Strength Increasing Additive Manufacturing Fused Filament Fabrication Technology, Based on Spiral Toolpath Material Deposition

Round 1

Reviewer 1 Report

Comments on Strength increasing additive manufacturing FDM technology, based on spiral toolpath material deposition

The paper addresses the most common issue of the FDM specimens – their anisotropic behavior due to the poor bonding strength of the filaments. With the introduction of a novel 3D-printing method, the paper claims that the strength of the printed specimens can be uniformly improved in all directions.
Although the work looks promising, it is felt that it could have been better presented. Some of the arguments were unclear due to unexplained notations, improper choice of words and the Serbian language.
Some points should be clarified before the publication of the work. In particular:
• A small section could have been dedicated for illustrating clearly the trajectory planning. For the sake of this, the authors refer to one of their previous works. However, short and clear illustrations for the path planning of different specimens could help the reader.
• A sample is printed in different stages. First, a cylindrical core is printed in the traditional fashion with the axis oriented in the vertical direction. Then the table along with the part is rotated 90 degrees. Successively, the cylinder is wound with helical filaments whose paths are calculated analytically. It is skeptical if this procedure will allow us to print a wide range of parts. A plate with a hole and a relatively small thickness can be mentioned as an example. Also, it is felt that the procedure hinders the flexibility of the 3D-printing. For example, the core of the cylinder which is printed always in the same direction may not be a suitable choice for all situations. Please, comment on this.
• It is difficult to infer anything from the compression tests. Since the original motive of this paper was to show the improved and uniform strength in different directions, both tensile and compressive tests must be done to calculate the strength in three perpendicular directions. Also, since the choice of the ‘screw trajectories’ have not been justified in the paper, it is assumed that the choice is made based on engineering sense. Use of alternating double
helical layers around the cylinder could reinforce the part in different directions making it quasi-isotropic. However, in the standard method of printing, the quasi-isotropic parts are obtained by altering the raster angle in each successive layer by 90 degrees. Hence, to establish the superior strength of the reported method, it is better to compare such quasi-isotropic cylindrical type specimen with another quasi-isotropic standard-type specimen.
• Lastly, in the bending test, the filament orientation of the standard type specimen is not explicitly mentioned. If the bending stress is supported by the inter-layer or inter-filament bonding, the results from the comparison is not very surprising. The right way will be to change the build orientation so that the bending stress is along the filament length and make the comparison. Please clarify this point.

Author Response

Thank you very much for your comments.
Grammar and language will be reworked.
Please see the attachment with point-by-point response to your comments.

Author Response File: Author Response.docx

Reviewer 2 Report

Reviewer comments

The manuscript entitled “Strength increasing additive manufacturing FDM technology, based on spiral toolpath material deposition” provide the study about algorithm for calculating the spiral toolpaths for the material deposition using multi-axis printing.

1)     The grammar and language used throughout the paper could use refining.  Some of the wording is confusing or unnecessary and with improvements to the style of writing, the paper would read much more smoothly and the overall quality would be greatly improved.

 

2)     In the introduction part, the authors have not provided a suitably comprehensive summary of relevant recent work. As to the knowledge of reviewer they are so many recently paper published specifically on the method for strength improvement and overall about additive manufacturing, the reviewer recommended to add following references:

[1]  Jo, W., Kwon, O. C., & Moon, M. W. (2018). Investigation of influence of heat treatment on mechanical strength of FDM printed 3D objects. Rapid Prototyping Journal, 24(3), 637-644.

[2]  Popescu, D., Zapciu, A., Amza, C., Baciu, F., & Marinescu, R. (2018). FDM process parameters influence over the mechanical properties of polymer specimens: A review. Polymer Testing, 69, 157-166.

[3]  Aliheidari, N., Christ, J., Tripuraneni, R., Nadimpalli, S., & Ameli, A. (2018). Interlayer adhesion and fracture resistance of polymers printed through melt extrusion additive manufacturing process. Materials & Design, 156, 351-361.

 

3)     In figure 11 b, indicate the type of actual samples in 11 b.

 

Overall, the work has novelty in terms method of 3D printing. However, it is better to add more fundamental discussions about the reasons behind the observations.

