A Comparative Study on the Wear Mechanisms of Uncoated and TiAlTaN-Coated Tools Used in Machining AMPCO^® Alloy

Reviewer #1

Comment/Suggestion

Action done

The abstract seems too generalized and needs to be oriented more towards the specific working and objectives

The authors appreciate the very relevant suggestion. Changes have been made to improve the abstract.

if the following are the keywords "chipping, coating delamination, adhesion, abrasion." then why not use them in the abstract?

The authors appreciate the very relevant suggestion; however, the abstract already contains those keywords: “The results obtained with coated tools were distinct from those obtained with uncoated tools. While uncoated tools suffered from substrate abrasion and adhesion, the coated tools suffered mainly from delamination, followed by chipping. Furthermore, f and L_cut significantly influence the quality of the machined surface. TiAlTaN-coated tools performed significantly worse than uncoated tools, proving that the coating needs significant improvements to be considered as an alternative in milling Cu-Be alloys.”

The first paragraph of the introduction included unnecessary things, like injection molding, insert molding, epoxy resin, etc; which need to be reduced up to 9 – 10 lines only. Even, the second paragraph needs to be omitted.

The authors appreciate the very relevant suggestion. The authors state that the information that is asked to be removed is important since Cu-Be alloys are mostly used in injection mould inserts, and therefore we try to give the broadest panorama to the reader. Nonetheless, the information was summarized.

The third and fourth paragraphs also need reduction, the author can try to build a short story by reducing the paragraphs from 1-6, if considering injection mold material and their machining as a potential application in their submitted manuscript

The authors appreciate the very relevant suggestion. Changes have been made to improve the introduction.

Apart from providing unnecessary information in the introduction section, the relevant and most important information related to the cutting tools in terms of uncoated and potential coatings is completely missing from the introduction

The authors appreciate the very relevant noting. Changes have been made to improve the introduction.

However, the last paragraph that describes the novelty and exact execution of work is not defended well and needs to be written again

The authors appreciate the very relevant suggestion. With the changes done to the abstract, this last paragraph is now more well sustained.

Moreover, the submitted manuscript is extraordinarily lengthy and must be adjusted and reduced to 30-31 pages

The authors thank your comment; however, that situation is due to the high number of photos used to show sampling SEM analysis of the tools, which is considered relevant to support the text and phenomena observed.

As this study is primarily focused on machining, the considerable parameters, and their levels should be written in a separate Table under Section-Heading 2

The authors appreciate the very relevant noting; but the machining levels can be found in a separate table, Table 7, within section 2.3 Milling process.

From where the reported properties are taken that are given in Table 4, any reference or authors obtained these through experimentation by themselves

The authors appreciate your comment. Table 4 presents the mechanical and physical properties of AMPCOLOY®83 and was provided by the AMPCO^® Metal Portugal, Ltd. in a physical datasheet. Hence it is written “Table 4 provides this alloy's specifications and physical and mechanical properties according to the supplier.”

What is SR, as reported in heading 2.4

The authors thank your relevant comment. SR stands for surface roughness and was already defined back in the abstract. Moreover, we also defined in the text itself, out of the abstract.

Under heading 2, how the coating is deposited on the cutting tool through PVD completely missing? or not deposited just used?

Thank you so much for your question. However, it was stated right after Figure 5 that the coating was deposited by sputtering: “TiAlTaN coating is used to protect the milling cutters' surface in machining and was fabricated by the PVD (Physical Vapor Deposition) technique, utilising a High-Power Impulse Magnetron Sputtering (HiPIMS) power source, a CemeCom CC800, in TeandM company (Coimbra, Portugal)”

Kindly write (a), (b), and (c) at the top of the figures reported in Fig. 8, and describe them in the respective section

The authors appreciate the very relevant suggestion; however, Figure 8 only has two composing photos, (a) and (b). Addressing the describing of the Fig 8, a reference was added bellow the same picture.

As it seems from 8 that the coating thickness is between 3.2-3.4 micro-meters, what happens it this thickness is greater or lesser than this range?

The authors appreciate the very relevant question. This is the usually recommended thickness range for this kind of tools. Less than that induces premature wear due to abrasion. More than that usually induces premature delamination due to adhesion lack. Thus, the selected range was around 3 microns, which is considered as safe for this purpose. Thinner coatings have already been tested by this group with bad results.

What is S700 and S1500 in the legends of Fig. 9, as not pointed out earlier? Is there consideration of two tools?

The authors appreciate your question. The tools’ designation adopted was already explained in the section 2.2 Cutting tools where “The tools reference used can be followed by "T0", representing the WC-Co uncoated tools, or "T1" for the TiAlTaN-coated ones. It is then accompanied by "L", "F", and "S", representing the L_cut, f, and s, respectively.”. This given explanation was to introduce further up the Table 7 tool references.

Are roughness values reported in Fig. 9 and Fig. 10 after the matching or before, like coated and uncoated cases?

The authors appreciate the very relevant question. Figure 9 reports to the thickness of the coating before machining and Figure 10 report to the AMPCO® surface roughness assessment for the different tools’ typologies, as seen in the bar graph label.

What is the significance of the reported code T0L27F750S126 and T1L27F750S126? Is this self-generated or from the standard? Similarly for other Sections like in 3.3.1.2.

