Itoigawa et al. Machining conditions were determined after some preliminary tests, which provided the best values to assess the viability of OoW grinding. These values are presented in Table 1. It was used a wheel cleaning system by compressed air jets, with two nozzles directed tangentially to the wheel surface, which assures better results for cylindrical grinding of advanced ceramics, as proved by the preliminary tests.
Before each test, the wheel was dressed, allowing for the same initial conditions of the tool. After dressing, the ceramic workpiece was normalized parallel to the grinding wheel. For each test, five hollow cylinders were used. In order to use the whole wheel width, two tests were conducted before each dressing. After these two tests, the wheel wear was measured by printing its profile on steel cylinders, and then the tool was dressed. Before each conventional lubri-refrigeration test, the cutting fluid concentration was evaluated by an Atago N-1 E manual refractometer, and then corrected if needed by adding more water or cutting fluid into the reservoir.
The wheel diametral wear was obtained through the printing of its profile on a steel workpiece, and then it was measured by Talymap Silver software, which provided the mean values for this variable, considering each lubri-refrigeration condition. Data acquisition of grinding power and acoustic emission data were obtained by Labview 7. The signals were then filtered and treated in Matlab, which provided average values for both variables. Acoustic emission signals were gathered by a Sensis DM12 sensor, which was fixed on the grinding machine tailstock, aiming to detect the possible variations of this variable, and consequently making it possible to relate it with the other output variables.
For the surface roughness values, it can be seen in Figure 11 that conventional lubri-refrigeration provided the lower values for all feed rates tested, due to the better capability to remove machined chips from the cutting zone abundant fluid flow. Those microchips lodged in the wheel scratch the workpiece surface, increasing its surface roughness. Part of this grout was removed by the compressed air jet, which cleans the wheel, providing then better results on the workpiece finishing, compared to MQL without wheel cleaning. However, it can be seen that MQL with water provided lower values for surface roughness, than when using traditional MQL.
A possible explanation for this better performance of air-oil-water mixture, in relation to air-oil traditional MQL is the fact that, following the same reasoning presented above, the water lower viscosity makes the grout less adherent to the wheel, and consequently easier to be removed from the wheel pores. For the roundness values presented in Figure 12 , the conventional lubri-refrigeration also presented the best results for all feed rates tested, due to the better ability of cleaning the wheel provided by this method.
Again it can be seen that the presence of water in the air-oil combination increases the roundness values, since they increased when using OoW. That was caused by the reduction of lubrication capability of this mixture, since there are lower amounts of oil. On the other side, when using only oil in combination with air traditional MQL , that it, when the lubrication capability is higher for MQL systems , the roundness values were higher than when using OoW This is possibly due to the fact that, despite the increase in the lubricating capability of traditional MQL, the combination of air-oil loses wheel cleaning capability, which also influences the results for roundness.
It can be concluded that acoustic emission was mainly influenced by the lubrication capability of the lubri-refrigeration method, and less influenced by the wheel cleanliness. As the lubrication capability increased, and wheel cleaning capability decreased, acoustic emission values were lower. Even when the wheel had machined chips loged into its pores as when using traditional MQL , the presence of oil on the grout provided less friction between the grains and lodged chips and the workpiece.
Observing Figure 14 , it can be noticed that the lower values of grinding power were obtained when using conventional lubri-refrigreration. When used traditional MQL, it can be seen that the required power tended to be slightly higher than when using OoW method.
On the other hand, OoW combines efficient cooling and lubrication in a way that grinding power necessary is lower. As previously mentioned, traditional MQL was the lubri-refrigeration method which was less effective in cleaning the wheel, that is, it is the condition on which more chips remained lodged in the wheel pores. Then, the friction between these adhered chips and the workpiece contributed to wear the wheel more intensely.
