Generating mechanism and formation criteria of kinked surface in peripheral end milling

A kinked surface is commonly generated in a peripheral end milling process. In this paper, the generating mechanism of a kinked surface in end milling is systematically analyzed and revealed under the convolution framework through the establishment of a surface generation and form error model. It is found that the shape and kink positions of a form error profile can be determined by the three angular parameters: the axial and radial immersion angles and the flute spacing angle. From these angular parameters, four types of flute/work engagement conditions are defined to serve as the kink formation criteria with each type generating its own distinctive surface error profile in both down and up milling configurations. These form error profiles are characterized by either a kink-free form or by a single or a combination of three types of kink forms, which are defined based on changes in the flute/work engagement conditions and the resulting slope discontinuity in the force profile. Based on the kink formation criteria, kink charts scaled in normalized axial and radial depths of cut are devised to identify the types of kinked surface generated at any given depths of cut. An algebraic closed-form expression for the positions of kink points is also derived. The proposed kink formation criteria, the kink chart and the kink height prediction are validated through experiments and by comparison with data extracted from previously published results.

► Four types of flute/work engagement conditions serving as kink criteria are defined.
► The type of flute engagement is determined by three angular process parameters.
► Each type of flute engagement is shown to generate a characteristic surface profile.
► Two types of kink forms can exist for down milling with an additional type in up milling.
► Kink charts are devised showing the types of kink form to be generated.