CHAPTER 6 FORMULATION OF A VEGETABLE OIL BASED CUTTING FLUID FOR HARD TURNING WITH MINIMAL FLUID APPLICATION 6.1 INTRODUCTION Performance enhancers

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1 CHAPTER 6 FORMULATION OF A VEGETABLE OIL BASED CUTTING FLUID FOR HARD TURNING WITH MINIMAL FLUID APPLICATION 6.1 INTRODUCTION Performance enhancers for increasing chip curl, improving rake face lubrication and increasing extraction of heat from the cutting tool are discussed in the previous sections. An attempt was made to develop a based on vegetable oil and this section presents information on issues related to the use of vegetable oils as metal s, the procedure for formulating a with coconut oil as the base and details of the cutting experiments conducted to evaluate the performance of the formulated for hard turning with minimal fluid application. It is reported that s based on coconut oil offered better cutting performance when compared to mineral oil based s. As it is 1% biodegradable, it does not possess any problems connected with disposal. It is highly environment and people friendly and causes no skin problems to workers exposed to it. It has got high oxidative and thermal stability. The long chain molecules of coconut oil are dipolar in nature and can create a dense, homogeneous and strong lubricating film on the contact surfaces that can absorb high pressures and offer better lubrication. 6.2 FORMULATION OF COCONUT OIL BASED CUTTING FLUID The work reported by Varadarajan et al. (2) was used as the basis for formulating a with coconut oil as the base. The formulation acted as an oil in water emulsion. The ingredients of the are presented in Table 6.1. Oleic acid is an unsaturated fatty acid which is used as an emulsifying or solubilizing agent. Besides serving as an agent for improving the lubricity of the, it also acts as friction modifier for lowering the friction coefficient. In water soluble s, triethanol amine is used to provide the alkalinity 128

2 needed to protect against rusting and it acts as an anti-oxidant. It also controls the evaporation rate of water in. Table 6.1 Composition of the concentrate Sl.No Content Percentage by volume 1 Coconut Oil 4% 2 Oleic Acid 4% 3 Triethanol Amine 2% Coconut oil based concentrate was formulated by mixing coconut oil with Oleic acid and Triethanol Amine in the ratio of 2:2:1 respectively. 4 cc of coconut oil was taken in a beaker and 4 cc of Oleic acid was added to it slowly in four steps. The mixture was stirred thoroughly using a mechanical stirrer and when the mixture became a homogeneous liquid, 2 cc of Triethanol Amine was added and stirred thoroughly so as to get a homogeneous mixture which can dissolve in water in all proportions and functions as oil in water emulsion. The oil in water emulsion prepared out of the concentrate was subjected to emulsion stability test as per IS 1448 specification Emulsion stability test as per IS 1448 Following procedure was adopted to test the stability of the emulsion as per IS Step 1: A CaSO 4 solution of total hardness equivalent to 45ppm was prepaid by dissolving.688gm of CaSO 4 per liter of distilled water. Step 2: Eight emulsion samples were prepared as shown in the Table 6.2. The requisite quantity of the concentrate was taken in a hypodermic syringe. The corresponding quantity of water was taken in a 15 ml measuring flask which was kept stirred using a stirrer so that a vortex was formed. The oil was poured in to the vortex thus formed. The stirring was continued for 2 more minutes after the last drop of oil was transferred. All the samples were allowed to stand for 48 hours and 129