On the other side, the most efficient method for wheel cleaning, which was conventional lubri-refrigeration, did not provide lower diametral wheel wear values, as it could be supposed by the aforementioned reasons. It is possible that the factor which caused high wheel wear was the low capability of lubrication of this abundant flow, which consists of oil diluted in water. When used a lubri-refrigeration method which is intermediary in terms of wheel cleaning and lubrication capability OoW , it was obtained a satisfactory combination of both variables, and the diametral wheel wear was not as high as the one obtained when using conventional lubri-refrigeration.
Based on the obtained results on this work, it can be concluded that, when grinding ceramics with diamond wheels, in similar conditions to the ones tested:. In terms of surface roughness, conventional lubri-refrigeration was the method which provided the best results, due to its better ability to clean the wheel, by removing the machined chips which lodge in the wheel pores. In terms of roundness, the results were similar to surface roughness. Conventional lubri-refrigeration was the most satisfactory method, while traditional MQL was the less satisfactory.
Acoustic emission signals generated from the process was strongly influenced by lubrication capability of the lubri-refrigeration methods it can be inferred that it is an indirect measurement of this capability. Thus, the higher acoustic emission values were obtained when using conventional lubri-refrigeration, while the lower was obtained for traditional MQL.
The lubri-refrigeration condition which provided the higher diametral wheel wear was the less efficient when considering wheel cleaning traditional MQL. However, the condition most efficient in cleaning the wheel abundant fluid flow was not the one which provided lower wheel wear, since it has poor lubrication capability.
According to Lee et al. The depth of cut can be thus increased, since the diametral Wheel wear would be lower, and, beyond that, it is possible to obtain better surface quality, reducing surface roughness and fulfilling efficiently the geometrical and shape requirements of the component.
Effect of compressed air jet. The apparent density was 3. The grinding wheel was a resin bonded diamond wheel DNV with dimensions of: mm external diameter x 15mm width x 5mm layer and internal diameter of mm. The cutting fluid used for minimal quantity of lubricant was a Rocol Cleancut, and the MQL application device was an ITW Chemical Accu-Lube, which allow independent flow rate regulation of oil and air. For the wheel cleaning compressed air jet, the air flow rate was 8. The measurement of roundness was conducted by a Taylor Hobson Talyrond 31C roundness meter, which provided the average value for each test.
Diametral wheel wear was measured by printing the wheel profile on an AISI steel workpiece. Then the average value was calculated by the software Talymap Silver. The microstructural analysis was made through the analysis of SEM micrographs, after adequate preparation of the workpieces. The cleaning nozzle placement is shown in Figure Figure 18 presents the results obtained for the average surface roughness R a. Analyzing the results obtained, it can be observed that the surface roughness value was lower for conventional lubri-refrigeration, in comparison to MQL technique, possibly caused by the better removal of machined chips from the cutting zone.
When using MQL, a grout is formed mixture of oil and chips , which is difficult to remove, causing an increase on the surface roughness.
In relation to MQL with wheel cleaning, it can be seen clearly an improvement of the results for this variable, when comparing to traditional MQL without wheel cleaning , but they still remained worse than the results for conventional lubri-refrigeration. This is due to the worse capability of removing the grout formed, and the heat generated on the cutting zone, when using MQL. In relation to the efficiency of the cleaning system by compressed air, it is a function of the air jet incident angle, since the pressure and flow rate were kept constant.
Thus, it can be noticed that the wheel cleaning conditions provided better results than when using traditional MQL, for all incident angles tested. Besides that, the angle which provided the best results was the tangent angle. Figure 19 shows the results obtained for diametral wheel wear, using as a reference the conventional lubri-refrigeration, since it is widely applied on the industries. Analyzing the results obtained, it can be seen that conventional lubri-refrigeration obtained again the best results, and the wheel cleaning method provide clear improvements when comparing to traditional MQL, with exceptions to the normal angle in this case which was very close to traditional MQL.
