Determination of the Shear Angle in the Orthogonal Cutting Process

Round 1

Reviewer 1 Report

In this article, the authors determine the shear angle by experimental, analytical and numerical simulation methods, and it is an interesting work. However, since the shear angle has been studied quite extensively, the work does not highlight its differences and advantages from other works, and the innovation points need to be further clarified. Therefore, the article needs to be improved before published in JMMP. The related questions are as follows:

1.      Sections 1 and 2 need to be combined. The content of the second section is also part of the introduction.

2.      In Section 2, the authors present the previous analytical, experimental and numerical methods for shear angle determination, respectively. However, it is not explained how the methods used in this paper are different from the previous methods. If the methods used in this paper are the same as the previous methods, what is the main innovation of this paper? Or what is the major difference between this paper and other studies?

3.      In lines 223 and 224, “Preformed copper pins are pressed into the bores”, what is the purpose of using copper pins?

4.      As we all know that tool wear affects the experimental results, so how can tool wear be ignored in the experiment?

5.      In line 300, what doe τ_t represent in Equation (11)?

6.      In lines 301 and 302, it hard to understand the direction of Fx and Fz, etc. Please mark the coordinate system in Figure 2, a.

7.      Please list the material parameters of cutting tool.

8.      How is the heat transfer between the tool and the workpiece calculated in the simulation?

9.      Please give the geometry of the workpiece and tool in the simulation model.

10.  According to Figure 5, it can be found that the shape of the chip is not yet stabilized (the compression ratio in each region is clearly not consistent), so the shear angle obtained in the simulation is inaccurate. In order to obtain more accurate results, the cutting simulation time should be extended, and the shear angle measurement should be performed when the shape of the chip is stable.

11.  The results and discussion section are more like a results presentation and lacks in-depth discussion.

12.  In lines 371 and 372, “The largest scatter of the measured values for the shear angle does not exceed 11% (see Figure 6).” It is hard to see the values from Figure 6, would better list them in table. Same in Lines 382.

13.  In lines 390-392, “A comparison of experimental and calculated values shows that the calculated values of shear angles for all of the cutting speeds and tool rake angles under study give somewhat overestimated results compared to the experimental values.” The results and discussion section are not a simple description of the results, but requires an analysis of the causes of such results. So, the reasons for the overestimated results need to be given.

 

14.  In lines 405-408, “One material model parameter - power coefficient of thermal softening m and the friction model parameter - friction coefficient shows practically absence of any influence on the shear angle value (see Figure 8, e and Figure 8, f). Thus, it is quite logical to use constant values, previously defined, of these two parameters in further simulations of the studied cutting process.” According to Figure 8, e, it can be found that power coefficient of thermal softening m has an effect on the shear angle (it just does not intersect with the experimental value). So, is this conclusion too absolute?

Author Response

Answers to the comments of Reviewer #1:

The authors are very grateful to Reviewer #1 for meticulously reviewing and interpreting the content of the paper.

Reviewer #1: In this article, the authors determine the shear angle by experimental, analytical and numerical simulation methods, and it is an interesting work. However, since the shear angle has been studied quite extensively, the work does not highlight its differences and advantages from other works, and the innovation points need to be further clarified. Therefore, the article needs to be improved before published in JMMP. The related questions are as follows:

English language and style are fine/minor spell check required

• English level checked and some corrections have been performed as recommended by the reviewer.

1. Sections 1 and 2 need to be combined. The content of the second section is also part of the introduction.

• The section 1 is combined with the section 2 as recommended by the reviewer. All changes carried out in the paper are marked in red font.

2. In Section 2, the authors present the previous analytical, experimental and numerical methods for shear angle determination, respectively. However, it is not explained how the methods used in this paper are different from the previous methods. If the methods used in this paper are the same as the previous methods, what is the main innovation of this paper? Or what is the major difference between this paper and other studies?

• For analytical determination of the shear angle, the previously developed analytical cutting model [25], which takes into account friction in the secondary and tertiary cutting zones, is used. In this way, the analytical model used differs significantly from the previously used ones for calculating the shear angle. To determine the shear angle by numerical simulation of the cutting process, a new technique is used. This technique is based on the hypothesis of existence the generalized parameters of the constitutive equation used as parameters of the machined material model. In other words, it is assumed that there exists a non-empty set of the plurality intersection the parameter sets of the constitutive equation defined for different cutting process conditions. To determine the generalized parameters of the machined material model, a software-developed algorithm for finding the plurality intersection of these parameters sets is used. The sets of constitutive equation parameters are determined by DOE (design of experiments) and refined by subsequent multiple iterations.
• The application of the above analytical and numerical cutting model to determine the shear angle allows the authors to consider the article presented for consideration as having significant and innovative differences from the known publications. In addition, among the known publications, there are practically no articles comparing experimental, analytical, and simulation methods for determining the shear angle simultaneously.

