Review Reports - Justification of the Application of Resource-Saving Technology for the Restoration of Metal-Intensive Rear Semi-Axles of Trucks Using Hot Plastic Deformation

Round 1

Reviewer 1 Report

Dear authors,

thank you for submitting your manuscript ‘Justification of the application of resource-saving technology for the restoration of metal-intensive semi-axles of rear axles of trucks using hot plastic deformation’.

Although your paper describes an interesting approach to apply ‘Re-Manufacturing’-concepts to forging components, your study misses any data on the obtained component after restoration. In order to ‘justify’ this process, comprehensive data on the microstructure and the mechanical properties of the restored component need to be collected and compared with a reference state. Due to the reheating of large volume fractions of the component with only small amounts of deformation afterwards, I would expect coarsening of different microstructural features like precipitates or grains. This could lead to early failure of the component. In terms of sustainability the present study misses resilient data on the impact of your process on, for example, the carbon footprint. Please find some further suggestions for you manuscript:

‘Hot Upsetting’ is a very uncommon term in this context. Within the materials science and engineering community ‘hot compression’ is used more frequently. The manuscript should be changed accordingly.

Line 61: The international reader does not know the steel alloy 47GT. Please give a composition range for this material and a heat treatment, as this information is mandatory for calculation the carbon footprint of this components.

Line 91: ‘Only selected parts that are not damaged, which may prevent the restoration of the functionality of the part, are put into production.’ Please give more information on the selection process.

Figure 3: It is not clear what ‘KH’ as a unit means. I would suggest using SI-units here.

Line 375-379: There is nothing new in this statement.

Additionally, the manuscript needs an extensive amount of editing before publishing. Please find some suggestions below:

Line 40-43: The sentence should be divided, as it is barely readable in this state.

Line 13-20: Literature starts with #13; should be change!

Line 61: The term resource needs to be defined more specifically as this statement is confusing.

Line 79: 1150-12000C change to 1150-1200°C

Line 100-103: The sentence should be divided, as it is barely readable in this state.

Line 127: ‘which is the place of the likely formation of the clamp.’ Should be: ‘... which is the most likely place for clamp formation.’

Line 147: 10000C change to 1000°C

Line 341: 12000C change to 1200°C

Kind regards

Author Response

Thank you for your valuable comments.

We tried to give answers.

It is established that during high-temperature deformation, the worn-out defective layer is displaced into the allowance zone and removed by cutting, and subsequent chemical and thermal treatment contributes to the restoration of the original structure and physical and mechanical properties of the working surfaces.

Grinding of grains to 2 ... 3 points, their reorientation and reduction of dispersion occurs under pressure of about 400 MPa along the shear planes, which contributes to surface hardening and reduction of segregation.

Metallographic studies have established that the structure of the hardened layer is fine-needle martensite with troostite inclusions in the transition zone, which meets the technical requirements of the manufacturer.

All this confirms the absence of a negative impact of additional micro-stresses on the performance and durability of the parts restored by the proposed method.

"Hot disorder" is an inaccuracy of translation, there should be a "hot sediment"3.

47Mn8 – designation by euronorm (structure: C~0,47%, Mn – 0,8-1,2%, Si – 0,1-0,22%, Cu – 0,3%, Ni – 0,3%, Ti – 0,06-0,12%, P<0,035%, Cr<0,3%, S<0,035%, Fe – other)

The selection of parts suitable for restoration is carried out by micrometreage of the repair fund. The defect revealed that the size distribution of the studied worn parts obeys the logarithmic distribution law of random variables, is uneven, and the semi-axes lose less than 5% of their mass during wear, and the value of the complex recovery coefficient ranges from 0.87 to 0.98, which indicates the inexpediency of recycling worn parts of this name.
This is a kilonewton, should be denoted by kN
The statement, taking into account the remark, is proposed to be redone as follows: "The restoration of worn-out long-spline semi-axes with a cylindrical shank includes welding to the non-working end face by butt welding of a cylindrical compensator compensating wear, the length of which is selected based on the volume of worn metal and allowances for subsequent cutting, after that, the workpiece is locally heated in the area of the worn-out spline surface to the temperature of the plasticity of the metal and its one-sided precipitation in the die with a detachable matrix punch with a reduced force, which allowed to achieve some reduction in the load on the deforming tool and increase the durability of the die tooling"
The rest of the comments were agreed and corrected.

Thanks.

