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Publications (10 of 18) Show all publications
Dahat, S., Hurtig, K., Andersson, J. & Scotti, A. (2020). A Methodology to Parameterize Wire + Arc Additive Manufacturing: A Case Study for Wall Quality Analysis. Journal of Manufacturing and Materials Processing, 4(1), Article ID 14.
Open this publication in new window or tab >>A Methodology to Parameterize Wire + Arc Additive Manufacturing: A Case Study for Wall Quality Analysis
2020 (English)In: Journal of Manufacturing and Materials Processing, Vol. 4, no 1, article id 14Article in journal (Refereed) Published
Abstract [en]

The objective of this work was the development of a methodology to parametrize wire + arc additive manufacturing (WAAM), aiming dimension repeatability, and tolerances. Parametrization of WAAM is a difficult task, because multiple parameters are involved and parameters are inter-dependent on each other, making overall process complex. An approach to study WAAM would be through operational maps. The choice of current (Im) and travel speed (TS) for the desirable layer width (LW) determines a parametrization that leads to either more material or less material to be removed in post-operations, which is case study chosen for this work. The work development had four stages. First stage, named ‘mock design’, had the objective of visualizing the expected map and reduce further number of experiments. At the second stage, ‘pre-requisite for realistic operational map’, the objective was to determine the operating limits of TS and Im with the chosen consumables and equipment. Within the ‘realistic operational map’ stage, a design for the experiments was applied to cover a parametric area (working envelope) already defined in the previous stage and long and tall walls were additively manufactured. Actual values of LW (external and effective layer width) were measured and an actual operating envelope was reached. According to the geometry-oriented case study, a surface waviness index (SWindex) was defined, determined, and overlapped in the envelope. It was observed that the walls with parameters near the travel speed limits presented higher SWindex. This operational map was further validated (fourth stage) by selecting a target LW and finding corresponding three parametric set (covering the whole range of operational map) to produce walls on which geometry characterization was carried out. After geometry characterization, obtained LW was compared with the target LW (the maximum values were very tied, with deviations from +0.3 to 0.5 mm), with a SWindex deviation at the order of 0.05. Both results evidence high reproductivity of the process, validating the proposed methodology to parametrize WAAM.

Keywords
CMT, GMAW, operational map, parameterization, printing quality, WAAM
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:hv:diva-15013 (URN)10.3390/jmmp4010014 (DOI)
Funder
Knowledge Foundation
Available from: 2020-02-24 Created: 2020-02-24 Last updated: 2020-02-24
da Silva, L. J., Souza, D. M., de Araújo, D. B., Reis, R. P. & Scotti, A. (2020). Concept and validation of an active cooling technique to mitigate heat accumulation in WAAM. The International Journal of Advanced Manufacturing Technology
Open this publication in new window or tab >>Concept and validation of an active cooling technique to mitigate heat accumulation in WAAM
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2020 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015Article in journal (Refereed) Epub ahead of print
Abstract [en]

This work aimed at introducing and exploring the potential of a thermal management technique, named as near-immersion active cooling (NIAC), to mitigate heat accumulation in Wire + Arc Additive Manufacturing (WAAM). According to this technique concept, the preform is deposited inside a work tank that is filled with water, whose level rises while the metal layers are deposited. For validation of the NIAC technique, Al5Mg single-pass multi-layer linear walls were deposited by the CMT® process under different thermal management approaches. During depositions, the temperature history of the preforms was measured. Porosity was assessed as a means of analyzing the potential negative effect of the water cooling in the NIAC technique. The preform geometry and mechanical properties were also assessed. The results showed that the NIAC technique was efficient to mitigate heat accumulation in WAAM of aluminum. The temperature of the preforms was kept low independently of its height. There was no measurable increase in porosity with the water cooling. In addition, the wall width was virtually constant, and the anisotropy of mechanical properties tends to be reduced, characterizing a preform quality improvement. Thus, the NIAC technique offers an efficient and low-cost thermal management approach to mitigate heat accumulation in WAAM and, consequently, also to cope with the deleterious issues related to such emerging alternative of additive manufacturing.

