| The rapid development of manufacturing industry has brought a prosperous world to human. However, limited available nature resources and environment problem have been increasingly serious when human enjoy the achievements of technological progress. In the process of mechanical machining, the excessive cutting fluids have caused a larger number of energy cost and ecological problem. To control the production costs and reduce the negative effects such as skin and breathing problems on machine operators, a new method of cooling and lubrication technology-MQL (Minimum Quantity Lubrication)-has been used to replace conventional cutting fluids. CMQL (Cryogenic Minimum Quantity Lubrication) which combines the advantage of refrigerated air and MQL can effectively control tool wear, reduce cutting forces, and obtain high surface quality compared with dry, wet, and even room-temperature MQL cutting conditions.In the machining process under CMQL condition, the factures of the nozzle position and cutting medium parameters can affect the cooling and lubrication performance. Internal cooling is being paid more and more attention as an effective means to conduct the cutting medium from the tool end to the tool tip directly without considering the tool position. The combination of CMQL and internal cooling cutters can promote the cooling and lubrication functions of the cutting medium. So, it is necessary to study the oil-air flow field parameters in CMQL condition, in the meantime, the machinability of internal cooling cutters is also analyzed.First, a square silicon was employed to collect the micro oil from different positions in the flow field. The formation of lubrication film is analyzed and the effects of jetting distance or different air flow rate on area fraction covered by droplets and oil diameter distribution are studied. Besides, the oil droplets deformations are discussed when they collide with the silicon plane. Experimental results show that shorter jetting distance can increase area fraction covered by droplets, and more air flow rate lead to smaller oil diameter. Oil which has larger size or high velocity is easily breakup to more micro oil when impacts to the plane.Then, numerical simulation of the characteristics of flow field was performed using commercial CFD software Fluent. The variations of the diameter, temperature and velocity of micro oil mist are studied in terms of the atomization parameters. An orthogonal experiment method is designed to optimize the atomization parameters. Experimental results show that oil mist with low temperature, high velocity and small size could be obtained from cryogenic air, large air flow rate and cutting oil flow rate.Lastly, a cutting experiment was designed to evaluate the cutting performance. Three coated milling cutters with different internal channel structures are employed in a side milling H13 steel experiment using the CMQL cutting medium to study chip morphology, cutting forces and tool wear. In the meantime, the relationship between tool wear propagation and cutting force variations is explored, and the influence of internal channel on the micro-droplets is also analyzed. In the perspective of ecology and environmental protection, internal cooling cutter with double helical channel is recommended in cutting of H13 steel under CMQL condition.Cryogenic minimum quantity lubrication has an important signification on improving processing environment, raising processed quality and reducing production costs. The study of the flow field characteristics and cutting performance could provide theoretical support to practical production. |
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