 

 

Author Response

Thank you very much for your comments.
Grammar and language will be reworked.
Please see the attachment with point-by-point response to your comments.

Author Response File: Author Response.docx

Reviewer 3 Report

I would like to thank the author for their work.  However, it seems like I am missing a lot of details on the authors idea and its novelty.  I believe they need to re-work their ideas before publication.

Introduction:

There is a significant body of work on FFF/FDM technologies with the materials used in the work.  The entire first page is a background on SLA, not FFF.  This paragraph needs to be completely re-made citing relevant literature in the area of FFF, not SLA.  Likewise, citations 1 to 7 are not relevant to this work. 

line 44: "devoid" is not the correct word choice.  I am not sure what you are trying to say here.

line 50: remove ", which was shown in"  this is part is not needed, only the citations.

line 61: "using new polymer materials with outstanding physical and chemical properties in 3D printing, 61 such as PEEK [16];"  This citation does not include data for multiple print orientations and is therefore not relevant to your point.

line 63: "pouring" is not an accurate term here, instead use "extruding". 

Section 2:

The flow chart of figure 3 is in Russian.  This isn't very helpful.

Figure 4 needs to be re-sized.  The majority of the image is not referenced in the text (the build volume) however the portions that are cited are extremely small.  The author should increase the ratio of build box to numbered area.

line 158: "The proposed approach also solves the problem of adhesion of the product to the table, which takes place with standard 3D printing."

The rod printed in your method also needs to adhere to the stage. 

I am very confused in this section.  It appears that a rod is printed vertically then rotated by 90 degrees, and the rod is then printed on while it rotates, this allows the final shape to be constructed.  Is the rod removed from the base and placed somewhere else before rotation occurs? Are there multiple print heads?  I find figures 5, 6, and 7 to be not very clear to describe the process (although the do point out motors and gear boxes, which is not as helpful).  This section needs to be re-worked to clearly identify the process.

Section 3:

I am not sure in what raster direction each part of the sample is made in.  Figure 11(b) and Figure 13 (b) help slightly, but this needs to be clarified earlier and in greater detail.

Figure 12, what is "standard" is it a control sample?  Is it a test sample?  How was it made?

How many samples were tested? What is the standard deviations? what is the statistically significant difference?

What about tensile testing?  The issue with printing annisotropy is typically not in compression testing, it is in tensile testing.  The author later claims: "The proposed technology allows to produce FDM 3D-printing products of almost any shape"  Are you able to print ISO tensile bars?

Table 2 is confusing and should be summarized as one value with the associated error and statistical significance per sample set.   These values are not very compelling without the clear denotation of a proper control sample and the associated errors.

Notes:

You should change FDM to FFF.  FDM is a Stratasys patented term, FFF (Fused Filament Fabrication) is the more general term.

"The authors come to the 39 opinion that this technology makes it possible to obtain objects that are not inferior in strength to 40 traditional methods, and in some cases superior to them." 

-Cite or remove.

How is your printer different then the commercially available "rotary 3D printers"?  There are a few on the market and were popular a few years ago.  I believe that is what you are using to make the core unit.  There isn't anything new or novel about that. Does your tool then rotate to the orientation in Figure 9?  If yes, this must be shown, otherwise, it seems like you just then place your rotary printed rod on a lathe-type printer.  I think the author needs to do a better job describing what is novel in this article.

Author Response

Thank you very much for your comments.
Grammar and language will be reworked.
Please see the attachment with revised manuscript. All changes highlighted using the "Track Changes" function in Microsoft Word.

 

Point 1: There is a significant body of work on FFF/FDM technologies with the materials used in the work.  The entire first page is a background on SLA, not FFF.  This paragraph needs to be completely re-made citing relevant literature in the area of FFF, not SLA.  Likewise, citations 1 to 7 are not relevant to this work.

 Response 1: A review of SLM / SLA technology is presented in the introduction to analyze the problem of the strength of products obtained by the methods of additive manufacturing as a whole, as well as to indicate the fundamental difference between FFF / FDM technology from SLM - anisotropy of products, which is one of the key points leading to small strength of printed objects.

