Effects of Mixing Speed and Mixing Time on Powder Segregation During Powder Mixing for Binder Jetting Additive Manufacturing: An Experimental Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study titled “Effects of mixing speed and mixing time on powder segregation during powder mixing for powder bed additive manufacturing: an experimental study” discusses the effect of two levels of two variables i.e., mixing speed and mixing time, on the density of the mixture. While the idea and methodology appear straightforward, the research work can be improved in several areas. Below are a few specific comments that can be improved:
1)    The authors mention powder bed additive manufacturing in the abstract and title, which seems unnecessary. It would be clearer to the readers if they could directly mention binder jetting.
2)    Another reason for comment 1 is that powders used in binder jetting may have different flow and cohesion properties compared to powders in laser-based or electron beam powder bed fusion processes. Therefore, the results may not be generalized for powder bed fusion processes.
3)    It would be insightful for readers if the authors could mention some examples of mixing two types of powder and mention why is it required in binder jetting. 
4)    The study does not mention the name, type, or properties of the powders for powder A and powder B.  Are they metals, ceramics, polymers or composites powders? How about other properties like, flowability, and morphology of the powder? This information seems relevant to the results of this study.
5)    Is there any reason the authors did not include the SEM images of the powders A and B?
6)    The authors mention that the mixing jar rotates at angles of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315° from the starting position. Do they believe that this rotation affects the powder properties or influence the segregation behavior? 
7)    Can the authors also explain the reason for the mixing ratio of 70% for powder A and 30% for powder B.  Is it because of the density difference between the powders? Or was it based on real-world applications or prior studies?
8)    If previous studies have shown contradictory results, would it not be better to include more levels of mixing speed and time? 
9)    It would be better for the readers if the authors could mention the environmental conditions like humidity and temperature during their experiment. Were all the experiments completed in one day or different days? 
10)    Could the material of the mixing jar and the powders be being mixed affect adhesion? 
11)    Is there any reason the authors did not include ANOVA or regression analysis?

Overall, the document can be improved with some clarifications regarding the reason for mixing powder and the properties of the powder used. Also, the research could be more insightful if the authors could include additional levels of mixing variables for a detailed analysis. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In the paper, the authors presented the results of research on the effect of powder mixing parameters on component segregation. The subject of the study fits quite well into the latest trends in industry, related to the increasingly widespread use of additive manufacturing processes. Understanding the relationships between individual process parameters is extremely important for ensuring high quality of products manufactured in this way. Unfortunately, the authors focused on analyzing the influence of only two factors in their work: mixing speed and time. It is a pity that the scope of the research conducted was not extended to include additional parameters, such as the type of powders, their geometry, size, percentage of individual components. Only such an approach would provide a full picture of the influence of parameters on the quality of additively manufactured products.

In its current form, the paper is an extended report on the research conducted, without a scientific aspect.

Important notes on the paper:

1. In the second chapter, the authors state that the shape and dimensions of powder particles were determined using a field emission electron microscope (SEM). However, the paper does not show any photographs relating to the geometry of individual powder particles. I propose to supplement the paper with this information and add a commentary on the effect of powder geometry on the mixing process.
2. The authors indicate that increasing the mixing speed and mixing time increase the segregation of both materials. Please provide a detailed analysis of the reasons for this state of affairs. What determines the increase in segregation in the conducted studies, since other researchers indicate the opposite trend?
3. The work requires thorough reconstruction and expansion.
4. The conclusions require rewording so that they also present the scientific aspect of the conducted research.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have satisfactorily addressed most of the comments. They have included SEM images of Powder A and Powder B and have provided relevant details about the powder materials. They have also discussed the ANOVA results.

However, the manuscript lacks a concrete rationale for the selection of powders, particularly in terms of particle morphology, size , and percentage mix ratios. The potential influence of powder particle adhesion to the material of mixing jar should be an important factor that has not been considered. The selection of variables and their levels seems rather limited for a study of this nature. Drawing conclusions based on only two levels of two variables seems inadequate, when previous studies have reported contradictory results.