Model for the Prediction of Deformations in the Manufacture of Thin-Walled Parts by Wire Arc Additive Manufacturing Technology

Round 1

Reviewer 1 Report

This work is very interesting. The following are the questions for this manuscript.

1) Some sentences must be modifed to be understood easily, such as:(1) in this case a mold(page 1,line21),(2) Ding et al. used again a weakly(page2,line 86),(3)the deposition direction and more precisely the deposition of the last layer are very influencing fators(page2, line 92) and so on.

2) The explanation of GMAW has been appeared page 1,lin33, so the same explanation in page3,line 119 should be deleted.

3) the Alpha Q 552 puls (EWM) welding equipment has been introduced in page 3, line 130. And it is repeat in page 4,line 149. The author should give us a pithy description.

4) Page5,line 157, travelspeed should be travel speed.

5) Page 5, line160, the table 1 give us the parameters to GMAW-based WAAM. Their are four program numbers and the author only give us one experimantal result(Figure 5). I want to know the best welding parameters that used in this manuscript. Or if the welding parameters of table 1 are all used to produce the mold in figure 5, please decrible the layer number and the welding parameters clearly.

6) For the figure 4, it is hardly to understand why the color of energy input is different if the welding parameter is the same in each layer. Repeatly, the author should describe the relationship between layer number and the welding parameters clearly.

7) Page 7,line 203"In the upper part, as there have not been thermal cooling-heating cycles" This sentence should be rewrite as "there have been thermal cooling-heating cycle " because the metal is also melt and solidfied during WAAm process. I guess the author want to say"temper bead is disappered in this layer"

8）Page8，line247，“The distribution parameters of double ellipsoidal heat source are assumed to be the same in the numerical simulation of all layer depositions.”  is opposite to the result of figure 4(different heat input)

9) Page 8, line 251"the element size in the deposition area is about 1 mm." Page 5,line 157"reduce the layer height to 1.3 mm." It means each layer occupies one grid(1mm) in z direction, so is it fine enough for the simulation of this mold?

10) In figure7 b), it shows that the maximum temperature of layer is less than 1000 decelsius degree. Is it right as melting point of ER70 is higher than 1400  celsius degree.

11) Figure 8 shows the temperature of mold measured by pyrometer. Is it infraded pyrometer? The radiant emissivity of the mold is lack of introdution. Why the maximum temperature of Figure 8 is less than 1000 decelsius degree.

 

Author Response

Reviewer 1

Authors would like to thank to the reviewer for their detailed comments and suggestions for the manuscript. Below, you will find a point by point description of how each comment was addressed in the manuscript. Original reviewer comments in regular typeface, responses in italic.

This work is very interesting. The following are the questions for this manuscript.

• Thanks for the evaluation and for the valuable review of the article that has improved it significantly

1) Some sentences must be modifed to be understood easily, such as:(1) in this case a mold(page 1,line21),(2) Ding et al. used again a weakly(page2,line 86),(3)the deposition direction and more precisely the deposition of the last layer are very influencing fators(page2, line 92) and so on.

• Revised as requested.

2) The explanation of GMAW has been appeared page 1,lin33, so the same explanation in page3,line 119 should be deleted.

• Changed as suggested

3) the Alpha Q 552 puls (EWM) welding equipment has been introduced in page 3, line 130. And it is repeat in page 4,line 149. The author should give us a pithy description.

• Authors have deleted second reference to Alpha Q 552

4) Page5,line 157, travelspeed should be travel speed.

• Revised as requested

5) Page 5, line160, the table 1 give us the parameters to GMAW-based WAAM. Their are four program numbers and the author only give us one experimantal result(Figure 5). I want to know the best welding parameters that used in this manuscript. Or if the welding parameters of table 1 are all used to produce the mold in figure 5, please decrible the layer number and the welding parameters clearly.

• Certainly, the text is misleading, so a paragraph describing the parameters has been included.

The manufacture of the piece has therefore been carried out with a combination of two transfer modes. A Cold-Arc transfer mode is used in the first ten passes, then an-other ten are made in Pulsed-GMAW at the same traverse speed and ends with the same conditions in the Pulsed-GMAW mode at higher travel speed. This strategy is considered adequate since in the first layers the Cold-Arc mode introduces less heat to the substrate, and it transitions to a Pulsed-GMAW mode where less splashes are produced and finally the speed is increased to introduce less energy so that it is prevented the collapse of the wall.

