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In the recent developments, demand for hard steels has been increased. The difficulty of Machining these material is increased due to its high hardness, toughness and strength using conventional method. In this project, die steel D2 is used as a workpiece for turning operation. This project aims to investigate the effect of blended vegetable oil based cutting fluid in turning D2 steel. The vegetable oils used were groundnut oil and cottonseed oil. These cutting fluids are used separately according to the experimental setup. These vegetable oil based cutting fluids are biodegradable, non-toxic, non-harmful to health for operators and it is not a fire hazard. The cutting tool used in this project is tungsten carbide tipped tool as it can withstand high hardness and high cutting speeds. Experimental investigations have been carried out by varying input parameters such as feeds, depth of cuts and spindle speeds. From these inputs, the output parameters are evaluated such as material removal rate and surface roughness. It is observed that MRR increases with increase in spindle speeds and feeds. The slight decrease in MRR is also observed with increasing depth of cut at varying speeds and feeds. Surface roughness values were also analysed in the investigation and it is observed that low roughness values were obtained with the use of groundnut oil based cutting fluid in the range of 1.65-4.11 Ra and high roughness values were obtained with the use of cottonseed oil based cutting fluid in the range of 3.13-4.93 Ra.
ABSTRACT:
In the recent developments, demand for hard steels has been increased. The difficulty of Machining these material is increased due to its high hardness, toughness and strength using conventional method. In this project, die steel D2 is used as a workpiece for turning operation. This project aims to investigate the effect of blended vegetable oil based cutting fluid in turning D2 steel. The vegetable oils used were groundnut oil and cottonseed oil. These cutting fluids are used separately according to the experimental setup. These vegetable oil based cutting fluids are biodegradable, non-toxic, non-harmful to health for operators and it is not a fire hazard. The cutting tool used in this project is tungsten carbide tipped tool as it can withstand high hardness and high cutting speeds. Experimental investigations have been carried out by varying input parameters such as feeds, depth of cuts and spindle speeds. From these inputs, the output parameters are evaluated such as material removal rate and surface roughness. It is observed that MRR increases with increase in spindle speeds and feeds. The slight decrease in MRR is also observed with increasing depth of cut at varying speeds and feeds. Surface roughness values were also analysed in the investigation and it is observed that low roughness values were obtained with the use of groundnut oil based cutting fluid in the range of 1.65-4.11 Ra and high roughness values were obtained with the use of cottonseed oil based cutting fluid in the range of 3.13-4.93 Ra.
KEYWORDS: Biodegradable, vegetable oils, Die steel D2, hard turning, surface roughness, MRR.
1.INTRODUCTION:
Nowadays, the demand for tough and hard materials has been increased. The metals having hardness value above 45HRc are very difficult to machine. So the demand for hard turning has been introduced and it is also used as an alternative to the grinding process by providing smooth surface finish. For hard turning operation, it involves high cutting speeds in between 70-300 m/min. HSS tools are used for cutting speeds not more than 50 m/min, so carbide tipped tools were used where it can with stand its hardness even at high cutting speeds without tool failure.
During machining large amount of heat is generated at the work piece, cutting tool and tool-work interface. The cutting tool has to withstand the temperature generated without losing its hardness. Every tool has certain limit to withstand the generated temperature, if it exceeds that limit the tool gets deformed plastically at the tip. Because of this tool failure occurs, it results in poor surface finish of the workpiece.
To avoid these effects, cutting fluids are introduced during machining. Cutting fluids are divided into four categories such as cutting oils, soluble oils, synthetic fluids and Semi synthetic fluids. Straight cutting oils which are used directly during machining have good lubricity but does not provide cooling action. They form smoke during machining and it is harmful to the operator. Straight cutting oils are used at low temperature and low speed operating conditions. Soluble oils are emulsified oils with oil in water emulsion. Soluble oil uses an emulsifier to blend oil with water and also to improve the stability of cutting fluid. Synthetic and semi-synthetic cutting fluids uses some of the chemical agents to blend with water. These chemical agents are added for rust prevention and resistance to biological attack. Synthetic fluids have good cooling properties and their lubricating properties are less when compared to others. Semi synthetic cutting fluids uses both synthetic fluid and emulsions. Semi synthetic cutting fluids contains oil in it, whereas synthetic cutting fluids do not contain any oil. Cutting fluids are used not only for cooling purpose but also to reduce the cutting forces by lubricating the surfaces between the work-tool interface. Cutting fluids helps in improving longer tool life and better surface finish of the product. Mineral oils are most widely used cutting fluids in machining. These mineral oils are nonbiodegradable which include long term pollution to the environment. For the sake of biodegradability, vegetable based cutting fluids are chosen as an alternative.
