Bending Properties of Lightweight Copper Specimens with Different Infill Patterns Produced by Material Extrusion Additive Manufacturing, Solvent Debinding and Sintering

Round 1

Reviewer 1 Report

Accept in present form.

Author Response

The authors thank the reviewer for the positive evaluation of the work.

Some minor English corrections to the manuscript were made to correct typos.

Reviewer 2 Report

Accept in present form

Author Response

Thanks for the positive evaluation of our work.

Reviewer 3 Report

The reviewed paper is carefully written. All figures are clearly presented and described. This is definitely paper which we can called “applied science” because scientific discussion is rather short. Instead we have very precise description of experiment and we can imagine possible application of presented results. In my opinion the paper is worth to publish after some minor corrections:

1. Table 1 and line 186 – it is written that six specimens per type of geometry were printed when I can see 6 sample only for hexagonal one.
2. When you discuss Figure 5 you compare the span for different infill geometry. I think that it is not clearly what span do you mean (between the edges or between the centre of shapes).
3. Line 284 only two plateaus are mentioned when in Figure 2 tree are visible (also at 1050 °C)
4. Figure 5 caption “seme” = the same
5. Line 359 Figure 8 instead of 7

Author Response

The authors thank the reviewer for its positive evaluation of the work. All the comments of the reviewer have been addressed as shown below point by point.

1. Table 1 and line 186 – it is written that six specimens per type of geometry were printed when I can see 6 sample only for hexagonal one.

Reply: The images shown in Figure 5 are not all the specimens produced are just some examples to illustrate some differences seen after solvent debinding. Also, not all the printed specimens were sintered due to space limitations in the sintering oven; therefore, a line in the text was added in the methodology section: "Six specimens per type of geometry were printed and solvent debound, but not all them were sintered since all did not fit in the sintering furnace"

2. When you discuss Figure 5 you compare the span for different infill geometry. I think that it is not clearly what span do you mean (between the edges or between the centre of shapes).

Reply: The authors are referring to the distance between the edges in the infill structure and perimeter structures. The word "span" has been replaced by "unsupported distance" to avoid confusion. 

3. Line 284 only two plateaus are mentioned when in Figure 2 three are visible (also at 1050 °C)

Reply: The following text has been added to explain the third plateau: Finally, a 1 h plateau at 1050 °C was used to sinter and densify the specimens.

4. Figure 5 caption “seme” = the same

Reply: The text has been corrected accordingly.

5. Line 359 Figure 8 instead of 7

Reply: The text has been corrected accordingly.

Reviewer 4 Report

Dear authors, I attach a pdf with some minor comments. In my opinion the methods are good described and the results are very clear. 

Comments for author File: Comments.pdf

Author Response

The authors thank the reviewer for the detailed examination of the manuscript and its positive evaluation of the work. Each of the concerns of the reviewer has been addressed as follows:

1. In line 51 delete: “Therefore, PBF of copper has been investigated”

Reply: The authors agree with the suggestion since the sentence is redundant.

2. what do you mean by high melting point and copper together?

Reply: Two types of metallic alloys have been processed by MEX: (i) low melting point alloys that can be directly melted and extruded in a MEX machine since they melt at around 450°C, and (ii) high melting point alloys that cannot be melted at the printer since they melt at over 1000°C, which includes copper. The authors did not specify the other metals since they are given in the references and include several types of steel and titanium alloys. The authors have modified the text as follows to clarify this issue: “It has been demonstrated that it is possible to use MEX for the production of complex-shaped parts not only from thermoplastics [20], fiber-filled composites [21], and low melting point (~ 450 °C) metallic alloys [22], but also high-melting-point (> 1000 °C) metallic alloys [15,23–30] such as copper [31], ceramics [15,32–39], and hard metals and cermets [40–42].”

3. it looks like it lost its quality while exporting

Reply: The quality of the figures was reduced when exporting the file to PDF because in the Word file they look fine. To prevent that the lower quality image makes the figures unreadable we have increased the size of most images in the manuscript. Please see the modified manuscript.

4. Referring to the particle size distribution, obtained with which method?

Reply: Particle size distribution was measured by laser scattering technique. The caption has been modified as: “Figure 1. (a) Particle size distribution measured by laser scattering and (b) shape of copper powder observed by scanning electron microscopy”.

5. Referring to the temperature set in the compounder, maybe this is not 100% clear to everyone. a schematic representation can help.

Reply: Authors agree with the reviewer and have added a schematic of the compounder (New Figure 2). Please see the modified manuscript.

6. Referring to Figure 2, same as previous. This kind of happens with all the plots in your article.

Reply: Problem happened when preparing the PDF file. The size of the figures has been increased.

7. Also, you can probably include which is a debinding and which a sintering step. why do you have a point at approx 1200min/650C? maybe you can complement the picture and caption with some of the info you explain in 3.3

Reply: The temperature profile diagram has been divided into debinding, sintering and cooling regions.  

The oven program accepts 10 temperatures and a rate have to be indicated, those 10 temperatures are marked by the red dots in the figure.

The caption of this figure now includes the following: “Figure 32. Thermal debinding and sintering profile. All heating rates were 2 K/min. 1 h debinding plateaus at 250 and 450 °C and 1 h sintering plateau at 1050 °C were used”

8. In line 288, so you have a scatter of only 0.1 wt%?

Reply: To clarify this point the manuscript has been modified as follows: “The mass loss from green to sintered parts was in the range of 7.89 to 8.19 wt.% (average and standard deviation of 7.95 ± 0.04  wt.%), with no dependence on the infill geometry or the presence of cover.”

9. In line 292, how would you modify this? it can be part of the discussion/conclusions afterward (maybe it is, I haven't reached it yet)

The slumping can be minimized by increasing the infill density, this is already discussed in the paper as follows: “The specimens with a 25% and 50% infill had material dips and roughness in the sections where no material was present underneath (Figure 7a and 7b). Specimens with a 75% infill had a smoother surface.”

 

10. Line 323, this is not necessarily that challenging. PBF hollowed parts are produced all the time and I don't see a great conceptual difference with BJ. What do you exactly intend with this sentence?

Reply: Hollow PBF and BJT parts can be produced, but they have to have an opening where the loose powder can be removed. Therefore, they are not fully enclosed, like the parts produced by MEX and MJT. The opening changes the mechanical integrity of the specimen. The phrase has been modified to point that out: “It would also be challenging to produce fully enclosed hollow parts with PBF or BJT since the loose powder is trapped inside the specimens unless a draining orifice is designed in the part.”