Analysis of Stainless Steel Waste Products Generated during Laser Cutting in Nitrogen Atmosphere
Round 1
Reviewer 1 Report
The manuscript presents the analysis of stainless steel and waste products generated during laser cutting in nitrogen atmosphere. The experiment methods are explained in detailed. But the result and discussion section are still not sufficient in my opinion.
First of all, the title of the manuscript is ‘Analysis of stainless steel and waste products generated during laser cutting in nitrogen atmosphere’. However, the article mainly focus on the analysis of waste products, the research about the surfaces morphology after cutting is too shallow. As the author summarized in the conclusion, when laser cutting metallic materials, it is mainly through the liquefaction of the metal surface to remove the material and the accompanying gases can prevent oxidation of the cut surface. The above conclusion lacks bright spot and originality.
To my understanding, laser cutting technology includes melting cutting, vaporization cutting, oxidation melting cutting and controlled fracture cutting. Different cutting techniques inevitably produce different cutting surfaces and wastes products.
Secondly, the possibility of application of the waste products is not sufficiently presented. In section 3.1 and 3.3, the author shows the component and size of the powder. Base on this, the author comes to a conclusion that the waste material may be reused for industrial applications such as additive manufacturing.
However, no experiments were carried out to verify the feasibility of the powders used in additive manufacturing. Therefore, I recommend that the author adds the evidence to verify the powders’ possibility.
In general, the research about the surfaces morphology after cutting is lack of innovation and the mechanism of waste production is not thoroughly studied. The most attractive point of this article is the possibility of application of the waste products, however, the author did not show the practical effect of waste products in additive manufacturing.
Finally, there are some mistakes in the text, such as:
- Figure 4 and Figure 4b in line 143-144 are incorrectly marked, which should be Figure 3;
- In line 154, Figure 3c and Figure 3d are not specified in the text;
- In Line 173, Figure 4a-f is not specified in the text;
- In line 183, no error bars are added in the bar chart in Figure 5;
- In line 199, the bar chart in Figure 6b should be shown separately after adding the error bars, and relevant explanations should be added in the paper;
- In line 264, the wrong unit of diameter should be μ
The reviewer believes this paper is not worth to be published in the present form.
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewer 1 Comments
In the beginning, we would like to express our gratitude to the Reviewer for the comments, corrections and rapid performance of the review process. All the questions and comments were very accurate and helpful and have assisted us to improve our manuscript to became clearer and more understandable for the Readers.
Below please find the answers to the Reviewer’s comments and corrections made in the manuscript text:
The manuscript presents the analysis of stainless steel and waste products generated during laser cutting in nitrogen atmosphere. The experiment methods are explained in detailed. But the result and discussion section are still not sufficient in my opinion.
Comment 1:
First of all, the title of the manuscript is ‘Analysis of stainless steel and waste products generated during laser cutting in nitrogen atmosphere’. However, the article mainly focus on the analysis of waste products, the research about the surfaces morphology after cutting is too shallow. As the author summarized in the conclusion, when laser cutting metallic materials, it is mainly through the liquefaction of the metal surface to remove the material and the accompanying gases can prevent oxidation of the cut surface. The above conclusion lacks bright spot and originality.
To my understanding, laser cutting technology includes melting cutting, vaporization cutting, oxidation melting cutting and controlled fracture cutting. Different cutting techniques inevitably produce different cutting surfaces and wastes products.
Response:
We are very grateful for this valuable comment. We agree that the proposed title may suggest that the presented work will be also dealing with the surface analysis of the cut material. In order to eliminate the unnecessary ambiguity that can arise, we have decided to remove the word “and” from the title. Hopefully, the new title will suggest that only the waste products are studied within the presented manuscript and is more unequivocal for the Readers. In the presented paper, we have not focused on the issues raised in the Reviewer’s comment: surfaces morphology after cutting and the influence of various cutting techniques on the component surface. Of course, we completely agree with the Reviewer that such properties are important and interesting for some scope of Readers. Nevertheless, the main aim of the presented work is the analysis of the produced waste powder. Due to that, the surface analysis is not deep. We wanted to present the surface and its chemical composition in order to show that the protective gas atmosphere fulfills its tasks and prevents the cut components from oxidation. The application of the protective gas atmosphere is very beneficial during the industrial cutting process due to the fact that further deoxidation of the surface is not needed and the components cutting process can be accelerated and simplified.
