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Int. J. Mech. Eng. & Rob. Res. 2014 Roshani U Shingarwade and Pankaj S Chavan, 2014

A REVIEW ON MQL IN REAMING

Roshani U Shingarwade1* and Pankaj S Chavan2

*Corresponding Author: Roshani U Shingarwade, roshanishingarwade@gmail.com

Modern era of mass production of holes with good surface finish and geometrical accuracy(cylindricity, roundness) is the basic requirement for precise assembly of different machinedcomponents. Even in today's industrial era, most of the machining operations are performedusing flood lubrication but flood lubrication contributes to adverse health effect and safety issues,including toxicity, lung diseases to operator and air pollution, etc. Because of this mentionedissues the use of cutting fluid needs to be minimized and hence the Minimal Quantity Lubrication(MQL) technology was introduced. MQL is the process to apply minute amount of lubrication tothe tool tip during machining. The lubricant is mixed with compressed air and forms aerosolmixture called as MQL. Conventional cutting fluids (flood lubrication) eliminate such problemsas higher cutting temperature, tool wear and greater dimensional deviation. But, they possess asignificant portion of the total machining cost. Thus machining under Minimum QuantityLubrication (MQL) condition has drawn the attention of researchers as an alternative to thetraditionally used flood lubrication with a view to minimizing the cooling and lubricating cost aswell as reducing cutting zone temperature, tool wear, surface roughness and dimensionaldeviation. It was observed that the use of MQL technology resulted in decrease of overall cost byabout 13% and it is possible to achieve effective lubrication of cutting process with extremelysmall quantity of oil. The result is not only high productivity but also longer tool life and costsaving.

Keywords: Reaming, Minimum Quantity Lubrication (MQL)

INTRODUCTIONCutting fluids applied in machining providelubrication and cooling, minimizing the heatproduced between the surface of theworkpiece and the tool and the contact area

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Int. J. Mech. Eng. & Rob. Res. 2014

1 Mechanical Department, Datta Meghe Institute of Technology & Research, Sawangi Meghe, Wardha, India.2 Mechanical Engineering Department, Deogiri Institute of Engg & Management Studies, Aurangabad, India.

between tool and chip. However, during thelast decade, a significant research has beenundertaken with the aim of diminishing thequantity of cutting fluids applied in production,due to the fact that the use of large amounts of

Review Article

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Int. J. Mech. Eng. & Rob. Res. 2014 Roshani U Shingarwade and Pankaj S Chavan, 2014

cutting fluids brings several drawbacks.Cutting fluids can be difficult and expensive torecycle; they can cause skin and lung diseasesto the operator and cause air pollution.

Other reasons for decreasing the quantityof cutting fluids are the costs related to thefluids, which have been evaluated to be in therange 7-17% of the overall manufacturing costs(De Chiffre et al., 2009).

The necessity to machine using less harmfulcutting fluids has prompted many researchersto investigate the use of minimum quantitylubrication. In order to minimize the use ofcutting fluids and to fulfill the demandsconcerning health work environment, theMinimal Quantity Lubrication (MQL) technologywas introduced (Nourredine Boubekri andVasim Shaikh, 2012).

MQL is a machining method that delivers aprecise amount of lubrication to the tool tip.The lubricant is mixed with compressed air andforms the desired air/oil aerosol mixture. Byusing MQL it is possible to achieve effectivelubrication of the cutting process with extremelysmall quantities of oil. The result is not onlyhigher productivity due to faster cutting speedsbut also longer tool life and cost savings oncooling lubricants. By abandoningconventional cooling lubricants and taking intoaccount only the use of this new technology,costs can be reduced significantly.

REAMING OPERATIONReaming is a common machining processwith the characteristic property of enlarging,smoothing and accurately sizing existingholes to tight tolerances. The quality of thehole depends on reamer geometry, cuttingconditions, application, stock removal,

lubrication and the quality of the holes to bereamed. Reaming is a finishing operationwhich normally follows drilling or core drilling.Since stock removal is small and must beuniform in reaming, the starting holes (drilledor otherwise produced) must have relativelygood roundness, straightness, and surfacefinish.

