Comparative Reliability Analysis of Milling Teeth Manufactured by Conventional Cutting Processes and Laser Cladding

Round 1

Reviewer 1 Report

The analysis of the durability of milling teeth shows that the evolution of wear intensifies after 6 hours of operation (to a different extent, but with both methods of producing the cutter head teeth) and is caused by self-braking during the rotation of the cutter head (self-braking causes one-sided wear of the blade).

It has been shown using analytical methods that the laser surfacing method is more advantageous because it reduces wear due to the reduction of self-braking during the rotation of the milling cutter. Reducing the self-locking of the cutter rotation results in a reduction in adhesion and abrasion, and thus extends the life of the cutter. Ultimately, economic efficiency increases.

The methods of analysis are correct, and the conducted considerations show the economic benefits of using laser methods of production or regeneration.

Author Response

Dear Editor,

Thank you very much for your suggestions!

Point 1. The analysis of the durability of milling teeth shows that the evolution of wear intensifies after 6 hours of operation (to a different extent, but with both methods of producing the cutter head teeth) and is caused by self-braking during the rotation of the cutter head (self-braking causes one-sided wear of the blade).

It has been shown using analytical methods that the laser surfacing method is more advantageous because it reduces wear due to the reduction of self-braking during the rotation of the milling cutter. Reducing the self-locking of the cutter rotation results in a reduction in adhesion and abrasion, and thus extends the life of the cutter. Ultimately, economic efficiency increases.

The methods of analysis are correct, and the conducted considerations show the economic benefits of using laser methods of production or regeneration.

Response 1:

Line 127-130

The micro hardness determinations on the deposition area (DM) revealed increased values compare to the body of the tooth (BM), close to those of the tungsten carbide tip. This allowed a symmetrical wear of the tooth body in operation and facilitated rotation around their own axis, avoiding self-locking and resulting in better tooth durability.

Author Response File: Author Response.docx

Reviewer 2 Report

In this paper, the authors compared the reliability of milling teeth manufactured by conventional cutting processes and laser cladding. SIgnificant issues exist as followings.

1) The introduction part describes a lot of useless information, for example, the first paragraph. You can write a textbook in this way. Besides, I am lost in the introduction. I can't get the point what the authors want to do, why it is meanful to conduct this study, and what has already been studied by others. The sentenses in L85-L87 are too general even though it's important. 

2) The description like L126-L127 just gave the coclusion without any supporting data. This should be avoided in a scientific article. 

3) Same as point 2), L219-L221 only provided the conclusion without any supporting data.

4) The data description is too tenuous to convince the readers, is there any other type of data aviable?

Author Response

Dear Editor,

Thank you very much for your recommandation. Below, you can find our responses!

Point 1. The introduction part describes a lot of useless information, for example, the first paragraph. You can write a textbook in this way. Besides, I am lost in the introduction. I can't get the point what the authors want to do, why it is meanful to conduct this study, and what has already been studied by others. The sentenses in L85-L87 are too general even though it's important.

Response 1:

We deleted the first paragraph from Introduction section.

Line 89-97

Literature references related to the determination of the reliability of milling teeth manufactured by metal deposition are rather scarce. In the field of welding loading processes, manufacturers do not provide detailed information.

In this respect, the paper refers to the reliability indices prediction of different types of milling teeth. The analyzed milling teeth were made using a high-performance, automated and robotic welding loading technology, in the active area, with laser and powder. They equipped a milling and they were tested in operation. Taking into account that the road rehabilitation requires millings equipped with a high number of teeth, we considered that it would be appropriate to achieve a comparative study of the milling teeth made by conventional procedures and those made by a modern, productive and actual process, respectively loading by laser powder welding.

Point 2. The description like L126-L127 just gave the conclusion without any supporting data. This should be avoided in a scientific article.

Response 2:

The results are sustained by micro hardness rezults.

Line 127-130

The micro hardness determinations on the deposition area (DM) revealed increased values compare to the body of the tooth (BM), close to those of the tungsten carbide tip. This allowed a symmetrical wear of the tooth body in operation and facilitated rotation around their own axis, avoiding self-locking and resulting in better tooth durability.

Point 3. Same as point 2), L219-L221 only provided the conclusion without any supporting data.

Response 3:

The analysis on various milling teeth manufactured by the processes described above showed that the analyzed teeth also have high reliability compared to teeth manufactured by conventional cutting procedures. The conclusions of the analysis are obvious (please see Figures 7, 8 and 9).

Point 4. The data description is too tenuous to convince the readers, is there any other type of data aviable?

Response 4:

The analysis and interpretation of the data regarding the reliability of the milling teeth was performed in accordance with the specialized literature.

