A Guiding Framework for Process Parameter Optimisation of Thermal Spraying

Round 1

Reviewer 1 Report

Dear authors, when I read the title and abstract, I was glad that someone decided to do such a paper. Unfortunately, as I went through the text, I noticed that there are many aspects that you need to take into consideration in order to bring the paper up to the level of the publication you have opted for. First of all, I am aware that an exhaustive approach to the subject is clearly impossible, as you said.

Among the observations I have made in part and in the body of the text, I mention:

- the title refers to all thermal spraying techniques, but you have mainly exemplified plasma deposition and secondarily HVOF - it would be better to rephrase the title and limit yourself only to these two,

- you have not correctly cited the papers from which you have taken data or conclusions,

- you should add more cited articles, as this is a paper generally based on previous sources,

- you applied DOE but you didn't specify where the data you took from,

- the way of exposition is not very scientifically sound and should be worked on - it needs to be more scientifically sound and not exposed as your own experience,

- you need to rephrase some sentences that are too long and lose their meaning.

However, I appreciate your courage to make such a synthesis, which is indeed very helpful to beginner engineers who want to work in the field of thermal spray coatings. 

Comments for author File: Comments.pdf

Author Response

Reviewer 1

Dear authors, when I read the title and abstract, I was glad that someone decided to do such a paper. Unfortunately, as I went through the text, I noticed that there are many aspects that you need to take into consideration in order to bring the paper up to the level of the publication you have opted for. First of all, I am aware that an exhaustive approach to the subject is clearly impossible, as you said.

Among the observations I have made in part and in the body of the text, I mention:

- the title refers to all thermal spraying techniques, but you have mainly exemplified plasma deposition and secondarily HVOF - it would be better to rephrase the title and limit yourself only to these two,

While agreeing to the fact that there could be alterative titles (suggested below), we feel that the framework presented applies to all thermal spray techniques and it is shown as test case by taking HVOF and APS. We request to retain the mention of thermal spray in the title for the wider benefits of the audience and search strings.

We provide our revised title as “A guiding framework for process parameter optimisation of thermal spraying”

- you have not correctly cited the papers from which you have taken data or conclusions,

Wherever data is taken from other literature, citations have been provided. If the citations are not provided, it is our own work with our industrial partners. We sprayed 8 YSZ powders to generate this data as part of the UK’s funded project titled “EPSRC NetworkPlus in Digitalised Surface Manufacturing”, some of the work has been documented through a series of seminars that could be viewed from the dedicated Youtube channel of the Network.

https://www.youtube.com/@dsmnetwork7248

As part of the scientific commitment of this Network, we ran a thermal spray week event with experts of spraying the transcripts of which can be viewed from here:

https://www.youtube.com/watch?v=nlDmhM1qhpQ&t=4114s

 https://www.youtube.com/watch?v=c_RyulgFX84

https://www.youtube.com/watch?v=hBjLwySsYyU

https://www.youtube.com/watch?v=ds7V6t0AYRs&t=41s

 

The learnings from those events have shaped the articulation of this manuscript, in its current form.

 

- you should add more cited articles, as this is a paper generally based on previous sources,

Additional citations are inserted appropriately.

 

- you applied DOE but you didn't specify where the data you took from,

The work was done in house as part of the DSM Network Demonstrators. We sprayed 8 YSZ powders to generate the raw data which followed analysis using minitab software.

 

- the way of exposition is not very scientifically sound and should be worked on - it needs to be more scientifically sound and not exposed as your own experience,

The primary author has extensive experience working with global conglomerate General Electric GE . The team has wealth of experience in working with thermal spray processes such as plasma spray , HVOF , Wire arc , cold spray and flame spray. The idea coined here was driven by the notion to reach out to industries in a fairly approachable manner while taking scientific understanding of the process in account. We have reworded the section but its difficult to change it too much as this deviates from the original goal of the work.

 

- you need to rephrase some sentences that are too long and lose their meaning.

Sentences are rephrased wherever necessary to retain the conciseness and retain the message to be conveyed

Author Response File: Author Response.docx

Reviewer 2 Report

The paper represents an easy to read overview of thermal spray aimed at a novice venturing in to thermal pray. The question is whether this rather basic and generalizing overview qualifies as a scientific article. I am sure the editor will be able to answer this question.

