Abstract:

The purpose of this study is to analyze the chip formation during the turning of process of a new high-temperature alloy GH4198, predict chip morphology using theoretical models, and elucidate the formation mechanism of saw tooth-shaped chips. The methodology involves conducting right-angle cutting experiments to record cutting forces, collecting chip samples, measuring geometric shapes, and calculating the shear angle. The influence of the tool bluntness radius on chip formation was analyzed, and the geometric shape of serrated chips was predicted based on utilizing slip line field theory. Orthogonal experiments were designed to analyze the effects of cutting speed and feed rate on the geometric shape of serrated chips. A three-stage physical model of serrated chip formation, considering the tool bluntness, was proposed based on adiabatic shear theory. The Johnson-Cook constitutive model and fracture criterion were chosen to establish a two-dimensional orthogonal cutting finite element model with thermal coupled, and its validity was confirmed by comparing experimental and simulated cutting force data. The mechanism of saw tooth chip formation was analyzed based on stress, equivalent plastic strain, and temperature changes during chip formation. Two-dimensional orthogonal cutting finite element models with varying tool bluntness radii were established. By examining the impact of tool bluntness radius on parameters such as stress and strain during chip formation, the study explored its influence on the shaping of serrated chips. The research found that as cutting speed and feed rate increased, the shear angle also increased, while chip thickness decreased with higher cutting speeds. At cutting speeds ranging from 10 to 30m/min, the relative error in predicted chip thickness ranged from 4.20% to 24.73%, and the relative error in simulated cutting forces ranged from 4.19% to 9.14%. The maximum compression ratios of chip thickness were 3.19, 2.78, and 2.26, with serration levels of 0.20, 0.36, and 0.58, respectively. At a cutting speed of 30m/min, chips exhibited significant cracks and an overall tilt in the saw tooth profile. With a feed rate of 0.05 to 0.15mm/r, the relative errors in predicted chip thickness were between 5.07% and 17.66%, and the relative errors in simulated cutting forces ranged from 6.42% to 14.23%. The maximum compression ratios of chip thickness were 2.82, 2.78, and 2.61, with serration levels of 0.12, 0.36, and 0.42, respectively. An increase in the tool bluntness radius led to a higher rate of material accumulation near the tool tip per unit time, exacerbating plastic deformation in the primary deformation zone. This enhanced the plowing and squeezing actions of the tool during cutting, causing increases in cutting force, stress, equivalent plastic strain, and temperature, thereby resulting in a greater degree of serration in the chips. The study concluded that the slip line field model could effectively predict the variation in chip thickness with changes in cutting parameters. As cutting parameters increased, the compression ratio of chip thickness showed a decreasing trend, while the degree of serration increased. The finite element model was utilized to analyze the patterns of equivalent plastic strain and temperature changes during chip formation, as well as the impact of the tool fillet radius on chip formation. The validity of the theoretical model of chip formation was confirmed, providing a theoretical basis and practical guidance for improving the integrity of machined surfaces.

Key words: cast &, wrought alloy GH4198, serrated chip, slip line field, finite element analysis, chip forming mechanism