powder bed fusion (PBF-LB/M) the high cooling rates lead to a dominantly ferritic microstructure, thus making a post-process heat treatment necessary. This sparks the interest in accelerating the manufacturing time by increasing scan speeds. Defocusing of the laser beam offers the possibility to alter the melt pool morphology and thereby the melting mode. Therefore, this study presents the influence of the defocusing distance for PBF-LB/M manufactured DSS parts. The melt pool becomes shallower and wider as the defocus distance increases, but also has a more uniform shape at high scan speeds compared to the focused beam. Furthermore, defocusing of the laser beam results in denser parts at scan speeds of up to 1800 mm/s, potentially facilitating higher build rates. The duplex microstructure could be restored by a post process heat-treatment.

Laser Metal Deposition (LMD) uses laser energy and powder material to create structures on existing components. It is capable of producing cost-effective multi-material compositions, such as reinforcing metals with ceramic particles for improved wear resistance. However, the use of dissimilar materials often leads to defects, particularly delamination. Previous studies have found a connection between these defects and specific airborne acoustic emissions (AE).

To mitigate the impact of defects, extensive optimization of process parameters and real-time process monitoring are recommended. For AE, precise localization of defects is crucial besides to time- and frequency-resolved information, especially while producing multiple components on a substrate material.

This study evaluates multi-sensor arrays for the localization of delamination defects. The research investigates the influence of localization algorithms and array patterns on the accuracy and reliability of defect localization. Experiments were conducted on a test platform with simulated acoustical events to determine the most suitable localization setup.

In the realm of laser-based powder bed fusion processes with metals (PBF-LB/M), spatter formation serves as a crucial stability criterion. However, existing analyses often adopt a qualitative approach, hindering meaningful comparisons between processes. The quantitative investigation of the advantages of beams with non-Gaussian intensity distribution as well as multi-beam processing strategies with regard to spatter formation is still largely unexplored. To address this gap, we present an experimental setup utilizing high-speed videography and individual particle tracking to measure spatter characteristics, count size, ejection angle, and velocity, within the PBF-LB/M process conditions. The investigation deals with focused and defocused Gaussian beams, a beam with ring-shaped intensity as well as processing with two coupled Gaussian beams for the PBF-LB/M of nickel-base alloy 625.

E-mobility turned in the last years to be an emerging market and one solution to fossil fuel free mobility for the future. E-mobility requires, compared to fossil-fueled mobility concepts, a huge amount of welding tasks, which have to guarantee different functionality, as for example high strength, ductility, but also low resistivity and tightness. Last is especially for housing or cases of aluminum in automotive challenging, as pores and cracks can occur. Pulsed laser welding presents, due to the adaptable heat input and the temporal modification of stress state and solidification conditions advantages for this type of applications. EN AW-6xxx group of aluminum alloys is mainly used for such components due to their favorable mechanical properties. However, these alloys are susceptible to hot cracking during solidification from the molten phase. This article aims to present a methodology for demonstrating the resulting strain during pulsed laser beam welding of hot crack susceptible aluminum alloys. It will highlight the influence of factors such as pulse shape, shielding gas, and flow rate on strain and strain rate.

This study investigates melt flow dynamics in asymmetric T-joint laser welding, particularly with sheets inclined up to 45°. This complex scenario requires filler wire, accessible only from the flat sheet side. High-speed imaging at the top and root captures transient phenomena leading to weld imperfections. Research on stainless-steel involved the impact of first-order welding parameters on the weld quality. This included multi-spot laser welding with two beams. The analysis focused on melt pool dynamics under these challenging conditions. The asymmetric root side’s geometry necessitates proper melt flow to form a favorable root topology, avoiding defects like wavy roots and porosity. Key observations included intermittent keyhole openings, transient melt flow effects, and potential spatter ejection at the bottom. The findings offer a comprehensive understanding of 3D asymmetric melt flow, laying the analytical groundwork for enhancing the weld quality.