Author Response File: Author Response.docx

Reviewer 3 Report

The origin of the experimental data should be precised: used sample geometry, sample number, test protocole, test equipement, results analysis method and their precision/error, etc...

The  reliability estimation method/protocole should be added to lead a minimum understanding: mathematic model, input parameter, output parameter, confidence interval esmimation method and their phjysical meaning etc... The main question is how can you estimate the reliability: with which physicial assumption, with which data, with which method ?

The result presented should be improved greatly:

- in the table 1/2/3, it is necessary to discuss the physical meaning of the 2 or 6 digital numbers after the point in considering the analysis precsion and the reliability of the experimental results;

- the results presented in figure 8 and 9 are not meaningful without the minimum information about the function of R(T), F(T) and h(T) and about their analysis method; 

Author Response

Dear Editor,

Thank you very much for your recommandation. Below, you can find our responses!

Point 1. The origin of the experimental data should be precised: used sample geometry, sample number, test protocole, test equipement, results analysis method and their precision/error, etc...

Response 1:

Line 145-152

Given the rough working conditions, the milling machine is stopped at regular intervals (approximately 2 hours), for cooling and inspection. The periodic inspection, in this case, consisted in the thorough analysis of each tooth (after flushing it with water), estimating the wear degree of each and the manner in which it was produced. Even if the degree of wear out in some milling teeth was high, the teeth were kept until the end of the working cycle (8 hours). The experimental data were obtained over a period of one month, on a milling equipped with 50 teeth, in operation for the rehabilitation of a section of asphalt road.

See also lines 187-190, 192-197.

Point 2. The  reliability estimation method/protocole should be added to lead a minimum understanding: mathematic model, input parameter, output parameter, confidence interval esmimation method and their phjysical meaning etc... The main question is how can you estimate the reliability: with which physicial assumption, with which data, with which method ?

Response 2:

Lines 153-184

There are a wide variety of reliability engineering tools that could be applied to estimate the reliability indices of the products or systems [23–28].

The most popular methods are least squares (LS) and maximum likelihood estimation (MLE), which are both implemented in reliability estimation.

Given a continuous random variable X, it is specified that [23-24, 30-31]:

• f(x) is the probability density function (PDF);
• F(x) is the cumulative density function (CDF).

If X is a continuous random variable, then the probability density function of X is a function f(x) such that for two numbers, a and b with a ≤ b:

The cumulative distribution function is a function F(x) of a random variable X and is defined for a number x by:

Specific to Normal distribution, the main indices are given by the follwing equations [23-24, 30-31]:

,

,

,

,

where μ is the mean and σ is the standard deviation.

Least Squares Estimation

Suppose observations of random variable . If a straight line is fitted such that the sum of the squares of the vertical observations of observed y_i from this line is minimum, then such a line is said to have the least squares property. The sum of squares is defined as [23]:

.

The equation of the fitted line is given by:

.

.

The condition is:

Substituting the values, it is obtained the equation system:

In this respects, the parameters are defined as:

Line 150-153, 192-197

Parametric analysis of distribution, in particular the least squares estimation was performed referring to the estimation of reliability indices of under study milling teeth.

Based on the data collected from the operation regarding the lifetime of the milling teeth, the most frequent distributions were considered in order to analyze the goodness-of-fit. Weibull, lognormal, exponential and normal probability distributions were considered for parametric distribution analysis. With a confidence interval (CI) of 95%, the point estimation of reliability and unreliability functions, means time to failure (MTTF) and hazard rates were estimated.

Point 3. - in the table 1/2/3, it is necessary to discuss the physical meaning of the 2 or 6 digital numbers after the point in considering the analysis precsion and the reliability of the experimental results;

Response 3:

In reliability analysis, two decimals are enough. Because it was used Minitab Software, by default the results have six decimals. It is our omission that we have not checked so that the numbers to be unitary.

- the results presented in figure 8 and 9 are not meaningful without the minimum information about the function of R(T), F(T) and h(T) and about their analysis method;

The chapter has been completed so that all reliability indicators are statistically defined (see Response 2).

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors should seriously reply to my previous comments. I am not satisfied to almost all the response. For example, in response 2, where is the hardness data? I should believe you didn't conduct the test if no data was provided!!

Author Response

Response to Reviewer 1 Comments

Dear Editor,

Thank you very much for valuable recommandation and the posibility to improve our work. Below, you can find our responses!

The authors should seriously reply to my previous comments. I am not satisfied to almost all the response. For example, in response 2, where is the hardness data? I should believe you didn't conduct the test if no data was provided!!

Point 2. The description like L126-L127 just gave the conclusion without any supporting data. This should be avoided in a scientific article.

