The authors have proposed a micro bubble coolant in which micro bubbles (20∼50μm in diameter) are included in water soluble coolant. In the previous study, it was confirmed that the tool life was improved by applying the micro bubble coolant to various machining operations such as drilling, turning and grinding. Also, purification effects of the micro bubble coolant were found. In this study, micro bubble coolant in which inert gases (N2 and CO2) were mixed was proposed to be applied to grinding processes for further improvement in grinding performances. When nitrogen gas (2L/min) was mixed with the micro bubble in the water soluble coolant (70L), amount of the dissolved oxygen in coolant decreased to 0.5mg/L. And concentration of the carbon dioxide gas in the coolant increased to 100mg/L when carbon dioxide gas (2L/min) was mixed in. From the result of grinding test on high speed steel, it was found that grinding performances improved when the micro bubble coolant with any of air, N2 and CO2 gases was used. The grinding force decreased by a factor of about 15% and the tool life increased by 20∼30%. When nitrogen gas was mixed in, the surface roughness improved by about 15%. In grinding stainless steels, performances such as grinding force, tool life and surface roughness improved by 10% when nitrogen gas was mixed in. In addition, a tendency of flank wear reduction and improvement in the surface roughness were observed when air micro bubble was mixed into the coolant in the turning of high carbon steel and Inconel 718 as well. When N2 micro bubble was generated in the coolant, a flank wear was reduced by 20% and surface roughness was improved by 30 to 40%. These effects were higher than the coolant with air micro bubble.

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