Analysis of Machinability on Properties of Inconel 718 Wire and Arc Additive Manufacturing Products

Round 1

Reviewer 1 Report

Dear Author(s), the manuscript ‘Analysis of Machinability and Machining Effects on Properties of Inconel 718 Wire and Arc Additive Manufacturing Products’, Manuscript ID: jmmp-2777491, have some weakness that must be revised suitably.

Please find below some, of the most significant issues:

1.      In the Abstract section, the main introduction to the Inconel 718 wall-shaped additive manufactured products must be provided. Authors should firstly present any general words on the area of research and then indicate any requirements and results.

2.      In the Introduction section, the motivation presented in lines 63-69 should be retrieved from the lacks in the current stage of knowledge, indicated by the critical review of the literature. Authors did not provide any critical words on the already published items that the motivation is not fully justified, even suitable.

3.      In the subsection 2.2 Material Properties (WAAM and Annealed), Authors should emphasize which properties are those crucial and must be improved. There are many information but their significance is unknown and not fully justified.

4.      Some of the values in experiment, included in subsection 2.3 Machining Parameters, like helix angle of 35°, are not justified and looks like selected arbitrarily. Authors must be more conscious in their studies. Also, why 21 passes?

5.      Similar to the previous, the sentences ‘The multiple cutting passes were executed with the same machining parameters for both samples, being a wet-side milling (Blaser Swisslube 2000 Universal coolant) procedure. As for the parameters, the cutting speed was chosen as 15 m/min, the spindle rate was set at 800 rpm, and the feed speed was set at 240 mm/min.’ did not allow to reader find any justifications of the parameter sets.

6.      For all of the equations presented in the manuscript, Authors should indicate which are newly proposed, if any, and which were calculated previously and then cite them to the primary sources. The clear discrepancies from the novelty and already published items are not provide.

7.      Some, even general, critical discussion in all of the subsections of section 3 must be added. Authors does not discuss any potential limitations of the study. Advantages and disadvantages must be addressed.

8.      What is the main proposal of the 3.2.1 Surface Appearance subsection in the 3.2 Surface Quality section? Authors must indicate the meaning of the eye view characterisation of the surface and try to reflect it to the devices studies, if possible. Currently, this subsection seems to be irrelevant, if not justified appropriately with experiment results.

9.      About the roughness measurement presented in subsection 3.2.2 Surface Roughness Analysis, what is the accuracy of the instrument? The selection of the profilometer (Kosaka Laboratory Surfcorder ET 200) must be justified.

10.  Similar to the previous issue, the instrument precision must be placed with an uncertainty and other errors amplifications. There are no details on the measurement repetitions minimising the error acquisitions. Please refer to the accuracy issues:

(1)   https://www.doi.org/10.1088/2051-672X/3/3/035004

(2)   https://www.doi.org/10.1016/j.measurement.2023.113853

(3)   https://www.doi.org/10.1007/s41871-020-00057-4

11.  In the subsection 3.4 Material-Affected Machinability, the disadvantages and limitations of the study should be presented more consciously, especially that reflect to the whole body of the experiment.

12.  Any potential, future studies should be proposed with an additional section like The outlook, Authors should indicate what was received and, respectively, what can be further proposed.

13.  The Conclusions section must be improved. Firstly, must be divided into separated and numbered gaps. Secondly, the detailed information must be separated from those general. Finally, one main purpose must be emphasized from other information.

14.  As a final suggestion, Authors must respect the main line of the experimental studies: critical review of the previous studies from the literature, clear motivation with the basis of the first step, proposal of the results further studied in the experiment, critical discussion of the subject and the result obtained, future proposals for an area of study justification, and general conclusions improved with selected detailed information.

15.  Additionally, the quality of some figures, e.g. Figures 1 and 2, must be significantly improved.

From the above, the reviewed manuscript must be improved significantly before any further processing by the Journal of Manufacturing and Materials Processing, if allowed by the Editor.