3 evaluated on the basis of separation, frothing, homogeneity and coloration. There was no trace of oil separation in any one of the 8 samples prepared and this is an indication of the stability emulsion as per IS 1448 specifications. Table 6.2 Emulsion ratios and the corresponding proportions of water and concentrate Sample No Emulsion ratio 5:1 1:1 15:1 2:1 25:1 3:1 5:1 8:1 Test water (ml) Concentrate (ml) Characterization of the concentrate Physical properties of the concentrate such as density, viscosity, ph value and refractive index were determined experimentally and summarized in Table 6.3 Table 6.3 Physical properties of the concentrate Properties Value Viscosity at 4 o C (centipoises) 83.5 Specific gravity (kg/m 3 ).933 ph value 7.7 Fuming point ( o C) 185 Refractive index FEASIBILITIES STUDIES It was decided to evaluate the feasibility of the formulation for hard turning with minimal fluid application. Cutting experiments were conducted on a Kirloskar Turn master- 35 lathe. AISI 434 steel with a hardness of 45 HRC was used as the work material. Bars of 7mm in diameter and 35 mm in length were used in this investigation. Multicoated hard metal inserts with sculptured rake 13

4 face geometry with a specification SNMG 1248 of Tague Tec was used in the investigation. The tool holder had a specification of PSBNR 2525M12. The minimal fluid application system used in the previous experiments was used in the present investigation. Cutting experiments were conducted to compare the performance of the coconut oil based formulation with a commercial mineral based and pure coconut oil during hard turning with minimal fluid application. This was accomplished by conducting a variable speed test, a variable speed test and a tool life test. The fluid application parameters were kept at values shown in Table 6.4. Table 6.4 Values of fluid application parameters kept constant Fluid application parameter Values Rate of fluid application, Q 5ml/min Pressure of the fluid injector, P 8 Bar Frequency of pulsing, N 3 pulses/min Percentage of concentrate, C 2%+rest water The depth of cut was maintained as 1.25 mm and the time of cut was maintained as 6 seconds for the variable speed test and the variable feed test. The cutting force was measured using a Kistler tool force dynamometer, surface roughness was measured using a stylus type surface meter (Perthen Make) and tool flank was measured using a tool maker s microscope and cutting temperature was measured using an extrapolative technique (Varadarajan et al., 2) based on finite element analysis as described early. The feed was kept at.1 mm/rev during the variable speed test and the cutting velocity was varied from 8 to 12 m/min at five intervals. The cutting velocity was kept at 8 m/min, and the feed was varied from.4 to.8 mm/rev at five equal levels. During the tool life test cutting velocity was kept at 8 m/min, feed at 1 mm/rev and depth of cut at 1.25 mm. Figure 6.1 presents a photograph of the experimental set up. 131

5 WORKPIECE TOOL WORK THERMOCOUPL TOOL HOLDER WITH INSERT NOZZLE AT THE TOOL WORK INTERFACE KISTLER DYNAMOMETE R Figure 6.1 Photograph of the experimental set up Results and Discussion Figures 6.2 (a) to 6.2 (d) present the variation of cutting force, cutting temperature, surface roughness and tool chip contact length as a function of cutting velocity. The variation of cutting force, cutting temperature, surface roughness and tool chip contact length with feed are presented in Figures 6.3 (a) to 6.3 (d) respectively. Low cutting forces and tool-chip contact lengths were observed when raw coconut oil was used as the when compared to that observed during the application of mineral oil based and the coconut oil based cutting fluid formulated as evident from Figures 6.2 (a), 6.2 (d), 6.3 (a) and 6.3 (d). Coconut oil has high thermal stability and the long chained molecules of coconut oil are dipolar in nature and can create a dense, homogeneous and strong lubricating film in the contact zones. The film can absorb high pressure and offer better lubrication resulting in reduction in tool-chip contact length and lower cutting force. But it was found that raw coconut oil could not bring forth low cutting temperatures as shown in Figure 6.2(b) and Figure 6.3 (b). This is due its low cooling ability. It was observed that the performance of mineral oil based was at par with that of coconut oil based in this aspect as both of them contained lubricant (oil) as well as coolant (water). 132

6 Cutting Temperature (T), o C Cutting Force (Fz), N Coconut oil based Mineral oil based Cutting Velocity (m/min) Figure 6.2 (a) Variation of cutting force as a function of cutting velocity during the application of mineral oil based, coconut oil based and raw coconut oil Coconut oil based Mineral oil based Cutting velocity (m/min) Figure 6.2 (b) Variation of cutting temperature as a function of cutting velocity during the application of mineral oil based, coconut oil based cutting fluid and raw coconut oil. 133