Response 2:

Line 129-133

The micro hardness determinations on the deposition area (DM) revealed increased values compare to the body of the tooth (BM), close to those of the tungsten carbide tip. This allowed a symmetrical wear of the tooth body in operation and facilitated rotation around their own axis, avoiding self-locking and resulting in better tooth durability.

Micro hardness determinations were also performed (see figure below), and the measured values are presented in Table 1.

Arrangement of micro hardness fingerprints in the section of the deposited cord

Table 1. Micro hardness determinations

The variation of micro hardness in characteristic areas

Point 3. Same as point 2), L219-L221 only provided the conclusion without any supporting data.

Point 4. The data description is too tenuous to convince the readers, is there any other type of data aviable?

Response 3 and 4:

Lines 145-152

Given the rough working conditions, the milling machine is stopped at regular intervals (approximately 2 hours), for cooling and inspection. The periodic inspection, in this case, consisted in the thorough analysis of each tooth (after flushing it with water), estimating the wear degree of each and the manner in which it was produced. Even if the degree of wear out in some milling teeth was high, the teeth were kept until the end of the working cycle (8 hours). The experimental data were obtained over a period of one month, on a milling equipped with 50 teeth, in operation for the rehabilitation of a section of asphalt road.

Lines 192-200

The probability plots of lifetime milling teeth are presented below.

Figure 7. The probability plots of lifetime milling teeth

The conclusions presented at Line 219-221 (“The analysis on various milling teeth manufactured by the processes described above showed that the analyzed teeth also have high reliability compared to teeth manufactured by conventional cutting procedures.”) are sustained by the comparative analysis, analysis which is obviously presented in Figures 8, 9 and 10 (please see the comparative analysis of reliability, unreliability and hazard rate). Also, the main statistic parameters of milling teeth life time data are synthetically presented in Table 3 and Table 4.

Table 3. Estimation of parameters for type I milling teeth.

Table 4. Estimation of parameters for type II milling teeth

Parametric analysis of distribution, in particular the least squares estimation was performed referring to the estimation of reliability indices of under study milling teeth. With a confidence interval (CI) of 95%, the point estimation of reliability and unreliability functions, means time to failure (MTTF) and hazard rates were estimated.

Please see chapter 3 – Results and discussion (Lines 191-258).

Author Response File: Author Response.docx

Reviewer 3 Report

in the revised version of the manuscript, author has made necessary corrections including all remarks from reviwers.

To lead a better unerstanding, some deteils should be improved:

- in the caption of figure 3, it is important to precise what correspond to the zones I, II  and III;

- in figure 4, 5 and 6(a), it is necessary to add a scale;

- the caption of the figure 8 and 9 are the same !!!, it is absolutley necessary to differentiate them because the content is not the same;

- the conclusion part is the fourth part not the fifth;

Author Response

Response to Reviewer 2 Comments

Dear Editor,

Thank you very much for valuable recommandation and the posibility to improve our work. Below, you can find our responses!

To lead a better unerstanding, some deteils should be improved:

Point 1.

- in the caption of figure 3, it is important to precise what correspond to the zones I, II  and III;

Response 1

Lines 74-77

We agree! We filled the caption zones.

Figure 3. Concept of welding cord deposition on the frustoconical section of the tooth:(1) tungsten carbide tip; (2) annular cords achieved by metal deposition; (3) tungsten carbide tip brazing area in the front hole; (4) frustoconical section of the milling cutter tooth; zone I - first cordon; zone II - third cordon; zone III - second cordon.

Point 2.

- in figure 4, 5 and 6(a), it is necessary to add a scale;

Response 2

In Figure 4 is presented the Experimental assembly. We do not know which scale should be added.

Figure 5: The loading methodology is specified in the literature.

In Figure 5(b) and 5(c) are specified the geometric appearance of the deposits in partially overlapping layers.

Lines 125-128

We agree!

In Figure 6 we specified the scale:

Figure 6. Views of macro and microstructural analysis of the powder and laser metal deposition area: (a) milling tooth macrostructure, 5X magnification ; (b) deposited material (DM), 100X magnification; (c) transition area (TA), 50X magnification; (d) base material (BM), 50X magnification.

Point 3.

- the caption of the figure 9 and 10 are the same !!!, it is absolutley necessary to differentiate them because the content is not the same;

Response 3

Line 247

We agree! It is our mistake!

We modified the caption: “Figure 10. Comparative analysis of hazard rate functions for analyzed milling teeth.”

Point 4.

- the conclusion part is the fourth part not the fifth;

Response 4

Line 259

We agree! Thank you very much for your observation. We modified the chapter number.

Author Response File: Author Response.docx