Author Response

Dear Reviewer,

Thank you for the opportunity to revise and further improve our work, the points that were mentioned in the revision were addressed and will be pointed out in this response,

Apart from the reviewer comments, other comments were also taking into consideration, like reviewing and reducing the size of the Title, and that the text might be too long, with that the text was revised in a way that it would not increase the number of words, in a significant manner. All the modifications to the texts, apart from the numbering of the references, are highlighted in red in the revised manuscript.

Comments:

1. In the Abstractsection, the main introduction to the Inconel 718 wall-shaped additive manufactured products must be provided. Authors should firstly present any general words on the area of research and then indicate any requirements and results.

Answer: The abstract was revised and improved, as the reviewer suggested, as seen in text:

Abstract: The wire and arc additive manufacturing (WAAM) is a metal deposition technique with a fast rate and possibility of high volume of deposition. Because of its fast deposition and high heat input, the manufactured products have a poor surface quality. This paper presents a study on the machining of Inconel 718 wall-shaped additive manufacturing (AM) products, a necessary step for the improvement of the surface quality. Considering the possibility that the characteristics of the milling processes of AM products might differ from those of traditionally manufactured parts, in this research, two types of Inconel 718 were studied and compared: one manufactured using WAAM, and the other was an Inconel 718 rolled bar (Aerospace Material Specifications 5662). Using the testing procedure, a conventional two flutes cutting tool was used to assess their machinability. For this process, multiple passes were performed at three different heights of the samples. Considering the peculiarities of the AM products, such as their uneven surfaces, dendritic microstructures, and anisotropy, the results were analyzed. After the machining operation, the effects on the products were also studied by analyzing their surface quality. This study found a higher stability in the cutting process for the AMS 5662 samples relative to the WAAM parts with less variability in the cutting forces overall, resulting in better surface quality. 

2. In the Introductionsection, the motivation presented in lines 63-69 should be retrieved from the lacks in the current stage of knowledge, indicated by the critical review of the literature. Authors did not provide any critical words on the already published items that the motivation is not fully justified, even suitable.

Answer: The introduction section was changed, in a way that more recent and different research regarding AM and the machining process of AM was further addressed for instance in text:

Regarding the problems of surface quality and defects, different methods are currently being applied to reduce AM-induced irregularities. Ranging from techniques that calculate and control the feed rate for deposition control [7], optimization of tool vector during manufacturing [8], and use of AI to achieve better products [9]. These possibilities are being explored in a way that the post-processing step is faster, and less material is wasted during the material removal process.

Even with the employ of techniques to improve the surface quality during deposition and reduce its defects, different uses of the deposited products as final parts, especially for uses such as the aerospace industry, which usually require wrought or cast materials to have an average surface roughness (Ra) of 3.2 μm or lower [10], a step that could improve this surface roughness, a post-processing step, is required.

The conventional machining process has been well-studied and documented for the different types of metallic alloys, diverse manufacturing processes, and various machining techniques (milling, turning, and drilling). However, when considering the novelty of AM systems and their products' peculiar characteristics (such as their microstructures, mechanical properties, and the possibility of anisotropy), there is a need for further study of the machining processes for AM goods.

However, research for the post-processing of Inconel 718 products built with different AM techniques is being performed [11-12], especially for products manufactured with the Powder Bed Fusion (PBF) technique, and showing that the wrought and AM alloys do not share the same machinability, data on the machining of WAAM is still considered lacking. Considering the peculiarities of each additive manufacturing process, like the deposition process, energy, and solidification rate, and the differences in the mechanical properties, for instance, lower yield and tensile strength for WAAM, and in the microstructure, finer grains for PBF [13], the machining process could present different outcomes, with that, the different steps on this research were performed. 

3. In the subsection 2 Material Properties (WAAM and Annealed), Authors should emphasize which properties are those crucial and must be improved. There are many information but their significance is unknown and not fully justified.

Answer: More information was added in other relevant topics, as to which properties impact the process in question.

4. Some of the values in experiment, included in subsection 3 Machining Parameters, like helix angle of 35°, are not justified and looks like selected arbitrarily. Authors must be more conscious in their studies. Also, why 21 passes?

