Strategies to Reduce Porosity in Al-Mg WAAM Parts and Their Impact on Mechanical Properties

Open AccessFeature PaperArticle Strategies to Reduce Porosity in Al-Mg WAAM Parts and Their Impact on Mechanical Properties by Maider Arana 1,2,* [OrcID] , Eneko Ukar 2, Iker Rodriguez 1, Amaia Iturrioz 1 [OrcID] and Pedro Alvarez 1 [OrcID] 1 LORTEK Technological Centre, Basque Research and Technology Alliance (BRTA), 20240 Ordizia, Spain 2 Mechanical Engineering Department, University of the Basque Country UPV/EHU, 48013 Bilbao, Spain * Author to whom correspondence should be addressed. Academic Editor: Eric Hug Metals 2021, 11(3), 524; https://doi.org/10.3390/met11030524 Received: 1 March 2021 / Revised: 16 March 2021 / Accepted: 18 March 2021 / Published: 23 March 2021 (This article belongs to the Special Issue Directed Energy Deposition of Metal Alloys) Download PDF Browse Figures Review Reports Citation Export Abstract With the advent of disruptive additive manufacturing (AM), there is an increasing interest and demand of high mechanical property aluminium parts built directly by these technologies. This has led to the need for continuous improvement of AM technologies and processes to obtain the best properties in aluminium samples and develop new alloys. This study has demonstrated that porosity can be reduced below 0.035% in area in Al-Mg samples manufactured by CMT-based WAAM with commercial filler metal wires by selecting the correct shielding gas, gas flow rate, and deposition strategy (hatching or circling). Three phase Ar+O2+N2O mixtures (Stargold®) are favourable when the hatching deposition strategy is applied leading to wall thickness around 6 mm. The application of circling strategy (torch movement with overlapped circles along the welding direction) enables the even build-up of layers with slightly thicker thickness (8 mm). In this case, Ar shielding gas can effectively reduce porosity if proper flow is provided through the torch. Reduced gas flows (lower than 30 Lmin) enhance porosity, especially in long tracks (longer than 90 mm) due to local heat accumulation. Surprisingly, rather high porosity levels (up to 2.86 area %) obtained in the worst conditions, had a reduced impact on the static tensile test mechanical properties, and yield stress over 110 MPa, tensile strength over 270 MPa, and elongation larger than 27% were achieved either for Ar circling, Ar hatching, or Stargold® hatching building conditions. In all cases anisotropy was lower than 11%, and this was reduced to 9% for the most appropriate shielding conditions. Current results show that due to the selected layer height and deposition parameters there was a complete re-melting of the previous layer and a thermal treatment on the prior bottom layer that refined the grain size removing the original dendritic and elongated structure. Under these conditions, the minimum reported anisotropy levels can be achieved.This research was supported by the Ministry of Science and innovation of the Spain Government through the program “Ayudas Destinadas a Centros Tecnológicos de Excelencia CERVERA Año 2019” from CDTI (Centro para el Desarrollo Tecnológico Industrial) in the frame of the CEFAM Project, grant CER-20191005

Analysis of the Influence of the Use of Cutting Fluid in Hybrid Processes of Machining and Laser Metal Deposition (LMD)

Hybrid manufacturing processes that combine additive and machining operations are gaining relevance in modern industry thanks to the capability of building complex parts with minimal material and, many times, with process time reduction. Besides, as the additive and subtractive operations are carried out in the same machine, without moving the part, dead times are reduced and higher accuracies are achieved. However, it is not clear whether the direct material deposition after the machining operation is possible or intermediate cleaning stages are required because of the possible presence of residual cutting fluids. Therefore, different Laser Metal Deposition (LMD) tests are performed on a part impregnated with cutting fluid, both directly and after the removal of the coolant by techniques such as laser vaporizing and air blasting. The present work studies the influence of the cutting fluid in the LMD process and the quality of the resulting part. Resulting porosity is evaluated and it is concluded that if the part surface is not properly clean after the machining operation, deficient clad quality can be obtained in the subsequent laser additive operation.This study was supported by the H2020 FoF13 PARADDISE Project (Grant Agreement No. 723440)

Numerical Model for Predicting Bead Geometry and Microstructure in Laser Beam Welding of Inconel 718 Sheets

