Optimization of EDM Machinability of Hastelloy C22 Super Alloys

Round 1

Reviewer 1 Report

Dear Authors,

The article entitled "Optimization of EDM Machinability of Hastelloy C22 Super Alloys" contains a lot of interesting information related to the optimization of the EDM process for cryogenically treated material. Through analyses according to the Taguchi method, ANOVA analysis, S/N ratio and gray relational analysis, the authors indicated the best process conditions due to roughness and material remove rate.

The results of the research are detailed, reliable and expand the knowledge of the EDM process as well as can be used in manufacturing process.

The article is related to the subject matter of the Machines journal and has potential for being cited.

Overall, the article is well-written, but needs some major corrections or additions. Detailed comments are included as follows:

A) General comments:

1. The Introduction is well prepared and contains 25 citations. Most references are cited separately and intentionally discussed. The analysis of the literature should concludes by pointing out knowledge gap and the need for additional/new research.

2. The authors use an MRR index based on weight measurements. However, I suggest applying a more typical indicator which determines volume loss (in mm³ per minute). All you have to do is consider the density of material to convert weight to volume. It appears it is important to analyze the tool wear rate (TWR) and other effectiveness indexes for the EDM process in parallel. For example: process ratio (G=MRR/TWR, E_EDM=MRR/Ra, and others...)

3. The use of the Ra parameter instead of the spatial parameter (Sa) requires clarification. If an analysis of the Ra parameter is to remain in the paper, several profiles should be measured on each sample and average values reported. The Ra values from each individual profile can vary significantly. The accuracy (standard deviation) should be specified then.

4. The article makes too few references to machining time, which is often (in manufacturing conditions) as important as surface quality. The data presented in Table 6 and the values of the "Total processing time" parameter should be used for accurate analysis and additional conclusions.

5. (Page 3) In the section "2.2 Material and electrode selection" the tested material (C22 alloy) should be described in more detail. What is most missing is its application and ISO/EN symbol.

6. (Page 4) Roughness measurement parameters may be a matter of discussion. The authors record that they used a cutoff of 0.8 mm and a sampling length of 5.6 mm. Why? For Ra values that are reported in Table 6 and vary from 2 to 10 μm, the recommended measurement distance is 15 mm with a 2.5 mm for cut-off.

7. (Page 8) What was the fitting function used in the graphs in Figure 3? Nonlinear surfaces are clearly visible in Fig. 3, and the data in Table 10 indicate that planar models have been studied.

8. (Figure 11) Is Figure presents difference between the observed response in experiment and fitted response from model (predicted vs actual)? If yes,the question is: for which model? For the model included in Table 10? If so, why is the content presented in the wrong order? It is difficult for the reader to figure out. It is necessary to consider reordering the following subsections.

 9. (Figure 11) No measurement points are marked on the plots. How are they positioned relative to the surface? How exactly does the surface represent the position of the points? What are the residuals?

 10. (Page 8) I believe the analysis in paragraphs 242-253 and Figure 4 are unnecessary. This content does not carry any numerically validated information. I suggest to analyze the surface geometrical structure by appropriate functional parameters.

 11. (Page 13) Table 7 includes predicted values of Ra and MRR. On the basis of what? What model was applied? The content of the paper should include an expanded interpretation of these values. The paragraph (lines 315-319) contains not enough detailed explanation.

 12. In many parts of the paper, the authors write about peak current as "Amperage" or "Amper" in short form. I suggest that you always use the precise, accepted form of naming technological parameters. Replace the expression "Amperage/Amper" in the text, tables and drawings with "Peak current, A" - with the unit, if needed).

13. (Page 14, line 325) What does "ideal" mean in the sentence: "When Table 8 was examined, the most ideal parameters observed for the average surface roughness and MRR were A₁B₁C₃ and A₂B₂C₁, respectively."? I suggest do not use this term. Perfect things do not exist.

14. (Lines: 108, 331, 394, 403, 422, 440, 441, ) "ideal"?