2. LITERATURE REVIEW:
The turnings of AISI 4340 steel with alumina insert along with three cutting fluids were used. It is observed that when using emulsion without mineral oil surface roughness was found to be 1.73 pm, while used with synthetic emulsion the roughness was found to be 1.89pm and by using emulsion with mineral oil the roughness was found to be 2.14pm. So it is observed from the results that the effect of cutting fluid based on emulsion without mineral oil resulted in better roughness values and longer tool life when compared to others1. The six different cutting fluids were used of which two are conventional type such as synthetic and mineral oil, other four cutting fluids are of vegetable based from sunflower and canola oil with different ratios of extreme pressure additives. These cutting fluids were used to reduce surface roughness and cutting forces while turning AISI 304L austenitic stainless steel. From the results it is observed that the effects of feed rate, spindle speed and depth of cut are the most influential parameters than cutting fluid to reduce surface roughness and cutting forces. The comparison was made between the cutting fluids and concluded that sunflower and canola based cutting fluids performed better than other cutting fluids2. In turning AISI 1040 steel, it was observed that there is a decrement in cutting forces, surface roughness and tool wear with an increase in emulsifier content. It is also found that high heat transfer rates, higher hardness and less roughness values were observed with high rate of emulsifier. The thermal conductivity, kinematic viscosity and PH value also increases with increase in content of emulsifier, whereas flash and fire points decreases with increase in amount of emulsifier3. The influence of vegetable oils on the performance of lubricant formed from a blend of vegetable oil and conventional engine oil was observed. The work represents the palm oil and soya bean based vegetable oil were mixed with commercial engine oil at 1:1 ratio by volume. The friction performance of both the vegetable oils when used purely was superior to that of engine oil, whereas for wear characteristics it was reversed. So when they blended with engine oil separately and used both the performance characteristics were Improved4. It was found that high pressure coolants increases tool life up to 300% while turning Ti6A14V when compared to flooded cooling. It is also found that lower tool life was achieved while turning Inconel 901 with high pressure coolants. High coolant pressures are employed during machining to reduce the temperature at the cutting zone up to 40% when compared to flooded cooling5. While turning AISI 1060 steel using vegetable oil it is found that cutting zone temperatures were reduced to 10% and cutting forces up to 13% when compared to dry machining6. The vegetable oil based cutting fluids such as palm oil and sunflower oil were selected for wetting capability and lubricity while grinding AISI 521000 steel by an alumina wheel. Sunflower oil was found to be the most effective vegetable oil based cutting fluid when compared to palm oil and conventional soluble oil. Sunflower oil based cutting fluid enhances G ratio and smooth surface fish. It also reduces grinding forces when compared to others7.The different types of cutting fluids such as karanja, neem and conventional cutting fluids are used while turning a mild steel and compared their performances with dry cutting conditions. The used vegetable based cutting fluids improved surface finish of the workpiece when compared to conventional cutting fluid and dry cutting condition. They explained the low viscosity of neem oil based cutting fluid than that of karanja oil based cutting fluid along with low temperature of neem oil based cutting fluid with respect to karanja oil based cutting fluid8. The soy based cutting fluid is used in their experimentation and evaluated the performance of this soy based cutting fluid over traditional petroleum based cutting fluids in turning AISI 4140 steel and 52100steel using carbide tool. The roughness value and tool wear were measured during the experimentation and the results shown that soybean based cutting fluid produced similar surface finish value as that of petroleum based cutting fluid in turning both the steels. Soybean based cutting fluid reduces tool wear compared to dry cutting condition. Even though soybean based cutting fluid underperformed when compared to petroleum based cutting fluid in reducing tool wear for both the steels9. The two different cutting fluids were used such as sesame and coconut oil based fluids with use of extreme pressure additives while machining AISI 1040 steel. Coconut oil shows very good results by reducing feed force by 30%, thrust force by 28%, cutting force by 20%, cutting tool temperature by 7%, and tool flank wear by 34% when compared to sesame oil based cutting fluid10. The two different fluids such as rap-seed oil and ester oil based cutting fluids with the use of sulphur and phosphor based extreme pressure additives while drilling AISI 316L austenitic stainless steel. The results shown that vegetable oil based fluids