Reviewer 2 Report

The present manuscript is about the justification of the application of resource saving technology for the restoration of metal-intensive semi axles of rare axles of trucks using hot plastic deformation. The following are the points which must need to be considered.

The authors could not explain well about the purpose of their work in the introduction section. There are lots of ambiguities to understand without considering properly the literature review from previous researches.
In the line 114, methodology section, it is said that modern measuring method of interferometry was used to determine the surface residual stresses in the butt welding zone of the restored parts which is not clear in the manuscript.
In the section 3.4, a graph of the dependence of the force on the value of upsetting is constructed but it is not clearly explained well what is the purpose of this graph.
In the section 3.5, it is said that subsequent production tests carried out on the modes obtained as a result of experimental data. But in the manuscript there is no information about experimental results.
There is lack of microstructure analysis to justify the behavior of material explained in lines 350-357.
The discussion and conclusion sections are also not explaining properly according to methodology and results of manuscript.

Comments for author File: Comments.pdf

Author Response

Thank you for your valuable comments.

We tried to give answers.

The purpose of this work is to substantiate the possibility of using resource-saving renovation technology for restoring extremely worn metal-intensive steel parts by hot plastic deformation combined with butt welding of compensating metal wear, using the example of semi-axles of rear axles of trucks, which is consistent with the modern direction of reuse of secondary raw materials currently undergoing economically unjustified disposal.
Agree with the remark: The text and sources 7,8,9,10 have been deleted (lines 114-117 and 409-416 are crossed out with red lines), the numbering of sources should also be adjusted
A phrase has been added at the end of Section 3.4 under the graph (Figure 3): The purpose of plotting the graph is to illustrate a visual representation of the nonlinear dependence of the deformation force on the amount of precipitation described by the formulas (1,2,9,11,12)
Agree with the remark: The phrase in section 3.5 has been deleted (lines 343-345)
Agree with the remark: The text in lines 350-361 has been deleted
Added text at the end of the conclusion:

The implementation of the technological process of restoring worn semi-axes in repair production using the results of the power calculations of pressing equipment and die tooling given in the article confirmed the possibility of obtaining high-quality forgings with uniform and sufficient allowances for further cutting by plastic deformation from worn parts.

The use of force calculations will allow in the future to choose the right forging and pressing equipment that provides both optimally sufficient and not excessive deformation force, as well as to design die tooling and forming elements with the necessary margin of safety and a pre-known specific load on the tool.

Reviewer 3 Report

The article contains an interesting modification of the plastic working process, which is used in a completely unclear manner. The authors should enrich the description with legible drawings (both Figures 1 and 2 should contain a complete shape, and the graph in Fig. 3 is illegible). The description of the modifications used and the method of introducing them to the process is understandable for technologists, but rather without outlining what the process is about and a broad description, it will be difficult to understand for the reader. I suggest enriching the description with additional drawings, charts and tables that will enable understanding of the issue. Moreover, after converting the savings of 0.9 million rubles into the more widely recognized currency, it is only EUR 11,000. I do not know if it is a sufficient indicator to emphasize in terms of the cost-consumption of the process. I suggest changing the addresses of the paper by submitting it to the Metals or Journal of Manufacturing and Materials Processing section.
What do the two curves in diagram 3 mean and how exactly were they obtained?
How was the property assessed after restoration of semi-axles?

Author Response

Thank you for your valuable comments.

We tried to give answers.

Added Figure 4 "Diagram of the process of processing a worn semi-axis by pressure in a die"

Figure 4 shows a scheme for processing a worn half-axis by pressure during its restoration.

The essence of the process is as follows.

Additional material that compensates for wear and creates allowances for cutting processing, in the form of a compensator 1 with a length of l, is pre-welded by butt welding to the non-working end face 2 of the half-axis 3. Then, locally heated in the zone of the spline surface 4, the half-axis 3 is clamped by the shank 5 with a wedge mechanism. In this case , the difference in the diameters of the untreated shank 5 at the clamping point is compensated by the stroke of the piston h0 built into the stamp of the hydraulic cylinder with the radius of the piston R0 . In the absence of such compensation for deviations in the dimensions of the shank 5, when the half-matrices 6 and 7 of the stamp are closed, the axis of the shank rod 5 may shift relative to the axis of the spline surface 4, which in turn will lead to a curvature of the half-axis 3.

