BAHIR DAR UNIVERSITY INSTITUTE OF TECHNOLOGY SCHOOL OF INDUSTRIAL & MECHANICAL ENGINEERING MANUFACTURING ENGINEERING
SEMINOR TOPIC ASSESSMENT ON EFFECT OF CUTTING FLUID ON MACHINING COURSE NAME GRADUATE SEMINOR COMPILED BY: TESFAYE KASSAHUN MSC/00017/03 SUBMITTED TO: Professor (Dr.) RANTAM UPPULA September, 2013
Abstract
During machining operation, friction between workpiece-cutting tool and cutting tool-chip interfaces result high temperature on cutting tool. At such elevated temperature the cutting tool if not enough hot hard may lose their form or stability quickly, wear out rapidly, resulting in increased cutting forces, higher surface roughness, shorter tool life and lowers the dimensional sensitiveness of work material. Different methods have been reported to protect cutting tool from the generated heat during machining operations. The selection of coated cutting tools is an expensive alternative and generally it is a suitable approach for machining hard materials. Another alternative is to apply cutting fluids in machining operation. Cutting fluids used to provide lubrication and cooling effects between cutting tool and workpiece and cutting tool and chip during machining operation. As a result, important benefits would be achieved such longer tool life, easy chip flow and higher machining quality in the machining processes. The selection, method of application, storage and disposal of cutting fluids should be carefully carried out to obtain optimum result in machining processes. Metal cutting fluids change the performance of machining operations because of their lubrication, cooling, and chip flushing functions. Besides, they are major source of pollution from machining industries. Minimum quantity of lubricant (MQL), dry machining, Cryogenic Machining and Air cooling are an alternative method for desirable control of cutting temperature. Key words: effect, cutting fluids, Machining, Environment, alternative method
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Acknowledgement
Throughout the course of this project, I have interacted with many people that have prejudiced to the development of my professional work as well as my personal growth. I would like to thank the following people& organization:
First of all, I wish to offer my sincerest gratitude and thanks for my course manager, Professor (Dr.) Rantam Uppula who was an outstanding advisor in all measures during my work with him. His professionalism, knowledge and keenness inspired and taught me a lot. Again I thank him for sincere priceless guidance, support and providing valuable suggestions to improve the content of this seminar project.
I need also to Thank Ato Tefera Enyew for constant monitoring and giving good comments. I have very much enjoyed and benefited from the intellectual discussions that we had during this time. Your constant encouragement has helped me to bring new ideas during preparing this project work.
I also would like to appreciate the cooperation and assistance I got from different organizations including ATTC, Harar TVET College & Harar Brewery Factory machine shop technical staffs for their collaboration during the assessment of this project.
Next I wish to express sincere appreciation to all my friends for their advice to do the study. I benefited greatly from the comments and wisdom these reviewers generously shared with me. Finally, I am beholden to the almighty God for giving me strength and courage for finishing my project work successfully.
Tesfaye Kassahun
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Table of Contents
Page Abstract--------------------------------------------------------------------------------------Acknowledgments--------------------------------------------------------------------------Table of contents ---------------------------------------------------------------------------List of tables --------------------------------------------------------------------------------List of figures -------------------------------------------------------------------------------1. Chapter 1 ------------------------------------------------------------------------------------1.1. Background --------------------------------------------------------------------------1.2. General objective of the project ---------------------------------------------------1.3. Specific objective of the project----------------------------------------------------1.4. Statement of the problem ----------------------------------------------------------1.5. Methodology ------------------------------------------------------------------------1.6. Beneficiary----------------------------------------------------------------------------1.7. Scope and limitations of the project-----------------------------------------------2. Literature Review---------------------------------------------------------------------------2.1.Effect of cutting fluid on machining -------------------------------------------------2.2.Functions of cutting fluids -----------------------------------------------------------2.2.1. Cooling----------------------------------------------------------------------------2.2.2. Lubrication-----------------------------------------------------------------------2.3.Chemistry of cutting fluids -----------------------------------------------------------2.3.1. Additives -----------------------------------------------------------------------2.4.Classification of Cutting Fluids ------------------------------------------------------2.4.1. Straight cutting oils -----------------------------------------------------------2.4.2. Soluble oil fluids (water Emulsifiable oils) --------------------------------2.4.3. Synthetic fluids ----------------------------------------------------------------2.4.4. Semi – synthetic fluids -------------------------------------------------------2.5.Important cutting fluid properties -------------------------------------------------2.5.1. Corrosion protection ----------------------------------------------------------2.5.2. Stability control----------------------------------------------------------------2.5.3. Transparency & viscosity ----------------------------------------------------2.5.4. Wetting & spreading----------------------------------------------------------2.5.5. Surface tension-----------------------------------------------------------------2.5.6. Small fat molecules------------------------------------------------------------2.6.Selection of a cutting fluid -----------------------------------------------------------2.6.1 Work piece material-----------------------------------------------------------2.6.2 Cutting tool materials---------------------------------------------------------2.6.3 Machining operations---------------------------------------------------------2.7.Method of application -----------------------------------------------------------------2.7.1. Manual application ------------------------------------------------------------2.7.2. Flooding ------------------------------------------------------------------------iii
i ii iii v vi 1 1 2 2 2 3 3 3 4 4 5 6 6 7 9 10 10 11 12 12 12 13 13 13 13 15 15 15 17 18 18 19 20 20
2.7.3. Misting --------------------------------------------------------------------------2.7.4. High pressure system----------------------------------------------------------2.7.5. Through the cutting tool system----------------------------------------------2.8.Influence cutting fluid Chip formation ----------------------------------------------2.9.Storage, cleaning and disposal of cutting fluids------------------------------------2.9.1 Storage and distribution-------------------------------------------------------2.9.2 Design consideration----------------------------------------------------------2.9.3 System cleaning----------------------------------------------------------------2.10. Environmental Impact---------------------------------------------------------------2.11. Fluid Management Administration------------------------------------------------2.11.1 Personnel and Training--------------------------------------------------------2.11.2 Operating procedure and tracking system-----------------------------------2.12. Monitoring and maintenance-------------------------------------------------------2.12.1 Recording usage and quality inspection-------------------------------------2.12.2 System maintenance------------------------------------------------------------2.13. Recycling and disposal---------------------------------------------------------------2.13.1 Recycling methods--------------------------------------------------------------2.13.2 Disposal--------------------------------------------------------------------------2.14. Health and safety----------------------------------------------------------------------2.14.1 Skin effects-----------------------------------------------------------------------2.15 Fluid exposure--------------------------------------------------------------------------3. Discussion and evaluation-----------------------------------------------------------------------3.1. Cutting fluid selection--------------------------------------------------------------------------3.2. Cutting fluid application methods------------------------------------------------------------3.3. Storage of cutting fluid-------------------------------------------------------------------------3.4. Disposal of cutting fluid-----------------------------------------------------------------------3.5. Alternatives to cutting fluids------------------------------------------------------------------3.5.1 Dry machining---------------------------------------------------------------------3.5.2 Minimum Quantity Lubrication (MQL) ---------------------------------------3.5.3 Liquid Nitrogen Technology----------------------------------------------------3.5.4 Air cooling-------------------------------------------------------------------------4. Conclusion and Recommendation --------------------------------------------------------------4.1. Conclusions------------------------------------------------------------------------------4.2. Recommendations -------------------------------------------------------------------------------5. References------------------------------------------------------------------------------------------
List of Tables Table 2.1 Selection guide for cutting fluids--------------------------------------------------------Table 2.2 Cutting fluid flow recommendations----------------------------------------------------16 21
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List of Figures Figure 2.1 Thin-wall milling of aluminum using a water-based cutting fluid on the milling cutter----------------------------------------------------------------------------------------------------------------Figure 2.2 Some components of mineral oil---------------------------------------------------------Figure 2.3 Instability in emulsions-------------------------------------------------------------------Figure 2.4 Region of contact between solid, liquid and vapor-----------------------------------Figure 2.5 Proper & improper methods of applying cutting fluids------------------------------Figure 2.6 Cutting fluid applications----------------------------------------------------------------Figure 2.7 Schematic of the cutting process with a single-point tool----------------------------Figure 2.8 Zones of deformation and friction in chip formation---------------------------------Figure 2.9 Types of chips obtained in metal cutting-----------------------------------------------Figure 2.10 A refractometer is used to measure coolant dilution---------------------------------4 8 9 14 19 20 22 22 23 27
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CHAPTER 1 INTRODUCTION 1.1 Background
The use of cutting fluids in metal cutting was first reported in 1894 by F. Taylor who noticed that cutting speed could be increased up to 33% without reducing tool life by applying large amounts of water in the cutting zone [1]. Cutting fluids increase tool life and improve the efficiency of the production systems providing both cooling and lubricating the work surface. The machining processes have an important place in the traditional production industry. Cost effectiveness of all machining processes has been eagerly investigated. This is mainly affected selection of suitable machining parameters like cutting speed, feed rate and depth of cut and cutting fluid according to cutting tool and workpiece material. The selection of optimum machining parameters will result in longer tool life, better surface finish and higher material removal rate. During machining process, friction between workpiece-cutting tool and cutting tool-chip interfaces cause high temperature on cutting tool. The effect of this generated heat decreases tool life, increases surface roughness and decreases the dimensional sensitiveness of work material. This case is more important when machining of difficult-to-cut materials, when more heat would be observed [1]. Various methods have been reported to protect cutting tool from the generated heat. Choosing coated cutting tools are an expensive alternative and generally it is a suitable approach for machining some materials such as titanium alloys, heat resistance alloys etc. The application of cutting fluids is another alternative to obtain higher material removal rates. Cutting fluids have been used widespread in all machining processes. However, because of their damaging influences on the environment, their applications have been limited in machining processes [6]. New approaches for elimination of cutting fluids application in machining processes have been examined and “dry machining” was presented as an important solution [6]. The development of new cutting tool materials also helped dry machining method to be a positive solution for cutting fluids applications. However, the usage of cutting fluids has been increased due to high production levels in the world. According to 1998 values, approximately 2.3x109 liter cutting fluids have been used in the machining operations and its cost value was around $ 2.75x109. North America had a big ratio, Europe continent was in the third order after Asia continent [4]. The first study about cutting fluids had been determined by W.H. Northcott in 1868 with a book entitled “A treaties on lathes and turning”. In the middle of 1890’s, F.W. Taylor emphasized that using cutting fluids would allow to use higher cutting speeds resulting in longer tool life and higher material
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removal rates [5]. It had been concluded that the application of cutting fluids in machining processes would make shaping process easier.
