Study on Chip Formation in Grinding of Nickel-Based Polycrystalline Superalloy GH4169

Based on the variation of the actual cutting depth during the grinding process, a 3D finite element (FE) simulation model for grinding nickel-based superalloy GH4169 with single abrasive was initially constructed. Then the morphological evolution of the grinding chips during the grinding process was studied. In addition, the effect of the single abrasive cutting depth and the grinding speed on chip morphology and segmentation frequency was investigated. Finally, experimental results with the same test parameters verify the finite element simulation results. The results showed that in the experimental grinding speed range, the sawtooth lamellar chip with the free surface being serrated and the contact surface being smooth due to the extrusion of the abrasive is easy to produce when grinding nickel-based superalloy GH4169. As the grinding speed increases, the chip morphology changes from a unitary lamellar chip to a continuous serrated chip, developing into a continuous ribbon chip. The chip segmentation frequency is mainly determined by grinding depth and grinding speed. To be specific, the smaller the grinding depth and the greater the grinding speed, the greater the chip formation frequency.

Serrated Chip Formation Induced Periodic Distribution of Morphological and Physical Characteristics in Machined Surface During High-Speed Machining of Ti6Al4V

Difficult-to-cut materials are widely used in aerospace and other industries. Titanium alloys are the most popular ones among them due to their high strength-to-weight ratio and high temperature resistance. However, in high-speed machining, the alloys are prone to produce serrated chips, which have a serious influence on surface integrity. In this study, a coupled Eulerian–Lagrangian method is used to simulate the orthogonal cutting of Ti6Al4V due to its advantages of avoiding element distortion and improving the data extraction efficiency. The internal relationship between serrated chip formation and periodic profile of machined surfaces is analyzed by the simulation results and experimental data which are obtained by optical microscope and white light interferometer. Furthermore, thermal–mechanical loads on machined surfaces are reconstructed based on the simulation results, and a coupled finite element and cellular automata approach is used to describe the dynamic recrystallization process within the area of the machined surface during the formation of a single serration. According to the results, the periodic fluctuation of cutting forces is attributed to the serrated chip formation phenomenon, which then leads to the periodic profile of machined surfaces. The period is about 60–70 µm, and its amplitude decreases with the increase of cutting speeds. Moreover, the loads on machined surfaces also show the same period due to serrated chip formation. As a result, the grain refinement layer thickness (about 2 ∼ 5 µm) in machined surfaces is related to the surface temperature and exhibits the same periodic characteristics along the cutting direction.

Numerical Analysis of Serrated Chip Formation Mechanism with Johnson-Cook Parameters in Micro-Cutting of Ti6Al4V

Previous studies have reported significant differences in the Johnson-Cook (J-C) parameters of Ti6Al4V alloy. Thus, various serrated chip morphologies, cutting forces, and cutting temperatures are obtained when different constitutive parameters are used for numerical and simulation analyses, which decreases the reliability of the simulation model. Therefore, it is necessary to investigate and analyze simulation errors due to differences in the J-C parameters. In this study, the mechanism of the serrated chip formation of Ti6Al4V is thoroughly analyzed using the uniformly proportional J-C parameters. The serrated chip sensitivity, shear band spacing, serrated segmentation frequency, chip serration intensity, temperature field, strain energy, and cutting force is obtained. This study aims to improve the accuracy and reliability of the micro-cutting simulation models, as well as a reference for the selection of J-C constitutive parameters of simulation with Ti6Al4V manufactured with different heat treatments and additive manufacturing.