Additive manufacturing of laser cutting nozzles by SLM: processing, finishing and functional characterization

Purpose - The purpose of this paper is to demonstrate the use of selective laser melting for producing single and double chamber laser cutting nozzles. The main aim is to assess a whole production chain composed of an additive manufacturing (AM) and consecutive finishing processes together. Beyond the metrological and flow-related characterization of the produced nozzles, functional analysis on the use of the produced nozzles are carried out through laser cutting experiments.Design/methodology/approach - SLM experiments were carried out to determine the correct compensation factor to achieve a desired nozzle diameter on steel with known processibility by SLM and using standard nozzle geometries for comparative purposes. The produced nozzles are finished through electrochemical machining (ECM) and abrasive flow machining (AFM). The performance of nozzles produced via additive manufacturing (AM) are compared to conventional ones on an industrial laser cutting system through cutting experiments with a 6 kW fibre laser. The produced nozzles are characterized in terms of pressure drop and flow dynamics through Schlieren imaging.Findings - The manufacturing chain was regulated to achieve 1 mm diameter nozzles after consecutive post processing. The average surface roughness could be lowered by approximately 80 per cent. The SLM produced single chamber nozzles would perform similarly to conventional nozzles during the laser cutting of 1 mm mild steel with nitrogen. The double chamber nozzles could provide complete cuts with oxygen on 5 mm-thick mild steel only after post-processing. Post-processing operations proved to decrease the pressure drop of the nozzles. Schlieren images showed jet constriction at the nozzle outlet on the as-built nozzles.Originality/value - In this work, the use of an additive manufacturing process is assessed together with suitable finishing and functional analysis of the related application to provide a complete production and evaluation chain. The results show how the finishing processes should be allocated in an AM-based production chain in a broader vision. In particular, the results confirm the functionality for designing more complex nozzle geometries for laser cutting, exploiting the flexibility of SLM process

Design and Pathway Programming of Freeform Thin-walled Geometries Produced by Laser Metal Deposition

Laser metal deposition (LMD) shows great promise for producing large components as well as thin-walled structures by additive manufacturing. Compared to the powder bed fusion (PBF) techniques, LMD can exploit further flexibility in terms of tool path programming. Layer-by-layer rastering commonly used in SLM is applicable also to the LMD process, where overhang structures remain a complex issue in the absence of support structures. Concerning thin-walled parts with a symmetry axis or those that evolve around an axis, more efficient strategies may be developed. Hence, this work discusses the use of different part programming strategies for thin-walled structures employing an LMD system based on a 6-axis anthropomorphic robot and a 2-axis rotary table. The work compares, layer-by-layer, continuous pathway, and oriented reference plane strategies, study of process parameters, build failure mechanisms, as well as geometric errors are discussed. Successful deposition of thin-walled organic and freeform tubular components in AISI 316L is demonstrated