1.2 General Objective of the project
The general objective of this project work is to create awareness for the technical operators that use cutting fluids wrongly in different manufacturing industries and technical institutions.
1.3 Specific objective of the project
The specific objective of this project work is: To study the different type of cutting fluids & the effect of these cutting fluids in machining performance. To probe the factors which affecting the cutting fluids. To build understanding in the correct use of cutting fluids & important benefits of cutting fluids for longer tool life, easy chip flow and higher machining quality in the machining processes. To understand in briefly the pros and cons of cutting fluids and the impact of these cutting fluids in the environment. To put forward the new technology, alternative method of cutting fluids (dry machining, Minimum Quantity Lubrication, Liquid Nitrogen Technology & air cooling) for machining process.
1.4 Statement of the problem
The production system of Ethiopia industries in today’s global market are focuses on manufacturing of different products. The products which are produced in these different manufacturing industries have a problem of getting good surface finish; have shorter tool life, and have good dimensional integrity due to improper utilization of cutting fluids. Some of the problems are:
Using proper cutting fluid for the correct type of materials, cutting tools and machine tool. Using correct method of application of cutting fluid. Storing of cutting fluids in a proper way. Disposal of cutting fluids in a manner which is acceptable. The influence of cutting fluid in the performance of machining process
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1.5 Methodology
The methodologies implemented to achieve the above listed objectives, by supervising different manufacturing industries and institutions that use cutting fluid for their machining process, through discussion with shop managers, survey of previous relevant works, and through qualitative analysis to analyze the effect of cutting fluids in machining process.
1.6 Beneficiary
From this project work a manufacturer who will work in Technical institutions and manufacturing industry can get good information regardless of the selection, method of application, effect and proper usage of cutting fluid.
1.7 Scope and Limitations of the project
The project mainly focuses on In Technical institution that works in different type of machines which use cutting fluids for machining processes. In big industries such as Harar Brewery Factory that uses cutting fluids in their machine shops for machining processes.
The limitations of this project
The study is limited to the three companies; this makes the study constricted, in addition to this there is also limitation of Time shortage for assessing this project work. Also shortage of giving the correct information’s about the usage of cutting fluids in manufacturing industries.
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CHAPTER 2 LITERATURE REVIEW
2.1 Effect of cutting fluid on Machining Cutting fluid (coolant) is any liquid or gas that is applied to the chip and/or cutting tool to improve cutting performance. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists), and air or other gases. They may be made from petroleum distillates, animal fats, plant oils, water and air, or other raw ingredients. Depending on context and on which type of cutting fluid is being considered, it may be referred to as cutting fluid, cutting oil, cutting compound, coolant, or lubricant [1]. Nowadays cutting fluids are special blends of chemical additives, lubricants and water formulated to meet the performance demands of the metalworking industry. As cutting operations became more severe, cutting fluid formulations became more complex. Cutting fluids are used in machine shops to improve the life and function of cutting tools. They are also a key factor in machine shop productivity and production of quality machined parts. Ninety-seven percent of the energy consumed in metal cutting is converted into heat; this heat can damage both the cutting tool & the workpiece. An overheated tool loses its hardness & shortens its life and an overheated workpiece can lose its dimensional integrity. The most effective cutting fluids keep the tool at a stable temperature, remove particulates, limit microbial growth, lubricate the working edge to maximize life of the tool and prevent rust formation or corrosion on the tool, and ensure safety for people handling it while not being hazardous to the environment [9]. Most metalworking and machining processes can benefit from the use of cutting fluid, depending on workpiece material. Common exceptions to this are machining cast iron and brass, which are machined dry [2]. Aluminum using a water-based cutting fluid on the milling cutter is illustrated in Fig2.1
Figure 2.1Thin-wall milling of aluminum using a water-based cutting fluid on the milling cutter. Source: cutting fluid Wikipedia, the free encyclopedia 4
Cutting fluids play a significant role in machining operations and impact shop productivity, tool life and quality of work. The primary function of cutting fluid is temperature control through cooling and lubrication [Aronson, et al., 1994]. A fluid's cooling and lubrication properties are critical in decreasing tool wear and extending tool life. Cooling and lubrication are also important in achieving the desired size, finish and shape of the workpiece [Sluhan, 1994]. A secondary function of cutting fluid is to flush away chips and metal fines from the tool/workpiece interface to prevent a finished surface from becoming marred and also to reduce the occurrence of built-up edge (BUE). Metal cutting involve a complex set of operating parameters, and the choice and effectiveness of a cutting fluid is determined by: The design, rigidity, and operating condition of the machine tool The speed, feed, and depth of cut The composition, finish, and geometry of the cutting tool The mode of fluid application The geometry of the material to be machined & Surface coatings The composition, microstructure, and residual stress distribution in the workpiece.
When properly applied, cutting fluids can increase productivity and reduce costs by making possible use of higher cutting speeds, higher feed rates, and greater depths of cut. The effective application of cutting fluids can also lengthen tool life, reduce surface roughness, improve dimensional accuracy, and decrease the amount of power consumed as compared to cutting dry [2]. 2.2 Functions of Cutting Fluids Depending on the machining operation being performed, a cutting fluid has one or more basic and supplementary functions. The basic functions are as follows: Cooling the tool, workpiece, and chip primarily at high cutting speeds Lubricating (reducing friction and minimizing erosion on the tool) primarily at low cutting speeds And some of supplementary functions include: Flushing chips away from the cutting zone Controlling built-up edge on the tool Protecting the workpiece, tooling and machine from corrosion Enabling part handling by cooling the hot surface Longer tool life Reduced thermal deformation of workpiece Better surface finish (in some applications)
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Ease of chip and swarf handling Lower energy consumption. Narrower tolerances of the work piece size.
2.2.1 Cooling Cutting fluids reduce the temperature of the metal cutting operation by transferring heat away from the workpiece and the tool. Machining operations create heat. This heat must be removed from the process. The chip helps carry away heat from the tool and work piece. Coolant takes heat from the chips, tool, and work piece. To be effective the fluid must be able to transfer heat very rapidly. The fluid absorbs the heat and carries it away. Some of the factors involved in cooling are as follows: Cooling effects due to the application of the cutting fluid increase the shear strength of the material being cut, thus increasing the forces required for metal cutting. Generally, this effect is small for most metals. The cooling effects of cutting fluids may be deleterious if the change in temperature caused in the cutting tool is abrupt and discontinuous. Abrupt changes in temperature may cause fracture and spalling of the tool; ceramic tooling is particularly sensitive in this regard. The cooling from cutting fluids is generally related to their thermal properties. In general, cooling efficiency is less for oil than for an emulsion and is greatest with a water solution. Cooling efficiency can be reduced by the heat transfer characteristics of high-viscosity fluids. High cutting speeds can initially improve the cooling because the viscosity of the cutting fluid decreases with temperature, but beyond a certain temperature this beneficial effect on cooling is no longer present. The effectiveness of cooling depends on the amount of surface wetting, fluid viscosity, chemical reactivity and molecular size, and the physical characteristics of fluid flow. 2.2.2 Lubrication. In a typical machining operation, two-thirds of the heat is created by the resistance of the work piece atoms to being sheared. The friction of the chip sliding over the cutting tool face creates the other one-third of the heat. Cutting fluids improve tool life and allow higher cutting speeds by reducing the amount of friction that occurs during the cutting process. Cutting fluids with good lubricating qualities can also: Allow the formation of a continuous chip when low cutting speeds result in the formation of discontinuous chips or serrated continuous chips (Figure 2.9)
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Reduce the frictional forces between the tool and the rake face. Reduce the size of the built-up edge or in some cases eliminate built-up edge formation. Total elimination of the built-up edge will produce a superior finish on the part being machined and will result in less frictional drag on the flank face.