performed better than mineral oil based fluids by reducing tool wear, better chip breaking, lesser cutting forces and also 117% increase in tool life11. The five different types of base oils such as petroleum based naphthenic oil, petroleum based 50/50 naphthenic/paraffinic oil blend, High oleic bio based canola oil, soya bean oil and bio based synthetic TMP ester. All these base oils were utilised in the form of both the emulsified oils and as the straight/neat oil under tapping torque test. Conventional soluble oil was also used as a standard of comparison to compare them with the above oils. These different fluids were tested on 1080 cold rolled steel using uncoated hardened steel tool. Under tapping test conditions it is reported that bio based straight oils significantly have higher tapping torque efficiencies relative to petroleum based oils. Both the petroleum based oils have slightly lower efficiency level as that of reference soluble oil. Canola and soya bean oils have same tapping torque efficiencies. The author also concluded that all the vegetable based oils performed better than petroleum based mineral oils12. The AISI D2 steel was used which is having high hardness of 66HRC for turning operation using coated carbide insert. Turning hard steels with high strength tools such as coated carbide inserts, cubic boron carbide nitride and mixed ceramic inserts have higher material removal rates, produce smooth surface finish etc. From the investigation the conclusions were made such as, on increasing cutting speed, surface roughness decreases while machining hard steel. On increasing depth of cut and feed, surface roughness increases13.Some of the machinability characteristics were evaluated while turning D2 steel using ceramic cutting tools. It is concluded that flank wear occurs in ceramic cutting tools with higher cutting speeds and also increases surface roughness. It is also concluded that cutting pressure is strongly influenced by feed rate and surface roughness is influenced by feed rate and cutting time14.
3. MACHINE AND MATERIAL:
3.1Workpiece material:
In this study, die steel is chosen as workpiece material. Die steel is air hardened, high carbon and high chromium tool steel. D2 steel contains carbon in the range of 1.5 to 2.35% and chromium in the range of 10 to 13%. It is heat treatable and it has hardness in the range of 55 to 62 HRC. D2 steel can also retain its hardness up to a temperature of 425°C. It has both wear and abrasion resistance properties. The physical properties and chemical composition of the workpiece is mentioned in Table 1.D2steel is one of the most widely used material for manufacturing dies and moulds. Though D2 steel possesses excellent mechanical properties and also can be used in different tooling applications, it is very difficult to machine. The typical applications of D2 steel includes stamping or forging dies, tools, punches, knives, slitters, shear blades, scrap choppers, tyre shredders etc.
3.2Tool material:
Carbide tips which are in the form of tungsten carbide or titanium carbide are the most common material brazed on cutting tool. HSS is the most commonly used cutting tool for machining but it cannot be used where high cutting speeds are involved so carbide tipped cutting tools are used as an alternative with can withstand high cutting speeds and high hardness at elevated temperatures. In this research, Tungsten carbide tipped tool is used. It has high modulus of elasticity, high thermal conductivity and high hardness. High strength and high rigidity of the material makes it use as a cutting tool. The impact resistance is also high as it is a hard material with high rigidity. The physical properties of the tool is mentioned in Table 2.
3.3Cutting fluids:
Cutting fluids plays an important role in removing the heat generated at the tool-work interface and also to provide lubrication. Here in this project, two individual vegetable oil based cutting fluids such as groundnut oil and cotton seed oil based cutting fluids were used. The physical properties of both the cutting fluids are listed in the Table 3.
1. Base oil - groundnut oil and cottonseed oil.
2. Liquid used - Distilled water.
3. Engine oil - 4T SAE40 used to carry away heat generated.
4. Emulsifier - liquid detergent used for proper blending of oil in water.
5. Additive - glycerol liquid used for lubrication.
3.3(a) Preparation of cutting fluid:
The cutting fluid preparation was made with help of magnetic stirrer equipment. This equipment was used for proper blending of cutting fluid.
Firstly the three types of vegetable oils were taken such as mustard oil, cotton seed oil and groundnut oil for preparing the cutting fluid. While preparing the cutting fluid it makes very difficult to blend mustard oil in water with required proportions because it is highly viscous than other two vegetable oils. Because of its high viscous nature and not able to blend with the distilled water by using emulsifier the use of mustard oil based fluid was rejected at the early stages of the experimentation. The other two vegetable oils shows very good results by proper blending with the distilled water with the help of emulsifier.
