Injection Flow Rate Threshold Preventing Atypical In-Cavity Pressure during Low-Pressure Powder Injection Molding
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Authors,
I am writing to you with regard to your manuscript focused on the Powder Injection Molding process. Upon initial review, I believe there are a number of areas that would benefit from revisions and further clarity.
1. In section 2.1, specifically lines 113-116, it would be beneficial to provide a more comprehensive overview of the experimental equipment used. This could be effectively presented in a tabular format for ease of reference.
2. The basis for selecting feedstock of 60 and 65 vol. % (as referenced in lines 119-120 and Table 1) is not clearly stated. Please provide the rationale behind this choice.
3. Similarly, Table 1 would benefit from a more detailed explanation as to why these particular parameter values were chosen.
4. Please provide a reference for the data presented in Table 2.
5. As for Figure 2, it is not clear whether the results presented are from your own research or if they are derived from another source. If the latter, please ensure appropriate citation is included.
6. For Figure 3, some revisions would enhance its clarity and comprehensibility:
- Fig. 3a: Should be standalone and larger for better visualization.
- Fig. 3b-3g: Consider separating these for better clarity and enlarging them for ease of viewing.
- Fig. 3h and 3i: These should be separated, and the main dimensions of the part and mold should be clearly indicated. This can be done within these figures or alternatively, in Figure 4.
7. Lastly, please provide more details about the pressure sensor used for collecting the experimental results in Fig. 6, such as its location, type, etc.
Sincerely,
Author Response
Dear Reviewer,
Please find the responses in the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsRef.: Ms. No. powders-2445534-peer-review-v1
Title: Injection flow rate threshold preventing atypical in-cavity pressure during low-pressure powder injection molding
Decision: Major revision
Comments to the authors:
The authors have presented an interesting work combining experimental and numerical approaches to study the impact of injection parameters (i.e., mold temperature, feedstock temperature, injection flow rate etc.) on mold in-cavity pressure and on the overall quality of green parts produced by low-pressure powder injection molding. The authors have come to a set of conclusions including an increase in mold and feedstock temperatures, and a decrease in solid loading decrease the mold in-cavity pressure, which depends on the feedstock (i.e., F60 and F65) viscosity. The authors observed the expected linear relationship between the pressure and feedstock flow rate using injection flow rates above the flow rate threshold (Qth), which is 7 cm3/s and 3 cm3/s for F60 and F65, respectively. Qth was found to be the minimum flow required to avoid atypical high in-cavity pressure leading in several visual defects such as weld lines, flow marks, cracks, sinks, and incomplete filling.
The manuscript is well-written. The literature review is adequate. Yet, the following issues need to be taken care of before the manuscript is being accepted for publication.
1. What is rationale of choosing 60 and 65 vol% of stainless-steel powders for preparing the feedstocks used in this study?
2. The experimental and numerical results shown in figures 6, 7 and 8 have differences; particularly a significant overestimation of pressures (more than 500 kPa) is visible in feedstock F65 in figure 8. The authors reported these discrepancies and mentioned that this is due to ignoring a few parameters in simulation particularly linked with the thermal transfer conditions seen in the LPIM. The authors need to specify those parameters. Yet, ignoring these parameters weaken the merit of results.
3. Authors need to modify the lines in figure 9. Particularly the lines representing 15 and 30 cm3/s are indistinguishable. Instead, authors should have used dotted and/or bold lines.
4. Only 3 references have been used to support the obtained results.
Comments on the Quality of English LanguageThe quality of English Language is good.
Author Response
Dear Reviewer,
Please find the responses in the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThis work represents an experimental and numerical study for low pressure powder injection molding. A study with different powder content, feedstock and mold temperatures as well as injections speeds is presented and modeled for a simple geometry and partially for a complex geometry. The authors present the results, compare them to the simulation and discuss both good and with a high level of detail. Thermal aspect are mentioned as major point for the deviation of simulation and experiments, which is partially verified with temperature measurements in the trials. The quality of the results and discussion is already quite high, but some points mentioned below should be addressed to improve the quality of the work.
Major points are:
1. In Eq. 1 it should be E*ln(gamma)*T (the T is missing)
2. The Temperature difference in Fig. 6c and d is higher compared to the ‘extreme conditions’ in Figure 7b (in case of T_feedstock=100°C), which should be mentioned in the explanation.
3. Why is the pressure for f65 at the end of filling in Fig. 7b constant? Is some border for pressure controlled filling reached here? Can this be compared to the simulation?
4. Are the experimental pressure and temperature curves the mean of multiple experiments? (They should not be one single experiment) How many experiments are performed? Add some scatter beams or minmax-shading so the reader has knowledge about the process uncertainty.
5. Since Poiseuille assumes a parabolic velocity distribution, an average shear rate as function of Q can be used to calculate the viscosity in case of assuming it to be constant 100 s^-1.
6. In the lines 390 and following you mentioned that software must be improved to model the LPIM process. However, a 4 year old moldflow version is used and at least some of your points have been addressed in newer versions (for example thermal boundary conditions). Discuss this better.
7. Point 4 also applies for Fig. 10. Have multiple experiments been performed and are the defects reproducable?
8. In Fig. 4 the simulation model for the complex geometry is shown. However no simulation results are ever shown. Is the simulation able to predict defect and segregation?
9. The outlook is quite short and only mentions points about the simulation. What are the further points to bee addressed for the LPIM process?
Minor points are:
1. There is a blue line in line 61
2. Line 70 starts with ‘in the past few years’ but the reference is over 15 years old.
3. At the end of line 198 it should be were not was.
4. In line 275 and following the decrease of pressure is explained with the decrease of viscosity since the viscosity since the feedstock is hotter. Of course, this is correct but in case of Fig.6a and b the decrease is because the feedstock cools down more slowly not because it is hotter.
5. Please give exact values for the shear rates used in line 278 and 279 since also exact values of viscosity are given.
6. Line 284: Calling a deviation of 35 % close is questionable, however the ongoing discussion is good.
7. The legend for the grey dotted line in Fig.8 is missing.
Author Response
Dear Reviewer,
Please find the responses in the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Authors,
The last version is good for publishing.
Sincerely yours,
Author Response
Thank you for your review.
Reviewer 2 Report
Comments and Suggestions for AuthorsAttached
Comments for author File: Comments.pdf
English is good
Author Response
See the attached file below
Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have addressed the concerns I raised in the first round of review. I am convinced by the Authors' responses.
