Process-Integrated Component Microtexturing for Tribologically Optimized Contacts Using the Example of the Cam Tappet—Numerical Design, Manufacturing, DLC-Coating and Experimental Analysis

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. It would be helpful to mention the type of engine that corresponds to the cam tappet parameters used in this work (Tables 1 and 2).

2. The reason for selecting 500 rpm for the full 3D simulation should be elaborated further. 

3. It is not clear how the ranges (or "parameter space") for the parameters used for the LHS experimental design were determined. This point needs to be addressed.

4. The images of the textured surfaces should be provided. This is important to check the integrity of the manufacturing process. Preferably, SEM images should be provided. The images shown in Table 7 and Fig. 4 are not sufficient.

5. It is not clear why the DLC coating for the textured surfaces led to higher friction while that of the non-textured surface, it was lower. The authors attribute this effect to the manufacturing process but the explanation is not clear. This point needs to be elaborated further in detail. 

6. In real application, it would not be feasible to expect positive effect of the coated textured surface after a long running-in period. Therefore, polishing would be the reasonable option. In this regard, the authors should provide more explanation about how much to polish, method to polish, etc.

Author Response

1. It would be helpful to mention the type of engine that corresponds to the cam tappet parameters used in this work (Tables 1 and 2).

Thank you very much for this comment. The cam geometry was derived from profilometric measurements of an BMW K48 camshaft. We mentioned this in the tables and added the description.

2. The reason for selecting 500 rpm for the full 3D simulation should be elaborated further. 

We selected this load point because this is where the minimum lubrication gap at the cam tip contact and at the same time the most solid friction occurs, which makes the load case particularly interesting regarding wear in the application. Accordingly, the greatest influence of the cam edges is also to be expected, which would differentiate the simulation from the 2D simulation. We have included the reason for the selection.

3. It is not clear how the ranges (or "parameter space") for the parameters used for the LHS experimental design were determined. This point needs to be addressed.

Many thanks for the tip. The parameters are based on the findings from preliminary work ([32] Marian) on the same cam tappet contact but have been extended somewhat. The textures for the flank contact have been extended due to the larger contact area. We have now included this with the source.

4. The images of the textured surfaces should be provided. This is important to check the integrity of the manufacturing process. Preferably, SEM images should be provided. The images shown in Table 7 and Fig. 4 are not sufficient.

Thank you for pointing this out, we were actually focusing more on the tool and the resulting wear rather than the textures on the manufactured tappet. We have now added a SEM image that shows the limitations of the manufacturing process. We have also captured the geometry of the different texture patterns using laser scanning microscopy and added figure 8. We have added the procedure accordingly in the methods section.

5. It is not clear why the DLC coating for the textured surfaces led to higher friction while that of the non-textured surface, it was lower. The authors attribute this effect to the manufacturing process but the explanation is not clear. This point needs to be elaborated further in detail. 

We assume that the tribologically unfavorable sharp-edged surface areas from the manufacturing process are also protected from wear by the DLC coating and therefore have a negative effect on the contact behavior. The harmful surface areas are therefore not smoothed as quickly, and the running-in period is considerably extended (as can be seen in the COF curves). We have now described this in more detail. The additional figures 6, 8 and 12 also clarify our interpretation.

6. In real application, it would not be feasible to expect positive effect of the coated textured surface after a long running-in period. Therefore, polishing would be the reasonable option. In this regard, the authors should provide more explanation about how much to polish, method to polish, etc.

Depending on the application, this is certainly true, which is why we have already mentioned the subsequent polishing process. However, this was not the focus of our work, which is why we did not go into this aspect in more detail and cannot make any statement about a suitable process for our coating. However, we have included this aspect as an interesting research question for the future.

Reviewer 2 Report

Comments and Suggestions for Authors

In the manuscript "Process-integrated component micro texturing for tribologically optimized contacts using the example of the cam tappet – Numerical design, manufacturing, DLC coating and experimental analysis", the tribological optimization of patterning and DLC coatings through numerical and experimental approaches from a production engineering perspective is described. On the other hand, results and discussions are lacking. Major revisions need to be addressed before the paper is to be accepted for publishing in this journal.

