Abrasive Water Jet Cutting of Hardox Steels—Quality Investigation

Round 1

Reviewer 1 Report

In this paper, surface quality of cuts made in Hardox™ by abrasive water jets were investigated with machining parameters While this paper has some merits, however, the paper needs to undertake major corrections in order to reach the acceptance level for its publication at the journal. Below are some specific points to consider:

• Introduction is not sufficient to describe the technical background of this research since much research already conducted in this area by other scientists. The authors did not provide in-depth helpful analysis on cutting mechanics particularly linking to the surface quality. The paper should provide a further in-depth discussion on it and the necessity of this research.

(2) Research methodology needs to describe with a detail picture of the experimental set-up.

(3) Experimental procedure is not clear. A detail diagram is required to clarify and describe the parameters mentioned in the experiment.

(4) The authors should include an image of the measured profile with a profilometer showing Ra, Rz values.

(5) How the Eq. 3 and Eq. 4 were derived?  Why only the angle is related with the Ra, Rz parameters?  The authors need to clarify this.

(6) It is not clear what is the significance of this research. The authors should focus on this point.  

(7) Language and grammar should be improved with proper scientific words.

Author Response

Dear reviewer,

thank you for your valuable comments aimed at improving the quality of our article.

We tried to improve the paper due to your comments. Please, find also our answers in a separate file.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript cannot be considered as a research article. There is missing a good introduction, which should correctly present related works. It does not present the novelty of the work. 

The methodology, research and discussion do not have any scientific features. There is poor analysis, the equations do not have physical significance. What is the contribution to science?

It is a very week article.

Author Response

Dear reviewer,
thank you for your critical commentary aimed at improving the quality of our publishing output. We tried to improve the paper due to your comments.

Please, find also our answers in a separate file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Unfortunately, it cannot be accepted that „The equations can be used both for a prediction of cutting variables and for a calculation of the cutting characteristics, such as traverse speeds, abrasive flow rates and other influencing cutting walls quality directly“ (ad Conclusions, lines 168-170).

Of course, the specific trend in the development of roughness measurement results in the WJ experiment can be experimentally described by "approximation" equations (1), (2), but not by equations (3), (4) as "analytical" prediction equations (as one-parametric dependencies). This is a fundamental error, so the text cannot be corrected.

In equations (3), (4) the physics dimensional test does not apply. Surface roughness is measured in the order of micrometers (left side of equations), not angle (right side of equations).

In equation (3), a strange term of 10^-14 mm is considered. The surface roughness is of the order of magnitude measurable in micrometers (correctly in tab. 1, tab. 2, tab. 3), but it cannot be measured in millimeters (repeatedly incorrectly in fig. 2, tab. 4, fig. 3).

Author Response

Dear reviewer,
thank you for your valuable comments aimed at improving the quality of our article.
We tried to improve the paper due to your comments. Moreover, we attached a separate file with answers to your review.

Author Response File: Author Response.pdf

Reviewer 4 Report

In the article "Abrasive Water Jet Cutting of Hardox Steels - Quality Investigation" the authors presented an interesting study on the influence of cutting process parameters of the water jet cutting of HardoxTM steels on surface quality. On the basis of the obtained results focused on the influence of processing conditions on the arithmetical mean deviation of the roughness profile (Ra) and height of the profile (Rz), mathematical models of the cutting process have been developed, which can be used to predict the quality of the surfaces machined by a high-pressure water jet. The research results obtained by the Authors have a wide range of applications.