6) For the figure 4, it is hardly to understand why the color of energy input is different if the welding parameter is the same in each layer. Repeatly, the author should describe the relationship between layer number and the welding parameters clearly.

• Figure 4 has been modified so that the energy regions are better observed, and a text has been added that clarifies the reason why the layers present different energy.

Analyzing the energy results it can be observed that the measured values of the machine control are not constant. This value depends both on the stick-out, the distance the wire goes out from the nozzle to the upper surface of the part and on fluctuations in travel speed, this type of energy behavior has already been reported previously by Wang et al. [16].

Figure 4. Evolution of energy during the manufacture of the mold

• Wang, B. Qi, B. Cong, M. Yang, Output characteristic and arc length control of pulsed gas metal arc welding process, Journal of Manufacturing Processes. 29 (2017) 427-437. https://doi.org/10.1016/j.jmapro.2017.08.007.

7) Page 7,line 203"In the upper part, as there have not been thermal cooling-heating cycles" This sentence should be rewrite as "there have been thermal cooling-heating cycle " because the metal is also melt and solidfied during WAAm process. I guess the author want to say"temper bead is disappered in this layer"

7)      Yes, thank you very much for the comment, the text has been modified as suggested.

8) Page8，line247, “The distribution parameters of double ellipsoidal heat source are assumed to be the same in the numerical simulation of all layer depositions.”  is opposite to the result of figure 4(different heat input)

8)      Sorry for the mistake not the heat source but power of heat source is assumed to same for all layers of the deposition. Authors rewrite the sentence and modify the text. However, in the figure 4 it can be seen that the energy is almost the similar at every layer. The little differences in energy can be because of many factors such as welding speed, waiting time, stick in and stick out of the filler etc.

9) Page 8, line 251"the element size in the deposition area is about 1 mm." Page 5,line 157"reduce the layer height to 1.3 mm." It means each layer occupies one grid(1mm) in z direction, so is it fine enough for the simulation of this mold?

9)      Simulation has been performed using several element sizes close to 1.3mm by keeping the total height constant. It is overserved that there is not any difference in the temperature variation in layers and in total deformation of the mold. Hence, in this paper the average element size is considered as 1mm.

10) In figure7 b), it shows that the maximum temperature of layer is less than 1000 decelsius degree. Is it right as melting point of ER70 is higher than 1400  celsius degree.

10)  It is convenient to clarify this point in the text. Thank you for reviewing this question, a small text has been added to the paper.The simulated temperatures and the measured temperatures are around one thousand degrees Celsius, although the melting temperature of the material is over one thousand four hundred. The simulation is focus on the quasi-stationary state of the process, where an abrupt drop in temperature is observed in the first moments of the deposition. It has been chosen to show the quasi-stationary state of the process, being more comparable to the measurements made on the material moments after deposition.

11) Figure 8 shows the temperature of mold measured by pyrometer. Is it infraded pyrometer? The radiant emissivity of the mold is lack of introdution. Why the maximum temperature of Figure 8 is less than 1000 decelsius degree.

11)  The following set-up have been considered for the temperature measurement with the pyrometer installed in the torch.The welding torch has been equipped with a compact Optris pyrometer, the measurement is made on the surface of the bead once deposited with a delay of 10 ms (estimated based on the travel speed used). The emissivity of the surface has been considered 0.9 for an incandescent body made of ER70 steel.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

In this work, the authors developed a model for the prediction of deformations in the manufacture of thin-walled parts by Wire Arc Additive Manufacturing technology. The research appears to be efficiently done and appropriately reported. The English text is very poor and needs review by a profitable professional in English. Nevertheless, there some questions and corrections that must be answered to improve and complete the document.

 

In the introduction, the authors must indicate the motivations and the background for the work. The motivations are relatively clear, however, the background that should describe the “state-of-the-art” is very poor. In my opinion, the authors of this work must improve the “state-of-the-art” of their work. The authors also didn’t indicate the innovation of their work relative to other and recent research works. Another fail in the introduction is their “hypothesis to be tested” to solve the problem that they want to overcome.