Answer: It was explained that the selection of the cutting tool, was that of a “common” type of cutting tool, since there is no knowledge regarding the optimization of the machining process for AM samples. Also, it was suggested that this could be a subject of future research, as in:

Other aspects of the machining process, such as tool wear, chip formation, and the optimization of the process itself for both tool geometry and machining parameters are also suggested for further research.

Regarding the number of passes, it was explained that the requirement used was the machining of a flat surface in all three heights, and the machining in a staircase shape for an easier identification of any deformations of the surfaces. As in text:

The choice for the number of machining passes to be performed took into considera-tion primarily the WAAM sample characteristics. Regarding the number of passes, it was considered necessary to machine flat surfaces to acquire data that had fixed radial and axial depths of cuts, for a comparison with the same parameters as the annealed sample, so to cut the sample until the removal of the surface deformations was deemed necessary. In the same manner, a limit to the number of passes was required to be established since thinning of the material wall could increase the possibility of inducing chatter vibration, and it was chosen to be 50% of the original width.

5. Similar to the previous, the sentences ‘The multiple cutting passes were executed with the same machining parameters for both samples, being a wet-side milling (Blaser Swisslube 2000 Universal coolant) procedure. As for the parameters, the cutting speed was chosen as 15 m/min, the spindle rate was set at 800 rpm, and the feed speed was set at 240 mm/min.’ did not allow to reader find any justifications of the parameter sets.

Answer: Information was added regarding the selection of the parameters, further explaining the choices. As seen in text:

Different aspects of the machining process were considered when selecting the ma-chining parameters. For instance, because the Inconel 718 is a material known as being hard to cut, the cutting parameters were chosen, taking that into consideration. Therefore, not only the range suggested by the company catalog was considered, but literature ex-amples were also considered, having not only a recommended cutting speed for carbide tools but also mentioning that the increase in feed speed should be considered for the pre-vention of rubbing, which affects work hardening and consequently tool life [24].

6. For all of the equations presented in the manuscript, Authors should indicate which are newly proposed, if any, and which were calculated previously and then cite them to the primary sources. The clear discrepancies from the novelty and already published items are not provide.

Answer: The equations in questions were not newly proposed, and with that information regarding it was added.

7. Some, even general, critical discussion in all of the subsections of section 3 must be added. Authors does not discuss any potential limitations of the study. Advantages and disadvantages must be addressed.

Answer: Limitations of the research and challenges were further addressed in different topics, namely, the lack of observation of tool wear, the separation between anisotropy and microstructure influences, and other aspects such as influence of porosity. As seen in text:

Another aspect of the manufacturing process that could hinder the machining process and the products themselves is the appearance of different defects that could happen throughout the deposition process. Porosity is quoted as one of the main concerns in the production by AM [44]; this kind of structure could lead to the initiation of cracks, which could be formed by different reasons, such as lack of fused material, trapped gases, and even contaminants [45].

Apart from the structural defects that the pores could be directly linked, it is explained that these kinds of structures directly influence the machining process, making the cutting procedure more difficult, linking the increase in porosity with higher instability of the cutting forces, higher surfacer roughness, and faster tool wear [46]. Even though this kind of formation could also appear in WAAM samples, due to it usually not being considered a problem for this specific kind of production process for most alloys [13], its influence was considered negligible and is not present in the discussions of the present paper.

Also not present in the discussions, in an isolated manner, is the anisotropic behavior of the WAAM Inconel 718. Although quoted as being a possible influence on the machining process, the effect of the anisotropy of this kind of product was not explored. To set apart the effects of this kind of property without the influence of the other characteristics of the sample was not achieved by the authors.

As explained in this topic, there are different characteristics that could make the machining process differ among the samples, and isolating the effect of each property would be a difficult task, mainly considering the effect of the microstructure on the different mechanical properties.

A further point worth discussing is that even though it was discoursed previously that the tools after cutting presented no excessive damage, and the volume of material re-moved was considered small, considering the difficulty of machining the Inconel 718 al-loy for both wrought and AM, the tool wear could be a hindrance to the cutting procedure, affecting the results for roughness and cutting forces as well.