The axial force Px of the shank 5 is necessary to ensure the immobility of the semi-axis 3 with a one-sided draft with a force Pi of the spline surface 4 with a welded compensator 1 and the exception of the occurrence of slippage. After clamping the part with a punch 8 fixed to the rod of the power hydraulic cylinder 9, deformation is performed with the force Pi of the spline end 4 by the punch 3 increasing as the resistance to the plasticity of the metal increases, forcing the compensating metal 1 to be pressed into the body of the semi-axis 3 and move the base metal to the worn surface 4, filling the engraving 10 formed by horizontally movable closed half-matrices 6 and 7. At the same time, the outer diameter of the spline surface 4 increases to 2R with simultaneous filling with hot metal spline depressions.

The above power calculations are necessary for the correct choice of forging and pressing equipment, the design of die tooling and forming elements with the necessary and sufficient strength indicators.

The theoretical curve in the diagram (Fig.3) was obtained after substituting numerical values into formulas (1), (2), (9), (11), (12)

It is proposed to replace lines 372-374 with:

The average annual economic effect of the introduction of the technology for restoring semi-axes by plastic deformation at the price of a new factory part of 9250 rubles., the cost of its restoration of 7400 rubles., capital expenditures of 900 thousand rubles., a discount coefficient of 0.15 and an annual program for the restoration of 2500 parts will amount to 4.49 million rubles., which after conversion at the exchange rate will amount to 54490 euros.

Reviewer 4 Report

The authors have conducted an investigation of the restoration of worn parts by plastic deformation and metal saving can be obtained through the fragments of worn-out similar or similar parts as compensators. The purpose and necessity of this study are well defined. But some comments should be answered by the authors before the publication of this paper:

1) Section 1 (Introduction) and section 2 (Methodology) are too scattering. For example, P2L64-74 can be combined and there is no need to separate it into two paragraphs. The same happened for P2L81-86.

Also, please add the reference for the statement of “the university method of sliding lines of A.D. Tomlenov was used (P3L107-108)”.

2) P10L383-389 needs to be separated as an entire section labeled “5. Conclusion”. It should not be included in the Discussion part.

3) The Discussion part can be written in more detail. For example, the average annual economic effect of the technology can be clarified clearly.

Author Response

Thank you for your valuable comments.

We tried to give answers.

Lines 64-74 are proposed to be amended as follows:

"In the case of semi-axles, which are an intermediate link in the transmission of torque from the rear axle gearbox to the wheel, deviations from the nominal dimensions in the area of the spline shank, discoloration, crumpling, spline breakage and deformation are most often observed during operation [4]. Currently, there are no technologies for their restoration in the repair facility[6]."

Lines 81-86 are proposed to be amended as follows:

"The technological route of the restoration process, consisting of operations: cleaning, defecation, welding of the compensator, deburring, pre-deformation heating, stamping, straightening, turning, slotting, hardening with HDPE heating and control, allows to eliminate the maximum permissible wear of the slots and the curvature of the half-axis rod."

Conclusions. A fundamentally new direction in the creation of technologies for the 383

restoration of extremely worn parts by plastic deformation with preliminary application 384

to non-working surfaces by contact butt welding or surfacing of a wear-compensating 385

metal is characterized by high efficiency. Metal saving is achieved by using fragments of 386

worn-out similar or similar parts as compensators. The properties of the restored sections 387

and surfaces are identical to the serial parts, and the regulated reliability is comparable to 388

the durability of the new product.

It is proposed to replace lines 372-374 with:

Round 2

Reviewer 2 Report

The authors improved the manuscripts as per suggestions indicated in the previous reviews. In my opinion the manuscript can be published in Sustainability.

Author Response

Thanks very much.

Reviewer 3 Report

The description of the process itself still seems incomplete and hard to understand. it seems obvious to add a process diagram. Figures 1 and 2 need to be improved as previously suggested. The description of the process in Fig. 4 is almost at the end of the article, which is a disturbance in the structure of scientific work. The introduced corrections do not exhaust the previously described problems with the presentation of the material. As for the cost and savings account, are all expenses / costs taken into account in the bill? If so, please indicate the time after which the investment return will be made. Statement "The use of force calculations will allow in the future to choose the right forging and pressing equipment that provides both optimally sufficient and not excessive deformation force, as well as to design die tooling and forming elements with the necessary margin of safety and a preknown specific load on the tool. "is not a conclusion. In general, the last sections are a summary. The corrections made are not sufficient for the article to be published.

Author Response

Thank you for your valuable advice and recommendations. The answers are presented in a file.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Paper can be accepted but authors still didnt make all corections. If the the depreciation period is 6 years, as for the expected profits, the presented modification has very low economic indicators.