(MQCL) in machining titanium alloy

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An experimental investigation on effect of minimum quantity cooling lubrication (MQCL) in machining titanium alloy (Ti6Al4V) Article in International Journal of Advanced Manufacturing Technology · June 2016 DOI: 10.1007/s00170-016-8969-6

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4 authors: Salman Pervaiz

Amir Rashid

Rochester Institute of Technology - Dubai C…

KTH Royal Institute of Technology

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Ibrahim Deiab

Cornel Mihai Nicolescu

University of Guelph

KTH Royal Institute of Technology



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Available from: Salman Pervaiz Retrieved on: 22 August 2016

An experimental investigation on effect of minimum quantity cooling lubrication (MQCL) in machining titanium alloy (Ti6Al4V) Salman Pervaiz, Amir Rashid, Ibrahim Deiab & Cornel Mihai Nicolescu

The International Journal of Advanced Manufacturing Technology ISSN 0268-3768 Int J Adv Manuf Technol DOI 10.1007/s00170-016-8969-6

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Author's personal copy Int J Adv Manuf Technol DOI 10.1007/s00170-016-8969-6

ORIGINAL ARTICLE

An experimental investigation on effect of minimum quantity cooling lubrication (MQCL) in machining titanium alloy (Ti6Al4V) Salman Pervaiz 1,2 & Amir Rashid 1 & Ibrahim Deiab 3 & Cornel Mihai Nicolescu 1

Received: 20 August 2015 / Accepted: 24 May 2016 # Springer-Verlag London 2016

Abstract During the machining operation, elevated temperatures are achieved at the cutting interface due to the presence of high plastic deformation and friction in between the tool and chip contacting area. Efficient heat dissipation from the cutting interface is required to achieve better machining performance. Elevated temperature in the cutting area results in lower tool life as it facilitates different types of wear mechanisms. Metal working fluids (MWFs) are employed to reduce heat and friction in the cutting zone, simultaneously to help in the flushing of waste particles. The MWFs are based on either water or petroleum oil and include several additives which make them non-biodegradable and toxic in nature. The minimum quantity lubrication (MQL) method offers a feasible substitute to the MWF-based conventional flood cooling method. In this study, a vegetable oil-based MQL system was mixed with sub-zero temperature air to design a new minimum quantity cooling lubrication (MQCL) system. The

* Salman Pervaiz [email protected] Amir Rashid [email protected] Ibrahim Deiab [email protected] Cornel Mihai Nicolescu [email protected] 1

Department of Production Engineering, KTH Royal Institute of Technology, Stockholm, Sweden

2

Department of Mechanical Engineering, American University of Sharjah, Sharjah, United Arab Emirates

3

School of Engineering, University of Guelph, Ontario, Canada

study investigates the machinability of Ti6Al4V using an MQCL system under various oil flow rates and compared its machining performance with both dry cutting and conventional flood cooling. For further evaluation, the study investigated surface roughness, flank wear, and associated wear mechanisms. It was found that in the MQCL system (60–70 ml/h), oil supply rates provided reliable machining performance at higher feed levels. Keywords Titanium . MQCL . Machinability . Wear . MQL . Turning . Tools . Biodegradable

1 Introduction Titanium alloys are categorized under difficult-to-cut materials. The in-built thermo-physical properties of these materials make the machining process very challenging [1, 2]. Titanium and its alloys have inherent favorable properties like extraordinary strength-to-weight ratio, corrosion resistance, and compatibility to operate at elevated temperatures. These desirable properties make their service performance reliable for the demanding sectors like aeronautic, petrochemical (oil and gas extraction), marine, power and energy generation, and biomedical etc. [3, 4]. During the machining phase, titanium alloys exhibit high strain hardening, high hot hardness, and high chemical affinity toward the cutting tool materials. At the same time, their low thermal conductivity and high heat capacity play a critical role toward the heat dissipation process. Generally, in the machining of titanium alloys, heat stays in the region near the nose and edge of the cutting tool. Due to the presence of high cutting temperature, tool wear mechanisms appear at the cutting tool resulting in very short tool life [5]. Metal working fluids (MWFs) are employed in the machining phase to reduce heat and friction in the cutting zone that