However, the manuscript contains a few discrepancies and doubts, which should be corrected:

1. An incorrect selection of the cutting process parameters results in striation formation, especially visible in the lower part of the cutting zone. The Hardox^TM steels surfaces cut by the abrasive water-jet should be analyzed for waviness parameters, g. maximum height of waviness profile Wt and mean width of profile elements within a sampling length WSm. The publication DOI: 10.3390/ma13194277 is good example, as an inspiration.
2. All process parameters (e.g. pressure, traverse speed) should be indicated by italic font in the article.
3. Arithmetical mean deviation of the roughness profile Ra and height of the profile unevenness Rz should be indicated by italic font in the article.
4. Authors should use commonly used abbreviations when describing cutting parameters: v is for traverse speed, m_a for abrasive mass flow, p for water jet pressure
5. The article misses Characteristics of the Samples section. Information about the cut materials - Hardox^TM steels (general characteristics, chemical composition, strength, physical properties).
6. The article misses photos and description of the waterjet cutting machine used.
7. It is recommended to add a view of the roughness measuring stand to the article and determine the measuring accuracy.
8. Traverse speed is a very important parameter of the process of cutting materials with a AWJ. This is often a critical parameter that is used to control the quality of cuts in industrial machine tools like OMAX centers. The experimental data should be approximated using other regression functions (i.e.: power functions) in the future.
9. The authors determined the influence of traverse speed on the Ra and Rz roughness parameters . The paper has no theoretical justification for this phenomenon.
10. In Figures 2 and 3 there is an error in the unit of measurement on the y axis. The roughness is measured in micrometers.
11. In Figures 2 and 3 the regression equations and the value of the determination factor R² have to be included.
12. Please reformat the references according exactly to the guidelines of the Processes.
13. I propose to cite few recent papers (from 2016 to 2019) focused on the abrasive water jet cutting of Hardox^TM
14. Line 18: Remove "Modelling" from the keywords.
15. Please place the Nomenclature before the References section.
16. Lines 24-28: In the nomenclature, change the unit to mm for the following parameters: water nozzle diameter, focussing tube diameter, material thickness, focussing tube length, stand-off distance.
17. Line 30: In the nomenclature, change the unit of measurement to g/min^-1 for the abrasive mass flow rate.
18. Line 31: In the nomenclature, replace "traverse speed of jet trace on the material surface" with "traverse speed mm/min^-1".
19. Line 29: In the nomenclature, replace "pressure of liquid before liquid nozzle" with "water jet pressure MPa".
20. Add Ra and Rz to the nomenclature section.
21. Line 79: In Experimental procedure, replace the term "Pressures inside the pumping system" with "Water jet pressure p".

In my opinion the subject of the paper fits well in scope of the journal and can be published in the Processes after corrections.

Best regards,

Reviewer

Comments for author File: Comments.pdf

Author Response

Dear reviewer,
thank you for your valuable, very attentive and detailed comments aimed at significantly improving the quality of our article.
We tried to correct the paper due to your comments. Please, find the attached file with our replies to your review.

Author Response File: Author Response.pdf

Reviewer 5 Report

The presented study is at the average level of the overall processing. It has errors and gaps both in the theoretical basis and in the experimental part. I enclose my comments and questions in the file. It is necessary for the authors to clearly define their own contribution in the field of science development in the division of material by water jet. I expect the study to be complemented by a highlight of my own contribution and the novelty of my study.

Comments for author File: Comments.pdf

Author Response

Dear reviewer,
thank you for your valuable, very attentive and detailed comments aimed at significantly improving the quality of our article.
The revised manuscript includes numerous improvements in each part, which reflect corrections and additions due to comments or questions from your and others reviews.
We tried to correct the paper and answer questions due to your comments in the attached file (simplified, please see also the revised paper).

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors responded to the previous queries, however the manuscript still needs improvement. Introduction should include more literature review.

It is not clear why there is a need to differentiate and establish the relationship of the measurement of Ra and Rz as either value is acceptable in practice. The authors were asked to include an image of the surface profile obtained with a profilometer showing Ra, Rz values. However, Fig. 3 does not show the surface profile measurements showing Ra and Rz. The authors should explain the surface profiles with distinction of Ra and Rz. Without mentioning the distinction of Ra & Rz and necessity of this differentiation between Ra & Rz, the proposed research methods seem very weak. Please cite the below paper during the explanation of  this issue:

[Ref] M. Azizur Rahman, Mustafizur Rahman, A. Senthil Kumar, Chip Perforation and ‘Burnishing–like’ Finishing of Al Alloy in Precision Machining, Precision Engineering, 50, pp. 393-409

Furthermore, the manuscript still has ambiguity that needs detail explanation. Below are some points:

1. In Abstract, the last line mentioned as “Equations were compared with experimental data and their overall uncertainty has been evaluated and presented” should be rewritten. Moreover, the authors should mention what are the outcomes and scientific contributions from this research so that it can be applied to other related applications.
2. Figure1 does not clearly show the process. Labelling of the components is not provided.
3. Author should also include a schematic diagram (for example shown in Ref.16) so that readers can understand the various experiments set up distances and parameters

[16] Rishi Pahujaa, M. Ramulua, Mohamed Hashish, Surface quality and kerf width prediction in abrasive water jet machining of metal-composite stacks   Compos. Part B Eng. 2019, 175, 107134.

4. It is not clear how the authors measured the cut surfaces as shown in Table 4.It should be explained clearly.
5. Moreover, there is no prior mention about what and how declination angle values measured. Is it same as Angle of impact θ? This should be clearly discussed. A clear image/sketch is required.
6. It is not clear “the results can be compared with model presented by Hlaváč [17]”. What model is referring? How is the comparison done?
7. In Table 5, mentioned typical series of roughness values Ra4, Rz4 (abrasive mass flow rate 220 g/min- and pressure 380 MPa are typical technological parameters used for cutting). How did the authors make this generalization? A reference should be included.
8. It is not clear what is “typical graph of relation” between traverse speed and surface roughness?
9. How the Equation (1) and (2) developed? It shows x1 (ma), x2 (p) is constant 220 g/min and 380 MPa in table 5.
10. What is the difference between the regression model (y= 0.0543x+17,503 and y= 0.013x+2291) shown in Figure 4 and with the Equation (1) and (2) proposed?
11. Please include a clear schematic diagram to explain the procedure of measurements of the angle of declination of the jet.
12. The ‘Discussion’ is not clearly focused. The authors should discuss their results with more scientific explanation.
13. In conclusion, “The largest influence of the monitored technological parameters on the roughness (Ra, Rz) was found for the mass flow of the abrasive, smaller influence was revealed for the cutting speed v.”. The authors should mention the reason for this influence.
14. “Derived regression models (Eqs. 1 and 2) show linear relationships”. It is not clear how these can be utilized for scientific phenomena which are mostly follow ‘non-linear’ pattern. This point should be explained.
15. “The models can be used both for a prediction of cutting variables and for a calculation of the cutting characteristics, such as traverse speeds, abrasive flow rates and other influencing cutting walls quality.” It is not clear as ‘cutting variables’ are something new here. It has not been mentioned before.
16. “The achieved results are utilizable for improvement of the control software of the CNC machines used for water jet and abrasive water jet cutting and complement the existing solutions in the scientific field and can be used to reduce operating costs and increase the economic efficiency of production systems with AWJ technology.” The authors need to justify this statement. How the improvement of the control software will be done?
17. Remove the future work from the ‘conclusion’. The paper should focus more on research mentioned in the current manuscript.

Author Response

Dear Reviewer,

thank you so much for valuable comments aimed at improving the quality of our article. Please, see the attached file.

Best regards,
Authors

Author Response File: Author Response.pdf

Reviewer 2 Report

The submitted revised manuscript has relatively improved. However, some comments have been inadequately responded. Overall, the revised manuscript has not high interesting level of structure and novelty. Hence, I strongly recommend rejecting the revised manuscript. The paper lacks fundamental physical aspects. E.g. compare the tightness of conformity in Fig. 4 and Fig. 5. It cannot be equal to one (Figure 5). Furthermore, equations (1) to (4) have no physical significance, look at the exponents minus 10 and 14.   It loses its real significance. In table 2 are the speeds v+ and v- why? This paper is written very badly from a scientific point of view. Therefore, I strongly insist on the rejection of this paper.