National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:hv:diva-15079 (URN)10.1007/s00170-020-05201-4 (DOI)
Note

Funders:  Brazilian Coordination for the Improvement of Higher Education Personnel (CAPES); Brazilian National Council for Scientific and Technological Development (CNPq)[302863/2016-8 and 315092/2018-1]

Available from: 2020-03-25 Created: 2020-03-25 Last updated: 2020-03-25
Yehorov, Y., da Silva, L. J. & Scotti, A. (2019). Balancing WAAM Production Costs and Wall Surface Quality through Parameter Selection: A Case Study of an Al-Mg5 Alloy Multilayer-Non-Oscillated Single Pass Wall. Journal of Manufacturing and Materials Processing, 3(2), 1-19
Open this publication in new window or tab >>Balancing WAAM Production Costs and Wall Surface Quality through Parameter Selection: A Case Study of an Al-Mg5 Alloy Multilayer-Non-Oscillated Single Pass Wall
2019 (English)In: Journal of Manufacturing and Materials Processing, E-ISSN 2504-4494, Vol. 3, no 2, p. 1-19Article in journal (Refereed) Published
Abstract [en]

The purpose of the study was to propose a strategy to assess the potential reduction of the production cost during wire+arc additive manufacturing (WAAM) based on the combination of wire feed speed (related to deposition rate) and travel speed (related to deposition time). A series of experiments, using a multilayer-non-oscillated single pass wall made of an Al-Mg alloy, was conducted. The quality of the wall was assessed through the lateral surface waviness and top layer undulation. The concepts of Surface Waviness and Buy-to-Apply indices were introduced. Initially, the range of travel speed (TS) that provided layers with acceptable quality was determined for a given wire feed speed (WFS), corresponding to a constant current. Then, the effect of the increase of production capacity of the process (though current raising, yet maintaining the ratio WFS/TS constant) on the wall quality for a given condition within the TS range was assessed. The results showed that the useful range of TS prevents too rough a waving surface below the lower limit and top surface undulation over the higher limit. However, inside the range, there is little quality variation for the case under study. Finally, simulations of deposition time were developed to demonstrate the weight of the TS on the final deposition time and wall quality as a function of a target wall width. This respective weight showed the existence of a complex and unpredictable, yet determined, power of a combination of TS, target wall geometry, and dead time between subsequent layers. It was verified to be possible to find optimized TS as a function of different target geometries. 

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
WAAM; GMAW; CMT; aluminum; wall quality; production cost
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-13793 (URN)10.3390/jmmp3020032 (DOI)
Available from: 2019-04-16 Created: 2019-04-16 Last updated: 2019-12-10Bibliographically approved
dos Santos Paes, L. E., Pereira, M., Weingaertner, W. L., Scotti, A. & Souza, T. (2019). Comparison of methods to correlate input parameters with depth of penetration in LASER welding. The International Journal of Advanced Manufacturing Technology, 101(5-8), 1157-1169
Open this publication in new window or tab >>Comparison of methods to correlate input parameters with depth of penetration in LASER welding
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2019 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 101, no 5-8, p. 1157-1169Article in journal (Refereed) Published
Abstract [en]

Despite the industrial relevance of LASER welding, determination of sustainable parameterization is still a challenge. Trial and error, or even not totally justified methodologies, are frequently applied on LASER welding parametrization. This approach potentially leads to a decrease of the process tolerance and, consequently, increasing the likelihood of imperfections, which means extra operational time and raising of the final cost. The present paper addresses a comparative discussion about five factors experimentally determined and frequently used to predict depth of penetration in LASER welding. The experiments were performed with a 10-kW fiber LASER. In a first batch, power was varied while welding speed was fixed at 1 m/min. In a second batch, welding speed was varied and power was kept at 10 kW. The first demonstrated concern on using these popular factors is the definition and quantification of LASER energy. For evidencing this aspect, two samples were processed with the same welding energy of 120 kJ/m, yet resulting in completely different penetrations. Eventually, an empirical model based on power as a factor allowed a more reliable prediction of the depth of penetration.