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results in enhanced machining performance. Utilization of these MWFs generally results in enhanced tool life, superior surface finish, and better chip elimination. The conventional MWFs are non-biodegradable and toxic in nature [6]. These MWFs also support microbial growth that result in the production of bacteria, fungal cells, and their biological products such as endotoxins, exotoxins, and mycotoxins [7]. Nowadays, MWFs are being questioned because of their disadvantages like, e.g., disposal issues, negative influence on the environment and the human health, and cost associated with their rectification and maintenance. Different countries have taken initiatives by making strict regulations to restrict the use of these harmful MWFs, e.g., Blue Angel certification in Germany, the SS 155434 code in Sweden, and VAMIL regulation in the Netherlands. As per literature [8], it has already been found that the cost of the cutting fluid was 7–17 % of the total cost involved in the manufacturing of the part. In spite of the issues associated with conventional flood cooling, their use is still essential to achieve economical tool life and desirable surface finish. As a substitute, near dry machining and minimum quantity lubrication (MQL) techniques are used where extremely low quantity of oil flow rates are employed to reduce friction at the tool-chip and toolworkpiece contacting regions, resulting in low cutting temperatures [9]. Many researchers have focused their work to investigate the utilization of vegetable-based oil in machining and MQL technique. In MQL systems, lubricants are supplied to the cutting zone by means of spraying. Another extension of the MQL system is minimum quantity cooling lubrication (MQCL) where very less quantity of lubricant/coolant is combined with compressed air. In such systems, oil is used to reduce friction whereas air enhances the cooling action. In MQL and MQCL systems, finely dispersed atomization is essential to achieve efficient lubrication at the tool-chip interface. Numerous researchers have explored the machining performance of MQL systems for machining Ti6Al4V using different types of cutting tool materials. Zeilmann and Weingaertner [10] performed machinability study with MQL arrangements on Ti6Al4V by utilizing uncoated and coated carbide drills. The study used both external and internal arrangements of coolant supply using an MQL booster system. The study checked the cutting temperature during testing and revealed that internally employed MQL arrangement performed better than did external settings. Rahim and Sasahara [11] examined the machinability of Ti6Al4V by employing palm oil-based and synthetic ester-based lubricants using MQL arrangements. The study used tool life, thrust force, torque, tool failure modes, wear mechanisms, and workpiece temperature to evaluate the machining performance of each cooling strategy. The study pointed out that flank wear, micro-chipping, adhesion, attrition, and thermal cracking were present in all cooling strategies for high-speed drilling of Ti6Al4V. However, severe thermal cracking was observed during the dry cutting

environment. The study revealed that the palm oil-based MQL system performed better than did the synthetic esterbased system. Wang et al. [12] executed orthogonal machining experiments on Ti6Al4V using fine grain uncoated carbide cutting tools by using three different cutting environments (dry, conventional flood, and MQL). The study utilized experimentation to establish the friction conditions under different cooling strategies, and then friction condition were incorporated in finite element modeling to estimate the cutting forces. The study focused on the calculation of friction angles using Oxley’s theoretical background and analyzed chip morphology as well. The study found that dry cutting was a feasible approach at low cutting speeds; however, the MQL system performed better at higher cutting speeds as it delivered better lubrication. The study also performed interrupted cutting experiments by creating slots. The MQL approach outperformed dry and flood cutting in the case of the two-slot interrupted cutting. The numerical and experimental outcomes were obtained in reasonable agreement. Cia et al. [13] performed endmilling experiments using a vegetable oil-based MQL system. The study was focused on the optimization of oil flow rate for the MQL system. The study utilized cutting force and tool wear comparison to estimate the machining performance of MQL arrangements. The study incorporated the vegetable oil flow rates ranging from 2–14 ml/h. The study revealed that diffusion wear was the main cause of cutting tool failure for the oil flow rates from 2–10 ml/h. However, for the oil flow rate of 14 ml/h diffusion wear was not present. Raza et al. [14] explored the machinability of a titanium alloy (Ti6Al4V) using several sustainable lubrication strategies. The study was conducted using six different strategies including conventional flood, conventional dry, MQL, chilled air, cryogenic (LN), and MQCL. The study successfully enlightens the potential of vegetable oil as a possible replacement for the conventional coolants/lubricants. Pervaiz et al. [15] investigated the cutting forces, tool wear mechanisms, and energy consumption for machining Ti6Al4V using different cutting environments. The study was focused on dry, mistbased and flood cutting environments. It was observed that abrasive wear mechanism was the principal wear pattern on the cutting edge. Su et al. [16] performed end-milling experiments using different cooling approaches on titanium alloys. The study examined cutting tool wear, failure modes, and associated wear mechanisms under dry, conventional flood, mist (nitrogen based), compressed cold nitrogen gas (CCNG) at 0, and −10 °C, and compressed cold nitrogen gas and oil mist (CCNGOM) as the cooling strategies. The study pointed out that enhancement in the cutting tool life was attained when CCNG was employed. The study also revealed that the CCNGOM cooling strategy outperformed others. Klocke et al. [17] explored the machinability of Ti6Al4V under high pressurized coolant when machining titanium