Figure 5- The authors must improve the resolution of this figure.

Lines 189 and 190- The authors claimed that “… carried out on the specimens…”. How many specimens in the total and for each direction?

About section 3.2: how many elements did you use in your simulations? Which kind of element was used in the simulation? What boundary conditions were used? how long did the simulations take? Quality of mesh: skewness and orthogonal quality? What converge criteria were used?

Line 269. The authors claimed, “… the real measurements is very good.” Despite the grammatical error, what is “very good” for you?

Figure 11: improve the quality of this figure.

Equations (2) and (3). Please explain the meaning of their parameters. The authors didn’t indicate the meaning of the parameters of the equations.

Figure 12: where is the legend of the colors in the figure?

Lines 344-345. The authors claimed, “… of pyrometric techniques is very accurate.” What is “very accurate” for you? Can you refer to the error between the two methods?

Line 348. The authors wrote, “… external sources of error described.”. Can you indicate the most important of these external sources of error?

Few formatting and/or grammatical errors, please see the follow lines: 122-123; 131; 149; 199; 213; 240; 290; 310.

Author Response

Reviewer 2

Authors would like to thank to the reviewer for their detailed comments and suggestions for the manuscript. Below, you will find a point by point description of how each comment was addressed in the manuscript. Original reviewer comments in regular typeface, responses in italic.

In this work, the authors developed a model for the prediction of deformations in the manufacture of thin-walled parts by Wire Arc Additive Manufacturing technology. The research appears to be efficiently done and appropriately reported. The English text is very poor and needs review by a profitable professional in English. Nevertheless, there some questions and corrections that must be answered to improve and complete the document.

In the introduction, the authors must indicate the motivations and the background for the work. The motivations are relatively clear, however, the background that should describe the “state-of-the-art” is very poor. In my opinion, the authors of this work must improve the “state-of-the-art” of their work. The authors also didn’t indicate the innovation of their work relative to other and recent research works. Another fail in the introduction is their “hypothesis to be tested” to solve the problem that they want to overcome.

·         Certainly, it is an important issue to show the novelty and innovation of the work clearlier, as well as the hypothesis we aim to test. The following paragraph has been added to the end of the Introduction section: “As it has been shown, the great majority of numeric models have been validated for thin walls, but FEM has not been successfully applied to a complex part of reduced thickness yet. So, broadly, it can be concluded that there is still a gap regarding the prediction of the complete real geometry of final complex parts by means of modelling and simulation. This gap is a concerning issue, since most of the real industrial parts are complex, and they present a combination of different geometries as curve and plane surfaces. So, in order to allow the complete industrial deployment of parts manufactured by WAAM, to determine if FEM analysis is suitable for predicting their temperature and distortion profiles is a key step. Consequently, in this research, a method development on predicting both the temperature each layer reaches and the deformed state of WAAM will be investigated by utilizing FEM analysis in a form of multi-layered process.”·         Besides, some paragraphs have been added to the end of the Introduction section in order to provide a complete background and the “state-of-the-art”. References [11] to [17] showed the “state-of-the-art” regarding FEM in WAAM, but more references ([18] to [20]) have been added specifically related to parts of ER70S-6 steel manufactured by GMAW, and we have compared this works to the present work, in the following text: “This steel is usually used in applications such as construction works, automotive industry, pipes, shafts and tanks, so it is an industrially relevant material. Up to now, researches are mainly focused on selecting optimal operation parameters regarding mechanical properties and microstructure, by means of experimental tests [18-19], but there is not a FE analysis of a complex part yet, aiming to predict final distortion.Additionally, Dttmann et al. [20] studied the machining of a part of this material manufactured by GMAW, so a tool as FEM, which can predict distortion and temperatures prior to this machining operation, is highly valuable.”

Figure 5- The authors must improve the resolution of this figure.

·         Figure 5 has been replaced to improve its quality

Lines 189 and 190- The authors claimed that “… carried out on the specimens…”. How many specimens in the total and for each direction?

• Six tensile tests have been carried out in each of the horizontal and vertical directions to determine the anisotropy of the mechanical properties.

About section 3.2: how many elements did you use in your simulations? Which kind of element was used in the simulation? What boundary conditions were used? how long did the simulations take? Quality of mesh: skewness and orthogonal quality? What converge criteria were used?

