Effect of Various Lubricating Strategies on Machining of Titanium Alloys: A State-of-the-Art Review

Round 1

Reviewer 1 Report

Comments to the authors

The manuscript entitled “Effect of Various Lubricating Strategies on Machining of Titanium Alloys: A State-of-the-Art Review” has been submitted by the author. However, there are still major concerns that need to be addressed before publication. Therefore, I recommend this work could be published after the major revision.

1. The background of this work is not clear. The authors should specify in a clearer way what novelty of this review.
2. The same type of review has been already reported. Author should explain in detail how this review will be helpful to readers.

1. Introduction part should be elaborate.
2. Author should explain in schematically, how Minimum Quantity Lubrication (MQL) method work on machining operation.

5. There are allot of typo error and ambiguous sentences, which need to be corrected for clear message from authors explanation.
6. Most of the references are outdated. Author should provide the latest references.

Author Response

The manuscript entitled “Effect of Various Lubricating Strategies on Machining of Titanium Alloys: A State-of-the-Art Review” has been submitted by the author. However, there are still major concerns that need to be addressed before publication. Therefore, I recommend this work could be published after the major revision.

1. The background of this work is not clear. The authors should specify in a clearer way what novelty of this review.

This article discusses the impact of lubricants on Titanium Alloy machining in terms of their lubricating cooling influence on power consumption, cutting forces, and surface finish.

1. The same type of review has been already reported. Author should explain in detail how this review will be helpful to readers.

This article discusses the requirement for alternative cryogenic cooling which is more economically beneficial in terms of manufacturing cost compared to other cooling strategies.

1. Introduction part should be elaborate.

The authors incorporated the suggestions in the revised manuscript.

1. Author should explain in schematically, how Minimum Quantity Lubrication (MQL) method work on machining operation.

Authors incorporated the suggestions in the revised manuscript in the section of Minimum quantity lubrication (MQL) machining strategy.

1. There are allot of typo error and ambiguous sentences, which need to be corrected for clear message from authors explanation.

In revised manuscript authors took more concern, and hopeful that there should be less type errors.

1. Most of the references are outdated. Author should provide the latest references.

In the revised manuscript, latest references have been added as below:

[1]        Pereira, O.; Rodríguez, A.; Fernández-Abia, A. I.; Barreiro, J.; López de Lacalle, L. N. Cryogenic and Minimum Quantity Lubrication for an Eco-Efficiency Turning of AISI 304. Journal of Cleaner Production, 2016, 139, 440–449. https://doi.org/10.1016/J.JCLEPRO.2016.08.030.

[2]        Pereira, O.; Rodríguez, A.; Barreiro, J.; Fernández-Abia, A. I.; de Lacalle, L. N. L. Nozzle Design for Combined Use of MQL and Cryogenic Gas in Machining. International Journal of Precision Engineering and Manufacturing-Green Technology 2017 4:1, 2017, 4 (1), 87–95. https://doi.org/10.1007/S40684-017-0012-3.

[3]        Pereira, O.; González, H.; Calleja, A.; Rodríguez, A.; Urbikaín, G.; López De Lacalle, L. N. Manufacturing of Human Knee by Cryogenic Machining: Walking towards Cleaner Processes. Procedia Manufacturing, 2019, 41, 257–263. https://doi.org/10.1016/J.PROMFG.2019.07.054.

[4]        Gross, D.; Appis, M.; Hanenkamp, N. Investigation on the Productivity of Milling Ti6al4v with Cryogenic Minimum Quantity Lubrication. MM Science Journal, 2019, 2019 (November), 3393–3398. https://doi.org/10.17973/MMSJ.2019_11_2019098.

[5]        Kaynak, Y.; Gharibi, A. Cryogenic Machining of Titanium Ti-5553 Alloy. Journal of Manufacturing Science and Engineering, Transactions of the ASME, 2019, 141 (4). https://doi.org/10.1115/1.4042605/474988.