Keywords
Autogenous LASER welding, Conduction LASER welding, Keyhole welding, Heat input, Power density, Power factor
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-13147 (URN)10.1007/s00170-018-3018-2 (DOI)000463240400004 ()2-s2.0-85056474097 (Scopus ID)
Note

First Online: 14 November 2018

Funders: CNPq

Available from: 2019-01-08 Created: 2019-01-08 Last updated: 2020-02-03Bibliographically approved
Yehorov, Y., da Silva, L. J. & Scotti, A. (2019). Exploring the use of switchback for mitigating homoepitaxial unidirectional grain growth and porosity in WAAM of aluminium alloys. The International Journal of Advanced Manufacturing Technology, 104(1-4), 1581-1592
Open this publication in new window or tab >>Exploring the use of switchback for mitigating homoepitaxial unidirectional grain growth and porosity in WAAM of aluminium alloys
2019 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 104, no 1-4, p. 1581-1592Article in journal (Refereed) Published
Abstract [en]

In this work, an alternative approach to prevent unidirectional grain growth in wire + arc additive manufacturing (WAAM) is proposed and assessed, by moving cyclically the torch forward and backward, likewise the welding technique known as switchback. A series of tests were planned with CMT (cold metal transfer) process to compare three wall-like build-ups, which uses different deposition patterns, namely, in one-way direction, reverse direction, and switchback. The same equivalent travel speed and number of deposited layers were kept among them. Longitudinal sections were taken to identify the grain growth behaviour. Finally, samples were removed from the walls for porosity evaluation. The results confirmed the characteristics of unidirectional grain growth, when one-way direction condition was employed, and the break of growth direction between layers, when reverse direction was used, yet a zig-zag pattern became present. Differently, the application of switchback showed no preferential or unidirectional grain growth, suggesting less anisotropy of mechanical properties. In addition, switchback reduced porosity. © 2019, The Author(s).

Keywords
Aluminum; Anisotropy; Gas metal arc welding; Porosity, Anisotropy of mechanical properties; Cold metal transfers; Deposition patterns; Forward-and-backward; Growth directions; Longitudinal section; Switchback; WAAM, Grain growth
National Category
Condensed Matter Physics
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14460 (URN)10.1007/s00170-019-03959-w (DOI)2-s2.0-85068187211 (Scopus ID)
Available from: 2019-10-02 Created: 2019-10-02 Last updated: 2020-01-14
Cruz-Crespo, A., Gonzalez, L. P., Rafael, Q. & Scotti, A. (2019). Flux for Hardfacing by Submerged Arc Welding from Ferrochrome-manganese and Slag from the Simultaneous Reduction of Chromite and Pyrolusite. Soldagem & Inspeção, 24, Article ID e2424.
Open this publication in new window or tab >>Flux for Hardfacing by Submerged Arc Welding from Ferrochrome-manganese and Slag from the Simultaneous Reduction of Chromite and Pyrolusite
2019 (Spanish)In: Soldagem & Inspeção, ISSN 0104-9224, E-ISSN 1980-6973, Vol. 24, article id e2424Article in journal (Refereed) Published
Abstract [en]

The obtaining of a flux for hardfacing by Submerged Arc Welding (SAW), using ferrochrome-manganese and slag obtained from the simultaneous carbothermal reduction of chromite and pyrolusite is addressed. The ferrochrome-manganese and the slag were obtained, conceiving that both products satisfy the requirements of the components (alloy system and matrix) of an agglomerated flux for hardfacing. The fusion-reduction process to obtain the alloy and the slag was carried out in a direct current electric arc furnace. The pouring was carried out into water to facilitate the separation and grinding of the cast products. An experimental flux was manufactured, using the obtained alloy and slag. Deposits were obtained by SAW, which were characterized in terms of: chemical composition, microstructure and hardness. It was concluded that the flux obtained from ferrochrome-manganese and slag from the simultaneous carbothermal reduction of chromite and pyrolusite, allows to deposit an appropriate metal for work under abrasion conditions, characterized by significant carbon and chromium contents and a martensitic microstructure predominantly, with hardness of 63 HRc.

