Comparative Analysis of the Impact of Additively Manufactured Polymer Tools on the Fiber Configuration of Injection Molded Long-Fiber-Reinforced Thermoplastics

Round 1

Reviewer 1 Report

The manuscript presents an interesting study on ‘Comparative analysis of the impact of additively manufactured polymer tools on the fiber configuration of injection molded long-fiber reinforced thermoplastics’. The manuscript is suitable for publication in Journal of Composites Science. There are few comments should be addressed in the revised version.

• Introduction include motivation and state of the art is too long and should be rewritten to focus on the research problem. In addition bullet points (Page 4) is not recommended in a scientific paper.
• Number of figures could be reduced or converted to tables
• On page 7, the STAMAX manufacturer was written as ‘Sabic’ in line 290 and ‘SABIC’ in line 294, which one is correct?
• On page 7, line 305, is there a specific sequence or reason of selecting the fiber content suggested? i.e. where are the 30% and 50% or why not 80% instead of 60%?
• On page, last Para, the fundamental definition of μCT is redundant.
• The scale or magnification bar is needed for Figure 17 and some fiber length measurements could be highlighted

Author Response

Thanks for the review. In the appedinx you will find a doc.file that contains the most relevant changes. We have rewritten the introduction and shortened it to the essentials contents as recommended. Unfortunately, we have seen only after the revision that we should have highlighted all changes by the "Track Changes" function of Word. Since there were only minor correction, we hope the explanations of the Review Report suits that concern. Explicit corrections are given with a line number. We are very sorry about that!

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper aims to compare the mechanical properties and the fiber microstructure of LFT parts produced by conventional injection molding into steel and aluminum molds with that parts made with additive manufactured molds. Furthermore, the possible amount of parts that can be produced with the molds manufactured by additive tooling is investigated and a little failure analysis is performed.

All in all this is a very interesting paper with many interesting results. The article contains a very detailed introduction basing on many literature sources. Ttis reminds the author of a market study and could be significantly reduced. However, the state of the art is very accurate and very well presented, although some passages from the second chapter 2. "Materials and Methods" belong to chapter 1.2 "State of the Art".

This mostly refers to the following sections of the experimentally determined fiber orientation 2.2.4, lines 402–406 and lines 412–437, but also applies to some parts of the experimentally determined fiber length. The methods of the investigation are clearly presented and some of them require a remarkably high amount of time and effort.

However, in chapter 2.2.3 it is not obvious how the individual segments are taken from the samples for the analysis of the fiber content (sawn, milled, etc.). Due to the fact that the positions are compared with each other, do all these segments have the same weight or volume? Furthermore, the related results are very interesting, but an evaluation along a defined path would have been helpful for figure 20 in particular. Finally, it would be more interesting for the reader to show a simulation of the disc, if such a simulation is done.

This would also allow to compare the temperature distribution of a conventional and an optimized cooling system similar to figure 10. The "Results" chapter is well prepared and easy to understand. The occurring tool damage and the mechanical properties are well explained. Out of the reviewer´s point of view, the defects shown in figure 17 are not air traps (inclusions of oxygen) but rather voids or vacuoles. Furthermore, it has to be pointed out that turbulence cannot occur in the plastic melt during the injection molding process. However, normal eddy or vortices can occur due to geometric changes (referring to line 114, 260, 598, 701).

The results of fiber length analysis are very interesting. An overview of the averaged fiber length depending on the fiber concentrations and the mold material would be interesting as well. Due to the high variance of the fiber orientation within injection molding, the fiber orientation is most important for the resulting mechanical properties. The investigation can show that besides the mechanical properties also the fiber microstructure of the different tools is quite comparable. However, the given explanation in the first lines of that chapter (673-678) better belong to the "State of the Art" followed by some explanations (line 678-691) that better belong to chapter 2 "Materials and Method".

Regarding the increasing edge layer thickness with increasing fiber concentration, the author names crystallization as a reason. This is absolutely correct, however the term "a faster cooling" might be confusing. Here, for sure, "a faster solidification" is meant, isn't it?

Finally, the author should check:

• a consistent format and spelling of the named affiliations,
• the numbering and references of the tables,
• the replacement of the trademarks after their first introduction, and
• the decimal separators especially in the figures.

Author Response

Thanks for the review. In the appedinx you will find a doc.file that contains the most relevant changes. We have rewritten the introduction and shortened it to the essentials contents as recommended. Unfortunately, we have seen only after the revision that we should have highlighted all changes by the "Track Changes" function of Word. Since there were only minor correction, we hope the explanations of the Review Report suits that concern. Explicit corrections are given with a line number. We are very sorry about that!

Author Response File: Author Response.pdf