Consolidation and Tow Spreading of Digitally Manufactured Continuous Fiber Reinforced Composites from Thermoplastic Commingled Tow Using a Five-Axis Extrusion System

Round 1

Reviewer 1 Report

The paper is interesting and has few contributions pertaining to 5-axis system however lags the fundamental physics and related analysis. 

Kindly consider the following comments;

The paper needs more reference and also the author must establish the contribution based on the systematic works of literature

The abstract must be more precise and crispy, what does the author mean by

"With more complex surface contours, to maintain perpendicularity of the extruder tip to the

surface requires more than 3 axes of motion."

The author's statement a 3-axis gantry system is limited to the production of nominally flat composite plates needs a reference or appropriate explanation. similarly

equations to find the nozzle/composite friction needs a reference

The graphs and figures are poorly drawn, kindly enhance the resolution

Also, there are numerous grammatical errors that need to be fixed

Author Response

Additional citations have been included.

The abstract has been adjusted to better reflect the effort.

Citations related to the nozzle/composite equation have been added.

Artwork has been adjusted.

Grammar has been considered and improved in revised version.

Author Response File: Author Response.pdf

Reviewer 2 Report

1. The authors should define symbols and acronyms when they are first used to improve clarity (eg. PET, PETG, τ)
2. Sections 3.3 and 3.4 - The authors are suggested to include a table to summarize the equipment setup used (new or old nozzle, with or without cooling, nozzle angle) in each of the experiments 
3. Figure 14 - Is the pulling force (axis title) the same as friction force (from figure title)? If yes, the authors should use the same name.
4. Section 4.3.1 - The authors are suggested to measure and report the void content and the interlaminar shear strength of the laminate produced to show that the consolidation is good.
5. Section 5. "A new nozzle design with a decreased outer diameter would reduce the unconsolidated region in the transition at these corners as well as allow for the application of consolidation pressure for any orientation of the hot end." - Has this been shown through experiments? The results section does not seem to include any results on the composite placement into concave corners using the new nozzle.
6. Section 5 - It is not clear which statements are concluding remarks for the current work and which statements point to potential for future imrpovements. 

Author Response

1. Done.
2. Additional specificity added to text. Rather than adding a table, the nozzle utilized is called out at the beginning of each section.
3. Done.
4. Void content added for the 5 laminates used in the 180 degree turns study. Measurement technique indicated and cited.  Further properties referenced.
5. Section 5 was rewritten to maintain a tighter focus in this manuscript on consolidation on the tooling surfaces rather than then effects at surface transitions.
6. Section 5 is rewritten to clarify.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript entitled: 'Consolidation and Tow Spreading of Digitally Manufactured Continuous Fiber Reinforced Composites from Thermoplastic Commingled Tow using A 5 Axis Extrusion System' reports modification of a laboratory 3-axis placement system to investigate consolidation on complex
contours, non-linear fiber paths, and the ability to manipulate tow width using placement nozzle orientation. The present manuscript is more a report than a technical, scientific study. I do not see any major scientific advancement nor interesting results with the present manuscript and hence I cannot recommend the manuscript for publication in the present form.

Author Response

Substantially rewritten in an attempt to emphasize importance of cooling for path control and nozzle inclination for tow geometry control.  These factors are important to future research in the area of digitally manufactured thermoplastic matrix composites and will need to be incorporated in process control to improve composite quality in the future.  Additional information on these topics is included in the rewritten manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

After minor revision amendment, I would recommend this article for publications. 

Thanks authors for addressing my comments. 

Best Luck

Author Response

In response to the reviewer, a spell check has been undertaken.

• In the title, "From" was changed to "from"
• in Section 3.3.1, line 4, "flate" was corrected to "flat"
• in Section 4.4, 2nd paragraph, line 9, "0.4mm, but" was changed to "0.4mm but"

Reviewer 2 Report

1. Equation 3: Definition for τ is missing

Author Response

Thank you.  For some reason during editing that definition was missed.

The paragraph preceding equation 3 has been edited to include:

"... where ‘τ’ is the mean shear strength of the bond between the tow and the bed, ..."

Reviewer 3 Report

Even though the authors have tried re-writing the manuscript, I still stick to my original comments, where I see little or no novelty/scientific advancement with the manuscript and hence cannot recommend it for publication.

Author Response

As indicated upon previous resubmission, the manuscript was substantially rewritten in an attempt to emphasize importance of cooling for path control and nozzle inclination for tow geometry control. These factors are important to future research in the area of digitally manufactured thermoplastic matrix composites and will need to be incorporated in process control to improve composite quality in the future. Additional information on these topics was included in the original rewrite of the manuscript.