[6]        An, Q.; Cai, C.; Zou, F.; Liang, X.; Chen, M. Tool Wear and Machined Surface Characteristics in Side Milling Ti6Al4V under Dry and Supercritical CO2 with MQL Conditions. Tribology International, 2020, 151, 106511. https://doi.org/10.1016/J.TRIBOINT.2020.106511.

[7]        Jamil, M.; Khan, A. M.; Gupta, M. K.; Mia, M.; He, N.; Li, L.; Sivalingam, V. K. Influence of CO2-Snow and Subzero MQL on Thermal Aspects in the Machining of Ti-6Al-4V. Applied Thermal Engineering, 2020, 177, 115480. https://doi.org/10.1016/J.APPLTHERMALENG.2020.115480.

[8]        Gajrani, K. K. Assessment of Cryo-MQL Environment for Machining of Ti-6Al-4V. Journal of Manufacturing Processes, 2020, 60, 494–502. https://doi.org/10.1016/J.JMAPRO.2020.10.038.

[9]        Kumar Mishra, S.; Ghosh, S.; Aravindan, S. Machining Performance Evaluation of Ti6Al4V Alloy with Laser Textured Tools under MQL and Nano-MQL Environments. Journal of Manufacturing Processes, 2020, 53, 174–189. https://doi.org/10.1016/J.JMAPRO.2020.02.014.

[10]      Rodríguez, A.; Calleja, A.; de Lacalle, L. N. L.; Pereira, O.; Rubio-Mateos, A.; Rodríguez, G. Drilling of CFRP-Ti6Al4V Stacks Using CO2-Cryogenic Cooling. Journal of Manufacturing Processes, 2021, 64 (March 2020), 58–66. https://doi.org/10.1016/j.jmapro.2021.01.018.

[11]      Grguraš, D.; Sterle, L.; Pušavec, F. Cutting Forces and Chip Morphology in LCO2 + MQL Assisted Robotic Drilling of Ti6Al4V. Procedia CIRP, 2021, 102, 299–302. https://doi.org/10.1016/J.PROCIR.2021.09.051.

[12]      Khanna, N.; Shah, P.; de Lacalle, L. N. L.; Rodríguez, A.; Pereira, O. In Pursuit of Sustainable Cutting Fluid Strategy for Machining Ti-6Al-4V Using Life Cycle Analysis. Sustainable Materials and Technologies, 2021, 29, 1–10. https://doi.org/10.1016/j.susmat.2021.e00301.

[13]      González, H.; Pereira, O.; de Lacalle, L. N. L.; Calleja, A.; Ayesta, I.; Munõa, J. Flank-Milling of Integral Blade Rotors Made in Ti6Al4V Using Cryo CO2 and Minimum Quantity Lubrication. Journal of Manufacturing Science and Engineering, Transactions of the ASME, 2021, 143 (9). https://doi.org/10.1115/1.4050548/1104369.

[14]      Chen, G.; Caudill, J.; Chen, S.; Jawahir, I. S. Machining-Induced Surface Integrity in Titanium Alloy Ti-6Al-4V: An Investigation of Cutting Edge Radius and Cooling/Lubricating Strategies. Journal of Manufacturing Processes, 2022, 74, 353–364. https://doi.org/10.1016/J.JMAPRO.2021.12.016.

[15]      Chen, G.; Chen, S.; Schoop, J.; Caudill, J.; Jawahir, I. S. The Influence of Sustainable Cooling Strategies and Uncut Chip Thickness on Surface Integrity in Finish Machining of Ti-6Al-4V Alloy. ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE), 2022, 2B-2021. https://doi.org/10.1115/IMECE2021-73236.

Author Response File: Author Response.pdf

Reviewer 2 Report

Please, see the file attached.

Comments for author File: Comments.pdf

Author Response

Reviews must be analysed following ideas from the main journals, they propose that 98% of key references over the last 10 years must explained and propose to the public debate

How can it be? No any Works by Pereira, Lopez de Lacalle, Aspinwall…at least they missed 14 works directly related with the topic, today CO2 cryogenics and MQL was defined by O. Pereira in of the group S, and the results were quite Good in Titanium. This is a review, so the 100% of the state of the art must be included. In many journals this is a cause of rejection, but in your case could be major.

