Abstract
Milling forces play an important role in the milling process and are generally calculated by the mechanistic or numerical methods; reliable model of cutting forces is very important for the simulation of milling process, which has big scientific significance to further improve machining quality. Ball helical milling technology is used to make holes based on the cutting principle of helical milling using ball end cutter, and due to the influence of spherical surface machining characteristic, the modeling of cutting force in ball helical milling is difficult. Therefore, the main purpose of this paper is to establish an analytical cutting force model in the ball helical milling process. Considering cutting characteristics in the axial feed, the kinematics of ball helical milling is first presented, then the chip thickness distribution in different directions along the cutting edges is predicted. Furthermore, based on the characteristics of helical milling technology and geometry shape of ball end cutter and the classical mechanical cutting force model, through the study on the ball-end milling mechanics, a new relatively accurate theoretical cutting force model is established. At the same time, cutting force coefficients are identified through instantaneous force method according to the Ti-alloy experimental research result. Finally, higher simulation precision of cutting force model in ball helical milling process is received.
Highlights
Helical milling has attracted much attention in typical hole-making technology for difficult-to-cut materials, such as titanium alloy and CFRP, during the machining process, the rotating cutter that traverses a helical trajectory to generate a hole of a diameter larger than that of the tool, it can adjust the eccentricity without changing tool to obtain different diameters of holes
Shang et al [6] developed a cutting force model and built a new calibration method of cutting force coefficients in helical milling process, but the results showed that average coefficients did not suit for helical milling process
Rey et al [7]set up a cutting forces model depending on the tool geometry and cutting conditions in taking into account the parameters defining the trajectory and the tool geometry, the influence of the side edge and the bottom edge was considered in detail, the radial and axial effects of the three-way cutting forces were considered respectively, and the corresponding unique coefficient identification experiment was carried out by analyzing the basic cutting process of each cutting edge respectively
Summary
Helical milling has attracted much attention in typical hole-making technology for difficult-to-cut materials, such as titanium alloy and CFRP, during the machining process, the rotating cutter that traverses a helical trajectory to generate a hole of a diameter larger than that of the tool, it can adjust the eccentricity without changing tool to obtain different diameters of holes. Yucesan [12] and Altintas [13] carried out an in-depth analysis of the mechanical dynamics of the milling process performed by ball-end cutters, analyzed the change of cutting force in the time domain, considered the instantaneous regenerated chip load and force coefficients, and established cutting force model. Due to the special characteristics of the ball-end cutter, the main contact area between the tool and the workpiece material is mainly the spherical cutting edge, so during the helical milling process, along with the axial feed, the instantaneous tool cut-in angle, cut-out angle, chip thickness and contact area change from time to time. Based on the basic machining principles of helical milling and the geometry of ball-end cutters, this paper considers the tool movement and material removal during cutting process, integrates mechanical principle to establish a relatively accurate cutting force model for ball helical milling process. Each flute is ground with constant radial rake and clearance angles
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