- Detailed comments are as below:

1. There is no specific information about the selected pattern, such as T_g, R_l1, T_l, R_l2, and R_g.

2. The friction coefficient of DLC after the run-in process was lowered. In general, the run-in of DLC occurs due to passive roughening of the surface or is a factor of roughness. Why is the friction coefficient of DLC lowered? What do the coefficient of friction and wear diameter shown in Figure 5 mean? It is common to represent the friction coefficient at steady state after a run-in period.

3. Where are the results from long-term testing that claim the textured a-C:H layer significantly reduced tappet wear?

4. Comparison and discussion of computational and experimental results are necessary. In order for simulation discussions to be appropriate, the reliability of the calculation results must be verified.

Author Response

1. There is no specific information about the selected pattern, such as T_g, R_l1, T_l, R_l2, and R_g.

Many thanks for the hint. We have now described the texture patterns used in more detail and added LSM images of all textures produced.

2. The friction coefficient of DLC after the run-in process was lowered. In general, the run-in of DLC occurs due to passive roughening of the surface or is a factor of roughness. Why is the friction coefficient of DLC lowered? What do the coefficient of friction and wear diameter shown in Figure 5 mean? It is common to represent the friction coefficient at steady state after a run-in period.

We assume that the tribologically unfavorable sharp-edged surface areas from the manufacturing process are also protected from wear by the DLC coating and therefore have a negative effect on the contact behavior at the start of the tests. The harmful surface areas are therefore not smoothed as quickly, and the running-in period is considerably extended (as can be seen in the COF curves). We have now described this in more detail. The additional figures also clarify our interpretation. We agree with you about the steady state friction coefficient, but the challenge is that the uncoated textures wear quite quickly in the test and then no real texture effect can be determined. To keep the results comparable, we therefore chose shorter test durations and determined the mean value of the entire test. The diameter is that of the wear calotte on the ball. We have also described this in the caption.

3. Where are the results from long-term testing that claim the textured a-C:H layer significantly reduced tappet wear?

In the previous version of the manuscript, we only showed the wear on one image as an example, as the difference is very clear, as is typical for coatings. While no wear can be measured on the coated tappet, it can be recognized with the naked eye on the uncoated tappet. However, an exact measurement of the wear volume is unfortunately not practical from a metrological point of view (no reference plane for the topography measurement and too little wear for a gravimetric measurement). We have now created additional LSM images that show the difference very clearly.

4. Comparison and discussion of computational and experimental results are necessary. In order for simulation discussions to be appropriate, the reliability of the calculation results must be verified.

It should be pointed out at this point that the simulation results should not be compared directly with the model tests. Instead, these must be considered independently, which is why we have not made any direct comparisons here. The simulation model was compared with models from the literature (model contacts and cam tappet model test bench) in the preliminary work mentioned. For the special issue, we wanted to focus on the results of the DFG priority program. Originally, tests on a cam tappet test bench were also planned, but unfortunately these were not carried out due to a malfunction of the test bench. The alternative model test was chosen to demonstrate fundamental differences, which was successful in this form. However, a transfer to the simulation is of course not permissible. Unfortunately, this limitation remains, but due to the special issue we have decided to include the results without describing direct correlations. We have adapted the text slightly to point this out.

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for involving me for the reviewing of the revised manuscript entitled "Process-integrated component micro texturing for tribologically optimized contacts using the example of the cam tappet – Numerical design, manufacturing, DLC coating and experimental analysis".The paper is very interesting and well written. However, there are still some issues that need to be answered before publication. 

 

Major problems:

1) The author should provide the overall morphology of the textured tappet after preparation. Furthermore, it is suggested to add a preparation process in Figure 1. 

2) The author should provide SEM and EDS images of DLC, as well as the microhardness after preparation. 