15. (Page 14, lines 328-331) This analysis is a duplication of an earlier paragraph. It brings nothing new.

16. (Page15-16) The models adopted (Table 10) and the ANOVA analysis do not consider the interaction. Why? It is important to include some interactions in model, e.g. "Peak current*Pulse-on time".

17. (Page 16, Table 10) The models are linear: y=a₀+a₁*x+b₂*y. This is not an incorrect choice. However, the explanation for the selection of this model is absent. All three models have also weakness. They contain a constant (a₀). This means if the ampere and pulse time values will be zero (the process is off), the model will still return a value different from zero or infinity! The model without a constant should be used.

18. (Page 16-17) Section "3.6 Estimation of optimum MRR and Ra" appears to be incomplete. First of all, the equations are missing after the first paragraph (line 362). Secondly, there is the question: What exactly is optimization supposed to consist of? Of determining the confidence interval (CI) value for eq. (5) and (6)? Maybe, the chapter should be titled "Interval estimation for Ra and MRR" and should include calculated specific confidence interval values.

19. (Page 20, lines 447-451) The indicated solution (parameters from Exp. #7) does not seem to be the optimal result, taking into account both criteria. The MRR value is one of the lowest, and it was supposed to be maximized. The adopted polyoptimization procedure does not bring the expected results.

20. (Fig. 12) The form of the chart is not grounded. The use of a line graph that connects points is unjustified. If we rearrange the order of experiments, the shape of the line will be changed. It is necessary to use a point or bar graph in this case.

21. The article ends with a Conclusion. This section is written properly but is in few parts a repetition of the abstract.

B) Text formatting and editing comments:

Page 1: The Abstract is 208 words (15 lines) and not follows exactly the authors' guidelines (200 words maximum).

Page 3, line 116: Redundant spaces in EDM machine designation.

Page 3, lines 122-123: The sentence "The formula for calculation of the MMR is given as Equation (1) [26, 27]." should end with a colon, and a comma and the word "where" should be added after the equation.

Page 3, lines 124-125: Missing subscript in the parameter/variable labels (W_i, W_f).

Page 3, line 126: Missing a period on the end of a sentence. 

Page 8, Fig. 3: Missing unit for pulse current.

Table 8: The left side has a written unit (μm for Ra and g/min for MRR). Is this correct? The values are negative! Perhaps the titles should be written as follows: "S/N for average surface roughness", " Response Table for avg. Ra (μm)", "S/N for MRR" and "Response Table for average MRR"?

Table 8: Is "Delta" a range? Is any reason do not write "Range"?

Figure 10: Why new designations of M1, M2 and M3 were implemented for UT, SCT and DCT materials? Please use the same labels and symbols throughout the entire paper, including floats (figures and tables).

Page 16, line 366: Missing subscript in the parameter/variable labels (T_Ra and T_MRR).

Page 17, line 375: Missing subscript in the parameter/variable labels (V_e, n_eff and T_dof).

Page 18, line 403: Missing superscript in the parameter/variable labels (x₀).

C) Comments to Back matter:

There is no information about patents, supplementary materials, acknowledgments or sources of funding of the study. There is missing Conflicts of Interest section.

With the necessary corrections, the article will be of an appropriate scientific level and can be recognized in the scientific community as having good quality and will have a high potential for citations.

Best Regards,
Reviewer

Author Response

Reviewer-1

Comments and Suggestions for Authors

Dear Authors,

The article entitled "Optimization of EDM Machinability of Hastelloy C22 Super Alloys" contains a lot of interesting information related to the optimization of the EDM process for cryogenically treated material. Through analyses according to the Taguchi method, ANOVA analysis, S/N ratio and gray relational analysis, the authors indicated the best process conditions due to roughness and material remove rate.

The results of the research are detailed, reliable and expand the knowledge of the EDM process as well as can be used in manufacturing process.

The article is related to the subject matter of the Machines journal and has potential for being cited.