Keywords
Flux; SAW; Hardfacing; Slag; Ferroalloys
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials Other Materials Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-14938 (URN)10.1590/0104-9224/SI24.24 (DOI)000496731100024 ()2-s2.0-85075105493 (Scopus ID)
Available from: 2020-02-05 Created: 2020-02-05 Last updated: 2020-03-02Bibliographically approved
Teixeira, F. R., Mota, C. A., Almeida, H. A. & Scotti, A. (2019). Operational behavior of the switchback GMAW process using a mechanized rig for arc movement. Journal of Materials Processing Technology, 269, 135-149
Open this publication in new window or tab >>Operational behavior of the switchback GMAW process using a mechanized rig for arc movement
2019 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 269, p. 135-149Article in journal (Refereed) Published
Abstract [en]

Switchback Gas Metal Arc Welding (GMAW) consists of a forward and backward periodic oscillation of the welding torch in the longitudinal direction of the joint. The present work has two objectives, to evaluate the use of a simple and practical device proposed for the switchback manipulation of the torch and to analyze the effect of the switchback parameters on the operational characteristic of the process. Two series of bead-on-plate depositions were planned, using the GMAW process with or without the switchback technique. To find an operational envelope, two levels of equivalent welding speeds were used for covering ranges of oscillation frequency and amplitude. A Ni superalloy was employed as deposition material, aiming at simulating weld overlays. Wire feeding speed, set voltage and contact tip-to-work distance (CTWD) were kept constant. The proposed device was evaluated and proved to be able to make the overlays with all combinations of planned parameters. It was demonstrated that if the backward length (B) is larger than half of the forward's (F), the torch passes more often over the same point of the deposit, and the oftener the torch passes over the same point, the lower the incidence of intermittent narrowing of the bead. By evaluating the surface aspect of the beads, the greater the F, the higher the likelihood of this irregularity. Penetration is shallower with switchback (reason demonstrated based on the fraction of stroke length that the arc is over the subtract), yet the bead surface presents more ripples. Another incident non-geometric conformity is the "dragon back" aspect of the bead, which is favored by faster equivalent welding speeds and high values of forward and backward speeds. The found operational envelope for the GMAW process with switchback was stablished with low-values of speeds and lengths of forward and backward strokes.

Keywords
Welding overlays, Switchback GMAW, Ni superalloys, Torch manipulator
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13546 (URN)10.1016/j.jmatprotec.2019.02.014 (DOI)000464299300015 ()2-s2.0-85061526377 (Scopus ID)
Note

Funders:CAPES; National Council for Scientific and Technological Development, 302863/2016-8, 01.10.0723.00

Available from: 2019-02-16 Created: 2019-02-16 Last updated: 2020-02-03Bibliographically approved
Li, P., Hurtig, K., Högström, M., Svensson, L.-E. & Scotti, A. (2018). A contribution to the study of negative polarity in GMA welding. The International Journal of Advanced Manufacturing Technology, 95(5-8), 2543-2553
Open this publication in new window or tab >>A contribution to the study of negative polarity in GMA welding
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2018 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 95, no 5-8, p. 2543-2553Article in journal (Refereed) Published
Abstract [en]

GMAW using the electrode with negative polarity (DCEN) has been frequently suggested as a potential means of increasing production capacity. The objective of this work was to further study the performance of negative polarity in GMAW of carbon steels. In this project phase, bead-on-plate welds were carried out in flat position to assess the effect of different potential shielding gas compositions on bead geometry, finishing and spattering. The characteristics were compared with DCEP at the same current, but depositing the same volume of material per unit of length (more industrial related comparison). The arc length was kept the same by adjusting voltage to reach shortest arcs, yet with suitable non short-circuiting metal transfer mode. An approach to measure bead convexity was also proposed and assessed. The results showed that DCEN is feasible as a means of increasing GMAW production capacity. However, to become DCEN applicable with GMAW, the results suggest an Ar based blend with around 6.5 % of O2 is the most appropriate shielding gas, as much as that there is a demand for a standard electronic controlled power source able to work in constant current mode. 

Keywords
Welding; Production; GMAW; Negative Polarity; Fusion rate; Weld bead geometry
National Category
Other Mechanical Engineering Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-11817 (URN)10.1007/s00170-017-1349-z (DOI)2-s2.0-85035104454 (Scopus ID)
Projects
Maplab
Funder
Region Västra Götaland, RUN 612-0254-15
Note

Funders: Swedish Agency for Economic and Regional Growth, 20200328.