Reduce adhesive wear by reducing adhesion between the tool and the chip or the workpiece. Produce insignificant lubricant effects in the case of extremely brittle materials that yield very small discontinuous chips.
Cutting fluid with good lubrication qualities can reduce the friction of the chip sliding over the tool face. The lubrication actually changes the shear angle, which reduces the shear path and produces a thinner chip. Good lubrication also reduces internal friction and heat through less molecular disturbance. Thus cutting fluid stabilizes the work piece temperature providing better control of its geometry. The relative importance of each of these functions depends on the work material, the cutting tool, the machining conditions, and the finish required on the part [3]. Two functions of cutting fluids include lubrication and cooling so that the frictional forces and temperature are reduced at the tool/workpiece interface. Schallbroch, schaumann and wallich gave an empirical formula relating tool life and temperature of the cutting tool, which is given by: T =K Eqn. 2.1
Where T = tool life, minute = temperature at chip tool interface, °C, n = an exponent, the value of which depends mainly on tool form & material K = constant From the above relation, it has been found that small changes in tool temperature can produce considerable changes in tool life. Hence, the cutting fluid, which may directly control the amount of heat at the chip tool interface, can play an important role in increasing tool life [2]. 2.3 Chemistry of Cutting Fluids In metal cutting fluids Solutions consist of a base fluid such as petroleum oil, a petroleum solvent, a synthetic fluid, or water. These base fluids can then be formulated with various additives that are soluble in the fluid. Emulsions, on the other hand, are composed of two phases: a continuous phase consisting of water and a discontinuous phase consisting of small particles of oil, petroleum, or synthetic fluid suspended in the water. These emulsions are commonly called soluble oils.
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Oil or synthetic solutions generally have the highest lubricating capabilities and the lowest cooling efficiencies. Water base solutions, on the other hand, have the highest cooling efficiencies and lower lubrication effectiveness. In general, emulsions tend to have moderate properties for both cooling and lubrication. Cutting oils have either naphthenic or paraffinic oil or a petroleum solvent as the primary ingredient. Paraffinic mineral oils differ from naphthenic base oils in two ways. First, paraffinic oils have a much higher concentration of straight-chain carbon atoms varying greatly in length, and second, they have a smaller concentration of ring compounds, such as naphthenic and polycyclic aromatic compounds. Paraffinic oils exhibit greater oxidation resistance than naphthenic oils and tend to maintain their viscosity over a wider temperature range. On the other hand, naphthenic oils tend to form more stable solutions of additives than the paraffinic oils. Water-base solutions have excellent heat transfer characteristics because of the high heat capacity of water. However, the purity of the water can significantly affect the performance of water-base cutting fluid solutions. Chemical components of mineral oil illustrated in Figure 2.2.
Figure 2.2 Some components of mineral oil. Source: ASM Metals Handbook
Emulsions consist of immiscible fluids that form a relatively stable mixture because of emulsifiers or surface-active chemicals (which are soluble in the fluids). Emulsions for metal cutting fluids consist primarily of a continuous phase of water containing suspended mineral oil or synthetic fluid. Clear emulsions can be produced when the suspended phase consists of sufficiently fine particle sizes, but in most cases emulsions have a milky white or blue-white color, depending on the chemistry of the additives. In these cases, the particle size is larger.
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The stability of emulsions is important in metal cutting operation, and the destabilization of an emulsion is to be avoided. Destabilization often occurs because of the buildup of minerals from frequent additions of impure water and the buildup of swarf from the machining operation. Splitting of the emulsion, when it occurs, generally results in the formation of two distinct liquids: water and the oil floating at the top. However, a phenomenon known as creaming may also occur, which produces a thick cream layer that floats on the surface. The presence of the cream may indicate that a process of breaking of the emulsion is about to begin. On the other hand, such mixtures may be advantageous in some metal cutting operations. Typical stages in the breaking of emulsions are illustrated in Figure 2.3.
Figure 2.3 Instability in emulsions. Source: ASM Metals Handbook
2.3.1 Additives. Some of the important classes of additives used in both solutions and emulsions are described below. Extreme-Pressure (EP) Additives These chemical compounds vary in structure and composition and are sufficiently reactive with the metals being machined to form relatively weak compounds at the tool/workpiece interface.They are primarily sulfurous additives (such as sulfurized esters of fatty acids), chloride additives (such as chlorinated hydrocarbons or chlorinated esters), or phosphorous additives (such as phosphoric acid esters). Solid lubricants such as molybdenum disulfide have also been used in small amounts. These solid lubricants deposit on the metallic surface and reduce the friction between the tool and the workpiece. Detergents Compounds such as long-chain alcohols, substituted benzene sulfonic acid, and petroleum sulfonic acids can reduce or prevent deposit formation on the workpiece. Antimisting Additives Airborne contamination by the metal cutting fluid in the plant is a longstanding problem that occurs when oil-base solutions are used. The addition of small quantities of acrylates or polybutanes will reduce mist formation by encouraging the buildup of larger particle sizes, which are heavier and much less readily airborne.
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Antifoaming Additives Foaming generally occurs when agitation from either the cutting operation or fluid handling introduces air into the fluid. To prevent or minimize the formation of foam, the free energy of the film surface must be reduced. Antifoaming agents have been developed for this purpose. Polyalkoxysiloxanes, fumed silica, high molecular weight amides, and polyglycols are effective in specific metal cutting fluids. Odor Masks High temperatures at the tool/workpiece interface heat the fluid and often result in odors that is disagreeable to the operator. Pine oil, cedar oil, and sassafras essence have been used to mask these odors, thus making the fluid more acceptable in long-term operations. Corrosion Inhibitors The corrosion of machine parts and the machine tool can be a problem, particularly with water base fluids. Sulfonates, borates, and benzotriazoles have been used as additives in cutting fluids to help prevent corrosion. Dyes Both oil- and water-soluble dyes are used to assist in the identification of the metalworking fluid and to help in identifying the location of the fluid with respect to the application technique. Antimicrobial Agents Microbial growth will take place in cutting fluids that intentionally or inadvertently contain water. Bacteria, fungi, and/or mold will grow, depending on the growth conditions and the competition for nourishment among these organisms. 2.4 Classification of cutting fluids Cutting fluids are used in metal machining for a variety of reasons such as improving tool life, reducing workpiece thermal deformation, improving surface finish and flushing away chips from the cutting zone. Practically all cutting fluids presently in use fall into one of four categories: Straight cutting oils Soluble oils Semi synthetic fluids Synthetic fluids
2.4.1 Straight cutting oils Straight cutting oils are non-emulsifiable and are used in machining operations in an undiluted form. They are composed of a base mineral or petroleum oil and often contain polar lubricants such as fats, vegetable oils and esters as well as extreme pressure additives such as Chlorine, Sulphur and Phosphorus. Straight oils provide the best lubrication and the poorest cooling characteristics among cutting fluids. Straight oils perform best in heavy duty machining operations and very critical grinding operations where lubricity is very important. These are generally slow speed operations where the cut is extremely heavy. Straight oils do not work well in high speed cutting operations because they do not
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dissipate heat effectively. Because they are not diluted with water and the carryout rate on parts is high, these oils are costly to use and, therefore, only used when a water dilutible fluid will not do the job or the machine tool is not designed to handle water dilutable products. Advantages of straight cutting oils Good lubricity, rust and corrosion protection Effective anti-weld qualities Do not go rancid Form stable solutions
Disadvantages of straight cutting oils Poor cooling Mist at higher speeds Flammable and smoke at higher speeds Not biodegradable and expensive to use [11].
2.4.2 Soluble Oil Fluids (Water Emulsifiable Oils) Soluble oil fluids form an emulsion when mixed with water. The concentrate consists of a base mineral oil and emulsifiers to help produce a stable emulsion. They are used in a diluted form (usual concentration = 3 to 10%) and provide good lubrication and heat transfer performance. They are widely used in industry and are the least expensive among all cutting fluids. They provide good cooling for high speed production operations & are safe to use on both ferrous & non-ferrous metals. Rancidity has always been the big problem with emulsifiable oils and the major reason for the development of the synthetic. Another more recent problem is disposal. When you combine these quality products with good service, control, filtration and additives, have the best cutting fluid system available today. Advantages of soluble oils Good lubricity ,cooling, Non-toxic & Non-flammable Effective anti-weld qualities & Adequate wetting abilities Good rust & corrosion protection Economical & Low viscosity Disadvantages of soluble oils Rancidity Emulsion stability Misting, Disposal Not biodegradable [11].