Overall, the article is well-written, but needs some major corrections or additions. Detailed comments are included as follows:

1. A) General comments:
2. The Introduction is well prepared and contains 25 citations. Most references are cited separately and intentionally discussed. The analysis of the literature should concludes by pointing out knowledge gap and the need for additional/new research.

Changes have been made to the article.

When the literature studies are examined, it is seen that the optimization performed in the processing parameters makes the EDM method more stable. In addition, although the studies provide information on the relationship between various input and output parameters for the processing of materials with EDM, they do not provide much information about the underlying mechanisms.

2. The authors use an MRR index based on weight measurements. However, I suggest applying a more typical indicator which determines volume loss (in mm³per minute). All you have to do is consider the density of material to convert weight to volume. It appears it is important to analyze the tool wear rate (TWR) and other effectiveness indexes for the EDM process in parallel. For example: process ratio (G=MRR/TWR, E_EDM=MRR/Ra, and others...)

Since the tool wear values were not taken into account in the experimental study, the data were not taken.

3. The use of the Ra parameter instead of the spatial parameter (Sa) requires clarification. If an analysis of the Ra parameter is to remain in the paper, several profiles should be measured on each sample and average values reported. The Ra values from each individual profile can vary significantly. The accuracy (standard deviation) should be specified then.

The average surface roughness measurements were performed at room temperature and conducted in three repetitions.

4. The article makes too few references to machining time, which is often (in manufacturing conditions) as important as surface quality. The data presented in Table 6 and the values of the "Total processing time" parameter should be used for accurate analysis and additional conclusions.

Since the processing parameters affecting the surface quality of the material were determined in the study, results were obtained about the surface quality and material wear amounts of the processing time.

5. (Page 3) In the section "2.2 Material and electrode selection" the tested material (C22 alloy) should be described in more detail. What is most missing is its application and ISO/EN symbol.

The detailed code of the material is included in the article.

6. (Page 4) Roughness measurement parameters may be a matter of discussion. The authors record that they used a cutoff of 0.8 mm and a sampling length of 5.6 mm. Why? For Ra values that are reported in Table 6 and vary from 2 to 10 μm, the recommended measurement distance is 15 mm with a 2.5 mm for cut-off.

In future studies, I will carry out the measurements taking into account your advice.

7. (Page 8) What was the fitting function used in the graphs in Figure 3? Nonlinear surfaces are clearly visible in Fig. 3, and the data in Table 10 indicate that planar models have been studied.

Changes have been made to the article.

8. (Figure 11) Is Figure presents difference between the observed response in experiment and fitted response from model (predicted vs actual)? If yes,the question is: for which model? For the model included in Table 10? If so, why is the content presented in the wrong order? It is difficult for the reader to figure out. It is necessary to consider reordering the following subsections.

Changes have been made to the article.

9. (Figure 11) No measurement points are marked on the plots. How are they positioned relative to the surface? How exactly does the surface represent the position of the points? What are the residuals?

Changes have been made to the article.

10. (Page 8) I believe the analysis in paragraphs 242-253 and Figure 4 are unnecessary. This content does not carry any numerically validated information. I suggest to analyze the surface geometrical structure by appropriate functional parameters.

Changes have been made to the article.

11. (Page 13) Table 7 includes predicted values of Ra and MRR. On the basis of what? What model was applied? The content of the paper should include an expanded interpretation of these values. The paragraph (lines 315-319) contains not enough detailed explanation.

Estimated values were calculated with the module using in Minitap program. Changes have been made to the article.

12. In many parts of the paper, the authors write about peak current as "Amperage" or "Amper" in short form. I suggest that you always use the precise, accepted form of naming technological parameters. Replace the expression "Amperage/Amper" in the text, tables and drawings with "Peak current, A" - with the unit, if needed).

Changes have been made to the article.

13. (Page 14, line 325) What does "ideal" mean in the sentence: "When Table 8 was examined, the most ideal parameters observed for the average surface roughness and MRR were A₁B₁C₃and A₂B₂C₁, respectively."? I suggest do not use this term. Perfect things do not exist.