Section 2 represents a cookbook for selection of the equipment, and gives a DOE example. As well as some basics of plume study by means of particle diagnostics or stationary deposit characteristics.

Section 3 deal with plume visual check, nozzle selection (health check advertised in heading is missing), low melting point material deposition and diagnostic techniques (rather than digital tools as described in the heading of sect 3.4).

In my opinion, the paper would benefit from rearranging the main topic and including more references as it is in fact a review paper. Therefore I suggest MAJOR REVISION of the paper.

Major comments:

The structure would benefit from rearrangement, I encourage the authors to consider the following:

1.       Introduction

2.       Equipment selection for classes of materials

3.       Diagnostic and characterization methods, DOE

4.       Other considerations (Tips and tricks)

The subsections should then be shuffled accordingly.

Minor comments

the TOC occupies one whole page, once the paper is restructured it may be possible to remove it

L55: to ‘medical implants’ is missing ‘from’

L62: missing space before reference, check also elsewhere

L72: the effect of feeder choice is reduced to maintenance cost, no clue is given on the application related difference of the feeder types

L93: Cold spray seem to bemissing inn the list despite bein included e.g. in fig 1

Figure 1 – non standard symbols are used for the flow-chart, some excersise is needed to see which branch corresponds to true and false

L129: – “The physics of athm….” The physics below basically consider dissociation and ionization, I encourage the authors to reflect it here and also to include some basic quantification of energies and temperatures

L142: – “plasma heat” seems a very vague term -> specific enthalpy ?

L162: –metric units would be preferred throughiut the paper

L184: “These two parameters are generally disregarded by the engineers for the sake of convenience of locating the part concerning the robot.” ???

L193: The suggestion of spray distance without the relevant background (substrate, feedstock, powder ) seems questionable

L220: the discuss CTE, but give emaple considering melting point

L224: the choice of axial or radial needs short explanation, with pro’s and con’s of each

L242: RFR needs reference

L245: ‘finalized’ brings confusion, I suggest ‘fixed’

Table 1 missing units, the experiment is not a full factorial DOE

Figure 5, units in wrong case (kW, kw,….),n ot clear what is in fig b)

L275: “Similarly, if the tensile strength requirement has 275 an upper limit and a lower limit, it is better to choose plasma or flame spray ?”.

L279 : gms-> g/s

L286 :arc generation -> discharge start

L291 : misaligned text with the arrows

L312 : ovality of plats CORRESPONDS to D1≠D2

L314 :the discussion below assumes repeatability of the splatting centre, a feature hardly seen for some torches

L323 : “Gas flow..” carrier ,plasma ?

L326: “not over oxidize the coating 326 than the specifications“ English

L360: Nozzle design -> Nozzle selection, where is the health check ?

L379 : digital tools -> diagnostic tools

 

 

Author Response

REVIEWER 2:

 

The paper represents an easy to read overview of thermal spray aimed at a novice venturing in to thermal pray. The question is whether this rather basic and generalizing overview qualifies as a scientific article. I am sure the editor will be able to answer this question. Section 2 represents a cookbook for selection of the equipment, and gives a DOE example. As well as some basics of plume study by means of particle diagnostics or stationary deposit characteristics. Section 3 deal with plume visual check, nozzle selection (health check advertised in heading is missing), low melting point material deposition and diagnostic techniques (rather than digital tools as described in the heading of sect 3.4).

 

A paragraph on health check of hardware is added in the section 3.2 . The word digital has been replaced with diagnostic wherever possible.  Also, acoustic emission generated frequencies that can be captured with piezo electric sensors and are quite useful in digitization of thermal spray data that will help recording. It has potential to render metallography and mechanical property testing obsolete. A pioneer work in this acoustic field is being done by our group and we are in the process of publishing this research paper soon. 

 

In my opinion, the paper would benefit from rearranging the main topic and including more references as it is in fact a review paper. Therefore I suggest MAJOR REVISION of the paper.

 

Major comments:

 

The structure would benefit from rearrangement, I encourage the authors to consider the following:

 

1. Introduction

 

2. Equipment selection for classes of materials

 

3. Diagnostic and characterization methods, DOE

 

4. Other considerations (Tips and tricks)

 

The subsections should then be shuffled accordingly.

 

More references are added and restructured the paper as suggested to make the rhythm better.