Authors are incorporated all the suggestions in the revised manuscript highlighted in yellow color as described below:

Pereira et al. [69] studied the modern cryogenic machining technologies and advocated the use of cryogenic and minimal quantity lubrication for an environmentally friendly turning operation. In a study, Pereira et al. [70] manufactured a knee prosthesis by using a Kondia HS1000 5-axis machining center to execute machining operations. Ti6Al4V grade 23 was utilized as the raw material for this project. In this work, a CO2 cryogenic machining environment was proposed to manufacture the product. The benefit of this configuration is that it not only incorporates economic and environmental aspects but also suggests a clean approach in which cutting fluid based on oils is restricted. Kaynak and Gharibi [71] used cryogenic cooling and dry machining to accomplish a high-speed cutting operation on Ti-5553. The experiments were carried out at various cutting speeds using cryogenic coolants such as carbon dioxide (CO2) and liquid nitrogen (LN2). Cryogenic machining increases the machining performance of the Ti-5553 alloy by significantly lowering tool wear, cutting temperature, and dimensional deviation of the machined components, according to this study. Cryogenic machining also resulted in smaller chips than dry machining. Gajrani [72] performed turning on Ti-6Al-4V in three different lubrication environments namely dry, MQL, and cryo-MQL. The study revealed a considerable increase in machining performance; the cryo-MQL environment reduced machining forces and workpiece surface roughness by 27% and 46%, respectively, compared to the dry environment. The morphology of the tool rake surface revealed a considerable drop in the contact length of the sliding-sticking zones. When compared to the dry and MQL settings, the elemental composition revealed a decline in workpiece material adherence on the tool rake surface. The study proposed cryo-MQL as a hybrid lubrication environment for Ti-6Al-4V machining. Rodríguez et al. [73] recommended using CO₂ cryogenic cooling during the drilling of CFRP-Ti6Al4V stacks. This recommendation was based on a comparative study between dry drilling and drilling using CO₂ cryogenic cooling. Implementation of liquified CO2 brought the tooltip temperature down leading to a reduction in damaged tool edges thereby enhancing the tool life.  

Chen et al. [79] investigated the impact of cutting-edge radii and various lubricant methods on the surface integrity of Ti-6Al-4V. To accomplish orthogonal cutting on Ti-6Al-4V, a variety of lubrication conditions, including dry, MQL, LN2, hybrid with LN2, and MQL with varied cutting edge radii were used. Substantial changes in the size and depth of machining-induced compressive residual stress fields were also seen in machining with increased cutting edge radii and hybrid cooling. In addition, when the cutting edge radius rose, the surface hardness rose marginally. Because of increased deformation stress and lower fracture strain at lower temperatures, cryogenic cooling (LN2) produces thinner deformation layers and wider deformation gradients. In another experiment, Chen et al. [80] investigated the surface integrity of Ti-6Al-4V during finish machining using dry, MQL, and cryogenic cooling techniques. According to the findings, with a minimum uncut chip thickness of 10 m, the pressures at the dry and MQL conditions caused fluctuations owing to the unsteady cutting process. This was due to frequent material buildup at the cutting edge, which implies that materials accumulated ahead of the cutting edge regularly as a result of the simultaneous impacts of sliding, ploughing, and cutting. Altogether, finish machining surface integrity and mechanical behaviors were observed during orthogonal machining of Ti-6Al-4V alloy with cryogenic cooling and minimal uncut chip thickness.

