Long-Term Behavior of Clinched Electrical Contacts

Round 1

Reviewer 1 Report

In my perspective, this paper should be minor revised before published in this journal. The comments are listed as below:

1. The title should be considered to recompose.

2. In the page 2, the description of Ref [8] should be checked.

3. In the page 2, the symbols of resistivity should be unified.

4. In the page 2, as the clinched joint is a non-line structure, what is the rationale of Eq (2)?

5. In the page 3, what is the mean of “ measuring length 1” ?

6. In the page 5, “Table1”should be checked carefully.

7. In the page 7, “Figure1”should be checked carefully.

Author Response

Dear Reviewer,
Thank you very much for reviewing our manuscript. Your comments were very helpful in further improving the paper.
I would like to respond to your comments below:

1. the title should be considered to recompose.
The title has been adjusted and shortened.
 
2. in the page 2, the description of Ref [8] should be checked.
The source reference has been corrected.
 
3. in the page 2, the symbols of resistivity should be unified.
 The symbols have been unified.

4. in the page 2, as the clinched joint is a non-linear structure, what is the rationale of Eq (2)?
Rj is the electrical resistance measured by the four-wire method.
 Equation 2 represents the composition of the joint resistance Rj. The variables Rf and Rb are force independent. The component Re is force and material dependent (eq.1).

5. in the page 3, what is the mean of "measuring length 1" ?
The designation measuring length l refers to the representation in Figure 4. A direct reference to it has been inserted.

In the page 5, "Table1 "should be checked carefully.
 The chemical composition data are correct.

7. in the page 7, "Figure1 "should be checked carefully.
The conductor designation was included in the figure and the measuring principle was explained in more detail.

We hope that we could address all open questions.

Kind regards
Jan Kalich

Reviewer 2 Report

The authors studied the long-term stability, hardness and microstructure of the mechanical clinched Al/Cu and Cu/Cu electrical contacts. I really commend the authors on the time expended on this experimental study and the thoroughness of the author. However, the authors need to address these comments to further improve the manuscript:

-          The major findings from this study have not presented in the abstract

-          Please check and correct this sentence where appropriate: “The total area in the overlap region between the contact pieces is the apparent contact area As. [8] However …”

-          “clinching joints” and “clinched joints” have been mentioned in this manuscript. Kindly stick to one in the entire manuscript.

-          Detailed information has been provided on current-carrying connections at the introduction section. However, a concluding sentence is required in this section to point to the primary work that was carried out

- The materials and methods section should include microstructure assessment (like the etchant, and microscope used)

Author Response

Dear Reviewer,

Thank you for reviewing our manuscript. Your comments were very helpful in further improving the paper.

I would like to address your comments below:

The major findings from this study have not presented in the abstract

The main results have been added to the abstract.

Please check and correct this sentence where appropriate: “The total area in the overlap region between the contact pieces is the apparent contact area As. [8] However …”

This statement is correct. However, since the overlap is the apparent contact area, the real contact area is only the metallic microcontacts "a-spots" within the clinched joint.

“clinching joints” and “clinched joints” have been mentioned in this manuscript. Kindly stick to one in the entire manuscript.

The terms were unified as "clinched joint

Detailed information has been provided on current-carrying connections at the introduction section. However, a concluding sentence is required in this section to point to the primary work that was carried out

At the end of the introduction, the references to the main investigations were added.

The materials and methods section should include microstructure assessment (like the etchant, and microscope used)

Data on metallographic specimen preparation and equipment technology were listed.

We hope that we could address all open questions.

Kind regards

Jan Kalich

Reviewer 3 Report

This paper deals with the long-term stability of the electrical resistance of clinched connections in the context of e-mobility. Although the topic of the paper is interesting, I cannot recommend publication of this paper in its current state. Publication can be considered if the authors thoroughly modify the manuscript and adequately answer the below questions.

·       Title: the term “binding mechanisms” is used only in the title. It is not clear what is meant  with this term. Please modify the title or explain clearly in the introduction.

·       This work is inspired by requirements from the e-mobility sector. It is stated that clinching enables to connect battery cells. Please include a schematic that visualizes this application. This will enhance the clarity of the paper. In this application, what are the requirements with respect to the mechanical loads?

·       Are the selected materials and their thickness relevant for battery cells?

·       The writing needs to be significantly improved. There are many vague statements.

