Weldability of Additive Manufactured Stainless Steel in Resistance Spot Welding

Round 1

Reviewer 1 Report

This paper presented a laboratory study on the weldability of AM steel by RSW. A wide range of literature has been reviewed to justify the need for this research. The abstract was well written. The experimental section also looks good and can be reproduced by future researchers/readers of this manuscript. The tensile testing section of the experiment is not clear. The results are presented well. It was concluded that the constant power method could improve weldability, especially for AM 316L steel. The conclusion was drawn based on the experimental observations and should be considered for publication. However, the followings need to be addressed before accepting the manuscript for publication:

1. Only similar materials were joined by the RSW method in this manuscript. C316 L steel with C316 L steel and AM316 L steel with AM316 L steel. How about joining C316 L with AM316L?

2.  When joining AM 316 L: what will happen if the welding time increased to 600 ms in CCC mode?

3.  In figure 6: in the cross-sectional analysis, which joints are they? I cannot find any matching welding power in figures 2 and 3. Is this section necessary, as all the cross-sections were already provided in figures 2 and 3?

4. Please include a scale bar in figure 7. What was the strain rate in your tensile shear test? What was the joining configuration? Please provide a figure. What are the surfaces presented here? Is it the top surface, the middle surface, or the bottom surface? 

5.  Microhardness profile: What is distance 0? Which is the datum point?

6. Improved Weldability through CPC Mode: The reviewer disagrees because of the lack of sufficient evidence. It is evident that for the CPC mode, the average power is around 7.5 kW, but for the CCC mode, the power is always less than 7 kW. This could be the reason for not getting good joints in CCC mode. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors provide an interesting welding technology focused study on the RSW of AM 316L. There are some comments that must be addressed. 

1. The authors may want to consider showing the weld lobe on a typical Nugget Diameter vs Weld Current plot rather than in a table. 

2. In Figure 4, the C 316L does not show a beta peak in the DRC. Is there any idea why that is?

3. The dynamic resistance (and also presumable the static resistance) of the AM 316L consistently appears to be higher. Given the chemistries and weld set-up is the same for both materials, the authors should add some discussion on why the resistance is different.

4. The authors observed a difference in base material hardness. The authors claim this is due to a difference in cooling rate and resultant microstructure. Since this is critical to the mechanical performance shown in the paper, the authors should include some micrographs to confirm these claims.

5. The authors should include some discussion on how well the AM parts can be integrated into industrial practice. There is an observed increased difficultly in weldability with the AM 316L for a ~2kN increase in tensile shear strength. Is this tradeoff worth it?

6. The study overall is quite simple and does not seem to provide any scientific novelty. I strongly recommend the authors either dive deeper into determining the differences leading increased resistance in the AM part or complete an extensive fracture/microstructure analysis to characterize the difference in weld failure. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript addresses the weldability of additively manufactured stainless steel in resistance spot welding. The manuscript is interesting, however, some physical phenomena should be described in detail to understand the results of the experimental activity.

A major revision is required to improve the quality of the manuscript, as it follows.

Comments to the authors:

1- I suggest revising the manuscript to an English mother tongue. There are several English grammar mistakes throughout the manuscript that must be corrected.

 

Introduction

1- “Several welding methods have been used applications such as gas tungsten arc welding (GTAW), shielded metal arc welding, and resistance spot welding (RSW) [3]”. The reference [3] only refers to RSW and not to the other welding techniques. Add further references.

2- the reference from 9 to 14 are not about RSW. I think it is not interesting to reference other welding techniques that are not the focus of the manuscript. I suggest introducing a much more coherent main text to the manuscript topic for an adequate state of the art. Moreover, which could be possible for the applications of RSW welded additive parts made of stainless steel? 

 

Experimental setup

1 The welding current (CCC control) and the power ranges(CPC) are missing in Table 2. 

2- The authors have stated that “..The electrode displacement was measured…” but no information is about the method used to measure it and how its signal has been time-synchronized with the other signals.

3- “…The electrode force and hold time were fixed at 3.4 kN and 167 ms…”. I suggest detailing the extent of the squeeze time and forge time. This is not clear from what is written in the text.

 

4- What is the theoretical density of additive steel? Which is the porosity distribution? How does porosity influence the thermal conductivity of steels? This is essential information for additive steel to understand the difference from bulk steel (i.e., Figures 4 and 5). I also suggest showing a representative metallographic image. 

 

Weld Lobe Analysis for Two Materials

1- the authors should explain why the Additive steel exhibits different trends in Figures 4 and 5. Which is the physical phenomenon under this behavior? How does the different additive microstructure influence these trends compared to bulk steel? 

 

Cross-section Analysis

1- Better images are required for Figure 7.

 

 

Improved Weldability through CPC Mode

1- the authors should explain in detail the physical phenomenon that makes the CPC mode better to improve the weldability of additive steels.

 

 

Conclusions

Conclusions should be rewritten according to the revised version of the manuscript.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The reviewer is satisfied with the response from the authors. 

Author Response

Thanks to your review.

Reviewer 3 Report

Dear authors,

some improvements have been made to the manuscript. However, some information still needs to be included. Sometimes, you have only provided answers to the reviewer without adding these considerations in the revised manuscript.

Particularly:

1- you should describe to the revised manuscript the extent of porosity in the additive sample and clearly explain, better quantitatively, the influence of porosity on the thermal conductivity of steels and, hence, on the welding process.

2- The authors should explain in the revised manuscript why the Additive steel exhibits different trends in Figures 4 and 5. 

3- Finally, the authors should explain in detail the physical phenomenon that makes the CPC mode better to improve the weldability of additive steels. This is not still explained in the revised manuscript. The authors have only stated: "As a result, it can be judged that the weldability is improved by applying the CPC mode to the material for which the proper welding section does not appear in the previous experiment." The reason for this result has not been explained yet in the revised manuscript.

Best regards.

Author Response

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Author Response File: Author Response.pdf