7 Tool Chip Contact length (Lc), mm Surface Rougness (Ra), µm Coconut oil based.5 Mineral oil based Cutting Velocity (m/min) Figure 6.2 (c) Variation of surface roughness as a function of cutting velocity during the application of mineral oil based, coconut oil based cutting fluid and raw coconut oil Coconut oil based Mineral oil based Cutting Velocity (m/min) Figure 6.2 (d) Variation of cutting force as a function of cutting velocity during the application of mineral oil based, coconut oil based and raw coconut oil. 134

8 Cutting Temperature (Tc), o C Cutting Force( Fz), N Coconut oil based Mineral oil based Feed (mm/rev) Figure 6.3 (a) Variation of cutting force as a function of feed rate during the application of mineral oil based, coconut oil based and raw coconut oil Coconut oil based Mineral oil based Feed (mm/rev) Figure 6.3 (b) Variation of cutting temperature as a function of feed rate during the application of mineral oil based, coconut oil based and raw coconut oil. 135

9 Tool Chip Contact length (Lc), mm Surface Roughness (Ra), µm Coconut oil based cutting fluid.5 Mineral oil based cutting fluid Feed (mm/rev) Figure 6.3 (c) Variation of surface roughness as a function of feed rate during the application of mineral oil based, coconut oil based and raw coconut oil Coconut oil based cutting fluid Mineral oil based cutting fluid Feed (mm/rev) Figure 6.3 (d) Variation tool chip contact length as a function of feed rate during the application of mineral oil based, coconut oil based and raw coconut oil. 136

10 Flank Wear (V b ), mm Coconut oil based.5 Mineral oil based Time (Sec) Figure 6.4 Variations of flank wear with time during turning with minimal fluid application using mineral oil based, coconut oil based and raw coconut oil. Figure 6.5 (a) SEM photograph of tool wear when coconut oil based was used. Figure 6.5 (b) SEM photograph of tool wear when raw coconut oil was used as. 137

11 Figure 6.5 (c) SEM photograph of tool wear when mineral oil based was used. Figure 6.6 (a) Chip microgram during the application of coconut oil based cutting fluid (V=8 m/min, f=1 mm/rev, d=1.25 mm) Figure 6.6 (b) Chip microgram during the application of raw coconut oil as cutting fluid (V=8 m/min, f=1 mm/rev, d=1.25 mm) 138

12 Figure 6.6 (c) Chip microgram during the application of mineral oil based cutting fluid (V=8 m/min, f=1 mm/rev, d=1.25 mm) Figures 6.2 (c) and 6.3 (c) clearly show that the application of coconut oil based resulted in the lowest values of surface roughness. This is due to the superiority of the lubricating ability of the coconut oil based when compared to that of mineral oil based on account of its structure and thermal stability. Reduction in cutting temperature and cutting force brought forth by better lubrication at the tool work interface reduced the tool wear and hence improved the surface finish. The superiority of coconut oil based cutting fluid was established further by the results of tool life test. The tool wear was the least during the application of coconut oil based during the whole length of tool life test (Figure 6.4). Moreover, SEM photographs (Figure 6.5 (a), (b) and (c)) of worn inserts indicated less damage to the cutting edge when coconut oil based and raw coconut oil were used. Table 6.5 Thickness of chips collected CHIP THICKNESS, t c (mm) Coconut oil based.19 Raw coconut oil as.15 Conventional mineral oil based.26 Chip microgram during the application of coconut oil based is shown in Figure 6.6 (a). The chip micrograph during the application of raw coconut oil is shown in Figure 6.6 (b). Figure 6.6 (c) presents the chip microgram when mineral oil based was used under the same cutting conditions. 139