·         Thank you so much for recommendation. Authors included the paragraph in the manuscript explaining question you have raised. It helps us to improve the manuscript in better way. “The overall geometry, including both filler and base metal, was discretized using 15398, 8-nodes brick elements. Free convection boundary conditions were set up on the base plate top and bottom surfaces and on the wall vertical surfaces. Convection coefficients values, set according to literature correlations, were: 8.5 W/m2K for the base plate top surface, 4.0 W/m2K for the bottom surface and 12.0 W/m2K for the wall vertical surface. A boundary condition of general radiation to environment was included, setting material emissivity was set to 0.3. Environment and material initial temperatures were set to 20⁰C.”

Line 269. The authors claimed, “… the real measurements is very good.” Despite the grammatical error, what is “very good” for you?

·         Authors totally agree with your comment. The statement does not have a very scientific sound, it has been replaced by: “despite that the fit between the simulation and the real measurements presents correct results with a difference of less than 100 degrees Celsius”

Figure 11: improve the quality of this figure.

·         Figure 11 has been replaced to improve its quality

Figure 11. Volume division on reference surfaces

Equations (2) and (3). Please explain the meaning of their parameters. The authors didn’t indicate the meaning of the parameters of the equations.

·         Equation parameters have been described and a nomenclature section added.

Figure 12: where is the legend of the colors in the figure?

·         The legend has been added to the colorbar of the figure

Lines 344-345. The authors claimed, “… of pyrometric techniques is very accurate.” What is “very accurate” for you? Can you refer to the error between the two methods?

·         Conclusions have been rewritten: The adjustment of the predicted values with the temperature measured by means of pyrometric techniques shows accurate fitting. Results shows deviation of less than a 5% in the temperature prediction

Line 348. The authors wrote, “… external sources of error described.”. Can you indicate the most important of these external sources of error?

·         A large waviness on the surface of the part walls is presented due to the WAAM process itself. Therefore, to determine the exact position of the wall is hard and not fully reliable. The conclusions have addressed this:The surface waviness of the part manufactured, which reaches 2 mm from peak to valley, is one of most important

Few formatting and/or grammatical errors, please see the follow lines: 122-123; 131; 149; 199; 213; 240; 290; 310.

• Revised as requested. Thank for the whole revision and excuse us for the errors.

Author Response File: Author Response.pdf

Reviewer 3 Report

The reviewer comments of the paper «Model for the prediction of deformations in the manufacture of thin-walled parts by Wire Arc Additive Manufacturing technology»

- Reviewer

The authors presented an article «Model for the prediction of deformations in the manufacture of thin-walled parts by Wire Arc Additive Manufacturing technology». However, there are several points in the article that require further explanation.

Comment 1:

The introduction needs to be expanded.

At the beginning of the introduction, it is necessary to complete the paragraph. However, explain why the material chosen for research is so important for the study. Provide a paragraph with relevant references for this material. Where is it applied? What are the benefits? What difficulties are observed in WAAM? Clearly identify "white spots".

It is useful to add an articles:

doi: 10.1007/s00170-021-06846-5 ; doi: 10.1007/978-981-15-5151-2_2

Comment 2:

2. Materials and Methods

Specify for all devices and measuring installations (Manufacturer, city, country).

Line 161. Better to use the degree formula editor. Like (kg/m^3).

Give the chemical composition of the test material in the table.

What is the hardness of the resulting product?

The quality and resolution of all figures needs to be improved.

Are the formulas executed in the formula editor? It feels like a figure. After each formula, all incoming physical quantities must be explained.

All methods should be clearly described in this section. In particular, the FEM. Where is the design scheme? What type of finite elements are used and why? What are the boundary conditions? What software is used and why? What are the characteristics of PC for FEM calculations? In general, all this should be described in detail and shown in the figure. What is the purpose of the calculations?

Comment 3:

3. Results

Are all formulas original? If not, please provide relevant citations.

Are all the figures original? If not, please provide appropriate citations and permissions.

In this section, it is necessary to conduct a deeper analysis of the results obtained. What does the model of temperature, deformation show? What conclusions follow from this in what scientific novelty and practical significance?

