Experimental and finite element analysis of the formation mechanism of serrated chips of nickel-based superalloy Inconel 718

The nickel-based superalloy Inconel 718 is a typical difficult-to-cut material due to its low thermal conductivity and high high-temperature strength. It has been used in a good many kinds of aeronautical key structures because of its high yield stress and anti-fatigue performance at high temperature. In this paper, the chip formation mechanism of Inconel 718 was studied by milling experiment and finite element (FE) simulation method. The change law of serrated chips was analyzed by carrying out single-factor method of cutting speed and feed rate. An equivalent two-dimensional (2D) cutting model was established to simulate the periodic interrupted cutting in the milling process. Moreover, the workpiece material and chip formation were simulated according to Johnson–Cook material constitutive and equivalent plastic failure rule considering the thermal effect of the contact area between the tools and chips was used to model chip separation. Based on experimental measurement and FE analysis results, Inconel 718 generates serrated chips regardless of its speed and feed rate. The serrated chips show more obvious regularity at high speed and high feed rate. Also, there are many micro-saws and microcracks on the free surface of the chip at low speed, which are caused by the micro-crack expansion on the free surface. At high speed, adiabatic shear behaviors occur in the first deformation zone, decreasing the strength of the adiabatic shear band material substantially. Since the shear slip velocity of the material along the adiabatic shear band is much higher than that in the adjacent area, serrated chips are formed.