Research on the End-Milling Surface Quality of Paulownia Based on Response Surface Model in Terms of Force and Chip Morphology
, Zhanwen Wu 1, Feng Zhang 1, Chaojun Song 1, Wei Hu 1, Zhaolong Zhu 2,3, Xiaolei Guo 1 and Pingxiang Cao 1,*
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsOverall manuscript assessment: content of the manuscript in general is clear and well-written, results are based on the experimental tests and easy to understand. At the same time the authors used some terms incorrectly, the manuscript contains sections with low scientific importance. The results of surface roughness have small interest from an industrial point of view. The list of references has not been prepared in accordance with the journal requirements and contains a limited number of publications on the topic of research. The manuscript contains a sufficient amount of experimental research but the scientific and practical significance of the results is low.
1. In the body (for example line 63) and title of the manuscript authors use terms “cutting”, “longitudinal cutting”. The meaning of the term cutting is very wide, but usually longitudinal cutting is the simple cutting process when cutter moves linearly and vector of feed rate is parallel to the fibre direction. Authors studied end-milling process when tool cutters move by the cycloid trajectory and cutting is complex: from the predominantly longitudinal at the beginning (when cutter contact with wood) to predominantly end-grain cutting at the end of the process (process when cutter of the mill contact with wood; from 90-0 to 90-90 cutting by Kivimaa 1950).
2. Figure 1. It seems that you used specimens with laminated wood (it was solid?). You may use the L, R and T directions to show the fibers orientation. The 3D model of the cutting tool is not clear. It is possible to use photo image of the tool with the edges and surfaces specification. Figure 1a shows the milling process (feed rate is vector), but used cutting angles are the static cutting angles and they should be specified when tool is static. Was the rake angle negative? Sum of the cutting angles should be 90 degrees.
3. Table 1 is not clear. It was the properties of the used specimens based on the separate tests? Was hardness and strength of the used wood differ from the other studies? In what climate specimens were kept until 14.8 moisture content?
4. Line 74. Cutting depth – milling depth?
5. Please specify the producer of the used cutting tool. I suggest to modify the Table 2 to varied (input) parameters of the tests. Information about the end mill can be presented in the text. It is less important. Did you measure and control the cutting edge (main) rounding? Only one tool was used for all the tests?
6. Table 3. The key moment of the results is that difference in 1-2 μm for wood surface roughness has low importance. Especially for so soft wood as Paulownia. And the quality of the surface after milling can be based on other parameters: flatness of the surface after cylindrical milling and uncut fibers which is important for subsequent priming and painting (furniture industry).
7. Authors specified the 5 repetitions for each factors combination. Please add values of the standard deviations for F and Ra in the table 3.
8. Authors measured cutting forces in three projections (usually Fx in the direction of the main cutting force component and Fz normal component but as you want). How many data you collected during the contact the cutting edge and the wood? Forces presented in the Table 3 are mean values or maximum values? Standard deviation between repetitions is also important parameter.
9. Speed is usually vector parameter, “n” can be specifies as rotations frequency.
10. I did not find where Equation 1 used in the research. If you use multiply label please use it every were and reduce its size (Equation 2).
11. Figure 3 is not necessary, authors can specify feed rate per cutting edge in the Figure 1.
12. Information between lines 117-127 is well-known and can be reduced.
13. Line 130. Here and below authors conclusion that cutting forces have impact on the surface quality (roughness) not correct. Rotational frequency and feed rate influence on the forces through the chip thickness (Uz) but surface after milling created only at the initial stage of the contact curve of the cutting edge with wood. So Uz with forces only negligible impact of the surface roughness.
14. The question is also how projection of cutting forces on Fz (figure 2, table 3) have so high absolute values. This is also reduce the quality of the experiment.
15. Please specify variation of the data in the Figures 4-6. It is possible to use box-plots for this purpose.
16. For my opinion chip morphology section has low importance because as was mentioned in the in paragraph 13 when you vary the rotational frequency and feed rate together with milling depth you change the amount of wood to cut off. And this will not have the influence (or very low influence) on the surface roughness after milling.
17. Table 5, line 2 – Ra is 7.59, in the Table 3 it is 6.59 μm. Where is the actual data?
18. Figure 10 has no interest, quality of the model is clear from the table 6. Table 7 is also not interesting, authors can specify significance of the coefficients in the model (line 254) and save the space.