Comment 4:

It will be useful to add a section of Nomenclature in which to sign all the physical quantities and abbreviations encountered in the article. There are many physical quantities in the text and such a section will help to find the description of the necessary element.

For example,

p             : Density (kg/m³)

WAAM : Wire arc additive manufacturing

etc.

Comment 5:

Conclusions.

In addition, it is necessary to more clearly show the novelty of the article and the advantages of the proposed method. What is the difference from previous work in this area? Show practical relevance.

Show quantitative and qualitative article results.

What is the error of the developed model?

Conclusions should reflect the purpose of the article.

Comment 6:

Abstract needs to be expanded.

Show the novelty and practical relevance.  

Show quantitative and qualitative article results.

What is the error of the developed model?

Comment 7:

Proofreading by a native English speaker is required. There are a lot of grammatical and stylistic mistakes.

 

The topic of the article is interesting, and relevant. However, the article should be very carefully improved and finalized. Authors should carefully study the comments and make improvements to the article step by step. Highlight all changes. After major changes can an article be considered for publication in the "Metals".

Author Response

Reviewer 3

Authors would like to thank to the reviewer for their detailed comments and suggestions for the manuscript. Below, you will find a point by point description of how each comment was addressed in the manuscript. Original reviewer comments in regular typeface, responses in italic

The reviewer comments of the paper «Model for the prediction of deformations in the manufacture of thin-walled parts by Wire Arc Additive Manufacturing technology»

- Reviewer

The authors presented an article «Model for the prediction of deformations in the manufacture of thin-walled parts by Wire Arc Additive Manufacturing technology». However, there are several points in the article that require further explanation.

• Thanks for the evaluation and for the valuable review of the article that has improved it significantly

Comment 1:

The introduction needs to be expanded.

At the beginning of the introduction, it is necessary to complete the paragraph. However, explain why the material chosen for research is so important for the study. Provide a paragraph with relevant references for this material. Where is it applied? What are the benefits? What difficulties are observed in WAAM? Clearly identify "white spots".

It is useful to add an articles:

doi: 10.1007/s00170-021-06846-5 ; doi: 10.1007/978-981-15-5151-2_2

• The introduction now includes the suggested work and more information about the application of this material

Comment 2:

1. Materials and Methods

Specify for all devices and measuring installations (Manufacturer, city, country).

• Revised as requested

Line 161. Better to use the degree formula editor. Like (kg/m^3). 

• Revised as requested

Give the chemical composition of the test material in the table.

• Table 1 showed the composition of the material according to the provider.

Table 1. Chemical composition of ER70S-6 steel wire (% of the weight)

Mn	Si	C	Cr	Cu	Ni	S	P	Mo	Ti	Zr
1.64	0.94	0.06	0.02	0.02	0.02	0.016	0.013	0.005	0.004	0.002

What is the hardness of the resulting product?

• Information about the hardness have been included

Additionally, a Vickers hardness test has been carried out at different heights, which places its hardness around 150 HV.

Table 2. Summary of mechanical characterization on the sample walls

Vickers Test

Hardness [HV]

151 ± 9

The quality and resolution of all figures needs to be improved

·         Figures have been replaced to improve its quality

Are the formulas executed in the formula editor? It feels like a figure. After each formula, all incoming physical quantities must be explained.

·         All formulas have been reintroduced. A nomenclature section has been included also to clarify physical quantities.

All methods should be clearly described in this section. In particular, the FEM. Where is the design scheme? What type of finite elements are used and why? What are the boundary conditions? What software is used and why? What are the characteristics of PC for FEM calculations? In general, all this should be described in detail and shown in the figure. What is the purpose of the calculations?

• Thank you so much for recommendation. Authors included the paragraph in the manuscript explaining question you have raised. It helps us to improve the manuscript in better way. “The overall geometry, including both filler and base metal, was discretized using 15398, 8-nodes brick elements. Free convection boundary conditions were set up on the base plate top and bottom surfaces and on the wall vertical surfaces. Convection coefficients values, set according to literature correlations, were: 8.5 W/m2K for the base plate top surface, 4.0 W/m2K for the bottom surface and 12.0 W/m2K for the wall vertical surface. A boundary condition of general radiation to environment was included, setting material emissivity was set to 0.3. Environment and material initial temperatures were set to20⁰C.A 3D non-linear transient model of single-pass multi-layer weld-based rapid prototyping with temperature dependent material properties well-presented using the finite element software MSC. Marc. So, in this study we used this software for the WAAM simulation. The number of FEM calculations that are carried out to analyses a transient calculation can influence the quality of the results and the resolution times and depends mainly on the characteristics of the calculation to be solved.”