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alloys. The study was performed on Ti6Al4V and Inconel 718 under longitudinal external turning with uncoated carbide cutting inserts. The study used parameters of tool temperature, chip formation, and cutting forces to analyze the machinability of Ti6Al4V. The coolant was pressurized up to 350 bars at a flow rate of 60 l/min. The study exposed that reduction in cutting tool temperature and improved tool wear was attained using high pressure coolant. However, a minor rise in the cutting force was witnessed when the lubricoolant was applied with high pressure and oil flow rate. Sun et al. [18] evaluated the machining performance of Ti6Al4V by using cryogenic compressed air as a cooling strategy. Compressed air was delivered in the cutting zone by arranging two nozzles facing the rake and flank faces. The study measured chip temperature, chip morphology, tool wear, and dynamic cutting forces to evaluate the machining performance. The study revealed that cryogenic compressed air cooling approach significantly reduced the wear on the cutting tool. Kramer et al. [19] examined the thermo-mechanical tool loads under high pressure lubricoolant strategy. The outcomes of cutting temperatures and tool wear were compared with the conventional flood cutting environment. The study revealed stable and unstable tool wear conditions with respect to the different cutting conditions and environments. Rotella et al. [20] studied the influence of cooling strategy toward the surface integrity and product service of the finished part. The study was conducted using dry, flood, MQL, and cryogenic cooling strategies. The study was focused on surface roughness and metallurgical conditions, including the microstructure, hardness, grain refinement, and phase transformation of the machined part. The study revealed that the cryogenic strategy provided the best sustainability-oriented results and also provided smaller grains. Wang et al. [21] conducted orthogonal machining experiments under continuous and intermittent turning arrangements for Ti6Al4V using dry, flood, and MQL strategies. The study observed cutting forces and the mean friction coefficient at the tool-chip interface was estimated for different coolant supplies. The study also provided FEM predicted results with experimental verification. In the present work, turning experiments were performed on Ti6Al4V using uncoated carbide. In order to analyze the influence of cutting speed and feed rate as major factors, depth of cut was kept constant. The study used five levels of oil flow rates ranging between 60 and 100 ml/h and dry and flood cooling environments to analyze the machining performance. The study analyzed surface finish, tool wear, and their associated wear mechanisms to investigate the machining performance.

2 Materials and experimental method The cutting tests were conducted using titanium alloy (Ti6Al4V). Ti6Al4V is the most widely used titanium alloy.