19. Conclusions. X, Y and Z direction is not clear here. Reader need to find the appropriate figures in the text body.
20. References 1, 12 are with no resource information. References 2, 14, 18 are not in the topic. Reference 20 has no pages or doi code if it is online publication.
Comments on the Quality of English LanguageEnglish language in general is clear and well-written.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsI thank the authors for their effort. I think the title should be more specific and shorter. The introduction is also brief and does not contain any information regarding the research conducted so far on the mechanical processing of Paulownia. In my opinion, it does not show the novelty in the perspective of the currently existing knowledge (perhaps it is worth pointing out the differences in relation to other species). I expect better justification. Some of the methodology is presented in a way that is not very legible (please enlarge the dimensions of the graphics), Tables 1 and 2 present values that I do not know what they refer to and how they were determined (the lack of methodology suggests literature data, but there are no references), table 2 contain data about the material, what material? Some information in the methodology is repeated, picture 3 does not add anything new. Table 3 presents results and it should not be part of the methodology. Section 3.1. has no sense. The graphics presented in the results section are difficult to read and are discussed briefly. There is no discussion, which is a basic element of scientific work, comparison with existing research and demonstration of novelties in their context. When reading it, it feels like a technical report. After reading the conclusions and the entire article, the reader is left with the question of what is really new in this article, even if there are such novelties, they are not sufficiently exposed in the discussion. Statistical methods were not included in the methodology.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript presents an interesting study on the longitudinal cutting quality of Paulownia. The work will interest the journal's readers, given the not-small application of this ultra-light wood in the last ten to twenty years.
I have the following recommendations for the esteemed authors:
1) In the Abstract, the main novelty of the study should be given more clearly - namely, the study of the cutting process of Paulownia. In this part, the main results of the research should be given more clearly.
2) The Introduction is quite limited in volume and should be expanded, in my opinion. Here, the need for research based on previous research (respectively to add references) for the cutting processes of other softwoods, as well as of Paulownia itself, should be clearly outlined.
3) There is no justification for the selected variation values of the cutting parameters in the Materials and Methods part. Please add one. Again, this would ideally be done based on previous research in the field.
4) In my opinion, without obligating authors when using D-optimal composition plans, citing the original publication would be a good idea (Box, G. E. P.; Wilson, K. B. On the Experimental Attainment of Optimum Conditions, Journal of the Royal Statistical Society: Series B (Methodological), Volume 13, Issue 1, January 1951, Pages 1–38, https://doi.org/10.1111/j.2517-6161.1951.tb00067.x). In this line of thought, I found no mention of the software used for the regression analysis.
5) In the Results and Discussion part, the comparative analysis with previous studies is reduced to confirming the direction of influence of the studied factors of earlier studies. It would be good to expand this analysis with the influence of the factors and the values obtained when cutting softwood.
6) In the Conclusions, the main novelty of the study and its main contribution should again be indicated much more clearly and distinctly.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Authors, thank you for the response and detailed descriptions. The manuscript significantly improved but still some comments and suggestions can be addressed to the Authors:
1. Effect of regional climate on specimens moisture content is interesting but usually before the tests all wood specimens should be conditioned at normal climate (20 oC, 65% RH) until the equilibrium moisture content will be reached. If the reviewer live in north and very cold climate does not mean that he will test wood always at -30 oC.
2. Effect of crack formation is well-known but it was studied only for simple cutting and low cutting speeds like several mm per second. You studied high-speed complex cutting. The presence of a crack has not been proven for these conditions before and here. And negligible effect of Uz on results authors proved themselves – by the mean Ra and its StD presented in new table 4.
3. The photo of the specimens in the response and high Fz now shows that the milling was not clear longitudinal.
4. What suggested to improve: new table 3 is too big and these data are clear, maybe try to combine it with table 4. Equation 1 has not readable elements.
5. Please think also about the terms in conclusion: cutting – milling, spindle speed – spindle rotational frequency.
Author Response
Thank you for your comments and suggestions, which were very helpful to revise and improve our manuscript entitled "Research on the Influence of the Paulownia Longitudinal Cutting Quality Based on Chip Morphology and Cutting Parameters". We have implemented the corrections you suggested in our manuscript. The yellow part with highlight of the text corresponds to the revision of reviewer#1. Please see our point-by-point responses to the comments below.
Author Response File: Author Response.pdf