A numerical model was developed for predicting the bead geometry and microstructure in laser beam welding of 2 mm thickness Inconel 718 sheets. The experiments were carried out with a 1 kW maximum power fiber laser coupled with a galvanometric scanner. Wobble strategy was employed for sweeping 1 mm wide circular areas for creating the weld seams, and a specific tooling was manufactured for supplying protective argon gas during the welding process. The numerical model takes into account both the laser beam absorption and the melt-pool fluid movement along the bead section, resulting in a weld geometry that depends on the process input parameters, such as feed rate and laser power. The microstructure of the beads was also estimated based on the cooling rate of the material. Features such as bead upper and bottom final shapes, weld penetration, and dendritic arm spacing, were numerically and experimentally analyzed and discussed. The results given by the numerical analysis agree with the tests, making the model a robust predictive tool.Thanks are addressed to H2020-FoF13-2016 PARADDISE project (contract number 723440). Special thanks are addressed to the University of the Basque Country (UPV-EHU) for the funding support received from the contracting call for the training of research staff in UPV-EHU 2015

Latest Developments in Industrial Hybrid Machine Tools that Combine Additive and Subtractive Operations

Hybrid machine tools combining additive and subtractive processes have arisen as a solution to increasing manufacture requirements, boosting the potentials of both technologies, while compensating and minimizing their limitations. Nevertheless, the idea of hybrid machines is relatively new and there is a notable lack of knowledge about the implications arisen from their in-practice use. Therefore, the main goal of the present paper is to fill the existing gap, giving an insight into the current advancements and pending tasks of hybrid machines both from an academic and industrial perspective. To that end, the technical-economical potentials and challenges emerging from their use are identified and critically discussed. In addition, the current situation and future perspectives of hybrid machines from the point of view of process planning, monitoring, and inspection are analyzed. On the one hand, it is found that hybrid machines enable a more efficient use of the resources available, as well as the production of previously unattainable complex parts. On the other hand, it is concluded that there are still some technological challenges derived from the interaction of additive and subtractive processes to be overcome (e.g., process planning, decision planning, use of cutting fluids, and need for a post-processing) before a full implantation of hybrid machines is fulfilledSpecial thanks are addressed to the Industry and Competitiveness Spanish Ministry for the support on the DPI2016-79889-R INTEGRADDI project and to the PARADDISE project H2020-IND-CE-2016-17/H2020-FOF-2016 of the European Union's Horizon 2020 research and innovation program

Study of the flexural behaviour and bonding strength of WC-Co metal matrix composite coatings produced by Laser Directed Energy Deposition

Surface coatings enable more durable and sustainable solutions to face the degradation of the functional surfaces of high-added-value components. Particularly, metal matrix composites (MMC) are known to mitigate friction efficiently. However, the bonding strength of MMCs severely limits their durability. Hence, it is not sufficient to focus on wear performance. In this work, the flexural strength and interfacial bonding of Stellite 6/WC MMCs produced by Laser Directed Energy Deposition were investigated. The manufactured coatings exhibited a strong bond to the substrate regardless of the WC content, as no delamination was observed. Additionally, all MMC coatings produced under different processing conditions and with the same composition showed similar elastoplastic behaviour, while specimens containing a higher WC% failed prematurely. This was ascribed to the local embrittlement of the reaction layer surrounding the WC particles, which were found to be crack initiation sites.Authors would like to acknowledge the Basque Government (Eusko Jaurlaritza) in call IT 1573-22 for the financial support of the research group

Vibrations Characterization in Milling of low Stiffness Parts with a Rubber-Based Vacuum Fixture

Fixtures are a critical element in machining operations as they are the interface between the part and the machine. These components are responsible for the precise part location on the machine table and for the proper dynamic stability maintenance during the manufacturing operations. Although these two features are deeply related, they are usually studied separately. On the one hand, diverse adaptable solutions have been developed for the clamping of different variable geometries. Parallelly, the stability of the part has been long studied to reduce the forced vibration and the chatter effects, especially on thin parts machining operations typically performed in the aeronautic field, such as the skin panels milling. The present work proposes a commitment between both features by the presentation of an innovative vacuum fixture based on the use of a vulcanized rubber layer. This solution presents high flexibility as it can be adapted to different geometries while providing a proper damping capacity due to the viscoelastic and elastoplastic behaviour of these compounds. Moreover, the sealing properties of these elastomers provide the perfect combination to transform a rubber layer into a flexible vacuum table. Therefore, in order to validate the suitability of this fixture, a test bench is manufactured and tested under uniaxial compression loads and under real finish milling conditions over AA2024 part samples. Finally, a roughness model is proposed and analysed in order to characterize the part vibration sources.Financial support from the Basque Government under the ELKARTEK Program (SMAR3NAK project, grant number KK-2019/00051) is gratefully acknowledged by the authors

Intelligent nozzle design for the Laser Metal Deposition process in the Industry 4.0