3. In lines 223 and 224, “Preformed copper pins are pressed into the bores”, what is the purpose of using copper pins?

• The purpose of using copper pins in holes is to prevent premature deformation of the near-surface layers of the machined material as the tool nears the holes. If the holes created to break parts of the workpiece are left empty when the tool passes over them, premature deformation of these holes will occur as the tool approaches. In this case, the chip root will be deformed and, of course, does not correspond to the chip root in the real cutting process. Therefore, the holes must be filled with a material that, on the one hand, will prevent premature deformation of the thin wall of these holes and, on the other hand, will be able to deform precisely at the moment the tool passes over the hole. As numerous experimental tests have shown, it is the use of copper pins that ensures the fracture of the hole wall as the tool passes over it (see Figure 2, b). This ensures an almost non-deformed shape of the chip root.

 

4. As we all know that tool wear affects the experimental results, so how can tool wear be ignored in the experiment?

• There is absolutely no doubt that tool wear has an enormous influence both on all characteristics of the cutting process, including the shear angle, and on the running of the process as a whole. However, studying the effect of tool wear on the shear angle is not the subject of the proposed paper. In addition, the consideration of tool wear as a separate influence parameter in experimental, analytical, and simulation methods for determining the shear angle implies both significant time consumption and a significant increase in the paper's volume. The authors plan to carry out such studies and present the results in the paper.

5. In line 300, what doe τt represent in Equation (11)?

• It was a mistake caused by the authors. Instead of t_t, it must be t_S. This discrepancy is corrected in equation 11.

6. In lines 301 and 302, it hard to understand the direction of Fx and Fz, etc. Please mark the coordinate system in Figure 2, a.

• The coordinate system is shown in Figure 2, a and Figure 2, b as recommended by the reviewer.

7. Please list the material parameters of cutting tool.

• The material parameters of the tool are additionally given in Table 1 as recommended by the reviewer.

8. How is the heat transfer between the tool and the workpiece calculated in the simulation?

• To perform numerical simulation of the cutting process a FE-model was developed in the FEM software environment DEFORM 2D/3D™ v. 11.0 (SFTC, Columbus, OH, USA) [73]. Heat transfer between the tool and the workpiece is automatically calculated in this integrated simulation environment, when initializing the need to calculate the heat transfer. In this case it is necessary to set the thermal properties of the materials to be contacted. The thermal properties of the materials to be contacted must be set (see e.g., Table 1).

9. Please give the geometry of the workpiece and tool in the simulation model.

• The geometry of the workpiece and tool is additionally shown in Figure 4. The linear dimensions of the tool in this model are irrelevant, since the tool is defined as a rigid body.

10. According to Figure 5, it can be found that the shape of the chip is not yet stabilized (the compression ratio in each region is clearly not consistent), so the shear angle obtained in the simulation is inaccurate. In order to obtain more accurate results, the cutting simulation time should be extended, and the shear angle measurement should be performed when the shape of the chip is stable.

• Figure 5 shows only the schemes of shear angle measurements. Shear angle measurements based on the numerical simulation of the orthogonal cutting process were performed on the finally formed chip. Figure 5 is corrected. It shows the chip shapes on which the measurements were carried out.

11. The results and discussion section are more like a results presentation and lacks in-depth discussion.

• In the third section of the article, "Results and Discussion," the authors' reasoning about the evaluation of the obtained results and the possible reasons for the difference between the experimental and modeled values of the shear angle, which is a discussion part of this section, have been added. These places in the text are marked in red font.

12. In lines 371 and 372, “The largest scatter of the measured values for the shear angle does not exceed 11% (see Figure 6).” It is hard to see the values from Figure 6, would better list them in table. Same in Lines 382.

• The measurement scatter value is undoubtedly better represented by a measurement table. However, in this case it is difficult to estimate the influence of cutting speed and tool rake angle on the shear angle and chip compression ratio with regard to Figure 6 and Figure 7. Therefore, the authors think that in this case it would be better to present these measurement results in the form of diagrams. However, in case the reviewer insists on presenting the results as a table, the authors could provide the measurements tables additionally to the dependency diagram in parallel.

13. In lines 390-392, “A comparison of experimental and calculated values shows that the calculated values of shear angles for all of the cutting speeds and tool rake angles under study give somewhat overestimated results compared to the experimental values.” The results and discussion section are not a simple description of the results, but requires an analysis of the causes of such results. So, the reasons for the overestimated results need to be given.

