Investigation on the inconsistencies of cutting force when laser assisted and high speed micro ball milling of Inconel 718

Inconel 718 is one of the extremely difficult to cut materials at room temperature due to the excessive tool wear and poor surface finish. Previous researchers has reported that the laser assisted machining (LAM) offers the ability to machine Inconel 718 more efficiently by providing the local heating of the workpiece prior to material removal. With increasing material removal temperature using a laser preheating technique from room temperature to 700 °C indicated the reduction of yield and materials strength at a certain depth in underneath surface. However, in laser assisted micro milling (LAMM) preheating temperature shall be reviewed to ensure that the resulting temperature does not worsen the properties of materials. By using higher preheating temperature the material becomes softer and it will result in the cutting process more difficult with increasing cutting force and this promotes higher tool wear. Moreover, the application of the micro ball mill needs deeply study due material removal mechanism is more complicated in groove cutting compare to side cutting. Generally, ball end mill is designed for lower depth of cut. In this study, the cutting force, chip formation and tool wear of conventional and LAMM on Inconel 718 have been measured and compared. Result of preheating technique using a laser beam shows an improvement in cutting force when ball milling of shallow groove. However, inconsistence force results were produced for the deep groove ball milling due to the ineffective materials removal and adhesion phenomenon on the rake surface of cutting tool. It also demonstrated that the application of preheating in softening the workpiece has consequently initiated the formation of connected chip, build up edge and the undeformed chip also piled in the up milling area. Lower preheating temperature is recommended in micro cutting compared to the macro cutting process because of tool size and cutting depth applied. Machining with lower spindle speed is more preferable to prevent the formation of connected chip and build up edge