Comment 2:
Secondly, the possibility of application of the waste products is not sufficiently presented. In section 3.1 and 3.3, the author shows the component and size of the powder. Base on this, the author comes to a conclusion that the waste material may be reused for industrial applications such as additive manufacturing.
However, no experiments were carried out to verify the feasibility of the powders used in additive manufacturing. Therefore, I recommend that the author adds the evidence to verify the powders’ possibility.
Response:
The powder material obtained in rather large amounts after laser cutting in nitrogen atmosphere in an industrially operated machine is an inconvenience for the companies due to the fact that there is a lack of good application (re-usage) possibilities for the powder. The produced powders are usually just collected in waste bins. The idea to use the powders in the additive manufacturing (AM) process would help to utilise the produced powders and not waste the obtained material. In this paper, we have focused on the detailed analysis of the powder material in order to verify whether it would be possible to apply it further in the additive manufacturing process. In our further work that we are preparing, we would like to show the application and the results of the additive manufacturing process using the obtained powder material.
The fact that the powder particles are mostly spherical with relatively small shape irregularities drew our attention to the possibility of using the powders in the AM process. These facts imply good flowability as well as good thermal conductivity of the powder. The way of the particle formation during laser cutting is similar to gas atomization, which is a common way to prepare powders for AM. In both cases, small droplets of melted metal solidify during their flight in a protective atmosphere and they obtain a spherical shape. In the metal powder atomization process, sizes of particles are also generated randomly, with subsequent sieving them (in the solid-state) [de Souza J, Oliveira-Motta CA, Machado TG, Giacomin A, Arabi HMA (2016), IJRES. 4:1–5]. This also suggests that the powders generated during laser cutting will have similar characteristics to those generated by the gas atomization method.
To better estimate the shapes of the particles, we performed an additional evaluation of the particles circularity. The results are added to Fig. 5a and they confirm that most of the particles have a regular (spherical) shape. Even though the particles are spherical and with known size distribution, the quality of the powder material can be improved easily as follows: The range of particle sizes, which is required for a particular AM usage, can be separated by sieving the powder by appropriate sieves. In this way, too small, too big or irregularly-shaped (e.g. elongated) particles can be removed. Thus, the share of regular, spherical, well recrystalized particles of desired sizes increases in the material.
We, of course, fully agree with the Reviewer’s comment that “no experiments were carried out to verify the feasibility of the powders used in additive manufacturing”. The claim was based on the literature analysis of the particles already applied for the additive manufacturing process (additional references are introduced to the manuscript text 20-23). The main idea behind the prepared manuscript was to study the material produced during the everyday operation of the laser machine. In everyday operation, the amount of generated metal powder is enormous taking into account the overall number of laser cutting companies. We wanted to perform a detailed analysis of the resulting powder in order to inspire the community to reuse generated powder in a useful way. We stated that the powders might have a potential application in AM process. As mentioned earlier, we will try to evidence the application of the material in the AM process in the further paper. We strongly believe the performed detailed analysis of the waste product will be interesting for the scope of Readers who deal with such materials; and they could also find some other applications for the powders beside the AM that we have not come up with. The presented analysis will be helpful for them and due to that, we hope that the Reviewer will change his mind and reconsider his opinion regarding the publication of our paper in the Metals journal without AM tests.