Table 1

Nominal chemical composition of Ti6Al4V

Element Wt.% Element Wt.% H N

0.015 0.05

V Al

Element Wt.% Element Wt.%

3.5–4.5 C 5.5–6.18 Fe

0.1 0.3

Ti

Balance

Out of the total titanium consumption, 50 % is based on Ti6Al4V. Raw material was available in the form of cylindrical rod. Stock of Ti6Al4V material was available under ASTM B381standard specifications. The composition of titanium alloy (Ti6Al4V) is shown below in Table 1. The mechanical properties of Ti6Al4V at room temperature are mentioned in Table 2. Uncoated cutting inserts were employed in the experiments. The mentioned turning insert has two cutting edges. Data for the cutting insert has been shown in Table 3. In order to apply MQCL arrangement internally, a specially designed tool holder from Mircona was used during the present study. The study was conducted using three different types of cooling approaches in order to examine the machining performance of Ti6Al4V. These cooling approaches were named as dry, conventional (emulsion) flood, and mixture of low temperature air with internal vegetable oil-based mist (MQCL). In the MQCL system, rapeseed oil was employed at the different flow rates ranging in between 60 and 100 ml/h. The rapeseed oil (ECULUBRIC E200L) was delivered by ACCU-Svenska AB. The flow rate of mist was controlled by regulating the oil supply, whereas air pressure was kept constant at 0.5 MPa and -4 °C. The information about the rapeseed oil is shown in Table 4. Machining experiments were conducted using a computer numeric control turning center. Table 5 shows the specifications of a CNC turning center. To examine the surface conditions obtained during the cutting operation, a Mitutoyo roughness tester (SJ 201P) was employed and surface finish was measured. A Mitutoyo tool maker microscope (TM 510) was employed to examine the extent of flank wear. The specifications for the TM 510 tool maker microscope and Mitutoyo roughness meter have been provided in the Table 5. To analyze the tool wear mechanisms, Tesla scanning electron microscope was employed. In order to investigate the outcomes appropriately, three levels of cutting speed and feed rate were utilized. However, five levels of oil flow rate were also employed during experimentation as shown in Table 6. The Table 2

Mechanical properties of Ti6Al4V at room temperature

Properties

Values

Properties

Values

Tensile strength Yield strength Elongation

993 MPa 830 MPa 14

Poison ratio Modulus of elasticity Hardness (HRC)

0.342 114 GPa 36

Author's personal copy Int J Adv Manuf Technol Table 3 Cutting tool and tool holder specifications

Cutting Tool

ISO Code: CCMT 12 04 04 MM H 13A

Material

Uncoated

Insert thickness

0.1875″

Rake

Positive

Nose radius

0.0157″

Relief angle Tool Holder:

7 Degrees

SCLC R 2525 M12-EB Holder has internal passages to provide MQCL lubricant at rake and flank face during machining

cutting conditions were selected as per the recommendation of the sandvik cutting tool catalogue. However, aggressive cutting conditions were avoided in this study. Kistler multichannel dynamometer was utilized for measuring the cutting forces generated during the machining operations. Figure 1 displays the schematic illustration of the experimental setup used for the current study.

3 Results and discussion 3.1 At cutting speed of 90 m/min The surface roughness results were plotted for a 90-m/min cutting speed and feed levels as shown in Fig. 2. It represents the surface roughness attained for dry, MQCL (60, 70, 80, 90, and 100 ml/h) and flood cooling strategies. The lower graph in Fig. 2 represents feed level of 0.1 mm/rev. To analyze it Table 4 E200L)

Characteristics of vegetable oil used in mist (ECULUBRIC

Properties

Description

Chemical description

A fraction of natural triglycerides, easily biodegradable substances Not hazard to human health

completely, Figs. 3, 4, and 5a should also be considered for cutting forces and tool wear. Figure 2 represents that feed level has a controlling influence on the surface roughness that is in accordance with the metal cutting theory. By increasing the feed level from 0.1 to 0.3 mm/rev, surface finish has also been increased from 1 to 4 μm approximately. Figures 2, 6, and 11 shows the surface roughness for different cutting speeds of 90, 120, and 150 m/ min. Cutting speed did not show any significant effect on the surface roughness for the range under consideration. At 90 m/ min and feed levels of 0.1, 0.2, and 0.3 mm/rev, different oil flow rates under MQCL arrangement did not show any remarkable change in surface roughness. As shown in Fig. 2, minor fluctuations (less than 1 μm) for surface roughness were observed for different oil flow rates under each feed level in the MQCL arrangement. Therefore, increasing the oil flow rates from 60 to 100 ml/h in the MQCL arrangement did not significantly affect the surface finish. The average values of the resultant cutting forces were reported for the analysis and comparison purposes. The feed at 0.1 mm/rev points out at the better performance of MQCL

Table 5

Health hazard Flash point Ignition point Density At 0 °C At −4 °C Dynamic viscosity At 0 °C At −4 °C Partition coefficient Source: [22]

325 °C 365 °C 0.9273 g/cm3 0.9297 g/cm3 2.881 N s/m2 3.652 N s/m2