The preparation involves distilled water taken in large cylindrical container. Before stirring, the distilled water was heated to a temperature of 50°C. The magnetic stirrer was placed in the container at the centre and the equipment was set to 900 rpm and a temperature of 40°C while stirring. Glycerol was added in the required proportion, it gets split into bubbles in the distilled water while stirring. The required proportion of both the base oil and engine oil was added in the distilled water. It is observed that oil gets accumulated at the top of the container by forming a separating layer with distilled water. The emulsifier, which is the liquid detergent was introduced into the container to blend both the oils with distilled water. Liquid detergent was used because it has both hydrophilic and hydrophobic properties that means it reacts with both water and oil by proper mixing of cutting fluid. Now the stirring process was continued for another 10 min for proper blending.
3.4Experimental setup:
All geared lathe is an automated machine used for operating many works such as turning, drilling, boring and thread cutting. It consists of 16 different spindle speeds which can be used with the help of levers provided. It is provided with a coolant tank included within the machine for the supply of cutting fluid during machining. A switch is provided for the automatic supply and cut off of the cutting fluid. The machine specifications are mentioned in Table 4.
3.5Preparation of samples:
The samples were prepared by turning the workpiece on both sides of the cylindrical specimen by step turning process. The process involves a total of9 experimental values with use of one cutting fluid and another 9 experimental values with the use of another cutting fluid.
The workpiece used was Die Steel D2 for preparing the samples. The step turning operation was carried out on all geared lathe machine. The tungsten carbide tipped tool was used for turning the die steel. The three different spindle speeds such as 305, 500, 835 rpm were used for the experimentation. The depth of cut used for turning each step was 0.5 mm. The machining length of 20 mm was used for each step and machining time was also calculated for each step. The table feed movement was automatically fed along with the spindle speed. The prepared cutting fluids were used separately on turning die steel according to the experimental setup.
4. RESULTS AND DISCUSSIONS:
4.1Effects of temperature on viscosity:
The prepared cutting fluid samples were tested to know its kinematic viscosity values at 40 C and at 100 C.
The results of the kinematic viscosities of ground nut oil and cotton seed oil based cutting fluids are mentioned in Table 5 and Table 6
4.2Effects of process parameters on Material removal rate (MRR):
Metal Removal Rate is the measurement of the material which is removed from a part in a given period of time. In this study, the effect of machining parameters such as speed, feed, depth of cut and the influence of different cutting fluids on the output parameters such as MRR and surface roughness has been carried out.
Theinput and output process parameters while turning die steel D2 with the use of both groundnut oil and cottonseed oil based cutting fluid are mentioned in table 7 and table 8
From Fig 6 It is shown that average material removal rate increases with increase in spindle speed with the use of both the cutting fluids. The volume of material removed was almost same with use of both the cutting fluids. From Fig 7 and Fig 8 It is shown that material removal rate increases with increase in feed at varying spindle speeds with use of both the cutting fluid.
4.3Effects of process parameters onSurface roughness:
The prepared step turning samples of die steel D2 were undertaken for surface roughness testing to know the roughness value Ra by using centre line average method. The roughness values of die steel D2 using groundnut oil and cottonseed oil based cutting fluid are mentioned in table 9 and table 10
From Fig 9 it is clear that average surface roughness values with respect to spindle speeds decreases with the use of groundnut oil based cutting fluid and increases with the use of cotton seed oil based cutting fluid.
From Fig 10 and Fig 11 it is shown that surface roughness values with respect to feed at varying speeds decreases with the use of groundnut oil based cutting fluid and increases with the use of cotton seed oil based cutting fluid.
6. CONCLUSION:
1. The material removal rate has been calculated while turning die steel D2 and it was found that MRR increases with increase in varying input parameters such as spindle speed, feed rate and depth of cut. The results shown that high MRR was found at a spindle speed of 835 rpm which is 6876.79mm3/min at 0.5 depth of cut, where the groundnut oil based cutting fluid was used. It is also found that high MRR was found at spindle speed of 835 rpm which is 6780mm3/min at 0.5 depth of cut, where cotton seed oil based cutting fluid was used.
2. The surface roughness values in turning die steel D2 with tungsten carbide tipped tool was also analysed in the investigation. It is found that surface roughness values in the range of 1.65 - 4.11 Ra were obtained with use of groundnut oil based cutting fluid. It is also found that surface roughness values in the range of 3.13 - 4.93 Ra were obtained with the use of cotton seed oil based cutting fluid.
3. It is observed that surface roughness values of die steel using groundnut oil based cutting fluid shown better results when compared to cottonseed oil based cutting fluid.
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