Chatter Identification of Three-Dimensional Elliptical vibration Cutting Process Based on Empirical Mode Decomposition and Feature Extraction

Round 1

Reviewer 1 Report

Paper title:

Chatter identification of three-dimensional elliptical vibration cutting process based on empirical mode decomposition and feature extraction

The reviewer's comments are as follows:

1-      Line 14, "friction reversal", please explain.

2-      Line 18, "to identify the cutting tool state", what do you mean by "cutting tool state"?

3-      Line 20, "at any point", which points?

4-      Line 36, 37, " However, research on the chatter identification has little in the non-resonant 3D-EVC machining processes", this sentence is incorrect, how researches chatter can be carried out in the non-resonant cutting?

5-      Line 38, "unstable vibration", please explain.

6-      Line 39, "fast spindle speed", please replace with "increasing the spindle speed".

7-      Line 39, "the great performance of diamond tool", please explain what do you mean by great performance.

8-      Line 40, "precision of the surface", please replace with "accuracy of the workpiece".

9-      Line 43, "friction reversal", please explain.

10-  Line 60, "a lot of noise", please recheck this expression.

11-  Line 62, "The free vibration is caused by impact during machining process", not understood.

12-   Line 101, "the cutting state of the tool", it is not of the tool only, it is of the whole machining system.

13-  Line 191, "the cutting heat signal", could you explain what do you mean by this expression? and how this signal will be used to identify the chatter occurrence?

14-   Sec. 2.2 is good, but the expected chatter frequency was not mentioned, it should be deduced from the natural frequency of the weakest element in the machining system, mostly the tool holder.

15-  Line 276, "spindle speed was set at 90 mm/min", please, recheck the unit

16-  Table 2, please check the value of the amplitude, "amplitude" can be replaced by "vibration amplitude".

17-  Line 288, "will have appeared", recheck the English.

18-  Figure 7 is not clear.

Author Response

Point 1: Line 14, “friction reversal”, please explain

 Response 1: Thank you for your question. Elliptical vibration cutting process, the cutting speed in the cutting depth direction is smaller than the chip flow out speed, and the frictional direction between the tool rake face and the chip is the same as that of the ordinary chip, and is opposite to the chip flow out direction. As the cutting speed in the cutting depth direction gradually increases, when the cutting speed in the cutting depth direction is larger than the chip outflow speed, the frictional direction between the tool rake face and the chip is reversed. Unlike normal cutting, the direction of friction is the same as the direction in which the chips flow out, which promotes the flow of chips and makes the friction a negative value.

 Point 2: Line 18 “to identify the cutting tool state”, what do you mean by “cutting tool state”?

 Response 2: The cutting state of the tool indicates three types of vibrations in which the tool is in a steady state, transition state, and chatter state during the cutting process.

 Point 3: Line 20, “at any point ”, which points?

Response 3 : Thanks for pointing it out.Any point is an arbitrary point on the intrinsic mode function that reflects the instantaneous frequency of the tool.

 Point 4: Line 36, 37, “However, research on the chatter identification has little in the non-resonant 3D-EVC machining processes”, this sentence is incorrect,how researches chatter can be carried out in the non-resonant cutting? 

Response 4: Thank you very much for your critical advice. According to the reviewer’s comments, we have made correction about the sentence. Please see lines 36 to 37 of the manuscript. Firstly, the three-way vibration displacement signal of the tool tip is collected by the displacement sensor; then converted into a frequency domain signal by Fourier transform, and the cutting state of the tool is determined according to the change of the frequency. At the same time, the empirical mode decomposition (EMD) decomposition of the vibration signal of the tool tip is performed to obtain the intrinsic mode function of the vibration signal. Then the mean square frequency and self-correlation coefficient of each intrinsic mode function are calculated. Finally, the chattering phenomenon in the non-resonant three-dimensional elliptical vibration cutting is identified.

Point 5: Line 38, “unstable vibration”, please explain

 Response 5: Thank you for your question. According to the reviewer’s suggestions, we have made explain about the “unstable vibration”. The unstable vibration of the tool refers to the unstable cutting of the tool caused by a series of unfavorable factors such as unreasonable tool selection, excessive feed rate, excessive cutting depth and excessive spindle speed during the cutting process.

 Point 6: Line 39, "fast spindle speed", please replace with "increasing the spindle speed".

 Response 6: Thanks for the reviewer’s suggestion. We modified this point based on your opinion. (Please see lines 39 of the manuscript).

 Point 7: Line 39, "the great performance of diamond tool", please explain what do you mean by great performance.

 Response 7: Thanks for your suggestion. We have made explain about "great performance". Diamond tool is a common tool used in precision machining technology. It has the advantages of high hardness and wears resistance, low friction coefficient, high elastic modulus, high thermal conductivity and low thermal expansion coefficient. It is used for difficult-to-machine materials such as non-metallic brittle materials, high wear-resistant materials, and composite materials.

 Point 8: Line 40, "precision of the surface", please replace with "accuracy of the work-piece".