Abstract: Based on a comparison … are defined for the used aluminum materials. This sentence cannot be understood. Please correct.

Craft production: is this relevant here?

Ambits about manufacturing: rephrase

…is the apparent contact area As.[8] However2, … => correct

Unevennesses => asperities?

“a-spot” is mentioned in the introduction, but the term is not explained at all. Please properly introduce this term.

Re has a different font size then Rf and Rb

Heat mesh method or heat network method? Use consistent terminology

“The temperature of the joints was calculated … and the unaffected temperature of the connected conductor”. Vague, at this the reader cannot understand “unaffected temperature”.

The five aging mechanisms force reduction… => The five aging mechanisms are force reduction…

The aim of clinching electrical conductors is to exploit the effects of surface enlargement and relative movement of the joining partners. => The aim of this study is to investigate this?

Vague statement: However, a-spots can increasingly be formed by a large forming operation??

Over-temperature? What is meant by this?

Fuhrmann [20] describes and analyses the same … on the operating time. Why is this statement here? What message do the authors want to convey?

The mechanical test before and after… to measure sufficient connection strength to secure the fragile current-carrying a-spots between the joining partners. Vague and unclear, please modify.

Chapter 3.1 => Section 3.1

…, which can be attributed to strain aging. => Please explain this statement.

… deformation of the cup => “cup”is used here for the first time. Not clear for the reader what this is about.

…,the range of the measured shear forces increases => what do you the authors mean with this statement?

, a change can be seen in Figure 12 in all three areas. The reader must compare Figs 12 and 10? Clarify.

…reaching the limited temperature => limiting? Temperature limit? Use consistently the same terminology !

·       Figure 5 until Figure Figure 14 are taken from reference [5]? This is a large amount of already published results? Can the authors comment on this?

·       Figure 1. Principle of the resistance measurement of clinched samples. => wrong numbering of the figure

·       Conclusions:

-          If the authors claim to deliver a first  fundamental description, then the accuracy and clarity of the text should be significantly improved

-          Vague: the clinching of current-carrying conductors … can be realized. Please write the conclusions in a concise manner.

-          Conclusions should be supported by the research results. “e.g. relative movement of the joining partners and the size of the bottom …but neutral for mechanical properties.” Is this a conclusion from the current paper? If yes, please explain. If it is correct that relative movement is beneficial, the decreasing the force-fit (more relative movement) is also beneficial? Yet, this would be in contradiction with the remainder of the conclusions.

-          “Therefore, the joint can fail.” Weird jump, no connection with the previous sentence. Please write a clear story.

Author Response

Dear Reviewer,

Thank you for reviewing our manuscript. Your comments were very helpful in further improving the paper.

I would like to address your comments below:

Title: the term “binding mechanisms” is used only in the title. It is not clear what is meant  with this term. Please modify the title or explain clearly in the introduction.

The title has been changed. The terms relating to the individual binding mechanisms have been added to the introduction and presented more precisely.

This work is inspired by requirements from the e-mobility sector. It is stated that clinching enables to connect battery cells. Please include a schematic that visualizes this application. This will enhance the clarity of the paper. In this application, what are the requirements with respect to the mechanical loads?

Clinching or joining of battery cells in E-mobility was cited from the literature research. An application from the area of clinched fuses has been included as a Figure. The basic requirements for electrical contacts are the same. However, the area of application, such as low voltage or high voltage, differs. The investigations carried out refer to the car electrical system in the low voltage range. An explanation of this has been included in the introduction.

Are the selected materials and their thickness relevant for battery cells?

The selected materials and component thicknesses correspond to the copper materials used in passenger car wiring systems. The aluminum materials represent a possible substitute material for copper. They are used in the bodywork area and must be qualified for ground contact.  

The writing needs to be significantly improved. There are many vague statements.

Abstract: Based on a comparison … are defined for the used aluminum materials. This sentence cannot be understood. Please correct.

This sentence has been corrected.

Craft production: is this relevant here?

Craft production is irrelevant here. However, for rework and repair concepts to consider.

We have decided to delete the “craft production”.

Ambits about manufacturing: rephrase

This sentence has been rephrased.

…is the apparent contact area As.[8] However2, … => correct

The citation has been corrected. The description of the apparent contact area is correct.

Unevennesses => asperities?

The terms were formulated more clearly.

“a-spot” is mentioned in the introduction, but the term is not explained at all. Please properly introduce this term.

