Review Reports - Features of Changes in the Parameters of Acoustic Signals Characteristic of Various Metalworking Processes and Prospects for Their Use in Monitoring

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Some clarification of the influence of random disturbing factors is necessary.

Comments for author File: Comments.pdf

Author Response

The paper discusses a material processing monitoring system based on the parameters of acoustic signals about the process. This requires selecting informative inputs to reliably characterize and model the process.

For effective control and management of the cutting process, it is necessary to know the physical nature of the phenomena occurring in the processing zone, the nature of their relationship and influence on the output parameters of the cutting process.

It is necessary to explain how the influence of random disturbing factors, which include uncontrolled changes in the physical and mechanical properties of the workpiece, is taken into account.

Response 1. Any technological process is accompanied by disturbances associated with the discreteness of the structure of materials and discreteness of the physical phenomena realized. They cannot be fully called disturbances, such is the physics of the processes. To reduce the influence of these phenomena on the results, filtering of AE signals is applied. Due to this, frequency ranges are selected where disturbances associated with the operation of other AE sources are minimized. To reduce the influence of disturbances related to the physics of the technological process itself, the RMS of signal amplitudes with different averaging period is used. However, the figures show that it is not possible to completely eliminate the influence of these disturbances. Too large averaging periods hide useful information.

In the paper, for example, the fluctuations of the signal amplitude after bandpass filtering can be seen in the figures (Figures 11; 13b; 17a,b; in the insets to Figures 19a and 21a). The results of the RMS transformations are shown in Figures 10b; 12a,b; 18b; in inset to Figure 19b. These figures also contain oscillations, showing the influence of random perturbations.

Section 2.1 has been clarified as suggested by the reviewer.

It is necessary to explain how the temperature parameter was taken into account and controlled, which is one of the most important in the material processing zone.

Response 2. The temperature in the machining zone is a very important parameter that is almost impossible to control in production conditions. Even laboratory conditions do not allow to give information about the temperature at the edge of the cutting edge. Methods of thermo-EMF control, thermistors embedded in cutters give only an approximate estimate of the temperature in the vicinity of the cutting edge. However, when the temperature of the workpiece in the cutting zone rises above a certain value, its mechanical properties begin to fall. And this already affects the parameters of AE signals. Separation of material portions begins to be accompanied by pulses that are more extended in time. The spectrum of such impulses is distorted: the amplitude of high frequencies begins to decrease. This moment is clearly reflected in Figure 17. That is, the temperature was not directly monitored, but its negative influence was displayed in the change of parameters of AE signals, which allows us to use these parameters for monitoring of technological processes.

It is also necessary to explain how the correlation of various disturbing factors was taken into account.

Response 3. Of course, correlation of perturbing factors is present. For example, along with the growth of tool wear, the temperature of the material increases and the process of chip formation changes. But the article did not set the task of differentiation of perturbing factors. The work is devoted to the search for an integral indicator showing the deterioration of the state of the technological process, which consists in the reduction of power density in the machining zone. This moment was monitored at different technological processes using the parameters of AE signals.

Clearer information is needed on the methodology for measuring AE signal parameters.

Response 4. The methodology of acoustic signal measurement is a very broad topic, widely presented in technical literature. It has its own specificity, depending on the type of primary transducers, the considered frequency range and the studied process. Within the framework of the article, the simplest methodology based on the control of vibration acceleration signals using accelerometers was applied. The methodology is designed to be applicable in a real production environment. Section 2.1 shows the composition of the hardware and an example of accelerometer installation, the main characteristics of which are presented in the table. The authors were forced to limit themselves to this information and references to literature sources due to limitations on the size of the paper. In this regard, they apologize to the reviewer.

Reviewer 2 Report

Comments and Suggestions for Authors

This work studied the acoustic signals obtained from various types of material processing, and established the relationship between the signal features and material processing process. I believe the readers will be interested in the topic. Before publication, following shortages must be overcomed to improve the overall quality of the manuscript.

1. Please provide the full name of WEDM in abstract when the abbreviation first appears.

2. In line 107 and 110, what are AC signals and VA signals? Please provide the full name.

3. Please provide the details of the acoustic emission sensor used in this work including the resonant frequency and operating frequency range. Please also show the procedure for eliminating the environmental noises in section 2.

4. The scale bar in Figure 21 is not clear.

5. The conclusions part should be more concise to show the major novelty and findings of this work. Avoid discussion.

6. It is too absolute to say “may be the only sources of information” in line 554. Also, the first conclusion can hardly serve as a conclusion because it is not directly associated with the experimental results of this work.

7. The studied characterization method using multiple AE parameters closely aligns with previous work (https://doi.org/10.1016/j.jmapro.2022.01.012, https://doi.org/10.1016/j.ijfatigue.2022.106860), and citation is recommended.