13 Thickness of the chips collected during experiments was measured using tool maker s microscope and is presented in Table 6.5. The chip thickness was.26 mm during the application of mineral oil based where as it was.19mm during the application of coconut oil based. It was as low as.15mm when raw coconut oil was used as. It was also observed that the chip sections contained less signs of distortions when the raw coconut oil was used as well as when coconut based was used. Chip thickness is an index of the frictional conditions at the tool chip interface. Better the rake face lubrication, thinner will be the chips and lesser will be the deformation and damages on its cross section. 6.4 EFFECT OF PERCENTAGE OF CONCENTRATE ON CUTTING PERFORMANCE It was decided to study the effect of the percentage of concentrate in the on cutting performance. Accordingly the percentage of the concentrate was varied at four levels as shown in Table 6.6. A tool life test was conducted using multicoated hard metal inserts with sculptured rake face with a specification SNMG AISI 434 steel with a hardness of 45 HRC was used as work material and the cutting experiments were carried out on a Kirloskar Turn master-35 lathe. The cutting velocity was kept at 8 m/min, feed at 1 mm/rev and depth of cut at 1.25 mm. The fluid application parameters were maintained at values as shown in Table 6.7. Flank wear was measured at an interval of 3 seconds using a tool maker s microscope and the results are presented in Figure 6.7. Table 6.6 Percentage of concentration in the Level % of concentrate % of water

14 Tool Wear (mm) Table 6.7 Values of fluid application parameters that were kept constant Fluid application parameters Values Rate of fluid application, Q 5ml/min Pressure of the fluid injector, P 8 bar Frequency of pulsing, F 3 pulses/min % 2% 3% 4% Time (Sec) Fig. 6.7 Variation of tool wears during tool life test Highest tool wear values are observed when the consisted of 1% concentrate and the rest water. When the composition was at level 2, ie 2% concentrate and the rest water, there was a reduction in the tool wear in the whole range. The tool wear characteristics marked still lower values when the composition was kept at level 3 (ie, 3% concentrate + 9% water). But when the percentage of concentrate was further increased to 4% there was only marginal reduction in the wear characteristics. Tool wear is decided by the combined effect of cooling and lubricating abilities of the. When the percentage of concentrate is more, the lubricating ability of the increases but its cooling ability comes down as the percentage of water is reduced. The will offer its best when there is a good balance between its lubricating and cooling abilities. It appears that when the percentage of concentrate was kept at 3% there is a good balance between its lubricating as well as cooling 141

15 ability. When the percentage of the concentrate was increased to 4% there was not much improvement in the wear characteristics which is in support of the concept mentioned above. Hence the percentage of concentrate in the may be maintained at 3% that will lead to better tool wear characteristic and at the same time can fetch a saving of 1% in the use of concentrate. 6.5 SUMMARY A was formulated with coconut oil as the base which can act as an oil in water emulsion during turning of hardened AISI 434 steel with minimal fluid application. The performance of the new was compared with that of a conventional mineral oil based and raw coconut oil by conducting cutting experiments. It was observed that the coconut oil based cutting fluid offered better cutting performance interns of low tool wear, low surface roughness, low cutting force and low cutting temperature when compared to mineral oil based and raw coconut oil. It was also observed that the percentage of concentrate in the can be maintained as 3% to achieve better cutting performance during turning of hardened AISI 434 steel with minimal fluid application. Cutting fluid with coconut oil as the base is environment as well as human friendly. It is biodegradable in nature and hence free from problems associated with disposal. Coconut oil based can fetch saving in terms of foreign exchange as it does not need mineral oils which are to be imported. The government can introduce legislation encouraging the use of cutting fluids based on vegetable oils like coconut oil which offers better cutting performance and at the same time free from environment related problems and problems related to storage and disposal. Moreover, use of s based on vegetable oils can bring forth considerable reduction in the quantities of petroleum products imported. 142