3) The author should provide a schematic diagram and photos of the friction testing machine to explain why it can be used to simulate the cam tappet contacts. 

4) Section2.3:  variants T_g and R_l1 and unfavorable variants (R_g, T_l and R_l2) were used. Why are they naming it that way? It is not conducive to reader understanding and reading. Suggest author to list them in a table. 

 

 

Other problems:

1) Suggest modifying the keywords in the descending order of scope and importance. Tribology is too large. 

2) When abbreviations first appear, the full name should be provided, e.g. LHS in Page5 Line185. 

3)  Fig. 5: The layouts can be improved. Some items are not clear enough to see. Suggest the author to further enlarge the image. In addition, why is the second legend a short line? Suggest author to replace it with a word, like original. 

4)  Fig. 6: The layouts can be improved.  Suggest the author to further enlarge Figure b and c. 

Comments on the Quality of English Language

Minor editing of English language required.

Author Response

Major problems:

1) The author should provide the overall morphology of the textured tappet after preparation. Furthermore, it is suggested to add a preparation process in Figure 1. 

 

Thank you for the helpful hint. We have included a description of the process steps. In addition, we have added SLM images of all texture patterns after their production at representative points. For the shallow texture patterns R_g, T_l1 and T_l2, these hardly differ over the tappet radius. For the deeper texture patterns T_g and R_l (for R<10mm), the textures in the edge areas deviate more strongly in some cases due to the radial material flow. We have visualized the limitations at the example rectangle texture with a further SEM image. However, these areas lie outside the friction track selected for the ball on disc tests.

2) The author should provide SEM and EDS images of DLC, as well as the microhardness after preparation. 

We made a FIB cut and included the corresponding SEM and EDS images. These clearly show that the layer structure is as planned. We also measured the microhardness of the coating.

3) The author should provide a schematic diagram and photos of the friction testing machine to explain why it can be used to simulate the cam tappet contacts. 

We have added an illustration of the test bench used and its function in Figure 3 It must be pointed out that the simulation results must not be compared directly with the model tests or the real cam tappet contact. Instead, these must be considered independently, which is why we have not made any direct comparisons here. For the scope of the selected special issue, we wanted to focus on the results of our DFG priority program (see funding). Tests on a cam tappet test bench were originally also planned there, but unfortunately these were not carried out due to a malfunction of the test bench. The alternative model test was chosen to demonstrate fundamental differences, which was successful in this form. However, as with all pure modelling tests, it is of course not possible to transfer the results to the simulation or the real application. Unfortunately, this limitation remains, but due to the special issue we have decided to include the results without describing direct correlations. We have adapted the text to point this out.

4) Section2.3:  variants T_g and R_l1 and unfavorable variants (R_g, T_l and R_l2) were used. Why are they naming it that way? It is not conducive to reader understanding and reading. Suggest author to list them in a table.

We have now described the texture patterns used in more detail and added LSM images of all textures produced in figure 8. Thank you for the comment.

Other problems:

1) Suggest modifying the keywords in the descending order of scope and importance. Tribology is too large. 

Thanks for the comment. We have removed Tribology as a keyword and adjusted the order.

2) When abbreviations first appear, the full name should be provided, e.g. LHS in Page5 Line185. 

We have reviewed the abbreviations accordingly and written them out when they first appear.

3)  Fig. 5: The layouts can be improved. Some items are not clear enough to see. Suggest the author to further enlarge the image. In addition, why is the second legend a short line? Suggest author to replace it with a word, like original. 

Many thanks for the comment. We have adjusted the illustration and added "uncoated" to the legend in line with the other illustrations.

4)  Fig. 6: The layouts can be improved.  Suggest the author to further enlarge Figure b and c. 

We have completely revised the figure and have now also added LSM images to better visualise the wear.

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript is devoted to numerical optimization, production and coating of textured tappets. There are the following remarks:

1. How does coating thickness affect tribological test results?

2. How thick is the DLC coating? What is the thickness of Cr adhesion layer, CrWC graduated interlayer and WC backing layer?