Reamers tend to follow the existingcenterline of the hole being reamed. Ifinsufficient stock removal is left in the holebefore reaming, the reamer can wear fasterthan normally and result in loss of diameteraccuracy. In general applications, averagesurface roughness for reaming is expected tobe in range between 0.8 mm and 3.2 mm buthigh-accuracy reaming can produce averagesurface roughness as low as 0.4 mm (DeChiffre et al., 2009). Currently, there is a widescale evaluation of the use of Metal Working

Figure 1: Reaming Operation

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Fluids (MWFs) in machining. Industries arelooking for ways to reduce the amount oflubricants in metal removing operations dueto the ecological, economical and mostimportantly occupational pressure (Khan et al.,2009). Cutting fluids, especially fluidscontaining oil, have become a huge problemdue to the health and environmental hazardsthey pose. Driven by an increased awarenessof environmental and health issues, industryhas made efforts to eliminate or reduce theirconsumption of these fluids. This can beachieved by implementing near-dry machiningor a Minimal Quantity of Lubrication (MQL)approach. In dry machining, increased frictionand adhesion occur at the tool-workpieceinterface which results in a high tool wear rate.In contrast, the MQL technique involves theapplication of a small quantity of lubricant thatis dispensed to the tool-workpiece interfaceby a compressed air flow. It has been foundthat MQL reduces the friction coefficient andcutting temperature compared to dry and floodconditions.

CONCEPT OF MQLMinimum Quantity Lubrication (MQL) is amachining method that delivers a preciseamount of lubrication to the tool tip. Thelubricant is mixed with compressed air andforms the desired air/oil aerosol mixture. MQL,also known as “Micro lubrication”, and “Near-Dry Machining” is the latest technique ofdelivering metal cutting fluid to the tool/workinterface. Using this technology, a little fluid,when properly selected and applied, can makea substantial difference in how effectively a toolperforms. In conventional operations utilizingflood coolant, cutting fluids are selected mainlyon the basis of their contributions to cutting

performance. In MQL however, secondarycharacteristics are important. These includetheir safety properties, (environment pollutionand human contact), biodegradability,oxidation and storage stability. This isimportant because the lubricant must becompatible with the environment and resistantto long term usage caused by lowconsumption. In MQL, lubrication is obtainedvia the lubricant, while a minimum coolingaction is achieved by the pressurized air thatreaches the tool/work interface. Further, MQLreduces induced thermal shock and helps toincrease the workpiece surface integrity insituations of high tool pressure (NourredineBoubekri and Vasim Shaikh, 2012).

Figure 2: Cutting with Minimal QuantityLubrication

Flow Rate (ml/h) Lubrication Type

0 Dry

<80 Minimal quantity lubrication

80-2000 Minimal flow lubrication

>2000 Flood lubrication

Table 1: Lubrication Types in Termsof Flow Rate

A classification of lubrication based on oilusage per time unit is given in Table 1 (DeChiffre et al., 2009).

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Types of MQL SystemsThere are two basic types of MQL deliverysystems: external spray and through-tool. Theexternal spray system consists of a coolant tankor reservoir which is connected with tubesfitted with one or more nozzles. The systemcan be assembled near or on the machine andhas independently adjustable air and coolantflow for balancing coolant delivery. It isinexpensive, portable, and suited for almostall machining operations. Through-tool MQLsystems are available in two configurations;based on the method of creating the air-oilmist. The first is the external mixing or one-channel system. Here, the oil and air are mixedexternally, and piped through the spindle andtool to the cutting zone. The advantages of suchsystems are simplicity and low cost; they aresuited to be retrofitted to existing machineswith high-pressure, through the tool coolantcapability. They are easy to service; no criticalparts are located inside the spindle. Thedisadvantage is that the oil-mist is subjectedto dispersion and separation during its travelfrom the nozzle. To minimize oil drop outs, amist of relatively fine particles is used, whichoften limits the amount of lubrication that canbe supplied to the cutting zone andconsequently affects the performance of thecutting process. The second configuration isthe internal mixing or two channel systems.Most commonly in a two channel system, twoparallel tubes are routed through the spindleto bring oil and air to an external mixing devicenear the tool holder where the mist is created.This approach requires a specially designedspindle. Such systems have less dispersionand dropouts and can deliver mist with largerdroplet sizes than external mixing devices.