Author Response

Dear Reviewer,

thank you so much for valuable comments aimed at improving the quality of our article.
Authors are very grateful for these points. The mistake happened as the calculation was performed with error in the data file entering the regression. We have re-calculated and corrected the regression and tightness of conformity as you can find in Figure 5. Thank you so much for the valuable comments aimed at improving the quality of our article.
Regarding "v+" and "v-" in Table 2: Transverse speeds v were used for sample thicknesses of 10 and 15 mm; v+ are increased speeds for 6mm samples because the speeds v for 6 mm sheet metal would leave minimal roughness and at the same time almost identically rough cut surfaces. Traverse speeds v- were used for 40mm sheet metal, as v would not be enough to cut the plate, so these decreased speeds were chosen.

Best regards,
Authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Ad Article „Abrasive Water Jet Cutting of Hardox Steels – Quality Investigation“

I really appreciate the opportunity to review the paper for the Journal Processes, so as not to reduce the quality of the prestigious journal, I do not recommend to publish it.

For example and concretlly (Conclusions 240-241 lines): „Simultaneously, the linear relationships (Eqs. 3 and 4) have been found also between declination angle values and roughness parameters Ra and Rz.“

The structure of the cut material is diverse, the system is multi-parametric. Authors try to demonstrate a direct, linear relationship between roughness and the size of the declination angle. But where exactly is the only, unambiguous, significant, declension angle „between the impinging jet axis and tangent to the striation curve at the selected depth“? Schema is missing. Example of a photograph of striations on the wall of the sample, ie on a section created by the action of a waterjet. Striations are only curved. However, the curvature may be different in different parts of the arc. Mathematically speaking: if we want to determine the degree of curvature of the arc of a given curve, it is also necessary to consider the length of this arc! Mathematicians, therefore, define the average curvature of a curve. The smaller the length of the arc, the more accurately the average curvature will characterize the curvature at different points. Of course, the greater the average curvature of the curve, the more the curve will deviate from its tangent. Only then can the dependence of the average curvature of the striations on the system parameters be investigated.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

thank you so much for valuable comments aimed at improving the quality of our article. To make clear method of the declination angle calculations, we added part with scheme and description.
Regarding more general comment - of course, abrasive water-jet cutting is a multiparametric process where the quality of the output characteristics relies on the inputs. That has been proven by various experiments and theoretical analyses and authors also personally know that topic.
Yet there are simultaneously numerous attempts of creating the models that characterize the cut area quality under specific conditions with regard to material type and thickness; technology head traverse speed and other parameters; the abrasive mass flow rate, grain size and many others. Our work is aimed to complement experiment-based models present in some other research works as some readers maybe appreciate such kind of information. In our opinion, the study of parameters in the presented combination and range is unique and the models under those conditions work effectively.

Best regards,
Authors

Author Response File: Author Response.pdf

Reviewer 4 Report

The Authors are to be congratulated for greatly improving their submission. Now the content of the revised article is much more precise, consistent and comprehensible and has more potential to be well cited. However, the manuscript contains a discrepancy, which should be corrected.  An error has appeared in Figure 5. For the cases under consideration, R² should not take the value equal to 1. I ask the authors to recalculate the value of the determination factor.



In my opinion the subject of the paper fits well in the scope of the journal and can be published in the Processes after correction.



Best regards,

Reviewer

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Authors are very grateful for your suggestion. The mistake happened as the calculation was performed with error in the data file entering the regression. We have re-calculated and corrected the regression and tightness of conformity as you can find in Figure 5. Thank you so much for the valuable comments aimed at improving the quality of our article.

Best regards,
Authors

Author Response File: Author Response.pdf

Reviewer 5 Report

The authors, within their means, replied by completing the required data, descriptions and explanations, which I asked of them. An exception is the addition of other measured parameters of the cultivated area after division by water jet. I reckon they didn't have them available anymore. The overall completion of information is sufficient for me.

Author Response

Dear Reviewer,

thank you so much for valuable comments aimed at improving the quality of our article.

Best regards,
Authors