 Response 8: Thanks for pointing it out. We modified this point based on your opinion. (Please see lines 41 of the manuscript.)

Point 9: Line 43, "friction reversal", please explain.

Response 9: Thank you for your question. Elliptical vibration cutting process, the cutting speed in the cutting depth direction is smaller than the chip flow out speed, and the frictional direction between the tool rake face and the chip is the same as that of the ordinary chip, and is opposite to the chip flow out direction. As the cutting speed in the cutting depth direction gradually increases, when the cutting speed in the cutting depth direction is larger than the chip outflow speed, the frictional direction between the tool rake face and the chip is reversed. Unlike normal cutting, the direction of friction is the same as the direction in which the chips flow out, which promotes the flow of chips and makes the friction a negative value.

 Point 10: Line 60, "a lot of noise ", please recheck this expression.

 Response 10: Thanks for pointing it out. We modified this point based on your opinion. (Please see lines 61 to 62 of the manuscript)

 Point 11: Line 62, "The free vibration is caused by impact during machining process", not understood.

 Response 11: Thank you for your question. We have made explain about the sentence. The free vibration is the machine system that is not driven by external forces, it can vibrate according to its own frequency. The free vibration of the machine tool has nothing to do with external factors and is related to its inherent properties.

Point 12: Line 101, "the cutting state of the tool", it is not of the tool only, it is of the whole machining system.

 Response 12: Thanks for pointing it out. We modified this point based on your opinion. (Please see lines 102 to 103 of the manuscript.)

 Point 13: Line 191, "the cutting heat signal", could you explain what do you mean by this expression?  and how this signal will be used to identify the chatter occurrence?

 Response 13: Thank you for your question. In the cutting process, almost all of the cutting power is converted into heat energy, which generates a large amount of heat, and the heat signal generated in the cutting process is called a cutting heat signal. The cutting heat signal is transmitted through the cutting temperature signal of the chip during the cutting process. Therefore, the influence of the cutting heat factor on the chatter is studied by checking the calculation of the cutting temperature theory and then measuring the cutting temperature to suppress the chatter cutting.

 Point 14: Sec. 2.2 is good, but the expected chatter frequency was not mentioned, it should be deduced from the natural frequency of the weakest element in the machining system, mostly the tool holder.

 Response 14: Thanks for pointing it out. The natural frequency of the tool holder is referred to Ref [3], here we choose the natural frequency is 50 HZ.

 Point 15: Line 276, "spindle speed was set at 90 mm/min", please, recheck the unit

 Response 15: Thanks for your suggestion. We modified this point based on your opinion. (Please see lines 276 of the manuscript.)

 Point 16: Table 2, please check the value of the amplitude, "amplitude" can be replaced by "vibration amplitude".

 Response 16: Thanks for pointing it out. The amplitude is in table 1.We modified this point based on your opinion. (Please see table 1 of the manuscript.)

 Point 17: Line 288, "will have appeared", recheck the English.

 Response 17: Thanks for your suggestion. We modified this point based on your opinion. (Please see lines 287 of the manuscript.)

 Point 18: Figure 7 is not clear.

Response 18: Thanks for pointing it out. According to the reviewer’s comments, we have made correction about the Figure. (Please see figure 7.)

Author Response File: Author Response.docx

Reviewer 2 Report

From my point of view all revisions have been made. Just a few minor flaws are still there:

Fig. 6. and Fig 7: : the captions of the three single diagrams are missing the values for the depth of cut ("Depth of cut is")

lines 331, 334, 338, 342: Roughness values NOT with index, just Ra (= capitol "R" and small "a")

390: "The experimental result shown" ? -> "The experimental results show/demonstrate"

Author Response

Point 1: Fig. 6.and Fig 7: the captions of the three single diagrams are missing the values for the depth of cut ("Depth of cut is")

 Response 1: Thanks for pointing it out. We modified this point based on your opinion. (Please see figure 6 and figure 7.)

 Point 2: lines 331, 334, 338, 342: Roughness values NOT with index, just Ra (= capitol "R" and small "a") 

 Response 2: Thanks for the reviewer’s suggestion. We have revised symbol according to the author’s advice. (Please see lines 330, 333, 337, 341 of the manuscript.)

 Point 3: "The experimental result shown"? -> "The experimental results show/demonstrate"

 Response 3: Thanks for pointing it out. We are very sorry for these mistakes we did, thanks for pointing out our mistakes. Modifications have been marked in red. (Please see lines 389 to 390 of the manuscript.)

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The coauthors have improved the article.

Just a minor comment:

In your response to comment #13, what you have described "cutting heat signal", cannot be used to predict  chatter occurrence, please delete this expression.

Author Response

Point 1: In your response to comment #13, what you have described "cutting heat signal", cannot be used to predict chatter occurrence, please delete this expression.

Response 1: Thanks for your suggestion. We have deleted this expression (Please see line 192 in the manuscript).

Author Response File: Author Response.docx