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2.4.3 Synthetic Fluids Synthetic fluids contain no petroleum or mineral oil base and instead are formulated from alkaline inorganic and organic compounds along with additives for corrosion inhibition. Synthetics often contain as many as 17 ingredients, including polymers, which are used to replace the oil and cutting additives found in soluble oils and semi-synthetics. Without oil, additives are required to control corrosion. Without oil however, synthetic coolants can offer superior cooling with extended tool and sump life. Synthetic fluids often provide the best cooling performance among all cutting fluids. Advantages of synthetic fluids Excellent cooling & Good wetting Good rust protection & low viscosity & stable solutions Resistant to rancidity and very little misting problems Non-toxic & completely non-flammable & non-smoking Easiest of all types to filter and dispose, biodegradable & Economical dilutions Disadvantages of synthetic fluids Insufficient lubricity for many heavy duty applications Metal safety on non-ferrous parts Residue can sometimes be a problem [11]. 2.4.4 Semi-synthetic fluids Semi synthetic fluids are essentially combination of synthetic (polymer) and soluble oil fluids and have characteristics common to both types. The cost and heat transfer performance of semi-synthetic fluids lay between those of synthetic and soluble oil fluids. A semi-synthetic coolant can contain anywhere from 5% - 35% oil. The smaller percentage of oil in semi-synthetics allows for heat to be dissipated much faster than with soluble oils, improving tool life and finish. Much like soluble oils, chlorine is sometimes added to improve heavy machining performance. Advantages of semi-synthetic fluids possess better corrosion protection than synthetic fluids & better cooling & wetting capabilities Easier handling and maintenance than mineral emulsions. Disadvantages of semi-synthetic fluids Misting, relatively poor stability in hard water Contaminated by foreign oils, some toxicity [11]. 2.5 Essential Cutting Fluid properties In addition to providing a good machining environment, a cutting fluid must fulfill the following requirements of properties.
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2.5.1 Corrosion Protection Cutting fluids must offer some degree of corrosion protection. Freshly cut ferrous metals tend to rust rapidly since any protective coatings have been removed by the machining operation. A good metalworking fluid will inhibit rust formation to avoid damage to machine parts and the workpiece. It will also impart a protective film on cutting chips to prevent their corrosion and the formation of difficult-to-manage chunks or clinkers. To inhibit corrosion, a fluid must prevent metal, moisture and oxygen from coming together. Chemical metalworking fluids now contain additives which prevent corrosion through formation of invisible, nonporous films. Two types of invisible, nonporous films are produced by metalworking fluids to prevent corrosion from occurring. These include polar and passivating films. Polar films consist of organic compounds (such as amines and fatty acids) which form a protective coating on a metals surface, blocking chemical reactions. Passivating films are formed by inorganic compounds containing oxygen (such as borates, phosphates and silicates). These compounds react with the metal surface, producing a coating that inhibits corrosion. 2.5.2 Stability Control In the early days of the industrial revolution, lard oil was used as a cutting fluid. After a few days, lard oil would start to spoil and give off an offensive odor. This rancidity was caused by bacteria and other microscopic organisms that grew and multiplied within the oil. Modern metalworking fluids are susceptible to the same problem. No matter how good the engineering qualities of a coolant, if it develops an offensive odor, it can cause problems for management. The toxicity of a fluid may also increase dramatically if it becomes rancid due to chemical decomposition, possibly causing the fluid to become a hazardous waste. Fluid rancidity shortens fluid life and may lead to increased costs and regulatory burdens associated with fluid disposal. A good cutting fluid resists decomposition during its storage and use. Most cutting fluids are now formulated with bactericides and other additives to control microbial growth, enhance fluid performance and improve fluid stability. 2.5.3 Transparency and Viscosity In some operations, fluid transparency or clarity may be a desired characteristic for a cutting fluid. Transparent fluids allow operators to see the workpiece more clearly during machining operations. Viscosity is an important property with respect to fluid performance and maintenance. Lower viscosity fluids allow grit and dirt to settle out of suspension. 2.5.4 Wetting and spreading To form a continuous film all over the surface rather than head up into isolated lenses, the fluid must have the tendency to spread over. In order to spread over the surface the molecules of the fluid must
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be more attracted to the surface than to each other. The contact angle
measures the tendency of
fluid to wet the surface. A contact angle of 180° means ‘zero’ tendency to wet while a contact angle of 0° infers complete wetting. This is schematically shown in figure 2.4 below.
Figure 2.4 Region of contact between solid, liquid and vapor. Source: Metal Cutting Theory and Practice To find out the contact angle , assume that the interfacial tension between solid and vapor, solid and considering all the forces acting in the horizontal
and liquid and liquid and vapor be directions: = And For complete wetting, +
Eqn. 2.2 Eqn. 2.3
is zero. Hence for condition of complete wetting, Eqn. 2.4
Equations 2.3 can also be found from energy considerations. If the system is in equilibrium, the net energy associated with this change is zero, or From which If the surface be rough instead of being smooth, the interfacial tension greater distance K Eqn. 2.5 and moves through a becomes
where K is a constant depending on the surface roughness and Eqn. 2.6
From the above analysis it is evident that the spreading tendency will increase with the increased surface roughness. To promote spreading and wetting of the cutting fluid over a surface the contact angle must be decreased for which the wetting agents are used. Most wetting agents function by
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decreasing the surface tension of the liquid (
), the interfacial tension
or both. However, such
lowering of the surface tension is not preferred in a cutting fluid. The wetting agents will act as an agent to reduce the interfacial tension thereby reducing contact angle [2]. 2.5.5 Surface tension Surface tension is a tensile force exerted across a line on the surface due to the effect of unbalanced attractive forces among the molecules of solid or liquid. Surface tension forces in the fluid regulate the flow in the capillaries and reach the tool point against the motion of the chip it would appear unlikely that the fluid can be in the front of a liquid as it penetrates the very fine labyrinth of capillaries. The fluid in the liquid state is carried very near to tool point due to the capillary action and adheres to the chip tool interface by the action of surface tension. 2.5.6 Small Fat Molecules It is well known that minute capillaries exist at the chip tool interface due to the fact the surface of a cutting tool can never be perfectly smooth. These capillaries are filled up with the cutting fluid. The organic compounds which are used as the cutting fluid possess long-chained structure and molar volume of the compound is such that it creates difficulty in the path of penetration of the cutting fluid, i.e. the entry into the capillaries in the chip tool interface zone is facilitated when short-chained structure are used in preference to the long-chained structure. 2.6 Selection criteria of a Cutting Fluid Metal cutting fluid selection depends on an evaluation of a large number of interrelated factors. Some of the pertinent factors have nothing to do with the particular metal cutting operation in question, but rather concern the ease of cleaning the part after production, the cost of recycling the fluid, the cost of fluid disposal, the possibility of adverse effects on operator health and safety, and the cost of the fluid itself. To select a fluid for your application, advantages and disadvantages of metalworking fluid products should be compared through review of product literature, supplier information, and usage history. Product performance information shared by other machine shops is another means of narrowing choices. Ultimately, the best indicator of fluid performance is through actual use. The following factors should be considered when selecting a fluid: Cost and life expectancy Fluid compatibility with work materials and machine components Speed, feed and depth of the cutting operation Type, hardness and microstructure of the metal being machined Ease of fluid maintenance and quality control
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Ability to separate fluid from the work and cuttings The products applicable temperature operating range Optimal concentration and pH ranges Storage practices, Ease of fluid recycling or disposal Process performance: Heat transfer performance Lubrication performance Chip flushing Fluid mist generation and Fluid stability (for emulsions) Corrosion inhibition
Environmental Performance and Health Hazard Performance
Table 2.1 provides general guidelines for the selection of fluids based on the material to be machined and the cutting operation involved.
Table 2.1 Selection guides for cutting fluids. Source: ASM Metals Handbook
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At best, these recommendations provide a starting point for evaluating the preferred cutting fluid in a given manufacturing environment. These recommendations are general guidelines. They are influenced by tool material and composition, workpiece material composition and treatment and the machine tool. Machining with tungsten carbide and ceramic tools can often be carried out more effectively without a cutting fluid on aluminum alloys, copper alloys, plastics, and steels, depending conditions. The selection of cutting fluids in machining processes depends on various factors. Among them three basic factors mentioned below [3]: Type of machined workpiece material Type of cutting tool material Type of machining processes
2.6.1 Workpiece Material The intrinsic machinability of metals can vary considerably within a specified composition because of variations in structure and homogeneity. Nevertheless, there are some general preferences in the selection of a cutting fluid for a given workpiece material, as follows: Free-Machining Steels The addition of lead, sulfur, and bismuth to steels improves their machinability. Water-base cutting fluids are most effective with these materials, particularly those containing sulfur-base additives as well as fatty esters. Low-carbon steels in the hot-rolled condition tend to be somewhat gummy. Emulsions and lowviscosity oils can be used effectively in machining these materials. Medium- and high-carbon steels as well as alloy compositions in the same carbon range are effectively machined with emulsions and water-base solutions, particularly if machining rates are high. Cast Iron Because swarf buildup must be avoided, water-base emulsions and solutions are effective. The greater the cutting speed, the more effective the water-base coolant. Stainless Steel Low-viscosity oils with chlorine, as well as sulfur EP additives, are effective. Emulsions containing sulfur and chlorine are effective fluids at higher cutting speeds. Copper Alloys Because of the formation of stringy chips and the ease of staining with active sulfur, fatty esters are used in oils, emulsions, and water-base solutions. Soap-base solutions have been used effectively in the machining of copper alloys. Aluminum Alloys Water-base solutions containing fatty esters and amides are effective. Lightweight oils containing a fatty ester are also effective, particularly for turning and milling operations. Titanium Alloys Lightweight oils containing chlorinated EP additives are effective. Emulsions containing chlorine have been found to be effective when grinding with a silicon carbide wheel.
