Drilling Defects and Process Optimization in Carbon Fiber-Reinforced Polymer Composites: A Review

Response to Reviewers

We sincerely appreciate the time and effort the reviewers and editor have dedicated to providing constructive feedback and valuable suggestions on our paper. These insights will significantly enhance the quality and overall standard of our manuscript, allowing us to make effective improvements. Each of your comments and recommendations has been carefully and accurately considered. Below your comments, we have provided detailed responses and made revisions accordingly. The revised sections are highlighted in yellow in the updated manuscript. Sections highlighted in yellow with black font indicate modifications made to the text, parts in red font signify deletions, and content in blue font represents additions to the article.

Point-by-point response to Comments and Suggestions for reviewer 1.

Comments 1: Authors must explicitly delineate the methodological innovation of this review in the Introduction. The manuscript, although comprehensive, presently resembles a standard narrative review. Clearly articulate how this work surpasses current reviews by incorporating thermomechanical coupling, interactions among defects, tools, and the environment, or trends in predictive modeling.

Response 1: Thank you for pointing this out. We agree with this comment. We have explicitly highlighted the innovative aspects of this review in the Introduction. Moreover, we have clearly articulated that this work incorporates thermomechanical coupling, interactions among defects/tools/environment, and trends in predictive modeling, thereby demonstrating how it differs from other articles. These points are specifically detailed in Paragraph 4 (lines 106–116) of the Introduction.

Comments 2: Authors should enhance the critical comparison among various defect mechanisms (delamination, burrs, tear-out) by explicitly addressing their relative severity, industrial significance, and performance implications (fatigue life, bearing strength, assembly tolerance), instead of considering them as predominantly independent phenomena.

Response 2: Thank you for pointing this out. We agree with this comment. We have strengthened the critical comparison among various defect mechanisms (delamination, burrs, tearing) and explicitly addressed their relative severity, industrial significance, and impact on performance (fatigue life, bearing strength, assembly tolerance). These revisions are reflected in Paragraph 6 of Section 2.1 (lines 287–291), Paragraph 2 of Section 2.2 (lines 384–391), and Paragraph 2 of Section 2.3 (lines 454–463).

Comments 3: Authors must include a comparative summary table that connects:

Type of defect

Preeminent physical mechanism

Regulating process parameters

Response 3: Thank you for pointing this out. We agree with this comment. We have revised Table 1 to align with the reviewer’s suggestions, as reflected in the updated Table 1.

Comments 4: Authors must explicitly delineate the methodological innovation of this review in the Introduction. The manuscript, although comprehensive, presently resembles a standard narrative review. Clearly articulate how this work surpasses current reviews by incorporating thermomechanical coupling, interactions among defects, tools, and the environment, or trends in predictive modeling.

Response 4: Thank you for pointing this out. We agree with this comment. We have elaborated on the interrelated roles of thrust force and torque in the delamination process in the manuscript. Both thrust force and torque are now considered in their influence on damage evolution, as detailed in Paragraph 2 of Section 2.1 (lines 180–194).

Comments 5: Authors must critically assess the shortcomings of current delamination metrics (Fd, Fa, Fda, Fv). The manuscript accurately acknowledges their static nature; however, it should elaborate further on:

Sensitivity to image thresholding

Weak correlation with residual mechanical performance

Absence of standardization among studies

Response 5: Thank you for pointing this out. We agree with this comment. We have critically evaluated the limitations of current delamination evaluation metrics (e.g., Fd, Fa, Fda, Fv). Further elaboration has been provided on the following issues: sensitivity to image thresholding, weak correlation with the residual mechanical properties of components, and the lack of standardization across different studies. These points are detailed in Paragraph 3 of Section 2.1 (lines 207–233).

Comments 6: Authors should enhance the discourse on dynamic damage evolution, especially during drill breakthrough, by integrating experimental, FEM, and data-driven methodologies into a cohesive conceptual framework.

Response 6: Thank you for pointing this out. We agree with this comment. We have strengthened the study of dynamic damage evolution during the drill breakthrough phase and integrated experimental, finite element analysis, and data-driven methodologies into a coherent conceptual framework.