Again, as the wheel cleaning was not so efficient in removing the material lodged, the results were harmed; however, this prejudice was lower when using the air jet with an incident angle tangent to the tool surface. Thus, it can be noted a coherence with the resuls obtained for surface roughness and diametral wheel wear.
Figure 20 presents the results obtained for roundness errors, for a clear comparison among the lubri-refrigeration conditions tested. However, wheel cleaning for other angles presented worse results than when using conventional lubri-refrigeration. With that, the most efficient angle was not the tangentially directed, as in surface roughness and wheel wear results. However, this angle provided also better results than traditional MQL, becoming also viable. The results for roundness did not behave as the expected, when considering surface roughness and Wheel wear, because this variable is more sensitive to the stiffness of the process, i.
Another one is the fact that the tangent angle was not the most efficient condition of wheel cleaning, as in the previous output variables evaluated. Figure 21 presents the results obtained for grinding power gathered in real-time , for each lubri-refrigeration condition. It can be noted that the conventional lubri-refrigeration test provided the lower grinding Power values, which is coherent with the results of surface roughness and diametral wheel wear.
That occurs probably due to the more efficient chip removal from the cutting zone, favoured by this lubri-refrigeration method. At the same time, this reaction generates higher components of tangential force, against wheel rotation, increasing thus grinding power values. Tangential compressed air jet generates higher forces against the wheel rotaion, increasing then the grinding power. Surface integrity is of undeniable importance, when concerning grinding operation. Damages caused to the material surface can affect it negatively, harming wear resistance, causing nucleation and propagation of cracks, and accelerating fatigue.
Scanning electron microscopy is a powerful technique of microstructural assessment and characterization, making possible to analyze the material surface as a consequence of each condition of grinding, specifically in the present situation. Analyzing Figure 22 , it is possible to notice that, when using conventional lubri-refrigeration, the fragile material removal mechanism prevailed. It is also noteworthy the good finishing surface, despite the fragile removal, which can cause microcracks.
Analysing Figure 23 , it can be seen that, when using MQL lubri-refrigeration, ductile material removal mode prevailed, which provided otpimal conditions of surface finishing, in relation to material strength, due to the reduced presence of microcracks, which are stress concentration agents. When observing Figure 24 , it can be noticed that ductile mode of material removal also prevailed, due to the use of the same cutting fluid as when applying traditional MQL. Moreover, this finishing surface is even better than when using MQL without Wheel cleaning, because this method could effectively remove the grout lodged in the pores, providing consequently better surface finishing.
A general analysis of the presented results indicates that conventional lubri-refrigeration is the method which provided better results for surface roughness, roundness and wheel wear. However, MQL with wheel cleaning system is also viable, when comparing to traditional MQL, since it provided better results concerning surface quality and wheel wear, in comparison with the latter.
The tangent jet from the wheel cleaning system was the best incidence angle tested. It clearly improved MQL technique; however, it could not provide results as good as when using conventional lubri-refrigeration. Nevertheless, MQL with wheel cleaning system has its own advantages, when concerning environmental and health hazards of cutting fluids, combining the vantages provided by MQL with better results, closer to the conventional lubri-refrigeration. Grinding power presented inversely proportional results, when comparing to surface roughness, diametral wheel wear and roundness, for the MQL with wheel cleaning jet.
This is due to the fact that, besides the influence of material removal, there is also the influence of fluid flow forces from the air jet wheel cleaning system. The higher the cleaning efficiency, higher grinding power values can be observed. Thus, it is possible to replace traditional lubri-refrigeration methods for new ones, as when using MQL with compressed air jets which, directed to the cutting surface, aim to clean the wheel, which improves its performance for the external cylindrical grinding.
As can be seen, minimum quantity lubrication — MQL can be widely applied in different machining processes, including grinding in many different application modes.
The increasing need of sustainable manufacture stimulated the researchers and the research itself , for it was aimed to study alternative lubri-cooling methods, such as the wheel cleaning and MQL with water, when grinding advanced ceramics. Nevertheless, if carefully applied in grinding, minimum quantity lubrication can provide satisfactory results concerning surface quality and microstructural integrity of the ceramics workpieces.