Comment 3:

1. Results

Are all formulas original? If not, please provide relevant citations. Are all the figures original? If not, please provide appropriate citations and permissions.

·         Figures are original to the article presented and the formulas are not original, but they have been part of the bibliography from the first investigations and it is difficult to know their origin.

In this section, it is necessary to conduct a deeper analysis of the results obtained. What does the model of temperature, deformation show? What conclusions follow from this in what scientific novelty and practical significance?

• Through the Finite Element Method, a study of temperature variation and total deformation of the WAAM mold part had been executed. The research covers both numerical and experimental analysis which was compared as final output of this research. The measuring techniques use for temperature measurement shows also similarity with the FEM results.

Comment 4:

It will be useful to add a section of Nomenclature in which to sign all the physical quantities and abbreviations encountered in the article. There are many physical quantities in the text and such a section will help to find the description of the necessary element.

For example,

p             : Density (kg/m³)

WAAM : Wire arc additive manufacturing

etc.

• Revised as requested and a Nomenclature section has been included.

Comment 5:

Conclusions.

In addition, it is necessary to more clearly show the novelty of the article and the advantages of the proposed method. What is the difference from previous work in this area? Show practical relevance.

• The main novelty presented by this article is the holistic vision of additive manufacturing by WAAM, with the use of finite element models to assist in the prediction of temperatures and deformations in the final part.

Show quantitative and qualitative article results.

• Thank you for highlighting this lack in the paper. The conclusions have been modified by adding quantifiable data.
• The finite element model predicts the process temperature. The adjustment of the predicted values with the temperature measured by means of pyrometric techniques shows accurate fitting. Results shows deviation of less than a 5% in the temperature prediction.
• The deformation prediction model allows to know qualitatively the deformation mode of the part. Qualitatively the results are correct but can be improved, due to the external sources of error described. The surface waviness of the part manufactured, which reaches 2 mm from peak to valley, is one of most important.

What is the error of the developed model?

• Simulation using MSC Marc/Mentat shows good agreement on distortion tendency compared to the results of experiment with relative percentage error up to only 20%,

Conclusions should reflect the purpose of the article.

• Last point covering the purpose of the article is added to the conclusions:

Finally, this paper has covered the purpose of prospecting the application of finite element simulation models for the prediction of deformations in thin-walled parts manufactured by WAAM technology.

Comment 6:

Abstract needs to be expanded.

Show the novelty and practical relevance.  

Show quantitative and qualitative article results.

What is the error of the developed model?

• The abstract of the paper has been rewritten:

This paper covers the application of this technology for the manufacture of thin-walled parts. A finite element model is presented for estimating the deformations in this type of parts. This paper presents a simulation model that predicts temperatures with less than 5% error and deformations of the final part that, although quantitatively has errors of 20%, qualitatively allows to know the deformation modes of the part. Knowing the part areas subject to greater deformation may allow the future adaptation of deposition strategies or redesigns for their adaptation.

Comment 7:

Proofreading by a native English speaker is required. There are a lot of grammatical and stylistic mistakes.

• The authors have significantly modified the paper in an attempt to meet your expectations and to have a good scientific quality.

The topic of the article is interesting, and relevant. However, the article should be very carefully improved and finalized. Authors should carefully study the comments and make improvements to the article step by step. Highlight all changes. After major changes can an article be considered for publication in the "Metals".

• Thanks for the evaluation and for the valuable review of the article that has improved it significantly

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The author answered the questions well. I think it can be accepted now.   One thing should be noticed : surface emissivity is 0.9 for steel. I hope the author could check this value as it may be high.

Reviewer 2 Report

The second version of the manuscript improved significantly when compared with the first version. So, in my opinion, the manuscript can be accepted for publication.

Reviewer 3 Report

The authors have done a good job of improving the article. However, before accepting the article, let the authors draw up the list of references in accordance with the requirements of the MDPI.