8. What is the main proposal of the 2.1 Surface Appearancesubsection in the 3.2 Surface Quality section? Authors must indicate the meaning of the eye view characterisation of the surface and try to reflect it to the devices studies, if possible. Currently, this subsection seems to be irrelevant, if not justified appropriately with experiment results.

Answer: The main proposal is to observe that there is an absence of both major defects during the machining process and also in the AM procedure like major pores and cracks.

9. About the roughness measurement presented in subsection 3.2.2 Surface Roughness Analysis, what is the accuracy of the instrument? The selection of the profilometer (Kosaka Laboratory Surfcorder ET 200) must be justified.
10. Similar to the previous issue, the instrument precision must be placed with an uncertainty and other errors amplifications. There are no details on the measurement repetitions minimising the error acquisitions. Please refer to the accuracy issues:

(1)   https://www.doi.org/10.1088/2051-672X/3/3/035004

(2)   https://www.doi.org/10.1016/j.measurement.2023.113853

(3)   https://www.doi.org/10.1007/s41871-020-00057-4

Answer: It was added information regarding how the experimental procedure was performed, with 10 different tests for each height, and average being calculated, also more information regarding the profilometer and its specifications was added. As seen in text:

As mentioned previously, to evaluate the surface quality of the machined samples beyond the visual aspects, the surface roughness values of the machined products were measured according to International Organization for Standardization 4288 [33]. A con-tact-based measurement system comprising of a profilometer (Kosaka Laboratory Surfcorder ET 200), equipment with reproducibility of 1 σ 0.3nm or less, and resolution of 0.1nm for Z and 0.1μm for X, was used to acquire the values for Ra (average of the profile measurements), Rz (the sum of the values for the highest peak and depth), and RSm (the average of the profile widths) [34]. The tests were performed 10 times in different locations for each case, with the movement of the stylus being performed in the direction of the milling, having the stylus traveling 4.8mm, with an evaluation length of 4 mm and 0.8 mm of sampling length.

11. In the subsection 3.4 Material-Affected Machinability, the disadvantages and limitations of the study should be presented more consciously, especially that reflect to the whole body of the experiment.

Answer: AS explained on answer 7, the limitations and challenges of the experimental process were better addressed throughout the text.

12. Any potential, future studies should be proposed with an additional section like The outlook, Authors should indicate what was received and, respectively, what can be further proposed.

Answer: It was indicated by another reviewer that the text was long, so it was included some proposals for future studies in the conclusion section, to not make the text even longer.

13. The Conclusionssection must be improved. Firstly, must be divided into separated and numbered gaps. Secondly, the detailed information must be separated from those general. Finally, one main purpose must be emphasized from other information.

Answer: The conclusion was reformulated, in numbered gaps and with more detailed information regarding the results. As seen in text:

              In this research, the WAAM Inconel 718 samples were machined, analyzed, and compared with a traditionally manufactured alloy, i.e., Aerospace Material Specifications (AMS) 5662. AMS 5662 is a rolled Inconel 718 that suffers annealing. The data of characteristics such as the cutting forces and surface roughness were used to analyze and assess the differences between both types of manufacturing procedures and to understand if the peculiarities of the WAAM samples also affect the machining process, some of the main points of this paper are highlighted below:

1)           The side milling of WAAM and Annealed Inconel 718 presented different results. First, when comparing the cutting forces between the two samples, the WAAM samples presented higher values of the maximum resultant cutting forces, with a difference of 7.85, 7.63 and 5.55% for layers 1, 2, and 3, respectively, indicating a more difficult cutting process for WAAM.

2)           When considering the results of the machining itself (the surface quality of the work-pieces), the Annealed samples presented better outcomes, not only showing fewer variations on the surfaces, as observed by the pictures, but also presenting lower values for surface roughness measurements, Ra, with differences of 50.39, 57.04 and 59.47% and differences for Rz of 68.78, 70.25, and70.34% for the layers 1, 2 and 3 respectively.