Laser Metal Deposition (LMD) is an AM (Additive Manufacturing) process that enables to build 3D geometries or enhance the surface properties of the base material by the generation of a coating. With the aim of integrating the AM inside the Industry 4.0 trend and improve the quality of the resulting parts, smart nozzles are required. Therefore, authors have developed an intelligent LMD nozzle by means of the integration of various sensing and control systems in a continuous coaxial LMD nozzle prototype. The nozzle is capable of regulating the laser power based on the temperature measurement of the melt pool. Moreover, it adjusts the powder flux that reaches the processing area according to an algorithm that ensures a constant powder income per surface unit area. Lastly, the nozzle evaluates the geometry of the deposited clad using an optical sensor

CAPACITACIÓN DE UTILLAJES FLEXIBLES PARA SU USO EN PROCESOS DE MECANIZADO DE ALTA CALIDAD: UN CASO DE APLICACIÓN DEL PARADIGMA INDUSTRIA 4.0

The incipient implementation of the Industry 4.0 paradigm has led to an increase in the machines sensoring level, in the processes optimization and, thus, in the product manufacturing with a higher added value. In this article a new aspect is described where, through the machine monitoring, the utilization of innovative elements as fixture is enabled for high quality machining processes. These innovative elements are characterized by the great flexibility offered by them as holding component and by their low costs. However, these elements lack the enough geometrical accuracy for applications where a high shape and surface quality product are needed. First of all, in order to have a clear vision of the singularities of each fixture type present on the state of the art, a nomenclature and a classification has been proposed based on their geometry characteristics. Hence, based on this classification, an analysis of the different fixturing solutions provided by the market has been made, enhancing the advantages of this solution against the existing ones. With the aim of demonstrating its suitability for certain machining applications, the behavior of these sort of flexible materials has been characterized. Besides, the sensors implementation has been analyzed in order to capacitate this solution for processes where tough tolerances on parts are demanded. Therefore, this survey demonstrates that, through the massive information gathering, not only an optimization of the existing technologies is obtained, but it is possible to develop innovative solutions that provide improved capacities to the already existing ones in the Industry.Financial support from the Basque Government under the ELKARTEK Program (AERO3NAK project, grant number KK-2017/00033) is gratefully acknowledged by the authors

Analysis of the Part Distortions for Inconel 718 SLM: A Case Study on the NIST Test Artifact

The present paper evaluates the misalignment and geometry distortion of the standard National Institute of Standards and Technology (NIST) test artifact in Inconel 718 alloy, when several layers with and without supports are employed to manufacture it by the Selective Laser Melting (SLM) process. To this end, a coordinate-measuring machine (CMM) is used to measure the geometrical distortion in each manufacturing configuration, following the same measurement protocol. The results show that the laser path strategy favors a thermal gradient which, consequently, induces geometrical distortions in the part. To prove this hypothesis, a numerical simulation is performed to determine the thermal gradient and the pattern of the residual stresses. It was found that the geometrical distortion certainly depends on the position of the feature position and laser strategy, where thermal cycles and residual thermal stresses had an impact in the end-part geometry, especially if a high strength-to-weight ratio commonly used in aeronautics is present.This work is supported by the Serra Húnter program (Generalitat de Catalunya) reference number [UPC-LE-304 (2018)] and by the Aeronautics Advanced Manufacturing Center (CFAA) in the JANO—Joint action toward digital transformation project framework. Diego Celentano acknowledges Pontificia Universidad Católica de Chile (PUC), Wallonie-Bruxelles International (WBI) and National Council for Scientific and Technological Research CONICYT (FONDECYT Projects No. 3180006 and 1180591) for the financial supports provided for this work

Abrasive Disc Performance in Dry-Cutting of Medium-Carbon Steel

Abrasive-cutting processes are widely used to obtain semi-finished products from metal bars, slabs, or tubes. Thus, the abrasive cutting-off process is applied when requiring precision cutting and productivity at a moderate price. Cut-off tools are discs composed of small abrasive particles embedded in a bonding material, called the binder. This work aims to compare the cutting performance of discs with different composition, in dry cutting of steel bars. To do that, disc wear was measured and disc final topography was digitalized in order to determine both disc surface wear patterns and if the abrasive particles bonding into the binder matrix was affected. In addition, X-Ray inspection gave information about the abrasive grit-binder bonding. Therefore, the method here presented allows identifying discs with a superior abrasive-cutting capability, by combining profilometry and tomography to define micrometrical aspects, grit size, and binder matrix structure. Results led to the conclusion that discs with high grit size and protrusion, high grit retention by bond material, and closer mesh of fiberglass matrix binder were the optimal solution.Authors are grateful to Basque government group IT IT1337-19 and Ministry of Mineco REF DPI2016-74845-R