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2.6.2 Cutting tool materials The second influential parameter for selection of cutting fluid in machining processes is the cutting tool material. Various cutting tool materials are commercially available for all kind of machining processes. High speed steel cutting tools can be used with all type of cutting fluids. However waterless cutting fluids are preferred when difficult-to-cut materials are machined. In case of the tungsten carbide (WC) cutting tools application, more cooling characteristics from cutting fluids are required. This is because of high generated heat in the interface of cutting tool and workpiece material. The negative effect of generated heat during machining with WC cutting tools causes rapid tool wear. Hence toll life will be shorter and surface finish quality falls [2]. Cubic boron nitrate (CBN) and polycrystalline diamonds (PCD) cutting tools have been found important place in machining processes. However, these cutting tools are expensive and they can protect their characteristics in high temperature machining conditions. They are generally used in finish machining operation to obtain high dimensional accuracy and excellent surface finish quality. The application of cutting fluids is not necessary when machining operations are carried out with these cutting tool materials. Ceramic and diamond cutting tools can also protect their characteristics at high temperatures. They are generally used in finish machining operation. In using ceramic cutting tools, air is sprayed into the cutting zone. The water based cutting fluids must be used when diamond type cutting tool materials are used [2]. 2.6.3 Machining Operation Each of the metal cutting operations has characteristics that often influence the effectiveness of a particular cutting fluid. The basic metal removal methods are turning, milling, drilling, and grinding. Turning Because the cutting tool is in continuous contact with the workpiece, access to the cutting area is restricted. Therefore, the cutting fluids of choice are those with a base fluid and additives of low molecular weight. In general, water-base solutions and emulsions are preferable for most turning operations. Milling Lubrication is generally more important than cooling in this operation because of the relatively low cutting speeds involved and the easy access to the cutting tool. compounded oils and emulsions are frequently preferred. Drilling Because of the constant engagement of the tool and workpiece and the difficulty of gaining access to the cutting area, drills with cutting fluid access ports should be used when possible.
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Therefore,
Solutions based on oil and water can be successfully used with sulfur and/or chlorine additives, although the specifics of the fluid chemistry are heavily influenced by the composition of the material being machined. Grinding Because of the high rotational speeds of the grinding wheels, the application of a fluid is extremely important to ensure fluid contact with the wheel and the workpiece. Furthermore, the relationship between the chemistry of the grinding wheel and that of the workpiece is also important. These interactions must be evaluated in choosing an appropriate cutting fluid for a specific grinding wheel material in a production situation. Generally, emulsions and water-base solutions are the fluids of choice, with a wide array of esters, amides, sulfur compounds, and chlorine compounds successfully used in the fluid formulation. Oil-base solutions are chosen when lubrication of the wheel is the critical. [3] 2.7 Methods of Application Correct application of the cutting fluid at the tool/workpiece interface is fundamental to the effective use of the fluid, and the method of application affects not only lubrication and cooling but also the efficiency in removing swarf and chips from the cutting operation. Frequently, more than one nozzle per tool should be used to optimize chip removal as well as cooling and lubrication. Some recommendations on the placement of the fluid stream are illustrated in Fig. 2.5
Every conceivable method of applying cutting fluid (e.g., flooding, spraying, dripping, misting, brushing) can be used, with the best choice depending on the application and the equipment available. For many metal cutting applications the ideal has long been high-pressure, high-volume pumping to force a stream of liquid (usually an oil-water emulsion) directly into the tool-chip interface, with walls around the machine to contain the splatter and a sump to catch, filter, and recirculate the fluid. 2.7.1 Manual application Application of a fluid from a can manually by the operator. It is not acceptable even in job-shop situations except for tapping and some other operations where cutting speeds are very low and friction is a problem. In this case, cutting fluids are used as lubricants. Manual application of a cutting fluid is effective only for very low volume production or tool room use. 2.7.2 Flooding In flooding, a steady stream of fluid is directed at the chip or tool-workpiece interface. Most machine tools are equipped with a recirculating system that incorporates filters for cleaning of cutting fluids. Cutting fluids are applied to the chip although better cooling is obtained by applying it to the flank face under pressure. Cutting fluid application, (Left) Rake face flooding by means of a recirculating system, (Right) Flank face application of the cutting fluid illustrated in Figure 2.6 below.
Flooding of the cutting area is the most widely used method of promoting lubrication, cooling, chip removal, and access to the cutting operation. A flood of cutting fluid is applied on the workpiece. The volume of fluid per unit time that is applied is critical in achieving optimum results. Volume recommendations vary from less than 1 L/min (0.25 gal./min) to more than 2000 L/min (500 gal./min), depending on feed, speed, and cutting tool material and geometry. The optimum pressure varies with operation. [3]
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2.7.3 Misting: Fluid droplets suspended in air provide effective cooling by evaporation of the fluid. Mist application in general is not as effective as flooding, but can deliver cutting fluid to inaccessible areas that cannot be reached by conventional flooding. A particularly effective method of applying a cutting fluid in drilling and cutoff operations involves the creation and application of the lubricant as a mist. Cutting fluid is atomized by a jet of air and the mist is directed at the cutting zone. The size of the mist droplets can be controlled, depending on the particular effects desired. In addition, more efficient use of the cutting fluid can also be achieved, particularly in the case of waterbase solutions and emulsions. Care must be taken when misting cutting fluids to prevent excessive buildup in the air and in the workplace in general. 2.7.4 High pressure system With the increasing speed and power of modern computer controlled machine tools, heat generation in machining has become a significant factor. Particularly effective is the use of high pressure refrigerated coolant systems to increase the rate of heat removal from the cutting zone. High pressures also are used in delivering the cutting fluid via specially designed nozzles that aim a powerful jet of fluid to the zone, particularly into the clearance or relief face of the tool. The pressures employed, which are usually in the ranges from 5.5 to 35 MPa, act as a chip breaker in situations where the chips produced would otherwise be long and continuous, interfering with the cutting operation. In order to avoid damage to the workpiece surface by impact from any particles present in the high-pressure jet, contaminant size in the coolant should not exceed 20μm [1].
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2.7.5 Through the cutting tool system The severity of various machining operations have been described in terms of the difficulty of supplying fluids into the cutting zone & flushing away the chips. For a more effective application, narrow passages can be produced in cutting tools, as well as in tool holders, through which cutting fluids can be applied under high pressure. Two applications of this method are in gun drilling with a long small hole through the body of the drill itself & in boring bars, where there is a long hole through the shank (tool holders), to which an insert is clamped [1]. 2.8 Influence of cutting fluid on chip formation Influence of cutting fluid is related to the frictional effects of metal cutting. Figure 2.7 shows a schematic of the cutting operation with a single-point tool. A tool moving with a velocity v and a depth of cut creates a chip of thickness that is greater than . The chip is generated at a shear
plane that makes an angle with the direction of cut. This angle, known as the rake angle, is an important variable in the mechanics of chip formation. The relief or clearance angle is also important because it provides potential access to the cutting zone for lubrication [3].
Figure 2.7 Schematic of the cutting process with a single-point tool. Source: ASM Metals Handbook
In considering the potential for improving the cutting process with a cutting fluid, Figure 2.8 illustrates the major areas of deformation and friction that occur during the generation of chips.
Figure 2.8 Zones of deformation and friction in chip formation. Source: ASM Metals Handbook 22
In Figure 2.8 zone 1 indicates the area of strain hardening that forms in the material being cut ahead of the tool. Micro cracking can take place in the zone, and relatively high temperatures result from the deformation and resultant strain hardening. In zone 2, the deformed chip moves out of the shear zone and flows up the surface of the tool. As the chip slides up the face of the rake of the tool, it generates more heat as a result of friction between the chip and the tool. In zone 3, as the tool traverses the freshly cut surface, further rubbing of the tool against the workpiece material takes place, thus generating friction and additional deformation. As chip formation proceeds, the tool edge forms a built-up edge (zone 4), which creates more local plastic deformation and friction. In zone 5, below the area of primary metal removal, additional plastic deformation takes place, along with some strain hardening. The geometry of the chips varies with the workpiece material and the cutting conditions.