3. Have you checked the uniformity of the coating thickness on the textures?

4. In Discussion, the authors write “In tribological contacts, a high roughness of the coating often leads to high friction and thus abrasive wear of the counterbody, if the coating exhibits a higher hardness than the contact partner, which in the case of the a-C: H coating against steel.” But numerical values ​​of roughness and hardness are not given.

5. Why did the authors choose DLC coatings?

6. Fig. 5 - the symbols along the horizontal axis are very difficult to interpret. It is necessary to add explanations to the figure caption  or change it to other symbols that are more understandable.

Author Response

1. How does coating thickness affect tribological test results?

We have planned a total coating thickness of 2.5-3 µm for our coating system, which corresponds to a typical DLC coating according to industrial standards. However, the coating development was not part of our work, which is why we cannot make any exact statements on this. However, we assume that the tribological behavior hardly changes even with slightly thicker or thinner coatings as long as the coating is not worn. The service life could possibly be increased by increasing the coating thickness. We have now added more detail to the characterization of the coating in the manuscript.

2. How thick is the DLC coating? What is the thickness of Cr adhesion layer, CrWC graduated interlayer and WC backing layer?

We made a FIB cut with corresponding SEM and EDS images and determined the resulting layer thicknesses. The exact transition from a-C:H:W to a-C:H is difficult to recognize in the SEM image, but can be estimated using the EDS measurement. We have added the figures and results to the manuscript.

3. Have you checked the uniformity of the coating thickness on the textures?

Many thanks for the interesting tip. We originally assumed that the textures should not have a major influence on the coating process due to the comparatively flat shape. We have now investigated this aspect in more detail and produced microsections of the coatings. We were unable to recognize any differences in the layer structure. We have added corresponding illustrations and our procedure to the manuscript.

4. In Discussion, the authors write “In tribological contacts, a high roughness of the coating often leads to high friction and thus abrasive wear of the counterbody, if the coating exhibits a higher hardness than the contact partner, which in the case of the a-C: H coating against steel.” But numerical values of roughness and hardness are not given.

We have now measured the roughness of the tappets with and without coating using LSM and also determined the microhardness of the coating.

5. Why did the authors choose DLC coatings?

We used these because DLC coatings for cam tappet contacts are also widely used in the industry and, in addition, other research work on cam tappet contact has already reported on the friction and wear reduction achieved by DLC coatings.

6. Fig. 5 - the symbols along the horizontal axis are very difficult to interpret. It is necessary to add explanations to the figure caption or change it to other symbols that are more understandable.

We have now described the texture patterns used in more detail and added LSM images of all textures produced. This should make it clear which texture patterns are meant by the designation.

Reviewer 5 Report

Comments and Suggestions for Authors

1.      The gap between the literature and this work is not clear enough. The authors only stated that previous research focused on the mechanism, and this work applied it to the practical part. The novelty of the paper was lack and therefore should be emphasized. In addition, the major contribution of this paper is in sufficient. Did this work contribute to simplification model or the coating application?

2.      Only tribometer tests were conducted in addition to the simplified simulation is insufficient for coating friction analysis. The experiments should be improved.

3.      Table 4, what was the thickness of each coating layer?

4.      Why did authors select FVA 3 as lubricant in Table 1 and 10μl PAO-40 as lubricant in Table 5? How did authors ensure the set-up parameters in simulation align with the real experiment?

5.      On page 8-9 line 296-304, the explanation of processing time and the simplified model should not be included in the “Results” section. Please adjust the content to “Materials and Methods” section.

6.      For Table 7, how did authors identify the challenges and solutions? Please include the references if this was collected based on literature. In addition, this section should not be considered as results if it was literature review. Otherwise, please explain the details if this was organized based on the authors’ work.

7.      The discussion of the simulation result is not clear. The results between the simulation and the experiment should be compared and discussed. In addition, supporting literature should be included to further prove the results.