Comment 3:
Finally, there are some mistakes in the text, such as:
Figure 4 and Figure 4b in line 143-144 are incorrectly marked, which should be Figure 3;
In line 154, Figure 3c and Figure 3d are not specified in the text;
In Line 173, Figure 4a-f is not specified in the text;
In line 183, no error bars are added in the bar chart in Figure 5;
In line 199, the bar chart in Figure 6b should be shown separately after adding the error bars, and relevant explanations should be added in the paper;
In line 264, the wrong unit of diameter should be μ
Response:
We are grateful for finding our oversights. All mistakes have been corrected and missing figures references were specified in the text.
The histograms were prepared based on the performed electron microscopy analysis of the particles images. Sizes of the particles were determined and based on that appropriate “bins” were chosen and the obtained results were assigned to the chosen bins. Subsequently, the number of particles in each bin was calculated. The histogram data was used for appropriate distribution function fitting. The obtained values describing the size distributions were evaluated from the fitted distribution curve and are provided with appropriate standard deviation values. We are not sure how the error bars for individual histogram bins should be evaluated because the error will depend on the determination of the individual particle size from the image analysis.
Author Response File: Author Response.pdf
Reviewer 2 Report
The article deals with an actual issue of reuse waste particles obtained during laser cutting. The authors suggest a possible solution to this problem. The presented results are valuable; however, the authors made some minor errors:
I suggest replacing the term “cutting of elements” by “cutting of parts” or “cutting of components”.
In subchapter 3.2 is a reference to Figure 4 (line 144), but obviously, it should be Figure 3 instead.
In line 264 is written: “… a mean diameter 27.2 am”. You probably did not mean atto meters (10-18 m). I suppose you wanted to write µm (10-6 m).
Perhaps, there should be found the answers to the following questions in the text:
In experiments were used dry nitrogen protective atmosphere in order to prevent oxidation of the laser processed material (line 83-85). And yet, Magnetite (Fe2O3) phase was the most common phase (74,2 %) of the studied material (Table 1). Does it mean the protective atmosphere was ineffective? Can you suggest any options on how to prevent particle oxidation (changing the flow or pressure of accompanied gas, etc.)?
Has protective gas and its pressure any influence on particle size?
The obtained microparticles had a dendritic structure (line 169), hollow-core (lines 169-170), increased oxygen content (lines 209-212). There were nanoparticles observed as well (line 190). Cannot be it a problem for a future application for additive manufacturing?
There was mentioned the required sizes of particles for additive manufacturing (lines 269-270). Are there any other requirements for particles used in additive manufacturing (e.g. purity, etc.)?
Author Response
Response to Reviewer 2 Comments
In the beginning, we would like to express our gratitude to the Reviewer for the comments, corrections and rapid performance of the review process. All the questions and comments were very accurate and helpful and have assisted us to improve our manuscript to became clearer and more understandable for the Readers.
Below please find the answers to the Reviewer’s comments and corrections made in the manuscript text:
The article deals with an actual issue of reuse waste particles obtained during laser cutting. The authors suggest a possible solution to this problem. The presented results are valuable; however, the authors made some minor errors:
Comment 1:
I suggest replacing the term “cutting of elements” by “cutting of parts” or “cutting of components”.
Response:
Thank you for the comment – the term “element” was replaced by “part” – line 13 and 262.
Comment 2:
In subchapter 3.2 is a reference to Figure 4 (line 144), but obviously, it should be Figure 3 instead.
Response:
Thank you for the comment – it is our oversight – number 4 is replaced by number 3 – line 143.
Comment 3:
In line 264 is written: “… a mean diameter 27.2 am”. You probably did not mean atto meters (10-18 m). I suppose you wanted to write µm (10-6 m).
Response:
Thank you for the comment – it is also our oversight – “am” is replaced by “μm” – line 268.
Comment 4:
In experiments were used dry nitrogen protective atmosphere in order to prevent oxidation of the laser processed material (line 83-85). And yet, Magnetite (Fe2O3) phase was the most common phase (74,2 %) of the studied material (Table 1). Does it mean the protective atmosphere was ineffective? Can you suggest any options on how to prevent particle oxidation (changing the flow or pressure of accompanied gas, etc.)?