Moreover, it results in environmentally friendly and technologically relevant gains. An open door for future research in this branch is the optimization of nozzles, cutting fluid composition and control of the machining parameters, allied with some computational modeling and simulation concerning thermal distribution and fluid flow. In addition, cost estimations should be done for each case, in order to enable more efficient applications of MQL in ceramic grinding. The costs related to this technology can be offset by lack of need for maintenance and disposal of cutting fluid, which today represents a considerable cost, due to the current standards aiming the environment preservation.
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Filgueira, R. Faria Jr. We are IntechOpen, the world's leading publisher of Open Access books. Built by scientists, for scientists. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Introduction Grinding is the most common designation used to define the machining process which uses a tool consisting of abrasive particles to promote material removal.
Grinding of ceramics Ramesh et al. MQL in grinding A relatively small amount of research has been conducted regarding the application of MQL in grinding. External cylindrical grinding 2. Grinding with diamond wheels The main objective of the present study was to evaluate the technique of minimum quantity of lubrication comparing to conventional cooling in the external cylindrical grinding of advanced ceramics, using a diamond wheel, analyzing output variables such as roughness, acoustic emission, G-ratio, circularity errors and scanning electron microscopy SEM analysis.
Acoustic emission Figure 4 presents the results of acoustic emission RMS , expressed in Volts V , according to the number of ground pieces. G-Ratio This item presents the G-Ratio for each equivalent thickness of cut and lubri-cooling condition. Scanning electron microscopy SEM Figure 6 represents the results for scanning electron microscopy SEM obtained conventional lubri-refrigeration x zoom.
Roundness Figure 8 shows an evolution of the roundness for all conditions tested. Surface roughness The figure below shows the results for the average surface roughness R a , on the comparison between conventional lubri-cooling and MQL in micrometers. Materials and methods Machining conditions were determined after some preliminary tests, which provided the best values to assess the viability of OoW grinding. Table 1. Machining conditions. Surface roughness For the surface roughness values, it can be seen in Figure 11 that conventional lubri-refrigeration provided the lower values for all feed rates tested, due to the better capability to remove machined chips from the cutting zone abundant fluid flow.
Roundness For the roundness values presented in Figure 12 , the conventional lubri-refrigeration also presented the best results for all feed rates tested, due to the better ability of cleaning the wheel provided by this method. Grinding power Observing Figure 14 , it can be noticed that the lower values of grinding power were obtained when using conventional lubri-refrigreration.
Conclusions Based on the obtained results on this work, it can be concluded that, when grinding ceramics with diamond wheels, in similar conditions to the ones tested: In terms of surface roughness, conventional lubri-refrigeration was the method which provided the best results, due to its better ability to clean the wheel, by removing the machined chips which lodge in the wheel pores. Wheel cleaning by a compressed air jet According to Lee et al. Each test was repeated twice, and five workpieces were used.
The feed rate used was 0. Surface roughness Figure 18 presents the results obtained for the average surface roughness R a. Diametral wheel wear Figure 19 shows the results obtained for diametral wheel wear, using as a reference the conventional lubri-refrigeration, since it is widely applied on the industries. Roundness Figure 20 presents the results obtained for roundness errors, for a clear comparison among the lubri-refrigeration conditions tested. Grinding power Figure 21 presents the results obtained for grinding power gathered in real-time , for each lubri-refrigeration condition.
Scanning electron microscopy SEM Surface integrity is of undeniable importance, when concerning grinding operation. Conclusions A general analysis of the presented results indicates that conventional lubri-refrigeration is the method which provided better results for surface roughness, roundness and wheel wear. Conclusions As can be seen, minimum quantity lubrication — MQL can be widely applied in different machining processes, including grinding in many different application modes. How to cite and reference Link to this chapter Copy to clipboard.
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