The minimum quantity of lubrication (MQL) technique is becoming increasingly more popular due to the safety of environment. Moreover, MQL technique not only leads to economical benefits by way of saving lubricant costs but also presents better machinability. However, the effect of MQL parameters on machining is still not clear, which needs to be overcome. In this paper, the effect of different modes of lubrication, i.e., conventional way using flushing, dry cutting and using the minimum quantity lubrication (MQL) technique on the machinability in end milling of a forged steel (50CrMnMo), is investigated. The influence of MQL parameters on tool wear and surface roughness is also discussed. MQL parameters include nozzle direction in relation to feed direction, nozzle elevation angle, distance from the nozzle tip to the cutting zone, lubricant flow rate and air pressure. The investigation results show that MQL technique lowers the tool wear and surface roughness values compared with that of conventional flood cutting fluid supply and dry cutting conditions. Based on the investigations of chip morphology and color, MQL technique reduces the cutting temperature to some extent. The relative nozzle-feed position at 120°, the angle elevation of 60° and distance from nozzle tip to cutting zone at 20 mm provide the prolonged tool life and reduced surface roughness values. This fact is due to the oil mists can penetrate in the inner zones of the tool edges in a very efficient way. Improvement in tool life and surface finish could be achieved utilizing higher oil flow rate and higher compressed air pressure. Moreover, oil flow rate increased from 43.8 mL/h to 58.4 mL/h leads to a small decrease of flank wear, but it is not very significant. The results obtained in this paper can be used to determine optimal conditions for milling of forged steel under MQL conditions.

Carbon fiber reinforced polymers (CFRP) T700 have got increasing demand in the aerospace industry due to their high specific strength, specific stiffness, and other unique properties. Due to their inhomogeneous, anisotropic, and thermal properties, it is challenging to achieve desired accuracy and to avoid from delamination, chip-off, cracking, and burning especially in the drilling process. The cutting force is the critical parameter which is required to minimize in order to drill a hole with better accuracy and minimize defects. In this research, the brittle fracture approach was adopted and a cutting force model was developed for CFRP-T700 based on the rotary ultrasonic drilling (RUD) process. The experimental RUD was carried out on CFRP-T700 material and found that the feed rate and spindle speed are two main parameters that affect the cutting force in RUD. The cutting force data obtained from the model and experimental setup were then analyzed and found that there is small variation even below 10 % (max value of variation is 8.5 % and the average value is 0.49 %) between simulated and measured values. So, the developed cutting force model was validated and found robust. Also, it was found that with four times increase of feed rate, there is also an increase of material removal rate (MRR) four times with the decrease in the cutting force. Moreover, this model will be much helpful to keep cutting force within limits through the optimal set of parameters as feed rate and spindle speed without extensive experimentation of such costly materials.