8.      There are some grammar and format mistakes, please carefully review and improved.

Comments on the Quality of English Language

There are some grammar and format mistakes, please carefully review and improved.

Author Response

1. The gap between the literature and this work is not clear enough. The authors only stated that previous research focused on the mechanism, and this work applied it to the practical part. The novelty of the paper was lack and therefore should be emphasized. In addition, the major contribution of this paper is in sufficient. Did this work contribute to simplification model or the coating application?

For this special issue, we wanted to focus on the results of our joint project in the DFG Priority program (see funding) to match the scope. Originally, tests on a cam tappet test bench were also planned, but unfortunately these could not be carried out due to a malfunction of the test bench. Nevertheless, in order to demonstrate fundamental differences, the alternative model test was chosen, which was also successful for this purpose. For this reason, however, it is not possible to transfer the results to the simulation without further ado. The novelty value of our contribution is therefore to some extent based on different aspects. On the one hand, to the authors' knowledge, such a simplified simulation model has never been analyzed in comparison to the more complex model. Similarly, there are no studies that have examined the tribological behavior of microtextures produced using this method. The direct coating of the components without prior post-treatment is also new. On the method side, the continuous workflow from design and production to coating and testing should be emphasized in particular, albeit with the aforementioned limitation that only model tests and no tests on the cam tappet test bench could be carried out. We have now emphasized these aspects more strongly in our manuscript.

2. Only tribometer tests were conducted in addition to the simplified simulation is insufficient for coating friction analysis. The experiments should be improved.

As already mentioned, the coating of the components was only one aspect of our work and not the sole focus. However, we have now added additional analyses of the DLC coating and examined the roughness, hardness and coating structure as well as the coating quality in the textures. The coating used is now described in much more detail.

3. Table 4, what was the thickness of each coating layer?

We made a FIB cut with corresponding SEM and EDS images and determined the resulting layer thicknesses. The exact transition from a-C:H:W to a-C:H is difficult to recognize in the SEM image, but can be estimated using the EDS measurement. We have added the figures and results to the manuscript.

4. Why did authors select FVA 3 as lubricant in Table 1 and 10μl PAO-40 as lubricant in Table 5? How did authors ensure the set-up parameters in simulation align with the real experiment?

Unfortunately, the FVA 3 oil was not available at the time of our tests, which is why we used a similar lubricant for the model tests. In any case, it is not possible to compare the simulation results with those of the tribometer tests. We have now mentioned this even more clearly in the manuscript.

5. On page 8-9 line 296-304, the explanation of processing time and the simplified model should not be included in the “Results” section. Please adjust the content to “Materials and Methods” section.

Thank you for pointing this out. We have now mentioned this aspect in the methods section.

6. For Table 7, how did authors identify the challenges and solutions? Please include the references if this was collected based on literature. In addition, this section should not be considered as results if it was literature review. Otherwise, please explain the details if this was organized based on the authors’ work.

As a large number of results were obtained as part of the DFG project mentioned above, we have only presented the technical manufacturing aspects in abbreviated form here. The results are all from our own work. We have now significantly expanded this section and explain the most important manufacturing aspects in more detail. The types of failure in the process that are not relevant to the tribological aspects are also listed in a table.

7. The discussion of the simulation result is not clear. The results between the simulation and the experiment should be compared and discussed. In addition, supporting literature should be included to further prove the results.

As already described, simulation and experiment cannot be compared directly. We have therefore gone into this point in more detail. We have now also added a comparative literature source for the simulation results, in which the load spectrum and procedure are very similar. In general, however, a comparison with literature values is difficult, as boundary conditions and assumptions are often different. The simulation model itself has already been compared with literature values in preliminary work using simple model contacts.

8. There are some grammar and format mistakes, please carefully review and improved.

Thank you for your comment, we have reviewed and improved the manuscript.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The revisions are appropriate.

Author Response

Thank you once again for your helpful review. We are very pleased that we were able to adequately implement the aspects you addressed.

