Recoater-Induced Distortions and Build Failures in Selective Laser Melting of Thin-Walled Ti6Al4V Parts

Round 1

Reviewer 1 Report

The current manuscript investigates the relation between the effect of recoater used in the SLM process and the expected failure during the building of thin-walled structures. The tile is important and some interesting results were presented. However, some issues should be considered as follows:

- A critical review should be presented in the introduction section according to the literature studies to illustrate the relation between optimizing the SLM parameters and the recoater type selection.   

- There should be a reference or source for the selective energy density and SLM process parameter.

- It is recommended to move Figure 2 and Table 2 to the results and discussion section. 

- The references of the presented equations in section 3 should be cited.

- The main point that should be clearly presented is to illustrate if the current computation model can be considered a generic model or limited to the Ti6Al4V material. The answer should be reflected in the title, abstract, and conclusion. 

- The discussion section lacks more references to support the analysis of the results.

- The numbering of sections needs to be carefully revised.  

- The paragraph starting from line #447 should be removed.

- It is recommended to present an example of a successful build process to justify and support the proposed strategies for reducing the warpage of additively manufactured thin-walled structures. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Paper is interesting, but the formal aspects are poor, introduction is poor as well and several figures must be improved. Recent works published opened new ways of discussion. MDPI must look for improving the paper quality.

·         SLM METAL STRUCTURES CAN BE STUDIED using Pole diagrams and a new view of grain growth theory, after the work published in the top journals and cover in 2022. Inc718 LPBFed parts were developed in structure and in mechanical characteristic i a two parts keynotes, one is “Stiffening near-net-shape functional parts of Inconel 718 LPBF considering material anisotropy and subsequent machining issues”, Mechanical Systems and Signal Processing 168, 108675 and the root fundamentals is “On the relationship between cutting forces and anisotropy features in the milling of LPBF Inconel 718 for near net shape parts”,  in IJ of Machine Tools. There the structures with EBSD and the consequences in mechanical properties are deeply explained.

·         the 3D-printing of different lightweight geometries is investigated, but thebligthest of all was published in MDPI, see A new approach in the design of microstructured ultralight components to achieve maximum functional performance, Materials 14 (7), 1588 Can you model and FEM these small features?

Figure 17 is very simple, you can don better adding: dimensions, metallographic textures.

Residual stresses in three orthogonal directions; did you check them experimentally?

Meshing is not clear in your figures, you can reduce them to only one figure.

How did you mesh the layer of the interface of pieces with plates?

Exchangers and antennas [13-16]: why did you use these general references. There are more accurate ones regarding metallographic textures and Pole diagrams.

Figure 1 is not nice, why the part is curved, can you explain the pieces arrangement better.

Table 1: Power laser is key, as it was shown in above works, discuss the value used. In some recent works the porosity is evaluated, as well in Dr. Coro´s works in MDPI, the XR tomography can show internal defect making different your simulations.Analysis of the influence of L-PBF porosity on the mechanical behavior of AlSi10Mg by XRCT-based FEM, Journal of Materials Research and Technology 22, 958-981

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The revised manuscript is significantly improved. However, there are some issues still need to be considered as follows:

- The title of the manuscript, abstract, and conclusion should include "Ti6 Al4V" as the applied material validated for the current study.

- The literature efforts for additive manufacturing of thin-walled structure of Ti6Al4V should be added to the introduction. 

- The dimension scale should be added to Figures 2, 3, and 4. 

- An example of a successful additively manufactured Ti6Al4V should be included to validate the proposed model .

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

May I kindly suggest that you review the previous comments? They contain valuable feedback that could greatly enhance the quality of your paper. In laser powder bed fusion (LPBF), grain growth refers to the increase in size of the metallic grains that make up the printed part. Grain growth can occur during the printing process or during post-print heat treatment, and it can have a significant effect on the quality of thin-walled structures. As the grains grow, they can cause a reduction in the strength and ductility of the material, as well as an increase in residual stress. In the case of thin walls, this can result in deformation or warping, which can compromise the dimensional accuracy of the part. Additionally, the larger grain size can lead to anisotropy in mechanical properties, which can further complicate the design and performance of the part.  To mitigate the effects of grain growth, several strategies can be employed, including controlling the printing parameters, optimizing the heat treatment process, and adding alloying elements to the powder feedstock. It is important to carefully consider the potential impact of grain growth on thin-walled structures during the design and fabrication of LPBF parts. So, you must address the topic and issue using the last references on the idea. On the other hand thin walls are really this: Stiffening near-net-shape functional parts of Inconel 718 LPBF considering material anisotropy and subsequent machining issues, Mechanical Systems and Signal Processing 168, 108675 the work in addition to missed one by you in Int J of Machine Tool and Manufacture gave the basics of anisotropy. So it really is in the scope of your work.

In addition, paper was not very improved. The rebuttal is longer than the work to improve the manuscript.

My opinion is between reject or major, thye paper needs reworks and really use the previous reviewers comments.

Figures needs scales, see Figure 2 it is too simple.

Figure 3: why did you use the FEM type of elements. FEM is now discussed in relation with anisotropy, anisotropy in thin walls is key.

Please resubmit soon.

Author Response

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Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Paper is of medium-high quality, revison was in the proper line. Follow the line in non distant future works.