Helical Milling of CFRP/Ti6Al4V Stacks Using Nano Fluid Based Minimum Quantity Lubrication (NF-MQL): Investigations on Process Performance and Hole Integrity

Abstract

The structural components in the aeronautical industry require CFRP/Ti6Al4V stacks to be processed together, which results in poor hole integrity due to the thermal properties of the materials and challenges related to processability. These challenges include quality variation of the machined holes because of the limitations in process properties. Therefore, a novel solution through helical milling is investigated in the study using nano fluid based minimum quantity lubrication (NF-MQL). The analysis of variance shows, for Ti6Al4V, eccentricity (PCR = 28.56%), spindle speed (Ti) (PCR = 42.84%), and tangential feed (PCR = 8.61%), and for CFRP, tangential feed (PCR = 40.16%), spindle speed (PCR = 28.75%), and eccentricity (PCR = 8.41%) are the most significant parameters for diametric error. Further on, the rise in the circularity error is observed because of prolonged tool engagement at a higher value of tangential feed. Moreover, the surface roughness of Ti was reduced with an increasing percentage of MoS2 in the lubricant. The spindle speed (37.37%) and lubricant (45.76%) have a potential influence on the processing temperature, as evident in the analysis of variance. Similarly, spindle speed Ti (61.16%), tangential feed (23.37%), and lubrication (11.32%) controlled flank wear, which is critical to tool life. Moreover, the concentration of MoS2 decreased edge wear from ~105 µm (0.5% concentration) to ~70 µm (1% concentration). Thorough analyses on process performance in terms of hole accuracy, surface roughness, processing temperature, and tool wear are carried out based on the physical science of the process for cleaner production. The NF-MQL has significantly improved process performance and hole integrity.

Using Nano-Fluids Minimum Quantity Lubrication (NF-MQL) to Improve Tool Wear Characteristics for Efficient Machining of CFRP/Ti6Al4V Aeronautical Structural Composite

“…The levels for the spindle speed of machining CFRP and Ti were selected after the literature review and the trial runs [5]. Spindle speed CFRP (rpm) 6500, 7000, 7500 Axial itch (mm) 1, 1.5, 2 An optimized combination of axial feed per tooth and tangential feed per tooth was used to reduce the effect of cutting forces that have an effect on the diametric variations.…”

“…Molybdenum disulfide (MoS 2 ) is a solid lubricant commonly used in tribological applications due to its excellent lubricating properties [35]. This film acts as a physical barrier between the surfaces, preventing direct metal-to-metal contact and reducing friction [5,17]. Sekhar et al [36] used 0.5-1.5% MoS 2 concentration and found 0.5% as optimal.…”

“…When MoS 2 is applied as a lubricant, it adheres to the metal surfaces and forms a thin film. This film acts as a physical barrier between the surfaces, preventing direct metal-to-metal contact and reducing friction [5,17]. The low friction coefficient of MoS 2 allows sliding surfaces to move more easily, which reduces the amount of heat generated by friction and minimizes wear.…”

“…Therefore, helical milling is preferred because of its operational and efficient process capabilities to machine holes with the least tool wear, and reduced bore damage. It produces approximately 3.3 times fewer axial forces compared with the forces produced in the conventional process [5].…”

“…The authors confirmed that the lubrication mechanism positively influenced the process and reduced the environmental burden as compared to conventional approaches. Mughal et al [5] carried out process-performance optimization during helical milling of CFRP/Ti6Al4V. The authors compared hole integrity, processing temperature, and surface quality against machining conditions.…”