Reviewer 2 Report

Comments and Suggestions for Authors

All comments raised in this revised manuscript have been addressed. I recommend it for publication.

Author Response

Thank you once again for your helpful review. We are very pleased that we were able to adequately implement the aspects you addressed.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have adequately addressed my concerns and the issues I have raised. I think it is ready for publication now. 

Author Response

Thank you once again for your helpful review. We are very pleased that we were able to adequately implement the aspects you addressed.

Reviewer 4 Report

Comments and Suggestions for Authors

No comments

Author Response

Thank you once again for your helpful review. We are very pleased that we were able to adequately implement the aspects you addressed.

Reviewer 5 Report

Comments and Suggestions for Authors

1.      The gap between the literature and this work is not clear enough. The authors only stated that previous research focused on the mechanism, and this work applied it to the practical part. The novelty of the paper was lack and therefore should be emphasized. In addition, the major contribution of this paper is in sufficient. Did this work contribute to simplification model or the coating application?

For this special issue, we wanted to focus on the results of our joint project in the DFG Priority program (see funding) to match the scope. Originally, tests on a cam tappet test bench were also planned, but unfortunately these could not be carried out due to a malfunction of the test bench. Nevertheless, in order to demonstrate fundamental differences, the alternative model test was chosen, which was also successful for this purpose. For this reason, however, it is not possible to transfer the results to the simulation without further ado. The novelty value of our contribution is therefore to some extent based on different aspects. On the one hand, to the authors' knowledge, such a simplified simulation model has never been analyzed in comparison to the more complex model. Similarly, there are no studies that have examined the tribological behavior of microtextures produced using this method. The direct coating of the components without prior post-treatment is also new. On the method side, the continuous workflow from design and production to coating and testing should be emphasized in particular, albeit with the aforementioned limitation that only model tests and no tests on the cam tappet test bench could be carried out. We have now emphasized these aspects more strongly in our manuscript.

The authors stated that there was a malfunction of the test bench and another test bench was selected, therefore, the experimental results could not be transferred to simulation. Then in this case, how could authors compare the simulation with the practical to ensure the accuracy? The novelty of “to some extent based on different aspects” is insufficient for an academic journal paper considering the assessment of the results.

2.      The discussion of the simulation result is not clear. The results between the simulation and the experiment should be compared and discussed. In addition, supporting literature should be included to further prove the results.

As already described, simulation and experiment cannot be compared directly. We have therefore gone into this point in more detail. We have now also added a comparative literature source for the simulation results, in which the load spectrum and procedure are very similar. In general, however, a comparison with literature values is difficult, as boundary conditions and assumptions are often different. The simulation model itself has already been compared with literature values in preliminary work using simple model contacts.

As the authors explained, the simulation from the other literature is difficult to be compared with the results in this work since the boundary conditions and assumptions are normally different. In this case, the results from the simplified model in this work should be compared with the experimental results in this work. It does not follow the scientific rigor if the simulation and the experiment both in this work cannot be directly compared. In this case, either the simulation or the experiment should be improved and supplemented.

3.      There are some grammar and format mistakes, please carefully review and improved.

Thank you for your comment, we have reviewed and improved the manuscript.

There are still mistakes, such as there are two “Figure 4”, and “I, we, us” in the manuscript. The entire content should be reviewed and modified.

Comments on the Quality of English Language

There are still mistakes, such as there are two “Figure 4”, and “I, we, us” in the manuscript. The entire content should be reviewed and modified.

Author Response

First, we would like to thank you once again for your helpful comments and are pleased that we have been able to implement most of them. In our opinion, the manuscript has improved considerably as a result. In particular, the limitations regarding the comparison of simulation and experiment are now explicitly described in the manuscript. We have addressed the open points again below and hope to provide a satisfactory answer here:

 

 

1. The gap between the literature and this work is not clear enough. The authors only stated that previous research focused on the mechanism, and this work applied it to the practical part. The novelty of the paper was lack and therefore should be emphasized. In addition, the major contribution of this paper is in sufficient. Did this work contribute to simplification model or the coating application?