They also have less lag time when changingtools between cuts or oil delivery rate during acut. However, the systems are more difficult tomaintain; critical parts are located inside thespindle (Nourredine Boubekri and VasimShaikh, 2012).

MQL Working PrincipleThe figure below shows a two-channel MQLsystem for through spindle (Internal) lubrication.

Figure 3: Through Spindle InternalLubrication

Figure 4: MQL Application Strategy TB

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In a two-channel system, the precise amountof oil is transported through a lance to a pipenozzle located at the tool holder’s base. Aslubricant moves through the lance and into thepipe nozzle, air supplied through the rotarytransmission travels down the spindle coolanttube that encapsulates the lance to the mixingchamber of the pipe nozzle, where it combineswith fluid to form an aerosol.

LITERATURE REVIEWLeonardo De Chiffre and S. Muller (2009)investigated the capability of reamingprocess using minimal quantity lubrication. Hestudied the influence of some parameters onthe hole quality (diameter, roundness,cylindricity and surface roughness) andcutting forces (reaming thrust and torque) inreaming of austenitic stainless steel. Theseparameters include reamer diameter (i.e.,depth of cut of 0.10 and 0.05 mm), cuttingspeed at 5 and 6 m/min, feed (i.e., feed rateat 49.7 and 33.1 mm/min), type of feed (returnof the tool after machining completion, i.e.,slow and rapid) and Minimal QuantityLubrication application. It was observed thata higher feed rate leads to higher processrepeatability in terms of Ra. A rapid reversefeed rate is not producing a worse surfacefinish and it is therefore preferable in orderto decrease machining time and enhanceproductivity. In particular, it was observed thatsmaller depth-of-cut 0.05 mm, TT applicationstrategy (both nozzles delivering from the topof the workpiece being reamed) and highercutting speed at 6 m/min lead to a less evensurface of the hole, especially on the bottomposition. MQL in reaming leads to high qualityresults in terms of hole dimensions andsurface finish (De Chiffre et al., 2009).

Nazmul Ahsan evaluated the performanceof Minimum Quantity Lubrication (MQL) indrilling operation. He experimentally observedthe performance of MQL in drilling AISI 1040steel by HSS drill and concluded thatroundness deviation was smaller under MQLcondition compared to dry and wet conditions.When high depth of cut was employed, thedrilling with dry condition was not possiblebecause of poor cooling and lubrication action.MQL may be attributed to effective lubricatingaction, which prevented chip sticking on thetool and made the cut favorable (Nazmul Ahsanand Md. Golam Kibria, 2010).

Nourredine Boubekri and Vasim Shaikh(2012) reviewed different literatures available onMQL and commented on different physicalphenomenon related to MQL. He concluded thatthe process of mist particles generation and theirphysical characteristics are yet to be determinedfor a whole class of machining processes andmachining conditions (Nourredine Boubekri andVasim Shaikh, 2012).

Khan performed experiments on alloysteel with vegetable oil based cutting fluidand found that the present MQL systemenabled reduction in the average chip-toolinterface temperature up to 10% ascompared to wet machining depending uponthe cutting conditions and even suchapparently small reduction, unlike commonbelief, enabled significant improvement inthe major machinability indices. The chipsproduced under both dry and wet conditionare of ribbon type continuous chips at lowerfeed rates and more or less tubular typecontinuous chips at higher feed rates. Whenmachined with MQL the form of these ductilechips did not change appreciably but their

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back surface appeared much brighter andsmoother. This indicates that the amount ofreduction of temperature and presence ofMQL application enabled favorable chip-toolinteraction and elimination of even trace ofbuilt up edge formation. Surface finish alsoimproved mainly due to reduction of wearand damage at the tool-tip by the applicationof MQL (Khan et al., 2009).

