Torque-Based Temperature Control in Friction Stir Welding by Using a Digital Twin
Round 1
Reviewer 1 Report
This paper presents a torque-based temperature control technique by means of a digital twin model. Its application to the welding of a 6082 aluminium alloy show the relevance of the technique proposed for the stationary phase of welding even if phenomenon such as vibrations will need to be addressed in future work to improve the strategy.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The area of implementation of the FSW technology in the industry has been growing increasingly. The necessity of developing this technology can be observed. Therefore research within this field is indispensable. The Authors presented their result of research, which are interesting and original. The reviewer has however several questions and doubts, therefore I’m asking for the explanation.
Questions and remarks:
1) As the Author says „the empirical approach is only valid for one specific tool geometry and aluminum alloy”, a question is arising why empirical method was developed only for one case, while testing was conducted for 3 steel grades. Therefore conducted research should be treated as exploratory study.
2) Suggested method of temperature measurement seems to be a half-measure as the thermocouple is not measuring the temperature of material but the tool. Did the Author compare the results of the temperature measurements from FSW head and thermocouples located on the welded material?
3) Thermocouple:
- Lack of the picture of a thermocouple (volumetric, superficial, contact, screw-in types of thermocouples).
- What was the reason of selecting the thermocouple wire diameter of 500 mm (0.5 mm)?
- Did the Author conducted the testing of the smaller diameter of the thermocouple wire?
- Thermocouple wire diameter of 500 mm is too large (it causes unnecessary and very high thermometric lag). Could you please explain that.
- What was the precise location of thermocouple (pin, shoulder)?
- What are the parameters of bonding adhesive (thermal conductivity)?
- Did the Author consider attaching the thermocouple using other method, e.g. by resistance welding or arc welding?
4) There is lack of the results of real temperature course (experiment) for various variants. Did the Author conduct such testing? To what extend FSW parameters and type of tool material have an influence on temperature results and change? Basing on this findings it would be possible to adjust the adequate temperature.
5) Did the Author check the phenomenon of heating and cooling of a tool as the result of abrupt (reversive) changes of technology parameters? In my opinion when the tool becomes heated then it has constant temperature. Could you please explain that.
6) Did the Author check what is the dynamics of temperature change in the tested method trying for instance to heat the tool using the other source of heat then that in FSW process?
7) Temperature in the welding area influences the structure and quality of FSW joint. From the reviewer’s experience it appears that the temperature (in welding area) depends more on a shoulder than the pin. The pin is responsible for stirring of material. If a shoulder heats material adequately then it is possible obtain correct joint (of a good quality). Author(s) however located the thermocouple on a pin. Did the Author try to measure the temperature of a shoulder? If yes, did the Author compare the results with temperature of a tool pin? Could you please explain that.
8) Results shown in Table 2 are doubtful. Results of experiment:
a) 11 and 14 in a range of „correction offset Tcorr in K” amounting to „0” (zero),
b) 12 and 13, travel speed differs markedly. Such results cannot be achieved („set welding temperature”). For the twofold increasing of travel speed (experiment 12 compared with experiment 13) and the same welding force (FZ) material puts up stronger resistance and therefore different (acquired??) temperature should be decidedly lower. The Table fails to show that. Could you please explain that.
9) In Fig. 4 and in its caption there is lacking exact data of tool rotational speed. It is known and should be given.
10 The comparison of „exp 2” and „exp 6” is doubtful. In order to obtain full and clear analysis the parameters of technology (rotational speed, transvers speed and axial force) should be the same. In both cases the parameters: axial force „FZ” and „rotational speed” are different. Could you please explain what was the idea to present such results.
11) Did the Author conduct research and check (if yes, please give the examples) what was the influence of e.g. increase of temperature by 50/30O C on the quality of FSW joints.
12) In this system - digital twin - the temperature was compared to the temperature measured during the experiment using thermocouples in the material - it was not shown how and where exactly.
13) No information about the type of adhesive. There are
few glues that are actually conductive and resistant to high temperature, which
for the FSW process is (average) over 400 degrees Celsius. Ordinary
adhesives are resistant to temperatures up to about 160 degrees. There are
high temperature adhesives up to 1500 degrees but conductive?
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear Authors,
The reviewed manuscript describes the procedure and results of experimental studies regarding the possibilities of measuring temperature during joining aluminum alloys by the FSW process. The work is original and relevant from the point of view of studying the mechanisms of forming of welded joints. Below are some of my comments that may be helpful when shaping the final version of the manuscript:
- Abstract: I suggest adding quantitative results: maybe those concerning measurement errors? Lines 20-21: "welds" - I think it would be better to use the more general term "welded joints".
- Lines 77-78: you do not need to enter a device name to aims of the work.
- Line 147: "Asm. 6 "- requires additional explanation.
- Line 220: "during the welds" = "during welding"? Check grammar.
- Tables 1 and 2 and text: sample geometry is not clearly described. I suggest adding to the manuscript text a figure with the shape of all the samples and delete in this case Appendix 3. Please check the terminology: “bead on plate” refers to the application of the deposit on the plate (surfacing); "Overlap weld": it sounds better: "overlap joint"; "bead on narrow plate": I have not encountered such a term in welding terminology.
- Consider including Appendixes in the main text. The article is not excessively long.