3)           The simulated results and the values of the average resultant forces also matched the idea that the annealed samples had overall better machinability, presenting lower cutting forces for all tested and simulated results. Not only for the values themselves, which was expected, but regarding its stability when considering the oscillations on cutting forces obtained in the WAAM samples, a fact that was also observed in the graph of the cutting forces for the experimental results.

4)           Although it is a relatively novel kind of research and a novel focus to be given to the machining aspect, the influence of the microstructure on the material removal process was discussed and presented as a major hypothesis to explain the manufacturing differences between the two materials study.

5)           It is encouraged to further explore the microstructure and its influences on the ma-chining procedure, considering that not only the additive manufacturing a technique that has grown in attention, but there is also a possibility that products with better surface quality and with a higher degree of dimension tolerance are necessary, demanding more control of the process and its results.

6)           Other aspects of the machining process, such as tool wear, chip formation, and the optimization of the process itself for both tool geometry and machining parameters are also suggested for further research.

14. As a final suggestion, Authors must respect the main line of the experimental studies: critical review of the previous studies from the literature, clear motivation with the basis of the first step, proposal of the results further studied in the experiment, critical discussion of the subject and the result obtained, future proposals for an area of study justification, and general conclusions improved with selected detailed information.
15. Additionally, the quality of some figures, e.g. Figures 1 and 2, must be significantly improved.

Answer: The quality of the pictures was improved, and some of them were merged for an easier understanding.

From the above, the reviewed manuscript must be improved significantly before any further processing by the Journal of Manufacturing and Materials Processing, if allowed by the Editor.

Reviewer 2 Report

Revise and reduce the title…too many words

State of the art: I see you missed people working in additive, even in IN718. For instance the programming is not mentioned in deep as it was defined in Feed rate calculation algorithm for the homogeneous material deposition of blisk blades by 5-axis laser cladding, The International Journal of Advanced Manufacturing Technology 74, 1219-1228 and the related works, because IN718 is now also in study regarding metallurgical effects in metal structured, by J.D. Perez. Revising I see many references missed and instead is Altintas book that is about machining and which models are improved by Pere or Urbikain as well. Side milling of WAAM and Annealed Inconel 718 presented different results. Thin walls was studied after de book by Bravo, del Sol (in MDPI), CIRP annals  on 2023 including milling of additive pieces by Machining stability improvement in LPBF printed components through stiffening by crystallographic texture control, so as summary you can make a fresher view of the state of the art.

You must take into account that machinability was not very studied linking metal structure and  milling directions, the only references till now is in IJMT&M by Perez who did a deep study of crystals, Taylor factor and dendrites growth.

Figure 1 and others of pieces can be merged in only one, with scale. Robot is not key in your approach. Figure 18 does not include scale, and conclusions do not give any number, they are general ideas only.

Table 4, roughness…why is this?. My explanation is the increase in hardness.                 

Explain dynamometer properties and how you controlled natural frequencies and other issues with the force measurements. You have works in mechatronics and IEEE explaining this.

Figure 16; are they cosnta values?. In Milling? Ok is in a rotation so engagement was very high for thin walls. Climb milling or downmilling?

Figure 11 show a accelerometer, too big for a thin wall, did you modify the meareuements as D.Olvera and G.urbikain proposed?

God work, perhaps a little long and with a no update state of the art. Next version must take into account all above points

Author Response

ear Reviewer,

Thank you for the opportunity to revise and further improve our work, the points that were mentioned in the revision were addressed and will be pointed out in this response,

It is important to mention that, since the reviewer pointed out that the text was perhaps a little long, the authors decided to not add much text, but still, little additions were performed.