However, a review of FFF technology in comparison with SLM really received less attention than it should. The introduction has been expanded; please see the attachment.

 

Point 2: line 44: "devoid" is not the correct word choice.  I am not sure what you are trying to say here.

Response 2: This phrase has been reformulated.

 

Point 3: line 61: "using new polymer materials with outstanding physical and chemical properties in 3D printing, 61 such as PEEK [16];"  This citation does not include data for multiple print orientations and is therefore not relevant to your point.

Response 3: Let me disagree. This block is devoted to consideration of all ways to increase the strength of products applicable in the FDM technology. One of these is the use of polymers, ceteris paribus providing greater strength of the interlayer interaction (and, accordingly, greater strength).

 

Point 4: line 63: "pouring" is not an accurate term here, instead use "extruding".

Response 4: Fixed, thank you.

 

Point 5: The flow chart of figure 3 is in Russian.  This isn't very helpful.

Response 5: The flowchart has been translated into English. I apologize, this is really an absurd oversight on our part.

 

Point 6: Figure 4 needs to be re-sized.  The majority of the image is not referenced in the text (the build volume) however the portions that are cited are extremely small.  The author should increase the ratio of build box to numbered area.

Response 6: Figure has been resized, thank you.

 

Point 7: line 158: "The proposed approach also solves the problem of adhesion of the product to the table, which takes place with standard 3D printing."

The rod printed in your method also needs to adhere to the stage.

Response 7: It really was a hasty remark. It has been removed.

 

Point 8: I am very confused in this section.  It appears that a rod is printed vertically then rotated by 90 degrees, and the rod is then printed on while it rotates, this allows the final shape to be constructed.  Is the rod removed from the base and placed somewhere else before rotation occurs? Are there multiple print heads?  I find figures 5, 6, and 7 to be not very clear to describe the process (although the do point out motors and gear boxes, which is not as helpful).  This section needs to be re-worked to clearly identify the process.

Response 8: The core is printed on the table of the same printer. Then the printer table rotates 90 degrees and the process of winding the material with the rotation of the table with the core around its axis. The removal of the core from the base occurs only once upon completion of printing of the entire product. During printing (when the table with the core is rotated 90 degrees), the core is secured to the table by supporting equipment ("raft", position 1, Figure 9).

Both core printing and winding of the bulk of the material is done by one print head.

 

Point 9: I am not sure in what raster direction each part of the sample is made in.  Figure 11(b) and Figure 13 (b) help slightly, but this needs to be clarified earlier and in greater detail.

Response 9: The location of the layers was separately shown in Figure 11.

 

Point 10: Figure 12, what is "standard" is it a control sample?  Is it a test sample?  How was it made?

Response 10: A «standard» sample is a sample made entirely by conventional layer-by-layer printing. To avoid ambiguity, the «standard» in the graphs and tables has been replaced by «3D».

 

Point 11: How many samples were tested? What is the standard deviations? what is the statistically significant difference?

Response 11: 3 or 4 samples of each type were tested in compression tests and 4 samples of each type in bending tests. Figure 13 shows the compression diagram for one sample of each type, and Figure 15 shows the average critical load for four samples.

The main purpose of the tests was to obtain a primary idea of ​​the strength properties of the resulting structures. We are currently preparing a new test series with a large number of samples.

 

Point 12: What about tensile testing?  The issue with printing annisotropy is typically not in compression testing, it is in tensile testing.  The author later claims: "The proposed technology allows to produce FDM 3D-printing products of almost any shape"  Are you able to print ISO tensile bars?

Response 12: We are able to produce samples for this type of test, but during the previous series of tests there were problems with the equipment for fixing the samples under tension. We are currently preparing a new series of tests, including tensile tests.

 

Point 13: Table 2 is confusing and should be summarized as one value with the associated error and statistical significance per sample set.   These values are not very compelling without the clear denotation of a proper control sample and the associated errors.

Response 13: The table is revised, the standard deviation values are entered.

 

Point 14: You should change FDM to FFF.  FDM is a Stratasys patented term, FFF (Fused Filament Fabrication) is the more general term.

Response 14: Thank you for this note. I will find out from the editor whether the title of paper can be changed at this stage.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Two remarks about point 3 and 4 of the response should be inserted. 