The authors thank your question. As mentioned above, the tools’ designation adopted was already explained in the section 2.2 Cutting tools.

As there are too many SEM images attached for tool wear analysis, this makes the manuscript lengthy. Authors need to paste the pictures side-by-side and create a master table that summarizes the wear type and other characteristics.

The authors appreciate the very relevant suggestion; however, the authors proceeded in this matter, because for each tool reference there were three cutting tools, and the SEM images presentations is nothing more nothing less than a sampling analysis.

Seem imbalance in the description of tool wear analysis and machine surface.

The authors appreciate the very relevant noting; however, as surface quality is quantifiably assessed by the measurement, tool-wear besides the quantification of the damage has also the qualification of the various wear mechanisms implied, which led to the imbalance between the surface quality assessment and the tool wear analysis. Besides, “A comparative study on the wear mechanisms of uncoated and TiAlTaN-coated tools used in machining AMPCO® alloy” is the title of the paper, clearly focusing on wear mechanisms, whose need to be described and shown.

4.3. Comparison with other used coatings in literature" This section seems unnecessary, as this is already very lengthy

The authors appreciate and understand the very relevant suggestion; nonetheless, in order to have a sort kind of validation of the work, the authors think it is paramount the comparison with other authors that had similar setups.

Bullet points should be used in reporting the conclusion with specific results conclusion

The authors appreciate and understand the very relevant suggestion. The conclusions are now built based on topics to better realize the results.

Reviewer #2

Comment/Suggestion

Action done

The primary wear mechanisms are very complicated; abrasion and adhesion are minor mechanisms

The authors appreciate the very relevant noting. From section 3.3 onwards, “primary wear mechanisms” reads now “main wear mechanisms”.

Delamination, chipping, important mechanism

The authors appreciate the very relevant noting and we agree on your statement.

Why the coating does not play important role on the surface quality

The authors appreciate the very relevant question. In fact, the coating played an important role, but not as we authors wanted. Due to the weak adhesion to the tool substrate, delamination took place during the milling process and, for longer cutting lenghts, three-body abrasion phenomena was always occurring for coated tools. “The coating did not play a beneficial role in the machined surface quality, as significantly high R_a values were obtained, and cracks were present in several tools, representing a wear mechanism that the coating was intended to prevent. The failure of the coating is attributed to poor adhesion of the coating to the substrate and to the deposition conditions used, which were not adequately optimised.”. Moreover, adhesion problems have been identified, situation that needs to be overcome in a near future, including an interlayer and fine-tunning the PVD deposition parameters. This is what we are doing right now in order to improve the results.

Reviewer #3

Comment/Suggestion

Action done

According to Table 7, it is hard to understand the effect of travel speed by two steps. 750 and 1500. At least 3 to 4 steps are recommended.

The authors appreciate the very relevant noting. Authors state that due to material and tools limitations was only possible to study three cutting lengths and two feed rates considering only one spindle speed. Bear in mind, for each tool reference were used three tools, totalling 36 tools, 18 WC-Co and 18 TiAlTaN-coated. As you certainly understand, budget limitations are usual in Research Centers. Moreover, the wear analysis is a time-consuming task limited by the time made available by the development of some thesis.

What is the significant parameter to form the microchips and their quantity without affecting the quality/surface roughness

The authors appreciate the very relevant question. However, we authors cannot answer correctly since numerical assessment and video recording were not done during milling operations. But we will take your suggestion into consideration in the future to understand that phenomenon.

The internal voids or hard precipitates have any effect on the chips formation, justify

The authors appreciate the very relevant question. However, authors cannot answer correctly since numerical assessment and video recording were not done during milling operations. However, we will take your suggestion into consideration in future works.

What is the mechanism to obtain the continuous increment of roughness for TiAlTaN coated material than others.

The authors appreciate the very relevant question. Regarding the increment of roughness, disregarding coated or uncoated tools, it is verifiable that the increase of the feed rate and the cutting length led to the increase of surface roughness, and the most influential one was the feed rate. The aftermath was further abrasion of the tool’s flank, that overcame into three-body abrasion situations; hence the continuous increment of the AMPCO® surface roughness. This is described in the body of the article.

Reviewer #1

Comment/Suggestion

Action done

For point 4, authors need to provide exact information, where they have made change regarding paragraph 3-4.

Thank you for your comment. We improved the information level regarding this specific topic. We apologise but due to the extensive modifications to the first part of the introduction, 1^st to 4^th paragraph the text is highlighted in yellow because there were many modifications adopted.

Similarly for Point 5, where authors have added the required information in the introduction section.

Thank you for your comment. We improved the information level regarding this specific topic. We apologise but due to the extensive modifications to the first part of the introduction, 1^st to 4^th paragraph the text is highlighted in yellow because there were many modifications adopted.

There are three images in the Fig. 8, previously it was pointed out to include (a), (b), (c) in this Figure.

Thank you for your advice. We included the reference (a), (b) and (c) in the images and completed the caption accordingly.

Manuscript needs to be shorten upto 33-35 Pages.

Despite there are no rules regarding the maximum number of pages of the articles in MDPI, we made an additional effort in reducing the article length up to 34 pages.

There are certain question as well, which authors not incorporate of Round 1, kindly address before going further.

Although the Reviewer is generic in this comment, we have revisited the first review and tried to improve the paper according to your suggestions and comments.