1-Revise and reduce the title…too many words

Answer: The title was revised, and reduced, new proposed title:

Analysis of Machinability on Properties of Inconel 718 Wire and Arc Additive Manufacturing Products

State of the art: I see you missed people working in additive, even in IN718. For instance the programming is not mentioned in deep as it was defined in Feed rate calculation algorithm for the homogeneous material deposition of blisk blades by 5-axis laser cladding, The International Journal of Advanced Manufacturing Technology 74, 1219-1228 and the related works, because IN718 is now also in study regarding metallurgical effects in metal structured, by J.D. Perez. Revising I see many references missed and instead is Altintas book that is about machining and which models are improved by Pere or Urbikain as well. Side milling of WAAM and Annealed Inconel 718 presented different results. Thin walls was studied after de book by Bravo, del Sol (in MDPI), CIRP annals  on 2023 including milling of additive pieces by Machining stability improvement in LPBF printed components through stiffening by crystallographic texture control, so as summary you can make a fresher view of the state of the art.

Answer: Throughout the text the state of the art was better addressed, not only on the introduction, but on different parts, for instance on introduction:

Regarding the problems of surface quality and defects, different methods are currently being applied to reduce AM-induced irregularities. Ranging from techniques that calculate and control the feed rate for deposition control [7], optimization of tool vector during manufacturing [8] and use of AI to achieve better products [9]. These possibilities are being explored in a way that the post-processing step is faster, and less material is wasted during the material removal process.

Even with the employ of techniques to improve the surface quality during deposition and reduce its defects, different uses of the deposited products as final parts, especially for uses such as the aerospace industry, which usually require wrought or cast materials to have an average surface roughness (Ra) of 3.2 μm or lower [10], a step that could improve this surface roughness, a post-processing step, is required.

The conventional machining process has been well-studied and documented for the different types of metallic alloys, diverse manufacturing processes, and various machining techniques (milling, turning, and drilling). However, when considering the novelty of AM systems and their products' peculiar characteristics (such as their microstructures, mechanical properties, and the possibility of anisotropy), there is a need for further study of the machining processes for AM goods.

However, research for the post-processing of Inconel 718 products built with different AM techniques is being performed [11-12], especially for products manufactured with the Powder Bed Fusion (PBF) technique, and showing that the wrought and AM alloys do not share the same machinability, data on the machining of WAAM is still considered lacking. Considering the peculiarities of each additive manufacturing process, like the deposition process, energy, and solidification rate, and the differences in the mechanical properties, for instance, lower yield and tensile strength for WAAM, and in the microstructure, finer grains for PBF [13], the machining process could present different outcomes, with that, the different steps on this research were performed.  

Other parts example:

Porosity is quoted as one of the main concerns in the production by AM [44]; this kind of structure could lead to the initiation of cracks, which could be formed by different reasons, such as lack of fused material, trapped gases, and even contaminants [45].

Apart from the structural defects that the pores could be directly linked, it is explained that these kinds of structures directly influence the machining process, making the cutting procedure more difficult, linking the increase in porosity with higher instability of the cutting forces, higher surfacer roughness, and faster tool wear [46]. Even though this kind of formation could also appear in WAAM samples, due to it usually not being considered a problem for this specific kind of production process for most alloys [13], its influence was considered negligible and is not present in the discussions of the present paper.

You must take into account that machinability was not very studied linking metal structure and  milling directions, the only references till now is in IJMT&M by Perez who did a deep study of crystals, Taylor factor and dendrites growth.

Answer: It was explained that although it was studied, it is still a novel direction of research, as seen in text.

Other authors also explore the possibility of the additive manufacturing deposition-induced microstructure directly affecting the machining process. For the particular case of the Inconel 718, and its microstructure, which is composed of columnar dendrites, not only the relation between cutting and dendritic directionality was studied, concluding that the machining process and its results are different with the different dendrites' direction [40], but also trying to improve the machining stability by performing different deposition strategies to change this directionality and consequently the relation between dendrites and cutting tool[41]. 

With that, although it is hypothesized that the microstructure and anisotropy played an important role in the effects of the material removal process, further research is deemed necessary to try and understand the possible different effects of those characteristics on the material removal process.

Figure 1 and others of pieces can be merged in only one, with scale. Robot is not key in your approach. Figure 18 does not include scale, and conclusions do not give any number, they are general ideas only.

Answer: The figures were revised, adding scale to them, and figure 1 merged, and improved in quality.