 

Minor comments

 

the TOC occupies one whole page, once the paper is restructured it may be possible to remove it

Table of contents removed after restructuring the headings

 

L55: to ‘medical implants’ is missing ‘from’ - Corrected

 

L62: missing space before reference, check also elsewhere – Checked everywhere and corrected

 

L72: the effect of feeder choice is reduced to maintenance cost, no clue is given on the application related difference of the feeder types- more details have been added and a reference have been provided about the fundamentals of the two main feeder types

 

L93: Cold spray seem to be missing inn the list despite bein included e.g. in fig 1. It is true. we have focussed on plasma spray , HVOF and flame spray as they are more used in industries in terms of volume of production parts sprayed. A note to this effect has been added just before conclusions.

 

Figure 1 – non standard symbols are used for the flow-chart, some excersise is needed to see which branch corresponds to true and false . Word “No” has been added wherever needed so that other possibilities are all implicitly “Yes”

 

L129: – “The physics of athm….” The physics below basically consider dissociation and ionization, I encourage the authors to reflect it here and also to include some basic quantification of energies and temperatures – The sentence have been modified.  Quantification of energies and temperature are not scope of this paper.

 

L142: – “plasma heat” seems a very vague term -> specific enthalpy ? The word heat has been replaced with energy.

 

L162: –metric units would be preferred throughiut the paper

 

L184: “These two parameters are generally disregarded by the engineers for the sake of convenience of locating the part concerning the robot.” ???

The paragraph has been edited to create more meaningful messages regarding robot programming

 

L193: The suggestion of spray distance without the relevant background (substrate, feedstock, powder ) seems questionable

These are all starting parameter suggestions to avoid multiple iterations. For example , a plasma spray process can’t be at 200 mm or 25 mm. So these numbers are starting guidance.

 

L224: the choice of axial or radial needs short explanation, with pro’s and con’s of each

Short explanation has been provided as a defintion

 

L242: RFR needs reference – reference provided

 

L245: ‘finalized’ brings confusion, I suggest ‘fixed’ – changed “finalized” to “fixed”

 

Table 1 missing units, the experiment is not a full factorial DOE – missing units have been added. Word full factorial DOE is changed to DOE

 

Figure 5, units in wrong case (kW, kw,….),not clear what is in fig b) – Fig 5 units are changed and kW is corrected. Fig 5b has been given additional explanation in the fig caption

 

L275: “Similarly, if the tensile strength requirement has 275 an upper limit and a lower limit, it is better to choose plasma or flame spray ?”. The sentence has been removed . From my experience, if there is a upper limit in the tensile strength, HVOF can’t meet the upper limit as it always exceeds the upper limit but plasma and flame spray has good control not to breach the upper limit.

 

L279 : gms-> g/s – Correction done to g/min

 

L286 :arc generation -> discharge start – arc generation has been changed to arc discharge

 

L291 : misaligned text with the arrows – The table has been modified to take error of moving arrows with text

 

L312 : ovality of plats CORRESPONDS to D1≠D2 – The symbol is changed

 

L314 :the discussion below assumes repeatability of the splatting centre, a feature hardly seen for some torches – spray plume needs to be in center otherwise it will lead to frequency robot path changes leading to manufacturing interruptions. This is a culture in asia pacific countries to do plume spot check often to correct plume deviations everyday in manufacturing shop floor.

 

L323 : “Gas flow..” carrier ,plasma ? – Plasma generation gas. Sentence has been corrected

 

L326: “not over oxidize the coating 326 than the specifications“ English – changed the language

 

L360: Nozzle design -> Nozzle selection, where is the health check ? – Added a paragraph on health checkup

 

L379 : digital tools -> diagnostic tools – changed in all places in the manuscript

 

 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors adressed all comments and carefully rearranged the paper. During this proces couple of issues emerged that can be adressed during MINOR revision in authors opinion.

L219 high coefficient of thermal expansion (CTE) -> thus often thereis a large CTE mismatch ….. ?

L270 needs rephrasing: For achieving high tensile strength for materials with high oxygen affinity, HVOF could be an alternative to achieve best adhesion properties with minimal oxidation (not sure is it about adesion or strength ?) –HVOF is good for adesion and strength.

Should the part commentedbelow go to section 3.2?

L273 selection of Plasma gun nozzle? Or does it hold olso for other torches?

L274 flown through the gun -> deposited (otherwise it suggests we are talking only axial here)

 

Author Response

All minor corrections incorporated.

Author Response File: Author Response.docx