Figure 2.9 Types of chips obtained in metal cutting. (a) Continuous chip. (b) Continuous chip with a secondary shear zone. (c) Continuous chip with a large primary shear zone. (d) Built-up edge in a continuous chip. (e) Inhomogeneous (serrated) continuous chip with regions of low and high shear in the primary zone. (f) Discontinuous chip. Source: ASM Metals Handbook 23
2.9 Storage, Cleaning, and Disposal of Cutting Fluids The contamination of coolants and lubricants is a constant problem, and cutting fluids are often recycled and reused. This requires careful attention to the storage, distribution, cleaning, and disposal of cutting fluids. 2.9.1 Storage and Distribution Fluids should be stored in a manner that minimizes potential contamination. Water contamination is the concern with oil-base fluids, and oil and particulate contamination is the concern with water-base fluids. In the case of tank storage, the water contamination of oils is of particular importance. Storage tanks require appropriate venting and periodic cleaning to prevent contamination problems. All fluid containers should be properly labeled for compliance with regulations governing the presence of hazardous materials in the workplace. Material safety data sheets must be available in the workplace for each material being used. Similar precautions should be instituted for sampling inprocess fluids. 2.9.2 Design Considerations. The design of all parts of the system that will be in contact with the cutting fluid should take into account the following: All surfaces in contact with the fluid should be as smooth as possible to minimize the deposit buildup of metallic or nonmetallic materials as well as microbial agglomeration. If flumes are constructed in the floor, they should be covered to prevent access of any outside waste material and should be designed to maximize fluid flow in order to minimize possible microbial growth or the buildup of fines and metal chips. All piping should be sized to maximize fluid flow and should contain as few bends as possible to facilitate cleaning. Further, the pipes should be sized so that they are full during operation, thus preventing the buildup of slime on the walls. Reservoirs should be constructed of materials that are not subject to chemical attack.
2.9.3 System Cleaning The reservoir, auxiliary piping, and application devices should be cleaned before the reservoir is filled with machining fluid. This cleaning of the system is important before the initial fill and is even important in subsequent filling cycles. Good cleaning practice consists of the following series of steps: Drain fluid from all lines, application devices, sumps, and/or reservoirs. Remove as much of the solids collected in the system (filters, lines, sump, reservoir, and so on) as possible.
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Charge with a suitable cleaner diluted with an appropriate fluid (water, solvent, oil) Circulate the cleaning solution for a sufficient length of time to remove residual machining fluid and accumulations (solids, liquid contaminants) in the total system. Drain the system as completely as possible and flush the system with the appropriate light oil, solvent (in the case of oil-base fluids), or water (in the case of water-base fluids). Proceed immediately to the next step in the cleaning cycle if the system is flushed with water. Rinse with a solution containing a biocide and a fungicide for at least two hour when waterbase solutions or emulsions are the machining fluids of choice. Mix the desired concentration of concentrate and water in a clean mixing vessel, using deionized water if available. The mixing should be carried out so as to ensure intimate contact of concentrate and water. The concentrate should always be added to the water to facilitate approximate mixing. The system should then be charge.
2.10 Environmental Impact. The global market of cutting fluids is around 600 million gallons prior to dilution. The environmental and cost issues concerned with the use, recovery, and cleaning of cutting fluids are of substantial importance. With the recently devised and introduced ISO14000 environmental series legislation, companies are looking for methods to reduce their consumption of cutting fluids. Companies are attempting to adopt more cost effective methods of recycling cutting fluids or removing them from the processes completely [3]. Companies are creating new fluid management practices that are utilizing more efficient methods of using cutting fluids. New machine technology, recycling methods and ultrafiltration techniques before disposal are helping to extend the life of cutting fluids and minimize their impact on the environment. Cutting fluids also pose a human health risk for those working in manufacturing environments. Alternative ways of dealing with the problem of contamination are: replace the cutting fluid at least twice per month, machine without cutting fluids (dry cutting), Use a filtration system to continuously clean the cutting fluid.
Disposed cutting fluids must be collected and reclaimed. There are a number of methods of reclaiming cutting fluids removed from working area. Systems used range from simple settlement tanks to complex filtration and purification systems. Chips are emptied from the skips into pulverize
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and progress to centrifugal separators to become a scrap material. Neat oil after separation can be processed and returned, after cleaning and sterilizing to destroy bacteria [3]. 2.11 Fluid Management Administration 2.11.1 Personnel & Training A successful fluid management program requires a great deal of cooperation among designated personnel. Suppliers of cutting equipment and fluids uphold good communication with management and employees in order to maintain fluid quality and extend the life of cutting fluids. Management must have a good understanding of the chemistry of cutting fluid and monitor fluid performance, cost data, and disposal procedures. 2.11.2 Operating Procedures & Tracking System Management must design a written standard operating procedure (SOP) for fluid usage/data collection and successfully followed by personnel. Following proper operating procedures while tracking cutting fluid usage and quality measurements allows personnel to identify a baseline for which fluids should be maintaining. Creating an informational database helps determine facility efficiency over time by comparing usage with amount being disposed and/or recycled. 2.12 Monitoring and Maintenance An important element of extending the life of cutting fluids includes general maintenance of metalworking equipment. 2.12.1 Recording Usage & Quality Inspection First and foremost, fluids should be mixed according to the manufacturer’s directions. Using untreated water with acceptable mineral content during initial mixing is recommended. However, in order to maintain fluid concentration after initial use, it is ideal to add pre-mixed fluids to the system after water loss from evaporation has occurred. The metalworking fluid manager establishes what factors need to be documented and tracked. These factors may include fluid pH, concentration levels, biological growth, water quality, foaming tendency, biocide use, particulates present, tramp oils, rust, rancidity, and color. Monitoring cutting fluid quality is essential to extending its life and anticipating problems. Periodic measurements and inspections are necessary for maintaining optimal fluid quality and performance. 2.12.2 System Maintenance An important element of extending the life of cutting fluids includes general maintenance of metalworking equipment. Dirt, oil, and other particulates remain in the system if not routinely cleaned and creates buildup and bacterial growth. Cutting fluid maintenance involves checking the concentration of soluble oil emulsions (using refractometers), pH (using a pH meter), the quantity of
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tramp oil (hydraulic oil leaking into the cutting fluid system) and the quantity of particulates in the fluid.
Figure 2.10 A refractometer is used to measure coolant dilution. Source: ASM Metals Handbook
Refractometers are very easy to use. Just place a few drops of fluid on the prism and hold the unit up to a light source. Look into the eyepiece and read the scale. To calibrate, just make sure the prism is clean and place a few drops of tap water on the prism. The separation line should be on zero. If not, turn the adjustment screw until it is. Remember, refractometers read on a Brix scale not actual percent. To get the actual percentage you must multiply the refractometer reading by your coolant's refractive index (on product data sheet). With most soluble oils the index is 1, so a Ref. reading of 5 X index of 1 = 5% concentration. However, many semi-synthetics, synthetics, grinding fluids, and some soluble oils can have a refractive index from 1.5 to 3. So a Ref. reading of 5 X index of 1.75 = 8.75% concentration. This is most critical with solutions designed to be run at lower concentrations, which have high indexes [2]. General cleaning and routine preventative maintenance procedures include particulate removal, tramp oils control, general contaminants removal and an annual machine cleaning and disinfection. Preventative procedures help to extend the life of cutting fluids by reducing the frequency of fluid recycling. 2.13 Recycling and Disposal 2.13.1 Recycling Methods Once fluid quality has reached a point where it can no longer be maintained at an optimal level, it needs to be recycled for contaminant separation or disposal. The most important part of the recycling process is determining when to recycle. Once cutting fluids have degraded to a certain point, they are unable to be recycled. That is why it is essential to monitor cutting fluid quality. There are many different types of recycling equipment available to remove contaminants from fluids. The most common recycling equipment used are skimmers and coalescers (removes tramp oils), settling tanks,
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magnetic separators, hydrocyclones, centrifuges (removes particulates), filtration equipment and flotation process (removes smaller particulates). Skimmers are used to separate the tramp oil from the coolant. These are typically slowly rotating vertical discs that are partially submerged below the coolant level in the main reservoir. As the disc rotates the tramp oil clings to each side of the disc to be scraped off by two wipers, before the disc passes back through the coolant. The wipers are in the form a channel that then redirects the tramp oil to a container where it is collected for disposal. Floating skimmers are also used in a situation where temperature or the amount of oil on the water becomes excessive. Recycling Indicators The pH is less than 8.0 Fluid concentration is less than 2% Appearance is dark gray to black Odor is strong rancid or sour
Recycling Selection & Schedule: How often cutting fluid needs to be recycled depends on fluid type, water quality, fluid contamination, machine usage and filtration, fluid control, and fluid age. The largest factor for determining a recycling schedule is the frequency of use. Generally, recycling can be done only a few times before it needs to be disposed. However, depending on the productivity level of the facility, cutting fluid may last only a few weeks or up to a few months long. Some manufacturers require that a recycling procedure is conducting at least once a month [2]. 2.13.2. Disposal Even with recycling, cutting fluid will eventually require proper disposal. Before disposal, metalworking facilities must have the ability to determine whether the fluids are hazardous or nonhazardous. Waste is considered hazardous is it meets one of three criteria: Exhibits one or more characteristics of a hazardous waste (ignitability, corrosivity, reactivity, and toxicity). Has been identified and listed as hazardous waste by the Environmental Protection Agency (EPA). Contains a mixture of hazardous waste and nonhazardous waste.