Table 4, roughness…why is this?. My explanation is the increase in hardness.                 

Answer: Our explanation lies in the lack of stability for the cutting procedure, not on the hardness itself, although this is just an hypothesis to explain this difference in surface quality, as seen in text:

As discussed previously, the instability of the cutting process for WAAM is thought to be the main reason behind those differences.

Explain dynamometer properties and how you controlled natural frequencies and other issues with the force measurements. You have works in mechatronics and IEEE explaining this.

Answer: Dynamometer properties were added, along with the charge amplifier, which had low and high pass filters to control issues during the machining process.

As previously mentioned, this study required a set of data concerning the cutting forces. To obtain this type of data, a multi-component piezoelectric dynamometer (Kistler Type 9272) with a measuring range of ± 5kN for the X and Y axes and -5 to 20 kN for the Z axis, having a hysteresis less or equal to 1% and linearity less or equal to ± 1%, was coupled with a five-axis machining center (OKK VM4) while using a charge amplifier (Kistler Type 5015A) with integrated high and low pass filters and the Keyence Wave Logger as data acquisition system.

Figure 16; are they cosnta values?. In Milling? Ok is in a rotation so engagement was very high for thin walls. Climb milling or downmilling?

Answer: Down milling process was performed.

Figure 11 show a accelerometer, too big for a thin wall, did you modify the meareuements as D.Olvera and G.urbikain proposed?

Answer: The accelerometer was located at the “middle” of the sample, but no further actions was performed for the modification of the measuremets.

God work, perhaps a little long and with a no update state of the art. Next version must take into account all above points

Reviewer 3 Report

This study conducted a comparative analysis of two Inconel 718 materials: one produced through the Wire and Arc Additive Manufacturing (WAAM) technique and the other a rolled bar of annealed Inconel 718 (Aerospace Material Specifications 5662). A conventional two-flute cutting tool was employed in the testing process to evaluate the machining performance of the samples. However, upon review, the manuscript was found to have several issues:

1.      The principles guiding the selection of the heat treatment process in Table 2 are not clarified.

2.      WAAM technology belongs to the additive manufacturing field. However, the primary challenges currently hindering the development of additive manufacturing are additive defects, with cracking and porosity being particularly prominent. While the manuscript discusses the influence of surface deformation on cutting forces, it is essential to acknowledge that defects also have an impact on cutting forces. Relevant discussions on this issue can be found in the following articles for reference: Additive Manufacturing. 2023. 69:103547; Journal of Materials Science & Technology. 2024. 177:44-58; Additive Manufacturing. 2022. 52:102680; Science. 2023. 379:89-94.

3.      In Section 3.2.2 Surface Roughness Analysis, the limited measurement range of Ra hinders the comprehensive validation of the manuscript's conclusions. The authors should characterize surface roughness over a broader flat area for a more thorough analysis.

4.      In Section 3.4 Material-Affected Machinability, the discussion involves the impact of grain size on material machinability, but there is a lack of material characterization. Are there corresponding experimental data or references supporting this discussion?

Moderate editing of English language required

Author Response

Dear Reviewer,

Thank you for the opportunity to revise and further improve our work, the points that were mentioned in the revision were addressed and will be pointed out in this response,

Apart from the reviewer comments, other comments were also taking into consideration, like reviewing and reducing the size of the Title, and that the text might be too long, with that the text was revised in a way that it would not increase the number of words, in a significant manner. All the modifications to the texts, apart from the numbering of the references, are highlighted in red in the revised manuscript.

This study conducted a comparative analysis of two Inconel 718 materials: one produced through the Wire and Arc Additive Manufacturing (WAAM) technique and the other a rolled bar of annealed Inconel 718 (Aerospace Material Specifications 5662). A conventional two-flute cutting tool was employed in the testing process to evaluate the machining performance of the samples. However, upon review, the manuscript was found to have several issues:

1. The principles guiding the selection of the heat treatment process in Table 2 are not clarified.

Answer: Text was revised to inform that this is the standard for the AMS5662 heat treatment, and not selected arbitrarily.