- In addition: correct references in the text: all names should not be in upper case.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Reviewer's remark 1
There is still no show how the thermocouple connector looks like and its contact with the material whose temperature is being measured !!!.
A clamp was used for temporary fixation of the thermocouple. This
means that the contact between the thermocouple and the tool is not constant (galvanic). The thermocouple is in loose (contact) contact. The reviewer's experience shows that after several temperature cycles the surface of the thermocouple junction will oxidize, which will lead to an increase in thermal resistance at the "thermocouple - metal" contact point. The temperature indicated for the next attempt will be lower.
How can the authors ensure that the thermocouple is in constant (continuous) contact with the tool?
Reviewer's remark 2
There is not much difference in price between the 250um and 500um thermocouple. The authors cannot explain (imperfect, erroneous) temperature measurement results at the expense of a thermocouple. The diameter of the thermocouple wire for the presented applications in the article should be a maximum of 100um. It can be done. Mechanically thermocouple wires with a diameter of 100um are also durable.
Temperature measurement using a 500um diameter thermocouple wire is used (not bad). It is acceptable for STATIC temperature measurements (slow changing), e.g. in heat treatment furnaces. However, the thermocouple with a diameter of 500um thermocouple wires brings a large unacceptable dynamic measurement error when used for FSW technology.
In the reviewer's opinion, this disqualifies the method of temperature measurement proposed by the authors for this technology, which requires high measurement dynamics.
Dear Authors, "dynamics in temperature measurements" in welding processes (welding) is very important !!!
The Authors do not feel what the dynamics of temperature measurement is and what is the time delay in temperature measurement resulting from:
- thermocouple diameter,
- methods of making a thermocouple connector,
- the method of mounting (contact) the thermocouple connector to the object whose temperature we want to measure.
ATTENTION AUTHORS WITH A 500mm DIAMETER IS INCREDIBLE and frivolous.
Reviewer's remark 3
The Reviewer's question concerns checking the dynamics of thermocouple readings. Have the authors checked dynamic states (changes), e.g. "
- change of welding technology parameters (e.g. linear speed 600/300),
- removing the tool from the welded material, and whether they checked the response (signal) from the thermocouple placed in the tool. In such cases, the tool temperature will remain at an unfavorably high level, because the tool has become hot and the temperature has been accumulated in the tool.
Such a test is easy to do. The dynamics of temperature measurement in the cooling phase can be determined. The effect of the temperature inertia of the head resulting from its mass will be visible.
Temperature measurement at the time the tool is introduced into the material will give the answer about the inertia (delay) during the heating of the tool.
Reviewer's remark 4
The authors claim that the signal was only used (and up to) for validation.
And what is validation.
The validation is confirmation by providing objective evidence that the requirements for a specific use or application have been met. When estimating the uncertainty of a measurement result, each uncertainty component that may be relevant in a given situation must be considered using appropriate analysis methods. It is assumed that validation is generally based on obtaining evidence that the control measures adopted within the framework of the plan are effective.
According to the reviewer, the temperature measurement presented by the authors is not reliable.
The methodology of temperature measurement in the Reviewer's opinion, in terms of the dynamics of its measurement and accuracy is incorrect. Therefore, the validation of the process (method) is also incorrect.
General remark
For the knowledge of the authors and editorial staff of the article. The authors did not check the dynamics of the thermocouple indications used in the tool. The reviewer from his experience claims that for the presented methodology of temperature measurement, i.e. i) 500um diameter of thermocouple wires, ii) volumetric thermocouple, iii) contact of the thermocouple with the tool, causes a delay in the temperature measurement (dynamics), which is a few to several seconds. This means that for a linear speed of 600mm / min, the temperature measurement (which the thermocouple will register) will correspond to a point distant from the current position of the FSW tool by several centimeters. Is this the subject of the article's authors?
Does it satisfy the authors. If so, please let the authors
include such information in the article.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
Replies:
- I must admit that we used different terms in relation to the thermocouple. The Authors referred to the external diameter of the sheathed thermocouple (0.5 mm). In turn, the Reviewer referred to the diameter of the thermocouple wires. As it turned out, the diameters of the wires of the thermocouple used by the Authors amount to 100um. I agree to the suggested approach. This dispels Reviewer’s doubts.
The lack of complete data in the aforesaid scope (the diameter of the opening in the tool and the diameter of the thermocouple wire) were the reason for the misunderstanding between the Reviewer and the Authors.
- In the Figure presented in the Authors’ replies (page 6), the time of changes in the welding technology parameters amounts to 70 ms. However, the time of response to the change of the aforesaid parameters (in the form of an increase in temperature) amounts to 5.8 s (response takes place between 12.7s and 18.5s). The Reviewer sees the foregoing as a delay in the temperature measurement channel (measurement dynamics). The Reviewer presumes that the Authors admit that the change in the technology parameters triggers an immediate change in temperature. However, the result is obtained after some time (5.8 s) and this time is the time of measurement delay. This information should be contained in the text of the article along with a related Figure. This information is important for technologists (readers).
- The information about the technical conditions of thermocouple attachment, i.e. the diameter of the opening in the tool (0.6 mm) and the diameter of the sheathed thermocouple should also be provided by the Authors in the article. Readers may suggest another solution.
- The Reviewer finds the explanation provided by the Authors exhaustive.
- The Reviewer agrees to the printing of the article after the introduction of the changes by the Authors. The changes do not need to be consulted with the Reviewer.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