8. In line 183, “signals АЕ” should be “АЕ signals”.

Comments on the Quality of English Language

No comment.

Author Response

Please provide the full name of WEDM in abstract when the abbreviation first appears.

Response 1. WEDM - Wire Electrical Discharge Machining. The abbreviation was introduced in the abstract where it was first mentioned. It was thought to be the traditional designation for the technology.

In line 107 and 110, what are AC signals and VA signals? Please provide the full name.

Response 2. We apologize for the errors made in editing the text. The acoustic emission (AE) abbreviation is present throughout. The abbreviation is explained in Section 1.

Please provide the details of the acoustic emission sensor used in this work including the resonant frequency and operating frequency range. Please also show the procedure for eliminating the environmental noises in section 2.

Response 3. Section 1 summarizes the basic characteristics of accelerometers, including resonant frequency and linear frequency range. Section 2.1 adds information on the methods used to reduce noise associated with process discretization. In the selected frequency ranges, other noise did not exceed 4%.

The scale bar in Figure 21 is not clear.

Response 4. We have bettered the quality of the scale bar.

The conclusions part should be more concise to show the major novelty and findings of this work. Avoid discussion.

Response 5. We agree with your opinion. But here we are in conflict with another reviewer, who demands to supplement the conclusions with numerical data. We could also mention that many readers read the abstract and conclusions beforehand, only then they can look at the content. Nevertheless, the first conclusion is redone and summarized.

It is too absolute to say “may be the only sources of information” in line 554. Also, the first conclusion can hardly serve as a conclusion because it is not directly associated with the experimental results of this work.

Response 6. The response to comment 5 already states the changes to the conclusions. The words "sole source of information" have been replaced with a more modest phrase. Although there are examples where this statement is appropriate.

The studied characterization method using multiple AE parameters closely aligns with previous work (https://doi.org/10.1016/j.jmapro.2022.01.012, https://doi.org/10.1016/j.ijfatigue.2022.106860), and citation is recommended.

Response 7. Thanks for the source of information. Have read and will reference in future articles.

In line 183, “signals АЕ” should be “АЕ signals”.

Response 8. Thank you, corrections have been made.

Reviewer 3 Report

Comments and Suggestions for Authors

The paper is good and interesting. It deals with the study of physical causes that differentially affect the parameters of the acoustic emission signal in different frequency ranges, and the possibilities of using several signal parameters to monitor various metalworking processes.

However I suggest the improvements as follows:

1. Please add the quantitative results in Abstract. Also the quantitative analysis should be shown in Conclusions.

2. All symbols used in the text should be explained (like Kf, ef etc.)

3. Figures 7-20 are not clear enough. Please improve their quality and accuracy.

4. Also please describe how the data presented in Figs 7-20 were obtained from presented research equipment. Please add such info.

5. Please add the statistical analysis of the obtained results - how many tests were carried out, how many samples were tested, what is the distribution of the results, average, mean, standard deviation etc.

Comments on the Quality of English Language

Extensive editing of English language required

Author Response

However I suggest the improvements as follows:

Please add the quantitative results in Abstract. Also the quantitative analysis should be shown in Conclusions.

Response 1. Quantitative results allowed by the abstract framework have been added. Quantitative results from the analysis of the figures in the paper have been added to the conclusions.

All symbols used in the text should be explained (like Kf, ef etc.).

Response 2. Clarifying information has been introduced in the text.

Figures 7-20 are not clear enough. Please improve their quality and accuracy.

Response 3. Figures 7-20 have been improved. Some have been increased in size and others have increased in resolution.

Also please describe how the data presented in Figs 7-20 were obtained from presented research equipment. Please add such info.

Response 4. The research equipment is presented in Section 2.1. An explanation of how the digital information recorded by the research equipment and presented in the figures was processed has been added to this section.

Please add the statistical analysis of the obtained results - how many tests were carried out, how many samples were tested, what is the distribution of the results, average, mean, standard deviation etc.

Response 5. Since the studies were conducted on technological equipment using different principles of energy impact and since several different models were investigated for each technology, the total number is close to 20. The studies were conducted on different materials and different modes over a long period of time. The number of samples can be approximated as several hundreds. The article presents a narrow range of experimental material devoted to the generality of the influence of power density of energy impact on the material at realization of different technological processes on the parameters of AE signals. AE parameters are considered as a means of monitoring changes in power density. Since the article deals with the commonality of trends in different technological processes, the statistical data are given minimal attention. RMS amplitudes and the parameter K_f, about which there is little information in the technical literature, are given in the figures. Information about the range of K_f changes when critical situations occur in the processing zone is added to the conclusions. It makes sense to give statistical information when studying a specific operation, and this is a whole article.