The term "a-spot" was introduced and explained.

Re has a different font size then Rf and Rb

The font sizes have been adjusted.

Heat mesh method or heat network method? Use consistent terminology

In the manuscript, only the term “heat network method” is used.

“The temperature of the joints was calculated … and the unaffected temperature of the connected conductor”. Vague, at this the reader cannot understand “unaffected temperature”.

This wording has been adjusted. This is the temperature distribution over the connected conductor.

The five aging mechanisms force reduction… => The five aging mechanisms are force reduction

This phrase has been corrected.

The aim of clinching electrical conductors is to exploit the effects of surface enlargement and relative movement of the joining partners. => The aim of this study is to investigate this?

The investigations aim to characterize and quantify the long-term behavior of clinched electrical contacts as a function of a thermal load.

This sentence was added to the introduction.

Vague statement: However, a-spots can increasingly be formed by a large forming operation??

The mechanisms for the possible formation of a-spots have been formulated. A large surface enlargement and a relative movement of the parts to each other during the joining process can generate these a-spots.

Over-temperature? What is meant by this?

Overtemperature is an increased temperature at the clinched joint compared to the homogeneous conductor material. This term has been removed and paraphrased by temperature difference.

Fuhrmann [20] describes and analyses the same … on the operating time. Why is this statement here? What message do the authors want to convey?

Fuhrmann investigated bolted aluminum bus bars in [20]. His results correspond to those presented here. However, the basic mechanisms for the formation of the joints are very different. In clinching, the components to be joined are formed, whereas in bolting they are not. However, the aging mechanisms that occur are identical. 

The mechanical test before and after… to measure sufficient connection strength to secure the fragile current-carrying a-spots between the joining partners. Vague and unclear, please modify.

The statements in this regard have been supplemented and clarified.

Chapter 3.1 => Section 3.1

The term has been renamed.

…, which can be attributed to strain aging. => Please explain this statement.

The concept of strain aging was explained in terms of its mechanisms and its influence on joint strength.

… deformation of the cup => “cup”is used here for the first time. Not clear for the reader what this is about.

The term "deformation of the cup" refers to the deformation of the punch-side joining partner at the clinched joint in a mechanical test such as shear testing. This is a term introduced in the field of clinching. The term has been replaced by a paraphrase.

…, the range of the measured shear forces increases => what do you the authors mean with this statement?

This refers to the increase in the standard deviation. The statement on this has been corrected.

, a change can be seen in Figure 12 in all three areas. The reader must compare Figs 12 and 10? Clarify.

For better comparability of the micrographs, they were combined into a figure to facilitate direct comparison.

…reaching the limited temperature => limiting? Temperature limit? Use consistently the same terminology !

The term "limit temperature" was used throughout the revision.

Figure 5 until Figure Figure 14 are taken from reference [5]? This is a large amount of already published results? Can the authors comment on this?

The images referred to here have been removed and a redesigned Figure replaced.

Figure 14 has been adapted from the source [5] by summarizing the hardness values in the individual areas.

Figure 1. Principle of the resistance measurement of clinched samples. => wrong numbering of the figure

All figures have been renumbered and checked for references in the text.

Conclusions:

If the authors claim to deliver a first fundamental description, then the accuracy and clarity of the text should be significantly improved

Vague: the clinching of current-carrying conductors … can be realized. Please write the conclusions in a concise manner.

The conclusion was revised and supplemented in a detailed form.

Conclusions should be supported by the research results. “e.g. relative movement of the joining partners and the size of the bottom …but neutral for mechanical properties.” Is this a conclusion from the current paper? If yes, please explain. If it is correct that relative movement is beneficial, the decreasing the force-fit (more relative movement) is also beneficial? Yet, this would be in contradiction with the remainder of the conclusions.

A relative movement of the joining partners during the clinching process is helpful for good electrical contact. The relative movement during the joining process does not influence the force-fit component. However, the force-fit component and the form-fit component are necessary during the mechanical connection test to counteract the relative movement of the components to each other. These explanations have been supplemented in the text and described in more detail.

“Therefore, the joint can fail.” Weird jump, no connection with the previous sentence. Please write a clear story.

This statement has been removed and the Conclusions presented in a more stringent form.

We hope that we could address all open questions.

Kind regards

Jan Kalich

Round 2

Reviewer 3 Report

The authors adequately answered all questions and changed the manuscript accordingly.