Bezerra (2001) focused on the effect ofmachining parameters when reamingAluminum-Silicon (SAE 322) alloy ondimensional stability and surface roughnessof reamed cylindrical holes using K10cemented carbide welded blade reamer. Theinput parameters depth of cut, cutting speed,feed rate, helix angle, number of blades, marginsize and rake face finishing of reamer wereindividually varied. The test result shows thatsatisfactory hole quality can be achievedduring reaming by employing smaller depth ofcut 0.2 and 0.3 mm, lower cutting speed of 25mm/min, higher feed rates between 0.20 and0.40 mm/rev as well as straight flute reamerswith many blades and small margins (0.20mm). Reaming at higher feed conditionsimproves the accuracy of holes produced atthe expense of an increase in powerconsumption and deterioration in the surfacefinish generated (Bezerra et al., 2001).

Ali focused on effect of MQL on cuttingperformance in turning medium carbon steelby uncoated carbide insert at different speedfeed combinations. He found that the MQLsystem enable the significant improvement inproductivity, product quality and overallmachining economy. It also increases thedimensional accuracy and surface finish (Ali,2011).

Thakur et al. (2009) investigated theoptimization of minimum quantity lubricationparameters in high speed turning of SuperalloyInconel 718 for sustainable development.Minimum Quantity Lubrication (MQL) underpulsed jet mode proved to be an effectiveapproach for low thermal conductivity andspecific heat difficult-to-cut material superalloyInconel 718 material. Also MQL under pulsedjet mode protects the operator’s health andreduces the detrimental effects on theenvironment (Thakur et al., 2009).

CONCLUSIONHigh costing and environmentally hazardousnature of conventional methods of lubrication(flood lubrication) resulted in development ofnew technique of lubrication known asMinimum Quantity Lubrication. Although thetechnique of MQL resulted in significantadvantages related to cost and environmentfriendly nature of machining operations, theprocesses of lubrication and cooling in MQLare yet to be well understood. The effect of MQLparameters on the surface quality, powerconsumption and nature of tool wear needs tobe explored in a wide manner. According tothe various literatures, the use of MQL resultedin cost savings on cooling lubricants along withthe longer tool life and high productivity.

REFERENCES1. Ali S M (2011), “Effect of MQL on Cutting

Performance in Turning Medium CarbonSteel by Uncoated Carbide Insert atDifferent Speed Feed Combinations”,Advances in Production Engineeringand Management, Vol. 3, pp. 185-196.

2. Bezerra A A, Machado A R, Souza A Mand Ezugwu E O (2001), “Effect of

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Machining Parameters When ReamingAluminium-Silicon (SAE 322) Alloy”,Journal of Materials ProcessingTechnology, Vol. 112, pp. 185-198.

3. De Chiffre L, Tosello M and Muller P(2009), “Investigation on Capability ofReaming Process Using Minimal QuantityLubrication”, CIRP Journal ofManufacturing Science and Technology,Vol. 2, pp. 47-54.

4. Khan M M M, Mithu M A H and Dhar N R(2009), “Effect of Minimum QuantityLubrication on Turning AISI 9310 AlloySteel Using Vegetable Oil-Based CuttingFluid”, Journal of Material ProcessingTechnology, Vol. 209, pp. 5573-5583.

5. Nazmul Ahsan A M M and Md. GolamKibria (2010), “Performance Evaluation of

Minimum Quantity Lubrication (MQL) inDrilling Operation” InternationalConference on Mechanical, Industrial andEnergy Engineering.

6. Nourredine Boubekri and Vasim Shaikh(2012), “Machining Using MinimumQuantity Lubrication: A TechnologySustainability”, International Journal ofApplied Science & Technology, Vol. 1,pp. 111-115.

7. Thakur D G, Ramamoorthy B andVijayaraghavan L (2009), “Optimization ofMinimum Quantity LubricationParameters in High Speed Turning ofSuperalloy Inconel 718 for SustainableDevelopment”, World Academy ofScience, Engineering and Technology,Vol. 54.