• In the paper's text, a discussion of the possible reasons for the difference between the experimental and modeled values of the shear angle has been added. These places in the text are marked in red font.

14. In lines 405-408, “One material model parameter - power coefficient of thermal softening m and the friction model parameter - friction coefficient shows practically absence of any influence on the shear angle value (see Figure 8, e and Figure 8, f). Thus, it is quite logical to use constant values, previously defined, of these two parameters in further simulations of the studied cutting process.” According to Figure 8, e, it can be found that power coefficient of thermal softening m has an effect on the shear angle (it just does not intersect with the experimental value). So, is this conclusion too absolute?

• Yes, the power coefficient of thermal softening m has some effect on the shear angle. And, of course, the fact that it does not intersect the experimentally measured value of the shear angle is of no special importance, since the influence of the coefficient m is realized together with the influence of other parameters of the constitutive equation. However, the effect of this coefficient on the shear angle is insignificant compared to the influence of other parameters of the constitutive equation on the studied cutting characteristic. Especially this influence is insignificant within the change limits of the coefficient m, which is possible and acceptable to use in the numerical simulation of the cutting process (from about 0.8 to 1.3). These considerations are added to the text of the paper’s revised version (lines 447 - 457) and marked in red font.

Reviewer 2 Report

- Extensive work done and the outcome would help researchers and engineers in similar field. 

- Minor changes could be adopted:

- Reduce the number of long sentences which complicate the flow of the sentence. E.g: line 29-32; Line 38 [could be removed]....

- The acronyms/symbols in Figure 1 needs to be labelled or identified beforehand. 

- Error bars calculation could be explained in the materials section. What 's the confidence interval? which method of analysis was used? is it median or mean?

- Additional statistical analysis could confirm the significance or non-significance of the differences. 

- Most Figures  could be relabelled to state what it is exactly instead of what to interpret from them. Example: Figure 5: FE Model of ........ showing the .....; Figure 6: The change in shear angle with respect to cutting speed and rake angle.; Figure 7, 8, 9, 10 : similar change as 6. 

- The conclusion could be supported with statistical analysis data and could be redone in bullet points so highlight the specific conclusions. 

Author Response

Answers to the comments of Reviewer #2:

The authors are very grateful to Reviewer #2 for meticulously reviewing and interpreting the content of the paper.

Reviewer #2:    Extensive work done and the outcome would help researchers and engineers in similar field. Minor changes could be adopted:

1. English language and style are fine/minor spell check required

• English level checked and some corrections have been performed as recommended by the reviewer.

2. Reduce the number of long sentences which complicate the flow of the sentence. E.g: line 29-32; Line 38 [could be removed]....

• The paper's text has been checked for long sentences. Some of these sentences are shortened, as is the sentence the reviewer mentioned (see lines 29-32 in the first version of the paper). The sentence on line 38 has been deleted. All changes carried out in the paper are marked in red font.

3. The acronyms/symbols in Figure 1 needs to be labelled or identified beforehand.

• The symbols depicted in the Figure 1 are described in the figure caption.

4. Error bars calculation could be explained in the materials section. What 's the confidence interval? which method of analysis was used? is it median or mean?

• The description of error bars calculation is given in the materials section as recommended by the reviewer. Since no significant discrepancies were observed among the measured values of the shear angle and chip compression ratio, the mean was used as a representative value of these measured data.

5. Additional statistical analysis could confirm the significance or non-significance of the differences.

• Undoubtedly, additional statistical analysis can confirm the significance or insignificance of the differences in the measured values of the shear angle and the chip compression ratio. However, the measured data show a clear monotonic change in their values depending on the cutting speed and the tool rake angle. In this case, according to the authors opinion, there is no doubt about the certainty of the measured values. Therefore, the authors suggest that additional statistical analysis in our particular case would not be able to significantly refine the obtained experimental dependencies.

6. Most Figures could be relabelled to state what it is exactly instead of what to interpret from them. Example: Figure 5: FE Model of ........ showing the .....; Figure 6: The change in shear angle with respect to cutting speed and rake angle.; Figure 7, 8, 9, 10 : similar change as 6.

• Figure captions from 5 to 10 are reformulated in accordance with the reviewer's recommendation.

7. The conclusion could be supported with statistical analysis data and could be redone in bullet points so highlight the specific conclusions.

• The conclusion is presented in bulleted paragraphs, which highlighted specific conclusions as recommended by the reviewer. In the conclusion, the differences in the shear angle determination by different methods are also given.

Round 2

Reviewer 1 Report

The authors have revised the paper properly. I congratulate the authors for their excellent work. It can be published in JMMP.