2.14 Health and Safety Although most cutting generally have a low order of toxicity, some compounds that are normally used as components of cutting fluids have been identified as having a greater potential for toxicity than others. Reduced contact with these chemicals is an important part of good manufacturing procedure when metal removal processes are involved.
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Cutting fluids present some mechanisms for causing illness or injury in workers. These mechanisms are based on the external (skin) or internal contact involved in machining work, including touching the parts and tooling; being splattered or splashed by the fluid; or having mist settle on the skin or enter the mouth and nose in the normal course of breathing. The mechanisms include the chemical toxicity or physical irritating ability of: The fluid itself. The metal particles (from previous cutting) that are borne in the fluid. The bacterial (fungal) populations that naturally tend to grow in the fluid over time. The biocides that are added to inhibit those life forms. The corrosion inhibitors that are added to protect the machine and tooling. The tramp oils that result from the way oils (the lubricants for the slide ways) inevitably finding their way into the coolant. 2.14.1 Skin Effects By far the most common effects from cutting fluids are skin disorders resulting from prolonged contact. The four major types of disorders that are critical for human beings are contact dermatitis, folliculitis and acne, pigmentary changes and benign and malignant tumors. 2.15 Fluid Exposure Reducing fluid exposure is the most effective way of reducing health risks associated with cutting fluid. There are a number of different methods of reducing worker exposure to cutting fluids. Choosing an appropriate cutting fluid is the first step towards reducing health risks. Facilities should have a good understanding of the Material Safety Data Sheet (MSDS) provided by the cutting fluid manufacturer [2].
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CHAPTER 3 DISCUSSION AND EVALUATION
To explore the effect, the proper usage, selection criteria, method of application, storage and disposal of cutting fluids; it is tried to assess three companies which is found in Harar. These three companies are Menschen für Menschen Foundation (Agro Technical & Technology College), Harar Brewery Factory and Harar TVET College is selected. During machining any workpiece materials, heat is generated at the (i) primary deformation zone due to shear and plastic deformation, (ii) chip-tool interface due to secondary deformation and sliding and (iii) work-tool interfaces due to rubbing. All such heat sources produce maximum temperature at the chip-tool interface, which substantially influence the chip formation mode, cutting forces and tool life. As stated on literature review the cutting fluids have been widely used in machining operations for cooling the tool, workpiece and chip, lubricating, flushing chips away from the cutting zone, protecting the workpiece, tooling and machine from corrosion, controlling built-up edge on the tool, longer tool life, narrower tolerances of the work piece size, reduced thermal deformation of workpiece and better surface finish (in some applications). However, certain manufacturing industries and Technical institutions which are found in Ethiopia have the problems of negligence and awareness of using cutting fluids for machining process. Among above listed supervised industries Harar Brewery Factory and Harar TVET College having the problem of Giving emphasis to have cutting fluid in organization by the management Method of application of cutting fluid in a proper way Stored a cutting fluid in a manner which is acceptable Disposal of a cutting fluid Cost of cutting fluid
These two companies’ managements give more emphasis about the cost of cutting fluids; the company’s management doesn’t have enough information about the effect of cutting fluid on quality of the product (spare part). Cost of a cutting fluid related expenses include the cost of installing a fluid supply system, fluid purchase and system maintenance, and discarded fluid (waste) treatment. Fluid related costs are large because high production manufacturing plants frequently utilize several cutting fluid reservoirs each containing thousands of gallons of cutting fluid reducing the amount of fluid
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employed can produce significant cost and waste savings. Sometimes users will reduce the coolant/water ratio significantly because they assume this will help cut costs. However, tool life can decrease rapidly if the proper amount of coolant is not used when operating the tool. Even if Menschen für Menschen Foundation (Agro Technical & Technology College), Harar Brewery Factory and Harar TVET College manufacturing industries and Technical institutions use cutting fluids for machining process, but the implementation of storage, application, selection criteria and disposal of cutting fluids are in the inappropriate way. This result in Shortening of tool life Corrosion of the machine, workpiece & cutting tools Bad surface finish of workpiece material Wider tolerances of the work piece size & dimensional errors. Difficulties in chip removals, this result in built up edge formation.
In this project work it is tried to show the comparison and difference between scientific review of cutting fluid selection criteria, method of application, storage and disposal of cutting fluids with the three supervised industries and institutions i.e. Menschen für Menschen Foundation (Agro Technical & Technology College), Harar Brewery Factory and Harar TVET college. 3.1 Cutting fluid selection criteria In Menschen für Menschen Foundation (Agro Technical & Technology College), Harar Brewery Factory and Harar TVET College existing cutting fluid selection criteria are different from one company to other company. For example in Menschen für Menschen Foundation (ATTC) selection criteria for cutting fluids which mentioned above in section (2.6) are considered but there are some criteria which did not consider by this organization, such as:
Possibility of adverse effects on operator health and safety Getting suitable cutting fluids for specific workpiece materials according to this literature review different workpiece materials use different type of cutting fluids Getting suitable cutting fluids for specific cutting tool materials E.g. high speed steel cutting materials can be used with all type of cutting fluids but others needs special cutting fluids for that special cutting tool.
So, Menschen für Menschen Foundation (Agro Technical & Technology College) did not contemplate the above mentioned criteria’s for the correct functioning of machining process.
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Due to these: The machine operator’s exposed for different types of skin disease. On the shop floor, the machine operators may be affected by the negative effects of cutting fluids, such as skin and respiratory problems. The surface finish of the material become decreased There is rapid tool wear. Hence tool life will be shorter and surface finish quality falls.
Most of the time Harar Brewery Factory and Harar TVET College use cutting fluids and seldom use water as cutting fluids for machining purpose. Because of this: The machine will expose for corrosion Tool life will be short The product which is machined has wider tolerance The product which is machined has poor quality surface finish
So to avoid the above mentioned problems it is better to use cutting fluids which is suggested on section Table 2.1 or it is better to use a general purpose cutting fluid such as WS 600N – which is economical and environment-friendly, long life water-soluble oil, suitable for all moderate machining and grinding operations on all ferrous and non-ferrous metals except titanium and magnesium and it will works best for all types of cutting tool materials as well as workpiece materials and for all type of machining process (turning, milling, grinding etc.) and it is best to use personal safety management system for the machine operator’s and it is conceivable to use dry machining or other alternative methods for machining process to get the desired surface qualities product and for the good health and safety of the machine operator’s. 3.2 Cutting fluid application methods Correct application of the cutting fluid at the tool/workpiece interface is fundamental to the effective use of cutting fluid, and the method of application affects not only lubrication and cooling but also the efficiency in removing swarf and chips from the cutting operation. Proper usage of cutting fluid applications are different from one company to the another company. In Menschen für Menschen Foundation (Agro Technical & Technology College) and Harar TVET College use flooding method of application of cutting fluid in which the workpiece material and cutting tool get enough amount of cutting fluid for the correct functioning of machining process. As a result machining operation becomes very easy.