Comments 7: Authors should refrain from presenting optimization studies in a sequential manner and instead categorize them by outcome, such as:

Strategies dominated by thrust force

Thermal management strategies

Strategies driven by chip evacuation

Response 7: Thank you for pointing this out. We agree with this comment. While we acknowledge that categorizing strategies by their outcomes can effectively highlight the underlying mechanisms, after careful consideration, we have chosen to retain the defect-based classification framework in this paper. This decision is primarily based on two considerations: First, it enables a more direct mapping between defect causes and suppression methods, thereby enhancing the logical coherence and problem-oriented focus of the review. Second, it facilitates a systematic explanation of the comprehensive effects of individual optimization methods (such as improving drill geometry) on reducing thrust force, enhancing heat dissipation, and promoting chip removal, thus more fully showcasing their value. Within each defect-specific section, we have emphasized the analysis of the core functional pathways of different strategies (e.g., whether they primarily focus on thrust force control). This approach aims to incorporate your insightful perspectives within the existing clear framework.

Comments 8: Authors must critically evaluate variable feed strategies in relation to advanced drill geometries, addressing trade-offs in industrial scalability, tool expenses, and process reliability.

Response 8: Thank you for pointing this out. We agree with this comment. We have integrated advanced drill geometries and critically evaluated variable feed strategies, discussing their trade-offs in terms of industrial scalability, tool costs, and process reliability. These revisions are detailed in Paragraph 1 of Section 3.4.3 (lines 1018–1037).

Comments 9: Authors must delineate more distinctly between laboratory-scale optimization and industrial feasibility, especially regarding cryogenic cooling and intricate multi-edge drill designs.

Response 9: Thank you for pointing this out. We agree with this comment. Thank you for pointing this out. We agree with this comment. We have clarified the distinctions between laboratory-scale optimization and industrial feasibility in areas such as cryogenic cooling and multi-edge drill designs. These clarifications are specified in Paragraph 1 of Section 3.3.1 (lines 867–872) and Paragraph 2 of Section 3.2.1 (lines 636–644).

Comments 10: Authors must examine the environmental and sustainability ramifications of cryogenic drilling (LN₂ versus CO₂), encompassing energy consumption, infrastructure requirements, and lifecycle considerations, which are becoming increasingly significant for manufacturing journals.

Response 10: Thank you for pointing this out. We agree with this comment. We have addressed the environmental and sustainability implications of cryogenic drilling strategies involving liquid nitrogen (LN₂) and carbon dioxide (CO₂) in the manuscript, encompassing energy consumption, infrastructure requirements, and lifecycle considerations. These discussions are detailed in Paragraph 1 of Section 3.3.1 (lines 793–805).

Comments 11: Authors must enhance clarity by explicitly correlating particular geometric attributes (point angle, chisel edge length, step height) with distinct damage suppression mechanisms, preferably accompanied by schematic illustrations.

Response 11: Thank you for pointing this out. We agree with this comment. We have correlated the geometric features of cutting tools (such as point angle, chisel edge length, and step height) with specific drilling damage suppression mechanisms, thereby providing an enhanced discussion on how optimizing tool geometry improves drilling defects. A schematic diagram (Fig. 10) has also been added to illustrate these relationships. These revisions are detailed in the second paragraph of the summary in Section 3.2.1 (lines 608–635).

Comments 12: Authors must include a concise comparison of tool coatings (diamond, DLC, TiAlN, multilayer nanocomposites) based on failure modes, emphasizing the reasons for the success or failure of specific coatings in CFRP, despite their high hardness.

Response 12: Thank you for pointing this out. We agree with this comment. We have incorporated a concise comparison of tool coatings (diamond, DLC, TiAlN, multilayer nanocomposites) based on failure modes in the review. Furthermore, we have elucidated the specific reasons for the success or failure of certain coatings in CFRP drilling, despite their high hardness. These additions are detailed in Paragraph 2 of Section 3.2.2 (lines 677–695).

Comments 13: Authors must examine the mechanisms of coating delamination and adhesion failure under cyclic thermal–mechanical loading, which are essential in high-volume drilling operations.

Response 13: Thank you for pointing this out. We agree with this comment. In accordance with your suggestion, we have investigated the spalling and adhesive failure mechanisms of coatings under cyclic thermomechanical loading. These factors contributing to coating failure are also discussed in relation to high-volume production. The relevant content is detailed in Paragraph 4 of Section 3.2.2 (lines 739–752).

Comments 14: Authors should eliminate minor redundancies in the Introduction where machining challenges are reiterated verbatim across paragraphs.

Response14: Thank you for pointing this out. We agree with this comment. We have removed the redundant passages regarding machining challenges in the Introduction.