Changes have been made to the article.

14. (Lines: 108, 331, 394, 403, 422, 440, 441, ) "ideal"?

Changes have been made to the article.

15. (Page 14, lines 328-331) This analysis is a duplication of an earlier paragraph. It brings nothing new.

Table 8 is explained in this section.

16. (Page15-16) The models adopted (Table 10) and the ANOVA analysis do not consider the interaction. Why? It is important to include some interactions in model, e.g. "Peak current*Pulse-on time".

Changes have been made to the article.

17. (Page 16, Table 10) The models are linear: y=a₀+a₁*x+b₂*y. This is not an incorrect choice. However, the explanation for the selection of this model is absent. All three models have also weakness. They contain a constant (a₀). This means if the ampere and pulse time values will be zero (the process is off), the model will still return a value different from zero or infinity! The model without a constant should be used.

Changes have been made to the article.

Linear regression models are relatively simple and provide an easy-to-interpret mathematical formula that can produce predictions.

18. (Page 16-17) Section "3.6 Estimation of optimum MRR and Ra" appears to be incomplete. First of all, the equations are missing after the first paragraph (line 362). Secondly, there is the question: What exactly is optimization supposed to consist of? Of determining the confidence interval (CI) value for eq. (5) and (6)? Maybe, the chapter should be titled "Interval estimation for Ra and MRR" and should include calculated specific confidence interval values.

Changes have been made to the article.

19. (Page 20, lines 447-451) The indicated solution (parameters from Exp. #7) does not seem to be the optimal result, taking into account both criteria. The MRR value is one of the lowest, and it was supposed to be maximized. The adopted polyoptimization procedure does not bring the expected results.

This situation arises because the amount of material wear is calculated in grams/minute. Calculations are based on the maximum.

20. (Fig. 12) The form of the chart is not grounded. The use of a line graph that connects points is unjustified. If we rearrange the order of experiments, the shape of the line will be changed. It is necessary to use a point or bar graph in this case.

Changes have been made to the article.

21. The article ends with a Conclusion. This section is written properly but is in few parts a repetition of the abstract.

Changes have been made to the article.

1. B) Text formatting and editing comments:
2. B) Metin biçimlendirme ve yorumları düzenleme:

Page 1: The Abstract is 208 words (15 lines) and not follows exactly the authors' guidelines (200 words maximum).

Page 3, line 116: Redundant spaces in EDM machine designation.

Changes have been made to the article.

Page 3, lines 122-123: The sentence "The formula for calculation of the MMR is given as Equation (1) [26, 27]." should end with a colon, and a comma and the word "where" should be added after the equation.

Changes have been made to the article.

Page 3, lines 124-125: Missing subscript in the parameter/variable labels (W_i, W_f).

Changes have been made to the article.

Page 3, line 126: Missing a period on the end of a sentence. 

Changes have been made to the article.

Page 8, Fig. 3: Missing unit for pulse current.

Changes have been made to the article.

Table 8: The left side has a written unit (μm for Ra and g/min for MRR). Is this correct? The values are negative! Perhaps the titles should be written as follows: "S/N for average surface roughness", " Response Table for avg. Ra (μm)", "S/N for MRR" and "Response Table for average MRR"?

Changes have been made to the article.

Table 8: Is "Delta" a range? Is any reason do not write "Range"?

Changes have been made to the article.

Figure 10: Why new designations of M1, M2 and M3 were implemented for UT, SCT and DCT materials? Please use the same labels and symbols throughout the entire paper, including floats (figures and tables).

Page 16, line 366: Missing subscript in the parameter/variable labels (T_Ra and T_MRR).

Changes have been made to the article.

Page 17, line 375: Missing subscript in the parameter/variable labels (V_e, n_eff and T_dof).

Changes have been made to the article.

Page 18, line 403: Missing superscript in the parameter/variable labels (x₀).

Changes have been made to the article.

1. C) Comments to Back matter:

There is no information about patents, supplementary materials, acknowledgments or sources of funding of the study. There is missing Conflicts of Interest section.