 

For this special issue, we wanted to focus on the results of our joint project in the DFG Priority program (see funding) to match the scope. Originally, tests on a cam tappet test bench were also planned, but unfortunately these could not be carried out due to a malfunction of the test bench. Nevertheless, in order to demonstrate fundamental differences, the alternative model test was chosen, which was also successful for this purpose. For this reason, however, it is not possible to transfer the results to the simulation without further ado. The novelty value of our contribution is therefore to some extent based on different aspects. On the one hand, to the authors' knowledge, such a simplified simulation model has never been analyzed in comparison to the more complex model. Similarly, there are no studies that have examined the tribological behavior of microtextures produced using this method. The direct coating of the components without prior post-treatment is also new. On the method side, the continuous workflow from design and production to coating and testing should be emphasized in particular, albeit with the aforementioned limitation that only model tests and no tests on the cam tappet test bench could be carried out. We have now emphasized these aspects more strongly in our manuscript.

 

The authors stated that there was a malfunction of the test bench and another test bench was selected, therefore, the experimental results could not be transferred to simulation. Then in this case, how could authors compare the simulation with the practical to ensure the accuracy? The novelty of “to some extent based on different aspects” is insufficient for an academic journal paper considering the assessment of the results.

 

As already mentioned, experiment and simulation cannot and should not be directly compared with each other in this article. In our opinion, however, we have communicated this accordingly in the manuscript. We apologize that the wording was somewhat misleading at this point. The manuscript contains new aspects that have not been investigated anywhere else. These have already been listed. We have accepted the fact that simulation and experiment are not directly related for the reasons already mentioned. We believe that it is better scientific practice to publish all the results of our DFG project in one article rather than splitting them into individual articles (e.g. simulation, experiment and production). We have added the resulting limitations in the manuscript to the best of our knowledge.

 

 

2. The discussion of the simulation result is not clear. The results between the simulation and the experiment should be compared and discussed. In addition, supporting literature should be included to further prove the results.

 

As already described, simulation and experiment cannot be compared directly. We have therefore gone into this point in more detail. We have now also added a comparative literature source for the simulation results, in which the load spectrum and procedure are very similar. In general, however, a comparison with literature values is difficult, as boundary conditions and assumptions are often different. The simulation model itself has already been compared with literature values in preliminary work using simple model contacts.

 

As the authors explained, the simulation from the other literature is difficult to be compared with the results in this work since the boundary conditions and assumptions are normally different. In this case, the results from the simplified model in this work should be compared with the experimental results in this work. It does not follow the scientific rigor if the simulation and the experiment both in this work cannot be directly compared. In this case, either the simulation or the experiment should be improved and supplemented.

 

Please excuse the misunderstanding at this point. The simplified 2D model that we describe in this paper represents a line contact as it is approximately present in the cam-tappet contact. This was compared with the 3D line contact in the article. However, the tribometer tests carried out (ball on disk) can only be modeled by a 3D point contact, which cannot be compared with the cam-tappet line contact in any respect. We have therefore dispensed with this inadmissible comparison for the reasons mentioned.

 

 

3. There are some grammar and format mistakes, please carefully review and improved.

 

Thank you for your comment, we have reviewed and improved the manuscript.

 

There are still mistakes, such as there are two “Figure 4”, and “I, we, us” in the manuscript. The entire content should be reviewed and modified.

 

Many thanks for pointing this out. An error has indeed crept into Figure 4 due to the newly added figures. This has now been renamed Figure 7. We have decided to use more active voice, as we believe this makes the text easier to read. "I" does not appear in the manuscript, as the text is always written from the perspective of all authors. "us" is also not included in the manuscript. If the MDPI would like to see changes to the wording in individual places, we will be happy to adapt them during the proofreading process.

Round 3

Reviewer 5 Report

Comments and Suggestions for Authors

n/a