Comments 15: Authors must maintain consistent terminology (e.g., “tear-out” versus “tearing,” “burr” versus “burrs”) throughout the manuscript.

Response15: Thank you for pointing this out. We agree with this comment. We have unified the terminology throughout the manuscript by replacing "tear-out" with "tearing" and using the plural form "burrs" consistently for "burr."

Comments 16: Authors should enhance figure captions to ensure they are more self-sufficient, particularly for mechanistic figures depicting delamination and burr formation.

Response16: Thank you for pointing this out. We agree with this comment. We have revised the captions related to burrs and tearing to make them more direct and clearer. The specific revisions are reflected in the captions of Figure 3 (lines 197–198), Figure 4 (lines 285–286), Figure 5 (lines 334–335), Figure 6 (lines 422–428), and Figure 7 (lines 480–481).

Comments 17: Authors must incorporate a future research roadmap in the Conclusion, organized as follows:

Real-time damage assessment

Physics-informed machine learning models

Standardized correlations between defects and performance

Eco-friendly drilling technologies

Response 17: Thank you for pointing this out. We agree with this comment. We have incorporated a future research roadmap in the Conclusion section, linking four key areas: real-time damage assessment, physics-informed machine learning models, standardized correlations between defects and performance, and eco-friendly drilling technologies. This addition is detailed in Paragraph 1 of the Conclusion (lines 1342–1351).

Comments 18: Authors should revise the conclusion to transcend mere summarization and offer explicit, forward-looking insights into unresolved challenges and emerging opportunities in CFRP drilling research.

Response18：Thank you for pointing this out. We agree with this comment. We have revised the Conclusion section to move beyond a simple summary of the article, providing clear and forward-looking insights into unresolved challenges and emerging opportunities in CFRP drilling research. This revision is reflected in Paragraphs 2–7 of the Conclusion (lines 1343–1352).

Response to Reviewers

We sincerely appreciate the time and effort the reviewers and editor have dedicated to providing constructive feedback and valuable suggestions on our paper. These insights will significantly enhance the quality and overall standard of our manuscript, allowing us to make effective improvements. Each of your comments and recommendations has been carefully and accurately considered. Below your comments, we have provided detailed responses and made revisions accordingly. The revised sections are highlighted in yellow in the updated manuscript. Sections highlighted in yellow with black font indicate modifications made to the text, parts in red font signify deletions, and content in blue font represents additions to the article.

Point-by-point response to Comments and Suggestions for reviewer 2.

Comments 1: the manuscript is too long, with a lot of details and hard to read and follow.

Response 1 : Thank you for your valuable feedback regarding the length of the manuscript. We fully understand and share your concerns about readability and coherence. This study aims to provide a comprehensive and in-depth review of the complex topic of CFRP drilling defects and process optimization, covering multiple aspects such as their mechanisms, influencing factors, and optimization strategies. As a result, it necessarily includes substantial details to ensure the completeness and depth of the arguments. In response to your comments, we have removed redundant explanations and refined the language throughout the manuscript to reduce its length and enhance clarity for readers.

Comments 2: for example, there are paragraph 3.5.4 Summary , after paragraph 3.6 Summary is again summary.

Response 2: Thank you for your valuable feedback. I have accepted your suggestion, specifically by removing the summary section of 3.6 from the manuscript.

Comments 3: figure 2 is not cited in the text.

Response 3 : Thank you for your valuable feedback. We have taken your suggestion into account and can confirm that Figure 2 is now properly cited in the last paragraph of the Introduction (line 114).

4. Response to editor

Dear Ms. Wilma Chen, 

I have received your valuable feedback—thank you very much! Through revisions to the manuscript, I have successfully reduced the similarity rate to below 30%. I would also like to specifically explain the matter of the corresponding author: the corresponding authors of the paper should include both Wu Shujing and Wang Jiaran, not just one person. This was an error during the system upload, and I sincerely apologize for the oversight. 

I will follow up by sending the copyright information for the figures and tables to your email for your review. Thank you once again for your understanding and support!

5. Additional clarifications

We have uploaded two revised versions: one with all changes tracked (with revision marks) and one without any revision marks (clean version). All responses to your esteemed comments provided above refer specifically to the version with tracked changes.

6. Acknowledgments

“Dear Editor and Reviewers: On behalf of my co-authors, we are very grateful to you for giving us an opportunity to revise our manuscript. We appreciate your positive and constructive comments and suggestions.