Response:
We are very grateful for this valuable comment. The protective nitrogen gas atmosphere is used in order to ensure the lack of oxidation of the cut material. The main purpose it fulfilled – the surface after cutting is free from oxides (Fig. 3) usually observed during laser cutting with the use of other laser machines. The studied powder is a waste material produced in a rather large amount during laser cutting. The powder particles are blown away by the nitrogen gas and oxidize outside of the protection atmosphere.
One idea to prevent the oxidation could be performing the laser cutting process in closed volume filled with protection gas. Nevertheless, such solution would be very unpractical in the sense of fast laser cutting for industrial applications. There are additional methods for production of nano and microparticles free from oxides but they are designed directly for such purpose. In the presented work we wanted to perform analysis of the waste powders in order to evaluate its potential applications. The produced powders are usually just collected in the waste bins. The idea to use the powders in the additive manufacturing process would help to utilize the produced powders and not to waste the obtained material.
Comment 4:
Has protective gas and its pressure any influence on particle size?
Response:
We suspect that such influence could be observed. The increased pressure would result in faster blowing the vaporised material out of the heat source and producing higher cooling gradient which would influence the particles size. The main goal of the presented work was focused on the analysis of the particles produced during everyday work parameters. All operating parameters were optimized for obtaining the most suitable cutting process without focus on the obtained powders. We wanted to examine the obtained powders as a side product of the laser cutting machine operations.
Comment 4 and 5:
The obtained microparticles had a dendritic structure (line 169), hollow-core (lines 169-170), increased oxygen content (lines 209-212). There were nanoparticles observed as well (line 190). Cannot be it a problem for a future application for additive manufacturing?
There was mentioned the required sizes of particles for additive manufacturing (lines 269-270). Are there any other requirements for particles used in additive manufacturing (e.g. purity, etc.)?
Response:
Thank you for the comments – they are very accurate. During the additive manufacturing process, a good homogeneity and controlled powder size is very important. In the performed analysis we wanted to present wide studies of the obtained powder. We are currently working on further experiments using the powder in the additive manufacturing process. Prior to the experiments we sift the powder in order to achieve smaller size distribution then observed in the raw material. Most of the powder material exhibit size between 5 and 60 μm which enables various selection of the desired size distribution for further application. Also, the circular shape of the powder material allows better packing. In order to cover such aspect of the waste powder, the circularity analysis was added to the manuscript text – inset to the Fig.5a and lines 180-182. Also, the conclusion part was extended and additional literature reference were added – lines 275-279, ref 19 and 20.
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
- Peaks in EDS spectras can not be higher than whole scale. We can not see the end of individual peak.
- Author should add table with wt. % of each element into every EDS spectrum figure.
- Name of elements is not readable in EDS spectras.
Author Response
Response to Reviewer 3 Comments
In the beginning, we would like to express our gratitude to the Reviewer for the comments, corrections and rapid performance of the review process. All the questions and comments were very accurate and helpful and have assisted us to improve our manuscript to became clearer and more understandable for the Readers.
Below please find the answers to the Reviewer’s comments and corrections made in the manuscript text:
Comments:
Peaks in EDS spectras can not be higher than whole scale. We can not see the end of individual peak.
Author should add table with wt. % of each element into every EDS spectrum figure.
Name of elements is not readable in EDS spectras.
Response:
We are very grateful for this valuable comment. We have changed the labels of the chemical elements and introduced tables containing wt.% of each element into each EDS spectrum figure. Furher, the spectra were scaled appropriately so that they are better visible; and the artificial peak in Fig 4c is not shown anymore. Such corrections will improve the readability of the spectra for the Readers.
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The author has basically addressed all my comments. The author has clearly explained the potential application of the powders in AM process and enhanced the overall quality of the manuscript. Before publishing, please make sure all the references are in order. (e.g. reference 18 to reference 20 and reference 10 to reference 12).