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It is better to use applications of cutting fluids of high-pressure, high-volume pumping in combination of flooding method of application to get the desired quality of surface finish, good dimensional accuracy and to increase life of the tool. However, in Harar Brewery Factory often used flooding method of application of cutting fluid and seldom used manual methods of application of cutting fluid. This is a type of method of application of a cutting fluid from a can manually by the operator. Manual application of a cutting fluid is effective only for very low volume production or tool room use. Owing to this, the machine, the cutting tool and workpiece material does not get sufficient amount of cutting fluid for machining process. So the effect of this problem is Getting poor quality product Tool life will be shorten Getting wider tolerance and dimensional error of the product Formation of built-up edge
So to avoid this it is better to use an applications high-pressure, high-volume pumping to force a stream of liquid directly into the tool-chip interface, with walls around the machine to contain the splatter and a sump to catch, filter, and recirculate the fluid. The advantage of using high pressure, high volume pumping is To flush chips away easily from cutting tool and workpiece material To avoid built-up edge formation The cutting tool and workpiece material get sufficient amount of cutting fluid this makes getting good quality products and dimensional accuracy. 3.3 Storage of cutting fluid Care of cutting oils begins with storage. Contamination with water, grit, dirt, or any impurities should be avoided. Best results are obtained by storing cutting fluids in a separate enclosure within the shop. The insides of tanks and receptacles should be kept clean but Menschen für Menschen Foundation (Agro Technical & Technology College), Harar Brewery Factory and Harar TVET College manufacturing industries and Technical institutions system of storage of cutting fluids are to some extent different. For example Menschen für Menschen Foundation (ATTC), and Harar Brewery Technical institution and manufacturing industry stored cutting fluids simply with plastic bottles and kept in shop. These cause problems If stays in shelf for more than one year it will develop bacteria on it this is dangerous for human being
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If it contaminant with other oils it will have adverse effect. If it is exposed for excessive temperature becomes spoiled
To avoid this problem and for the correct functioning of this cutting fluid for longer time it is better to store cutting fluids underground which has good ventilation. It is best to arrange storage of cutting oils so that it will not be subjected to any extended periods of freezing or overheating. Repeated extreme temperature changes will eventually impair the oils and cause separation of the ingredients which contribute to better machining and it is better to store cutting fluids for not more than three years. 3.4 Disposal of cutting fluids Even with the best fluid management program, cutting fluid will not last indefinitely and will eventually require disposal. Environmental regulations are making disposal increasingly difficult. Old, used cutting fluid must be disposed of when it is fetid or chemically degraded and has lost its usefulness. As with used motor oil or other wastes, its impact on the environment should be mitigated. Menschen für Menschen Foundation (Agro Technical & Technology College), Harar Brewery Factory and Harar TVET College disposal method of cutting fluids is very poor. Because it is dispose in an open environment. Due to this a lot of problem occur in the environment Cutting fluids may damage soil and water resources, causing serious environmental impacts The soil becomes useless because it will deteriorate with bacteria’s
To avoid this it is best to use alternative ways of dealing with the problem of contamination. Disposed cutting fluids must be collected and reclaimed. There are a number of methods of reclaiming cutting fluids removed from working area. Systems used range from simple settlement tanks to complex filtration and purification systems. Chips are emptied from the skips into a pulverizer and progress to centrifugal separators to become a scrap material. Neat oil after separation can be processed and returned, after cleaning and sterilizing to destroy bacteria. Generally the different negative effect of cutting fluid will guide to use the new alternatives to cutting fluids. These include the use of dry machining, Minimum Quantity Lubricant and Cryogenic Machining (Liquid Nitrogen Technology) and chilled air. 3.5 Alternatives to cutting Fluids 3.5.1 Dry Machining New technology in metalworking equipment has made it possible to produce the same results without the use of cutting fluids. The new type of equipment is designed to eliminate the need for cutting fluid without losing the benefits associated with using cutting fluids. The new equipment has
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an added coating that insulates it from heat and friction. Dry cutting eliminates waste, maintains cleaner cuttings, and metal cuttings can be added directly to other scrap metal. Dry cutting also creates a cleaner and safer environment for workers. The potential drawbacks are initial startup costs to purchase equipment as well as a higher potential for machine rusting. However, if long term costs of cutting fluid recycling and disposal are considered, dry cutting may be a competitive or even superior option. 3.5.2 Minimum Quantity Lubricant (MQL) MQL or semi-dry machining is very similar to dry machining. MQL requires a very small quantity of lubricant delivered precisely to the cutting surface. Nearly all of the lubricant used in the cutting process is either deposited on the equipment or vaporized from heat. Thus, there is no cutting fluid waste generated but only very small quantities that may require an extra cleaning procedure and proper ventilation. Fluid selection is important for MQL because it must be a superior fluid such as vegetable oil or synthetic oil. The costs of these superior fluids are higher but eliminate the need for costly fluid recycling and disposal services. MQL may be an ideal option because of the elimination of fluid waste while maintaining the benefits of using oil, but the specific fluid delivery method for individual facilities requires an in depth understanding of the technical aspects of MQL that could make it unfeasible to use this method. 3.5.3 Liquid Nitrogen Technology (Cryogenic Machining) More recent developments in machining include the use of cryogenic gases such as nitrogen or carbon dioxide as a coolant. Using small diameter nozzle and at temperature of -200°C. Liquid nitrogen is injected into the cutting zone. Liquid nitrogen is a cheaper alternative for facilities because it is an abundant gas present in the air and cuttings chips have no residual oil on them. Because of the reduction in temperature, tool hardness is maintained and tool life is enhanced, thus allowing higher cutting speeds. Also, the chips are more brittle; hence, machinability is increased. Furthermore, the nitrogen simply evaporates and therefore has no adverse environmental impact. The only dangers that it possesses is the extremely low temperatures that can potentially cause frostbite as well as non-combustible explosions due to pressure increases from warming. However, nitrogen is a safe and environmentally friendly alternative if handled correctly. Another alternative is coupling nitrogen with carbon dioxide, which has been found to eliminate environmental problems associated with the traditional petroleum-based flooded lubricant systems. 3.5.4 Air cooling Employing chilled and compressed air for cooling in machining operations is a relatively new technique which has attracted many researchers. As in this technique the cooling media is air, it
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could be defined as the cleanest and most environmentally friendly method of cooling in cutting operations. Most studies indicated that using chilled air as coolant in machining resulted in longer tool life. The effect of chilled air on the surface finish is highly dependent on the machining parameters. In general it could be claimed that air cooling produces lower surface roughness than dry cutting. However, the produced surface roughness is higher than that made by MQL or emulsion coolant [14].
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CHAPTER 4 CONCLUSION AND RECOMMENDATION 4.1 Conclusions
The proper method of applications and selection criteria of cutting fluids for machining processes generally provides various benefits such as longer tool life, higher surface finish quality and better dimensional accuracy. Method of applications, selection criteria, storage and disposal of cutting fluids are likely to remain an important consideration in many metal removal operations for the foreseeable future. Selection criteria for cutting fluids used in Menschen für Menschen Foundation (Agro Technical & Technology College) does not consider health hazard performance, fluid compatibility with work materials and machine components. Because of this machine operators got skin diseases and the products got have problem on surface qualities. When considering selection criteria of Harar Brewery Factory and Harar TVET College doesn’t consider most of factors such as fluid compatibility with work & cutting tool, getting suitable cutting fluids for specific cutting tools etc. due to this machine will expose for corrosion, tool life will shorten and poor dimensional integrity. Cutting fluid method applications in Menschen für Menschen Foundation (Agro Technical & Technology College) and Harar TVET use flooding methods of application. So it is better to use a combination of flooding with high pressure, high volume pumping. Whereas cutting fluid application in Harar brewery factory use often flooding and seldom use manual application. This manual application method does not good for machining process because the machine does not get enough amount cutting fluids this leads to poor quality of surface finish and poor dimensional integrity and wider tolerance. Storage of cutting fluid in Menschen für Menschen Foundation (Agro Technical & Technology College) and Harar TVET Colleges stored cutting fluids in plastic bottles and kept in shop for longer time shelf life of cutting fluids is two years, so it is not good store cutting fluids for more than two years in addition to this scientific way suggests storing cutting fluids underground with good ventilation. Disposal of cutting fluid in Menschen für Menschen Foundation (Agro Technical & Technology College) and Harar TVET College are tremendously not acceptable because it discharge in an environment, this will affect the soil and society. It is good to retreat used cutting fluids and dispose in a manner which is acceptable.
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4.2 Recommendations
The following recommendations are proposed for Harar Brewery, Harar TVET college, Menschen für Menschen Foundation (Agro Technical and Technology College and some of them are equally likely to be implemented for other similar process industries in Ethiopia. It is recommended that, all manufacturing industries and Technical institutions must consider choosing proper cutting fluids for right type of cutting tool materials as well as workpiece materials and machining process. It is good to use correct method of application of cutting fluids. It is better to use fluid management system in the companies. It is better not to store cutting fluids for more than two years and it is good to won’t be exposed to high temperature and high cooling conditions. It is best to retreat dispose fluids in a manner that will not affect the environment.
Generally It is recommend that all manufacturing industries and Technical institutions To use new approaches of alternatives methods for reducing cutting fluids application in machining processes such as dry machining, Minimum Quantity Lubricant and Cryogenic Machining (Liquid Nitrogen Technology) and chilled air. New coating technologies for various cutting tools have provided important advantages to reduce cutting fluid application in machining operation.
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5. References
1. Amitabha Bhattacharyya, Metal Cutting Theory and Practice; New central book agency (P) Ltd. (1996). 2. ASM Handbook committee, ASM Handbook Machining volume 16. 3. E. Brinksmeier, A. Walter, R. Janssen, P. Diersen, Aspects of cooling lubrication reduction in machining advanced materials, Proceedings of the Institution of Mechanical Engineers, Journal of Engineering Manufacture, 1999. 4. Kalpakjian, S.; Schmid, S. Manufacturing Engineering and Technology; Prentice Hall, Upper Saddle River, NJ - USA, 2001, 5. M.A. El Baradie, Cutting Fluids, Part I: Characterisation, Journal of Materials Processing Technology 56 (1996). 6.M.B. Da Silva, J. Wall bank, Lubrication and application method in machining, Lubrication and Tribology 50 (1998). 7. MC Shaw. Metal Cutting Principles. Oxford: Clarendon Press, 1984 8.M. Sokovic, K. Mijanovic, Ecological aspects of the cutting fluids and its influence on quantifiable parameters of the cutting processes, Journal of Materials Processing Technology 109 (2001). 9. W.J. Bartz, Ecological and environmental aspects of cutting fluids, Lubrication Engineering 57 (2001). Journals 10. Journal of Achievements in Materials and Manufacturing Engineering. Volume 25 issue 2. December 2007 11. Journal of manufacturing process, Metalworking fluids-coolant selection.mht
12. Journal of manufacturing process, Machine shop 1- cutting fluids and types.mht 13. Journal of cutting fluid health hazard evaluation. National Institute for Safety and Health.
Retrieved June 18, 2009. 14. Journal of manufacturing process, the essentials for choosing the right cutting fluid. www.rsleads.com/209-223 September 2002.
