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. 2018 Aug 16;11(8):1449.
doi: 10.3390/ma11081449.

Analysis of Favorable Process Conditions for the Manufacturing of Thin-Wall Pieces of Mild Steel Obtained by Wire and Arc Additive Manufacturing (WAAM)

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Free PMC article

Analysis of Favorable Process Conditions for the Manufacturing of Thin-Wall Pieces of Mild Steel Obtained by Wire and Arc Additive Manufacturing (WAAM)

José Luis Prado-Cerqueira et al. Materials (Basel). .
Free PMC article

Abstract

One of the challenges in additive manufacturing (AM) of metallic materials is to obtain workpieces free of defects with excellent physical, mechanical, and metallurgical properties. In wire and arc additive manufacturing (WAAM) the influences of process conditions on thermal history, microstructure and resultant mechanical and surface properties of parts must be analyzed. In this work, 3D metallic parts of mild steel wire (American Welding Society-AWS ER70S-6) are built with a WAAM process by depositing layers of material on a substrate of a S235 JR steel sheet of 3 mm thickness under different process conditions, using as welding process the gas metal arc welding (GMAW) with cold metal transfer (CMT) technology, combined with a positioning system such as a computer numerical controlled (CNC) milling machine. Considering the hardness profiles, the estimated ultimate tensile strengths (UTS) derived from the hardness measurements and the microstructure findings, it can be concluded that the most favorable process conditions are the ones provided by CMT, with homogeneous hardness profiles, good mechanical strengths in accordance to conditions defined by standard, and without formation of a decohesionated external layer; CMT Continuous is the optimal option as the mechanical properties are better than single CMT.

Keywords: GMAW; WAAM; additive manufacturing; cold metal transfer; hardness; mechanical properties; microstructure; thermal input.

Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Figures

Figure A1
Figure A1
Brinell hardness tests applied to WAAM samples and identification of indentation points; images with red frame showing points located more clearly between layers.
Figure A2
Figure A2
SEM images showing no decohesionated layer formation in the upper edge of the surface. (a) Sample nº 2, CMT process; (b) Sample nº 3, CMT Adv. pol. 0; (c) Sample nº 4, CMT Adv. pol. 0; (d) Sample nº 5, CMT Adv. pol. −5; (e) Sample nº 6, CMT Adv. pol. +5; (f) Sample nº 7, CMT Cont.
Figure 1
Figure 1
Setup of the integrated WAAM system in the positioning table.
Figure 2
Figure 2
Examples of geometries obtained by WAAM: (a) Piece obtained by continuous trajectory and complex geometry in x-y direction; (b) Piece obtained by continuous trajectory and growing geometry in z direction.
Figure 3
Figure 3
Manufacturing of samples nº 1 to 6: (a) Top view; (b) Lateral view.
Figure 4
Figure 4
Location of the cross-section analyzed and the position of the substrate: (a) Samples nº 1 to 6, showing the location of the cross-section analyzed with sample nº 4; (b) Tool path during the deposition process in sample nº 7 and the final sample obtained.
Figure 5
Figure 5
Brinell hardness tests applied to WAAM samples and identification of indentation points.
Figure 6
Figure 6
Brinell hardness profiles for the WAAM samples: (a) Sample nº 1, MIG (conventional); (b) Sample nº 2, CMT process; (c) Sample nº 3, CMT Adv. pol. 0; (d) Sample nº 4, CMT Adv. pol. 0; (e) Sample nº 5, CMT Adv. pol. −5; (f) Sample nº 6, CMT Adv. pol. +5; (g) Sample nº 7, CMT; (h) Mean hardness values with standard deviations and thermal inputs.
Figure 7
Figure 7
Scanning electronic microscopy (SEM) at the surface in Sample nº 1 (MIG conventional). (a) Decohesionated layer found; (b) Layer SEM image at 20 µm of scale.
Figure 8
Figure 8
SEM Micrographs at interface between layers in Sample nº 1 (MIG conventional).

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