2. WAAM technology belongs to the additive manufacturing field. However, the primary challenges currently hindering the development of additive manufacturing are additive defects, with cracking and porosity being particularly prominent. While the manuscript discusses the influence of surface deformation on cutting forces, it is essential to acknowledge that defects also have an impact on cutting forces. Relevant discussions on this issue can be found in the following articles for reference: Additive Manufacturing. 2023. 69:103547; Journal of Materials Science & Technology. 2024. 177:44-58; Additive Manufacturing. 2022. 52:102680; Science. 2023. 379:89-94.

Answer: Information regarding the porosity and cracking, and its influence on the machining process was added in the text, along with the information that although usually the WAAM samples do not suffer from this kind of problem, It should be addressed. As seen in text:

Another aspect of the manufacturing process that could hinder the machining process and the products themselves is the appearance of different defects that could happen throughout the deposition process. Porosity is quoted as one of the main concerns in the production by AM [44]; this kind of structure could lead to the initiation of cracks, which could be formed by different reasons, such as lack of fused material, trapped gases, and even contaminants [45].

Apart from the structural defects that the pores could be directly linked, it is explained that these kinds of structures directly influence the machining process, making the cutting procedure more difficult, linking the increase in porosity with higher instability of the cutting forces, higher surfacer roughness, and faster tool wear [46]. Even though this kind of formation could also appear in WAAM samples, due to it usually not being considered a problem for this specific kind of production process for most alloys [13], its influence was considered negligible and is not present in the discussions of the present paper.

3. In Section 3.2.2 Surface Roughness Analysis, the limited measurement range of Ra hinders the comprehensive validation of the manuscript's conclusions. The authors should characterize surface roughness over a broader flat area for a more thorough analysis.

Answer: The surface roughness process analysis, along with more information regarding the profilometer specifications was added to the text. As seen:

As mentioned previously, to evaluate the surface quality of the machined samples beyond the visual aspects, the surface roughness values of the machined products were measured according to International Organization for Standardization 4288 [33]. A contact-based measurement system comprising of a profilometer (Kosaka Laboratory Surfcorder ET 200), equipment with reproducibility of 1 σ 0.3nm or less, and resolution of 0.1nm for Z and 0.1μm for X, was used to acquire the values for Ra (average of the profile measurements), Rz (the sum of the values for the highest peak and depth), and RSm (the average of the profile widths) [34]. The tests were performed 10 times in different locations for each case, with the movement of the stylus being performed in the direction of the milling, having the stylus traveling 4.8mm, with an evaluation length of 4 mm and 0.8 mm of sampling length.

4. In Section 3.4 Material-Affected Machinability, the discussion involves the impact of grain size on material machinability, but there is a lack of material characterization. Are there corresponding experimental data or references supporting this discussion?

Answer: Although there is no experimental data regarding material characterization, explanations concerning the difference between the dendritic formations from WAAM Inconel 718, are present, informing that the grain size differ greatly from the usual wrought material. As seen in text :

However, the WAAM Inconel 718 and AMS 5662 present several differences in regard to other properties. Owing to their manufacturing characteristics and primarily because the material deposition is based around a sudden increase in temperature and rapid posterior cooling, the WAAM workpieces present a different type of microstructure [20]. Mainly owing to this different microstructure, the mechanical properties will differ. 

This microstructure differs from the AMS5662, which comprises grains sharing roughly the same diameter through different directions. The WAAM Inconel 718, in contrast, is composed of columnar dendrites with large grain boundaries (as large as 200 µm), with various diameters across multiple directions as opposed to the average 26.7 µm diameter of the AMS5662 grains [21]. The presence of the dendrites in the microstructure causes it to be anisotropic, with different directionality and a peculiar texture.

Round 2

Reviewer 1 Report

Dear Authors,

I have found your responses suitable and the submission improved appropiately that the manuscript in its current, revised form, can be considered for publication in a quality journal as the Journal of Manufacturing and Materials Processing is.

Regards,

Reviewer