After this  the paper in my opinion is suitable for publication.

Author Response

Thank you very much for your comments!

We included two short remarks from the first response into the manuscript (lines 205..209 and 253..257).

Reviewer 3 Report

First, I must say that your new printer is fantastic, and should be published!  However, the article needs work on focus and including relevant data.  I feel that the work does not sufficiently characterize or describe the printer, but instead only briefly covers the "academic" parts of the printer.  The article instead focuses on parts produced by the printer, almost as a "sales pitch" and does not characterize the positives and negatives to sufficient quality.  I do enjoy the section on the slicing software, and feel as though a similar section could be used to provide a more in-depth analysis of the hardware, part rotation, and part registration process.  

To be published in an academic article the work should be able to be recreated by a reader.  That is the purpose of publication.  I can understand not publishing specifics of the patented material, but not the general mechanics of the printer.  I have reviewed other unique printer formats, and they have even included dimensional specifics of parts, part numbers, etc.  This article barely describes the process, and does not explain motion control, materials, design specifics, or custom parts and why they are customized in such a fashion.  These should be requirements if one is publishing on a machine.

I also suggest the author look into some other physical properties that can be used to compare to traditional 3D printing.  Specifically, I am talking about possible part polymer density and final surface finish.  These two areas are the primary commercial focus in printers, and I feel that this article does not adequately characterize the printer without some information in this area.  For example, "The proposed approach also reduces effect of shrinkage of the material during cooling on the mechanical properties of the product."  Where is the data to back up this point?

The idea is fantastic!  The data presented supports the motivation!  However, there is not sufficient characterization or description of the printer.  Because of this, the paper would be extremely difficult to reproduce or to even determine if the printer would fit's one's needs.  I would even guess that this printer can be used as a "traditional" or a "rotational" printer, which is equally as impressive, but the two modes should also be tested and compared.

The potential of this work is fantastic, the data presented does not fit with the goals of the paper.  The work also does not really "help" a reader to figure out how to advance the field.

I.E. the paper implies "we made a great printer, part mechanical properties have been shown to be better using this method and we verify this previous research" which is not academic.   The paper should be: "We made a great printer, these are the details how and why we made it this way, here is how it compares in accuracy, finish, print time, and mechanically."   

 

Important points:

I completely disagree with the about the inclusion of SLM.  If your article is about FFF, the worst thing to do is not mention FFF in the entire first paragraph of your work.  Then you mention "These flaws arn't (never use "arnt" use "are not") in fused filament fabrication."  If the flaws are not in FFF, then why talk about them at all!  It wastes the readers time.

The primary purpose of this article is the unique printing technique.  I have noticed that the slicing software has been patented, and this is great!  However, as this is a "Machine" journal, I believe the author should include a bit more about the machine in the publication.  This included how well the machine performs beyond mechanical, we need surface finish data, print time, print accuracy, verified printed infill percentages.  These are all very important pieces of information!

 

Short notes:

Acronyms should not be used in the title "e.g. FFF"  you also need to define the acronym before using in text.  "We used Fused Filament Fabrication, FFF, to make our item."

Figure 8:  I suggest altering the figure to have multiple colors highlighting the build platform.  Also break into Figure 8a and Figure 8b showing the build platform in both orientations (a) for rod printing b) for rotational printing)

I appreciate the author altering "standard" to "3D," it might be clearer if the author used "traditional 3D Printing" or "traditional FFF."

 

Again, the printer is awesome.  But the article, as written, does not help a general scientist to replicate the tool or the work.

Author Response

Thank you for your comments!

Please see the attachment.

Author Response File: Author Response.docx

Round 3

Reviewer 3 Report

Thank you for your extensive edits, I think they are very helpful with developing the scientific merit of your work.

I believe that your article would be greatly improved by including the suggestions of my last review however, I understand the difficulties involved.

However, you must include actual pictures of the developed printer.  You have no images proving that you made what you describe (only CAD and printed parts). I believe that these should replace Figure 8 a) and b).  

 

Thank you!

Author Response

Thank you for your comments! We surely will take account of these suggestions on the next article.

Figures 8 have been replaced in this manuscript.