With the necessary corrections, the article will be of an appropriate scientific level and can be recognized in the scientific community as having good quality and will have a high potential for citations.

Best Regards,
Reviewer

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper is at a good quality and the research is well detailed. However, some points need the author inputs:

1- The author based his research on average surface roughness Ra. Ra alone is not a conclusive metric of surface roughness, please include other metrics like peak-to-valley roughness (Rz). also consider area surface roughness Sa and Sz.

2- The author did not specify the pulse-off time and flushing pressure. Please include them.

Author Response

Comments and Suggestions for Authors

The paper is at a good quality and the research is well detailed. However, some points need the author inputs:

• The author based his research on average surface roughness Ra. Ra alone is not a conclusive metric of surface roughness, please include other metrics like peak-to-valley roughness (Rz). also consider area surface roughness Sa and Sz.

Changes have been made to the article.

2- The author did not specify the pulse-off time and flushing pressure. Please include them.

Changes have been made to the article.

Round 2

Reviewer 1 Report

Dear Authors,

I accept your explanations and consider them as sufficient. The changes made to the content of the manuscript are significant and add the necessary content according to the review comments.

However, please revise a few points from the previous review:

1) Please replace all the terms "ideal" that appears in the article with more appropriate ones.

2) Table 10: Your explanation of model selection is insufficient ("Linear regression models are relatively simple and provide an easy-to-interpret mathematical formula that can produce predictions.") I still suggest that the models for Ra and MRR should be replaced with a model without constant value. It can be linear models, but without constant. In my opinion, a logarithmic or log-normal model would be more advantageous in this case.

3) The changes made in Table 8 may not be sufficient or require additional details for the reader. Previous comments on this aspect remain in effect:

a) If "Delta" means range, write "Range".

b) The left-side tables have a unit (μm) for Ra and (g/min) for MRR, but the values are negative! Why? Perhaps the titles should be written as follows: "S/N for average surface roughness", "S/N for MRR". And for right-side tables: "Response Table for avg. Ra (μm)", and "Response Table for average MRR"?

Best regards,
Reviewer

Author Response

Reviewer-1

Comments and Suggestions for Authors

Dear Authors,

I accept your explanations and consider them as sufficient. The changes made to the content of the manuscript are significant and add the necessary content according to the review comments.

However, please revise a few points from the previous review:

Changes have been made to the article.

1) Please replace all the terms "ideal" that appears in the article with more appropriate ones.

2) Table 10: Your explanation of model selection is insufficient ("Linear regression models are relatively simple and provide an easy-to-interpret mathematical formula that can produce predictions.") I still suggest that the models for Ra and MRR should be replaced with a model without constant value. It can be linear models, but without constant. In my opinion, a logarithmic or log-normal model would be more advantageous in this case.

Changes have been made to the article.

3) The changes made in Table 8 may not be sufficient or require additional details for the reader. Previous comments on this aspect remain in effect:

1. b) Sol taraftaki tablolarda Ra için bir birim (μm) ve MRR için (g/dak) vardır, ancak değerler negatiftir! Neden? Niye? Belki de başlıklar şöyle yazılmalıdır: "Ortalama yüzey pürüzlülüğü için S/N", "MRR için S/N". Ve sağ taraftaki tablolar için: "Ortalama Ra (μm) için Yanıt Tablosu" ve "Ortalama MRR için Yanıt Tablosu"?
2. a) If "Delta" means range, write "Range".

Changes have been made to the article.

1. b) The left-side tables have a unit (μm) for Ra and (g/min) for MRR, but the values are negative! Why? Perhaps the titles should be written as follows: "S/N for average surface roughness", "S/N for MRR". And for right-side tables: "Response Table for avg. Ra (μm)", and "Response Table for average MRR"?

I can't make the arrangements you mentioned because it doesn't fit in the table. If the results are above one, the signal-to-noise ratio is negative.

Best regards,

Reviewer

Author Response File: Author Response.pdf