Available from: 2017-11-26 Created: 2017-11-26 Last updated: 2020-04-02Bibliographically approved
Mishchenko, A., Wu, L., da Silva, V. K. & Scotti, A. (2018). Analysis of residual stresses resulting from the surface preparation for X-ray diffraction measurement. Journal of the Brazilian Society of Mechanical Sciences and Engineering, 40(2), Article ID 94.
Open this publication in new window or tab >>Analysis of residual stresses resulting from the surface preparation for X-ray diffraction measurement
2018 (English)In: Journal of the Brazilian Society of Mechanical Sciences and Engineering, ISSN 1678-5878, E-ISSN 1806-3691, Vol. 40, no 2, article id 94Article in journal (Refereed) Published
Abstract [en]

There is no consensus in the literature on the need to remove preprocessing layers from the material prior to the measurement of residual stresses by X-ray diffractometer. Thus, the purpose of this work was to evaluate the residual stresses induced by material preprocessing and its evolution during the preparation of the surface by electrolytic removal. Sample surfaces were pre-processed by grinding and sandblasting and the resulting residual stresses were measured by X-ray diffractometry. At each removal stage, the evolution of residual stresses, hardness and microstructure of the surface were verified. It was concluded that different preprocessing methods can induce surface residual stresses of either tension or compression, reaching different depths. Removal by electrolytic method of the modified layer has shown itself capable of reducing significantly the magnitude of the residual stresses induced by preprocessing. On the other hand, the depth of deformed grains or surface hardness proved to be incapable of predicting the depth of induced residual stresses. Finally, it was discussed whether or not the layers removed by this method reveal the subsurface stresses and if the removal should take place before or after a second processing.

Keywords
Residual stress, X-ray diffraction, Preprocessing, Surface stresses, Electrolytic removal
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-12055 (URN)10.1007/s40430-018-1036-5 (DOI)000424641000042 ()2-s2.0-85041305145 (PubMedID)2-s2.0-85041305145 (Scopus ID)
Note

First Online: 29 January 2018

Funders: Brazilian National Council for Scientific and Technological Development (CNPq), 302863/2016-8 and 149308/2014-0; Minas Gerais State Agency for Research and Development (FAPEMIG), TEC—APQ-01992-15.

Available from: 2018-02-07 Created: 2018-02-07 Last updated: 2019-03-06Bibliographically approved
Jorge, V. L., Alves Santos, C. H., Scotti, F. M., Larquer, T. R., Mota, C. P., Reis, R. P. & Scotti, A. (2018). Development and Evaluation of Wire Feeding Pulsing Techniques for Arc Welding: Desenvolvimento e Avaliação de Técnicas para Pulsação da Alimentação de Arame em Soldagem a Arco. Soldagem & Inspeção, 23(3), 326-339
Open this publication in new window or tab >>Development and Evaluation of Wire Feeding Pulsing Techniques for Arc Welding: Desenvolvimento e Avaliação de Técnicas para Pulsação da Alimentação de Arame em Soldagem a Arco
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2018 (Portuguese)In: Soldagem & Inspeção, ISSN 0104-9224, E-ISSN 1980-6973, Vol. 23, no 3, p. 326-339Article in journal (Refereed) Published
Abstract [en]

Applying pulsed wire feeding techniques is one of the new approaches for welding, such as for GTAW and GMAW. However, these techniques invariably require specific feeders and/or welding torches, limiting its implementation due to the high costs of the equipment. Thus, the current work aims to introduce and exploratorily evaluate techniques to pulse the wire feeding that works independently from the feeder and/or torch. The first technique is electromechanically driven, and the second one based on electromagnetics. The effects of amplitude and frequency of the pulsed feeding were evaluated in terms of weld bead formation over plates and of the corresponding electric signals. For GTAW, the pulsed wire feeding is capable of modifying the weld bead and make the metal transfer from the wire to the pool more regular. For GMAW, it was found that the pulsing of the wire feeding can interfere with the process, being capable of turning an irregular globular metal transfer into a regular one, while decreasing the mean current and affecting the bead formation. Overall, it is concluded that pulsed wire feeding can affect the processes, even when made independently from the feeder and torch, opening a field for development of derivative welding technologies.

Keywords
Pulsed wire feeding, GTAW, GMAW
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-13476 (URN)10.1590/0104-9224/SI2303.03 (DOI)000455417300003 ()2-s2.0-85062828238 (Scopus ID)
Available from: 2019-02-04 Created: 2019-02-04 Last updated: 2019-05-28Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-1005-5895

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