Furthermore, Pereira et al. [81] presented a revolutionary cryogenic nozzle design. The development and optimization of CFD (ANSYS Fluent) simulation-derived nozzle outlets for CO2 + MQL cooling were carried out with a primary focus on nozzle diameter. The suggested models were confirmed by actual trials, and a prototype nozzle was created based on the data collected in the study (a CO2 velocity of 325 m/s is required to allow sustainable machining). Based on these research outcomes, three nozzle diameters (0.5, 1, and 1.5 mm) were considered by the researchers for their CFD model. Along with his teammates, Pereira then assessed the comparative effectiveness of each nozzle design based on normal average velocity at a distance of 20 mm from the outlet, noticing that the CO2 velocity was best preserved with the 1.5 mm. According to this finding, when tested, the 1.5 mm nozzle achieved the largest spray distance of 40 mm (compared to 10 mm and 18 mm for the 0.5 mm and 1.0 mm nozzles, correspondingly). Taking inspiration from the works of Pereira & his team, Gross et al. [82] performed preliminary CO2 + MQL nozzle optimization tests on Ti-6Al-4V, accompanied by cryogenic CNC milling experiments. During the process, it was discovered that when MQL was sprayed with compressed air, there were a high number of lubricant splashes on the oil trail. When the MQL was used in combination with CO2, no such splashing occurred. The researchers observed this as an anticipated result of the CO2 jet's enhanced flow speed (compared to compressed air) concentrating the oil droplets.

Taking into account the main ideas of the paper, they are well organized, some points to get more from literature and propose to readers:

• CO2 on ti6Al4V with MQL, and other related alloys ask for a section or subsection. Doing that you can complete all the missed ideas.

Suggestions are incorporated in the revised manuscript as follows:

An et al. [53] examined the tool wear and machined surface properties of Ti6Al4V during the side milling operation. Four sustainable cooling environments namely dry, supercritical carbon dioxide (scCO2), scCO2 with antifreeze water-based minimum quantity lubrication (scCO2-WMQL), and scCO2 with oil-on-water based MQL (scCO2-OoWMQL) were employed during the process. A continuous wavelet transform was used to study the comprehensive properties of the machined surface profile. The findings demonstrated that scCO2-OoWMQL outperformed scCO2 as a novel sustainable and efficient cooling and lubricating approach. Jamil et al. [54] investigated the effect of CO2-snow and subzero MQL on Ti-6Al-4V. The machining operation was carried out under flood, CO2-snow, and MQL conditions, and heat transfer capabilities of CO2-snow and subzero MQL were examined. According to the study, the order of overall greater machinability is CO2-snow > flood cooling > subzero MQL. Furthermore, the considerably greater heat transfer behavior of CO2-snow in machining led to less tool wear (i.e., a longer tool life) and better surface quality. In conclusion, the CO2 snow has shown encouraging results that justified its use in the machining sector.

Grguraš et al. [68] used carbide tools to perform robotic drilling on Ti6Al4V and studied chip morphology and cutting forces in an LCO2 + MQL environment. The results show a significant association between LCO2 flow rate and thrust force owing to material hardness, as well as a significant correlation between torque and MQL flow rate due to the simultaneous impacts of cutting zone lubrication and the chip evacuation process. Due to a conjunction of lower temperatures and lubrication threshold, dry drilling demonstrates significant chip adherence to the tool, whereas LCO2 + MQL aided drilling enhances chip breakability and minimizes workpiece-material adhesion.

Figure 6. Friction coefficient: how did they do it?

The directional cutting force (Fr, Ft) could be calculated by experimental cutting force (Fx, Fy) by using the transformation method. In the end milling, the friction coefficient was the ratio of Fr to Ft.

• In pursuit of sustainable cutting fluid strategy for machining Ti-6Al-4V using life cycle analysis in Sustainable Materials and Technologies. Explain Figure 8

Author have given a detailed description in the revised manuscript which are highlighted in yellow color and also described below:

The reduction in flank wear was noted 71.3%, 53.9% and 44.1% with 0.5% wt., 0.3% wt., and 0.1% wt. concentration respectively. Additionally, a less adhered layer on the rake face and Build-up-Edge (BUE) was formed with nano lubrication. Furthermore, the worn area and material adhesion on the rake faces was observed to be lower using GO Nanofluid compared to conventional cutting fluid as shown in (Fig.8).

The ideas must be completed, you can resubmit a more complete date. Please I kindly encourage you to provide another version soon.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Authors did the significantly modification of the paper. Now the paper should be accepted. 

Reviewer 2 Report

My comments were taken into account. Accepted.